JP7578128B2 - Foamable adhesive sheet and method for producing structure - Google Patents

Description

This disclosure relates to a foamable adhesive sheet and a method for manufacturing a structure using the same.

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 adjust the balance between foaming ratio and adhesive strength, making it difficult to obtain the desired foaming and adhesive properties.

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 a structure using the foamable adhesive sheet, which is capable of obtaining excellent foaming and adhesive properties suitable for a specified gap.

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, and the foamable adhesive sheet is provided with a foamable adhesive sheet in which, when a compressive load is applied to the foamable adhesive sheet, the temperature is raised at a predetermined heating rate, and the displacement is measured by thermomechanical measurement, the sum of the initial thickness of the foamable adhesive sheet and the amount of displacement at a predetermined temperature of 160°C or more and less than 200°C is 100% or more and 308% or less with respect to a gap setting value of 100%.

Another embodiment of the present disclosure provides a method for manufacturing a structure, comprising a step of arranging a foamable adhesive sheet having an adhesive layer between a first member and a second member, and a step of foaming and curing the foamable adhesive sheet by heating to bond the first member and the second member, the adhesive layer containing a thermosetting adhesive and a foaming agent, the foamable adhesive sheet being subjected to a compressive load, heated at a predetermined heating rate, and displacement measured by thermomechanical measurement, the sum of the initial thickness of the foamable adhesive sheet and the amount of displacement at a predetermined temperature of 160°C or more and less than 200°C is 100% or more and 308% or less with respect to a gap setting value of 100%, the gap setting value being the distance of the gap after the foamable adhesive sheet is arranged between the first member and the second member.

Another embodiment of the present disclosure provides a method for manufacturing a structure, comprising a step of arranging a foamable adhesive sheet having an adhesive layer between a first member and a second member, and a step of foaming and curing the foamable adhesive sheet by heating to bond the first member and the second member, wherein the adhesive layer contains a thermosetting adhesive and a foaming agent, the heating temperature in the bonding step is 150°C or higher and lower than 200°C, and the foamable adhesive sheet is heated to the heating temperature at a predetermined heating rate by applying a compressive load by thermomechanical measurement, and the sum of the initial thickness and the amount of displacement of the foamable adhesive sheet is set to 121% or higher and 168% or lower of a gap setting value of 100%, and the gap setting value is the distance of the gap after the foamable adhesive sheet is arranged between the first member and the second member.

The present disclosure provides a foamable adhesive sheet and a method for manufacturing a structure using the foamable adhesive sheet, which can obtain excellent foaming and adhesive properties suitable for a specified gap.

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

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.

In order for a foamable adhesive sheet to fill the gaps between components and bond them together, it needs to have foaming properties that will make the thickness of the foamable adhesive sheet after foaming and hardening at least equal to the gap between the components. However, as mentioned above, it is difficult to balance the foaming ratio and adhesive strength with a foamable adhesive sheet. Therefore, there is still room for further study to determine the foaming and adhesive properties that are suitable for the desired gap.

Conventionally, the foaming characteristics of a foamable adhesive sheet have been evaluated, for example, by the foaming ratio of the foamable adhesive sheet. In general, the foaming ratio of a foamable adhesive sheet refers to the foaming ratio when the foamable adhesive sheet is foamed and cured without any external pressure being applied to the foamable adhesive 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 it is under external pressure. Therefore, the conditions for measuring the expansion 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 measurement (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 foamable adhesive 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. Therefore, it is believed that thermomechanical measurement can obtain measured values that reflect the foaming and curing behavior of the foamable adhesive sheet.

The inventors of the present disclosure therefore focused on the foaming characteristics of the foamable adhesive sheet measured by thermomechanical measurement, and after extensive research into the foaming and adhesive properties of the foamable adhesive sheet, discovered that there is a correlation between the amount of displacement measured when the foaming characteristics of the foamable adhesive sheet are measured by thermomechanical measurement and the adhesive strength of the foamable adhesive sheet after foaming and curing. They also discovered that when the sum of the initial thickness of the foamable adhesive sheet and the amount of displacement measured by thermomechanical measurement is within a specified range for the desired gap, the adhesive strength of the foamable adhesive sheet after foaming and curing is high. The present disclosure is based on such findings.

The manufacturing method of the foamable adhesive sheet and structure disclosed herein is 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, and the foamable adhesive sheet is subjected to a thermomechanical measurement in which a compressive load is applied, the temperature is raised at a predetermined heating rate, and the displacement is measured. The sum of the initial thickness of the foamable adhesive sheet and the amount of displacement at a predetermined temperature of 160° C. or more and less than 200° C. is 100% or more and 308% or less with respect to a gap setting value of 100%.

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.

Figure 4 is a graph showing an example of a thermomechanical measurement (TMA) curve for a foamable adhesive sheet, in which a compressive load is applied, the temperature is raised at a predetermined heating rate, and the displacement is measured, with the horizontal axis representing temperature and the vertical axis representing displacement. In the foamable adhesive sheet of the present disclosure, the sum of the initial thickness of the foamable adhesive sheet and the displacement at a predetermined temperature in the TMA curve as shown in Figure 4 is within a predetermined range for the gap setting value.

In the foamable adhesive sheet of the present disclosure, the sum of the initial thickness of the foamable adhesive sheet and the amount of displacement at a specified temperature measured by thermomechanical measurement is within a specified range for the gap setting value, so that excellent foaming and adhesive properties suitable for the gap setting value can be obtained. Therefore, it is possible to obtain a foamable adhesive sheet that is optimal for filling the gap between components and joining components to each other for the gap setting value.

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 measurement, the sum of the initial thickness of the foamable adhesive sheet and the amount of displacement at a predetermined temperature of 160°C or more and less than 200°C is 100% or more and 308% or less with respect to the gap setting value of 100%. The sum of the initial thickness of the foamable adhesive sheet and the amount of displacement is preferably 112% or more and 308% or less, and more preferably 138% or more and 308% or less, with respect to the gap setting value of 100%. By having the sum of the initial thickness of the foamable adhesive sheet and the amount of displacement within the above range, foaming characteristics and adhesive characteristics suitable for the gap setting value can be obtained.

Here, the thermomechanical measurement 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. Then, the amount of displacement at a specified temperature is obtained. As a thermomechanical measurement device, for example, a thermomechanical analyzer TMA7100 manufactured by Hitachi High-Tech Science Corporation can be used.

The amount of displacement at a given temperature refers to the amount of displacement that occurs with expansion when the given temperature is reached, with the amount of displacement at 25°C being set to 0 in the TMA curve. The unit of displacement is "μm."

When determining the amount of displacement at a given temperature, the given temperature is any temperature between 160°C and 200°C. This is because when the given temperature is within the above range, the foamable adhesive sheet can have good heat resistance. Therefore, it can be applied to applications requiring heat resistance around automobile engines and similar applications. Also, if the given temperature is lower than the above range, the amount of displacement at the given temperature tends to be small. Therefore, the adhesive strength may decrease. In this case, there is a possibility that interface destruction may easily occur between the adhesive sheet and the member after foaming and hardening. Here, in the microcapsule type foaming agent, a thermal expansion agent such as hydrocarbon is encapsulated inside the shell made of resin. In the case of the microcapsule type foaming agent, when heated, the resin constituting the shell softens and the pressure of the thermal expansion agent such as hydrocarbon increases, causing the microcapsule type foaming agent to expand. Since the shell becomes thinner due to expansion, if heating is continued, the thermal expansion agent will escape from the microcapsule type foaming agent and the microcapsule type foaming agent will shrink. Therefore, in the case of the microcapsule type foaming agent, the amount of displacement tends to decrease after reaching the maximum amount of displacement in the TMA curve. Therefore, if the specified temperature is higher than the above range, the amount of displacement at the specified temperature will be small, and as a result, the adhesive strength may decrease. Therefore, in this disclosure, the specified temperature is set to any temperature between 160°C and 200°C.

In a foamable adhesive sheet, the amount of displacement 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 amount of displacement tends to be large. On the other hand, if the particle size of the foaming agent is small, the amount of displacement tends to be small. Also, for example, if the content of the foaming agent is large, the amount of displacement tends to be large. On the other hand, if the content of the foaming agent is small, the amount of displacement tends to be small.

The initial thickness of the foamable adhesive sheet is the thickness of the foamable adhesive sheet before foaming, and refers to the thickness of the foamable adhesive sheet at room temperature after a sample of the foamable adhesive sheet is set in the thermomechanical measuring device. Specifically, as described above, the foamable adhesive sheet is first punched out with a φ4 mm jig to prepare a sample. Next, the sample is placed in an aluminum container with a φ5 mm, and an aluminum plate with a φ4 mm is placed on the sample. In this state, the expansion/compression probe of the thermomechanical measuring device is brought into contact with the sample at a load of 100 mN, and the thickness after the aluminum plate and the sample are sufficiently smoothly brought into contact with each other is taken as the initial thickness of the foamable adhesive sheet. Note that, when the foamable adhesive sheet has a separator, the initial thickness of the foamable adhesive sheet refers to the thickness of the foamable adhesive sheet excluding the separator. The unit of the initial thickness of the foamable adhesive sheet is "μm".

The gap setting value is preferably, for example, 100 μm or more and 500 μm or less, and more preferably 200 μm or more and 400 μm or less. The present disclosure is suitable for cases where the gap setting value is relatively small as described above. The definition of the gap setting value will be described later. The unit of the gap setting value is "μm."

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 is 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) Materials (a) Foaming Agent The foaming agent in the present disclosure is a foaming agent that undergoes a foaming reaction by heat. As the foaming agent, a foaming agent generally used in the adhesive layer of a foamable adhesive sheet can be used.

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 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 foaming agent may be, for example, a microcapsule type foaming agent. The microcapsule type foaming agent preferably has a core of a thermal expansion agent such as a hydrocarbon and a shell of a resin such as an acrylonitrile copolymer.

As the blowing agent, for example, organic blowing agents or inorganic blowing agents may be used. Examples of organic blowing agents include azo blowing agents such as azodicarbonamide (ADCA), azobisformamide, and azobisisobutyronitrile, fluorinated alkane blowing agents such as trichloromonofluoromethane, hydrazine blowing agents such as paratoluenesulfonylhydrazide, semicarbazide blowing agents such as p-toluenesulfonylsemicarbazide, triazole blowing agents such as 5-morpholyl-1,2,3,4-thiatriazole, and N-nitroso blowing agents such as N,N-dinitrosoterephthalamide. On the other hand, examples of inorganic blowing agents include ammonium carbonate, ammonium hydrogen carbonate, ammonium nitrite, ammonium borohydride, and azides.

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

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 may be, 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, based on 100 parts by mass of the resin component contained in the adhesive layer. On the other hand, the foaming agent content may be, for example, 25 parts by mass or less, 20 parts by mass or less, or 15 parts by mass or less, based on 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 applicable even when the member does not have transparency, such as a metal member.

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 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 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 part 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.

Furthermore, as described below, when the foamable adhesive sheet has a first adhesive layer and a second adhesive layer as adhesive layers, the acrylic resin content in the first adhesive layer and the second adhesive layer may be the same or different from each other.

(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. Furthermore, phenol-based hardeners and imidazole-based hardeners 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 adhesiveness 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 patterns such as stripes and dots. The surface of the adhesive layer may also 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 layers. In addition, when the foamable adhesive sheet of the present disclosure has a first adhesive layer and a second adhesive layer as the adhesive layers, the sheet may have the first adhesive layer and the second adhesive layer in this order, or may have the first adhesive layer, a substrate, and a 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, may be 140°C or higher, or may be 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. 5, 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. 5 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 intermediate layer and the second intermediate layer are not particularly limited as long as they can increase the adhesion between the substrate and the first adhesive layer or the second adhesive layer and can relieve stress, and are appropriately selected depending on the materials of the substrate, the first adhesive layer, and the second adhesive layer. Examples include polyester, polyvinyl chloride, polyvinyl acetate, polyurethane, polymers obtained by copolymerizing at least two or more of these, crosslinked products thereof, and mixtures thereof.

The crosslinked material is a crosslinked material obtained by crosslinking the above resin with a curing agent. Examples of the curing agent include isocyanate-based curing agents.

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 thickness of the foamable adhesive sheet here is different from the initial thickness of the foamable adhesive sheet described above.

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.

The method for producing the foamable adhesive sheet disclosed herein 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, the first adhesive layer and the second adhesive layer can be 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, the first adhesive layer can be formed by applying and drying an adhesive composition to one side of the substrate, and the second adhesive layer can be formed by applying and drying an adhesive composition to one side of the separator, and the second adhesive layer and the separator can be laminated to the other side of the substrate.

B. Method for Producing a Structure The method for producing a structure in the present disclosure has two embodiments. Each embodiment will be described below.

1. First embodiment A first embodiment of the method for manufacturing a structure in the present disclosure is a method for manufacturing a structure having a placement step of placing a foamable adhesive sheet having an adhesive layer between a first member and a second member, and a bonding step of foaming and curing the foamable adhesive sheet by heating to bond the first member and the second member, wherein the adhesive layer contains a thermosetting adhesive and a foaming agent, and the foamable adhesive sheet is subjected to a thermomechanical measurement to apply a compressive load, raise the temperature at a predetermined heating rate, and measure the displacement. The sum of the initial thickness of the foamable adhesive sheet and the amount of displacement at a predetermined temperature of 160° C. or more and less than 200° C. is 100% or more and 308% or less with respect to a gap setting value of 100%, and the gap setting value is the distance of the gap after the foamable adhesive sheet is placed between the first member and the second member.

Figures 6(a) and (b) are process diagrams illustrating a method for manufacturing a structure of this embodiment. First, as shown in Figure 6(a), a foamable adhesive sheet 10 is placed between a first member 20a and a second member 20b. Next, as shown in Figure 6(b), the adhesive layer of the foamable adhesive sheet 10 is foamed and cured by heating. After foaming and curing, the first member 20a and the second member 20b are bonded (joined) by the adhesive sheet 11. This results in a structure 100 in which the adhesive sheet 11 is placed between the first member 20a and the second member 20b.

In addition, in the foamable adhesive sheet of this embodiment, the sum of the initial thickness of the foamable adhesive sheet and the amount of displacement at a given temperature in the TMA curve as shown in Figure 4 is within a given range for the gap setting value.

The gap setting value is the distance of the gap after the foamable adhesive sheet is placed between the first member and the second member. For example, in FIG. 6(a), 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 is the gap setting value.

In the manufacturing method of the structure of this embodiment, the foamable adhesive sheet described above is used. Therefore, it is possible to obtain excellent foaming and adhesive properties suited to the gap setting value. Therefore, it is possible to select and use a foamable adhesive sheet that is optimal for the gap setting value in order to fill the gap between components and to join the components together.

The foamable adhesive sheet used in the method for manufacturing the structure of this embodiment and each step of the method for manufacturing the structure of this embodiment are described below.

(1) Foamable Adhesive Sheet In the foamable adhesive sheet used in this embodiment, when a compressive load is applied to the foamable adhesive sheet, the temperature is raised at a prescribed heating rate, and the displacement is measured by thermomechanical measurement, the sum of the initial thickness of the foamable adhesive sheet and the amount of displacement at a prescribed temperature of 160° C. or higher and lower than 200° C. falls within a prescribed range for the gap setting value.

The foamable adhesive sheet can be the same as the foamable adhesive sheet described above.

In this embodiment, the gap setting value is the gap distance after the foamable adhesive sheet is placed between the first member and the second member.

(2) Arranging Step The arranging step in this embodiment is a step of arranging a foamable adhesive sheet having an adhesive layer between the first member and the 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; 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, etc. can be mentioned.

The first and second members are appropriately selected depending on the application of the structure. 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.

(3) Adhesion Step The adhesion step in this embodiment is a step of foaming and curing the foamable adhesive sheet by heating, thereby adhering the first member and the second member.

The heating temperature in the bonding process is preferably set so that the sum of the initial thickness of the foamable adhesive sheet and the amount of displacement at a predetermined temperature is 100% or more and 308% or less, and more preferably 112% or more and 294% or less, of the gap setting value of 100% when the foamable adhesive sheet is heated at a predetermined heating rate under a compressive load by thermomechanical measurement and the displacement is measured. If the heating temperature is lower than the above range, the amount of displacement is small, so that foaming is insufficient and the adhesive strength may decrease. In this case, there is a possibility that interface failure may occur between the adhesive sheet and the first or second member after foaming and hardening. Also, as described above, in the case of a microcapsule type foaming agent, the amount of displacement tends to decrease after reaching the maximum amount of displacement in the TMA curve. Therefore, if the heating temperature is higher than the above range, the amount of displacement decreases after reaching the maximum amount of displacement, and as a result, the thickness of the adhesive layer at the time of foaming cannot be maintained, and the adhesive strength may decrease.

Specifically, the heating temperature is preferably 160°C or higher and 190°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.

2. Second embodiment A second embodiment of the method for producing a structure in the present disclosure is a method for producing a structure having a disposing step of disposing a foamable adhesive sheet having an adhesive layer between a first member and a second member, and a bonding step of foaming and curing the foamable adhesive sheet by heating to bond the first member and the second member, wherein the adhesive layer contains a thermosetting adhesive and a foaming agent, the heating temperature in the bonding step is 150°C or more and less than 200°C, and the foamable adhesive sheet is heated to the heating temperature at a predetermined heating rate by thermomechanical measurement while applying a compressive load, and the total of the initial thickness and the amount of displacement of the foamable adhesive sheet when the foamable adhesive sheet is heated to the heating temperature at a predetermined heating rate and the displacement is measured is set to be 121% or more and 168% or less with respect to a gap setting value of 100%, and the gap setting value is the distance of the gap after the foamable adhesive sheet is disposed between the first member and the second member.

Figure 7 is a graph showing an example of a TMA curve, with time on the horizontal axis and displacement on the vertical axis, obtained by applying a compressive load to a foamable adhesive sheet, heating it to a predetermined temperature at a predetermined heating rate, and measuring the displacement, using a thermomechanical measurement (TMA) curve. In the manufacturing method of the structure of this embodiment, the heating temperature in the bonding step is set to 150°C or higher and lower than 200°C, and the sum of the initial thickness of the foamable adhesive sheet and the displacement in the TMA curve for the foamable adhesive sheet, for example as shown in Figure 7, is set to be within a predetermined range for the gap setting value.

In the foamable adhesive sheet of this embodiment, the heating temperature in the bonding process is set to 150°C or higher and lower than 200°C, and the sum of the initial thickness of the foamable adhesive sheet and the amount of displacement measured by thermomechanical measurement of the foamable adhesive sheet is set within a predetermined range for the gap setting value, thereby obtaining excellent foaming and adhesive properties suitable for the gap setting value. Therefore, the heating conditions in the bonding process can be optimized for the gap setting value.

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, regarding the heating conditions, 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, the relationship T1≦T2 is satisfied. However, when the inventors of the present disclosure investigated the heating conditions for foaming and curing a foamable adhesive sheet, it was found that even when the foaming start temperature of the foaming agent and the curing start temperature of the adhesive layer have a predetermined relationship, the adhesive strength may decrease. Note that the foaming start temperature and maximum foaming temperature of the foaming agent are foaming characteristics of the foaming agent alone, and cannot be said to be foaming characteristics of the foamable adhesive sheet.

In contrast, in this embodiment, the heating conditions are set based on the initial thickness of the foamable adhesive sheet and the amount of displacement measured by thermomechanical measurement of the foamable adhesive sheet. As described above, the measurement conditions for thermomechanical analysis can be made to approximate the foaming and curing conditions of the actual foamable adhesive sheet. Therefore, it is believed that thermomechanical measurement can obtain measured values that reflect the foaming and curing behavior of the foamable adhesive sheet.

The foamable adhesive sheet used in the method for manufacturing the structure of this embodiment and each step of the method for manufacturing the structure of this embodiment are described below.

(1) Expandable Adhesive Sheet The expandable adhesive sheet used in this embodiment 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 section "A. Foamable adhesive sheet" above.

(2) Arrangement step The arrangement step in this embodiment is a step of arranging a foamable adhesive sheet having an adhesive layer between the first member and the second member. The arrangement step and the first and second members can be the same as those in the first embodiment.

(3) Adhesion Step The adhesion step in this embodiment is a step of foaming and curing the foamable adhesive sheet by heating, thereby adhering the first member and the second member.

In this embodiment, the heating temperature in the bonding process is set to 150°C or more and less than 200°C, and when the foamable adhesive sheet is heated to the heating temperature at a predetermined heating rate by thermomechanical measurement while applying a compressive load, and the displacement is measured, the sum of the initial thickness and the displacement of the foamable adhesive sheet is 121% or more and 168% or less with respect to the gap setting value of 100%. In particular, it is preferable to set the heating temperature in the bonding process to 150°C or more and less than 200°C, and the sum of the initial thickness and the displacement of the foamable adhesive sheet is 149% or more and 168% or less with respect to the gap setting value of 100%. By setting the heating temperature within the above range, the heating conditions in the bonding process can be optimized with respect to the gap setting value.

Here, the thermomechanical measurement 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 a temperature of 25°C to a predetermined heating temperature, a heating rate of 20°C/min, a load of 10 mN, and compression mode, and the displacement associated with the expansion or contraction of the sample is measured. As a thermomechanical measurement device, for example, a thermomechanical analyzer TMA7100 manufactured by Hitachi High-Tech Science Corporation can be used.

Specifically, the heating temperature is preferably 160°C or higher and 190°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.

The above gap setting value is the same as the gap setting value described in the above section "A. Foamable adhesive sheet."

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 II]
First, an adhesive composition was prepared having the composition shown in Table 1 below. Details of each material shown in Table 1 are shown below.

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 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 9]
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 on one surface. Next, 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. Then, the substrate was 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 second 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 this order. This resulted in a foamable adhesive sheet in which the first adhesive layer, substrate, intermediate layer, second adhesive layer, and second separator were arranged in this order.

[Evaluation 1]
(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. In this state, the expansion and compression probe of the thermomechanical measuring device was brought into contact with the sample at a load of 100 mN, and the thickness of the sample after the aluminum plate and the sample were brought into contact sufficiently smoothly was taken as the initial thickness of the foamable adhesive sheet. Next, a thermomechanical measurement was performed under the conditions of a temperature of 25°C to 250°C, a heating rate of 20°C/min, a load of 10 mN, and a compression mode, and the displacement associated with the expansion or contraction of the sample was measured. Then, the amount of displacement at each temperature was determined.

(2) 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). In addition, the foamable adhesive sheet was cut into a size of 12.5 mm x 25 mm. The separator was peeled off from the foamable adhesive sheet. Next, the foamable adhesive sheet was placed between the spacers, and another metal plate was placed so that one end of the metal plate overlapped, and fixed with a clip to obtain a test piece. The test piece was then placed in a thermal oven (manufactured by Yamato Scientific Co., Ltd., DN610) and heated to foam and cure the first adhesive layer and the second adhesive layer of the foamable adhesive sheet under the heating conditions of a temperature rise rate of 20°C/min and heating temperatures of 160°C, 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.

As shown in test numbers 1 to 9, in the foamable adhesive sheets of manufacturing examples 1 to 6, the sum of the initial thickness of the foamable adhesive sheet and the amount of displacement at a specified temperature of 160°C or higher and less than 200°C, measured by TMA, was within the specified range for the gap setting value. In the case of these foamable adhesive sheets, a comparison of test numbers 1 to 9 with test numbers 10 to 12 showed that the adhesive strength was high when the heating temperature in the bonding process was 160°C or higher and 190°C or lower.

[Evaluation 2]
(1) Thermomechanical analysis (TMA)
As the 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 an aluminum container with a φ5 mm so that the second adhesive layer was at the bottom, and an aluminum plate with a φ4 mm was placed on the sample. In this state, the expansion and compression probe of the thermomechanical measuring device was brought into contact with the aluminum plate at a load of 100 mN, and the thickness of the sample after the aluminum plate and the sample were brought into contact sufficiently smoothly was taken as the initial thickness of the foamable adhesive sheet. Next, a thermomechanical measurement was performed under the conditions of a temperature of 25°C to the final temperature, a heating rate of 20°C/min, a load of 10 mN, and a compression mode, and the displacement associated with the expansion or contraction of the sample was measured. At this time, the final temperatures were 150°C, 160°C, 180°C, 190°C, and 200°C.

(2) Adhesive Strength The shear strength (adhesive strength) was measured in the same manner as in Evaluation 1. Regarding the heating conditions for the foamable adhesive sheet, the heating temperatures were 150°C, 160°C, 180°C, 190°C, and 200°C.

From Table 2, it can be seen that the adhesive strength is high when the heating temperature in the bonding process is 150°C or higher and lower than 200°C, and when the temperature is such that the sum of the initial thickness of the foamable adhesive sheet and the amount of displacement measured by TMA is within a specified range relative to the gap setting value.

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 structure

Claims (7)

A foamable adhesive sheet having an adhesive layer,
The adhesive layer contains a thermosetting adhesive and a foaming agent,
The foamable adhesive sheet is used in a case where the foamable adhesive sheet is disposed between a first member and a second member, and then the foamable adhesive sheet is heated to foam and harden the foamable adhesive sheet, thereby bonding the first member and the second member;
The distance of the gap after the foamable adhesive sheet is disposed between the first member and the second member is defined as a gap setting value, and the gap setting value is defined as D;
In the foamable adhesive sheet, a compressive load is applied, the temperature is increased at a predetermined heating rate, and the displacement is measured by thermomechanical measurement. When the initial thickness of the foamable adhesive sheet is T ₁ and the amount of displacement at a predetermined temperature of 160° C. or more and less than 200° C. is δ ₁ ,
The foamable adhesive sheet is designed to satisfy the following formula:
The foamable adhesive sheet , wherein the gap setting value D is 300 μm or more and 400 μm or less, and the sum of the initial thickness T ₁ of the foamable adhesive sheet and the displacement amount δ ₁ is 413 μm or more and 923 μm or less .
100≦[(T ₁ + δ ₁ )/D]×100≦308 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 positioning step of positioning a foamable adhesive sheet having an adhesive layer 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;
A method for producing a structure having the following steps:
The adhesive layer contains a thermosetting adhesive and a foaming agent,
The distance of the gap after the foamable adhesive sheet is disposed between the first member and the second member is defined as a gap setting value, and the gap setting value is defined as D;
In the foamable adhesive sheet, a compressive load is applied, the temperature is increased at a predetermined heating rate, and the displacement is measured by thermomechanical measurement. When the initial thickness of the foamable adhesive sheet is T ₁ and the amount of displacement at a predetermined temperature of 160° C. or more and less than 200° C. is δ ₁ ,
The foamable adhesive sheet is designed to satisfy the following formula:
a set gap value D of 300 μm or more and 400 μm or less, and a sum of an initial thickness T ₁ of the foamable adhesive sheet and the displacement amount δ ₁ of 413 μm or more and 923 μm or less .
100≦[(T ₁ + δ ₁ )/D]×100≦308 The method for manufacturing the structure according to claim 3, wherein the heating temperature in the bonding step is 160°C or higher and 190°C or lower. a positioning step of positioning a foamable adhesive sheet having an adhesive layer 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;
A method for producing a structure having the following steps:
The adhesive layer contains a thermosetting adhesive and a foaming agent,
The heating temperature in the bonding step is 150° C. or higher and lower than 200° C., and
The distance of the gap after the foamable adhesive sheet is disposed between the first member and the second member is defined as a gap setting value, and the gap setting value is defined as D;
In the foamable adhesive sheet, a compressive load is applied, the temperature is raised to the heating temperature at a predetermined heating rate, and the displacement is measured by thermomechanical measurement. When the initial thickness of the foamable adhesive sheet is T ₂ and the amount of displacement is δ ₂ ,
A method for producing a structure, wherein the heating temperature in the bonding step is set so as to satisfy the following formula:
121≦[(T ₂ + δ ₂ )/D]×100≦168 The method for manufacturing the structure according to claim 5, wherein the heating temperature in the bonding step is 160°C or higher and 190°C or lower. The method for manufacturing a structure according to any one of claims 3 to 6, wherein the foamable adhesive sheet has a first adhesive layer and a second adhesive layer as the adhesive layers, and has the first adhesive layer, a substrate, and the second adhesive layer in this order.

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