JP2024110102A - Foamable adhesive sheet, method for producing foamable adhesive sheet, method for producing article, and method for inspecting quality of foamable adhesive sheet - Google Patents

Abstract

To provide a foamable adhesive sheet that offers improved adhesive strength, a method for producing a foamable adhesive sheet, a method for producing an article, and a method for testing the quality of a foamable adhesive sheet.SOLUTION: A foamable adhesive sheet includes an adhesive layer. The adhesive layer includes a thermosetting adhesive and a foamer. The foamer includes thermally expandable microcapsules. Using thermomechanical analysis, when a compressive load is applied, the temperature is increased at a predetermined rate, and the displacement is measured, the maximum extrapolated displacement temperature is at least -35°C below and at most -10°C below the maximum foaming temperature of the foamer.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a foamable adhesive sheet, a method for manufacturing a foamable adhesive sheet, a method for manufacturing an article, and a method for inspecting the quality of a foamable adhesive sheet.

Adhesives that bond components together are used in a variety of fields, and many bonding methods are known.

For example, Patent Documents 1 and 2 disclose adhesive sheets that contain a foaming agent (foamable adhesive sheets). A method of using a foamable adhesive sheet is known in which the foamable adhesive sheet is placed between components, and then heated to foam and harden the foamable adhesive sheet, thereby bonding the components together.

Such foamable adhesive sheets are required to have foaming properties to fill the gaps between components, and adhesive properties to bond the components together.

JP 2000-53944 A Patent No. 6223477

However, when a foamable adhesive sheet is heated to foam and harden, both foaming and hardening occur, making it difficult to balance foaming and hardening, resulting in problems such as a decrease in foaming ratio and a decrease in adhesive strength. As such, it is difficult to balance foaming ratio and adhesive strength, making it difficult to obtain the desired foaming and adhesive properties.

Conventionally, the heating conditions for foaming and curing a foamable adhesive sheet are set based on, for example, the foaming start temperature of the foaming agent, the maximum foaming temperature of the foaming agent, and the curing start temperature of the adhesive. For example, Patent Document 2 discloses that the heating conditions satisfy the relationship T1≦T2 when the thermal foaming temperature (foaming start temperature) of the thermal foaming agent is T1 and the curing start temperature of the adhesive layer is T2. However, when the inventors of the present disclosure investigated the heating conditions for foaming and curing a foamable adhesive sheet, they found that the adhesive strength may decrease even when the foaming start temperature of the foaming agent and the curing start temperature of the adhesive layer have a predetermined relationship.

The present disclosure has been made in consideration of the above-mentioned circumstances, and has as its main objective the provision of a foamable adhesive sheet and a method for manufacturing an article using the foamable adhesive sheet, which can improve adhesive strength.

One embodiment of the present disclosure provides a foamable adhesive sheet having an adhesive layer, the adhesive layer containing a thermosetting adhesive and a foaming agent, the foaming agent being a thermally expandable microcapsule, and the foamable adhesive sheet being subjected to a compressive load, heated at a predetermined heating rate, and the displacement measured by thermomechanical analysis, the maximum displacement extrapolated temperature is equal to or greater than the maximum foaming temperature of the foaming agent minus 35°C and equal to or less than the maximum foaming temperature of the foaming agent minus 10°C.

Another embodiment of the present disclosure provides a method for producing a foamable adhesive sheet having an adhesive layer, the adhesive layer containing a thermosetting adhesive and a foaming agent, the foaming agent being a thermally expandable microcapsule, and the method for producing a foamable adhesive sheet includes an inspection step for inspecting the quality of the foamable adhesive sheet by applying a compressive load, raising the temperature at a predetermined heating rate, and measuring the displacement, thereby determining the maximum displacement amount and the maximum displacement extrapolation temperature by thermomechanical analysis.

Another embodiment of the present disclosure provides a method for manufacturing an article, which includes an inspection step for inspecting the quality of a foamable adhesive sheet having an adhesive layer by thermomechanical analysis, applying a compressive load, raising the temperature at a predetermined heating rate, and measuring the displacement, thereby determining the maximum displacement amount and the maximum displacement extrapolation temperature, an arrangement step for arranging the foamable adhesive sheet between a first member and a second member, and an adhesion step for foaming and curing the foamable adhesive sheet by heating, and adhering the first member and the second member, wherein the adhesive layer contains a thermosetting adhesive and a foaming agent, and the foaming agent is a thermally expandable microcapsule.

Another embodiment of the present disclosure provides a quality inspection method for a foamable adhesive sheet having an adhesive layer, the adhesive layer containing a thermosetting adhesive and a foaming agent, the foaming agent being a thermally expandable microcapsule, and the method uses thermomechanical analysis to determine the maximum displacement and the maximum displacement extrapolation temperature when a compressive load is applied, the temperature is increased at a predetermined heating rate, and the displacement is measured.

The present disclosure provides a foamable adhesive sheet that can improve adhesive strength, and a method for manufacturing an article using the foamable adhesive sheet.

1 is a schematic cross-sectional view illustrating a foamable adhesive sheet according to the present disclosure. 1 is a schematic cross-sectional view illustrating a foamable adhesive sheet according to the present disclosure. 1 is a schematic cross-sectional view illustrating a foamable adhesive sheet according to the present disclosure. 1 is a graph illustrating a TMA curve for a foamable adhesive sheet. 1 is a graph illustrating a TMA curve for a blowing agent. 1 is a schematic cross-sectional view illustrating a foamable adhesive sheet according to the present disclosure. 1A to 1C are process diagrams illustrating a method for producing a foamable adhesive sheet according to the present disclosure. 1 is a process diagram illustrating a method for manufacturing an article according to the present disclosure.

Below, an embodiment of the present disclosure will be described with reference to the drawings. However, the present disclosure can be implemented in many different forms, and should not be interpreted as being limited to the description of the embodiment exemplified below. In addition, in order to make the explanation clearer, the drawings may show the width, thickness, shape, etc. of each part in a schematic manner compared to the actual form, but these are merely examples and do not limit the interpretation of the present disclosure. In this specification and each figure, elements similar to those described above with respect to the previous figures are given the same reference numerals, and detailed explanations may be omitted as appropriate.

In this specification, when describing a mode in which another component is placed on a certain component, the term "above" or "below" includes both cases in which another component is placed directly above or below a certain component so as to be in contact with the component, and cases in which another component is placed above or below a certain component with another component in between, unless otherwise specified. Also, in this specification, when describing a mode in which another component is placed on the surface of a certain component, the term "on the surface side" or "on the surface", includes both cases in which another component is placed directly above or below a certain component so as to be in contact with the component, and cases in which another component is placed above or below a certain component with another component in between, unless otherwise specified.

In this specification, "sheet" also includes materials called "films."In addition, "films" also includes materials called "sheets."In addition, the numerical ranges in this specification are average value ranges.

Here, in a foamable adhesive sheet having an adhesive layer containing a thermosetting adhesive and a foaming agent, for example, the curing reaction of the thermosetting adhesive and the foaming of the foaming agent may gradually progress during production or storage. If this occurs, there is a risk that the adhesive strength will decrease when components are bonded together using the foamable adhesive sheet. If the adhesive strength decreases, the reliability, durability, etc. of the components bonded by the foamable adhesive sheet will be impaired.

As mentioned above, foaming and adhesive properties are required for foaming adhesive sheets.

Conventionally, the foaming characteristics of foamable adhesive sheets have been evaluated, for example, by the foaming start temperature and maximum foaming temperature of the foaming agent, and the foaming ratio of the foamable adhesive sheet.

However, the foaming start temperature and maximum foaming temperature of the foaming agent are the foaming characteristics of the foaming agent alone, and cannot be said to be the foaming characteristics of the foamable adhesive sheet.

In general, the expansion ratio of a foamable adhesive sheet refers to the expansion ratio when the foamable adhesive sheet is foamed and cured without any external pressure being applied to the sheet.

On the other hand, when a foamable adhesive sheet is used to bond components together, the foamable adhesive sheet is sandwiched between the components and foamed and cured, so the foamable adhesive sheet is foamed and cured while being subjected to external pressure. Therefore, the conditions for measuring the foaming ratio of a foamable adhesive sheet are significantly different from the actual foaming and curing conditions of the foamable adhesive sheet.

In contrast, when measuring the foaming characteristics of a foamable adhesive sheet by thermomechanical analysis (TMA), the foamable adhesive sheet is heated while a compressive load is applied, and the displacement associated with the thermal expansion of the foamable adhesive sheet is measured. In this case, the foamable adhesive sheet is foamed and cured while a certain degree of compressive load is applied to the sheet. Therefore, the measurement conditions for thermomechanical analysis can be closer to the actual foaming and curing conditions of a foamable adhesive sheet than the measurement conditions for the expansion ratio of conventional foamable adhesive sheets. It is therefore believed that thermomechanical analysis can obtain measured values that reflect the foaming and curing behavior of the foamable adhesive sheet.

The inventors of this disclosure therefore focused on the foaming characteristics of foamable adhesive sheets measured by thermomechanical analysis, and as a result of extensive research, discovered that the foaming characteristics of a foamable adhesive sheet can be evaluated by the maximum foaming amount and maximum displacement extrapolation temperature determined by thermomechanical analysis of the foamable adhesive sheet. This disclosure is based on such findings.

The foamable adhesive sheet, the method for manufacturing the foamable adhesive sheet, the method for manufacturing the article, and the method for inspecting the quality of the foamable adhesive sheet according to the present disclosure are described in detail below.

A. Foamable Adhesive Sheet The foamable adhesive sheet of the present disclosure is a foamable adhesive sheet having an adhesive layer, the adhesive layer containing a thermosetting adhesive and a foaming agent, the foaming agent being a thermally expandable microcapsule, and a compressive load is applied, the temperature is increased at a predetermined heating rate, and the displacement is measured by thermomechanical analysis, and the maximum displacement extrapolated temperature is the maximum foaming temperature of the foaming agent minus 35°C or more and the maximum foaming temperature of the foaming agent minus 10°C or less.

The foamable adhesive sheet of the present disclosure will be described with reference to the drawings. FIGS. 1 to 3 are schematic cross-sectional views illustrating the foamable adhesive sheet of the present disclosure. The foamable adhesive sheet 10 in FIG. 1 has an adhesive layer 1. The foamable adhesive sheet 10 in FIG. 2 has a first adhesive layer 1a and a second adhesive layer 1b. The foamable adhesive sheet 10 in FIG. 3 has a first adhesive layer 1a, a substrate 2, and a second adhesive layer 1b, in that order. In addition, the adhesive layer 1, the first adhesive layer 1a, and the second adhesive layer 1b all contain a thermosetting adhesive and a foaming agent.

In the present disclosure, the foaming agent is a thermally expandable microcapsule. In the thermally expandable microcapsule, a thermally expandable agent such as a hydrocarbon is encapsulated inside a shell made of a resin. Here, when the thermally expandable microcapsule is heated, the resin constituting the shell softens and the pressure of the thermally expandable agent such as a hydrocarbon increases, causing the thermally expandable microcapsule to expand. Since the shell becomes thinner due to the expansion, if heating is continued, the thermally expandable agent escapes from the thermally expandable microcapsule, causing the thermally expandable microcapsule to shrink. Therefore, when the foaming characteristics of the foaming agent are measured by thermomechanical analysis (TMA), a TMA curve with temperature on the horizontal axis and displacement on the vertical axis, for example, as shown in FIG. 4, is obtained. In the TMA curve for the foaming agent as shown in FIG. 4, the temperature showing the maximum displacement is defined as the maximum foaming temperature T _max2 of the foaming agent.

5 is a graph showing an example of a TMA curve in which a compressive load is applied to a foamable adhesive sheet, the temperature is increased at a predetermined heating rate, and the displacement is measured by thermomechanical analysis (TMA), with the temperature on the horizontal axis and the displacement on the vertical axis. In a TMA curve for a foamable adhesive sheet containing thermally expandable microcapsules as a foaming agent, there is usually a peak associated with expansion (foaming). In the TMA curve for a foamable adhesive sheet as shown in FIG. 5, the temperature at the intersection of a straight line showing the maximum displacement and a tangent drawn at a point where the gradient is maximum on the curve on the low-temperature side of the peak associated with expansion (foaming) is set as the maximum displacement extrapolation temperature T _max1 of the foamable adhesive sheet. In the foamable adhesive sheet of the present disclosure, in the TMA curve for a foamable adhesive sheet as shown in FIG. 5, the maximum displacement extrapolation temperature T _max1 is within a predetermined range with respect to the maximum foaming temperature T _max2 of the foaming agent.

In the foamable adhesive sheet of the present disclosure, the adhesive strength can be improved by the maximum displacement extrapolation temperature _Tmax1 determined by thermomechanical analysis being within a predetermined range relative to the maximum foaming temperature _Tmax2 of the foaming agent. The maximum displacement extrapolation temperature can be an indicator of the foaming behavior of the foamable adhesive sheet. The maximum displacement extrapolation temperature being within a predetermined range relative to the maximum foaming temperature of the foaming agent makes it possible to obtain sufficient foaming behavior. As a result, it is believed that the adhesive strength is improved.

The components of the foamable adhesive sheet in this disclosure are described below.

1. Properties In the foamable adhesive sheet of the present disclosure, when a compressive load is applied, the temperature is raised at a predetermined heating rate, and the displacement is measured by thermomechanical analysis, the maximum displacement extrapolation temperature is preferably not less than the maximum foaming temperature of the foaming agent -35°C and not more than the maximum foaming temperature of the foaming agent -10°C, and is preferably not less than the maximum foaming temperature of the foaming agent -32°C and not more than the maximum foaming temperature of the foaming agent -16°C. By having the maximum displacement extrapolation temperature within the above range, the adhesive strength can be improved.

In the foamable adhesive sheet of the present disclosure, when a compressive load is applied, the temperature is raised at a predetermined heating rate, and the displacement is measured by thermomechanical analysis, the maximum displacement extrapolation temperature may be within a predetermined range relative to the maximum foaming temperature of the foaming agent, and specifically, it is preferably 140°C or higher and 160°C or lower, and more preferably 141°C or higher and 157°C or lower. When the maximum displacement extrapolation temperature is within the above range, the heat resistance can be improved. Therefore, it can be applied to applications requiring heat resistance such as around automobile engines.

In addition, in the foamable adhesive sheet of the present disclosure, when a compressive load is applied, the temperature is increased at a predetermined heating rate, and the displacement is measured by thermomechanical analysis, the temperature at which the maximum displacement is observed is preferably, for example, 180°C or higher and 220°C or lower. If the temperature at which the maximum displacement is observed is within the above range, the heat resistance can be improved.

Here, the thermomechanical analysis of the foamable adhesive sheet is performed by the following method. First, the foamable adhesive sheet is punched out with a φ4 mm jig to prepare a sample. Next, the sample is placed in an aluminum container with φ5 mm, and an aluminum plate with φ4 mm is placed on the sample. Next, thermomechanical measurement is performed under the conditions of temperature: 25°C to 250°C, heating rate: 20°C/min, load: 10 mN, and compression mode, and the displacement due to the expansion or contraction of the sample is measured. As the thermomechanical measurement device, for example, a thermomechanical analyzer TMA7100 manufactured by Hitachi High-Tech Science Corporation can be used.

The above maximum displacement is the maximum value of the displacement in the TMA curve for the foamable adhesive sheet.

The maximum displacement extrapolation temperature is the temperature at the intersection of the straight line showing the maximum displacement in the TMA curve for the foamable adhesive sheet and the tangent drawn at the point where the gradient is maximum on the curve on the low-temperature side of the peak associated with expansion (foaming).

The maximum foaming temperature of the foaming agent is measured by thermomechanical analysis. Specifically, the foaming temperature of the foaming agent is the temperature that indicates the maximum amount of displacement when the foaming agent is heated at a predetermined heating rate under a compressive load and the displacement is measured by thermomechanical analysis. The maximum foaming temperature of the foaming agent will be described later.

Here, the thermomechanical analysis of the foaming agent is carried out by the following method. First, 0.1 mg of the foaming agent is weighed out. Next, the foaming agent is evenly placed in an aluminum container with a diameter of 5 mm, and an aluminum plate with a diameter of 4 mm is placed on the foaming agent. Next, thermomechanical measurement is carried out under the conditions of temperature: 25°C to 250°C, heating rate: 20°C/min, load: 10 mN, and compression mode, and the displacement due to the expansion or contraction of the sample is measured. As the thermomechanical measurement device, for example, a thermomechanical analyzer TMA7100 manufactured by Hitachi High-Tech Science Corporation can be used.

In a foamable adhesive sheet, the above-mentioned maximum displacement amount can be controlled, for example, by adjusting the particle size and content of the foaming agent. For example, if the particle size of the foaming agent is large, the maximum displacement amount tends to be large. On the other hand, if the particle size of the foaming agent is small, the maximum displacement amount tends to be small. Also, for example, if the content of the foaming agent is large, the maximum displacement amount tends to be large. On the other hand, if the content of the foaming agent is small, the maximum displacement amount tends to be small.

In addition, in the case of a foamable adhesive sheet, the above-mentioned maximum displacement extrapolation temperature can be controlled, for example, by adjusting the viscosity or hardness of the adhesive layer. For example, if the viscosity of the adhesive layer is high, the maximum displacement extrapolation temperature tends to be high. On the other hand, if the viscosity of the adhesive layer is low, the maximum displacement extrapolation temperature tends to be low. Also, for example, if the adhesive layer is hard, the maximum displacement extrapolation temperature tends to be high. On the other hand, if the adhesive layer is soft, the maximum displacement extrapolation temperature tends to be low.

In addition, the foamable adhesive sheet of the present disclosure preferably has a high adhesive strength after foaming and curing. The shear strength (adhesive strength) based on JIS K6850 corresponding to ISO 4587 may be, for example, 1.50 MPa or more, 1.80 MPa or more, or 2.10 MPa or more at 23°C. In addition, the shear strength (adhesive strength) may be, for example, 0.50 MPa or more, 0.75 MPa or more, or 1.00 MPa or more at 130°C. For example, in a high-strength acrylic foam adhesive tape that does not require heating, the shear strength (adhesive strength) is about 1 MPa or more and 2 MPa or less at room temperature, and there is no heat resistance at 200°C. Therefore, if the shear strength (adhesive strength) is in the above range at 23°C, there is an advantage in terms of strength. In addition, if the shear strength (adhesive strength) is in the above range at 130°C, it can be applied to applications that require heat resistance around an automobile engine or similar.

In addition, the foamable adhesive sheet of the present disclosure preferably has high electrical insulation after foaming and curing. After foaming and curing of the foamable adhesive sheet, the dielectric breakdown voltage based on JIS C2107 corresponding to IEC 60454-2 is preferably, for example, 3 kV or more, and more preferably 5 kV or more. With the dielectric breakdown voltage in the above range, application to rust prevention and around copper wires becomes possible. Furthermore, after foaming and curing of the foamable adhesive sheet, the thermal conductivity is preferably, for example, 0.1 W/mK or more, and more preferably 0.15 W/mK or more. With the thermal conductivity in the above range, it is possible to miniaturize parts and promote the curing reaction when heated.

2. Adhesive Layer The adhesive layer in the present disclosure contains a thermosetting adhesive and a foaming agent.

(1) Material (a) Foaming Agent The foaming agent in the present disclosure is a thermally expandable microcapsule. As the foaming agent, a thermally expandable microcapsule that is generally used in the adhesive layer of a foamable adhesive sheet can be used.

Thermal expansion microcapsules preferably have a core made of a thermal expansion agent such as a hydrocarbon, and a shell made of a resin such as an acrylonitrile copolymer.

The foaming agent may be used alone or in combination of two or more.

The foaming start temperature of the foaming agent is preferably equal to or higher than the softening temperature of the base of the thermosetting adhesive such as epoxy resin, and equal to or lower than the activation temperature of the curing reaction of the base of the thermosetting adhesive such as epoxy resin. The foaming start temperature of the foaming agent is, for example, 70°C or higher, and may be 100°C or higher. If the foaming start temperature is too low, foaming may start early, and foaming may occur in a state where the flexibility and fluidity of the resin component is low, making it difficult to produce uniform foaming. On the other hand, the foaming start temperature of the foaming agent is, for example, 210°C or lower. If the foaming start temperature is too high, the resin component may deteriorate.

The foaming start temperature of the foaming agent can be determined by thermomechanical analysis.

The softening temperature of the base material of a thermosetting adhesive, such as an epoxy resin, can be measured using the ring and ball softening temperature test method specified in JIS K7234.

The maximum foaming temperature of the foaming agent is, for example, preferably 160°C or higher and 200°C or lower, more preferably 168°C or higher and 195°C or lower, and even more preferably 168°C or higher and 178°C or lower. If the maximum foaming temperature is too low, the foaming agent may shrink, making it impossible to maintain the thickness of the adhesive layer at the time of foaming, and the adhesive strength may decrease. On the other hand, if the maximum foaming temperature is too high, the foaming agent may not expand sufficiently, and the adhesive strength may decrease.

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. The average particle size of the foaming agent is preferably equal to or less than the thickness of the adhesive layer, and may be, for example, 44 μm or less, 30 μm or less, or 24 μm or less.

The average particle size of the foaming agent is the particle size at 50% of the cumulative value in the particle size distribution obtained by the laser diffraction scattering method. When measuring the average particle size of the foaming agent, the adhesive layer is dissolved in a solvent to separate the foaming agent. The solvent is not particularly limited as long as it is capable of dissolving components other than the foaming agent contained in the adhesive layer, and is appropriately selected depending on the type of thermosetting adhesive contained in the adhesive layer. For example, a solvent used in the adhesive composition used to form the adhesive layer can be used. Specifically, methyl ethyl ketone, ethyl acetate, toluene, etc. can be used.

The foaming ratio at the maximum foaming temperature of the foaming agent is, for example, 1.5 times or more, and may be 3 times or more. On the other hand, the foaming ratio at the maximum foaming temperature of the foaming agent is, for example, 15 times or less, and may be 10 times or less.

The foaming agent content is, for example, 0.5 parts by mass or more, 2 parts by mass or more, 3 parts by mass or more, 4 parts by mass or more, or 5 parts by mass or more, relative to 100 parts by mass of the resin component contained in the adhesive layer. On the other hand, the foaming agent content is, for example, 25 parts by mass or less, 20 parts by mass or less, or 15 parts by mass or less, relative to 100 parts by mass of the resin component contained in the adhesive layer. If the foaming agent content is too high, the thermosetting adhesive content will be relatively low, which may reduce the adhesive strength after foaming and curing.

(b) Thermosetting adhesive The thermosetting adhesive in the present disclosure may be a thermosetting adhesive generally used for the adhesive layer of a foamable adhesive sheet. Thermosetting adhesives are also applicable to components that do not have transparency, such as metal components.

Examples of thermosetting 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 thermosetting adhesive is preferably an epoxy resin adhesive. In other words, the thermosetting adhesive preferably contains an epoxy resin and a curing agent. In general, epoxy resin adhesives have excellent mechanical strength, heat resistance, insulating properties, chemical resistance, etc., have little shrinkage upon curing, and can be used for a wide range of applications.

Below, we will explain an example where the thermosetting adhesive is an epoxy resin adhesive.

(i) Epoxy resin The epoxy resin in the present disclosure is a compound that has at least one epoxy group or glycidyl group and is cured by a crosslinking polymerization reaction in combination with a curing agent. The epoxy resin also includes a monomer having at least one epoxy group or glycidyl group.

Epoxy resins include, for example, aromatic epoxy resins, aliphatic epoxy resins, alicyclic epoxy resins, and heterocyclic epoxy resins. Specific examples of epoxy resins include bisphenol-type epoxy resins such as bisphenol A-type epoxy resins and bisphenol F-type epoxy resins, novolac-type epoxy resins such as bisphenol A novolac-type epoxy resins and cresol novolac-type epoxy resins, and modified epoxy resins such as urethane-modified epoxy resins and rubber-modified epoxy resins. Other specific examples include biphenyl-type epoxy resins, stilbene-type epoxy resins, triphenolmethane-type epoxy resins, alkyl-modified triphenolmethane-type epoxy resins, triazine-nucleus-containing epoxy resins, dicyclopentadiene-modified phenol-type epoxy resins, naphthalene-type epoxy resins, glycol-type epoxy resins, and pentaerythritol-type epoxy resins. The epoxy resin may be one type or two or more types.

Bisphenol A type epoxy resins can exist in a liquid state at room temperature or in a solid state at room temperature, depending on the number of repeating units in the bisphenol skeleton. Bisphenol A type epoxy resins in which the main chain has 2 or more and 10 or less bisphenol skeletons, for example, are solid at room temperature. Bisphenol A type epoxy resins are particularly preferred because they can improve heat resistance.

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.

(ii) Acrylic resin In the present disclosure, when the thermosetting adhesive is an epoxy resin-based adhesive, the adhesive layer may further contain an acrylic resin compatible with the epoxy resin. The acrylic resin is a resin compatible with the epoxy resin. Since the acrylic resin is compatible with the epoxy resin, it is easy to improve the toughness of the adhesive layer. As a result, the adhesiveness after foaming and curing can be improved. Furthermore, it is considered that the acrylic resin acts as a compatibilizer for the foaming agent (for example, a foaming agent whose shell is a resin of acrylonitrile copolymer), and uniformly disperses and foams, thereby improving the adhesiveness after foaming and curing. In addition, the flexibility of the acrylic resin is exerted, and the adhesion to the substrate after foaming and curing and the crack resistance after foaming and curing can be improved. In addition, the compatibility of the acrylic resin with the epoxy resin allows the hardness of the surface of the adhesive layer to be kept high. On the other hand, if the acrylic resin is incompatible with the epoxy resin, a soft portion is formed on the surface of the adhesive layer, so that the interface with the first member and the second member becomes difficult to slip, and the workability may be reduced.

The acrylic resin in the present disclosure 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 adhesive layer with a scanning electron microscope (SEM) or a transmission electron microscope (TEM) from the absence of micron-sized islands. More specifically, the average particle size of the islands is preferably 1 μm or less. In particular, the average particle size of the islands may be 0.5 μm or less, or may be 0.3 μm or less. It is preferable to have a large number of samples, for example 100 or more. The area to be observed is in the range of 100 μm x 100 μm, or in the case where the thickness of the adhesive layer is 100 μm or less, in the range of the thickness x 100 μm.

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 homopolymer of an acrylic acid ester monomer, a mixed component containing two or more of the above homopolymers, or a copolymer of two or more of the acrylic acid ester monomers, containing one or more copolymers. The acrylic resin may also be a mixed component of the above homopolymer and the above copolymer. The concept of methacrylic acid is also included in the "acrylic acid" of the acrylic acid ester monomer. Specifically, the acrylic resin may be a mixture of a methacrylate polymer and an acrylate polymer, or an acrylic acid ester polymer such as acrylate-acrylate, methacrylate-methacrylate, or methacrylate-acrylate. Among them, it is preferable that the acrylic resin contains a copolymer of two or more acrylic acid ester monomers ((meth)acrylic acid ester copolymer).

Examples of the monomer components constituting the (meth)acrylic acid ester copolymer include the monomer components described in JP 2014-065889 A. The monomer components may have the polar groups described above. Examples of the (meth)acrylic acid ester copolymer include ethyl acrylate-butyl acrylate-acrylonitrile copolymer, ethyl acrylate-acrylonitrile copolymer, and butyl acrylate-acrylonitrile copolymer. Note that "acrylic acid" such as methyl acrylate and ethyl acrylate also includes "methacrylic acid" such as methyl methacrylate and ethyl methacrylate.

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

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

The acrylic copolymer may not have polar groups, or may be a modified product in which the above-mentioned polar groups have been introduced into a portion of the acrylic copolymer. The modified product is easily compatible with epoxy resins, and therefore has improved adhesive properties.

Among them, the acrylic resin is preferably a (meth)acrylic acid ester 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)acrylic acid ester copolymer has a first polymer portion that is a soft segment and a second polymer portion that is a hard segment. By adding such a copolymer, the toughness of the adhesive layer after curing is improved, and the adhesive strength can be further increased.

The manifestation of the above effect can be presumed as follows: By using an acrylic resin that has both soft and hard segments, such as the above (meth)acrylic acid ester copolymer, the hard segments contribute to heat resistance, and the soft segments contribute to toughness and flexibility, resulting in an adhesive layer with good heat resistance, toughness, and flexibility.

At least one of the first polymer portion and the second polymer portion contained in the (meth)acrylic acid ester copolymer has compatibility with epoxy resins. When the first polymer portion has compatibility with epoxy resins, flexibility can be increased. When the second polymer portion has compatibility with epoxy resins, cohesion and toughness can be increased.

Among these, the (meth)acrylic acid ester copolymer is preferably a block copolymer, and is particularly preferably an A-B-A block copolymer in which the compatible portion is polymer block A and the incompatible portion is polymer block B. Furthermore, it is more preferably an A-B-A block copolymer in which the first polymer portion is the incompatible portion and the second polymer portion is the compatible portion, and the first polymer portion is polymer block B and the second polymer portion is polymer block A.

The (meth)acrylic acid ester copolymer may be a modified product in which the above-mentioned polar group is introduced into a portion of the first polymer portion or the second polymer portion.

A specific example of a (meth)acrylic acid ester copolymer having the above-mentioned first polymer portion and second polymer portion is the above-mentioned MMA-BA-MMA copolymer.

The content of the acrylic resin is, for example, 1 part by mass or more, 3 parts by mass or more, 5 parts by mass or more, 7 parts by mass or more, or 10 parts by mass or more, when the resin component contained in the adhesive layer is taken as 100 parts by mass. If the content of the acrylic resin is too small, the adhesiveness after foaming and curing and the adhesion of the adhesive layer to the substrate may decrease. On the other hand, the content of the acrylic resin is, for example, 60 parts by mass or less, 50 parts by mass or less, 40 parts by mass or less, 35 parts by mass or less, or 30 parts by mass or less, when the resin component contained in the adhesive layer is taken as 100 parts by mass. If the content of the acrylic resin is too high, the film strength may decrease.

(iii) Curing Agent As the curing agent in the present disclosure, a curing agent generally used in an epoxy resin-based adhesive can be used.

The curing agent is preferably a solid at 23°C. A curing agent that is a solid at 23°C can have a longer storage stability (pot life) than a curing agent that is a liquid at 23°C. The curing agent may be a latent curing agent. The curing agent is usually a curing agent that undergoes a curing reaction by heat. The curing agent may be used alone or in combination of two or more types.

The reaction start temperature of the curing agent is, for example, 110°C or higher, and may be 130°C or higher. If the reaction start temperature is too low, the reaction starts early, and curing occurs in a state where the flexibility and fluidity of the resin component is low, and uniform curing may be difficult. On the other hand, the reaction start temperature of the curing agent is, for example, 200°C or lower. If the reaction start temperature is too high, the resin component may deteriorate. In addition, when a resin with high heat resistance, such as a phenolic resin, is used in addition to the epoxy resin, the resin component is less likely to deteriorate, so the reaction start temperature of the curing agent may be, for example, 300°C or lower. The reaction start temperature of the curing agent can be determined by differential scanning calorimetry (DSC).

Specific examples of curing agents 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.

Examples of imidazole-based curing agents include 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. It is also preferable that the imidazole-based curing agent has a hydroxyl group. Since crystallization occurs due to hydrogen bonds between hydroxyl groups, the reaction initiation temperature tends to be high.

Examples of phenol-based hardeners include phenol resins. Examples of phenol resins include resol-type phenol resins and novolac-type phenol resins. From the viewpoints of adhesion to the substrate after foaming and curing and crack resistance after foaming and curing, phenol-type novolac resins with a Tg of 110°C or less are particularly preferred. A phenol-based hardener and an imidazole-based hardener may be used in combination. In that case, it is preferable to use an imidazole-based hardener as a curing catalyst.

Examples of amine-based hardeners include aliphatic amines such as diethylenetriamine (DETA), triethylenetetramine (TETA), and metaxylylenediamine (MXDA); aromatic amines such as diaminodiphenylmethane (DDM), m-phenylenediamine (MPDA), and diaminodiphenylsulfone (DDS); alicyclic amines; and polyamidoamines. In addition, examples of amine-based hardeners that can be used include dicyandiamide-based hardeners such as dicyandiamide (DICY), organic acid dihydrazide-based hardeners, amine adduct-based hardeners, and ketimine-based hardeners.

Examples of acid anhydride curing agents include alicyclic acid anhydrides (liquid acid anhydrides) such as hexahydrophthalic anhydride (HHPA) and methyltetrahydrophthalic anhydride (MTHPA); and aromatic acid anhydrides such as trimellitic anhydride (TMA), pyromellitic anhydride (PMDA), and benzophenonetetracarboxylic acid (BTDA).

Examples of isocyanate-based curing agents include blocked isocyanates.

Examples of thiol-based curing agents include ester-bonded thiol compounds, aliphatic ether-bonded thiol compounds, and aromatic ether-bonded thiol compounds.

In particular, it is preferable to use a curing agent other than an imidazole-based curing agent in combination with an imidazole-based curing agent. In this case, it is preferable to use the imidazole-based curing agent as a curing catalyst.

The content of the curing agent is, for example, 1 part by mass or more and 40 parts by mass or less, when the resin component contained in the adhesive layer is 100 parts by mass. For example, when an imidazole-based curing agent is used as the main component as the curing agent, the content of the curing agent is preferably, for example, 1 part by mass or more and 15 parts by mass or less, when the resin component contained in the adhesive layer is 100 parts by mass. On the other hand, when a phenol-based curing agent is used as the main component as the curing agent, the content of the curing agent is preferably, for example, 5 parts by mass or more and 40 parts by mass or less, when the resin component contained in the adhesive layer is 100 parts by mass. Note that using an imidazole-based curing agent or a phenol-based curing agent as the main component as the curing agent means that the mass ratio of the imidazole-based curing agent or the phenol-based curing agent is the highest in the curing agent.

(c) Other Components In the adhesive layer of the present disclosure, for example, when the thermosetting adhesive is an epoxy resin adhesive, the adhesive layer may contain only the above-mentioned epoxy resin and acrylic resin as the resin component, or may further contain other resins, such as urethane resin.

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

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

The adhesive layer may contain additives such as silane coupling agents, fillers, antioxidants, light stabilizers, ultraviolet absorbers, lubricants, plasticizers, antistatic agents, crosslinking agents, and colorants, as necessary. Examples of silane coupling agents include epoxy-based silane coupling agents. Examples of fillers include inorganic fillers such as calcium carbonate, aluminum hydroxide, magnesium hydroxide, antimony trioxide, zinc borate, molybdenum compounds, and titanium dioxide. Examples of antioxidants include phenol-based antioxidants and sulfur-based antioxidants.

(2) Adhesive layer The thickness of the adhesive layer is not particularly limited, but is preferably equal to or greater than the average particle size of the foaming agent. The thickness of the adhesive layer is, for example, 10 μm or more and 200 μm or less, may be 15 μm or more and 150 μm or less, or may be 20 μm or more and 100 μm or less. If the adhesive layer is too thin, there is a possibility that the adhesion to the substrate and the adhesion after foaming and curing cannot be sufficiently obtained. In addition, if the adhesive layer is too thick, there is a possibility that the surface quality will deteriorate.

The thickness of the adhesive layer is a value measured from a cross section in the thickness direction of the foamable adhesive sheet observed with a transmission electron microscope (TEM), a scanning electron microscope (SEM), or a scanning transmission electron microscope (STEM), and can be the average value of the thicknesses at 10 randomly selected locations. The same method can be used to measure the thicknesses of other layers of the foamable adhesive sheet.

The adhesive layer may be a continuous layer or a discontinuous layer. Examples of discontinuous layers include stripes and dots. The surface of the adhesive layer may have an uneven shape such as an embossed shape.

The adhesive layer can be formed, for example, by applying an adhesive composition and removing the solvent. Examples of application methods include roll coating, reverse roll coating, transfer roll coating, gravure coating, gravure reverse coating, comma coating, rod coating, blade coating, bar coating, wire bar coating, die coating, lip coating, and dip coating.

The adhesive composition may or may not contain a solvent. In this specification, the term "solvent" is used in a broad sense to include not only a strict solvent (a solvent that dissolves a solute) but also a dispersion medium. 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 them as necessary. As a mixing and dispersing method, a general kneading and dispersing machine such as a two-roll mill, a three-roll mill, a pebble mill, a tron mill, a Szegvari attritor, 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 co-kneader, an intensive mixer, a tumbler, a blender, a disperser, a homogenizer, or an ultrasonic disperser can be used.

The foamable adhesive sheet of the present disclosure may have an adhesive layer, and may have, for example, only one adhesive layer, or may have a first adhesive layer and a second adhesive layer as the adhesive layer. In addition, when the foamable adhesive sheet of the present disclosure has a first adhesive layer and a second adhesive layer as the adhesive layer, the sheet may have the first adhesive layer and the second adhesive layer in this order, or the sheet may have the first adhesive layer, the substrate, and the second adhesive layer in this order. When a substrate is disposed between the first adhesive layer and the second adhesive layer, the handleability and workability of the foamable adhesive sheet can be improved. On the other hand, when the foamable adhesive sheet does not have a substrate, the thickness of the entire foamable adhesive sheet can be reduced. Therefore, for example, the foamable adhesive sheet can be inserted into a narrow gap.

3. Substrate The foamable adhesive sheet according to the present disclosure has a first adhesive layer and a second adhesive layer as adhesive layers, and may have a substrate between the first adhesive layer and the second adhesive layer.

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

Examples of substrates include resin substrates and nonwoven fabrics.

Examples of resins contained in the resin substrate include polyester resins such as polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate (PEN), and aromatic polyester; polycarbonate; polyarylate; polyurethane; polyamide resins such as polyamide and polyetheramide; polyimide resins such as polyimide, polyetherimide, and polyamideimide; polysulfone resins such as polysulfone and polyethersulfone; polyetherketone resins such as polyetherketone and polyetheretherketone; polyphenylene sulfide (PPS); and modified polyphenylene oxide. The glass transition temperature of the resin is, for example, 80°C or higher, and may be 140°C or higher, or 200°C or higher. Liquid crystal polymers (LCPs) may also be used as the resin.

Examples of nonwoven fabrics 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.

The substrate may be surface-treated to improve adhesion to the adhesive layer.

The thickness of the substrate is not particularly limited and may be, for example, 2 μm to 200 μm, 5 μm to 100 μm, or 9 μm to 50 μm.

4. Other Components The foamable adhesive sheet of the present disclosure may have other components, if necessary, in addition to the adhesive layer and substrate described above.

(1) Intermediate layer The foamable adhesive sheet of the present disclosure may have a first intermediate layer between the substrate and the first adhesive layer. The foamable adhesive sheet of the present disclosure may have a second intermediate layer between the substrate and the second adhesive layer. The first intermediate layer or the second intermediate layer is disposed, thereby improving the adhesion of the first adhesive layer or the second adhesive layer to the substrate. Furthermore, the first intermediate layer or the second intermediate layer is disposed, for example, to relieve the stress applied to the bent portion when the foamable adhesive sheet is folded, or to relieve the stress applied to the cut portion when the foamable adhesive sheet is cut. As a result, lifting or peeling of the first adhesive layer or the second adhesive layer from the substrate can be suppressed when the foamable adhesive sheet is bent or cut.

For example, in the foamable adhesive sheet 10 shown in FIG. 6, a first intermediate layer 3a is disposed between the substrate 2 and the first adhesive layer 1a, and a second intermediate layer 3b is disposed between the substrate 2 and the second adhesive layer 1b. Note that, although the foamable adhesive sheet 10 in FIG. 6 has both the first intermediate layer 3a and the second intermediate layer 3b, it may have only one of them.

The foamable adhesive sheet may have at least one of a first intermediate layer and a second intermediate layer. For example, it may have only the first intermediate layer arranged between the substrate and the first adhesive layer, or it may have only the second intermediate layer arranged between the substrate and the second adhesive layer, or it may have 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. Of these, it is preferable that the first intermediate layer is arranged between the substrate and the first adhesive layer, and the second intermediate layer is arranged between the substrate and the second adhesive layer.

The materials contained in the first and second intermediate layers are not particularly limited as long as they can increase the adhesion between the substrate and the first and second adhesive layers and can relieve stress, and are appropriately selected depending on the materials of the substrate, the first and second adhesive layers. Examples include polyester, polyvinyl chloride, polyvinyl acetate, polyurethane, copolymers of at least two of these, crosslinked products thereof, and mixtures thereof.

The crosslinked body is a crosslinked body obtained by crosslinking the above-mentioned resin with a curing agent. Examples of the curing agent include isocyanate-based curing agents. In addition, for example, when the reactive group/NCO equivalent is 1, it is preferable to add the isocyanate-based curing agent in a ratio of 0.5% by mass or more and 20% by mass or less to the resin.

In particular, it is preferable that the first intermediate layer and the second intermediate layer contain a crosslinked resin. Note that a crosslinked resin is one that does not melt even at high temperatures. This can improve the adhesive strength at high temperatures, i.e., heat resistance.

The thickness of the first and second intermediate layers is not particularly limited, but may be, for example, 0.1 μm or more, 0.5 μm or more, or 1 μm or more. If the first and second intermediate layers are too thin, the effect of suppressing peeling of the first and second adhesive layers from the substrate when the foamable adhesive sheet is bent or cut may not be sufficiently obtained. On the other hand, the thickness of the first and second intermediate layers may be, for example, 4 μm or less, or 3.5 μm or less. The first and second intermediate layers themselves usually do not have high heat resistance, so if the first and second intermediate layers are too thick, the heat resistance (adhesive strength at high temperatures) may decrease.

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

(2) Separator The foamable adhesive sheet according to the present disclosure may have a first separator on the side of the first adhesive layer opposite the second adhesive layer, and may have a second separator on the side of the second adhesive layer opposite the first adhesive layer.

The first separator and the second separator 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 sufficient to protect the first adhesive layer and the second adhesive layer. Examples of such first separators and second separators include release films and release papers. In addition, the first separator and the second separator may have a single-layer structure or a multi-layer structure.

Examples of single-layer separators include fluororesin films.

In addition, examples of separators with a multi-layer structure include laminates having a release layer on one or both sides of a base layer. Examples of base layers include resin films such as polypropylene, polyethylene, and polyethylene terephthalate, and papers such as fine paper, coated paper, and impregnated paper. Materials for the release layer are not particularly limited as long as they have releasability, and examples include silicone compounds, organic compound-modified silicone compounds, fluorine compounds, aminoalkyd compounds, melamine compounds, acrylic compounds, polyester compounds, and long-chain alkyl compounds. These compounds can be of any type, including emulsion, solvent, or solventless.

5. Foamable Adhesive Sheet The thickness of the foamable adhesive sheet in the present disclosure is, for example, 10 μm or more, and may be 20 μm or more. On the other hand, the thickness of the foamable adhesive sheet is, for example, 1000 μm or less, and may be 200 μm or less.

The uses of the foamable adhesive sheet in the present disclosure are not particularly limited. The foamable adhesive sheet in the present disclosure can be used, for example, when bonding two components together by placing the foamable adhesive sheet between two components and then heating the foamable adhesive sheet to foam and harden it. Specifically, the foamable adhesive sheet in the present disclosure is used to bond the coil and stator in a motor, or the rotor and permanent magnet in an embedded magnet motor.

B. Manufacturing method of a foamable adhesive sheet The manufacturing method of a foamable adhesive sheet in the present disclosure is a manufacturing method of a foamable adhesive sheet having an adhesive layer, the adhesive layer containing a thermosetting adhesive and a foaming agent, the foaming agent being a thermally expandable microcapsule, and the method has an inspection step of inspecting the quality of the foamable adhesive sheet by applying a compressive load, raising the temperature at a predetermined heating rate, and measuring the displacement, thereby determining the maximum displacement amount and the maximum displacement extrapolation temperature by thermomechanical analysis.

Figure 7 is a process diagram illustrating a method for producing a foamable adhesive sheet according to the present disclosure. In the method for producing a foamable adhesive sheet, first, a foamable adhesive sheet production process is performed to produce a foamable adhesive sheet. Next, an inspection process is performed to inspect the quality of the foamable adhesive sheet. In the inspection process, a compressive load is applied, the temperature is increased at a predetermined heating rate, and the displacement is measured. The quality of the foamable adhesive sheet is inspected by determining the maximum displacement amount and the maximum displacement extrapolation temperature by thermomechanical analysis.

As mentioned above, the measurement conditions for thermomechanical analysis can be made close to the foaming and curing conditions of an actual foamable adhesive sheet. Therefore, it is believed that thermomechanical analysis can obtain measured values that reflect the foaming and curing behavior of the foamable adhesive sheet. In addition, the maximum displacement and maximum displacement extrapolation temperature obtained by thermomechanical analysis have good reproducibility.

Therefore, in the present disclosure, the foaming characteristics of a foamable adhesive sheet can be easily, reproducibly, and accurately inspected by determining the maximum displacement amount and the maximum displacement extrapolation temperature by thermomechanical analysis. In addition, by inspecting the foaming characteristics of a foamable adhesive sheet, the desired foaming characteristics can be secured. This makes it possible to suppress a decrease in adhesive characteristics due to changes in foaming characteristics. Therefore, in the present disclosure, a foamable adhesive sheet with good foaming and adhesive characteristics can be obtained.

Below, each step of the manufacturing method of the article disclosed herein is explained.

1. Foamable Adhesive Sheet Manufacturing Process The method for manufacturing the foamable adhesive sheet of the present disclosure is not particularly limited.

For example, when the foamable adhesive sheet has only one adhesive layer and does not have a substrate, an adhesive layer can be formed by applying an adhesive composition to one side of a separator and drying it. The separator can then be peeled off.

For example, when the foamable adhesive sheet has a first adhesive layer and a second adhesive layer as adhesive layers and does not have a substrate between the first adhesive layer and the second adhesive layer, an adhesive composition for forming the first adhesive layer is applied to the first separator and dried to form the first adhesive layer, and an adhesive composition for forming the second adhesive layer is applied to the second separator and dried to form the second adhesive layer, and a laminate of the first separator and the first adhesive layer and a laminate of the second separator and the second adhesive layer are laminated together. The first separator and the second separator may then be peeled off.

For example, when the foamable adhesive sheet has a first adhesive layer, a substrate, and a second adhesive layer in this order, a method can be used in which the first adhesive layer and the second adhesive layer are formed by applying and drying an adhesive composition to both sides of the substrate. The first adhesive layer and the second adhesive layer can be formed sequentially or simultaneously. For example, a method can be used in which the first adhesive layer is formed by applying and drying an adhesive composition to one side of the substrate, and the second adhesive layer is formed by applying and drying an adhesive composition to one side of the separator, and the second adhesive layer and the separator are laminated to the other side of the substrate.

2. Inspection Step In the inspection step of the present disclosure, the quality of the foamable adhesive sheet is inspected by thermomechanical analysis by applying a compressive load, raising the temperature at a predetermined heating rate, measuring the displacement, and determining the maximum displacement amount and the maximum displacement extrapolation temperature.

The thermomechanical analysis of the foamable adhesive sheet can be the same as that described above in the section "A. Foamable adhesive sheet."

In this disclosure, the foaming characteristics of a foamable adhesive sheet are examined using the maximum displacement and maximum displacement extrapolation temperature determined by thermomechanical analysis.

For example, when the maximum displacement immediately after the production of the foamable adhesive sheet is defined as the first maximum displacement, and the maximum displacement after a predetermined time has elapsed at a predetermined temperature after the production of the foamable adhesive sheet is defined as the second maximum displacement, the absolute value of the difference between the first maximum displacement and the second maximum displacement is preferably within 94 μm, more preferably within 80 μm, and even more preferably within 73 μm. If the absolute value of the difference between the first maximum displacement and the second maximum displacement is within the above range, the foaming characteristics of the foamable adhesive sheet can be maintained. This makes it possible to suppress a decrease in the adhesive characteristics due to a change in the foaming characteristics.

For example, when the maximum displacement extrapolation temperature immediately after the manufacture of the foamable adhesive sheet is defined as the first maximum displacement extrapolation temperature, and the maximum displacement extrapolation temperature after a predetermined time has elapsed at a predetermined temperature since the manufacture of the foamable adhesive sheet is defined as the second maximum displacement extrapolation temperature, the absolute value of the difference between the first maximum displacement extrapolation temperature and the second maximum displacement extrapolation temperature is preferably within 30°C, more preferably within 25°C, and even more preferably within 20°C. If the absolute value of the difference between the first maximum displacement extrapolation temperature and the second maximum displacement extrapolation temperature is within the above range, the foaming characteristics of the foamable adhesive sheet can be maintained. This makes it possible to suppress a decrease in the adhesive characteristics due to a change in the foaming characteristics.

Specifically, if the absolute value of the difference between the first maximum displacement amount and the second maximum displacement amount is within a predetermined range, and the absolute value of the difference between the first maximum displacement extrapolation temperature and the second maximum displacement extrapolation temperature is within a predetermined range, it can be determined that the quality of the foamable adhesive sheet is ensured.

For example, in a foamable adhesive sheet, the maximum displacement extrapolation temperature is preferably at least the maximum foaming temperature of the foaming agent minus 35°C and at most the maximum foaming temperature of the foaming agent minus 10°C, and more preferably at least the maximum foaming temperature of the foaming agent minus 32°C and at most the maximum foaming temperature of the foaming agent minus 16°C. By having the maximum displacement extrapolation temperature within the above range, it is possible to ensure the desired foaming characteristics and also improve the adhesive strength.

Specifically, if the maximum displacement extrapolation temperature is within a specified range, it can be determined that the quality of the foamable adhesive sheet is ensured.

C. Manufacturing method of an article The manufacturing method of an article in the present disclosure includes an inspection step of inspecting the quality of a foamable adhesive sheet having an adhesive layer by applying a compressive load, raising the temperature at a predetermined heating rate, and measuring the displacement by determining the maximum displacement amount and the maximum displacement extrapolation temperature by thermomechanical analysis, an arrangement step of arranging the foamable adhesive sheet between a first member and a second member, and an adhesion step of foaming and curing the foamable adhesive sheet by heating to adhere the first member and the second member, wherein the adhesive layer contains a thermosetting adhesive and a foaming agent, and the foaming agent is a thermally expandable microcapsule.

8(a) to (c) are process diagrams illustrating a method for manufacturing an article according to the present disclosure. First, an inspection process is performed to inspect the quality of the foamable adhesive sheet 10 as shown in FIG. 8(a). Specifically, although not shown, the foamable adhesive sheet 10 is subjected to a compressive load, heated at a predetermined heating rate, and the maximum displacement and the maximum displacement extrapolated temperature are obtained by thermomechanical analysis when the displacement is measured. Next, if the above-mentioned maximum displacement and maximum displacement extrapolated temperature meet the predetermined criteria in the inspection process, a placement process is performed to place the foamable adhesive sheet 10 between the first member 20a and the second member 20b as shown in FIG. 8(a). Next, as shown in FIG. 8(c), a bonding process is performed to foam and harden the adhesive layer of the foamable adhesive sheet 10 by heating, and bond the first member 20a and the second member 20b. The first member 20a and the second member 20b are bonded (joined) by the adhesive sheet 11 after foaming and hardening. This results in an article 100 in which the adhesive sheet 11 is disposed between the first member 20a and the second member 20b.

In the present disclosure, as described in the above section "B. Method for manufacturing a foamable adhesive sheet," the foaming characteristics of the foamable adhesive sheet can be easily, reproducibly, and accurately inspected by determining the maximum displacement amount and the maximum displacement extrapolation temperature by thermomechanical analysis. In addition, by inspecting the foaming characteristics of the foamable adhesive sheet, the desired foaming characteristics can be secured. This makes it possible to suppress the deterioration of the adhesive characteristics due to changes in the foaming characteristics. Therefore, in the method for manufacturing an article in the present disclosure, a foamable adhesive sheet whose foaming characteristics and adhesive characteristics are guaranteed by performing an inspection process can be used. As a result, the adhesive strength between the first member and the second member can be improved. Therefore, the quality of the adhesiveness, reliability, durability, etc. can be improved. Furthermore, the yield can be increased. In addition, if the above maximum displacement amount and maximum displacement extrapolation temperature do not meet the predetermined standards in the inspection process, the foamable adhesive sheet is not used, thereby preventing wasteful consumption of the first member and the second member and reducing production costs.

The foamable adhesive sheet used in the method for manufacturing the article in this disclosure and each step in the method for manufacturing the article in this disclosure are described below.

(1) Foamable Adhesive Sheet The foamable adhesive sheet used in the present disclosure has an adhesive layer, and the adhesive layer contains a thermosetting adhesive and a foaming agent.

The adhesive layer in the foamable adhesive sheet can be the same as the adhesive layer described in the above section "A. Foamable adhesive sheet 2. Adhesive layer."

The other configurations of the foamable adhesive sheet can be the same as those described in the above section "A. Foamable adhesive sheet."

(2) Inspection Process In the inspection process of the present disclosure, the quality of the foamable adhesive sheet is inspected by thermomechanical analysis, in which a compressive load is applied to the foamable adhesive sheet, the temperature is raised at a predetermined heating rate, and the displacement is measured, and the maximum displacement amount and the maximum displacement extrapolation temperature are determined.

The inspection process can be the same as that described in the above section "B. Method for manufacturing foamable adhesive sheet 2. Inspection process."

(3) Arranging Step The arranging step in the present disclosure is a step of arranging a foamable adhesive sheet having an adhesive layer between a first member and a second member.

The method of placing the foamable adhesive sheet between the first and second members is appropriately selected depending on the type of the first and second members. For example, a method of placing a foamable adhesive sheet on one of the first and second members and placing the other member on the surface of the foamable adhesive sheet opposite the one member; a method of inserting a foamable adhesive sheet into the gap between the first and second members; a method of placing a foamable adhesive sheet in a hole or groove of the first member, and then inserting a second member into the gap after placing the foamable adhesive sheet in the hole or groove of the first member, etc. Also, for example, when the first member has a hole or groove and the second member is placed and bonded in the hole or groove of the first member, a method of attaching a foamable adhesive sheet to the second member, and then placing the second member to which the foamable adhesive sheet has been attached in the hole or groove of the first member, and a method of attaching a foamable adhesive sheet to the hole or groove of the first member, and then placing the second member in the hole or groove of the first member to which the foamable adhesive sheet has been attached, and the like can be mentioned.

The first and second members are appropriately selected depending on the application of the article. The first and second members are preferably members that require adhesion and insulation. For example, they are parts of a motor. Specifically, they include the coil and stator of a motor, and the rotor and permanent magnet of an embedded magnet motor.

In addition, the gap distance after the foamable adhesive sheet is placed between the first member and the second member may be, for example, 10 μm or more and 380 μm or less, and may be 85 μm or more and 285 μm or less. The present disclosure is suitable for cases in which the gap distance is relatively small as described above.

The distance of the gap after the foamable adhesive sheet is placed between the first member and the second member is, for example, in FIG. 8(b), the sum of the distances d1 and d2 of the gaps G1 and G2 after the foamable adhesive sheet 10 is placed between the first member 20a and the second member 20b.

(4) Bonding Step The bonding step in the present disclosure is a step of heating the foamable adhesive sheet to foam and harden it, thereby bonding the first member and the second member.

The heating temperature in the bonding process is, for example, preferably at least 20°C below the maximum foaming temperature of the foaming agent and at most 30°C above the maximum foaming temperature of the foaming agent, and more preferably at least 10°C above the maximum foaming temperature of the foaming agent and at most 30°C above the maximum foaming temperature of the foaming agent. If the heating temperature is higher than the above range, even if the thermosetting adhesive is cured, the foaming agent may shrink, making it impossible to maintain the thickness of the adhesive layer at the time of foaming, and the adhesive strength may decrease. On the other hand, if the heating temperature is lower than the above range, the foaming agent may not expand sufficiently, and the adhesive strength may decrease. In this case, there is a possibility that interfacial failure may easily occur between the adhesive sheet and the first or second member after foaming and curing.

Specifically, the heating temperature is preferably 150°C or higher and 200°C or lower, and more preferably 180°C or higher and 200°C or lower. By keeping the heating temperature within the above range, heat resistance can be improved. This makes it possible to apply the material to areas around automobile engines and other applications that require similar heat resistance.

D. Quality Inspection Method for Foamable Adhesive Sheets The quality inspection method for foamable adhesive sheets in the present disclosure is a quality inspection method for foamable adhesive sheets having an adhesive layer, the adhesive layer containing a thermosetting adhesive and a foaming agent, the foaming agent being a thermally expandable microcapsule, and a compressive load is applied, the temperature is increased at a predetermined heating rate, and the displacement is measured, and the maximum displacement amount and the maximum displacement extrapolation temperature are obtained by thermomechanical analysis.

In the present disclosure, as described above in the section "B. Method for manufacturing a foamable adhesive sheet," the foaming characteristics of a foamable adhesive sheet can be easily, reproducibly, and accurately inspected by determining the maximum displacement amount and the maximum displacement extrapolation temperature by thermomechanical analysis. In addition, by inspecting the foaming characteristics of a foamable adhesive sheet, the desired foaming characteristics can be ensured. This makes it possible to suppress deterioration of adhesive characteristics due to changes in foaming characteristics. Therefore, by carrying out the quality inspection method for a foamable adhesive sheet in the present disclosure, quality control of the foamable adhesive sheet can be performed. Furthermore, the quality of articles manufactured using the foamable adhesive sheet can be improved.

The quality inspection method for the foamable adhesive sheet in this disclosure may be the same as that described in the above section "B. Foamable adhesive sheet manufacturing method 2. Inspection process."

This disclosure is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and anything that has substantially the same configuration as the technical ideas described in the claims of this disclosure and has similar effects is included within the technical scope of this disclosure.

[Production Examples I to III]
First, adhesive compositions having the compositions shown in Table 1 below were prepared.

Acrylic resin: PMMA-PBuA-PMMA (partially acrylamide groups), Tg: -20°C, 120°C, Mw: 150,000
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
Epoxy resin B: BPA phenoxy type, solid at room temperature, softening temperature: 110°C, epoxy equivalent: 8000g/eq, Mw: 50,000
Epoxy resin C: bisphenol A type, liquid at room temperature, epoxy equivalent: 184 to 194 g/eq
Epoxy resin D: diaminodiphenylmethane type, highly viscous liquid, epoxy equivalent: 110 to 130 g/eq
Epoxy resin E: silicone modified, epoxy equivalent: 1200 g/mol
Hardener 1: α-(hydroxy(or dihydroxy)phenylmethyl)-ω-hydropoly[biphenyl-4,4'-diylmethylene(hydroxy(or dihydroxy)phenylenemethylene)]
Hardener 2: 2-phenyl-4,5-dihydroxymethylimidazole, average particle size: 3 μm, melting point: 230° C., reaction start temperature: 145° C. to 155° C., active region: 155° C. to 173° C. (manufactured by Shikoku Chemical Industry Co., Ltd., 2PHZ-PW)

Thermal foaming agent 1: Thermally expandable microcapsule, average particle size 13 μm, expansion start temperature 123-133°C, maximum expansion temperature 168-178°C, core: hydrocarbon, shell: thermoplastic polymer Thermal foaming agent 2: Thermally expandable microcapsule, average particle size 21 μm, expansion start temperature 123-133°C, maximum expansion temperature 180-195°C, core: hydrocarbon, shell: thermoplastic polymer Thermal foaming agent 3: Thermally expandable microcapsule, average particle size 21 μm, expansion start temperature 120-130°C, maximum expansion temperature 175-190°C, core: hydrocarbon, shell: thermoplastic polymer Silane coupling agent: 3-glycidoxypropyltrimethoxysilane Solvent: Methyl ethyl ketone

[Production Examples 1 to 3]
As a substrate, a polyethylene naphthalate film (PEN film, Toyobo Film Solutions Co., Ltd., Teonex Q51, thickness 25 μm) was prepared, with an intermediate layer having a thickness of 5 μm or less arranged on one surface. The adhesive composition was applied to the surface of the substrate opposite to the intermediate layer using an applicator so that the thickness after drying was 45 μm. The substrate was then dried in an oven at 100° C. for 3 minutes to form a first adhesive layer.

Next, the adhesive composition was applied to the surface of the intermediate layer opposite the substrate using an applicator so that the thickness after drying was 45 μm. The resulting layer was then dried in an oven at 100°C for 3 minutes to form a second adhesive layer.

Next, a release film (PET separator, manufactured by Nippa Corporation, PET50x1-J2, thickness 50 μm) was laminated as a separator on the surface of the second adhesive layer of the laminate having the first adhesive layer, substrate, intermediate layer, and second adhesive layer in that order. This resulted in a foamable adhesive sheet in which the first adhesive layer, substrate, intermediate layer, second adhesive layer, and separator were arranged in that order.

[Example 1 and Comparative Examples 1-2]
A foamable adhesive sheet was produced in the same manner as in Production Example 1. Thereafter, the sheet was stored at the storage temperature shown in Table 3 for 2 hours.

[Examples 2 to 4]
A foamable adhesive sheet was produced in the same manner as in Production Example 1, except that the thicknesses of the first adhesive layer and the second adhesive layer were changed as shown in Table 3. The sheet was then stored at the storage temperature shown in Table 3 for 2 hours.

[evaluation]
(1) Thermomechanical analysis (TMA)
As a thermomechanical measuring device, a thermomechanical analyzer TMA7100 manufactured by Hitachi High-Tech Science Corporation was used. First, the foamable adhesive sheet was punched out with a φ4 mm jig to prepare a sample. Next, the sample was placed in a φ5 mm aluminum container so that the second adhesive layer was at the bottom, and a φ4 mm aluminum plate was placed on the sample. Next, thermomechanical measurement was performed under the conditions of temperature: 25°C to 250°C, heating rate: 20°C/min, load: 10 mN, and compression mode, and the displacement associated with the expansion or contraction of the sample was measured. Then, the maximum displacement amount and the maximum displacement extrapolation temperature were obtained.

For Example 1, thermomechanical analysis was performed on the foamable adhesive sheet immediately after production and after storage. For Examples 2 to 4 and Comparative Examples 1 and 2, thermomechanical analysis was performed on the foamable adhesive sheet after storage.

(2) Shear adhesive strength Two metal plates (cold-rolled steel plate SPCC-SD) with a thickness of 1.6 mm, width of 25 mm, and length of 100 mm were prepared. A spacer was placed at one end of one of the metal plates with a gap of 15 mm. The thickness of the spacer was 300 μm (thickness of five sheets of Kapton tape P-221 made by Nitto Denko Corporation) or 370 μm (thickness of two sheets of Kapton tape P-221 made by Nitto Denko Corporation and one sheet of fluororesin adhesive tape 8410 made by Teraoka Seisakusho). For Examples 1 to 4 and Comparative Examples 1 and 2, the thickness of the spacer was 370 μm. In addition, the foamable adhesive sheet was cut into a size of 12.5 mm x 25 mm. The foamable adhesive sheet was in a state in which the separator was peeled off. Next, the foamable adhesive sheet was placed between the spacers, and another metal plate was placed so that one tip overlapped, and fixed with a clip to obtain a test piece.Then, the test piece was placed in a thermal oven (manufactured by Yamato Scientific Co., Ltd., DN610) and heated to foam and harden the first adhesive layer and the second adhesive layer of the foamable adhesive sheet.At this time, the heating conditions for Production Examples 1 to 3 were a heating rate of 20°C/min, and heating temperatures of 150°C, 160°C, 170°C, 180°C, 190°C, and 200°C.In addition, the heating conditions for Comparative Examples 1 to 2 and Examples 1 to 4 were a heating rate of 13°C/min, and heating temperatures of 180°C and 200°C.

After heating, the test pieces were subjected to measurement of shear strength (adhesive strength) using a tensile tester Tensilon RTF1350 (manufactured by A&D Co., Ltd.) in accordance with JIS K6850. The measurement conditions were a tensile speed of 10 mm/min and a temperature of 23°C.

For Examples 1 to 4 and Comparative Examples 1 and 2, the shear adhesive strength was measured for the foamable adhesive sheets after storage.

From Table 2, it was found that when the maximum displacement extrapolation temperature obtained by TMA is within a specified range relative to the maximum foaming temperature of the foaming agent (production examples 1 and 2), the shear adhesive strength is high, at 1.50 MPa or more, regardless of the heating temperature in the bonding process. Also, from Table 3, it was found that when the maximum displacement extrapolation temperature obtained by TMA is within a specified range relative to the maximum foaming temperature of the foaming agent (production examples 1 to 4), the shear adhesive strength is high.

In addition, a comparison of Example 1 and Comparative Examples 1 and 2 in Table 3 revealed that the maximum displacement and maximum displacement extrapolation temperature determined by TMA differed depending on the storage temperature. This suggests that the quality of a foamable adhesive sheet can be inspected by determining the maximum displacement and maximum displacement extrapolation temperature using TMA.

The present disclosure provides the following [1] to [8].
[1]
A foamable adhesive sheet having an adhesive layer,
The adhesive layer contains a thermosetting adhesive and a foaming agent,
The foaming agent is a thermally expandable microcapsule, and when a compressive load is applied, the temperature is raised at a predetermined heating rate, and the displacement is measured by thermomechanical analysis, the maximum displacement extrapolated temperature is not less than the maximum foaming temperature of the foaming agent -35°C and not more than the maximum foaming temperature of the foaming agent -10°C.
[2]
The adhesive layer includes a first adhesive layer and a second adhesive layer,
The foamable adhesive sheet according to [1], which has the first adhesive layer, a substrate, and the second adhesive layer in this order.
[3]
A method for producing a foamable adhesive sheet having an adhesive layer, comprising the steps of:
The adhesive layer contains a thermosetting adhesive and a foaming agent,
The method for producing a foamable adhesive sheet, wherein the foaming agent is a thermally expandable microcapsule, and the method comprises an inspection step of inspecting the quality of the foamable adhesive sheet by thermomechanical analysis, by applying a compressive load, raising the temperature at a predetermined heating rate, measuring the displacement, and determining the maximum displacement amount and the maximum displacement extrapolation temperature.
[4]
an inspection step of inspecting the quality of a foamable adhesive sheet having an adhesive layer by thermomechanical analysis, by applying a compressive load, raising the temperature at a predetermined heating rate, and measuring the displacement, thereby determining the maximum displacement amount and the maximum displacement extrapolation temperature;
a step of disposing the foamable adhesive sheet between a first member and a second member;
a bonding step of heating the foamable adhesive sheet to foam and harden it, thereby bonding the first member and the second member;
having
The adhesive layer contains a thermosetting adhesive and a foaming agent,
The method for producing an article, wherein the foaming agent is a thermally expandable microcapsule.
[5]
The method for producing an article according to [4], wherein in the foamable adhesive sheet, the maximum displacement extrapolated temperature is at least 35°C below the maximum foaming temperature of the foaming agent and at most 10°C below the maximum foaming temperature of the foaming agent.
[6]
The method for producing an article according to [4] or [5], wherein the heating temperature in the bonding step is at least the maximum foaming temperature of the foaming agent minus 20°C and at most the maximum foaming temperature of the foaming agent plus 30°C.
[7]
The method for manufacturing an article described in any one of [4] to [6], wherein the foamable adhesive sheet has a first adhesive layer and a second adhesive layer as the adhesive layer, and has the first adhesive layer, a substrate, and the second adhesive layer in this order.
[8]
A quality inspection method for a foamable adhesive sheet having an adhesive layer, comprising the steps of:
The adhesive layer contains a thermosetting adhesive and a foaming agent,
The foaming agent is a thermally expandable microcapsule, and a quality inspection method for a foaming adhesive sheet is performed by applying a compressive load, raising the temperature at a predetermined heating rate, and measuring the displacement, thereby determining the maximum displacement amount and the maximum displacement extrapolation temperature by thermomechanical analysis.

REFERENCE SIGNS LIST 1 adhesive layer 1a first adhesive layer 1b second adhesive layer 2 substrate 3a first intermediate layer 3b second intermediate layer 10 foamable adhesive sheet 11 foamed and cured adhesive sheet 20a first member 20b second member 100 article

Claims (8)

A foamable adhesive sheet having an adhesive layer,
The adhesive layer contains a thermosetting adhesive and a foaming agent,
The foaming agent is a thermally expandable microcapsule, and when a compressive load is applied, the temperature is raised at a predetermined heating rate, and the displacement is measured by thermomechanical analysis, the maximum displacement extrapolated temperature is not less than the maximum foaming temperature of the foaming agent -35°C and not more than the maximum foaming temperature of the foaming agent -10°C. The adhesive layer includes a first adhesive layer and a second adhesive layer,
The foamable adhesive sheet according to claim 1 , comprising the first adhesive layer, a substrate, and the second adhesive layer in this order. A method for producing a foamable adhesive sheet having an adhesive layer, comprising the steps of:
The adhesive layer contains a thermosetting adhesive and a foaming agent,
The foaming agent is a thermally expandable microcapsule, and the method for producing a foamable adhesive sheet includes an inspection step of inspecting the quality of the foamable adhesive sheet by thermomechanical analysis, by applying a compressive load, raising the temperature at a predetermined heating rate, measuring the displacement, and determining the maximum displacement amount and the maximum displacement extrapolation temperature. an inspection step of inspecting the quality of a foamable adhesive sheet having an adhesive layer by thermomechanical analysis, by applying a compressive load, raising the temperature at a predetermined heating rate, and measuring the displacement, thereby determining the maximum displacement amount and the maximum displacement extrapolation temperature;
a positioning step of positioning the foamable adhesive sheet between a first member and a second member;
a bonding step of foaming and curing the foamable adhesive sheet by heating to bond the first member and the second member;
having
The adhesive layer contains a thermosetting adhesive and a foaming agent,
The method for producing an article, wherein the foaming agent is a thermally expandable microcapsule. The method for manufacturing an article according to claim 4, wherein the maximum displacement extrapolation temperature in the foamable adhesive sheet is equal to or greater than the maximum foaming temperature of the foaming agent minus 35°C and equal to or less than the maximum foaming temperature of the foaming agent minus 10°C. The method for manufacturing an article according to claim 4 or 5, wherein the heating temperature in the adhesion step is at least 20°C below the maximum foaming temperature of the foaming agent and at most 30°C above the maximum foaming temperature of the foaming agent. The method for manufacturing an article according to claim 4 or 5, wherein the foamable adhesive sheet has a first adhesive layer and a second adhesive layer as the adhesive layer, and has the first adhesive layer, a substrate, and the second adhesive layer in this order. A quality inspection method for a foamable adhesive sheet having an adhesive layer, comprising the steps of:
The adhesive layer contains a thermosetting adhesive and a foaming agent,
The foaming agent is a thermally expandable microcapsule, and a quality inspection method for a foaming adhesive sheet is performed by applying a compressive load, raising the temperature at a predetermined heating rate, and measuring the displacement, thereby determining the maximum displacement amount and the maximum displacement extrapolation temperature by thermomechanical analysis.

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