CN118749018A - Foamable adhesive sheet and method for producing article - Google Patents

Abstract

The invention provides a foaming adhesive sheet, which sequentially comprises a first adhesive layer, a base material and a second adhesive layer, wherein the first adhesive layer and the second adhesive layer contain a curing adhesive, at least one of the first adhesive layer and the second adhesive layer also contains a foaming agent, the initial adhesion force of the first adhesive layer is more than 0gf and less than 10gf, the initial adhesion force of the second adhesive layer is more than 10gf and less than 500gf, and the ring stiffness is more than 50mN/10 mm.

Description

Foamable adhesive sheet and method for producing article

Technical Field

The present invention relates to a foamable adhesive sheet and a method for producing an article using the same.

Background Art

Adhesives for bonding components to each other are widely used in various fields. For example, adhesives are used when fixing another component in a hole, groove, etc. of a component. Specifically, in an internal magnet type motor, adhesives are used when fixing a permanent magnet to a hole in a magnetic core.

Liquid adhesives are the mainstream adhesives used in electric motors. However, in the case of liquid adhesives, there are problems such as uneven coating, overflow, and liquid dripping, which complicate the bonding process.

On the other hand, in recent years, it has been proposed to use a sheet-like adhesive (foaming adhesive sheet) containing a foaming agent instead of a liquid adhesive (see, for example, Patent Document 1). The foaming adhesive sheet can suppress the occurrence of the above-mentioned inconveniences in the case of the liquid adhesive.

Prior art literature

Patent Literature

Patent Document 1: Japanese Patent No. 6874867

Summary of the invention

Problems to be solved by the invention

For example, when fixing another component in a hole, groove, etc. of one component, as described in Patent Document 1, a foamable adhesive sheet is attached to the other component for temporary fixation, and another component with a foamable adhesive sheet attached is arranged in the hole, groove, etc. of one component, and then the foamable adhesive sheet is foamed and cured, thereby the two components can be bonded and fixed.

In the case of fixing another component in a hole, a groove, etc. of a component, there is a tendency to narrow the gap between two components. Therefore, for the foamable adhesive sheet used, it is required that the overall thickness is thin. However, if the thickness of the foamable adhesive sheet is thin, then when the foamable adhesive sheet is transported, the foamable adhesive sheet is easily drooped due to its own weight. For example, when the foamable adhesive sheet is transported by adsorption, if the thickness of the foamable adhesive sheet is thin, then the two ends of the foamable adhesive sheet are easily drooped due to their own weight. Therefore, when the foamable adhesive sheet is transported by adsorption and attached to another component, there are such problems as bending, twisting, flexing, bubble mixing, etc. of the foamable adhesive sheet when attached. Furthermore, if the foaming adhesive sheet is attached to another member in such a defective state, a bulge will be generated in the foaming adhesive sheet, so when another member to which the foaming adhesive sheet is attached is inserted into a hole, a groove, etc. of a member, the foaming adhesive sheet will rub against and may peel off. In this case, the adhesiveness after foaming and curing is reduced, and the reliability is reduced.

In the above-mentioned bonding and fixing method, the foamable adhesive sheet is attached to another member for temporary fixing by utilizing the adhesiveness of the foamable adhesive sheet. However, if the adhesiveness of the foamable adhesive sheet is high, there is a problem that the insertability is reduced when inserting another member to which the foamable adhesive sheet is attached into a hole, groove, etc. of a member.

The first embodiment of the present invention has been made in view of the above-mentioned actual situation, and a main object of the present invention is to provide a foamable adhesive sheet having excellent adhesion and insertability.

In addition, when fixing another component in a hole, groove, etc. of one component, for example, as described in Patent Document 1, a foaming adhesive sheet is attached to the other component for temporary fixation, and another component to which a foaming adhesive sheet is attached is arranged in the hole, groove, etc. of one component, and then the foaming adhesive sheet is foamed and cured, so that the two components can be bonded and fixed.

When one member is fixed to a hole, groove, or the like of another member, there is a tendency for the gap between the two members to become narrow. Therefore, the foamable adhesive sheet used is required to be thin in overall thickness.

Thus, for a foamable adhesive sheet, it is proposed to arrange adhesive layers on both sides of a substrate and to make the two adhesive layers have different properties. For example, Patent Document 1 discloses making the expansion coefficients of the two adhesive layers different.

However, for the foamable adhesive sheet, when the two adhesive layers are different, curling may occur sometimes. In particular, if the thickness of the foamable adhesive sheet is reduced, curling becomes easy to occur. In this case, there is a problem that the foamable adhesive sheet is prevented from being attached to the component or the foamable adhesive sheet floats or peels off. In this case, the adhesion after foaming and curing is reduced, and the reliability becomes low.

In addition, if the thickness of the foamable adhesive sheet is thin, then when the foamable adhesive sheet is transported, the foamable adhesive sheet is easily drooped due to its own weight. For example, when the foamable adhesive sheet is transported by adsorption, if the thickness of the foamable adhesive sheet is thin, then the two ends of the foamable adhesive sheet are easily drooped due to their own weight. Therefore, when the foamable adhesive sheet is transported by adsorption and attached to the component, there are such problems as bending, twisting, bending, bubble mixing, etc. of the foamable adhesive sheet when attached. And then, if the foamable adhesive sheet is attached to the component under the state with such undesirable situation, then a bulge is generated in the foamable adhesive sheet, so when another component to which the foamable adhesive sheet is attached is inserted in the hole, groove, etc. of a component, the foamable adhesive sheet is rubbed, and there is also such a problem of peeling off. In this case, the adhesiveness after the foaming and curing will also be reduced, and the reliability becomes low.

The second embodiment of the present invention has been made in view of the above-mentioned actual situation, and a main object of the present invention is to provide a foamable adhesive sheet which can suppress curling and has excellent adhesion.

Means for solving problems

One embodiment of the first embodiment of the present invention provides a foamable adhesive sheet, which is a foamable adhesive sheet having a first adhesive layer, a substrate and a second adhesive layer in sequence, wherein the first adhesive layer and the second adhesive layer contain a curable adhesive, and at least one of the first adhesive layer and the second adhesive layer further contains a foaming agent, the initial tack (Japanese: タック) of the first adhesive layer is greater than 0 gf and less than 10 gf, the initial tack of the second adhesive layer is greater than 10 gf and less than 500 gf, and the ring stiffness (Japanese: ループスティフネス) is greater than 50 mN/10 mm.

Another embodiment of the first embodiment of the present invention provides a foamable adhesive sheet, which is a foamable adhesive sheet having a first adhesive layer, a substrate, a second adhesive layer and an adhesive layer in sequence, wherein the first adhesive layer and the second adhesive layer contain a curable adhesive and a foaming agent, the adhesive layer contains a pressure-sensitive adhesive or a curable adhesive, the initial adhesion of the first adhesive layer is greater than 0 gf and less than 10 gf, the initial adhesion of the adhesive layer is greater than 10 gf, and the ring stiffness is greater than 50 mN/10 mm.

One embodiment of the second embodiment of the present invention provides a foaming adhesive sheet, which is a foaming adhesive sheet having a first adhesive layer, a substrate, and a second adhesive layer in sequence, the composition of the first adhesive layer is different from the composition of the second adhesive layer, the first adhesive layer and the second adhesive layer contain a thermosetting adhesive, and at least one of the first adhesive layer and the second adhesive layer further contains a foaming agent. After standing for 15 hours at a temperature of 60°C and a humidity of less than 10% RH, the curling radius of the foaming adhesive sheet is greater than 15 mm, and the ring stiffness is greater than 45 mN/10 mm.

Another embodiment of the present invention provides a method for manufacturing an article, comprising: a configuration step of configuring the foamable adhesive sheet between a first component and a second component; and a bonding step of foaming and curing the foamable adhesive sheet to bond the first component to the second component.

Effects of the Invention

The foamable adhesive sheet in the first embodiment of the present invention has the effect of being excellent in adhesion and insertion properties.

The foamable adhesive sheet according to the second embodiment of the present invention can suppress curling and has an effect of being excellent in adhesion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view illustrating a foamable adhesive sheet of the present invention.

FIG. 2 is a schematic plan view and a schematic cross-sectional view illustrating an example of a ring stiffness measuring device.

FIG. 3 is a schematic diagram for explaining a method for measuring ring stiffness.

FIG. 4 is a schematic diagram for explaining a method for measuring ring stiffness.

FIG. 5 is a schematic cross-sectional view illustrating the foamable adhesive sheet of the present invention.

FIG. 6 is a schematic cross-sectional view illustrating the foamable adhesive sheet of the present invention.

FIG. 7 is a schematic cross-sectional view illustrating the foamable adhesive sheet of the present invention.

FIG. 8 is a process diagram illustrating a method for manufacturing an article of the present invention.

FIG. 9 is a process diagram illustrating a method for manufacturing an article of the present invention.

FIG. 10 is a schematic diagram for explaining a method for measuring the sagging amount.

FIG. 11 is a schematic diagram for explaining a method for measuring the radius of curvature of curl.

FIG. 12 is a schematic cross-sectional view illustrating the foamable adhesive sheet of the present invention.

FIG. 13 is a schematic cross-sectional view illustrating the foamable adhesive sheet of the present invention.

FIG. 14 is a process diagram illustrating a method for manufacturing an article of the present invention.

DETAILED DESCRIPTION

Hereinafter, the embodiments of the present invention will be described with reference to the accompanying drawings, etc. However, the present invention can be implemented in a variety of different ways and should not be construed as being limited to the contents of the embodiments illustrated below. In addition, in order to make the description clearer, the accompanying drawings sometimes schematically represent the width, thickness, shape, etc. of each part compared to the actual method, but it is only an example after all and does not limit the interpretation of the present invention. In addition, in this specification and each figure, the same symbols are sometimes used for the same elements as those described previously with respect to the figures that have already appeared, and the detailed description is appropriately omitted.

In this specification, when expressing the manner of arranging other members on a certain member, if it is simply expressed as "on..." or "under...", unless otherwise specified, it includes two cases: the case where the other member is arranged directly above or directly below the certain member in a manner of contacting with the certain member, and the case where the other member is arranged above or below the certain member with another member further interposed therebetween. In addition, in this specification, when expressing the manner of arranging other members on the surface of a certain member, if it is simply expressed as "on the side of..." or "on the surface of...", unless otherwise specified, it includes two cases: the case where the other member is arranged directly above or directly below the certain member in a manner of contacting with the certain member, and the case where the other member is arranged above or below the certain member with another member further interposed therebetween.

In this specification, a “sheet” also includes a member referred to as a “film.” In this specification, a “film” also includes a member referred to as a “sheet.”

Hereinafter, the present invention is divided into a first embodiment and a second embodiment, and each embodiment is described.

I. First Embodiment

First, a method for producing a foamable adhesive sheet and an article using the same according to a first embodiment of the present invention will be described.

A. Foam adhesive sheet

The foamable adhesive sheet in this embodiment has two embodiments. Hereinafter, each embodiment will be described.

a) First Embodiment

A first embodiment of the foamable adhesive sheet in the present embodiment is a foamable adhesive sheet having a first adhesive layer, a substrate, and a second adhesive layer in sequence, wherein the first adhesive layer and the second adhesive layer contain a curable adhesive, and at least one of the first adhesive layer and the second adhesive layer further contains a foaming agent. The initial adhesion of the first adhesive layer is greater than 0 gf and less than 10 gf, the initial adhesion of the second adhesive layer is greater than 10 gf and less than 500 gf, and the ring stiffness is greater than 50 mN/10 mm.

Fig. 1 is a schematic cross-sectional view illustrating a foamable adhesive sheet in this embodiment. The foamable adhesive sheet 10 in Fig. 1 has a first adhesive layer 1, a substrate 2, and a second adhesive layer 3 in sequence. The first adhesive layer 1 and the second adhesive layer 3 contain a curable adhesive, and at least one of the first adhesive layer 1 and the second adhesive layer 3 further contains a foaming agent. In addition, the initial adhesion of the first adhesive layer 1 and the initial adhesion of the second adhesive layer 3 are respectively within a specified range, and the ring stiffness of the foamable adhesive sheet 10 is within a specified range.

In this embodiment, by making the initial adhesion of the second adhesive layer within a specified range, the second adhesive layer with good adhesion to the component can be made. Specifically, when another component is bonded and fixed in a hole, groove, etc. of a component, that is, when the surface of the second adhesive layer of the foamable adhesive sheet is attached to another component, another component to which the foamable adhesive sheet is attached is inserted into a hole, groove, etc. of a component, and then the foamable adhesive sheet is foamed and solidified to bond one component to another component, by making the initial adhesion of the second adhesive layer within a specified range, the surface of the second adhesive layer of the foamable adhesive sheet can be attached to another component by utilizing the initial adhesion of the second adhesive layer, and the adhesion of the second adhesive layer to the component can be improved. Thus, when another component to which the foamable adhesive sheet is attached is inserted into a hole, groove, etc. of a component, the peeling and positional displacement of the foamable adhesive sheet can be suppressed.

In addition, in this embodiment, the initial adhesion of the second adhesive layer is within a predetermined range, so that the second adhesive layer can be made to have good reworkability. Therefore, for example, in the above-mentioned bonding and fixing method, when the surface of the second adhesive layer of the foaming adhesive sheet is attached to a component by utilizing the initial adhesion of the second adhesive layer, the positional deviation of the foaming adhesive sheet can be corrected.

In addition, in this embodiment, by making the initial adhesion of the second adhesive layer within a specified range, for example, when the second adhesive layer is formed by a transfer method, the floating of the second adhesive layer can be suppressed. In addition, as described later, when the second spacer is configured on the side opposite to the first adhesive layer of the second adhesive layer, by making the initial adhesion of the second adhesive layer within a specified range, the second spacer can be easily peeled off, which can improve operability.

In addition, in the present embodiment, since the initial adhesion of the first adhesive layer is below the specified value, the first adhesive layer can be made substantially non-adhesive (no initial adhesion), and the first adhesive layer with good sliding property can be made. Therefore, for example, in the above-mentioned bonding and fixing method, when another member with a foaming adhesive sheet is inserted into a hole, a groove, etc. of a member, another member with a foaming adhesive sheet can be smoothly inserted, and insertability can be improved. Thus, the peeling and positional displacement of the foaming adhesive sheet can be suppressed. In addition, in the above-mentioned bonding and fixing method, when another member is moved relative to a member to align the positions of the members to each other, another member can be smoothly moved relative to a member under the state that another member is inserted into a hole, a groove, etc. of a member, and positional alignment can be easily performed.

In addition, in this embodiment, since the initial adhesion of the first adhesive layer is below a predetermined value, the first adhesive layer is substantially non-adhesive (no initial adhesion), and thus can be made into a first adhesive layer with good sliding properties and good anti-blocking properties. Therefore, the operability of the foamable adhesive sheet can also be improved.

In addition, in this embodiment, as described above, since the second adhesive layer has excellent adhesion to the component and the first adhesive layer has excellent sliding property, it is possible to suppress the peeling and positional displacement of the foamable adhesive sheet. Therefore, it is possible to suppress the reduction of the adhesiveness of the foamable adhesive sheet after foaming and curing caused by the peeling and positional displacement of the foamable adhesive sheet, and it is possible to reduce the uneven bonding strength of the foamable adhesive sheet after foaming and curing caused by the peeling and positional displacement of the foamable adhesive sheet. Therefore, by using the foamable adhesive sheet of this embodiment, the bonding strength is high, and high reliability and high quality bonding can be achieved.

Here, when another component is bonded and fixed in a hole, groove, etc. of a component, there is a tendency to narrow the gap between the two components as described above. Therefore, for the foamable adhesive sheet used, the overall thickness is required to be thin. However, if the thickness of the foamable adhesive sheet is thin, the foamable adhesive sheet is easy to sag due to its own weight when the foamable adhesive sheet is transported. Therefore, the inventors of the present invention focus on the rigidity (stiffness) of the foamable adhesive sheet. If the thickness of the foamable adhesive sheet is thick, there is a tendency for the rigidity to increase. However, since the thickness of the foamable adhesive sheet originally needs to be thin, it is not suitable to thicken the thickness of the foamable adhesive sheet. In addition, when the foamable adhesive sheet has an adhesive layer on both sides of the substrate, if the thickness of the substrate is thick, there is a tendency for the rigidity to increase. However, if the thickness of the substrate is relatively thickened under the state of thinning the thickness of the foamable adhesive sheet, the thickness of the adhesive layer is relatively thinned, so there is a risk that the bonding properties and foaming properties of the adhesive layer are reduced. In addition, there is usually a tendency that the larger the adhesiveness (initial tack), the softer it is, and the smaller the adhesiveness (initial tack), the harder it is. Therefore, when the foamable adhesive sheet has an adhesive layer with adhesiveness (initial tack), there is a tendency that rigidity becomes lower. And the inventors of the present invention have found that: by setting the ring rigidity of the foamable adhesive sheet to a specified range, the foamable adhesive sheet can be suppressed from sagging due to its own weight. Further, it is found that: by making the first adhesive layer in the first adhesive layer and the second adhesive layer substantially non-adhesive (no initial tack), the insertability is good, and rigidity is also improved.

It should be noted that the ring stiffness is a parameter indicating the stiffness of a sheet or film. The larger the value of the ring stiffness, the stronger the stiffness of the sheet or film. The ring stiffness is used as a parameter indicating the strength of the stiffness of sheets and films used in packaging materials, but it is not very common in the field of adhesive sheets.

In the foamable adhesive sheet of the present embodiment, since the ring rigidity is more than the specified value, the stiffness can be enhanced. Therefore, when the foamable adhesive sheet is transported, the foamable adhesive sheet can be suppressed from sagging due to its own weight. Therefore, for example, when the foamable adhesive sheet is adsorbed and transported and attached to another member, the bending, twisting, deflection, bubble mixing, etc. of the foamable adhesive sheet can be suppressed when attached. Therefore, the adhesion can be improved. Further, the situation of bulging in the foamable adhesive sheet due to these undesirable conditions can be suppressed, so when another member to which the foamable adhesive sheet is attached is inserted into the hole, groove, etc. of a member, the foamable adhesive sheet can be made less prone to friction. Therefore, the peeling of the foamable adhesive sheet during insertion can be suppressed. Therefore, from such a viewpoint, by using the foamable adhesive sheet of the present embodiment, the bonding strength is high, and high reliability and high-quality bonding can be achieved.

Here, "adhesion" is a concept included in "bonding". Sometimes there is a distinction in that adhesion is used to mean a temporary bonding phenomenon, while bonding is used to mean a substantially permanent bonding phenomenon (Iwanami Shoten Physical and Chemical Dictionary, 5th edition). "Adhesion" and "adhesive strength" refer to the properties of bonding by pressure sensitivity and the adhesive strength at that time.

It should be noted that, in this specification, unless otherwise specified, "the adhesiveness of the adhesive layer" and "the adhesive strength of the adhesive layer" refer to the adhesiveness and adhesive strength of the adhesive layer before curing. In addition, in this specification, unless otherwise specified, "the adhesiveness of the adhesive layer" and "the adhesive strength of the adhesive layer" refer to the adhesiveness and adhesive strength of the adhesive layer after curing.

Hereinafter, each structure of the foamable adhesive sheet of this embodiment will be described.

1. Features

In this embodiment, the initial tack of the first adhesive layer is 0 gf or more and less than 10 gf, and may be 5 gf or less, or 2 gf or less. By making the initial tack of the first adhesive layer within the above range, the first adhesive layer can be made substantially non-adhesive (without initial tack), and can be made into a first adhesive layer with good sliding properties and anti-blocking properties.

In the present embodiment, the initial tack of the second adhesive layer is more than 10gf, can be more than 30gf, can also be more than 50gf. If the initial tack of the second adhesive layer is too low, then for example in the above-mentioned bonding and fixing method, when the surface of the second adhesive layer of the foamable adhesive sheet is attached to another member using the initial tack of the second adhesive layer, the adhesion of the second adhesive layer and another member may be reduced, or, when another member with the foamable adhesive sheet attached is inserted into the hole, groove, etc. of a member, the foamable adhesive sheet peels off or the position of the foamable adhesive sheet is offset due to the poor adhesion of the second adhesive layer and another member, and thus there is the possibility that the adhesion of the first adhesive layer and the second adhesive layer after foaming and curing is reduced or the bonding strength produces unevenness. In addition, the initial tack of the second adhesive layer is less than 500gf, can be less than 400gf, can also be less than 300gf. If the initial adhesion of the second adhesive layer is too high, reworkability is reduced. For example, in the above-mentioned bonding and fixing method, when the surface of the second adhesive layer of the foaming adhesive sheet is attached to another component using the initial adhesion of the second adhesive layer, it may become difficult to correct the positional deviation of the foaming adhesive sheet.

Here, the initial adhesion of the first adhesive layer and the second adhesive layer can be measured by a probe initial adhesion test. As a probe initial adhesion tester, for example, an initial adhesion tester "TAC-II" manufactured by RHESCA can be used. It should be noted that the details of the method for measuring the initial adhesion of the first adhesive layer and the second adhesive layer are described in the items of the embodiments described later.

In the present embodiment, the initial adhesion of the first adhesive layer can be set within a specified range by, for example, adjusting the composition of the first adhesive layer. Specifically, in the first adhesive layer containing an epoxy resin and a curing agent, by using an epoxy resin that is solid at room temperature, or by using a curing agent that is solid at room temperature, the adhesion of the first adhesive layer can be reduced. In addition, in the first adhesive layer containing an epoxy resin and a curing agent, by making it contain an epoxy resin with a high softening temperature, or by making it contain an epoxy resin with a large weight-average molecular weight, the adhesion of the first adhesive layer can be reduced. For example, by making the first adhesive layer contain a plurality of epoxy resins with different softening temperatures, that is, by making the first adhesive layer contain one epoxy resin and other epoxy resins with a softening temperature of more than 25°C and more than 10°C higher than the softening temperature of the above-mentioned one epoxy resin, the adhesion of the first adhesive layer can be reduced. In addition, for example, by making the first adhesive layer contain a plurality of epoxy resins with different weight average molecular weights, that is, by making the first adhesive layer contain one epoxy resin and another epoxy resin with a weight average molecular weight of 370 or more and 300 or more greater than the weight average molecular weight of the above-mentioned one epoxy resin, the adhesion of the first adhesive layer can be reduced. More specifically, in the first adhesive layer containing epoxy resin and curing agent, as described later, a first epoxy resin with a low softening temperature and a low molecular weight and a second epoxy resin with a high softening temperature and a high molecular weight are contained as epoxy resins, thereby reducing the adhesion of the first adhesive layer. In addition, in the first adhesive layer containing epoxy resin and curing agent, as described later, an acrylic resin compatible with epoxy resin is contained, thereby reducing the adhesion of the first adhesive layer.

In the present embodiment, the initial tack of the second adhesive layer can be controlled by adjusting the composition of the second adhesive layer, for example. Specifically, if an epoxy resin that is liquid at room temperature is used in the second adhesive layer containing epoxy resin and curing agent, or a curing agent that is liquid at room temperature is used, there is a tendency that the adhesion of the second adhesive layer becomes higher. In addition, if in the second adhesive layer containing epoxy resin and curing agent, an epoxy resin with a low softening temperature is contained, or an epoxy resin with a small weight-average molecular weight is contained, there is a tendency that the adhesion of the second adhesive layer becomes higher. In addition, by adding tackifying resin (tackifier) in the second adhesive layer, there is a tendency that the adhesion of the second adhesive layer becomes higher. It should be noted that, although there is a tendency that the adhesion becomes higher if a curing agent that is liquid at room temperature is used, storage stability may be reduced, and therefore it is preferred to adjust the initial tack of the second adhesive layer by adjusting the characteristics, types, etc. of components such as epoxy resins other than the curing agent.

In the present embodiment, the static friction coefficient of the surface opposite to the second adhesive layer of the first adhesive layer is preferably 0.33 or less, can be 0.30 or less, or can be 0.26 or less. By making the static friction coefficient of the surface of the first adhesive layer within the above range, the first adhesive layer with good sliding properties can be made. In addition, the above-mentioned static friction coefficient can be, for example, 0.16 or more.

Here, the static friction coefficient of the surface of the first adhesive layer can be obtained according to JIS K7125 corresponding to ISO 8295. Specifically, the static friction coefficient between the first adhesive layer of the foamable adhesive sheet and the metal plate is measured by the following method. First, the foamable adhesive sheet is cut into 80mm×200mm. Then, the foamable adhesive sheet is placed on a horizontally placed rectangular metal plate (SUS plate), and a sliding sheet (63mm×63mm, weight 200g, bottom surface: felt) is placed on the first adhesive layer of the foamable adhesive sheet. The friction force is measured under the conditions of a test speed of 100mm/min, a test length of 50mm, a force sensor of 10N, and a temperature of 23°C, and the static friction coefficient is calculated. The device can use, for example, a friction measuring machine FRICTION TESTER TR-2 manufactured by Toyo Seiki Seisakusho Co., Ltd.

In the present embodiment, the static friction coefficient of the surface of the first adhesive layer can be controlled, for example, by adjusting the composition of the first adhesive layer. Specifically, when the first adhesive layer also contains a foaming agent, the static friction coefficient of the surface of the first adhesive layer can be controlled by the average particle size and content of the foaming agent contained in the first adhesive layer. More specifically, if the average particle size of the foaming agent becomes larger, there is a tendency for the static friction coefficient of the surface of the first adhesive layer to become smaller. In addition, if the content of the foaming agent becomes more, there is a tendency for the static friction coefficient of the surface of the first adhesive layer to become smaller.

In the present embodiment, the arithmetic mean roughness (Ra) of the surface of the first adhesive layer opposite to the second adhesive layer is preferably 0.3 μm or more, 0.5 μm or more, or 0.7 μm or more. By making the Ra of the first adhesive layer within the above range, a first adhesive layer with good sliding properties can be made. In addition, the Ra of the first adhesive layer can be, for example, 1.5 μm or less, 1.3 μm or less, or 1.1 μm or less.

Here, Ra of the first adhesive layer can be measured using a white interferometer. Specifically, Ra of the first adhesive layer can be measured using a white interferometer NewView7300 manufactured by Zygo Corporation under the conditions of an observation field of view of 0.55 mm×0.55 mm and a sampling interval of 0.55 μm.

In this embodiment, the Ra of the first adhesive layer can be controlled, for example, by adjusting the composition of the first adhesive layer. Specifically, when the first adhesive layer further contains a foaming agent, the Ra of the first adhesive layer can be controlled by the average particle size and content of the foaming agent contained in the first adhesive layer. More specifically, if the average particle size of the foaming agent increases, there is a tendency for the Ra of the first adhesive layer to increase. In addition, if the content of the foaming agent increases, there is a tendency for the Ra of the first adhesive layer to increase.

In the foamable adhesive sheet of the present embodiment, the ring stiffness is 50mN/10mm or more, preferably 75mN/10mm or more, and more preferably 100mN/10mm or more. By making the ring stiffness of the foamable adhesive sheet within the above range, for example, when the foamable adhesive sheet is transported by adsorption and attached to a component, the foamable adhesive sheet can be suppressed from sagging due to its own weight, and good adhesion can be achieved. On the other hand, the upper limit of the ring stiffness is not particularly limited.

The ring stiffness is a parameter indicating the stiffness of a film or sheet as described above. Hereinafter, a method for measuring the ring stiffness will be described with reference to FIGS. 2 to 4 .

Fig. 2 (a) is a schematic plan view showing a ring stiffness tester, and Fig. 2 (b) is a cross-sectional view of the A-A line of Fig. 2 (a). The test piece of the foamable adhesive sheet 10 is a rectangular shape with a long side and a short side. In the present embodiment, the length L1 of the long side of the test piece of the foamable adhesive sheet 10 is set to 200mm, and the length L2 of the short side is set to 10mm. As the ring stiffness tester 30, the Loop Stiffness Tester (registered trademark) made by Toyo Seiki Seisakusho Co., Ltd. can be used. It should be noted that, about the length L1 of the long side of the test piece of the foamable adhesive sheet 10, as long as a pair of chucks 31 described later can be utilized to hold the test piece of the foamable adhesive sheet 10, then it can be adjusted.

The ring stiffness tester 30 has a pair of chucks 31 for holding a pair of ends of the test piece of the foamable adhesive sheet 10 in the long side direction and a supporting member 32 for supporting the chucks 31. The chucks 31 have a first chuck 31a and a second chuck 31b. The foamable adhesive sheet 10 is pre-configured on a pair of first chucks 31a, and the second chuck 31b has not yet held the foamable adhesive sheet 10 between the first chuck 31a and the second chuck 31b. As described later, the foamable adhesive sheet 10 is held between the first chuck 31a and the second chuck 31b of the chucks 31 during measurement. The second chuck 31b can be connected to the first chuck 31a via a hinge mechanism.

First, as shown in Fig. 2 (a), (b), the test piece of the foaming adhesive sheet 10 is placed on the first chuck 31a of a pair of chuck portions 31 separated by an interval L3. At this time, in the present embodiment, the interval L3 is set in such a way that the length of the ring portion 41 described later (hereinafter also referred to as the ring length) becomes 60mm. In addition, the test piece of the foaming adhesive sheet 10 is configured in such a way that the inner surface 40x is the surface of the first adhesive layer and the outer surface 40y is the surface of the second adhesive layer. Next, as shown in Fig. 3 (a), the second chuck 31b is configured on the test piece of the foaming adhesive sheet 10 in such a way that the end of the long side direction of the test piece of the foaming adhesive sheet 10 is held between the first chuck 31a.

Next, as shown in FIG. 3( b), at least one of the pair of chuck portions 31 is slid on the supporting member 32 in the direction in which the interval between the pair of chuck portions 31 is reduced. Thus, a ring portion 41 can be formed on the foam adhesive sheet 10. The test piece of the foam adhesive sheet 10 shown in FIG. 3( b) has a ring portion 41, a pair of intermediate portions 42, and a pair of fixed portions 43. The pair of fixed portions 43 is a portion of the test piece of the foam adhesive sheet 10 that is gripped by the pair of chuck portions 31. The pair of intermediate portions 42 is a portion of the test piece of the foam adhesive sheet 10 that is located between the ring portion 41 and the pair of intermediate portions 42. The chuck portion 31 is slid on the supporting member 32 until the inner surfaces 40x of the pair of intermediate portions 42 of the foam adhesive sheet 10 contact each other. Thus, a ring portion 41 with a ring length of 60 mm can be formed. The loop length of the loop portion 41 is the length between the position P1 where the surface of the loop portion 41 of one second chuck 31b intersects with the test piece of the foam adhesive sheet 10 and the position P2 where the surface of the loop portion 41 of the other second chuck 31b intersects with the test piece of the foam adhesive sheet 10. The above-mentioned interval L3 is a value obtained by adding 2×t to the length of the loop portion 41 when the thickness of the test piece of the foam adhesive sheet 10 is ignored. t is the thickness of the second chuck 31b of the chuck portion 31.

Next, as shown in FIG4(a), the posture of the chuck portion 31 is adjusted in such a manner that the protruding direction Y of the ring portion 41 becomes horizontal relative to the chuck portion 31. For example, the supporting member 32 is moved in such a manner that the normal direction of the supporting member 32 is moved to the horizontal direction, thereby adjusting the posture of the chuck portion 31 supported by the supporting member 32. In the example shown in FIG4(a), the protruding direction Y of the ring portion 41 is consistent with the thickness direction of the chuck portion 31. In addition, in the protruding direction Y of the ring portion 41, a force sensor 35 is prepared at a position separated from the second chuck 31b.

4(b), the load cell 35 is moved toward the ring portion 41 of the test piece of the foamable adhesive sheet 10 so that the load cell 35 contacts the ring portion 41. The distance Z1 is the distance between the load cell 35 and the second chuck 31b of the chuck portion 31.

Thereafter, as shown in Fig. 4(b) to (c), the ring portion 41 is pressed by the load cell 35 to the chuck portion 31 side by a distance Z2. In the present embodiment, the distance Z2 is set to 15 mm.

Next, as shown in FIG. 4( c ), the load sensor 35 is moved toward the chuck portion 31 by a distance Z2, and the load sensor 35 is pressed into the ring portion 41 of the test piece of the foaming adhesive sheet 10. After the value of the load applied to the load sensor 35 by the ring portion 41 stabilizes, the load value is recorded. The load value obtained in this way is set as the ring stiffness of the foaming adhesive sheet 10. In this specification, unless otherwise specified, the environment for measuring the ring stiffness is a temperature of 23° C. and a relative humidity of 50%.

When measuring the ring stiffness of the foamable adhesive sheet, if the foamable adhesive sheet has a first spacer and a second spacer as described below, the ring stiffness of the foamable adhesive sheet is measured after the first spacer and the second spacer are peeled off.

In the present embodiment, the ring rigidity of the foamable adhesive sheet can be controlled by adjusting the thickness and composition of the first adhesive layer, the thickness and composition of the second adhesive layer, and the thickness and composition of the substrate. For example, if the thickness of the substrate is thick, there is a tendency that the ring rigidity becomes larger. In addition, for example, if the thickness of the first adhesive layer is thick, there is a tendency that the ring rigidity becomes larger. Therefore, it is preferred to adjust the thickness of each layer in a manner to obtain the desired ring rigidity. In addition, if the composition of the first adhesive layer is adjusted to reduce the initial adhesion of the first adhesive layer, there is a tendency that the ring rigidity becomes larger.

The foamable adhesive sheet in this embodiment preferably has high adhesiveness after foaming and curing. After foaming and curing, the shear strength (adhesive strength) of the foamable adhesive sheet based on JIS K6850 corresponding to ISO 4587 at 23°C can be, for example, 1.50 MPa or more, 1.80 MPa or more, or 2.10 MPa or more.

In addition, the above-mentioned shear strength (adhesive strength) at 130°C can be, for example, 0.50 MPa or more, 0.75 MPa or more, or 1.00 MPa or more. For example, in a high-strength acrylic foam adhesive tape that does not require heating, the shear strength (adhesive strength) is 1 MPa or more and 2 MPa or less at room temperature, and there is no heat resistance at 200°C. Therefore, if the above-mentioned shear strength (adhesive strength) is within the above-mentioned range at 23°C, it has superiority in strength. In addition, if the above-mentioned shear strength (adhesive strength) is within the above-mentioned range at 130°C, it can be applied to applications requiring heat resistance around the engine of an automobile or close thereto.

The electrical insulation of the foamable adhesive sheet in the present embodiment after foaming and curing is high. After the foaming and curing of the foamable adhesive sheet, the insulation breakdown voltage based on JISC2107 corresponding to IEC60454-2 is preferably more than 3kV, more preferably more than 5kV. By making the above-mentioned insulation breakdown voltage the above-mentioned range, it is possible to prevent rust and be applied to copper wires. In addition, after the foaming and curing of the foamable adhesive sheet, the thermal conductivity is preferably more than 0.05W/mK. By making the above-mentioned thermal conductivity the above-mentioned range, it is possible to seek miniaturization of parts, and it is possible to promote the curing reaction during heating.

2. First bonding layer

(1) Material of the first adhesive layer

The first adhesive layer in this embodiment contains a curable adhesive.

(a) Curable Adhesive

As the curable adhesive contained in the first adhesive layer in the present embodiment, a curable adhesive commonly used in the adhesive layer of the foamable adhesive sheet can be used. As the curable adhesive, for example, heat-curable adhesives and light-curable adhesives can be cited. Among them, heat-curable adhesives are preferred. Heat-curable adhesives can also be used when the components are not transparent, such as metal components.

Examples of curable adhesives include epoxy resin adhesives, acrylic resin adhesives, phenolic resin adhesives, unsaturated polyester resin adhesives, alkyd resin adhesives, urethane resin adhesives, and thermosetting polyimide resin adhesives.

Among them, the curable adhesive is preferably an epoxy resin adhesive. That is, the curable adhesive preferably contains an epoxy resin and a curing agent. Generally, the epoxy resin adhesive has excellent mechanical strength, heat resistance, insulation, chemical resistance, etc., has small curing shrinkage, and can be used for a wide range of purposes.

Hereinafter, an example will be described in which the curable adhesive is an epoxy resin adhesive.

(i) Epoxy resin

The epoxy resin in the present embodiment is a compound having at least one epoxy group or glycidyl group, and curing by cross-linking polymerization reaction when used in combination with a curing agent. The epoxy resin also includes a monomer having at least one epoxy group or glycidyl group.

As the epoxy resin, an epoxy resin commonly used in the adhesive layer of a foamable adhesive sheet can be used. Among them, in the curable adhesive, as the epoxy resin, it is preferred to contain: a first epoxy resin having a softening temperature of 50°C or more and an epoxy equivalent of 5000 g/eq or less, and a second epoxy resin having a softening temperature higher than the first epoxy resin and a weight average molecular weight of 20,000 or more. By using the first epoxy resin and the second epoxy resin in combination, the adhesion (initial adhesion) of the first adhesive layer can be reduced, and a foamable adhesive sheet with good sliding properties can be obtained. In addition, a first adhesive layer with good anti-blocking properties and adhesion after foaming and curing can be obtained.

For example, when only seeking to improve the adhesiveness after foaming and curing, it is effective to use low molecular weight (low epoxy equivalent) epoxy resins compared to high molecular weight (high epoxy equivalent) epoxy resins. However, when using low molecular weight (low epoxy equivalent) epoxy resins, for example, when the foamable adhesive sheet is wound into a roll, the low molecular weight (low epoxy equivalent) epoxy resins assimilate with each other and are prone to adhesion.

In contrast, when using the first epoxy resin with a relatively low softening temperature (relatively high crystallinity) and low molecular weight (low epoxy equivalent), if the first epoxy resin becomes a temperature above the softening temperature, it rapidly melts and changes into a low-viscosity liquid state. Therefore, it is easy to improve the adhesion after foaming and curing. On the other hand, the first epoxy resin is relatively high in crystallinity, so compared with the epoxy resin with relatively low crystallinity or the epoxy resin without crystallinity, it is possible to suppress the generation of adhesion. However, when using only the first epoxy resin, the generation inhibition effect of adhesion is likely to be insufficient, and the adhesion (initial adhesion) of the first adhesive layer is likely to become too high. Therefore, by further using the second epoxy resin with a higher softening temperature (lower crystallinity) and high molecular weight, it is possible to improve the generation inhibition effect of adhesion, and the adhesion (initial adhesion) of the first adhesive layer is suppressed to be low.

(i-1) First epoxy resin

The softening temperature of the first epoxy resin is above 50°C, and the epoxy equivalent is below 5000g/eq. Compared with the second epoxy resin described later, the first epoxy resin has a lower softening temperature (higher crystallinity). Since the first epoxy resin has high crystallinity and low molecular weight, it is easy to improve the adhesion and anti-blocking properties after foaming and curing. In addition, since the first epoxy resin has a low molecular weight, it is possible to increase the crosslinking density, and a first adhesive layer with good mechanical strength, chemical resistance, and curability can be obtained. In addition, it is preferred that the first epoxy resin is a solid epoxy resin at room temperature (23°C).

The softening temperature of the first epoxy resin is usually 50° C. or higher, and may be 55° C. or higher, or 60° C. or higher. On the other hand, the softening temperature of the first epoxy resin is, for example, 150° C. or lower. The softening temperature can be measured by a ring and ball method in accordance with JIS K7234.

The epoxy equivalent of the first epoxy resin is, for example, 5000 g/eq or less, 3000 g/eq or less, 1000 g/eq or less, or 600 g/eq or less. On the other hand, the epoxy equivalent of the first epoxy resin is, for example, 90 g/eq or more, 100 g/eq or more, or 110 g/eq or more. The epoxy equivalent can be measured by a method according to JIS K7236 corresponding to ISO 3001 (Plastics Epoxy compounds-Determination of epoxy equivalent), and is the number of grams of resin containing 1 gram equivalent of epoxy groups.

The first epoxy resin may be a monofunctional epoxy resin, a difunctional epoxy resin, a trifunctional epoxy resin, or a tetrafunctional or higher-functional epoxy resin.

In addition, the weight average molecular weight (Mw) of the first epoxy resin is usually less than the weight average molecular weight (Mw) of the second epoxy resin described later. The Mw of the first epoxy resin is, for example, less than 6000, less than 4000, or less than 3000. On the other hand, the Mw of the first epoxy resin is, for example, more than 400. Mw is a value converted to polystyrene when measured by gel permeation chromatography (GPC).

The melt viscosity of the first epoxy resin at 150°C is, for example, 0.005 Pa·s or more, 0.015 Pa·s or more, 0.03 Pa·s or more, 0.05 Pa·s or more, or 0.1 Pa·s or more. If the melt viscosity is too low, good foaming properties may not be obtained. In addition, if the melt viscosity of the first epoxy resin is too low (if the crystallinity of the first epoxy resin is too high), the adhesion (initial adhesion) of the obtained first adhesive layer may become high. It is speculated that the reason is that if the melt viscosity of the first epoxy resin is too low (if the crystallinity of the first epoxy resin is too high), when it is compatible with the second epoxy resin or acrylic resin, its crystallinity is greatly reduced, and the Tg of the first adhesive layer is reduced. On the other hand, the melt viscosity of the first epoxy resin at 150°C is, for example, less than 10 Pa·s, less than 5 Pa·s, or less than 2 Pa·s.

If the melt viscosity is too high, the uniformity of the obtained first adhesive layer may be reduced. The melt viscosity can be determined by measuring the solution using a Brookfield single cylinder rotational viscometer and a constant temperature metal bath for heating the solution in accordance with JIS K6862 corresponding to ISO 2555 (Resins in the liquid state or as emulsions or dispersions Determination of Brookfield RV viscosity).

Next, the composition of the first epoxy resin is described. As the first epoxy resin, for example, aromatic epoxy resins, aliphatic epoxy resins, alicyclic epoxy resins, and heterocyclic epoxy resins can be cited. As specific examples of the first epoxy resin, bisphenol-type epoxy resins such as bisphenol A epoxy resin and bisphenol F epoxy resin; bisphenol A novolac-type (Japanese: ノボラック type) epoxy resin, cresol novolac-type epoxy resin and other novolac-type epoxy resins; modified epoxy resins such as urethane-modified epoxy resins and rubber-modified epoxy resins. In addition, as other specific examples, biphenyl-type epoxy resins, stilbene-type epoxy resins, trisphenol methane-type epoxy resins, alkyl-modified trisphenol methane-type epoxy resins, epoxy resins containing triazine cores, dicyclopentadiene-modified novolac-type epoxy resins, naphthalene-type epoxy resins, glycol-type epoxy resins, and pentaerythritol-type epoxy resins can be cited. The first epoxy resin may be one type or two or more types.

Depending on the number of repeating units of the bisphenol skeleton, the bisphenol A type epoxy resin may exist in a liquid state at room temperature, or may exist in a solid state at room temperature. A bisphenol A type epoxy resin having a main chain bisphenol skeleton of, for example, 2 or more and 10 or less is solid at room temperature. In particular, bisphenol A type epoxy resin is preferred in that it can improve heat resistance.

In particular, the first epoxy resin is preferably a bisphenol A novolac type epoxy resin represented by the following general formula (1).

[Chemical formula 1]

In the general formula (1), ^R1 is a group represented by _CmH2m (m is 1 to 3), ^R2 and ^R3 are each independently a group represented by _{CpH2p +1} ( _p is 1 to 3), and n is 0 to 10.

In the general formula (1), m in ^R1 is preferably 1, that is, ^R1 is preferably _-CH2- . Similarly, p in ^R2 and ^R3 is preferably 1, that is, ^R2 and ^R3 are preferably _-CH3 . In addition, hydrogen bonded to the benzene ring in the general formula (1) may be substituted by other elements or other groups.

When the resin component contained in the first adhesive layer is set to 100 mass parts, the content of the first epoxy resin is, for example, more than 1 mass part, can be more than 3 mass parts, can also be more than 5 mass parts, can also be more than 10 mass parts, can also be more than 15 mass parts, can also be more than 25 mass parts. If the content of the first epoxy resin is too little, the adhesion and anti-blocking properties after foaming and curing are likely to be reduced. On the other hand, when the resin component contained in the first adhesive layer is set to 100 mass parts, the content of the first epoxy resin is, for example, less than 90 mass parts, can be less than 80 mass parts, can also be less than 70 mass parts, can also be less than 60 mass parts, can also be less than 50 mass parts, can also be less than 40 mass parts. If the content of the first epoxy resin is too much, the content of the second epoxy resin and acrylic resin is relatively reduced, and it is possible that non-adhesiveness, anti-blocking, adhesion to substrate after foaming and curing, crack resistance after foaming and curing and adhesion after foaming and curing are not balanced.

(i-2) Second epoxy resin

The softening temperature of the second epoxy resin is higher than that of the first epoxy resin, and the weight average molecular weight is greater than 20,000. Compared with the first epoxy resin, the second epoxy resin has a higher softening temperature (lower crystallinity). Since the second epoxy resin has lower crystallinity and higher molecular weight, it is easy to improve anti-blocking properties. In addition, since the second epoxy resin has lower crystallinity and higher molecular weight, it is possible to suppress the increase in adhesion (initial adhesion) caused by the first epoxy resin. In addition, the second epoxy resin is preferably an epoxy resin that is solid at room temperature (23°C).

The weight average molecular weight (Mw) of the second epoxy resin is usually greater than the weight average molecular weight (Mw) of the first epoxy resin. The Mw of the second epoxy resin is usually 20,000 or more, and may be 30,000 or more, or 35,000 or more. On the other hand, the Mw of the second epoxy resin is, for example, 100,000 or less.

The epoxy equivalent of the second epoxy resin may be larger, smaller, or the same as that of the first epoxy resin. The epoxy equivalent of the second epoxy resin is, for example, 4000 g/eq or more, 5000 g/eq or more, or 6000 g/eq or more. On the other hand, the epoxy equivalent of the second epoxy resin is, for example, 20000 g/eq or less.

The second epoxy resin may be a monofunctional epoxy resin, a difunctional epoxy resin, a trifunctional epoxy resin, or a tetrafunctional or higher-functional epoxy resin.

The softening temperature of the second epoxy resin is usually higher than the softening temperature of the first epoxy resin. The difference between the two is, for example, 10°C or more, 20°C or more, or 30°C or more. The softening temperature of the second epoxy resin is, for example, 80°C or more, or 90°C or more. On the other hand, the softening temperature of the second epoxy resin is, for example, 180°C or less.

The configuration of the second epoxy resin is the same as that of the first epoxy resin described above, and therefore description thereof is omitted here.

When the resin component contained in the first adhesive layer is set to 100 mass parts, the content of the second epoxy resin is, for example, more than 10 mass parts, more than 15 mass parts, more than 20 mass parts, more than 25 mass parts, more than 30 mass parts, more than 35 mass parts, more than 40 mass parts, more than 45 mass parts. If the content of the second epoxy resin is too little, the adhesiveness becomes high, and the anti-blocking property is likely to be reduced. On the other hand, when the resin component contained in the first adhesive layer is set to 100 mass parts, the content of the second epoxy resin is, for example, less than 90 mass parts, less than 85 mass parts, less than 80 mass parts, less than 75 mass parts. If the content of the second epoxy resin is too much, the content of the first epoxy resin and acrylic resin is relatively less, and it is possible not to balance the anti-blocking property, the adhesion to the substrate after foaming and curing, the crack resistance after foaming and curing, and the adhesiveness after foaming and curing.

The ratio of the first epoxy resin to the total of the first epoxy resin and the second epoxy resin is, for example, 5% by mass or more, 10% by mass or more, 15% by mass or more, or 20% by mass or more. On the other hand, the ratio of the first epoxy resin is, for example, 80% by mass or less, 75% by mass or less, or 60% by mass or less.

The ratio of the total of the first epoxy resin and the second epoxy resin to the total epoxy resin contained in the first adhesive layer is, for example, 50 mass % or more, 70 mass % or more, 90 mass % or more, or 100 mass %.

(ii) Acrylic resin

When the curable adhesive is an epoxy resin adhesive, the first bonding layer can further contain an acrylic resin compatible with epoxy resin. Acrylic resin is a resin compatible with epoxy resin. Since acrylic resin is compatible with epoxy resin, it is easy to improve the toughness of the first bonding layer. As a result, the adhesion after foaming and curing can be improved. In addition, it is believed that acrylic resin plays a role as a compatibilizer of a foaming agent (for example, the foaming agent of the resin of the shell portion is acrylonitrile copolymer) and is evenly dispersed and foamed, so that the adhesion after foaming and curing improves. In addition, the flexibility brought by acrylic resin can be brought into play, and the improvement of the adhesion of the substrate after foaming and curing and the improvement of the crack resistance after foaming and curing can be sought. In addition, by making acrylic resin compatible with epoxy resin, the hardness on the first bonding layer surface can be kept high. On the other hand, if acrylic resin is incompatible with epoxy resin, a soft position is formed on the first bonding layer surface, so sometimes the interface with the adherend becomes difficult to slide, and operability is reduced.

The acrylic resin in the present embodiment is compatible with the epoxy resin. Here, the compatibility of the acrylic resin with the epoxy resin can be confirmed, for example, by observing the cross section of the first adhesive layer of the foaming adhesive sheet with a scanning electron microscope (SEM) or a transmission electron microscope (TEM) without producing micron-sized islands. More specifically, the average particle size of the island is preferably less than 1 μm. Among them, the average particle size of the island can be less than 0.5 μm, or less than 0.3 μm. The more samples, the more preferred, for example, more than 100. The observed area is in the range of 100 μm × 100 μm, or, when the thickness of the first adhesive layer is less than 100 μm, it is carried out in the range of thickness × 100 μm.

The weight average molecular weight (Mw) of the acrylic resin is, for example, 50,000 or more, 70,000 or more, or 100,000 or more. The first epoxy resin has high crystallinity, and there is a possibility that the melt viscosity (or dynamic viscoelasticity) will become too low when heated, and shrinkage may occur during curing after foaming (from the end of foaming of the foaming agent to the curing of the first adhesive layer). However, by using an acrylic resin with a certain molecular weight, the melt viscosity can be prevented from becoming too low, and shrinkage is not likely to occur during curing after foaming. On the other hand, the Mw of the acrylic resin is, for example, 1,500,000 or less. The weight average molecular weight of the acrylic resin can be measured by GPC (eluent: THF, standard substance: PS, sample: 20 μL, flow rate: 1 mL/min, column temperature: 40°C).

The glass transition temperature (Tg) of the acrylic resin is, for example, 90° C. or higher, or 100° C. or higher. On the other hand, the Tg of the acrylic resin is, for example, 180° C. or lower. Tg can be measured by thermal analysis such as differential scanning calorimetry (DSC) in accordance with JIS K7121 corresponding to ISO 3146.

The storage modulus (E') of the acrylic resin at the foaming start temperature may be 1×10 ⁶ Pa or less. By making E' low at the start of foaming, the fluidity is improved and good foaming properties can be obtained. On the other hand, E' at the foaming start temperature is, for example, 1×10 ⁵ Pa or more. It should be noted that the foaming start temperature is a temperature that varies depending on the type of foaming agent. In addition, when two or more foaming agents are used as the foaming agent, the starting temperature of the main foaming reaction is taken as the foaming start temperature.

The storage modulus (E') of the acrylic resin at the curing start temperature may be 1×10 ⁵ Pa or more. As described above, shrinkage may occur during curing after foaming (from the end of foaming of the foaming agent to the curing of the first adhesive layer), but by making E' at the curing start temperature large, shrinkage can be suppressed and good shape retention can be obtained. It should be noted that the curing start temperature is a temperature that varies depending on the type of curing agent. In addition, when two or more curing agents are used as the curing agent, the starting temperature of the main curing reaction is used as the curing start temperature.

The average value of the storage modulus (E') of the acrylic resin at 0°C to 100°C may be 1×10 ⁶ Pa or more. By making the average value of E' before foaming high, good non-adhesiveness and anti-blocking properties can be obtained. On the other hand, the average value of the storage modulus (E') at 0°C to 100°C is, for example, 1×10 ⁸ Pa or less.

The acrylic resin may have a polar group. Examples of the polar group include an epoxy group, a hydroxyl group, a carboxyl group, a nitrile group, and an amide group.

The acrylic resin may be a mixed component comprising two or more homopolymers, or a component comprising one or more copolymers, wherein the homopolymer is a homopolymer of an acrylate monomer, and the copolymer is a copolymer of two or more acrylate monomers. In addition, the acrylic resin may be a mixed component of the above homopolymer and the above copolymer. The "acrylic acid" of the acrylate monomer also includes the concept of methacrylic acid. Specifically, the acrylic resin may be a mixture of a methacrylate polymer and an acrylate polymer, or may be an acrylate polymer such as acrylate-acrylate, methacrylate-methacrylate, or methacrylate-acrylate. Among them, the acrylic resin preferably comprises a copolymer of two or more acrylate monomers (a (meth)acrylate copolymer).

As the monomer components constituting the (meth)acrylate copolymer, for example, the monomer components described in Japanese Patent Publication No. 2014-065889 can be cited. The above-mentioned monomer components may have the above-mentioned polar groups. As the above-mentioned (meth)acrylate copolymer, for example, ethyl acrylate-butyl acrylate-acrylonitrile copolymer, ethyl acrylate-acrylonitrile copolymer, butyl acrylate-acrylonitrile copolymer can be cited. It should be noted that "acrylic acid" of methyl acrylate, ethyl acrylate, etc. also includes "methacrylic acid" of methyl methacrylate, ethyl methacrylate, etc.

As the above-mentioned (meth)acrylate copolymer, a block copolymer is preferred, and an acrylic block copolymer such as a methacrylate-acrylate copolymer is more preferred. Examples of the (meth)acrylate constituting the acrylic block copolymer include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, and benzyl acrylate. These "acrylic acids" also include "methacrylic acids".

Specific examples of methacrylate-acrylate copolymers include acrylic copolymers such as methyl methacrylate-butyl acrylate-methyl methacrylate (MMA-BA-MMA) copolymers. MMA-BA-MMA copolymers also include block copolymers of polymethyl methacrylate-polybutyl acrylate-polymethyl methacrylate (PMMA-PBA-PMMA).

The acrylic copolymer may not have a polar group, or may be a modified product in which the polar group is partially introduced. The modified product is easily compatible with the epoxy resin, so the adhesiveness is further improved.

Among them, the acrylic resin is preferably a (meth)acrylate copolymer having a first polymer portion having a glass transition temperature (Tg) of 10° C. or less and a second polymer portion having a glass transition temperature (Tg) of 20° C. or more. Such a (meth)acrylate copolymer has a first polymer portion that is a soft segment and a second polymer portion that is a hard segment.

The above effects can be inferred as follows: by using an acrylic resin having both soft segments and hard segments such as the (meth)acrylate copolymer, the hard segments contribute to heat resistance and the soft segments contribute to toughness or flexibility, thereby obtaining a first adhesive layer having good heat resistance, toughness and flexibility.

At least one of the first polymer part and the second polymer part contained in the (meth)acrylate copolymer is compatible with the epoxy resin. When the first polymer part is compatible with the epoxy resin, the flexibility can be improved. In addition, when the second polymer part is compatible with the epoxy resin, the cohesion and toughness can be improved.

When one of the first polymer part or the second polymer part is not compatible with the epoxy resin, the (meth)acrylate copolymer has a compatible part, which is a polymer part compatible with the epoxy resin, and an incompatible part, which is a polymer part incompatible with the epoxy resin. In this case, when the (meth)acrylate copolymer is added, the compatible part is compatible with the epoxy resin, and the incompatible part is incompatible with the epoxy resin, so fine phase separation occurs. As a result, a fine sea-island structure is expressed. The sea-island structure varies depending on the type of (meth)acrylate copolymer, the compatibility of the first polymer part and the second polymer part contained in the (meth)acrylate copolymer, and the presence or absence of modification based on the introduction of polar groups. For example, the sea-island structure includes: a sea-island structure in which the compatible part of the cured epoxy resin and the (meth)acrylate copolymer is a sea and the incompatible part of the (meth)acrylate copolymer is an island; a sea-island structure in which the incompatible part of the (meth)acrylate copolymer is a sea and the compatible part of the cured epoxy resin and the (meth)acrylate copolymer is an island; and a sea-island structure in which the (meth)acrylate copolymer is a sea and the cured epoxy resin is an island. By having such a sea-island structure, stress can be easily dispersed, so that interface damage can be avoided and excellent adhesion can be obtained after foaming and curing.

Among the above-mentioned (meth)acrylate copolymers, block copolymers are preferred, and A-B-A block copolymers having a compatible site as polymer block A and an incompatible site as polymer block B are particularly preferred. In addition, A-B-A block copolymers having a first polymer part as an incompatible site, a second polymer part as a compatible site, a first polymer part as polymer block B, and a second polymer part as polymer block A are preferred. By using such an A-B-A block copolymer as an acrylic resin, in the case of a sea island structure in which the compatible site of the cured epoxy resin and the (meth)acrylate copolymer is a sea and the incompatible site of the (meth)acrylate copolymer is an island, the island portion can be reduced. In addition, in the case of a sea island structure in which the incompatible site of the (meth)acrylate copolymer is a sea and the compatible site of the cured epoxy resin and the (meth)acrylate copolymer is an island, or in the case of a sea island structure in which the (meth)acrylate copolymer is a sea and the cured epoxy resin is an island, the sea portion can be reduced.

The (meth)acrylate copolymer may be a modified product in which the polar group is introduced into a part of the first polymer portion or the second polymer portion.

The upper limit of Tg of the first polymer part contained in the (meth)acrylate copolymer is 10°C or less, and can be 0°C or less, and can be -10°C or less in particular. On the other hand, the lower limit of Tg is -150°C or more, and can be -130°C or more, and can be -110°C or more in particular.

The Tg of the first polymer portion can be calculated by the following formula based on the Tg (K) of each homopolymer described in "POLYMER HAND BOOK 3rd Edition" (published by John Wiley & Sons, Ink.).

1/Tg(K)＝W ₁ /Tg ₁ +W ₂ /Tg ₂ +····+W _n /Tg _n

W _n : mass fraction of each monomer

Tg _n : Tg (K) of the homopolymer of each monomer, and generally disclosed values such as the values in Polymer Handbook (3rd Ed., J. Brandrup and E. H. Immergut, WILEY INTERSCIENCE) may be used. The same applies to the Tg of the second polymer part described later.

The first polymer part contained in the above-mentioned (meth)acrylate copolymer may be a homopolymer or a copolymer, and preferably a homopolymer. The monomer components and polymer components constituting the first polymer part may be monomer components and polymer components that can obtain the first polymer part having a Tg within a predetermined range, and examples thereof include acrylate monomers such as butyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate, and methyl acrylate, other monomers such as vinyl acetate, acetal, and urethane, polar group-containing monomers containing the above-mentioned polar groups, and copolymers such as EVA.

The lower limit of Tg of the second polymer part contained in the (meth)acrylate copolymer is 20°C or higher, and can be 30°C or higher, and particularly can be 40°C or higher. On the other hand, the upper limit of Tg can be 150°C or lower.

The second polymer part contained in the (meth)acrylate copolymer may be a homopolymer or a copolymer, and preferably a homopolymer. The monomer component constituting the second polymer part may be any monomer component that can obtain the second polymer part having a Tg within a predetermined range, and examples thereof include: acrylic acid ester monomers such as methyl methacrylate, acrylamide, styrene, vinyl chloride, amide, acrylonitrile, cellulose acetate, phenol, carbamate, vinylidene chloride, methylene chloride, methacrylonitrile and other monomers, and polar group-containing monomers containing the above-mentioned polar groups.

Specific examples of the (meth)acrylate copolymer having the first polymer part and the second polymer part include the above-mentioned MMA-BA-MMA copolymer.

When the resin component contained in the first adhesive layer is set to 100 mass parts, the content of acrylic resin is, for example, more than 1 mass part, can be more than 3 mass parts, can also be more than 5 mass parts, can also be more than 7 mass parts, can also be more than 10 mass parts. If the content of acrylic resin is too little, then the adhesion to the substrate after foaming and curing, the crack resistance after foaming and curing and the adhesion after foaming and curing are likely to reduce. On the other hand, when the resin component contained in the first adhesive layer is set to 100 mass parts, the content of acrylic resin is, for example, less than 60 mass parts, can be less than 50 mass parts, can also be less than 40 mass parts, can also be less than 35 mass parts, can also be less than 30 mass parts. If the content of acrylic resin is too much, then the content of the first epoxy resin and the second epoxy resin is relatively reduced, and it is possible to balance the adhesion to the substrate after non-adhesiveness, anti-blocking, foaming and curing, the crack resistance after foaming and curing and the adhesion after foaming and curing. In addition, if the content of acrylic resin is too much, then the film strength is likely to reduce.

(iii) Curing agent

As the curing agent in the present embodiment, a curing agent commonly used in epoxy resin adhesives can be used. The curing agent is preferably solid at room temperature (23° C.). A curing agent that is solid at room temperature can extend the storage stability (applicable life) compared to a curing agent that is liquid at room temperature. In addition, the curing agent may be a latent curing agent. In addition, the curing agent may be a curing agent that undergoes a curing reaction by heat, or a curing agent that undergoes a curing reaction by light. In addition, the curing agent may be used alone, or two or more types may be used.

The reaction starting temperature of the curing agent is, for example, above 110°C, and may be above 130°C. If the reaction starting temperature is too low, the reaction starts at an early stage, and curing occurs in a state where the softness and fluidity of the resin component are low, and it may be difficult to uniformly cure. On the other hand, the reaction starting temperature of the curing agent is, for example, below 200°C. If the reaction starting temperature is too high, the resin component may deteriorate. It should be noted that, in the case of using a resin with high heat resistance such as a phenolic resin in addition to an epoxy resin, since the resin component deteriorates less, the reaction starting temperature of the curing agent may be, for example, below 300°C. The reaction starting temperature of the curing agent can be obtained by differential scanning calorimetry (DSC).

Specific examples of the curing agent include imidazole-based curing agents, phenol-based curing agents, amine-based curing agents, acid anhydride-based curing agents, isocyanate-based curing agents, and thiol-based curing agents.

As imidazole curing agents, for example, imidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2-methylimidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole, 2-isopropylimidazole, 2-phenylimidazole, carboxylates of imidazole compounds, and adducts with epoxy compounds can be cited. In addition, the imidazole curing agent preferably has a hydroxyl group. Since crystallization occurs through hydrogen bonding between hydroxyl groups, there is a tendency for the reaction starting temperature to become higher.

As the phenolic curing agent, for example, phenolic resin can be mentioned. In addition, as the phenolic resin, for example, resol type phenolic resin and novolac type phenolic resin can be mentioned. From the viewpoints of adhesion to the substrate after foaming and curing, crack resistance after foaming and curing, etc., phenolic novolac resins with a Tg of 110° C. or less are particularly preferred. In addition, a phenolic curing agent and an imidazole curing agent can also be used in combination. In this case, it is preferred to use an imidazole curing agent as a curing catalyst.

Examples of the amine-based curing agent include aliphatic amines, aromatic amines, alicyclic amines, and polyamides.

Examples of the aliphatic amines include diethylenetriamine (DETA), triethylenetetramine (TETA), meta-xylylenediamine (MXDA), etc. Examples of the aromatic amines include diaminodiphenylmethane (DDM), meta-phenylenediamine (MPDA), diaminodiphenylsulfone (DDS), etc.

As the amine-based curing agent, a dicyandiamide-based curing agent such as dicyandiamide (DICY), an organic acid dihydrazide-based curing agent, an amine adduct-based curing agent, or a ketimine-based curing agent can be used.

Examples of the acid anhydride curing agent include alicyclic acid anhydrides (liquid acid anhydrides) and aromatic acid anhydrides.

Examples of the alicyclic acid anhydride (liquid acid anhydride) include hexahydrophthalic anhydride (HHPA), methyltetrahydrophthalic anhydride (MTHPA), etc. Examples of the aromatic acid anhydride include trimellitic anhydride (TMA), pyromellitic anhydride (PMDA), benzophenonetetracarboxylic dianhydride (BTDA), etc.

Examples of the isocyanate curing agent include blocked isocyanate.

Examples of the thiol-based curing agent include ester bond-type thiol compounds, aliphatic ether bond-type thiol compounds, and aromatic ether bond-type thiol compounds.

When the resin component contained in the first adhesive layer is set to 100 parts by mass, the content of the curing agent is, for example, more than 1 part by mass and less than 40 parts by mass. For example, when the imidazole curing agent as a curing agent is used as the main component, when the resin component contained in the first adhesive layer is set to 100 parts by mass, the content of the curing agent is, for example, preferably more than 1 part by mass and less than 15 parts by mass. On the other hand, when the phenol curing agent as a curing agent is used as the main component, when the resin component contained in the first adhesive layer is set to 100 parts by mass, the content of the curing agent is, for example, preferably more than 5 parts by mass and less than 40 parts by mass. It should be noted that the use of the imidazole curing agent or the phenol curing agent as the main component of the curing agent means that the mass proportion of the imidazole curing agent or the phenol curing agent in the curing agent is the largest.

(b) Foaming agent

The first adhesive layer in this embodiment may contain a foaming agent or may not contain a foaming agent, and preferably contains a foaming agent. By containing a foaming agent, the surface roughness becomes larger, the friction coefficient becomes smaller, and the sliding property becomes better. Therefore, among the first adhesive layer and the second adhesive layer, it is preferred that the first adhesive layer with low initial adhesion contains a foaming agent.

As the foaming agent, a foaming agent commonly used in the adhesive layer of a foamable adhesive sheet can be used. In addition, the foaming agent may be a foaming agent that generates a foaming reaction by heat or a foaming agent that generates a foaming reaction by light.

The foaming starting temperature of the foaming agent is preferably above the softening temperature of the main agent of the curable adhesive such as epoxy resin and below the activation temperature of the curing reaction of the main agent of the curable adhesive such as epoxy resin. The foaming starting temperature of the foaming agent is, for example, above 70°C, and can be above 100°C. If the foaming starting temperature is too low, the reaction starts at an early stage, and foaming occurs in a state where the softness and fluidity of the resin component are low, and it may be difficult to produce uniform foaming. On the other hand, the foaming starting temperature of the foaming agent is, for example, below 210°C. If the foaming starting temperature is too high, the resin component may deteriorate.

The softening temperature of the main component of a curable adhesive such as an epoxy resin can be measured using the ring and ball softening temperature test method specified in JIS K7234.

Examples of the foaming agent include microcapsule-type foaming agents, which preferably have a thermal expansion agent such as hydrocarbon as a core and a resin such as an acrylonitrile copolymer as a shell.

In addition, as the foaming agent, for example, an organic foaming agent or an inorganic foaming agent can be used. As the organic foaming agent, for example, there can be mentioned: azo foaming agents such as azodicarbonamide (ADCA), azobiscarbonamide, and azobisisobutyronitrile; fluorinated alkane foaming agents such as trichloromonofluoromethane; hydrazine foaming agents such as p-toluenesulfonylhydrazide; semicarbazide foaming agents such as p-toluenesulfonylsemicarbazide; triazole foaming agents such as 5-morpholinyl-1,2,3,4-thiotriazole; N-nitroso foaming agents such as N,N-dinitrosoterephthalamide. On the other hand, as the inorganic foaming agent, for example, there can be mentioned ammonium carbonate, ammonium bicarbonate, ammonium nitrite, ammonium borohydride, and azides.

The average particle size of the foaming agent may be, for example, 10 μm or more, 13 μm or more, or 17 μm or more. By setting the average particle size of the foaming agent to the above range, the static friction coefficient of the surface of the first adhesive layer can be reduced, and the first adhesive layer with good sliding properties can be made. In addition, the average particle size of the foaming agent is preferably less than the thickness of the first adhesive layer, for example, 44 μm or less, 30 μm or less, or 24 μm or less.

It should be noted that the average particle size of the foaming agent is the particle size at the cumulative value of 50% in the particle size distribution obtained by the laser diffraction scattering method. In addition, when measuring the average particle size of the foaming agent, the first adhesive layer is dissolved in a solvent to separate the foaming agent. The solvent is not particularly limited as long as it is a solvent that can dissolve the components other than the foaming agent contained in the first adhesive layer. It can be appropriately selected according to the type of curable adhesive contained in the first adhesive layer. For example, a solvent used in the adhesive composition for forming the first adhesive layer can be used. Specifically, methyl ethyl ketone, ethyl acetate, toluene, etc. can be used.

When the resin component contained in the first adhesive layer is set to 100 parts by mass, the content of the foaming agent is, for example, more than 0.5 parts by mass, more than 2 parts by mass, more than 3 parts by mass, more than 4 parts by mass, or more than 5 parts by mass. On the other hand, relative to 100 parts by mass of the resin component contained in the first adhesive layer, the content of the foaming agent is, for example, less than 25 parts by mass, less than 20 parts by mass, or less than 15 parts by mass. If the content of the foaming agent is too little, the static friction coefficient of the surface of the first adhesive layer is likely to become larger. In addition, if the content of the foaming agent is too much, the content of the curable adhesive is relatively less, so the adhesion after the foaming and curing is likely to be reduced.

(c) Other ingredients

Regarding the first adhesive layer in the present embodiment, for example, when the curable adhesive is an epoxy resin adhesive, the first adhesive layer may contain only epoxy resin and acrylic resin as resin components, or may further contain other resins. Examples of other resins include urethane resins.

The total ratio of the first epoxy resin, the second epoxy resin and the acrylic resin to the resin component contained in the first adhesive layer is, for example, 70 mass % or more, 80 mass % or more, 90 mass % or more, or 100 mass %.

The content of the resin component contained in the first adhesive layer may be, for example, 60 mass % or more, 70 mass % or more, 80 mass % or more, or 90 mass % or more.

The first adhesive layer may contain additives such as silane coupling agents, fillers, antioxidants, light stabilizers, ultraviolet absorbers, lubricants, plasticizers, antistatic agents, crosslinking agents, colorants, etc. as needed. As silane coupling agents, for example, epoxy silane coupling agents can be cited. As fillers, for example, inorganic fillers such as calcium carbonate, aluminum hydroxide, magnesium hydroxide, antimony trioxide, zinc borate, molybdenum compounds, titanium dioxide can be cited. As antioxidants, for example, phenolic antioxidants and sulfur antioxidants can be cited.

(2) Composition of the first adhesive layer

In the case where the first adhesive layer also contains a foaming agent, the first adhesive layer can be foamed at a foaming ratio of, for example, more than 4 times and less than 15 times. For example, when only the first adhesive layer of the first adhesive layer and the second adhesive layer contains a foaming agent, the foaming ratio can be, for example, more than 5 times, more than 7 times, or more than 9 times. In addition, in the above case, the foaming ratio can be, for example, less than 14 times, less than 13 times, or less than 12 times. On the other hand, for example, when both the first adhesive layer and the second adhesive layer contain a foaming agent, the foaming ratio can be, for example, more than 5 times, more than 6 times, or more than 7 times. In addition, in the above case, the foaming ratio can be, for example, less than 14 times, less than 12 times, or less than 10 times. Whether the foaming ratio is too small or too large, the adhesion after foaming and curing is likely to be reduced.

Here, the expansion ratio can be obtained according to the following formula.

Foaming ratio (times) = thickness of the first adhesive layer after foaming and curing / thickness of the first adhesive layer before foaming and curing

The thickness of the first adhesive layer is not particularly limited, but when the first adhesive layer contains a foaming agent, it is preferably greater than the average particle size of the foaming agent, for example, greater than 10 μm, greater than 15 μm, or greater than 20 μm. If the first adhesive layer is too thin, it may not be possible to fully obtain the adhesion to the substrate and the adhesion after foaming and curing. On the other hand, the thickness of the first adhesive layer is, for example, less than 200 μm, less than 150 μm, or less than 100 μm. If the first adhesive layer is too thick, the surface quality (Japanese: surface quality) may deteriorate.

Here, the thickness of the first adhesive layer is a value measured by observing the cross section of the foaming adhesive sheet in the thickness direction using a transmission electron microscope (TEM), a scanning electron microscope (SEM) or a scanning transmission electron microscope (STEM), and can be set as the average value of the thickness of 10 randomly selected locations. It should be noted that the method for measuring the thickness of other layers possessed by the foaming adhesive sheet can also be handled in the same manner.

The first adhesive layer may be a continuous layer or a discontinuous layer. Examples of the discontinuous layer include patterns such as stripes and dots. In addition, the surface of the first adhesive layer may have a concave-convex shape such as embossing.

The first adhesive layer can be formed, for example, by applying an adhesive composition containing the above-mentioned curable adhesive and foaming agent and removing the solvent. Examples of the coating method include roll coating, reverse roll coating, transfer roll coating, gravure coating, gravure reverse coating, comma coating, rod coating, blade coating, rod coating, wire bar coating, die coating, die lip coating, and dip coating.

The adhesive composition may contain a solvent or may not contain a solvent. It should be noted that the solvent in this specification not only includes a strict solvent (a solvent that dissolves a solute) but also includes a broad meaning of a dispersion medium. In addition, the solvent contained in the adhesive composition is volatilized and removed when the adhesive composition is applied and dried to form an adhesive layer.

The adhesive composition can be obtained by mixing the above-mentioned components and kneading and dispersing as needed. As a mixing and dispersing method, a common kneading and dispersing machine can be used, such as a double roll mill, a triple roll mill, a gravel mill, a Trom mill, a Szegvari mill, a high-speed impeller disperser, a high-speed stone mill, a high-speed impact mill, a disperser, a high-speed mixer, a ribbon blender, a worm kneader, a strong kneading machine, a tumble mixer, a blender, a dispensing machine, a homogenizer, and an ultrasonic disperser.

3. Second bonding layer

(1) Material of the second adhesive layer

The second adhesive layer in this embodiment contains a curable adhesive.

(a) Curable Adhesive

The curable adhesive contained in the second adhesive layer in the present embodiment may be the same as the curable adhesive used in the first adhesive layer described above. Among them, the curable adhesive is preferably an epoxy resin-based adhesive.

Hereinafter, an example will be described in which the curable adhesive is an epoxy resin adhesive.

(i) Epoxy resin

The epoxy resin in this embodiment may be the same as the epoxy resin used in the above-mentioned first adhesive layer.

As the epoxy resin, epoxy resins generally used for adhesive layers of foamable adhesive sheets can be used.

Examples of the epoxy resin include aromatic epoxy resins, aliphatic epoxy resins, alicyclic epoxy resins, and heterocyclic epoxy resins. Specific examples of the epoxy resin are the same as those of the first epoxy resin used in the first adhesive layer.

The epoxy resin may be a monofunctional epoxy resin, a difunctional epoxy resin, a trifunctional epoxy resin, or a tetrafunctional or higher-functional epoxy resin.

Among them, epoxy resins that are liquid at room temperature, such as bisphenol A epoxy resin and bisphenol F epoxy resin, and epoxy resins with low softening points are preferably used as epoxy resins because the initial adhesion of the second adhesive layer can be easily adjusted within a predetermined range by using these epoxy resins.

(ii) Acrylic resin

When the curable adhesive is an epoxy resin adhesive, the second adhesive layer may further contain an acrylic resin compatible with the epoxy resin to improve film-forming properties.

The acrylic resin may be the same as the acrylic resin used in the above-mentioned first adhesive layer.

(iii) Curing agent

As the curing agent in the present embodiment, it can be the same as the curing agent used in the above-mentioned first adhesive layer. In addition, as the curing agent, a solid curing agent can be used at room temperature, and a liquid curing agent can also be used at room temperature, but, from the viewpoint of storage stability, it is preferably used to be a solid curing agent at room temperature.

(b) Foaming agent

The second adhesive layer in this embodiment may or may not contain a foaming agent, but preferably contains a foaming agent. By making both the first adhesive layer and the second adhesive layer contain a foaming agent, the adhesion between the first adhesive layer and the second adhesive layer after foaming and curing can be improved.

The foaming agent may be the same as the foaming agent used in the first adhesive layer.

(c) Other ingredients

The second adhesive layer in the present embodiment may contain only epoxy resin and acrylic resin as resin components, or may further contain other resins, such as urethane resins, when the curable adhesive is an epoxy resin-based adhesive.

The total ratio of the epoxy resin and the acrylic resin to the resin component contained in the second adhesive layer is, for example, 70 mass % or more, 80 mass % or more, 90 mass % or more, or 100 mass %.

The content of the resin component contained in the second adhesive layer may be, for example, 60 mass % or more, 70 mass % or more, 80 mass % or more, or 90 mass % or more.

The second adhesive layer may contain additives as necessary. The additives may be the same as those used in the first adhesive layer.

(2) Composition of the Second Adhesive Layer

When the second adhesive layer also contains a foaming agent, the second adhesive layer can be foamed at a foaming ratio of, for example, 1.5 times or more and 12 times or less. For example, when both the first adhesive layer and the second adhesive layer contain a foaming agent, the foaming ratio can be, for example, 2 times or more, 3 times or more, or 4 times or more. In addition, in the above case, the foaming ratio can be, for example, 10 times or less, 9 times or less, or 8 times or less. Whether the foaming ratio is too small or too large, the adhesion after foaming and curing is likely to be reduced.

The thickness of the second adhesive layer may be the same as the thickness of the first adhesive layer.

The second adhesive layer may be a continuous layer or a discontinuous layer. In addition, the surface of the second adhesive layer may have a concavo-convex shape such as embossing.

The second adhesive layer may be formed by the same method as the above-mentioned first adhesive layer.

4. Substrate

The substrate in this embodiment is disposed between the first adhesive layer and the second adhesive layer described above.

The substrate preferably has insulating properties. In addition, the substrate is preferably in the form of a sheet. The substrate may have a single-layer structure or a multi-layer structure. In addition, the substrate may have a porous structure inside or may not have a porous structure.

Examples of the substrate include a resin substrate and a nonwoven fabric.

Examples of the resin contained in the resin substrate include polyester resin, polycarbonate, polyarylate, polyurethane, polyamide resin, polyimide resin, polysulfone resin, polyetherketone resin, polyphenylene sulfide (PPS), and modified polyphenylene ether.

As the polyester resin, for example, polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate (PEN), aromatic polyester, etc. can be cited. In addition, as the polyamide resin, polyamide, polyether amide, etc. can be cited. In addition, as the polyimide resin, polyimide, polyether imide, polyamide-imide, etc. can be cited. In addition, as the polysulfone resin, polysulfone, polyether sulfone, etc. can be cited. In addition, as the polyether ketone resin, polyether ketone, polyether ether ketone, etc. can be cited.

The glass transition temperature of the resin is, for example, 80° C. or higher, 140° C. or higher, or 200° C. or higher. In addition, a liquid crystal polymer (LCP) can be used as the resin.

Examples of the nonwoven fabric include nonwoven fabrics containing fibers such as cellulose fibers, polyester fibers, nylon fibers, aramid fibers, polyphenylene sulfide fibers, liquid crystal polymer fibers, glass fibers, metal fibers, and carbon fibers.

In order to improve the adhesion with the first adhesive layer and the second adhesive layer, the substrate may be subjected to a surface treatment.

The thickness of the substrate is preferably thinner than the thickness of the first adhesive layer and thinner than the thickness of the second adhesive layer. By making the thickness of the substrate thinner than the thickness of the first adhesive layer and the thickness of the second adhesive layer, the thickness of the foamable adhesive sheet can be reduced, and the thickness of the first adhesive layer and the thickness of the second adhesive layer can be relatively thickened. Therefore, the thickness of the foamable adhesive sheet can be reduced without reducing the adhesive properties and foaming properties of the first adhesive layer and the second adhesive layer, thereby improving the insertability.

Specifically, the thickness of the substrate is 200 μm or less, 100 μm or less, or 50 μm or less. In addition, the thickness of the substrate is, for example, 2 μm or more, 5 μm or more, or 9 μm or more.

5. Other components

(1) First intermediate layer and second intermediate layer

The foamable adhesive sheet in the present embodiment can have the first intermediate layer between substrate and the first adhesive layer. In addition, the foamable adhesive sheet in the present embodiment can have the second intermediate layer between substrate and the second adhesive layer. By configuring the first intermediate layer and the second intermediate layer, the adhesion of the first adhesive layer and the second adhesive layer to the substrate can be improved. In addition, by configuring the first intermediate layer and the second intermediate layer, for example, the stress applied to the bending portion when the foamable adhesive sheet is bent can be relaxed, or the stress applied to the cutting portion when the foamable adhesive sheet is cut can be relaxed. As a result, when the foamable adhesive sheet is bent or cut, the first adhesive layer and the second adhesive layer can be suppressed from floating or peeling off from the substrate.

For example, in the foamable adhesive sheet 10 shown in Fig. 5, a first intermediate layer 4 is arranged between the substrate 2 and the first adhesive layer 1, and a second intermediate layer 5 is arranged between the substrate 2 and the second adhesive layer 3. It should be noted that in Fig. 5, the foamable adhesive sheet 10 has both the first intermediate layer 4 and the second intermediate layer 5, but may have only one of them.

The foamable adhesive sheet only needs to have at least one of the first intermediate layer and the second intermediate layer. For example, it can have only the first intermediate layer arranged between the substrate and the first adhesive layer, or only the second intermediate layer arranged between the substrate and the second adhesive layer, or both the first intermediate layer arranged between the substrate and the first adhesive layer and the second intermediate layer arranged between the substrate and the second adhesive layer.

The materials contained in the first intermediate layer and the second intermediate layer are not particularly limited as long as they can improve the adhesion between the substrate and the first adhesive layer and the second adhesive layer and can relieve stress, and can be appropriately selected according to the materials of the substrate, the first adhesive layer and the second adhesive layer, etc. For example, polyester, polyvinyl chloride, polyvinyl acetate, polyurethane, polymers obtained by copolymerizing at least two of them, crosslinked products thereof, and mixtures thereof, etc. can be cited.

The crosslinked product is a crosslinked product formed by crosslinking the above-mentioned resin using a curing agent. As the curing agent, for example, an isocyanate curing agent can be cited. In addition, for example, when the reactive group/NCO equivalent is set to 1, it is preferred to add the isocyanate curing agent in a ratio of 0.5 mass % or more and 20 mass % or less relative to the resin.

The first intermediate layer and the second intermediate layer preferably contain a cross-linked resin. It should be noted that the cross-linked resin refers to a resin that does not melt even when it is heated to a high temperature. This can improve the adhesive force at high temperatures, that is, the heat resistance.

The thickness of the first intermediate layer and the second intermediate layer is not particularly limited, for example, more than 0.1 μm, more than 0.5 μm, or more than 1 μm. If the first intermediate layer and the second intermediate layer are too thin, it is possible to fully obtain the effect of the first adhesive layer and the second adhesive layer peeling off from the base material when the bending and cutting of the foaming adhesive sheet are suppressed. On the other hand, the thickness of the first intermediate layer and the second intermediate layer is, for example, less than 4 μm, and less than 3.5 μm. The first intermediate layer and the second intermediate layer themselves are usually not high in heat resistance, so if the first intermediate layer and the second intermediate layer are too thick, heat resistance (adhesion under high temperature) is likely to reduce.

The first intermediate layer and the second intermediate layer can be formed, for example, by applying the resin composition and removing the solvent. Examples of the coating method include roll coating, reverse roll coating, transfer roll coating, gravure coating, gravure reverse coating, comma coating, rod coating, blade coating, rod coating, wire bar coating, die coating, die lip coating, and dip coating.

(2) First spacer and second spacer

The foamable adhesive sheet in this embodiment may have a first spacer on the surface of the first adhesive layer opposite to the second adhesive layer. In addition, the foamable adhesive sheet in this embodiment may have a second spacer on the surface of the second adhesive layer opposite to the first adhesive layer.

The first spacer and the second spacer are not particularly limited as long as they can be peeled off from the first adhesive layer and the second adhesive layer, and can have a strength that can protect the first adhesive layer and the second adhesive layer. As such first spacer and second spacer, for example, release film, release paper, etc. can be cited. In addition, the first spacer and the second spacer can have a single-layer structure or a multi-layer structure.

Examples of the single-layer separator include fluororesin films and the like.

In addition, as a separator of a multilayer structure, for example, a laminate having a release layer on one side or both sides of a substrate layer can be cited. As the substrate layer, for example, resin films such as polypropylene, polyethylene, polyethylene terephthalate, woodfree paper, coated paper, impregnated paper and the like can be cited. As the material of the release layer, as long as it is a material with release properties, it is not particularly limited, for example, organosilicon compounds, organic compound-modified organosilicon compounds, fluorine compounds, aminoalkyd compounds, melamine compounds, acrylic compounds, polyester compounds, long-chain alkyl compounds and the like can be cited. These compounds can use any of emulsion type, solvent type or solvent-free type.

The first separator and the second separator can be the same or different. Among them, it is preferred that the first separator has heavy peeling properties and the second separator has light peeling properties. In the foam adhesive sheet, the first adhesive layer is substantially non-adhesive (no initial adhesion), and the second adhesive layer has initial adhesion. Therefore, for example, when the rotor and the permanent magnet are bonded in an embedded magnet type motor, after the foam adhesive sheet is arranged on the second member, the second member equipped with the foam adhesive sheet is inserted into the hole of the first member, by attaching the surface of the second adhesive layer of the foam adhesive sheet to the second member, the surface of the first adhesive layer of the foam adhesive sheet is made to be the surface side, thereby improving the adhesion between the second member and the foam adhesive sheet during insertion, and the insertability of the second member equipped with the foam adhesive sheet. In this case, since the second separator is peeled off from the first separator and the second separator, the second separator can be made easier to peel off than the first separator by making the first separator have heavy peeling properties and the second separator have light peeling properties.

It should be noted that light peeling and heavy peeling refer to the degree of force required to peel the first separator and the second separator from the first adhesive layer and the second adhesive layer, and light peeling means that the peeling force is smaller than that of heavy peeling.

6. Foam adhesive sheet

The thickness of the foamable adhesive sheet in the present embodiment is, for example, 10 μm or more, or 20 μm or more. On the other hand, the thickness of the foamable adhesive sheet is, for example, 1000 μm or less, or 200 μm or less.

The use of the foamable adhesive sheet in this embodiment is not particularly limited. The foamable adhesive sheet in this embodiment can be used, for example, in the following situations: the foamable adhesive sheet is arranged between two components, and then the foamable adhesive sheet is foamed and solidified, thereby bonding the two components to each other. Among them, the foamable adhesive sheet in this embodiment is preferably used in the following situation: after the foamable adhesive sheet is arranged on the second component, the second component equipped with the foamable adhesive sheet is inserted into the hole of the first component, and the foamable adhesive sheet is foamed and solidified, thereby bonding the first component and the second component.

The method for producing the foamable adhesive sheet in the present embodiment is not particularly limited, and can be appropriately selected according to the layer structure of the foamable adhesive sheet. For example, the following two methods for producing the foamable adhesive sheet can be mentioned.

In the manufacturing method of the first foamable adhesive sheet, for example, first, an adhesive composition for forming a first adhesive layer is applied to one surface of a substrate and dried to form the first adhesive layer. In addition, an adhesive composition for forming a second adhesive layer is applied to a second spacer and dried to form a second adhesive layer. Next, a laminate of a substrate and the first adhesive layer is laminated with a laminate of a second spacer and the second adhesive layer. Thus, a foamable adhesive sheet is obtained. It should be noted that a first intermediate layer and a second intermediate layer may also be formed. In this method, since the drying process for the first adhesive layer is one time, a foamable adhesive sheet can be manufactured efficiently.

In the manufacturing method of the second foamable adhesive sheet, for example, first, an adhesive composition for forming a first adhesive layer is applied to one side of a substrate and dried to form the first adhesive layer. Then, an adhesive composition for forming a second adhesive layer is applied to the other side of the substrate and dried to form the second adhesive layer. Then, a second spacer is laminated on the second adhesive layer. Thus, a foamable adhesive sheet is obtained. It should be noted that a first intermediate layer and a second intermediate layer may also be formed.

b) Second Embodiment

A second embodiment of the foamable adhesive sheet in the present embodiment is a foamable adhesive sheet having a first adhesive layer, a substrate, a second adhesive layer and an adhesive layer in sequence, wherein the first adhesive layer and the second adhesive layer contain a curable adhesive and a foaming agent, the adhesive layer contains a pressure-sensitive adhesive or a curable adhesive, the initial adhesive force of the first adhesive layer is greater than 0 gf and less than 10 gf, the initial adhesive force of the adhesive layer is greater than 10 gf, and the ring stiffness is greater than 50 mN/10 mm.

Fig. 6 is a schematic cross-sectional view illustrating a foamable adhesive sheet in this embodiment. The foamable adhesive sheet 10 in Fig. 6 sequentially comprises a first adhesive layer 1, a substrate 2, a second adhesive layer 3 and an adhesive layer 6. The first adhesive layer 1 and the second adhesive layer 3 contain a curable adhesive and a foaming agent, and the adhesive layer 6 contains a pressure-sensitive adhesive or a curable adhesive. In addition, the initial adhesion of the first adhesive layer 1 and the initial adhesion of the adhesive layer 6 are respectively within a prescribed range, and the ring stiffness of the foamable adhesive sheet 10 is within a prescribed range.

In the present embodiment, by making the initial adhesive force of the adhesive layer within a specified range, it is possible to make an adhesive layer with good adhesion to the component. Specifically, when another component is bonded and fixed in a hole, groove, etc. of a component, that is, when the surface of the adhesive layer of the foamable adhesive sheet is attached to another component, and another component to which the foamable adhesive sheet is attached is inserted into a hole, groove, etc. of a component, and then the foamable adhesive sheet is foamed and solidified to bond one component to another component, by making the initial adhesive force of the adhesive layer within a specified range, it is possible to utilize the initial adhesive force of the adhesive layer to attach the surface of the adhesive layer of the foamable adhesive sheet to another component, and it is possible to improve the adhesion of the adhesive layer to the component. Thus, when another component to which the foamable adhesive sheet is attached is inserted into a hole, groove, etc. of a component, it is possible to suppress the peeling and positional displacement of the foamable adhesive sheet.

In addition, in the present embodiment, since the initial adhesion of the first adhesive layer is below the specified value, the first adhesive layer can be made substantially non-adhesive (no initial adhesion), and the first adhesive layer with good sliding property can be made. Therefore, for example, in the above-mentioned bonding and fixing method, when another member with a foaming adhesive sheet is inserted into a hole, a groove, etc. of a member, another member with a foaming adhesive sheet can be smoothly inserted, and insertability can be improved. Thus, the peeling and positional displacement of the foaming adhesive sheet can be suppressed. In addition, in the above-mentioned bonding and fixing method, when another member is moved relative to a member to align the positions of the members to each other, another member can be smoothly moved relative to a member under the state that another member is inserted into a hole, a groove, etc. of a member, and positional alignment can be easily performed.

In addition, in this embodiment, since the initial adhesion of the first adhesive layer is below a predetermined value, the first adhesive layer is substantially non-adhesive (no initial adhesion), and thus can be made into a first adhesive layer with good sliding properties and good anti-blocking properties. Therefore, the operability of the foamable adhesive sheet can also be improved.

In addition, in this embodiment, as described above, due to the excellent adhesion between the adhesive layer and the member and the excellent sliding property of the first adhesive layer, the peeling and positional displacement of the foamable adhesive sheet can be suppressed. Therefore, the reduction of the adhesiveness of the foamable adhesive sheet after foaming and curing caused by the peeling and positional displacement of the foamable adhesive sheet can be suppressed, and the uneven bonding strength of the foamable adhesive sheet after foaming and curing caused by the peeling and positional displacement of the foamable adhesive sheet can be reduced. Therefore, by using the foamable adhesive sheet of this embodiment, the bonding strength is high, and high reliability and high quality bonding can be achieved.

In addition, in the foamable adhesive sheet of the present embodiment, since the ring rigidity is more than the specified value, the stiffness can be enhanced. Therefore, when the foamable adhesive sheet is transported, the situation that the foamable adhesive sheet droops due to its own weight can be suppressed. Therefore, for example, when the foamable adhesive sheet is adsorbed and transported and attached to another component, the situation that the foamable adhesive sheet is bent, twisted, flexed, bubbles are mixed in, etc. when attached can be suppressed. Therefore, the adhesion can be improved. Further, the situation that the foamable adhesive sheet is raised due to these undesirable conditions can be suppressed, so when another component to which the foamable adhesive sheet is attached is inserted into the hole, groove, etc. of a component, the foamable adhesive sheet can be made less prone to friction. Therefore, the peeling of the foamable adhesive sheet during insertion can be suppressed. Therefore, from such a viewpoint, by using the foamable adhesive sheet of the present embodiment, the bonding strength is high, and high reliability and high-quality bonding can be achieved.

Hereinafter, each structure of the foamable adhesive sheet of this embodiment will be described.

1. Features

The initial adhesive force of the first adhesive layer in this embodiment is the same as the initial adhesive force of the first adhesive layer in the above-mentioned first embodiment.

In the present embodiment, the initial tack of adhesive layer is more than 10gf, can be more than 30gf, can also be more than 50gf.If the initial tack of adhesive layer is too low, then for example in the above-mentioned bonding and fixing method, when utilizing the initial tack of adhesive layer to attach the face of the adhesive layer of foamable adhesive sheet to another member, the adhesion of adhesive layer and another member may reduce, or, when inserting another member with foamable adhesive sheet in the hole, groove etc. of a member, because of the poor adhesion of adhesive layer and another member, the foamable adhesive sheet peels off or the positional displacement of foamable adhesive sheet etc., and there is the first adhesive layer after foaming and curing and the adhesion of adhesive layer to reduce or the possibility of uneven bonding strength generation.In addition, the initial tack of adhesive layer is below 500gf, can be below 400gf, can also be below 300gf.

In this embodiment, the initial tack of the second adhesive layer is not particularly limited. The initial tack of the second adhesive layer is preferably less than 10 gf. In this case, the initial tack of the second adhesive layer may be the same as the initial tack of the first adhesive layer.

The method for measuring the initial tack of the first adhesive layer, the second adhesive layer, and the pressure-sensitive adhesive layer is the same as that described in the first embodiment.

The method for controlling the initial adhesion of the first adhesive layer and the second adhesive layer is the same as that described in the first embodiment.

In this embodiment, the static friction coefficient of the surface of the first adhesive layer opposite to the second adhesive layer and the arithmetic mean roughness (Ra) of the surface of the first adhesive layer opposite to the second adhesive layer are the same as those described in the first embodiment.

The ring stiffness of the foamable adhesive sheet of this embodiment is the same as the ring stiffness of the foamable adhesive sheet of the first embodiment. It should be noted that in this embodiment, when the test piece of the foamable adhesive sheet is placed on the ring stiffness measuring instrument, the test piece of the foamable adhesive sheet is arranged in such a way that the inner surface is the surface of the first adhesive layer and the outer surface is the surface of the adhesive layer.

The adhesiveness after foaming and curing and the electrical insulation property after foaming and curing of the foamable adhesive sheet in this embodiment are the same as those described in the first embodiment.

2. First bonding layer

The first adhesive layer in this embodiment contains a curable adhesive and a foaming agent. The material and structure of the first adhesive layer can be the same as those of the first adhesive layer in the first embodiment described above.

3. Second bonding layer

The second adhesive layer in this embodiment contains a curable adhesive and a foaming agent. The material and structure of the second adhesive layer may be the same as those of the first adhesive layer in the first embodiment, or may be the same as those of the second adhesive layer in the first embodiment.

4. Adhesive layer

The adhesive layer in this embodiment is disposed on the surface of the second adhesive layer opposite to the substrate, and contains a pressure-sensitive adhesive or a curing adhesive. In addition, the adhesive layer does not substantially contain a foaming agent.

As the pressure-sensitive adhesive contained in the adhesive layer in the present embodiment, a common pressure-sensitive adhesive can be used.

In addition, the curable adhesive contained in the adhesive layer in this embodiment may be the same as the curable adhesive used in the second adhesive layer.

The thickness of the adhesive layer is not particularly limited, and may be, for example, 2 μm to 100 μm, 3 μm to 75 μm, or 5 μm to 50 μm. If the adhesive layer is too thin, sufficient adhesion may not be obtained.

The adhesive layer may be a continuous layer or a discontinuous layer. As the discontinuous layer, for example, patterns such as stripes and dots may be mentioned. In addition, the surface of the adhesive layer may have a concave-convex shape such as embossing.

The method for forming the adhesive layer may be the same as the method for forming the first adhesive layer and the second adhesive layer.

5. Substrate

The substrate in this embodiment is disposed between the first adhesive layer and the second adhesive layer. The substrate is the same as the substrate in the first embodiment.

6. Other components

(1) First intermediate layer and second intermediate layer

The foamable adhesive sheet in the present embodiment may have a first intermediate layer between the substrate and the first adhesive layer. In addition, the foamable adhesive sheet in the present embodiment may have a second intermediate layer between the substrate and the second adhesive layer. The first intermediate layer and the second intermediate layer are the same as the first intermediate layer and the second intermediate layer in the above-mentioned first embodiment.

For example, in the foamable adhesive sheet 10 shown in Fig. 7, the first intermediate layer 4 is arranged between the substrate 2 and the first adhesive layer 1, and the second intermediate layer 5 is arranged between the substrate 2 and the second adhesive layer 3. It should be noted that in Fig. 7, the foamable adhesive sheet 10 has both the first intermediate layer 4 and the second intermediate layer 5, but may have only one of them.

(2) First spacer and second spacer

The foamable adhesive sheet in this embodiment may have a first spacer on the side of the first adhesive layer opposite to the second adhesive layer. In addition, the foamable adhesive sheet in this embodiment may have a second spacer on the side of the adhesive layer opposite to the second adhesive layer. The first spacer and the second spacer may be the same as the first spacer and the second spacer in the first embodiment described above.

7. Foam adhesive sheet

The thickness and application of the foamable adhesive sheet in this embodiment are the same as those in the first embodiment.

The method for producing the foamable adhesive sheet in the present embodiment is not particularly limited, and can be appropriately selected according to the layer structure of the foamable adhesive sheet.

B. Method of manufacturing the article

The method for manufacturing an article in the present invention comprises: a placement step of placing the foamable adhesive sheet between a first member and a second member; and a bonding step of foaming and curing the foamable adhesive sheet to bond the first member and the second member.

Fig. 8 (a) to (c) are process diagrams showing an example of a method for manufacturing an article in the present embodiment. First, as shown in Fig. 8 (a), the surface of the second adhesive layer 3 of the foamable adhesive sheet 10 is attached to the second member 20b. Next, as shown in Fig. 8 (b), the second member 20b having the foamable adhesive sheet 10 is inserted into the hole of the first member 20a. Next, as shown in Fig. 8 (c), the first adhesive layer 1 and the second adhesive layer 3 of the foamable adhesive sheet 10 are foamed and cured, for example, by heating. The first member 20a and the second member 20b are bonded (joined) using the adhesive sheet 13 having the foamed and cured first adhesive layer 11 and the second adhesive layer 12. Thus, the article 100 having the adhesive sheet 13 arranged between the first member 20a and the second member 20b is obtained.

Fig. 9 (a) to (c) are process diagrams showing another example of the method for manufacturing the article in this embodiment. In Fig. 9 (a), foamable adhesive sheets are attached to both sides of the second member 20b. It should be noted that the configuration process and the bonding process are the same as those of Fig. 8 (a) to (c).

Hereinafter, a method for manufacturing the article in this embodiment will be described.

1. Foam adhesive sheet

In the method for manufacturing an article in the present embodiment, the above-mentioned foamable adhesive sheet is used as the foamable adhesive sheet.

When the foamable adhesive sheet has the first spacer and the second spacer, when the foamable adhesive sheet is disposed between the first member and the second member, the first spacer and the second spacer are peeled off from the foamable adhesive sheet and then used.

In addition, since the details of the foamable adhesive sheet have been described in the above-mentioned section "A. Foamable adhesive sheet", the description here is omitted.

2. Configuration process

In the configuration process of the present embodiment, as a method for configuring the foaming adhesive sheet between the first member and the second member, it can be appropriately selected according to the types of the first member and the second member, etc. For example, when the first member has a hole or a groove and the second member is configured in the hole or the groove of the first member, when the first member and the second member are fixed by bonding, the second adhesive layer or the surface of the adhesive layer of the foaming adhesive sheet is attached to the second member by using the initial adhesive force of the second adhesive layer or the adhesive layer of the foaming adhesive sheet, and then the second member to which the foaming adhesive sheet is attached is configured in the hole or the groove of the first member; the foaming adhesive sheet is configured in the hole or the groove of the first member, and the second adhesive layer or the surface of the adhesive layer of the foaming adhesive sheet is attached to the hole or the groove of the first member by using the initial adhesive force of the second adhesive layer or the adhesive layer of the foaming adhesive sheet, and then the second member is configured in the hole or the groove of the first member to which the foaming adhesive sheet is attached.

3. Bonding process

In the bonding process of the present embodiment, as a method for foaming and curing the foamable adhesive sheet, heating or light irradiation can be cited. Among them, it is preferred to foam and cure the foamable adhesive sheet by heating. The method based on heating can also be applied when the first member and the second member are not transparent, such as metal members.

The heating conditions are appropriately set according to the type of curable adhesive and foaming agent contained in the first adhesive layer and the second adhesive layer, the type of substrate, etc. The heating temperature can be set to, for example, 130° C. to 200° C. The heating time can be set to, for example, 3 minutes to 3 hours.

II. Second Embodiment

Next, a method for producing a foamable adhesive sheet and an article using the same according to a second embodiment of the present invention will be described in detail.

A. Foam adhesive sheet

The foaming adhesive sheet in this embodiment is a foaming adhesive sheet having a first adhesive layer, a substrate and a second adhesive layer in sequence, the composition of the first adhesive layer is different from that of the second adhesive layer, the first adhesive layer and the second adhesive layer contain a thermosetting adhesive, at least one of the first adhesive layer and the second adhesive layer further contains a foaming agent, and the curling radius of the foaming adhesive sheet after being left to stand for 15 hours at a temperature of 60°C and a humidity of less than 10% RH is greater than 15 mm, and the ring stiffness is greater than 45 mN/10 mm.

Fig. 1 is a schematic cross-sectional view illustrating a foamable adhesive sheet in this embodiment. The foamable adhesive sheet 10 in Fig. 1 has a first adhesive layer 1, a substrate 2, and a second adhesive layer 3 in sequence. The first adhesive layer 1 and the second adhesive layer 3 contain a thermosetting adhesive, and at least one of the first adhesive layer 1 and the second adhesive layer 3 further contains a foaming agent. In addition, the curvature radius of the curl of the foamable adhesive sheet 10 after being left at a predetermined temperature and a predetermined humidity for a predetermined time is within a predetermined range, and the ring stiffness is within a predetermined range.

Here, when another component is bonded and fixed in a hole, groove, etc. of a component, there is a tendency to narrow the gap between two components as described above. Therefore, for the foamable adhesive sheet used, it is required that the overall thickness is thin. However, when the foamable adhesive sheet has the first adhesive layer, base material and the second adhesive layer successively, when the composition of the first adhesive layer and the second adhesive layer is different, if the thickness of the foamable adhesive sheet is thin, curling occurs easily. In addition, if the thickness of the foamable adhesive sheet is thin, then when the foamable adhesive sheet is transported, the foamable adhesive sheet is easily drooped because of its own weight.

In this regard, in the present embodiment, by making the radius of curvature of the curling after standing for a predetermined time at a predetermined temperature and a predetermined humidity within a predetermined range, the curling can be suppressed even when the thickness of the foamable adhesive sheet is thin when the composition of the first adhesive layer and the second adhesive layer is different. Therefore, for example, when the foamable adhesive sheet is inserted between two components, after the foamable adhesive sheet is configured in a hole, groove, etc. of a component, when another component is inserted into the hole, groove, etc. of a component configured with the foamable adhesive sheet, after the foamable adhesive sheet is configured in another component, when another component configured with the foamable adhesive sheet is inserted into the hole, groove, etc. of a component, the insertability can be made good. In addition, for example, when the initial adhesion of the first adhesive layer is lower than the initial adhesion of the second adhesive layer, when the surface of the second adhesive layer of the foamable adhesive sheet is attached to the component using the initial adhesion of the second adhesive layer, the floating and peeling of the foamable adhesive sheet relative to the component can be suppressed. In addition, in the above case, it is possible to suppress the occurrence of bending, twisting, bending, inclusion of bubbles, etc. of the foamable adhesive sheet during attachment. Therefore, it is possible to suppress adhesion defects after foaming and curing.

In addition, the inventors of the present invention focus on the rigidity (stiffness) of the foamable adhesive sheet. It is believed that if the thickness of the foamable adhesive sheet is thick, there is a tendency for the rigidity to increase, so curling can be suppressed and sagging due to self-weight can be suppressed. However, in the case where the gap between the two components is narrow, if the thickness of the foamable adhesive sheet is thickened, the insertion property will deteriorate. In this way, since the thickness of the foamable adhesive sheet originally needs to be thin, it is not suitable to thicken the thickness of the foamable adhesive sheet. It is also believed that if the thickness of the substrate is thick, there is a tendency for the rigidity to increase, curling can be suppressed and sagging due to self-weight can be suppressed. However, if the thickness of the substrate is thickened, the thickness of the foamable adhesive sheet becomes thicker, so as to deteriorate the insertion property in the same way as above. In addition, if the thickness of the substrate is relatively thickened under the state of thinning the thickness of the foamable adhesive sheet, the thickness of the first adhesive layer and the second adhesive layer becomes relatively thinner, so there is a risk that the bonding properties and foaming properties of the first adhesive layer and the second adhesive layer are reduced.

Furthermore, the inventors of the present invention have further conducted studies and found that by setting the ring rigidity of the foamable adhesive sheet to a predetermined range, it is possible to suppress the foamable adhesive sheet from sagging due to its own weight.

It should be noted that the ring stiffness is a parameter indicating the stiffness of a sheet or film. The larger the value of the ring stiffness, the stronger the stiffness of the sheet or film. The ring stiffness is used as a parameter indicating the strength of the stiffness of sheets and films used in packaging materials, for example, but it is not very common in the field of adhesive sheets.

In the foamable adhesive sheet of the present embodiment, since the ring rigidity is more than the specified value, the stiffness can be enhanced. Therefore, when the foamable adhesive sheet is transported, the situation that the foamable adhesive sheet droops due to its own weight can be suppressed. Therefore, for example, when the foamable adhesive sheet is adsorbed and transported and attached to a component, the situation that the foamable adhesive sheet is bent, twisted, flexed, bubbles are mixed in, etc. when attached can be suppressed. Therefore, the adhesion can be improved. Further, the situation that a bulge is generated in the foamable adhesive sheet due to these undesirable conditions can be suppressed, so when another component to which the foamable adhesive sheet is attached is inserted into a hole, a groove, etc. of a component, the foamable adhesive sheet can be made less prone to friction. Therefore, the peeling of the foamable adhesive sheet during insertion can be suppressed.

Therefore, by using the foamable adhesive sheet in the present embodiment, the adhesive strength is high, and high-reliability and high-quality bonding can be achieved.

Here, "adhesion" is a concept included in "bonding". Sometimes there is a distinction in that adhesion is used to mean a temporary bonding phenomenon, while bonding is used to mean a substantially permanent bonding phenomenon (Iwanami Shoten Physical and Chemical Dictionary, 5th edition). "Adhesion" and "adhesive strength" refer to the properties of bonding by pressure sensitivity and the adhesive strength at that time.

It should be noted that, in this specification, unless otherwise specified, "the adhesiveness of the adhesive layer" and "the adhesive strength of the adhesive layer" refer to the adhesiveness and adhesive strength of the adhesive layer before curing. In addition, in this specification, unless otherwise specified, "the adhesiveness of the adhesive layer" and "the adhesive strength of the adhesive layer" refer to the adhesiveness and adhesive strength of the adhesive layer after curing.

Hereinafter, each structure of the foamable adhesive sheet in this embodiment will be described.

1. Features

For the foamable adhesive sheet in the present embodiment, the radius of curvature of the curling after standing for 15 hours at a temperature of 60°C and a humidity of 10%RH or less is 15 mm or more, preferably 20 mm or more, and more preferably 25 mm or more. By making the radius of curvature the above range, curling can be suppressed. Therefore, for example, when the foamable adhesive sheet is inserted between two components, after the foamable adhesive sheet is arranged in a hole, groove, etc. of a component, when another component is inserted into a hole, groove, etc. of a component in which the foamable adhesive sheet is arranged, after the foamable adhesive sheet is arranged in another component, when another component in which the foamable adhesive sheet is arranged is inserted into a hole, groove, etc. of a component, the insertability can be made good. In addition, for example, when the initial adhesion of the first adhesive layer is lower than the initial adhesion of the second adhesive layer, when the surface of the second adhesive layer of the foamable adhesive sheet is attached to the component using the initial adhesion of the second adhesive layer, the floating and peeling of the foamable adhesive sheet relative to the component can be suppressed. In addition, in the above-mentioned case, it is possible to suppress the bending, twisting, deflection, bubble mixing, etc. of the foamable adhesive sheet when attached. Therefore, it is possible to suppress the poor bonding after the foaming and curing. On the other hand, the larger the radius of curvature, the smaller the curling, so the upper limit of the radius of curvature is not particularly limited.

It should be noted that, when the foamable adhesive sheet is used for bonding the coil and stator in the motor, or bonding the rotor and permanent magnet in the embedded magnet type motor, the length of the foamable adhesive sheet is mostly about 100 mm. Therefore, in this embodiment, when the length of the test piece of the foamable adhesive sheet is set to 100 mm, the test piece can be practical as long as it is not around one circle in the length direction, and the above-mentioned radius of curvature is set to 15 mm or more.

In addition, the thermosetting adhesive shrinks during curing and shrinks due to heat shrinkage. Curling occurs due to this shrinkage. It is generally believed that thermosetting adhesives begin to shrink at around 60°C. Therefore, the main shrinkage factor of thermosetting adhesives is heat. Therefore, in order to eliminate the influence of humidity, in this embodiment, the conditions of 60°C and 15 hours are set, and the humidity is set to below 10% RH.

Here, the curvature radius of the curl of the foamable adhesive sheet can be measured by the following method.

First, the foaming adhesive sheet is cut into a square of 50 mm × 50 mm to make a test piece for curling measurement. At this time, as shown in Figure 11 (a), the side direction of the square is set to the MD direction and TD direction of the foaming adhesive sheet 10. It should be noted that the MD direction of the foaming adhesive sheet refers to the length direction of the foaming adhesive sheet when the foaming adhesive sheet is made into a strip. In addition, the TD direction of the foaming adhesive sheet refers to the direction orthogonal to the MD direction. The MD direction and TD direction of the foaming adhesive sheet can be determined by the following method. In the case where the foaming adhesive sheet is a strip, the length direction of the foaming adhesive sheet is set to the MD direction. In addition, in the case where the foaming adhesive sheet is a single sheet, when it is known in advance that the substrate, the first adhesive layer and the second adhesive layer are anisotropic, the tensile strength and elongation of the substrate, the first adhesive layer and the second adhesive layer can be measured, and the MD direction and TD direction of the foaming adhesive sheet can be determined based on their tensile strength and elongation. In addition, in the case where the foaming adhesive sheet is in a single sheet form, when the anisotropy of the substrate, the first adhesive layer, and the second adhesive layer are unknown, the foaming adhesive sheet can be cut into a circle with a diameter of about 50 mm, and a test piece for direction measurement can be prepared. The test piece for direction measurement can be left to stand at a temperature of 60°C, and the direction in which the test piece for direction measurement is curled can be regarded as the MD direction of the foaming adhesive sheet.

Next, the curling test piece is left to stand at a temperature of 60°C and a humidity of less than 10% RH for 15 hours. At this time, when at least one of the first adhesive layer and the second adhesive layer is adhesive, the curling test piece is placed in a state where the surface of the adhesive layer is not in contact with the surroundings. Among them, the curling test piece is preferably in a state where no dead weight is applied in the curling direction. Next, the curling chord length d of the curling test piece as shown in Figure 11(b) is measured. Then, the radius of curvature r is calculated using the following formula.

L＝r×θ

d＝2×r×sin(θ/2)

(In the above formula, L represents the arc length, d represents the chord length, r represents the radius of curvature, and θ represents the central angle.)

It should be noted that, regarding the chord length d, the curvature radius r was calculated by measuring the direction of the chord length d in the MD direction, the TD direction, and the direction at 45° to the MD direction. And, the smallest value of the curvature radius r in these cases was adopted. When the direction of the chord length d was set to the MD direction or the TD direction, the arc length L was 50 mm. In addition, when the direction of the chord length d was set to the direction at 45° to the MD direction, the arc length L was L = 50 × √2 = 70.7 mm.

In the present embodiment, the radius of curvature of the curl of the above-mentioned foamable adhesive sheet can be controlled by adjusting the thickness and hardness of each layer, for example. For example, if the thickness of the substrate is thick, there is a tendency for the radius of curvature to become larger. In addition, for example, if the hardness of the substrate is high, there is a tendency for the radius of curvature to become larger. In addition, for example, in the case where the hardness of the first adhesive layer is higher than the hardness of the second adhesive layer, there is a tendency that the thicker the thickness of the second adhesive layer, the larger the radius of curvature. In addition, in the case where the hardness of the first adhesive layer and the second adhesive layer is the same, if the thickness of the first adhesive layer and the second adhesive layer is the same, there is a tendency that the radius of curvature becomes larger.

It should be noted that the hardness of the first adhesive layer and the second adhesive layer can be controlled by adjusting the composition of the first adhesive layer and the second adhesive layer. In addition, in the first adhesive layer and the second adhesive layer, there is a tendency that the hardness becomes higher if the initial adhesive force is low, and the hardness becomes lower if the initial adhesive force is high. In addition, in the first adhesive layer and the second adhesive layer, there is a tendency that the hardness becomes higher if the storage modulus is high, and the hardness becomes lower if the storage modulus is low. In addition, in the first adhesive layer and the second adhesive layer, there is a tendency that the hardness becomes higher if the pencil hardness is high, and the hardness becomes lower if the pencil hardness is low. In addition, in the first adhesive layer and the second adhesive layer, there is a tendency that the hardness becomes higher if the static friction coefficient is low, and the hardness becomes lower if the pencil hardness is high.

In the foamable adhesive sheet in the present embodiment, the ring rigidity is more than 45mN/10mm, preferably more than 75mN/10mm, more preferably more than 100mN/10mm. Ring rigidity refers to the parameter representing the intensity of the stiffness of film or sheet as described above. By making the ring rigidity of the foamable adhesive sheet be the above-mentioned range, the stiffness of the foamable adhesive sheet can be strengthened. Therefore, when the foamable adhesive sheet is configured between 2 components, insertability can be made good. In addition, for example, when the foamable adhesive sheet is transported by absorption and attached to the component, the situation that the foamable adhesive sheet droops because of its own weight can be suppressed, and the adhesion can be made good. On the other hand, the upper limit of the ring rigidity is not particularly limited.

The method for measuring the ring rigidity is the same as that described in the above “I. First Embodiment A. Foamable Adhesive Sheet a) First Embodiment 1. Characteristics” column, and thus the description here is omitted.

It should be noted that in the measurement of the ring stiffness of the foamable adhesive sheet, when the test piece of the foamable adhesive sheet 10 is arranged on the ring stiffness measuring device 30, the measurement is performed for both the case where the inner surface 40x is the surface of the first adhesive layer and the outer surface 40y is the surface of the second adhesive layer, and the case where the inner surface 40x is the surface of the second adhesive layer and the outer surface 40y is the surface of the first adhesive layer. And, the larger value of the ring stiffness in these cases is adopted.

When measuring the ring stiffness of the foamable adhesive sheet, if the foamable adhesive sheet has a spacer as described below, the ring stiffness of the foamable adhesive sheet is measured after the spacer is peeled off. This is because when the foamable adhesive sheet is arranged between two components, the spacer is peeled off from the foamable adhesive sheet.

In the present embodiment, the ring stiffness of the foamable adhesive sheet can be controlled by adjusting the thickness and hardness of each layer. For example, if the thickness of the substrate is thick, there is a tendency for the ring stiffness to become larger. In addition, for example, if the hardness of the substrate is high, there is a tendency for the ring stiffness to become larger. In addition, for example, when the hardness of the first adhesive layer is higher than the hardness of the second adhesive layer, there is a tendency that the thicker the thickness of the first adhesive layer, the larger the ring stiffness. In addition, if the hardness of the first adhesive layer and the second adhesive layer is high, there is a tendency for the ring stiffness to become larger.

It should be noted that the method for controlling the hardness of the first adhesive layer and the second adhesive layer is as described above.

The foamable adhesive sheet in this embodiment preferably has high adhesiveness after foaming and curing. In addition, the foamable adhesive sheet in this embodiment preferably has high electrical insulation after foaming and curing. The description of these viewpoints is the same as the description in the above-mentioned "I. First embodiment A. Foamable adhesive sheet a) First embodiment 1. Characteristics" column, so the description here is omitted.

2. First adhesive layer and second adhesive layer

In this embodiment, the first adhesive layer and the second adhesive layer contain a thermosetting adhesive. In addition, at least one of the first adhesive layer and the second adhesive layer further contains a foaming agent. In addition, the composition of the first adhesive layer is different from the composition of the second adhesive layer.

Here, the difference between the composition of the first adhesive layer and the composition of the second adhesive layer means that at least one of the type and content of the main agent constituting the thermosetting adhesive, the type and content of the curing agent constituting the thermosetting adhesive, the type and content of the resin component other than the main agent constituting the thermosetting adhesive, the type and content of the foaming agent, and the type and content of the additive is different.

Among them, it is preferred that the first adhesive layer and the second adhesive layer contain a thermosetting adhesive and a foaming agent, and the composition of the first adhesive layer is different from that of the second adhesive layer.

(1) Characteristics of the first adhesive layer and the second adhesive layer

(a) Hardness

In this embodiment, it is preferred that the hardness of the first adhesive layer and the second adhesive layer be different. When the hardness of the first adhesive layer and the second adhesive layer is different, the foamable adhesive sheet is prone to curling. Therefore, when the hardness of the first adhesive layer and the second adhesive layer is different, this embodiment is effective.

The hardness of the first adhesive layer and the second adhesive layer is not particularly limited as long as it is a parameter that can measure the hardness of the first adhesive layer and the second adhesive layer. In addition, as an index of the hardness of the first adhesive layer and the second adhesive layer, for example, the initial adhesion of the first adhesive layer and the second adhesive layer; the thermal properties such as the glass transition temperature of the first adhesive layer and the second adhesive layer; etc. can be used.

(b) Initial adhesion

In the present embodiment, it is preferred that the initial tack of the first adhesive layer is different from that of the second adhesive layer. Here, there is usually a tendency in the adhesive layer that the larger the adhesiveness (initial tack), the softer it is, and the smaller the adhesiveness (initial tack), the harder it is. Therefore, in the case where the initial tack of the first adhesive layer and the second adhesive layer is different, the foaming adhesive sheet is prone to curling. Therefore, in the case where the initial tack of the first adhesive layer and the second adhesive layer is different, the present embodiment is effective.

In addition, when the initial adhesion of the first adhesive layer and the second adhesive layer is different, when the initial adhesion of the first adhesive layer is lower than the initial adhesion of the second adhesive layer, it is preferred that the initial adhesion of the first adhesive layer is, for example, 0 gf or more and less than 10 gf, and the initial adhesion of the second adhesive layer is, for example, 10 gf or more and 500 gf or less. In this case, the initial adhesion of the first adhesive layer can be, for example, 5 gf or less, or 2 gf or less. In addition, in this case, the initial adhesion of the second adhesive layer can be, for example, 30 gf or more, or 50 gf or more. In addition, the initial adhesion of the second adhesive layer can be, for example, 400 gf or less, or 300 gf or less.

In the above case, since the initial adhesive force of the first adhesive layer and the second adhesive layer is different, the foamable adhesive sheet is likely to curl. Therefore, this embodiment is effective.

In addition, in the above case, by making the initial adhesion of the second adhesive layer within the above range, the second adhesive layer with good adhesion to the component can be made. Specifically, when another component is bonded and fixed in a hole, groove, etc. of a component, the surface of the second adhesive layer of the foamable adhesive sheet is attached to another component, and another component to which the foamable adhesive sheet is attached is inserted into the hole, groove, etc. of a component, and then the foamable adhesive sheet is foamed and solidified to bond one component to another component, the initial adhesion of the second adhesive layer is made within a specified range, thereby the surface of the second adhesive layer of the foamable adhesive sheet can be attached to another component by utilizing the initial adhesion of the second adhesive layer, and the adhesion of the second adhesive layer to the component can be improved. Thus, when another component to which the foamable adhesive sheet is attached is inserted into the hole, groove, etc. of a component, the peeling and positional displacement of the foamable adhesive sheet can be suppressed.

In addition, in the above case, by making the initial adhesion of the second adhesive layer within the above range, the second adhesive layer can be made to have good reworkability. Therefore, for example, in the above-mentioned bonding and fixing method, when the surface of the second adhesive layer of the foaming adhesive sheet is attached to the component by utilizing the initial adhesion of the second adhesive layer, the positional deviation of the foaming adhesive sheet can be corrected.

In addition, in the above case, by making the initial adhesion of the second adhesive layer within the above range, for example, when the second adhesive layer is formed by a transfer method, it is possible to suppress the floating of the second adhesive layer. In addition, as described later, when a spacer is arranged on the side of the second adhesive layer opposite to the substrate, by making the initial adhesion of the second adhesive layer within a specified range, it is possible to easily peel off the spacer and improve operability.

In addition, in the above-mentioned case, by making the initial adhesion of the first adhesive layer within the above-mentioned range, the first adhesive layer can be made substantially non-adhesive (no initial adhesion), and the first adhesive layer with good sliding property can be made. Therefore, for example, in the above-mentioned bonding and fixing method, when another member with a foaming adhesive sheet is inserted into a hole, a groove, etc. of a member, another member with a foaming adhesive sheet can be smoothly inserted, and insertability can be improved. Thus, the peeling and positional displacement of the foaming adhesive sheet can be suppressed. In addition, in the above-mentioned bonding and fixing method, when another member is moved relative to a member to align the positions of the members to each other, another member can be smoothly moved relative to a member under the state that another member is inserted into a hole, a groove, etc. of a member, and positional alignment can be easily performed.

In addition, in the above case, by making the initial adhesion of the first adhesive layer within the above range, the first adhesive layer is substantially non-adhesive (no initial adhesion), so that the first adhesive layer can be made into a first adhesive layer with good sliding properties and good anti-blocking properties. Therefore, the operability of the foamable adhesive sheet can also be improved.

In addition, in the above case, as described above, since the second adhesive layer has excellent adhesion to the member and the first adhesive layer has excellent sliding properties, it is possible to suppress the peeling and positional displacement of the foamable adhesive sheet. Therefore, it is possible to suppress the decrease in the adhesiveness of the foamable adhesive sheet after foaming and curing due to the peeling and positional displacement of the foamable adhesive sheet, and it is possible to reduce the unevenness of the adhesive strength of the foamable adhesive sheet after foaming and curing due to the peeling and positional displacement of the foamable adhesive sheet.

Therefore, in the above-mentioned case, by using the foamable adhesive sheet in the present embodiment, the adhesive strength is high, and high-reliability and high-quality bonding can be achieved.

On the other hand, the initial adhesion of the first adhesive layer and the second adhesive layer may be made equal.

In addition, the initial adhesion of the first adhesive layer and the second adhesive layer can also be made relatively low. In this case, the initial adhesion of the first adhesive layer and the second adhesive layer is preferably, for example, more than 0gf and less than 10gf, respectively. In this case, the initial adhesion of the first adhesive layer and the second adhesive layer can be, for example, less than 5gf, or less than 2gf, respectively. By making the initial adhesion of the first adhesive layer and the second adhesive layer respectively in the above-mentioned range, the first adhesive layer and the second adhesive layer can be made substantially non-adhesive (no initial adhesion), and the first adhesive layer and the second adhesive layer with good sliding properties can be made. Therefore, for example, when the foamable adhesive sheet is inserted between two components, after the foamable adhesive sheet is configured in the hole, groove, etc. of a component, another component is inserted in the hole, groove, etc. of a component configured with the foamable adhesive sheet, after the foamable adhesive sheet is configured in another component, another component is inserted in the hole, groove, etc. of a component configured with the foamable adhesive sheet, insertability can be improved. Thus, it is possible to suppress the peeling and positional deviation of the foamable adhesive sheet. In addition, when the positions of the components are aligned by moving the other component relative to one component, the other component can be smoothly moved relative to one component in a state where the foamable adhesive sheet is arranged between the two components, and the positional alignment can be easily performed. In addition, by making the initial adhesion of the first adhesive layer and the second adhesive layer within the above range, the first adhesive layer and the second adhesive layer can be made into good anti-blocking properties. Therefore, the operability of the foamable adhesive sheet can also be good.

Here, the initial adhesion of the first adhesive layer and the second adhesive layer can be measured by a probe initial adhesion test. As a probe initial adhesion tester, for example, an initial adhesion tester "TAC-II" manufactured by RHESCA can be used. It should be noted that the details of the method for measuring the initial adhesion of the first adhesive layer and the second adhesive layer are described in the items of the embodiments described later.

In the present embodiment, the initial adhesion of the first adhesive layer and the second adhesive layer can be controlled by adjusting the composition of each adhesive layer, for example.

Specifically, in an adhesive layer containing an epoxy resin and a curing agent, by using an epoxy resin that is solid at room temperature, or by using a curing agent that is solid at room temperature, the adhesiveness of the adhesive layer can be reduced. On the other hand, in an adhesive layer containing an epoxy resin and a curing agent, if an epoxy resin that is liquid at room temperature, or a curing agent that is liquid at room temperature, is used, the adhesiveness of the adhesive layer tends to be increased.

In addition, in the adhesive layer containing epoxy resin and curing agent, by making it contain epoxy resin with high softening temperature or epoxy resin with large weight average molecular weight, the adhesiveness of the adhesive layer can be reduced. On the other hand, in the adhesive layer containing epoxy resin and curing agent, if it contains epoxy resin with low softening temperature or epoxy resin with small weight average molecular weight, there is a tendency that the adhesiveness of the adhesive layer becomes higher. For example, by making the adhesive layer contain multiple epoxy resins with different softening temperatures, that is, by making the adhesive layer contain one epoxy resin and other epoxy resins with softening temperature of 25°C or more and 10°C or more higher than the softening temperature of the above-mentioned one epoxy resin, the adhesiveness of the adhesive layer can be reduced. In addition, for example, by making the adhesive layer contain multiple epoxy resins with different weight average molecular weights, that is, by making the adhesive layer contain one epoxy resin and other epoxy resins with weight average molecular weight of 370 or more and 300 or more than the weight average molecular weight of the above-mentioned one epoxy resin, the adhesiveness of the adhesive layer can be reduced. More specifically, as described below, the adhesive layer containing the epoxy resin and the curing agent contains a first epoxy resin having a low softening temperature and a low molecular weight and a second epoxy resin having a high softening temperature and a high molecular weight as epoxy resins, thereby reducing the tackiness of the adhesive layer.

In addition, as described later, the adhesive layer containing the epoxy resin and the curing agent may contain an acrylic resin compatible with the epoxy resin, thereby reducing the tackiness of the adhesive layer.

Furthermore, by adding a tackifier resin (tackifier) to the adhesive layer, there is a tendency for the adhesiveness of the adhesive layer to increase.

It should be noted that although the use of a curing agent that is liquid at room temperature tends to increase the adhesiveness, the storage stability may be reduced. Therefore, it is preferable to adjust the initial tack of the adhesive layer by adjusting the properties and types of components other than the curing agent, such as epoxy resin.

(c) Storage modulus

In the present embodiment, preferably make the viscoelasticity of the first adhesive layer different from that of the second adhesive layer.Here, usually in the adhesive layer, there is a tendency that the higher the storage modulus is, the harder it is, the lower the storage modulus is, the softer it is.Therefore, when the storage modulus of the first adhesive layer and the second adhesive layer is different, the foaming adhesive sheet curls easily.Therefore, when the storage modulus of the first adhesive layer and the second adhesive layer is different, the present embodiment is effective.

When the storage modulus of the first adhesive layer and the second adhesive layer are different, and the storage modulus E'(25) of the first adhesive layer at 25°C is higher than the storage modulus E'(25) of the second adhesive layer, it is preferred that the storage modulus E'(25) of the first adhesive layer is, for example, 1.0×10 ⁶ Pa or more and 1.0×10 ¹⁰ Pa or less, and the storage modulus E'(25) of the second adhesive layer is, for example, 1.0×10 ³ Pa or more and less than 1.0×10 ⁶ Pa. In this case, the storage modulus E'(25) of the first adhesive layer may be, for example, 1.0×10 ⁷ Pa or more. In this case, the storage modulus E'(25) of the second adhesive layer may be, for example, 1.0×10 ⁴ Pa or more and 1.0×10 ⁵ Pa or less.

In addition, in the above case, by making the storage modulus of the second adhesive layer within the above range, the second adhesive layer with good adhesion to the component can be made. Specifically, when another component is bonded and fixed in a hole, groove, etc. of a component, the surface of the second adhesive layer of the foamable adhesive sheet is attached to another component, and another component with the foamable adhesive sheet attached is inserted into the hole, groove, etc. of a component, and then the foamable adhesive sheet is foamed and solidified to bond one component to another component, the storage modulus of the second adhesive layer is made within a specified range, thereby the flexibility of the second adhesive layer can be utilized to follow the concave and convex of the component, thereby improving the adhesion of the second adhesive layer. Thus, when another component with the foamable adhesive sheet attached is inserted into the hole, groove, etc. of a component, the peeling and positional displacement of the foamable adhesive sheet can be suppressed.

In addition, in the above case, by making the storage modulus of the second adhesive layer within the above range, the second adhesive layer can be made to have good reworkability. Therefore, for example, in the above-mentioned bonding and fixing method, when the surface of the second adhesive layer of the foaming adhesive sheet is attached to the component by utilizing the flexibility of the second adhesive layer, the positional deviation of the foaming adhesive sheet can be corrected.

In addition, in the above case, by making the storage modulus of the second adhesive layer within the above range, for example, when the second adhesive layer is formed by a transfer method, the floating and deformation of the second adhesive layer can be suppressed. In addition, as described later, when a spacer is arranged on the side opposite to the substrate of the second adhesive layer, by making the storage modulus of the second adhesive layer within the specified range, the spacer can be easily peeled off, which can improve operability.

In addition, in the above-mentioned case, by making the storage modulus of the first adhesive layer within the above-mentioned range, the first adhesive layer with good sliding property can be made. Therefore, for example, in the above-mentioned bonding and fixing method, when another member with a foaming adhesive sheet attached is inserted into a hole, a groove, etc. of a member, the other member with a foaming adhesive sheet attached can be smoothly inserted, and the insertability can be improved. Thus, the peeling and positional displacement of the foaming adhesive sheet can be suppressed. In addition, in the above-mentioned bonding and fixing method, when the positions of the members are aligned with each other by moving the other member relative to one member, the other member can be smoothly moved relative to one member in a state where the other member is inserted into a hole, a groove, etc. of one member, and the positional alignment can be easily performed.

Furthermore, in the above case, by setting the storage elastic modulus of the first adhesive layer within the above range, the first adhesive layer can have good sliding properties and good anti-blocking properties, thereby improving the handling properties of the foamable adhesive sheet.

On the other hand, the first adhesive layer and the second adhesive layer may have the same storage modulus.

In addition, the storage modulus of the first adhesive layer and the second adhesive layer may be both high. In this case, the storage modulus E'(25) of the first adhesive layer and the second adhesive layer at 25°C is preferably, for example, 1.0×10 ⁶ Pa or more and 1.0×10 ¹⁰ Pa or less. In this case, the storage modulus E'(25) of the first adhesive layer and the second adhesive layer may be, for example, 1.0×10 ⁷ Pa or more. By making the storage modulus E'(25) of the first adhesive layer and the second adhesive layer within the above range, the first adhesive layer and the second adhesive layer can be the first adhesive layer and the second adhesive layer with good sliding properties. Therefore, for example, when inserting the foamable adhesive sheet between two components, after the foamable adhesive sheet is configured in the hole, groove, etc. of a component, another component is inserted into the hole, groove, etc. of a component configured with the foamable adhesive sheet, after the foamable adhesive sheet is configured in the hole, groove, etc. of another component, another component configured with the foamable adhesive sheet is inserted into the hole, groove, etc. of a component, insertability can be improved. Thus, the peeling and positional displacement of the foamable adhesive sheet can be suppressed. In addition, when the position alignment of the components is performed by moving another component relative to a component, another component can be smoothly moved relative to a component under the state that the foamable adhesive sheet is configured between the two components, and position alignment can be easily performed. In addition, by making the E'(25) of the first adhesive layer and the second adhesive layer respectively within the above-mentioned range, the first adhesive layer and the second adhesive layer that are also good in anti-adhesion can be made. Therefore, the operability of the foamable adhesive sheet can be made also good.

Here, the storage modulus of the first adhesive layer and the second adhesive layer can be measured, for example, by a dynamic mechanical property test in accordance with JIS K7244-4: 1999. As a dynamic mechanical property tester, for example, a dynamic viscoelasticity measuring device manufactured by TA Instruments can be used. In addition, the measurement conditions can be set as: accessory mode: compression mode, frequency: 1 Hz, temperature: 25°C, and heating rate: 10°C/min.

In the present embodiment, the storage elastic modulus of the first adhesive layer and the second adhesive layer at 25° C. can be controlled by adjusting the composition of each adhesive layer, for example.

Specifically, in the adhesive layer containing epoxy resin and curing agent, by using epoxy resin that is solid at room temperature, or by using curing agent that is solid at room temperature, the storage modulus of the adhesive layer can be increased. On the other hand, in the adhesive layer containing epoxy resin and curing agent, if epoxy resin that is liquid at room temperature, or curing agent that is liquid at room temperature is used, the storage modulus of the adhesive layer tends to be lowered.

In addition, in the adhesive layer containing epoxy resin and curing agent, the storage modulus of the adhesive layer can be increased by making it contain epoxy resin with high softening temperature or epoxy resin with large weight average molecular weight. On the other hand, in the adhesive layer containing epoxy resin and curing agent, if it contains epoxy resin with low softening temperature or epoxy resin with small weight average molecular weight, there is a tendency that the storage modulus of the adhesive layer becomes low.

For example, by making the adhesive layer contain multiple epoxy resins with different softening temperatures, that is, by making the adhesive layer contain one epoxy resin and other epoxy resins with a softening temperature of 25°C or more and 10°C or more higher than the softening temperature of the above epoxy resin, the storage modulus of the adhesive layer can be increased. In addition, for example, by making the adhesive layer contain multiple epoxy resins with different weight-average molecular weights, that is, by making the adhesive layer contain one epoxy resin and other epoxy resins with a weight-average molecular weight of 370 or more and 300 or more greater than the weight-average molecular weight of the above epoxy resin, the storage modulus of the adhesive layer can be increased. More specifically, in the adhesive layer containing an epoxy resin and a curing agent, as described later, a first epoxy resin with a low softening temperature and a low molecular weight and a second epoxy resin with a high softening temperature and a high molecular weight are contained as epoxy resins, thereby increasing the storage modulus of the adhesive layer.

In addition, the adhesive layer containing the epoxy resin and the curing agent may contain an acrylic resin compatible with the epoxy resin as described later, thereby increasing the storage modulus of the adhesive layer.

It should be noted that if a curing agent that is liquid at room temperature is used, the storage modulus tends to be lower, but the storage stability may be reduced. Therefore, it is preferable to adjust the storage modulus of the adhesive layer by adjusting the properties and types of components other than the curing agent, such as epoxy resin.

(d) Pencil hardness

In the present embodiment, preferably make the pencil hardness of the surface of the first adhesive layer and the second adhesive layer different.Here, usually in the adhesive layer, there is a tendency that the pencil hardness of the surface is higher and harder, and the pencil hardness of the surface is lower and softer.Therefore, when the pencil hardness of the surface of the first adhesive layer and the second adhesive layer is different, the foaming adhesive sheet is easy to curl.Therefore, when the pencil hardness of the surface of the first adhesive layer and the second adhesive layer is different, the present embodiment is effective.

In the case where the pencil hardness of the surface of the first adhesive layer and the second adhesive layer is different, when the pencil hardness of the surface of the first adhesive layer is higher than the pencil hardness of the surface of the second adhesive layer, it is preferred that the pencil hardness of the surface of the first adhesive layer is, for example, HB or more, and the pencil hardness of the surface of the second adhesive layer is, for example, less than HB. In this case, the pencil hardness of the surface of the first adhesive layer may be, for example, HB or more and 2H or less, or may be, for example, F or more and 2H or less. In addition, in this case, the pencil hardness of the surface of the second adhesive layer may be, for example, B or less. It should be noted that, in the case where the initial adhesion of the second adhesive layer is high and the pencil hardness of the surface of the second adhesive layer cannot be measured, the pencil hardness of the surface of the second adhesive layer is considered to be 6B or less.

In addition, in the above case, by making the pencil hardness of the surface of the first adhesive layer within the above range, the sliding property of the first adhesive layer can be improved, and the anti-blocking property of the first adhesive layer can also be improved. On the other hand, if the pencil hardness of the surface of the first adhesive layer is too high, the adhesion of the first adhesive layer to the substrate may be reduced.

In the above case, by setting the pencil hardness of the surface of the second adhesive layer to be within the above range, it is possible to obtain good adhesion of the second adhesive layer to the member.

On the other hand, the pencil hardness of the surfaces of the first adhesive layer and the second adhesive layer may be the same.

In addition, also can make the pencil hardness on the surface of the first adhesive layer and the second adhesive layer all higher.In this case, the pencil hardness on the surface of the first adhesive layer and the second adhesive layer is for example preferably more than HB respectively, can be more than HB and below 2H, can also be more than F and below 2H.Be above-mentioned scope by making the above-mentioned pencil hardness, thereby can make sliding good, and then can make anti-blocking also good.On the other hand, if the above-mentioned pencil hardness is too high, then make the adhesive layer reduce the adhesion of base material sometimes.

Here, the pencil hardness can be obtained according to JIS K5600. Specifically, the following method can be cited. First, prepare an A4-sized foaming adhesive sheet and place it on a glass plate. Then, according to JIS K5600, use a pencil hardness tester (with a level) to measure the pencil hardness of the surface of the foaming adhesive sheet where the adhesive layer to be tested is arranged. The measurement conditions are set as: an angle of 45° with the horizontal state of the pencil, a load of 750g, a test speed of 1mm/sec, a test length of 20mm, and a temperature of 23°C. Moreover, the maximum pencil hardness on the surface of the adhesive layer of the foaming adhesive sheet without damage under visual observation is used as the pencil hardness. The pencil hardness tester can use, for example, KT-VF2378-12 made by TQC.

In the present embodiment, the pencil hardness of the surface of the first adhesive layer and the second adhesive layer can be controlled, for example, by the composition of the first adhesive layer and the second adhesive layer. Specifically, the pencil hardness can be controlled by the average particle size and content of the foaming agent contained in the adhesive layer. More specifically, the pencil hardness can be increased by increasing the average particle size of the foaming agent. In addition, the pencil hardness can be increased by increasing the content of the foaming agent. In addition, for example, the pencil hardness can be increased by including an inorganic filler in the adhesive layer. In addition, for example, the pencil hardness can be increased by including a component having a rigid structure in the adhesive layer. Specifically, in the adhesive layer containing an epoxy resin and a curing agent, a phenolic resin can be cited as a component having a rigid structure.

(e) Static friction coefficient

In the present embodiment, preferably make the static friction coefficient on the surface of the first adhesive layer and the second adhesive layer different.Here, usually in the adhesive layer, there is a tendency that the friction coefficient on the surface is lower, the harder, the higher the friction coefficient on the surface is softer.Therefore, when the static friction coefficient on the surface of the first adhesive layer and the second adhesive layer is different, the foaming adhesive sheet is easily curled.Therefore, when the static friction coefficient on the surface of the first adhesive layer and the second adhesive layer is different, the present embodiment is effective.

When the static friction coefficients of the surfaces of the first adhesive layer and the second adhesive layer are different, and the static friction coefficient of the surface of the first adhesive layer is lower than that of the surface of the second adhesive layer, it is preferred that the static friction coefficient of the surface of the first adhesive layer is, for example, less than 0.34, and the static friction coefficient of the surface of the second adhesive layer is, for example, more than 0.34. In this case, the static friction coefficient of the surface of the first adhesive layer can be, for example, less than 0.30, or less than 0.26. In addition, the static friction coefficient of the surface of the first adhesive layer can be, for example, more than 0.16. In addition, in this case, the static friction coefficient of the surface of the second adhesive layer can be, for example, more than 0.38.

In the above case, by setting the static friction coefficient of the surface of the first adhesive layer to be within the above range, the sliding property of the first adhesive layer can be improved.

On the other hand, the static friction coefficients of the surfaces of the first adhesive layer and the second adhesive layer may be the same.

In addition, the static friction coefficient of the surface of the first adhesive layer and the second adhesive layer can also be made higher. In this case, the static friction coefficient of the surface of the first adhesive layer and the second adhesive layer can be, for example, less than 0.34, less than 0.30, or less than 0.26. In addition, the above-mentioned static friction coefficient can be, for example, more than 0.16. By making the above-mentioned static friction coefficient the above-mentioned range, it is possible to make the sliding property good.

Here, the static friction coefficient can be obtained according to JIS K7125. Specifically, the following method can be cited. First, the foamable adhesive sheet is cut into 80mm×200mm. Then, the foamable adhesive sheet is placed on a horizontally placed rectangular metal plate, and a sliding sheet (63mm×63mm, weight 200g, bottom surface: felt) is placed on the surface of the foamable adhesive sheet with the adhesive layer to be tested. The friction force is measured under the conditions of a test speed of 100mm/min, a test length of 50mm, a force sensor of 10N, and a temperature of 23°C, and the static friction coefficient between the surface of the foamable adhesive sheet with the adhesive layer to be tested and the metal plate is calculated. The device can use a friction measuring machine FRICTION TESTER TR-2 manufactured by Toyo Seiki Co., Ltd. In addition, the metal plate can use, for example, a stainless steel plate made of SUS304 and having a surface roughness Ra of 0.05μm.

In the present embodiment, the static friction coefficient of the surface of the first adhesive layer and the second adhesive layer can be controlled by, for example, adjusting the composition of the first adhesive layer and the second adhesive layer, or adjusting the pencil hardness of the surface of the first adhesive layer and the second adhesive layer. Specifically, the static friction coefficient can be controlled by the average particle size and content of the foaming agent contained in the adhesive layer. More specifically, if the average particle size of the foaming agent becomes larger, there is a tendency for the static friction coefficient to become smaller. In addition, if the content of the foaming agent becomes more, there is a tendency for the static friction coefficient to become smaller. In addition, if the pencil hardness of the surface of the adhesive layer becomes higher, there is a tendency for the static friction coefficient to become smaller.

(2) Materials of the First Adhesive Layer and the Second Adhesive Layer

The first adhesive layer and the second adhesive layer in this embodiment contain a thermosetting adhesive. In addition, at least one of the first adhesive layer and the second adhesive layer further contains a foaming agent.

(a) Thermosetting adhesive

As the thermosetting adhesive contained in the first adhesive layer and the second adhesive layer in this embodiment, a thermosetting adhesive generally used in an adhesive layer of a foamable adhesive sheet can be used. The thermosetting adhesive can be applied even when a member is not transparent, such as a metal member.

In addition, examples of the thermosetting adhesive include epoxy resin adhesives, acrylic resin adhesives, phenolic resin adhesives, unsaturated polyester resin adhesives, alkyd resin adhesives, urethane resin adhesives, and thermosetting polyimide resin adhesives.

Among them, the thermosetting adhesive is preferably an epoxy resin adhesive. That is, the thermosetting adhesive preferably contains an epoxy resin and a curing agent. Generally, the epoxy resin adhesive has excellent mechanical strength, heat resistance, insulation, chemical resistance, etc., has small curing shrinkage, and can be used for a wide range of purposes.

Hereinafter, an example will be described in which the thermosetting adhesive is an epoxy resin adhesive.

(i) Epoxy resin

The epoxy resin in the present embodiment is a compound having at least one epoxy group or glycidyl group, and curing by cross-linking polymerization reaction when used in combination with a curing agent. The epoxy resin also includes a monomer having at least one epoxy group or glycidyl group.

As the epoxy resin, epoxy resins generally used for adhesive layers of foamable adhesive sheets can be used.

When the initial adhesion of the first adhesive layer is lower than that of the second adhesive layer, the thermosetting adhesive contained in the first adhesive layer having the lower initial adhesion preferably contains the first epoxy resin and the second epoxy resin described below as epoxy resins. In addition, when the initial adhesion of the first adhesive layer and the second adhesive layer are both low, the thermosetting adhesive contained in the first adhesive layer and the second adhesive layer preferably contains the first epoxy resin and the second epoxy resin described below as epoxy resins.

Specifically, the thermosetting adhesive preferably contains as epoxy resin: a first epoxy resin having a softening temperature of 50°C or higher and an epoxy equivalent of 5000 g/eq or less, and a second epoxy resin having a softening temperature higher than the first epoxy resin and a weight average molecular weight of 20,000 or more. By using the first epoxy resin and the second epoxy resin in combination, the adhesion (initial adhesion) of the adhesive layer can be reduced, and a foamable adhesive sheet with good sliding properties can be obtained. Furthermore, a first adhesive layer with good anti-blocking properties and adhesion after foaming and curing can be obtained.

For example, when only seeking to improve the adhesiveness after foaming and curing, it is effective to use low molecular weight (low epoxy equivalent) epoxy resins compared to high molecular weight (high epoxy equivalent) epoxy resins. However, when using low molecular weight (low epoxy equivalent) epoxy resins, for example, when the foamable adhesive sheet is wound into a roll, the low molecular weight (low epoxy equivalent) epoxy resins assimilate with each other and are prone to adhesion.

In contrast, when using the first epoxy resin with relatively low softening temperature (relatively high crystallinity) and low molecular weight (low epoxy equivalent), if the first epoxy resin becomes a temperature above the softening temperature, it rapidly melts and changes into a low-viscosity liquid state. Therefore, it is easy to improve the adhesion after foaming and curing. On the other hand, the first epoxy resin is relatively high in crystallinity, so compared with the epoxy resin with relatively low crystallinity or the epoxy resin without crystallinity, it is possible to suppress the generation of adhesion. However, when only using the first epoxy resin, the generation inhibition effect of adhesion is likely to be insufficient, and the adhesion (initial adhesion) of the adhesive layer is likely to become too high. Therefore, by further using the second epoxy resin with higher softening temperature (lower crystallinity) and high molecular weight, it is possible to improve the generation inhibition effect of adhesion, and the adhesion (initial adhesion) of the adhesive layer is suppressed to be low.

On the other hand, when the initial tack of the first adhesive layer is lower than that of the second adhesive layer, it is preferred to use, as the epoxy resin in the second adhesive layer having a high initial tack, an epoxy resin that is liquid at room temperature, such as bisphenol A epoxy resin or bisphenol F epoxy resin, or an epoxy resin with a low softening point. This is because the use of these epoxy resins makes it easy to adjust the initial tack of the second adhesive layer to within a specified range.

Regarding the above-mentioned first epoxy resin and second epoxy resin, since they are the same as the descriptions in the "(i-1) First epoxy resin" and "(i-2) Second epoxy resin" columns in "I. First embodiment A. Foaming adhesive sheet a) First embodiment 2. First adhesive layer (1) Material of first adhesive layer (a) Curable adhesive (i) Epoxy resin", the description here is omitted.

(ii) Acrylic resin

When the thermosetting adhesive is an epoxy resin adhesive, the bonding layer can further contain an acrylic resin compatible with epoxy resin. Acrylic resin is a resin compatible with epoxy resin. Since acrylic resin is compatible with epoxy resin, it is easy to improve the toughness of the bonding layer. As a result, the adhesion after foaming and curing can be improved. In addition, it is believed that acrylic resin plays a role as a compatibilizer of a foaming agent (for example, the foaming agent of the resin of the shell portion is acrylonitrile copolymer) and is evenly dispersed and foamed, so that the adhesion after foaming and curing improves. In addition, the flexibility brought by acrylic resin can be brought into play, and the improvement of the adhesion of the substrate after foaming and curing and the improvement of the crack resistance after foaming and curing can be sought. In addition, by making acrylic resin compatible with epoxy resin, the hardness of the bonding layer surface can be kept high. On the other hand, if acrylic resin is incompatible with epoxy resin, a soft position is formed on the bonding layer surface, so sometimes the interface with the adherend becomes difficult to slide, and operability is reduced.

The description of the acrylic resin in this embodiment is the same as that in the above “I. First Embodiment A. Foamable Adhesive Sheet a) First Embodiment 2. First Adhesive Layer (1) Material of First Adhesive Layer (a) Curable Adhesive (ii) Acrylic Resin” column, so the description here is omitted.

(iii) Curing agent

As the curing agent in the present embodiment, a curing agent that undergoes a curing reaction by heat can be used, and a curing agent commonly used for epoxy resin adhesives can be used. The curing agent is preferably solid at room temperature (23° C.). A curing agent that is solid at room temperature can extend the storage stability (applicable life) compared to a curing agent that is liquid at room temperature. In addition, the curing agent can be a latent curing agent. In addition, the curing agent can be used alone or in combination of two or more.

It should be noted that when the initial tack of the first adhesive layer is lower than that of the second adhesive layer, a curing agent that is solid at room temperature or a curing agent that is liquid at room temperature can be used in the second adhesive layer having a higher initial tack. However, from the viewpoint of storage stability, it is preferred to use a curing agent that is solid at room temperature.

The description of the curing agent is the same as that in the above “I. First Embodiment A. Foamable Adhesive Sheet a) First Embodiment 2. First Adhesive Layer (1) Material of First Adhesive Layer (a) Curable Adhesive (iii) Curing Agent”, and therefore the description here is omitted.

(b) Foaming agent

In the present embodiment, at least one of the first adhesive layer and the second adhesive layer contains a foaming agent.

Among them, it is preferable that both the first adhesive layer and the second adhesive layer contain a foaming agent. In this case, the adhesiveness of the first adhesive layer and the second adhesive layer after foaming and curing can be improved.

On the other hand, when only one of the first adhesive layer and the second adhesive layer contains a foaming agent, when the foaming agent is a microcapsule-type foaming agent, it can be expected that the foaming agent functions as a filler. Therefore, it is believed that there is a tendency that the adhesive layer containing the foaming agent becomes hard and the adhesive layer not containing the foaming agent becomes soft. Therefore, it is believed that: when only one of the first adhesive layer and the second adhesive layer contains a foaming agent, the foamable adhesive sheet is prone to curling. Therefore, it is believed that: when only one of the first adhesive layer and the second adhesive layer contains a foaming agent, this embodiment is effective.

In addition, when the hardness of the first adhesive layer is harder than that of the second adhesive layer, the first adhesive layer with higher hardness preferably contains a foaming agent. When the first adhesive layer contains a foaming agent, the surface roughness is increased, the friction coefficient is reduced, and the sliding property is improved.

The foaming agent is a foaming agent that generates a foaming reaction by heat, and a foaming agent generally used in an adhesive layer of a foamable adhesive sheet can be used.

The description of the foaming agent is the same as that in the above “I. First Embodiment A. Foamable Adhesive Sheet a) First Embodiment 2. First Adhesive Layer (1) Material of First Adhesive Layer (b) Foaming Agent”, and therefore the description here is omitted.

(c) Other ingredients

For example, when the thermosetting adhesive is an epoxy resin adhesive, the adhesive layer in the present invention may contain only epoxy resin and acrylic resin as resin components, or may further contain other resins. Examples of other resins include urethane resins.

The description of these other components is the same as that in the above “I. First Embodiment A. Foamable Adhesive Sheet a) First Embodiment 2. First Adhesive Layer (1) Materials of First Adhesive Layer (c) Other Components”, and thus the description here is omitted.

(3) Composition of the First Adhesive Layer and the Second Adhesive Layer

When the first adhesive layer and the second adhesive layer contain a foaming agent, the first adhesive layer and the second adhesive layer can be foamed at a foaming ratio of, for example, 1.5 times or more and 15 times or less. The foaming ratio can be, for example, 3.5 times or more, 4 times or more, or 4.5 times or more. In addition, in the above case, the foaming ratio can be, for example, 9 times or less, 8.5 times or less, or 8 times or less.

Here, the expansion ratio can be obtained according to the following formula.

Foaming ratio (times) = thickness of adhesive layer after foaming and curing / thickness of adhesive layer before foaming and curing

The thickness of the first adhesive layer and the second adhesive layer is not particularly limited. When the adhesive layer contains a foaming agent, it is preferably above the average particle size of the foaming agent, for example, above 10 μm, above 15 μm, or above 20 μm. On the other hand, the thickness of the first adhesive layer and the second adhesive layer is, for example, below 200 μm, below 150 μm, or below 100 μm. If the thickness of the adhesive layer is too thin, it is possible that the adhesion to the substrate and the adhesion after foaming and curing cannot be fully obtained. In addition, when the initial adhesion of the first adhesive layer is lower than the initial adhesion of the second adhesive layer, if the thickness of the first adhesive layer with low initial adhesion is too thin, the radius of curvature of the curling of the foamable adhesive sheet after standing for a specified time at a specified temperature and a specified humidity may become smaller. On the other hand, if the thickness of the adhesive layer is too thick, the surface quality may deteriorate.

Here, the thickness of the first adhesive layer and the second adhesive layer are respectively the values measured by observing the cross section of the foaming adhesive sheet in the thickness direction using a transmission electron microscope (TEM), a scanning electron microscope (SEM) or a scanning transmission electron microscope (STEM), and can be set as the average value of the thickness of 10 randomly selected locations. It should be noted that the method for measuring the thickness of other layers possessed by the foaming adhesive sheet can also be handled in the same manner.

The first adhesive layer and the second adhesive layer may be continuous layers or discontinuous layers. As discontinuous layers, for example, patterns such as stripes and dots may be cited. In addition, the surfaces of the first adhesive layer and the second adhesive layer may have concave-convex shapes such as embossing.

The first adhesive layer and the second adhesive layer can be formed, for example, by applying an adhesive composition containing the above-mentioned thermosetting adhesive and foaming agent and removing the solvent. Examples of the coating method include roll coating, reverse roll coating, transfer roll coating, gravure coating, gravure reverse coating, comma coating, rod coating, blade coating, rod coating, wire bar coating, die coating, die lip coating, and dip coating.

The adhesive composition may contain a solvent or may not contain a solvent. It should be noted that the solvent in this specification not only includes a strict solvent (a solvent that dissolves a solute) but also includes a broad meaning of a dispersion medium. In addition, the solvent contained in the adhesive composition is volatilized and removed when the adhesive composition is applied and dried to form an adhesive layer.

The adhesive composition can be obtained by mixing the above-mentioned components and kneading and dispersing as needed. As a mixing and dispersing method, a common kneading disperser can be used, such as a double roll mill, a triple roll mill, a gravel mill, a Trom mill, a Szegvari grinder, a high-speed impeller disperser, a high-speed stone mill, a high-speed impact mill, a disperser, a high-speed mixer, a ribbon blender, a worm kneader, a strong kneading machine, a tumble mixer, a blender, a dispensing machine, a homogenizer, and an ultrasonic disperser.

3. Substrate

The substrate in this embodiment is disposed between the first adhesive layer and the second adhesive layer described above.

The substrate preferably has insulating properties. In addition, the substrate is preferably in the form of a sheet. The substrate may have a single-layer structure or a multi-layer structure. In addition, the substrate may have a porous structure inside or may not have a porous structure.

The description of the substrate is the same as that in the above-mentioned "I. First Embodiment A. Foamable Adhesive Sheet a) First Embodiment 4. Substrate", and thus the description here is omitted.

4. Curl Adjustment Layer

The foamable adhesive sheet in this embodiment may have a curl adjustment layer on the side of the second adhesive layer opposite to the substrate. For example, when the initial adhesion of the first adhesive layer is lower than the initial adhesion of the second adhesive layer, the foamable adhesive sheet is prone to curling, but by configuring the curl adjustment layer on the side of the second adhesive layer opposite to the substrate, curling can be suppressed.

For example, in a foamable adhesive sheet 10 shown in FIG. 12 , the curl adjusting layer 7 is disposed on the surface of the second adhesive layer 3 opposite to the substrate 2 .

The curl adjusting layer may be, for example, a spacer for protecting the second adhesive layer or a fiber layer. The curl adjusting layer is preferably a spacer. The spacer is removable, and when a foaming adhesive sheet is arranged between two components, the spacer is peeled off from the foaming adhesive sheet, so that the thickness of the foaming adhesive sheet can be reduced, and the insertability can be improved.

(1) Isolation

In this embodiment, the spacer may be disposed on the surface of the second adhesive layer opposite to the substrate.

As long as the spacer can be peeled off from the second adhesive layer, it is not particularly limited and can have the strength of the degree that can protect the second adhesive layer. As such a spacer, for example, a release film, a peeling paper etc. can be enumerated. In addition, the spacer can have a single-layer structure or a multi-layer structure.

Examples of the single-layer separator include fluororesin films and the like.

In addition, as a separator of a multilayer structure, for example, a laminate having a release layer on one side or both sides of a substrate layer can be cited. As the substrate layer, for example, resin films such as polypropylene, polyethylene, polyethylene terephthalate, woodfree paper, coated paper, impregnated paper and the like can be cited. As the material of the release layer, as long as it is a material with release properties, it is not particularly limited, for example, organosilicon compounds, organic compound-modified organosilicon compounds, fluorine compounds, aminoalkyd compounds, melamine compounds, acrylic compounds, polyester compounds, long-chain alkyl compounds and the like can be cited. These compounds can use any of emulsion type, solvent type or solvent-free type.

(2) Fiber layer

In this embodiment, the fiber layer may be disposed on the surface of the second adhesive layer opposite to the substrate. When the second adhesive layer contains a thermosetting adhesive and a foaming agent, the fiber layer is a layer that allows the thermosetting adhesive to pass or permeate when the second adhesive layer foams and expands.

Examples of the form of the fiber layer include nonwoven fabric, paper, felt, knitted fabric, and woven fabric.

Examples of the fibers constituting the fiber layer include basalt fibers, vinylon fibers, polyarylate fibers, polyethylene fibers, polypropylene fibers, silicon carbide fibers, cellulose fibers, polyester fibers, nylon fibers, aramid fibers, polyphenylene sulfide fibers, liquid crystal polymer fibers, and glass fibers.

The density of the fiber layer is not particularly limited as long as the thermosetting adhesive can be passed through or permeated when the second adhesive layer is foamed and expanded, and may be, for example, 200 g/cm ³ or less, 100 g/cm ³ or less, or 50 g/cm ³ or less. If the density of the fiber layer is too high, the voids in the fiber layer will decrease, making it difficult for the thermosetting adhesive to pass through or permeate when the second adhesive layer is foamed, and there is a possibility that sufficient bonding strength cannot be obtained after the second adhesive layer is foamed and cured. On the other hand, the density of the fiber layer may be, for example, 3 g/cm ³ or more, 5 g/cm ³ or more, or 7 g/cm ³ or more.

Here, the density (g/cm ³ ) of the fiber layer can be calculated by dividing the weight per unit area (g/cm ² ) of the fiber layer by the thickness (cm) of the fiber layer.

The weight per unit area of the fiber layer can be measured by the following method. First, take 10 test pieces of the fiber layer of 100 mm × 100 mm in size and measure the mass (g) of each test piece. Next, divide the mass (g) of each test piece by the area (cm ² ) of each test piece to calculate the weight per unit area (g/cm ² ) of each test piece. Calculate the average value of the weight per unit area of the 10 test pieces in total and use the average value as the weight per unit area.

It should be noted that the density of the fiber layer can be adjusted by the manufacturing method and manufacturing conditions of the fiber layer.

The thickness of the fiber layer is not particularly limited as long as the thermosetting adhesive can pass through or permeate when the second adhesive layer is foamed and expanded, and is, for example, 100 μm or less, 80 μm or less, or 60 μm or less. If the thickness of the fiber layer is too thick, the amount of thermosetting adhesive that passes through or permeates the second adhesive layer during foaming decreases, and the adhesive force of the second adhesive layer after foaming and curing may decrease. On the other hand, the thickness of the fiber layer is, for example, 6 μm or more, 8 μm or more, or 10 μm or more. If the thickness of the fiber layer is too thin, adhesion may occur when the fiber layer is processed into a roll.

As a method for configuring a fiber layer on the surface of the second adhesive layer opposite to the substrate, examples include: a method of attaching the fiber layer by utilizing the adhesiveness of the second adhesive layer; a method of attaching the fiber layer to the second adhesive layer via a layer having adhesiveness different from the second adhesive layer; a method of applying an adhesive composition diluted with a solvent onto the fiber layer and drying it; a method of heating and laminating the second adhesive layer and the fiber layer; or a method obtained by a combination of these methods, etc.

5. The first intermediate layer and the second intermediate layer

The foamable adhesive sheet in the present embodiment can have the first intermediate layer between substrate and the first adhesive layer. In addition, the foamable adhesive sheet in the present embodiment can have the second intermediate layer between substrate and the second adhesive layer. By configuring the first intermediate layer and the second intermediate layer, the adhesion of the first adhesive layer and the second adhesive layer to the substrate can be improved. In addition, by configuring the first intermediate layer and the second intermediate layer, for example, the stress applied to the bending portion when the foamable adhesive sheet is bent can be relaxed, or the stress applied to the cutting portion when the foamable adhesive sheet is cut can be relaxed. As a result, when the foamable adhesive sheet is bent or cut, the first adhesive layer and the second adhesive layer can be suppressed from floating or peeling off from the substrate.

For example, in the foamable adhesive sheet 10 shown in Fig. 13, the first intermediate layer 4 is arranged between the substrate 2 and the first adhesive layer 1, and the second intermediate layer 5 is arranged between the substrate 2 and the second adhesive layer 3. It should be noted that in Fig. 13, the foamable adhesive sheet 10 has both the first intermediate layer 4 and the second intermediate layer 5, but may have only one of them.

The foamable adhesive sheet only needs to have at least one of the first intermediate layer and the second intermediate layer. For example, it may have only the first intermediate layer disposed between the substrate and the first adhesive layer, or only the second intermediate layer disposed between the substrate and the second adhesive layer, or both the first intermediate layer disposed between the substrate and the first adhesive layer and the second intermediate layer disposed between the substrate and the second adhesive layer. It is preferred that the first intermediate layer is disposed between the substrate and the first adhesive layer, and the second intermediate layer is disposed between the substrate and the second adhesive layer.

The description of the materials, thickness, manufacturing method, etc. contained in the above-mentioned first intermediate layer and second intermediate layer is the same as the description in the above-mentioned "I. First embodiment A. Foamable adhesive sheet a) First embodiment 5. Other structures (1) First intermediate layer and second intermediate layer" column, so the description here is omitted.

6. Foam adhesive sheet

The thickness of the foamable adhesive sheet in the present embodiment is, for example, 10 μm or more, or 20 μm or more. On the other hand, the thickness of the foamable adhesive sheet is, for example, 1000 μm or less, or 200 μm or less.

The use of the foamable adhesive sheet in this embodiment is not particularly limited. The foamable adhesive sheet in this embodiment can be used, for example, in the following situations: the foamable adhesive sheet is arranged between two components, and then the foamable adhesive sheet is foamed and solidified, thereby bonding the two components to each other. For example, in the case where the initial adhesion of the first adhesive layer is lower than the initial adhesion of the second adhesive layer, the foamable adhesive sheet in this embodiment is preferably used in the following situation: after the surface of the second adhesive layer of the foamable adhesive sheet is attached to the second component, the second component to which the foamable adhesive sheet is attached is inserted into the hole, groove, etc. of the first component, and the foamable adhesive sheet is heated to be foamed and solidified, thereby bonding the first component to the second component. In addition, for example, when the initial adhesion of the first adhesive layer and the second adhesive layer is low, the foamable adhesive sheet in this embodiment is preferably used in the following cases: inserting the foamable adhesive sheet between the first member and the second member, heating the foamable adhesive sheet to make it foam and solidify, thereby bonding the first member and the second member; after the foamable adhesive sheet is arranged in the second member, the second member arranged with the foamable adhesive sheet is inserted into the hole, groove, etc. of the first member, and the foamable adhesive sheet is heated to make it foam and solidify, thereby bonding the first member and the second member; after the foamable adhesive sheet is arranged in the hole, groove, etc. of the first member, the second member is inserted into the hole, groove, etc. of the first member arranged with the foamable adhesive sheet, and the foamable adhesive sheet is heated to make it foam and solidify, thereby bonding the first member and the second member; etc. Specifically, the foamable adhesive sheet in this embodiment can be used for bonding the coil and the stator in the motor, and bonding the rotor and the permanent magnet in the embedded magnet type motor.

The method for producing the foamable adhesive sheet in the present embodiment is not particularly limited, and can be appropriately selected according to the layer structure of the foamable adhesive sheet.

B. Method of manufacturing the article

The method for manufacturing an article in this embodiment includes: a placement step of placing the foamable adhesive sheet between a first member and a second member; and a bonding step of heating the foamable adhesive sheet to foam and cure it, thereby bonding the first member and the second member.

Figures 14(a) to (b) are process diagrams showing an example of a method for manufacturing an article in this embodiment. First, as shown in Figure 14(a), a foamable adhesive sheet 10 is arranged between a first member 20a and a second member 20b. Next, the first adhesive layer 1 and the second adhesive layer 3 of the foamable adhesive sheet 10 are heated to foam and solidify. Thus, as shown in Figure 14(b), an adhesive sheet 15 having a foamed and solidified first adhesive layer 11 and second adhesive layer 13 is used to bond (join) the first member 20a and the second member 20b. Thus, an article 100 having an adhesive sheet 15 arranged between the first member 20a and the second member 20b is obtained.

9( a ) to ( c ) are process diagrams showing another example of the method for manufacturing the article in the present embodiment.

First, as shown in FIG. 9(a), a foamable adhesive sheet 10 is arranged on the second member 20b. At this time, in the foamable adhesive sheet 10, when the initial adhesive force of the first adhesive layer 1 is lower than the initial adhesive force of the second adhesive layer 3, the surface of the second adhesive layer 3 of the foamable adhesive sheet 10 is attached to the second member 20b by utilizing the initial adhesive force of the second adhesive layer 3. Next, as shown in FIG. 9(b), the second member 20b having the foamable adhesive sheet 10 is inserted into the hole of the first member 20a. Next, as shown in FIG. 9(c), the first adhesive layer 1 and the second adhesive layer 3 of the foamable adhesive sheet 10 are heated to foam and solidify. The first member 20a and the second member 20b are bonded (joined) by utilizing the adhesive sheet 15 having the foamed and solidified first adhesive layer 11 and the second adhesive layer 13. Thus, an article 100 having the adhesive sheet 15 arranged between the first member 20a and the second member 20b is obtained.

Hereinafter, a method for manufacturing the article in this embodiment will be described.

1. Foam adhesive sheet

In the method for producing an article in the present embodiment, the above-mentioned foamable adhesive sheet is used as the foamable adhesive sheet.

When the foamable adhesive sheet has a spacer, when the foamable adhesive sheet is disposed between the first member and the second member, the spacer is peeled off from the foamable adhesive sheet and then used.

In addition, since the details of the foamable adhesive sheet have been described in the above-mentioned section "A. Foamable adhesive sheet", the description here is omitted.

2. Configuration process

In the configuration process of the present embodiment, as a method for configuring the foaming adhesive sheet between the first member and the second member, it can be appropriately selected according to the structure of the foaming adhesive sheet, the types of the first member and the second member, etc. For example, there can be cited: when the second member is bonded and fixed in the hole or groove of the first member, when the initial adhesion of the first adhesive layer in the foaming adhesive sheet is lower than the initial adhesion of the second adhesive layer, a method of attaching the surface of the second adhesive layer of the foaming adhesive sheet to the second member by utilizing the initial adhesion of the second adhesive layer of the foaming adhesive sheet, and then arranging the second member to which the foaming adhesive sheet is attached in the hole or groove of the first member; a method of attaching the surface of the second adhesive layer of the foaming adhesive sheet to the hole or groove of the first member by utilizing the initial adhesion of the second adhesive layer of the foaming adhesive sheet, and then arranging the second member in the hole or groove of the first member to which the foaming adhesive sheet is attached; and the like. In addition, for example, the following methods can be cited: when the second member is bonded and fixed in the hole or groove of the first member, when the initial bonding forces of the first adhesive layer and the second adhesive layer in the foam adhesive sheet are both low, a method of arranging the foam adhesive sheet between the first member and the second member; a method of arranging the foam adhesive sheet on the second member and then arranging the second member arranged with the foam adhesive sheet in the hole or groove of the first member; a method of arranging the foam adhesive sheet in the hole or groove of the first member and then arranging the second member in the hole or groove of the first member arranged with the foam adhesive sheet; and the like.

3. Bonding process

In the bonding step of the present embodiment, the foamable adhesive sheet is heated to be foamed and cured. The method based on heating can also be applied to the case where the first member and the second member are not transparent, such as metal members.

The heating conditions can be appropriately set according to the type of thermosetting adhesive and foaming agent contained in the first adhesive layer and the second adhesive layer, the type of substrate, etc. The heating temperature can be set to, for example, 130° C. to 200° C. In addition, the heating time can be set to, for example, 3 minutes to 3 hours.

It should be noted that the present invention is not limited to the above-mentioned embodiments. The above-mentioned embodiments are illustrative, and technical solutions having substantially the same structure and having the same effects as the technical ideas described in the scope of protection claimed in the present invention are all included in the technical scope of the present invention.

Example

I. Example of the first embodiment

[Manufacturing example]

First, adhesive compositions 1 to 3 having the following compositions were prepared.

<Adhesive composition 1>

Acrylic resin (PMMA-PBuA-PMMA (partially acrylamide), Tg: -20°C, 120°C, Mw: 150,000): 13 parts by mass

Epoxy resin A (bisphenol A novolac type, solid at room temperature, softening temperature: 70°C, epoxy equivalent: 210 g/eq, Mw: 1300, melt viscosity at 150°C: 0.5 Pa·s): 40 parts by mass

Epoxy resin B (BPA phenoxy type, solid at room temperature, softening temperature: 110°C, epoxy equivalent: 8000 g/eq, Mw: 50,000): 42 parts by mass

Curing agent A (α-(hydroxy (or dihydroxy) phenylmethyl)-ω-hydropoly [biphenyl-4,4'-diylmethylene (hydroxy (or dihydroxy) phenylenemethylene)]): 6 parts by mass

Curing catalyst (2-phenyl-4,5-dihydroxymethylimidazole, average particle size: 3 μm, melting point: 230°C, reaction starting temperature 145°C to 155°C, active region 155°C to 173°C (manufactured by Shikoku Chemical Industry Co., Ltd., 2PHZ-PW)): 8 parts by mass

Foaming agent (heat-expandable microcapsules, average particle size 10 μm to 16 μm, expansion starting temperature 123°C to 133°C, maximum expansion temperature 168°C to 178°C, core: hydrocarbon, shell: thermoplastic polymer): 13.5 parts by mass

Solvent (methyl ethyl ketone): 150 parts by mass

<Adhesive composition 2>

Acrylic resin (PMMA-PBuA-PMMA (partially acrylamide), Tg: -20°C, 120°C, Mw: 150,000): 40 parts by mass

Epoxy resin C (bisphenol A type, liquid at room temperature, epoxy equivalent: 184 to 194 g/eq): 45 parts by mass

Epoxy resin D (diaminodiphenylmethane type, high viscosity liquid, epoxy equivalent: 110-130 g/eq): 65 parts by mass

Epoxy resin E (silicone modified, epoxy equivalent: 1200 g/mol): 20 parts by mass

Silane coupling agent (3-glycidoxypropyltrimethoxysilane): 2 parts by mass

Curing agent B (phenol-formaldehyde polycondensate softening point 80°C, hydroxyl equivalent 104 g/mol): 6 parts by mass

Curing catalyst (2-phenyl-4,5-dihydroxymethylimidazole, average particle size: 3 μm, melting point: 230°C, reaction starting temperature 145°C to 155°C, active region 155°C to 173°C (manufactured by Shikoku Chemical Industry Co., Ltd., 2PHZ-PW)): 10 parts by mass

Foaming agent: heat-expandable microcapsules, average particle size 10 μm to 16 μm, expansion starting temperature 123°C to 133°C, maximum expansion temperature 168°C to 178°C, core: hydrocarbon, shell: thermoplastic polymer: 20 parts by mass

Solvent (methyl ethyl ketone): 114 parts by mass

<Adhesive composition 3>

Acrylic resin (PMMA-PBuA-PMMA (partially acrylamide), Tg: -20°C, 120°C, Mw: 150,000): 10 parts by mass

Epoxy resin A (bisphenol A novolac type, solid at room temperature, softening temperature: 70°C, epoxy equivalent: 210 g/eq, Mw: 1300, melt viscosity at 150°C: 0.5 Pa·s): 15 parts by mass

Epoxy resin C (bisphenol A type, liquid at room temperature, epoxy equivalent: 184 to 194 g/eq): 23 parts by mass

Epoxy resin F (aliphatic multifunctional epoxy compound, epoxy equivalent: 173 g/eq): 13 parts by mass

Silane coupling agent (3-glycidoxypropyltrimethoxysilane): 1 part by mass

Curing agent B (phenol-formaldehyde polycondensate softening point 80°C, hydroxyl equivalent 104 g/mol): 19 parts by mass

Curing catalyst (2-phenyl-4,5-dihydroxymethylimidazole, average particle size: 3 μm, melting point: 230°C, reaction starting temperature 145°C to 155°C, active region 155°C to 173°C (manufactured by Shikoku Chemical Industry Co., Ltd., 2PHZ-PW)): 2 parts by mass

Foaming agent: heat-expandable microcapsules, average particle size 10 μm to 16 μm, expansion starting temperature 123°C to 133°C, maximum expansion temperature 168°C to 178°C, core: hydrocarbon, shell: thermoplastic polymer: 8.5 parts by mass

Storage stabilizer (boric acid ester compound): 9 parts by mass

Solvent (methyl ethyl ketone): 39 parts by mass

[Example I-1]

As a substrate, a polyethylene naphthalate (PEN) film (manufactured by Toyobo Co., Ltd., Teonex Q5100, thickness 25 μm) was used. In addition, with respect to 100 parts by mass of the polyester polymer, 15 parts by mass of a curing agent (polyisocyanate) and 0.3 parts by mass of a catalyst (tris(dimethylaminomethyl)phenol) were mixed, and further diluted with methyl ethyl ketone (MEK) so that the solid content became 15% by mass to prepare a resin composition. On one side of the above-mentioned substrate, the above-mentioned resin composition was applied with a rod coater, and dried in an oven at 100°C for 1 minute to form a first intermediate layer with a thickness of 2 μm. Next, the above-mentioned adhesive composition 1 was applied to the surface opposite to the substrate of the above-mentioned first intermediate layer using an applicator in a manner that the thickness after coating becomes 50 μm. Then, it was dried in an oven at 100°C for 3 minutes to form a first adhesive layer.

Next, as a second spacer, a release film (PET spacer, manufactured by Nippa, PET50×1-J2, thickness 50 μm) was used, and the adhesive composition 2 was applied to the release treated surface of the release film using an applicator so that the thickness after application was 50 μm. Then, it was dried in an oven at 100° C. for 3 minutes to form a second adhesive layer.

Next, the surface of the second adhesive layer of the laminate having the second spacer and the second adhesive layer is laminated on the surface of the substrate having the substrate, the first intermediate layer and the first adhesive layer, thereby obtaining a foamable adhesive sheet having the first adhesive layer, the first intermediate layer, the substrate, the second adhesive layer and the second spacer arranged in sequence.

[Example I-2]

A foamable adhesive sheet was prepared in the same manner as in Example I-1 except that the thickness of the first adhesive layer and the second adhesive layer was set to 45 μm.

[Example I-3]

A foamable adhesive sheet was prepared in the same manner as in Example I-1, except that the adhesive composition 3 was used to form the second adhesive layer and the thickness of the second adhesive layer was set to 45 μm.

[Comparative Example I-1]

A foamable adhesive sheet was prepared in the same manner as in Example I-1, except that the adhesive composition 2 was used to form the first adhesive layer.

[Comparative Example I-2]

A foamable adhesive sheet was prepared in the same manner as in Comparative Example I-1 except that a polyphenylene sulfide (PPS) film (TORELINA 25-3030, manufactured by Toray Industries, Inc., thickness 25 μm) was used as the substrate.

[Comparative Example I-3]

A foamable adhesive sheet was prepared in the same manner as in Comparative Example I-1 except that the thickness of the substrate (PEN film) was changed to 50 μm.

[Comparative Example I-4]

A foamable adhesive sheet was prepared in the same manner as in Comparative Example I-1 except that a polyethylene terephthalate (PET) film (manufactured by Toray Industries, Inc., Lumirror #25-S105, thickness 50 μm) was used as the substrate.

[evaluate]

(1) Initial adhesion of the first adhesive layer and the second adhesive layer

Regarding the initial adhesion of the first adhesive layer, a 5 mm diameter cylindrical stainless steel probe was pressed to the surface of the first adhesive layer of the foamable adhesive sheet at a temperature of 25° C. using an initial adhesion tester "TAC-II" manufactured by RHESCA, with a load of 10.0 gf and a speed of 30 mm/min, and after holding for 1.0 second, the probe was peeled off at a speed of 30 mm/min to measure the load during peeling. The measurement was performed 5 times, and the average value was taken as the initial adhesion.

The initial tack of the second adhesive layer was measured in the same manner as the initial tack of the first adhesive layer. At this time, the initial tack of the second adhesive layer was measured after the second separator was peeled off from the foamable adhesive sheet.

(2) Ring stiffness

After peeling off the second spacer from the foamable adhesive sheet, a rectangular test piece with a width of 10 mm and a length of 200 mm was made, and the ring stiffness was measured using the above-mentioned ring stiffness determination method. As a determination device, a LoopStiffness Tester (registered trademark) made by Toyo Seiki Manufacturing Co., Ltd. was used. The environment during the determination was set to a temperature of 23°C and a relative humidity of 50%.

(3) Droop

Figure 10 (a)～(b) is the schematic diagram of the determination method of the sagging amount of explanation foamable adhesive sheet.For foamable adhesive sheet 10, after peeling off the second spacer, cut into the size of width 10mm, length 100mm, make test piece.In addition, fixture 51 is rectangular parallelepiped shape, and the lower surface 51a of fixture 51 is rectangular shape, and is plane, is set to level.In addition, double-sided adhesive tape 52 (3M company system " Y-4920-25 ") is attached to the lower surface 51a of fixture 51.

First, as shown in FIG. 10( a), under normal temperature and humidity, the surface of the double-sided adhesive tape 52 of the clamp 51 is attached to the center of the foaming adhesive sheet 10 to fix the foaming adhesive sheet 10. The attachment area is set to 10 mm×10 mm. At this time, when the surface of the double-sided adhesive tape 52 of the clamp 51 is attached to the surface of the first adhesive layer of the foaming adhesive sheet 10, the adhered surface is the first adhesive layer. On the other hand, when the surface of the double-sided adhesive tape 52 of the clamp 51 is attached to the surface of the second adhesive layer of the foaming adhesive sheet 10, the adhered surface is the second adhesive layer.

Next, as shown in Fig. 10(b), the fixture 51 is raised in the vertically upward direction. At this time, the end 10a of the foamable adhesive sheet 10 sags in the vertically downward direction. Moreover, the surface S1 of the double-sided adhesive tape 52 of the fixture 51 is used as the reference plane, and the distance in the vertical direction from the reference plane S1 to the end 10a of the foamable adhesive sheet 10 is measured, which is taken as the sag amount F. Regarding the sag amount, three test pieces are made from the foamable adhesive sheet, and each of the test pieces is measured once, and the average value of the three test pieces is calculated.

(4) Adhesion

As with the above-mentioned determination of sagging amount, the face of the double-sided adhesive tape of the fixture is attached to the center of the test piece of the foamable adhesive sheet, and after fixing the foamable adhesive sheet, the fixture is raised in the vertical upward direction. At this time, the face of the double-sided adhesive tape of the fixture is attached to the face of the first adhesive layer of the foamable adhesive sheet. Then, a metal plate is configured below the foamable adhesive sheet raised by the fixture, the fixture is removed in the vertical downward direction, and the foamable adhesive sheet is attached to the metal plate. Then, the state of the foamable adhesive sheet is observed visually, and the adhesion is evaluated according to the following benchmark.

A: The foamable adhesive sheet can be attached without bending or inclusion of air bubbles.

B: The foamable adhesive sheet was bent and bubbles were mixed in.

(5) Insertion property (sliding property of the first adhesive layer during insertion)

Prepare a foamable adhesive sheet cut into 5.5cm×8.0cm, a hollow cylinder 1 with an outer diameter of 22mm, a thickness of 1.5mm, and a length of 60mm, and a hollow cylinder 2 with an outer diameter of 18mm, a thickness of 1.0mm, and a length of 80mm. In addition, peel off the second spacer from the foamable adhesive sheet, and attach the second adhesive layer to the outer diameter of the cylinder 2 in a manner such that the short side is located in the circumferential direction, and configure the foamable adhesive sheet. Then, slowly press the cylinder 2 by hand, insert it into the hollow gap of the cylinder 1, and evaluate the sliding property of the first adhesive layer at this time. The evaluation criteria are shown below.

A: It will not get stuck when inserted.

B: It gets stuck during insertion (the first adhesive layer sticks to the cylinder 1 and the insertability is poor).

[Table 1]

First bonding layer Second adhesive layer Example I-1 Adhesive composition 1 Adhesive composition 2 Example I-2 Adhesive composition 1 Adhesive composition 2 Example I-3 Adhesive composition 1 Adhesive composition 3 Comparative Example I-1 Adhesive composition 2 Adhesive composition 2 Comparative Example I-2 Adhesive composition 2 Adhesive composition 2 Comparative Example I-3 Adhesive composition 2 Adhesive composition 2 Comparative Example I-4 Adhesive composition 2 Adhesive composition 2

[Table 2]

According to the comparison between Examples I-1 to I-3 and Comparative Examples I-3 to I-4, and the comparison between Examples I-1 to I-3 and Comparative Examples I-1 to I-2, it was confirmed that when the ring stiffness is 50 mN/10 mm or more, the sagging amount is reduced and the adhesion is good. In addition, in Examples I-1 to I-3, since the initial adhesion of the first adhesive layer and the initial adhesion of the second adhesive layer are within the specified range, the insertion property is also good.

II. Example of the Second Embodiment

[Manufacturing example]

First, adhesive compositions A and B having the following compositions were prepared.

<Adhesive composition A>

Acrylic resin (PMMA-PBuA-PMMA (partially acrylamide), Tg: -20°C, 120°C, Mw: 150,000): 13 parts by mass

Epoxy resin A (bisphenol A novolac type, solid at room temperature, softening temperature: 70°C, epoxy equivalent: 210 g/eq, Mw: 1300, melt viscosity at 150°C: 0.5 Pa·s): 40 parts by mass

Epoxy resin B (BPA phenoxy type, solid at room temperature, softening temperature: 110°C, epoxy equivalent: 8000 g/eq, Mw: 50,000): 42 parts by mass

Curing agent A (α-(hydroxy (or dihydroxy) phenylmethyl)-ω-hydropoly [biphenyl-4,4'-diylmethylene (hydroxy (or dihydroxy) phenylenemethylene)]): 6 parts by mass

Curing catalyst (2-phenyl-4,5-dihydroxymethylimidazole, average particle size: 3 μm, melting point: 230°C, reaction starting temperature 145°C to 155°C, active region 155°C to 173°C (manufactured by Shikoku Chemical Industry Co., Ltd., 2PHZ-PW)): 8 parts by mass

Foaming agent (heat-expandable microcapsules, average particle size 10 μm to 16 μm, expansion starting temperature 123°C to 133°C, maximum expansion temperature 168°C to 178°C, core: hydrocarbon, shell: thermoplastic polymer): 13.5 parts by mass

Solvent (methyl ethyl ketone): 150 parts by mass

<Adhesive composition B>

Acrylic resin (PMMA-PBuA-PMMA (partially acrylamide), Tg: -20°C, 120°C, Mw: 150,000): 40 parts by mass

Epoxy resin C (bisphenol A type, liquid at room temperature, epoxy equivalent: 184 to 194 g/eq): 45 parts by mass

Epoxy resin D (diaminodiphenylmethane type, high viscosity liquid, epoxy equivalent: 110-130 g/eq): 65 parts by mass

Epoxy resin E (silicone modified, epoxy equivalent: 1200 g/mol): 20 parts by mass

Silane coupling agent (3-glycidoxypropyltrimethoxysilane): 2 parts by mass

Curing agent B (phenol-formaldehyde polycondensate softening point 80°C, hydroxyl equivalent 104 g/mol): 6 parts by mass

Curing catalyst (2-phenyl-4,5-dihydroxymethylimidazole, average particle size: 3 μm, melting point: 230°C, reaction starting temperature 145°C to 155°C, active region 155°C to 173°C (manufactured by Shikoku Chemical Industry Co., Ltd., 2PHZ-PW)): 10 parts by mass

Foaming agent: heat-expandable microcapsules, average particle size 10 μm to 16 μm, expansion starting temperature 123°C to 133°C, maximum expansion temperature 168°C to 178°C, core: hydrocarbon, shell: thermoplastic polymer: 20 parts by mass

Solvent (methyl ethyl ketone): 114 parts by mass

[Example II-1]

As a substrate, polyethylene naphthalate (PEN film, manufactured by TOYOBO FILMSOLUTIONS, Teonex Q51, thickness 25 μm) was used. In addition, with respect to 100 parts by mass of polyester polymer, 15 parts by mass of curing agent (polyisocyanate) and 0.3 parts by mass of catalyst (tris(dimethylaminomethyl)phenol) were mixed, and further diluted with methyl ethyl ketone (MEK) so that the solid content became 15% by mass to prepare a resin composition. On one side of the above-mentioned substrate, the above-mentioned resin composition was applied with a rod coater, and it was dried in an oven at 100°C for 1 minute to form a first intermediate layer with a thickness of 2 μm. Next, the above-mentioned adhesive composition A was applied to the surface opposite to the substrate of the above-mentioned first intermediate layer using an applicator in a manner that the thickness after coating becomes 27 μm. Then, it was dried in an oven at 100°C for 3 minutes to form a first adhesive layer.

Next, a release film (PET spacer, manufactured by Nippa, PET50×1-J2, thickness 50 μm) was used as a spacer, and the adhesive composition B was applied to the release treated surface of the release film using an applicator so that the thickness after application was 51 μm. Then, it was dried in an oven at 100° C. for 3 minutes to form a second adhesive layer.

Next, the second adhesive layer surface of the laminate having the spacer and the second adhesive layer is laminated on the surface of the substrate of the laminate having the substrate, the first intermediate layer and the first adhesive layer. Then, the spacer is peeled off. Thus, a foamable adhesive sheet having the first adhesive layer, the first intermediate layer, the substrate and the second adhesive layer arranged in sequence is obtained.

[Examples II-2 to II-5]

A foamable adhesive sheet was prepared in the same manner as in Example II-1 except that the thicknesses of the first adhesive layer and the second adhesive layer were set to the thicknesses shown in Table 2 below.

[Comparative Example II-1]

A laminate having a substrate, a first intermediate layer, and a first adhesive layer was obtained in the same manner as in Example II-1. This laminate was used as a foamable adhesive sheet.

[Comparative Example II-2]

A laminate having a substrate, a first intermediate layer, and a first adhesive layer was obtained in the same manner as in Example II-3. This laminate was used as a foamable adhesive sheet.

[Comparative Example II-3]

The first intermediate layer is formed on the substrate in the same manner as in Example II-1. In addition, the second adhesive layer is formed on the spacer in the same manner as in Example II-3. Next, the surface of the second adhesive layer of the stacked body having the spacer and the second adhesive layer is laminated on the surface of the substrate having the substrate and the first intermediate layer. Then, the spacer is peeled off. Thus, a foamable adhesive sheet having the first intermediate layer, the substrate and the second adhesive layer arranged in sequence is obtained.

[Comparative Examples II-4 to II-5]

A foamable adhesive sheet was prepared in the same manner as in Comparative Example II-3 except that the thickness of the second adhesive layer was set to the thickness shown in Table 2 below.

[Comparative Example II-6]

A foamable adhesive sheet was prepared in the same manner as in Example II-1 except that the thicknesses of the first adhesive layer and the second adhesive layer were set to the thicknesses shown in Table 2 below.

[evaluate]

(1) Initial adhesion of the first adhesive layer and the second adhesive layer

Regarding the initial adhesion of the first adhesive layer, a 5 mm diameter cylindrical stainless steel probe was pressed to the surface of the first adhesive layer of the foamable adhesive sheet at a temperature of 25° C. using an initial adhesion tester "TAC-II" manufactured by RHESCA, with a load of 10.0 gf and a speed of 30 mm/min, and after holding for 1.0 second, the probe was peeled off at a speed of 30 mm/min to measure the load during peeling. The measurement was performed 5 times, and the average value was taken as the initial adhesion.

The initial tack of the second adhesive layer was measured in the same manner as the initial tack of the first adhesive layer.

(2) Ring stiffness

A rectangular test piece with a width of 10 mm and a length of 200 mm was prepared from the foamable adhesive sheet, and the loop stiffness was measured using the loop stiffness measurement method described above. As a measuring instrument, a Loop Stiffness Tester (D-R) manufactured by Toyo Seiki Seisaku-sho Co., Ltd. was used. The environment during the measurement was set to a temperature of 23°C and a relative humidity of 50%.

(3) Adhesion

Figure 10 (a) ~ (b) is a schematic diagram of the evaluation method of the adhesion of the foamable adhesive sheet. For the foamable adhesive sheet 10, it is cut into a size of 10mm in width and 100mm in length to make a test piece. In addition, the fixture 51 is a rectangular parallelepiped shape, and the lower surface 51a of the fixture 51 is a rectangular shape and is a plane, which is set to be horizontal. In addition, a double-sided adhesive tape 52 (3M company "Y-4920-25") is attached to the lower surface 51a of the fixture 51.

First, as shown in FIG. 10( a), under normal temperature and humidity, the surface of the double-sided adhesive tape 52 of the clamp 51 is attached to the center of the foamable adhesive sheet 10 to fix the foamable adhesive sheet 10. The attached area is set to 10 mm × 10 mm. At this time, the surface of the double-sided adhesive tape 52 of the clamp 51 is attached to the surface of the first adhesive layer of the foamable adhesive sheet 10.

Next, as shown in FIG10( b), the clamp 51 is raised in the vertically upward direction. Next, although not shown in the figure, a metal plate is arranged below the foam adhesive sheet raised by the clamp, the clamp is removed in the vertically downward direction, and the foam adhesive sheet is attached to the metal plate. Then, the state of the foam adhesive sheet is visually observed, and the adhesion is evaluated according to the following criteria.

A: The foamable adhesive sheet can be attached without bending or inclusion of air bubbles.

B: The foamable adhesive sheet was bent and bubbles were mixed in.

[Table 3]

Table 3 shows that the adhesiveness is good when the radius of curvature of the curl of the foamable adhesive sheet after being left at a predetermined temperature and humidity for a predetermined time is greater than or equal to a predetermined value and the ring stiffness of the foamable adhesive sheet is greater than or equal to a predetermined value.

In addition, in this invention, for example, the following inventions are provided.

[1] A foamable adhesive sheet comprising a first adhesive layer, a substrate, and a second adhesive layer in this order,

The first adhesive layer and the second adhesive layer contain a curable adhesive.

At least one of the first adhesive layer and the second adhesive layer further contains a foaming agent.

The initial adhesive force of the first adhesive layer is greater than or equal to 0 gf and less than 10 gf.

The initial adhesive force of the second adhesive layer is greater than or equal to 10 gf and less than or equal to 500 gf.

The foamable adhesive sheet has a ring stiffness of 50 mN/10 mm or more.

[2] The foamable adhesive sheet according to [1], wherein the first adhesive layer contains the foaming agent.

[3] The foamable adhesive sheet according to [2], wherein the first adhesive layer and the second adhesive layer contain the foaming agent.

[4] A foamable adhesive sheet comprising a first adhesive layer, a substrate, a second adhesive layer and an adhesive layer in this order,

The first adhesive layer and the second adhesive layer contain a curable adhesive and a foaming agent.

The adhesive layer contains a pressure-sensitive adhesive or a curable adhesive.

The initial adhesive force of the first adhesive layer is greater than or equal to 0 gf and less than 10 gf.

The initial adhesion of the adhesive layer is 10 gf or more.

The foamable adhesive sheet has a ring stiffness of 50 mN/10 mm or more.

[5] The foamable adhesive sheet according to [4], wherein the initial tack of the second adhesive layer is 0 gf or more and less than 10 gf.

[6] The foamable adhesive sheet according to any one of [1] to [5], wherein the thickness of the substrate is thinner than the thickness of the first adhesive layer and the thickness of the second adhesive layer.

[7] A foamable adhesive sheet comprising a first adhesive layer, a substrate, and a second adhesive layer in this order,

The composition of the first adhesive layer is different from that of the second adhesive layer.

The first adhesive layer and the second adhesive layer contain a thermosetting adhesive.

At least one of the first adhesive layer and the second adhesive layer further contains a foaming agent, and the curling radius of the foamable adhesive sheet after being left to stand for 15 hours at a temperature of 60° C. and a humidity of 10% RH or less is 15 mm or more.

The foamable adhesive sheet has a ring stiffness of 45 mN/10 mm or more.

[8] The foamable adhesive sheet according to [7], wherein the first adhesive layer and the second adhesive layer contain the foaming agent.

[9] The foamable adhesive sheet according to [7] or [8], wherein the thickness of the substrate is thinner than the thickness of the first adhesive layer and the thickness of the second adhesive layer.

[10] The foamable adhesive sheet according to any one of [7] to [9], wherein the initial tack of the first adhesive layer is greater than or equal to 0 gf and less than 10 gf, and the initial tack of the second adhesive layer is greater than or equal to 10 gf and less than or equal to 500 gf.

[11] The foamable adhesive sheet according to any one of [7] to [10], wherein the foamable adhesive sheet has a curl adjusting layer on the surface of the second adhesive layer opposite to the substrate.

[12] A method for manufacturing an article, comprising:

a placement step of placing the foamable adhesive sheet described in any one of [1] to [11] between the first member and the second member; and

The bonding step is to heat the foamable adhesive sheet to foam and solidify it, thereby bonding the first member and the second member.

Description of Reference Numerals

1…First bonding layer

2…Substrate

3…Second bonding layer

4…First intermediate layer

5…Second middle layer

6… Adhesive layer

7…Curl Adjustment Layer

10…Foamable adhesive sheet

15…Adhesive sheet after foaming and curing

20a ... first component

20b…Second member

100…Items

Claims (12)

1. A foaming adhesive sheet comprising a first adhesive layer, a base material and a second adhesive layer in this order,

The first adhesive layer and the second adhesive layer contain a curable adhesive,

At least one of the first adhesive layer and the second adhesive layer further contains a foaming agent,

The primary adhesion of the first adhesive layer is 0gf or more and less than 10gf,

The primary adhesion of the second adhesive layer is 10gf or more and 500gf or less,

The ring stiffness of the foaming adhesive sheet is more than 50mN/10 mm.

2. The foamable adhesive sheet according to claim 1, wherein the first adhesive layer contains the foaming agent.

3. The foamable adhesive sheet according to claim 2, wherein the first adhesive layer and the second adhesive layer contain the foaming agent.

4. A foaming adhesive sheet comprising a first adhesive layer, a base material, a second adhesive layer and an adhesive layer in this order,

The first adhesive layer and the second adhesive layer contain a curable adhesive and a foaming agent,

The adhesive layer contains a pressure sensitive adhesive or a curable adhesive,

The primary adhesion of the first adhesive layer is 0gf or more and less than 10gf,

The adhesive layer has an initial adhesion of 10gf or more,

The ring stiffness of the foaming adhesive sheet is more than 50mN/10 mm.

5. The foamable adhesive sheet according to claim 4, wherein the primary adhesion of the second adhesive layer is 0gf or more and less than 10gf.

6. The foamable adhesive sheet according to claim 1, wherein a thickness of the base material is thinner than a thickness of the first adhesive layer and a thickness of the second adhesive layer.

7. A foaming adhesive sheet comprising a first adhesive layer, a base material and a second adhesive layer in this order,

The composition of the first adhesive layer is different from the composition of the second adhesive layer,

The first adhesive layer and the second adhesive layer contain a thermosetting adhesive,

At least one of the first adhesive layer and the second adhesive layer further contains a foaming agent, and the radius of curvature of the curl of the foamable adhesive sheet after being left for 15 hours at a temperature of 60 ℃ and a humidity of 10% RH or less is 15mm or more,

The ring stiffness of the foaming adhesive sheet is more than 45mN/10 mm.

8. The foamable adhesive sheet according to claim 7, wherein the first adhesive layer and the second adhesive layer contain the foaming agent.

9. The foamable adhesive sheet according to claim 7, wherein the thickness of the base material is thinner than the thickness of the first adhesive layer and the thickness of the second adhesive layer.

10. The foamable adhesive sheet according to claim 7, wherein the primary adhesion of the first adhesive layer is 0gf or more and less than 10gf, and the primary adhesion of the second adhesive layer is 10gf or more and 500gf or less.

11. The foamable adhesive sheet according to claim 7, wherein the foamable adhesive sheet has a curl adjustment layer on a side of the second adhesive layer opposite to the base material.

12. A method of manufacturing an article, comprising:

A disposing step of disposing the foamable adhesive sheet according to any one of claims 1 to 11 between a first member and a second member; and

And a bonding step of heating the foamable adhesive sheet to foam and cure the foamable adhesive sheet, and bonding the first member and the second member.