Expandable adhesive sheet and method for producing article

Abstract

To provide a foaming adhesive sheet with excellent adhesion of an adhesive layer to a substrate.SOLUTION: The present disclosure provides a foaming adhesive sheet comprising a substrate and an adhesive layer placed on at least one side of the substrate, wherein the adhesive layer includes a curable adhesive and a foaming agent. The peeling force of the side on which the adhesive layer is placed is 2.0 N or more as measured by SAICAS (Surface And Interfacial Cutting Analysis System) method.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a foamable adhesive sheet and a method for producing an article using the same. [Background technology]

[0002] Adhesives for bonding members together are used in a variety of fields, and many bonding methods are known.

[0003] For example, Patent Documents 1 and 2 disclose adhesive sheets containing a foaming agent (foamable adhesive sheets). Patent Document 1 discloses an adhesive sheet having expandable adhesive layers on one or both sides of a substrate, the expandable adhesive layers containing an epoxy resin including a multifunctional epoxy resin, a phenolic resin as a curing agent, an imidazole compound as a curing catalyst, and a temperature-sensitive foaming agent, with a release agent applied to the surface of at least one of the expandable adhesive layers. Patent Document 2 also discloses an adhesive sheet including a substrate, thermally expandable adhesive layers provided on both sides of the substrate, and adhesive-permeable layers provided on the surface of each adhesive layer, through which the adhesive can permeate when the adhesive thermally expands. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2016 / 163514 [Patent Document 2] Japanese Patent Application Publication No. 2019-203062 Summary of the Invention [Problem to be solved by the invention]

[0005] A known method for using a foamable adhesive sheet is to place the foamable adhesive sheet between components and then foam and harden the foamable adhesive sheet to bond the components together.

[0006] When a foamable adhesive sheet has an adhesive layer on one or both sides of a substrate, the adhesive layer may lift or peel off from the substrate when the foamable adhesive sheet is folded or during processing steps such as cutting the foamable adhesive sheet. Furthermore, if there are burrs on components, when inserting a foamable adhesive sheet into a gap between components or between components, or when inserting one component into the gap after placing a foamable adhesive sheet on the other component, the foamable adhesive sheet may get caught on the burrs, causing the adhesive layer to lift or peel off from the substrate. Therefore, further improvement in the adhesion of the adhesive layer to the substrate is desired for foamable adhesive sheets.

[0007] However, in foamable adhesive sheets, because the adhesive layer contains a foaming agent, the adhesive layer tends to have lower adhesion compared to adhesive layers that do not contain a foaming agent. Furthermore, to improve handling and workability, it is desirable for the adhesive layer before foaming and curing to be non-tacky (tack-free), but in this case, the adhesive layer tends to have lower adhesion. Furthermore, for example, when foaming and curing the adhesive layer by heating, a heat-resistant substrate is used, but generally, heat-resistant substrates often have low adhesion.

[0008] The present disclosure has been made in view of the above circumstances, and has as its main object to provide a foamable adhesive sheet in which the adhesive layer has excellent adhesion to the substrate. [Means for solving the problem]

[0009] One embodiment of the present disclosure provides a foamable adhesive sheet having a substrate and an adhesive layer disposed on at least one side of the substrate, the adhesive layer containing a curable adhesive and a foaming agent, and having a peel strength of 2.0 N or more on the side on which the adhesive layer is disposed, as measured by the SAICAS method (hereinafter, Surface and Interfacial Cutting Analysis System is abbreviated as SAICAS).

[0010] Another embodiment of the present disclosure provides a method for manufacturing an article, comprising: a placement step of placing the above-mentioned foamable adhesive sheet between a first member and a second member; and a bonding step of foaming and curing the foamable adhesive sheet to bond the first member and the second member together. [Effects of the Invention]

[0011] The foamable adhesive sheet of the present disclosure exhibits the effect of excellent adhesion of the adhesive layer to the substrate. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic cross-sectional view showing an example of a foamable adhesive sheet according to the present disclosure. [Figure 2] FIG. 2 is a schematic cross-sectional view showing another example of a foamable adhesive sheet according to the present disclosure. [Figure 3] FIG. 2 is a schematic cross-sectional view showing another example of a foamable adhesive sheet according to the present disclosure. [Figure 4] FIG. 1 is a schematic perspective view showing another example of a foamable adhesive sheet according to the present disclosure. [Figure 5] 1 is a schematic cross-sectional view showing an example of a method for manufacturing an article according to the present disclosure. [Figure 6] FIG. 1 is a schematic cross-sectional view illustrating a method for testing adhesiveness. DETAILED DESCRIPTION OF THE INVENTION

[0013] Embodiments of the present disclosure will be described below with reference to the drawings and the like. However, the present disclosure can be implemented in many different forms, and should not be construed as being limited to the description of the embodiments exemplified below. Furthermore, to clarify the explanation, the drawings may schematically depict the width, thickness, shape, etc. of each part compared to the actual form, but these are merely examples and are not intended to limit the interpretation of the present disclosure. Furthermore, in this specification and each drawing, elements similar to those previously described with reference to the preceding drawings will be designated by the same reference numerals, and detailed descriptions may be omitted as appropriate.

[0014] In this specification, when describing a mode in which another component is placed on a certain component, the terms "above" or "below" are used, unless otherwise specified, to include both a case in which another component is placed directly above or below a certain component so as to be in contact with the component, and a case in which another component is placed above or below a certain component with another component interposed therebetween. Also, in this specification, when describing a mode in which another component is placed on the surface of a certain component, the terms "on the surface side" or "on the surface" are used, unless otherwise specified, to include both a case in which another component is placed directly above or below a certain component so as to be in contact with the component, and a case in which another component is placed above or below a certain component with another component interposed therebetween.

[0015] In this specification, the term "sheet" also includes a member called a "film." In addition, the term "film" also includes a member called a "sheet." In addition, the numerical ranges in this specification are ranges of average values.

[0016] The inventors of the present disclosure conducted extensive research into the adhesion of a foamable adhesive sheet having an adhesive layer on one or both sides of the substrate to a substrate. For example, Patent Document 1 discloses an L-shaped bending test in which the foamable adhesive sheet is bent once at 90° into an L-shape to evaluate the adhesion of the adhesive layer to the substrate. However, as described above, foamable adhesive sheets have high requirements for the adhesive layer's adhesion to the substrate, and it has been found that simply satisfying the adhesion test in the L-shaped bending test is not sufficient and may not be practically usable. Furthermore, as a result of extensive research, the inventors of the present disclosure have discovered that to obtain a foamable adhesive sheet that is practically usable, it is necessary to conduct an adhesion test under more stringent conditions than the L-shaped bending test, specifically, to satisfy the adhesion test in a cross bending test in which the foamable adhesive sheet is bent twice at 180° into a cross shape, as described below. The inventors have also found that by setting the peel strength of the adhesive layer side of a foamable adhesive sheet, as measured by the SAICAS method, to a predetermined value or greater, it is possible to obtain a foamable adhesive sheet that satisfies not only the adhesion test in an L-shaped bending test but also the adhesion test in a cross bending test, thereby achieving a foamable adhesive sheet that is suitable for practical use. The present disclosure is based on this finding.

[0017] The foamable adhesive sheet according to the present disclosure and the method for producing an article using the same will be described in detail below.

[0018] A. Foam adhesive sheet The foamable adhesive sheet of the present disclosure has a substrate and an adhesive layer arranged on at least one side of the substrate, the adhesive layer containing a curable adhesive and a foaming agent, and the peel strength of the side on which the adhesive layer is arranged is 2.0 N or more, as measured by the SAICAS method.

[0019] 1 and 2 are schematic cross-sectional views illustrating foamable adhesive sheets according to the present disclosure. Foamable adhesive sheet 10 in FIG. 1 has a substrate 2 and an adhesive layer 1 disposed on one side of substrate 2. Foamable adhesive sheet 10 in FIG. 2 has a substrate 2 and a first adhesive layer 1a disposed on one side of substrate 2 and a second adhesive layer 1b disposed on the other side of substrate 2. Adhesive layer 1, first adhesive layer 1a, and second adhesive layer 1b contain a curable adhesive and a foaming agent. The foamable adhesive sheet 10 in FIG. 1 has a peel strength of at least a predetermined value on the side on which adhesive layer 1 is disposed, measured by the SAICAS method. Furthermore, the foamable adhesive sheet 10 in FIG. 2 has a peel strength of at least a predetermined value on the side on which first adhesive layer 1a and second adhesive layer 1b are disposed, measured by the SAICAS method. When the foamable adhesive sheet has adhesive layers on both sides, it is preferable that the peel strength on both sides is a predetermined value or more. However, since the foamable adhesive sheet of the present disclosure can be used by paying attention to the folding direction and the direction in which the surface faces, it is sufficient that the peel strength on either side is a predetermined value or more.

[0020] In the foamable adhesive sheet of the present disclosure, the peel strength of the surface on which the adhesive layer is disposed, as measured by the SAICAS method, is equal to or greater than a predetermined value, thereby enabling the foamable adhesive sheet to have excellent adhesion of the adhesive layer to the substrate. Specifically, as described below, the foamable adhesive sheet of the present disclosure can be made to satisfy not only adhesion in an L-shaped bending test but also adhesion in a cross bending test. Therefore, for example, even when the foamable adhesive sheet is folded when disposed between components, lifting or peeling of the adhesive layer from the substrate can be suppressed. Furthermore, even if the components have burrs when the foamable adhesive sheet is disposed between components, lifting or peeling of the adhesive layer from the substrate can be suppressed. Therefore, a foamable adhesive sheet that can withstand practical use can be provided.

[0021] Hereinafter, each component of the foamable adhesive sheet according to the present disclosure will be described.

[0022] 1. Characteristics of foam adhesive sheets In the foamable adhesive sheet of the present disclosure, the peel strength of the surface on which the adhesive layer is disposed, as measured by the SAICAS method, is 2.0 N or more, optionally 3.0 N or more, optionally 3.5 N or more, or optionally 4.0 N or more. Furthermore, the peel strength of the surface on which the adhesive layer of the foamable adhesive sheet is disposed is, for example, 6.0 N or less, optionally 5.5 N or less, or optionally 5.0 N or less. When the peel strength of the surface on which the adhesive layer of the foamable adhesive sheet is disposed falls within the above range, the foamable adhesive sheet can have excellent adhesion of the adhesive layer to the substrate.

[0023] In addition, when adhesive layers are arranged on both sides of the substrate, as described above, it is sufficient that the peel strength of either side of the foamable adhesive sheet is within the above range, and it is preferable that the peel strength of both sides of the foamable adhesive sheet is within the above range.

[0024] The peel force of the surface of the foamable adhesive sheet on which the adhesive layer is disposed can be measured using the SAICAS method. The SAICAS method is also known as the surface-interface cutting method. When measuring the peel force of the surface of the foamable adhesive sheet on which the adhesive layer is disposed using the SAICAS method, a cutting blade is first placed in contact with the adhesive layer side of the foamable adhesive sheet and moved relative to the foamable adhesive sheet at a constant speed in both horizontal and vertical directions simultaneously. That is, the cutting blade cuts the adhesive layer at an angle. Next, when the cutting blade reaches a predetermined depth from the adhesive layer side of the foamable adhesive sheet that is equal to or greater than the thickness of the adhesive layer, a significant change in the force applied to the cutting blade is observed, and the horizontal force applied to the cutting blade decreases. At this point, the cutting blade is moved relative to the foamable adhesive sheet only in the horizontal direction to perform the cutting. The horizontal force applied to the cutting blade when moving the cutting blade relative to the foamable adhesive sheet only in the horizontal direction corresponds to the peel force of the surface on which the adhesive layer is disposed. In this disclosure, this peel force is defined as 2.0 N or greater.

[0025] In the foamable adhesive sheet of the present disclosure, for example, the adhesive layer may be disposed directly on the substrate, or an intermediate layer may be disposed between the substrate and the adhesive layer as described below. In either case, after cutting by moving the cutting blade relatively to the foamable adhesive sheet at a constant speed simultaneously in both the horizontal and vertical directions, a large change in the force on the cutting blade is initially observed, and at the point when the horizontal force on the cutting blade decreases, the cutting blade is moved relatively to the foamable adhesive sheet only in the horizontal direction to perform cutting. In this case, the interface when cutting by moving the cutting blade relatively to the foamable adhesive sheet only in the horizontal direction will be the interface between the adhesive layer and the layer adjacent to the adhesive layer, or the interface located between the adhesive layer and the substrate, and this interface is likely to become a peel interface.

[0026] Details of the method for measuring the peel strength of the surface of the foamable adhesive sheet on which the adhesive layer is disposed by the SAICAS method will be described in the Examples section below.

[0027] In the present disclosure, the peel strength of the surface of the foamable adhesive sheet on which the adhesive layer is disposed, as measured by the SAICAS method, can be made equal to or greater than a predetermined value by, for example, disposing an intermediate layer between the substrate and the adhesive layer, applying a surface treatment to the surface of the substrate on which the adhesive layer is disposed, adjusting the composition of the adhesive layer, adjusting the average thickness of the adhesive layer, or adjusting the combination of materials for the substrate, intermediate layer, and adhesive layer.

[0028] For example, as described below, by placing an intermediate layer between the substrate and the adhesive layer, or by performing a surface treatment on the surface of the substrate on which the adhesive layer is to be placed, the adhesion of the adhesive layer to the substrate can be improved, and the peel force can be increased.

[0029] Furthermore, when adjusting the composition of the adhesive layer, for example, in an adhesive layer containing an epoxy resin and a curing agent, by adding a polymer component having a flexible structure, the flexibility and toughness of the adhesive layer can be increased, the adhesion of the adhesive layer to the substrate can be improved, and the peel force can be increased. Specific examples of the polymer component having a flexible structure include acrylic resins that are compatible with epoxy resins, as described below. Furthermore, for example, in an adhesive layer containing an epoxy resin and a curing agent, by not adding a component that reduces toughness, the decrease in toughness of the adhesive layer can be suppressed, the adhesion of the adhesive layer to the substrate can be improved, and the peel force can be increased. Specific examples of the component that reduces toughness include phenolic resins, as described below. Furthermore, for example, by increasing the molecular weight of the components contained in the adhesive layer, the viscosity and cohesiveness of the adhesive layer can be increased, the adhesion of the adhesive layer to the substrate can be improved, and the peel force can be increased. Specifically, examples of such a method include increasing the molecular weight of at least one of the epoxy resin and the curing agent in an adhesive layer containing an epoxy resin and a curing agent, or increasing the molecular weight of at least one of the epoxy resin, the acrylic resin, and the curing agent in an adhesive layer containing an epoxy resin, an acrylic resin, and a curing agent.

[0030] Furthermore, when adjusting the average thickness of the adhesive layer, for example, by increasing the average thickness of the adhesive layer as described below, the adhesion of the adhesive layer to the substrate can be improved, and the peel force can be increased.

[0031] Furthermore, when adjusting the combination of materials for the substrate, intermediate layer, and adhesive layer, for example, as described below, when the substrate contains polyphenylene sulfide or polyethylene, the intermediate layer contains a cross-linked polyester resin, and the adhesive layer contains an epoxy resin and a curing agent, the adhesive layer tends to have higher adhesion to the substrate, and the peel force can be increased.

[0032] In the foamable adhesive sheet of the present disclosure, the adhesive layer is preferably substantially non-tacky (tack-free). In this case, it is preferable that the adhesive layer is disposed on the outermost surface. By having a substantially non-tacky (tack-free) adhesive layer, the foamable adhesive sheet can be provided with good sliding properties and blocking resistance. This improves the handleability and workability of the foamable adhesive sheet. Specifically, when a foamable adhesive sheet is disposed between components to bond the components, the foamable adhesive sheet can be smoothly inserted into the gap between the components or the gap between the components, or after the foamable adhesive sheet is disposed on one component, the other component can be smoothly inserted into the gap.

[0033] Here, non-tacky is generally used mainly to mean low adhesive strength, and in the present disclosure, "non-tacky" refers to a state in which the foamable adhesive sheet can be wound into a roll and then easily unwound without resistance.

[0034] When the adhesive layer is substantially non-adhesive, specifically, the adhesive strength of the adhesive layer is preferably 0 N / 25 mm or more and 0.1 N / 25 mm or less, and may be 0.05 N / 25 mm or less, or may be 0.02 N / 25 mm or less. When the adhesive strength of the adhesive layer is within the above range, the adhesive layer can be made substantially non-adhesive, and a foamable adhesive sheet with good sliding properties and blocking resistance can be obtained.

[0035] For example, Patent Document 1 discloses providing a release agent layer on the surface of an expandable adhesive layer. However, if a release agent layer is provided on the surface of the adhesive layer, the adhesive properties of the adhesive layer may be reduced after foaming and curing. In contrast, a foamable adhesive sheet in which the adhesive layer is substantially non-sticky does not require a release layer or release sheet for the purpose of imparting blocking resistance or slip properties, and the adhesive layer can be provided on the outermost surface. This allows for a foamable adhesive sheet in which the adhesive layer has good adhesive properties after foaming and curing.

[0036] When adhesive layers are disposed on both sides of the substrate, the adhesive strength of at least one adhesive layer should be within the above range. For example, when a foamable adhesive sheet is disposed between components to bond them together, the foamable adhesive sheet may be first disposed on one component, and then the other component may be inserted into the gap after the foamable adhesive sheet has been disposed on the other component. In such cases, when inserting the other component into the gap after the foamable adhesive sheet has been disposed on one component, it is sufficient that the surface of the foamable adhesive sheet that comes into contact with the other component has good slip properties. Therefore, the adhesive strength of at least one adhesive layer should be within the above range.

[0037] When adhesive layers are disposed on both sides of the substrate, for example, the adhesive strength of either one of the adhesive layers may be within the above range, or the adhesive strength of both adhesive layers may be within the above range, but it is particularly preferable that the adhesive strength of both adhesive layers be within the above range.

[0038] The adhesive strength of the adhesive layer can be measured in accordance with JIS Z0237:2009 (Test methods for adhesive tapes and adhesive sheets) and Method 1 of the adhesive strength test method (a test method in which the tape or sheet is peeled off at an angle of 180° from a stainless steel test plate at a temperature of 23°C and a humidity of 50%). Details of the method for measuring the adhesive strength of the adhesive layer are described in the Examples section below.

[0039] In the present disclosure, the adhesive strength of the adhesive layer can be adjusted to a predetermined value or less by, for example, adjusting the composition of the adhesive layer. Specifically, in an adhesive layer containing an epoxy resin and a curing agent, the adhesive strength can be reduced by using an epoxy resin that is solid at room temperature or a curing agent that is solid at room temperature. Furthermore, in an adhesive layer containing an epoxy resin and a curing agent, the adhesive strength can be reduced by adding an epoxy resin with a high softening temperature or an epoxy resin with a low weight-average molecular weight. More specifically, in an adhesive layer containing an epoxy resin and a curing agent, the adhesive strength can be reduced by adding a first epoxy resin with a low softening temperature and a low molecular weight and a second epoxy resin with a high softening temperature and a high molecular weight, as described below. Furthermore, in an adhesive layer containing an epoxy resin and a curing agent, the adhesive strength can be reduced by adding an acrylic resin that is compatible with the epoxy resin, as described below.

[0040] In the foamable adhesive sheet of the present disclosure, the pencil hardness of the surface facing the adhesive layer may be, for example, HB or higher, or may be F or higher. When the pencil hardness of the surface facing the adhesive layer of the foamable adhesive sheet of the present disclosure is F or higher, the slipperiness and insertion properties can be further improved. Specifically, when the pencil hardness of the surface facing the adhesive layer of the foamable adhesive sheet is within the above range, frictional resistance tends to be reduced, improving the slipperiness. Furthermore, when inserting a foamable adhesive sheet into a gap between components or between components, or when inserting one component into the gap after placing the foamable adhesive sheet on the other component, having the pencil hardness within the above range can prevent the end surface of the component from digging into the adhesive layer. In particular, when there are burrs on the end surfaces of the components, the adhesive layer is less likely to get caught on the burrs on the end surface of the component, improving insertion properties. Therefore, for example, when bonding components together by placing a foamable adhesive sheet between components, the foamable adhesive sheet can be smoothly inserted into the gap between components or between components, or when one component is inserted into the gap after placing the foamable adhesive sheet on the other component. Furthermore, by having the pencil hardness in the above range, it is possible to prevent the adhesive layer side of the foamable adhesive sheet from being worn away when the foamable adhesive sheet is placed between members. Furthermore, the pencil hardness may be, for example, 2H or less. If the pencil hardness is too high, the adhesive layer may have poor adhesion to the substrate.

[0041] When adhesive layers are disposed on both sides of the substrate, the pencil hardness of at least one of the foamable adhesive sheet surfaces may be within the above range, and for example, the pencil hardness of either one of the surfaces may be within the above range, or the pencil hardness of both surfaces may be within the above range. In particular, it is preferable that the pencil hardness of both surfaces of the foamable adhesive sheet be within the above range.

[0042] The pencil hardness can be determined in accordance with JIS K5600. Details of the method for measuring pencil hardness will be described in the Examples section below.

[0043] The pencil hardness of the adhesive layer side of the foamable adhesive sheet of the present disclosure can be controlled, for example, by the composition of the adhesive layer. Specifically, the pencil hardness can be controlled by the average particle size and content of the foaming agent contained in the adhesive layer. More specifically, the pencil hardness can be increased by increasing the average particle size of the foaming agent. Furthermore, the pencil hardness can be increased by increasing the content of the foaming agent. Furthermore, the pencil hardness can be increased, for example, by including an inorganic filler in the adhesive layer. Furthermore, the pencil hardness can be increased, for example, by including a component having a rigid structure in the adhesive layer. Specifically, in an adhesive layer containing an epoxy resin and a curing agent, an example of the component having a rigid structure is a phenolic resin.

[0044] In the foamable adhesive sheet of the present disclosure, the static friction coefficient of the surface facing the adhesive layer may be, for example, 0.34 or less, 0.30 or less, or 0.26 or less. Furthermore, the static friction coefficient may be, for example, 0.16 or more. When the static friction coefficient of the surface facing the adhesive layer of the foamable adhesive sheet of the present disclosure is 0.30 or less, the sliding properties and insertability can be further improved. Therefore, for example, when a foamable adhesive sheet is disposed between components to bond the components, the foamable adhesive sheet can be smoothly inserted into the gap between the components or the gap between the components, or after the foamable adhesive sheet is disposed between one component, the other component can be smoothly inserted into the gap.

[0045] When adhesive layers are disposed on both sides of the substrate, the static friction coefficient of at least one of the two sides of the foamable adhesive sheet may be within the above range, for example, the static friction coefficient of either one side may be within the above range, or the static friction coefficients of both sides may be within the above range. Of these, it is preferable that the static friction coefficients of both sides of the foamable adhesive sheet are within the above range.

[0046] The static friction coefficient can be determined in accordance with JIS K 7125. Details of the method for measuring the static friction coefficient will be described in the Examples section below.

[0047] The static friction coefficient of the adhesive layer side surface of the foamable adhesive sheet of the present disclosure can be controlled, for example, by adjusting the composition of the adhesive layer or by adjusting the pencil hardness of the adhesive layer side surface of the foamable adhesive sheet. Specifically, the static friction coefficient can be controlled by the average particle size and content of the foaming agent contained in the adhesive layer. More specifically, the static friction coefficient tends to decrease as the average particle size of the foaming agent increases. Furthermore, the static friction coefficient tends to decrease as the foaming agent content increases. Furthermore, the static friction coefficient tends to decrease as the pencil hardness of the adhesive layer side surface of the foamable adhesive sheet increases.

[0048] The foamable adhesive sheet of the present disclosure preferably has good shape retention. The bending moment based on JIS P 8125 is, for example, 40 gf·cm or more, and may be 50 gf·cm or more. On the other hand, the bending moment is, for example, 600 gf·cm or less, and may be 150 gf·cm or less.

[0049] The foamable adhesive sheet of the present disclosure preferably has high adhesiveness after foaming and curing. The shear strength (adhesive strength) based on JIS K6850 at 23°C may be, for example, 2.10 MPa or more, 2.40 MPa or more, or 3.0 MPa or more. Furthermore, the shear strength (adhesive strength) at 200°C may be, for example, 0.27 MPa or more, 0.55 MPa or more, or 0.58 MPa or more.

[0050] The foamable adhesive sheet of the present disclosure preferably has high electrical insulation properties after foaming and curing. The breakdown voltage based on JIS C 2107 is preferably, for example, 3 kV or more, and more preferably 5 kV or more. Furthermore, the adhesive sheet after foaming and curing preferably has thermal conductivity of, for example, 0.1 W / mK or more, and more preferably 0.15 W / mK or more.

[0051] 2.Adhesive layer The adhesive layer in the present disclosure is disposed on at least one surface of the substrate and contains a curable adhesive and a foaming agent.

[0052] (1) Adhesive layer material (a) Hardening adhesive The curable adhesive contained in the adhesive layer of the present disclosure may be a curable adhesive generally used in the adhesive layer of a foamable adhesive sheet. Examples of the curable adhesive include heat-curable adhesives and light-curable adhesives. Of these, heat-curable adhesives are preferred. Heat-curable adhesives can be applied even to components that are not transparent, such as metal components.

[0053] The curable adhesive is preferably an epoxy resin-based adhesive. That is, the curable adhesive preferably contains an epoxy resin and a curing agent. Generally, epoxy resin-based adhesives produce hard and tough cured films, making them suitable for bonding components made of hard materials such as metal or glass. Metal components are prone to burrs during processing. For example, when inserting a foamable adhesive sheet into a gap between components or between components, or inserting a component into a gap after placing a foamable adhesive sheet on one component, the foamable adhesive sheet may get caught on the burrs on the metal component, causing the adhesive layer to lift or peel off from the substrate. In contrast, the present disclosure provides excellent adhesion of the adhesive layer to the substrate, thereby preventing the adhesive layer from lifting or peeling off from the substrate. Therefore, the present disclosure is useful when using an epoxy resin-based adhesive. Furthermore, epoxy resin-based adhesives generally have excellent heat resistance, insulating properties, chemical resistance, and the like, and exhibit little shrinkage upon curing, making them suitable for a wide range of applications.

[0054] Furthermore, when the curable adhesive is an epoxy resin adhesive, the curable adhesive preferably further contains an acrylic resin that is compatible with the epoxy resin. By using an acrylic resin that is compatible with the epoxy resin, the toughness of the adhesive layer can be increased, and the adhesion of the adhesive layer to the substrate can be improved.

[0055] (i) Epoxy resin The epoxy resin in this disclosure is a compound that has at least one epoxy group or glycidyl group and cures by crosslinking polymerization in combination with a curing agent. The epoxy resin also includes a monomer having at least one epoxy group or glycidyl group.

[0056] The epoxy resin can be any epoxy resin commonly used in the adhesive layer of a foamable adhesive sheet. In particular, the curable adhesive preferably contains a first epoxy resin having a softening temperature of 50°C or higher and an epoxy equivalent of 5,000 g / eq or less, and a second epoxy resin having a softening temperature higher than that of the first epoxy resin and a weight-average molecular weight of 20,000 or more. By using a combination of the first and second epoxy resins, a foamable adhesive sheet with excellent blocking resistance and adhesive properties after foaming and curing can be obtained. Furthermore, the adhesive layer's tackiness can be reduced, resulting in a foamable adhesive sheet with excellent slip properties.

[0057] For example, if the only goal is to improve adhesiveness after foaming and curing, it is more effective to use a low-molecular-weight (low-epoxy equivalent) epoxy resin than a high-molecular-weight (high-epoxy equivalent) epoxy resin. However, if a low-molecular-weight (low-epoxy equivalent) epoxy resin is used, for example, when the foamable adhesive sheet is wound into a roll, the low-molecular-weight (low-epoxy equivalent) epoxy resins tend to assimilate with each other, making blocking more likely to occur.

[0058] In contrast, when a first epoxy resin having a relatively low softening temperature (relatively high crystallinity) and a low molecular weight (low epoxy equivalent weight) is used, the first epoxy resin rapidly melts and changes into a low-viscosity liquid when heated to a temperature above its softening temperature. This facilitates improved adhesiveness after foaming and curing. Meanwhile, because the first epoxy resin has relatively high crystallinity, it can suppress blocking compared to epoxy resins with relatively low crystallinity or no crystallinity. However, using only the first epoxy resin may result in insufficient blocking suppression or excessive tackiness of the adhesive layer. Therefore, by further using a second epoxy resin having a relatively high softening temperature (relatively low crystallinity) and a high molecular weight, it is possible to improve the blocking suppression effect and reduce the tackiness of the adhesive layer.

[0059] (i-1) First epoxy resin The first epoxy resin has a softening temperature of 50°C or higher and an epoxy equivalent of 5000 g / eq or lower. The first epoxy resin has a relatively low softening temperature (relatively high crystallinity) compared to the second epoxy resin described below. The first epoxy resin has relatively high crystallinity and a low molecular weight, which makes it easy to improve adhesion and blocking resistance after foaming and curing. Furthermore, the first epoxy resin has a low molecular weight, which makes it possible to increase the crosslink density, resulting in an adhesive layer with good mechanical strength, chemical resistance, and curing properties. Furthermore, the first epoxy resin is preferably an epoxy resin that is solid at room temperature (23°C).

[0060] The softening temperature of the first epoxy resin is usually 50° C. or higher, and may be 55° C. or higher, or 60° C. or higher. On the other hand, the softening temperature of the first epoxy resin is, for example, 150° C. or lower. The softening temperature can be measured by the ring and ball method in accordance with JISK 7234.

[0061] The epoxy equivalent of the first epoxy resin is, for example, 5000 g / eq or less, and may be 3000 g / eq or less, 1000 g / eq or less, or 600 g / eq or less. On the other hand, the epoxy equivalent of the first epoxy resin is, for example, 90 g / eq or more, and may be 100 g / eq or more, or 110 g / eq or more. The epoxy equivalent can be measured by a method in accordance with JIS K7236 and is the number of grams of resin containing 1 gram equivalent of epoxy groups.

[0062] The first epoxy resin may be a monofunctional epoxy resin, a difunctional epoxy resin, a trifunctional epoxy resin, or a tetrafunctional or higher functional epoxy resin.

[0063] The weight-average molecular weight (Mw) of the first epoxy resin is usually smaller than the weight-average molecular weight (Mw) of the second epoxy resin described below. The Mw of the first epoxy resin is, for example, 6,000 or less, and may be 4,000 or less, or 3,000 or less. On the other hand, the Mw of the first epoxy resin is, for example, 400 or more. Mw is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

[0064] The melt viscosity of the first epoxy resin at 150°C is, for example, 0.005 Pa·s or more, or may be 0.015 Pa·s or more, 0.03 Pa·s or more, 0.05 Pa·s or more, or 0.1 Pa·s or more. If the melt viscosity is too low, good foaming properties may not be obtained. Furthermore, if the melt viscosity of the first epoxy resin is too low (if the crystallinity of the first epoxy resin is too high), the resulting adhesive layer may have high tackiness. This is presumably because if the melt viscosity of the first epoxy resin is too low (if the crystallinity of the first epoxy resin is too high), its crystallinity is significantly reduced when it is mixed with the second epoxy resin or the acrylic resin, resulting in a decrease in the Tg of the entire adhesive composition. On the other hand, the melt viscosity of the first epoxy resin at 150°C is, for example, 10 Pa·s or less, or may be 5 Pa·s or less, or 2 Pa·s or less. If the melt viscosity is too high, the resulting adhesive layer may have poor uniformity. The melt viscosity can be determined in accordance with JIS K6862 by measurement using a Brookfield type single cylinder rotational viscometer and a thermocell for heating the solution.

[0065] Next, the composition of the first epoxy resin will be described. Examples of the first epoxy resin include aromatic epoxy resins, aliphatic epoxy resins, alicyclic epoxy resins, and heterocyclic epoxy resins. Specific examples of the first epoxy resin 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 first epoxy resin may be one type or two or more types.

[0066] Bisphenol A epoxy resins can exist in a liquid state or a solid state at room temperature depending on the number of repeating units in the bisphenol skeleton. Bisphenol A epoxy resins having, for example, 2 to 10 bisphenol skeletons in the main chain are solid at room temperature. Bisphenol A epoxy resins are particularly preferred because they can improve heat resistance.

[0067] In particular, the first epoxy resin is preferably a bisphenol A novolac epoxy resin represented by the following general formula (1).

[0068] [ka]

[0069] In general formula (1), R 1 is C m H 2m (m is 1 or more and 3 or less), and R 2 and R 3are each independently, C p H 2p+1 (p is 1 or more and 3 or less), and n is 0 or more and 10 or less.

[0070] In general formula (1), R 1 m in is 1, that is, R 1 is preferably -CH2-. Similarly, R 2 and R 3 p in is 1, that is, R 2 and R 3 is preferably —CH 3 . Furthermore, the hydrogen bonded to the benzene ring in general formula (1) may be substituted with other elements or other groups.

[0071] The content of the first epoxy resin, based on 100 parts by mass of the resin components contained in the adhesive layer, may be, for example, 1 part by mass or more, 3 parts by mass or more, 5 parts by mass or more, 10 parts by mass or more, 15 parts by mass or more, or 25 parts by mass or more. If the content of the first epoxy resin is too low, the adhesiveness and blocking resistance after foaming and curing may be reduced. On the other hand, the content of the first epoxy resin, based on 100 parts by mass of the resin components contained in the adhesive layer, may be, for example, 90 parts by mass or less, 80 parts by mass or less, 70 parts by mass or less, 60 parts by mass or less, 50 parts by mass or less, or 40 parts by mass or less. If the content of the first epoxy resin is too high, the contents of the second epoxy resin and acrylic resin may be relatively low, which may make it difficult to achieve a balance between the adhesiveness of the adhesive layer to the substrate, the blocking resistance, and the adhesiveness after foaming and curing.

[0072] (i-2) Second epoxy resin The second epoxy resin has a softening temperature higher than that of the first epoxy resin and a weight-average molecular weight of 20,000 or more. The second epoxy resin has a relatively high softening temperature (relatively low crystallinity) compared to the first epoxy resin. The second epoxy resin has relatively low crystallinity and a high molecular weight, which makes it easy to improve blocking resistance. Furthermore, the second epoxy resin has relatively low crystallinity and a high molecular weight, which can suppress an increase in adhesion (tackiness) caused by the first epoxy resin. Furthermore, the second epoxy resin is preferably an epoxy resin that is solid at room temperature (23°C).

[0073] The weight average molecular weight (Mw) of the second epoxy resin is usually larger than the weight average molecular weight (Mw) of the first epoxy resin. The Mw of the second epoxy resin is usually 20,000 or more, and may be 30,000 or more, or even 35,000 or more. On the other hand, the Mw of the second epoxy resin is, for example, 100,000 or less.

[0074] The epoxy equivalent of the second epoxy resin may be greater than, less than, or the same as the epoxy equivalent of the first epoxy resin. The epoxy equivalent of the second epoxy resin is, for example, 4000 g / eq or more, 5000 g / eq or more, or even 6000 g / eq or more. On the other hand, the epoxy equivalent of the second epoxy resin is, for example, 20000 g / eq or less.

[0075] The second epoxy resin may be a monofunctional epoxy resin, a difunctional epoxy resin, a trifunctional epoxy resin, or a tetrafunctional or higher functional epoxy resin.

[0076] The softening temperature of the second epoxy resin is usually higher than that of the first epoxy resin. The difference between the two temperatures is, for example, 10°C or higher, and may be 20°C or higher, or even 30°C or higher. The softening temperature of the second epoxy resin is, for example, 80°C or higher, and may be 90°C or higher. On the other hand, the softening temperature of the second epoxy resin is, for example, 180°C or lower.

[0077] The constitution of the second epoxy resin is the same as that of the first epoxy resin described above, and therefore description thereof will be omitted here.

[0078] The content of the second epoxy resin, based on 100 parts by mass of the resin components contained in the adhesive layer, may be, for example, 10 parts by mass or more, 15 parts by mass or more, 20 parts by mass or more, 25 parts by mass or more, 30 parts by mass or more, 35 parts by mass or more, 40 parts by mass or more, or 45 parts by mass or more. If the content of the second epoxy resin is too low, blocking resistance may be reduced. On the other hand, the content of the second epoxy resin, based on 100 parts by mass of the resin components contained in the adhesive layer, may be, for example, 90 parts by mass or less, 85 parts by mass or less, 80 parts by mass or less, or 75 parts by mass or less. If the content of the second epoxy resin is too high, the contents of the first epoxy resin and acrylic resin may be relatively low, which may make it difficult to achieve a balance between the adhesion of the adhesive layer to the substrate, blocking resistance, and adhesion after foaming and curing.

[0079] The proportion of the first epoxy resin relative to the total of the first epoxy resin and the second epoxy resin is, for example, 5% by mass or more, or alternatively 10% by mass or more, or 15% by mass or more, or even 20% by mass or more, while the proportion of the first epoxy resin is, for example, 80% by mass or less, or alternatively 75% by mass or less, or alternatively 60% by mass or less.

[0080] Furthermore, the total proportion of the first epoxy resin and the second epoxy resin to all epoxy resins contained in the adhesive layer is, for example, 50% by mass or more, or may be 70% by mass or more, or 90% by mass or more, or may be 100% by mass.

[0081] (ii) Acrylic resin The acrylic resin in the present disclosure is a resin compatible with epoxy resin. Because the acrylic resin is compatible with epoxy resin, it is easy to improve the toughness of the adhesive layer. As a result, the adhesion of the adhesive layer to the substrate can be improved. Furthermore, improved toughness of the adhesive layer can improve adhesion after foaming and curing. Furthermore, it is believed that the acrylic resin acts as a compatibilizer for the foaming agent (e.g., a foaming agent whose shell is an acrylonitrile copolymer resin), uniformly dispersing and foaming, thereby improving adhesion after foaming and curing. Furthermore, the compatibility of the acrylic resin with the epoxy resin can maintain high hardness on the surface of the adhesive layer. On the other hand, if the acrylic resin is incompatible with the epoxy resin, a flexible portion is formed on the surface of the adhesive layer, which can make the interface with the adherend less slippery and reduce workability.

[0082] The acrylic resin in the present disclosure is compatible with the epoxy resin. The compatibility of the acrylic resin with the epoxy resin can be confirmed, for example, by observing the cross section of the adhesive layer of the foamable adhesive sheet with a scanning electron microscope (SEM) or a transmission electron microscope (TEM) and finding no 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 even 0.3 μm or less. A large number of samples, for example, 100 or more, is preferred. The area to be observed is a range of 100 μm × 100 μm, or, if the average thickness of the adhesive layer is 100 μm or less, a range of the average thickness × 100 μm.

[0083] The weight-average molecular weight (Mw) of the acrylic resin is, for example, 50,000 or more, or may be 70,000 or more, or even 100,000 or more. The first epoxy resin has relatively high crystallinity, which can result in a low melt viscosity (or dynamic viscoelasticity) when heated, potentially causing shrinkage during curing after foaming (between the time when the foaming agent finishes foaming and the time when the adhesive composition cures). However, by using an acrylic resin with a certain molecular weight, it is possible to prevent the melt viscosity from becoming too low, making it less likely for shrinkage to occur during curing after foaming. Meanwhile, the Mw of the acrylic resin is, for example, 1,500,000 or less. The weight-average molecular weight of the acrylic resin can be measured by GPC (eluent: THF, standard: PS, sample: 20 μL, flow rate: 1 mL / min, column temperature: 40°C).

[0084] The glass transition temperature (Tg) of the acrylic resin is, for example, 90° C. or higher, and may be 100° C. or higher. On the other hand, the Tg of the acrylic resin is, for example, 180° C. or lower. Tg can be measured by thermal analysis such as a differential scanning calorimeter (DSC) in accordance with JIS K 7121.

[0085] Acrylic resin has a storage modulus (E') of 1 x 10 at the foaming initiation temperature. 6 A low E' at the foaming initiation temperature can improve fluidity and provide good foaming properties. On the other hand, E' at the foaming initiation temperature can be, for example, 1 x 10 5 The foaming initiation temperature is equal to or higher than 100 Pa. The foaming initiation temperature varies depending on the type of foaming agent. When two or more foaming agents are used, the foaming initiation temperature is the temperature at which the main foaming reaction begins.

[0086] Acrylic resin has a storage modulus (E') of 1 x 10 at the curing initiation temperature. 5The viscosity may be 100 Pa or more. As mentioned above, shrinkage may occur during curing after foaming (between the time when the foaming of the foaming agent is completed and the time when the adhesive composition is cured). However, if E' at the curing initiation temperature is large, shrinkage can be suppressed and good shape retention can be obtained. The curing initiation temperature varies depending on the type of curing agent. When two or more curing agents are used as the curing agent, the initiation temperature of the main curing reaction is taken as the curing initiation temperature.

[0087] In addition, the average storage modulus (E') of acrylic resin at temperatures between 0°C and 100°C is 1 x 10 6 The average value of E' before foaming may be high, thereby obtaining good blocking resistance. On the other hand, the average value of the storage modulus (E') at temperatures between 0°C and 100°C may be, for example, 1 x 10 8 Pa or less.

[0088] The acrylic resin may have a polar group, such as an epoxy group, a hydroxyl group, a carboxyl group, a nitrile group, or an amide group.

[0089] The acrylic resin is a homopolymer of an acrylic acid ester monomer, and may be a mixed component containing two or more of the above homopolymers, or may be a copolymer of two or more acrylic acid ester monomers and may be a component containing one or more copolymers. The acrylic resin may also be a mixed component of the above homopolymer and the above copolymer. The acrylic acid ester monomer "acrylic acid" also includes the concept of methacrylic acid. Specifically, the acrylic resin may be a mixture of a methacrylate polymer and an acrylate polymer, or may be an acrylic acid ester polymer such as acrylate-acrylate, methacrylate-methacrylate, or methacrylate-acrylate. In particular, the acrylic resin preferably contains a copolymer of two or more acrylic acid ester monomers (a (meth)acrylic acid ester copolymer).

[0090] Examples of the monomer component constituting the (meth)acrylic acid ester copolymer include the monomer components described in JP 2014-065889 A. The monomer component may have the polar group described above. Examples of the (meth)acrylic acid ester copolymer include an ethyl acrylate-butyl acrylate-acrylonitrile copolymer, an ethyl acrylate-acrylonitrile copolymer, and a 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.

[0091] The (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. In these examples, "acrylic acid" also includes "methacrylic acid."

[0092] Specific examples of methacrylate-acrylate copolymers include acrylic copolymers such as methyl methacrylate-butyl acrylate-methyl methacrylate (MMA-BA-MMA) copolymer, which also includes block copolymers of polymethyl methacrylate-polybutyl acrylate-polymethyl methacrylate (PMMA-PBA-PMMA).

[0093] The acrylic copolymer may have no polar groups, or may be a modified product in which the above-mentioned polar groups have been partially introduced. Such modified products are more compatible with epoxy resins, thereby further improving adhesiveness.

[0094] Among these, 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 lower and a second polymer portion having a glass transition temperature (Tg) of 20° C. or higher. Such a (meth)acrylic acid ester copolymer has the first polymer portion that becomes a soft segment and the second polymer portion that becomes a hard segment.

[0095] The manifestation of the above-mentioned effect can be presumed as follows: By using an acrylic resin having both a soft segment and a hard segment, such as the above-mentioned (meth)acrylic acid ester copolymer, the hard segment contributes to heat resistance, and the soft segment contributes to toughness or flexibility, so that an adhesive layer having good heat resistance, toughness, and flexibility can be obtained.

[0096] 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. Furthermore, when the second polymer portion has compatibility with epoxy resins, cohesion and toughness can be increased.

[0097] When either the first polymer portion or the second polymer portion is incompatible with the epoxy resin, the (meth)acrylic acid ester copolymer has a compatible portion, which is a polymer portion that is compatible with the epoxy resin, and an incompatible portion, which is a polymer portion that is incompatible with the epoxy resin. In this case, when the (meth)acrylic acid ester copolymer is added to an adhesive composition, the compatible portion is compatible with the epoxy resin, and the incompatible portion is incompatible with the epoxy resin, causing fine phase separation. As a result, a fine sea-island structure is formed. The sea-island structure varies depending on the type of (meth)acrylic acid ester copolymer, the compatibility of the first polymer portion and the second polymer portion contained in the (meth)acrylic acid ester copolymer, and whether or not modification by introduction of polar groups has been performed, and examples include a sea-island structure in which the compatible portions of the cured epoxy resin and the (meth)acrylic acid ester copolymer are the sea and the incompatible portions of the (meth)acrylic acid ester copolymer are the islands, a sea-island structure in which the incompatible portions of the (meth)acrylic acid ester copolymer are the sea and the compatible portions of the cured epoxy resin and the (meth)acrylic acid ester copolymer are the islands, and a sea-island structure in which the (meth)acrylic acid ester copolymer is the sea and the cured epoxy resin is the islands. Such a sea-island structure makes it easier to disperse stress, thereby preventing interfacial failure and achieving excellent adhesion after foaming and curing.

[0098] The (meth)acrylic acid ester copolymer is preferably a block copolymer, and particularly preferably an ABA block copolymer having a polymer block A as the compatible portion and a polymer block B as the incompatible portion. Furthermore, an ABA block copolymer having a first polymer portion as the incompatible portion and a second polymer portion as the compatible portion, polymer block B as the first polymer portion, and polymer block A as the second polymer portion, is preferred. By using such an ABA block copolymer as the acrylic resin, the island portions can be reduced in a case where a sea-island structure is formed in which the compatible portions of the cured epoxy resin and the (meth)acrylic acid ester copolymer are the sea and the incompatible portions of the (meth)acrylic acid ester copolymer are the islands. Furthermore, the sea portions can be reduced in a case where a sea-island structure is formed in which the incompatible portions of the (meth)acrylic acid ester copolymer are the sea and the compatible portions of the cured epoxy resin and the (meth)acrylic acid ester copolymer are the islands, or in a case where the (meth)acrylic acid ester copolymer is the sea and the cured epoxy resin is the islands.

[0099] 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 segment or the second polymer segment.

[0100] The Tg of the first polymer portion contained in the (meth)acrylic acid ester copolymer is 10°C or less, and can be in the range of -150°C or more and 10°C or less, particularly in the range of -130°C or more and 0°C or less, and particularly in the range of -110°C or more and -10°C or less.

[0101] The Tg of the first polymer portion can be calculated using the following formula based on the Tg(K) of each homopolymer described in "POLYMERHANDBOOK, Third Edition" (published by John Wiley & Sons, Inc.). 1 / Tg(K)=W1 / Tg1+W2 / Tg2+····+W n / Tg n W n ; mass fraction of each monomer Tgn This is the Tg (K) of the homopolymer of each monomer, and publicly available values ​​such as those in the Polymer Handbook (3rd Ed., J. Brandrup and E.H. Immergut, Wiley Interscience) may be used. The same applies to the Tg of the second polymer portion described below.

[0102] The first polymer portion contained in the (meth)acrylic acid ester copolymer may be either a homopolymer or a copolymer, but is preferably a homopolymer. The monomer and polymer components constituting the first polymer portion may be any monomer and polymer components capable of obtaining a first polymer portion having a Tg within a predetermined range, and examples thereof include acrylate monomers such as butyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate, and methyl acrylate, other monomers such as vinyl acetate, acetal, and urethane, polar group-containing monomers containing the above-mentioned polar groups, and copolymers such as EVA.

[0103] The Tg of the second polymer portion contained in the (meth)acrylic acid ester copolymer is 20°C or higher, and can be within the range of 20°C or higher and 150°C or lower, particularly within the range of 30°C or higher and 150°C or lower, and particularly within the range of 40°C or higher and 150°C or lower.

[0104] The second polymer portion contained in the (meth)acrylic acid ester copolymer may be either a homopolymer or a copolymer, but is preferably a homopolymer. The monomer component constituting the second polymer portion may be any monomer component capable of obtaining a second polymer portion having a Tg within a predetermined range, and examples thereof include acrylic acid ester monomers such as methyl methacrylate, other monomers such as acrylamide, styrene, vinyl chloride, amide, acrylonitrile, cellulose acetate, phenol, urethane, vinylidene chloride, methylene chloride, and methacrylonitrile, and polar group-containing monomers containing the above-mentioned polar groups.

[0105] A specific example of the (meth)acrylic acid ester copolymer having the first polymer portion and the second polymer portion is the MMA-BA-MMA copolymer.

[0106] The content of the acrylic resin, based on 100 parts by mass of the resin components contained in the adhesive layer, may be, 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. If the content of the acrylic resin is too low, the adhesion of the adhesive layer to the substrate and the adhesion after foaming and curing may be reduced. On the other hand, the content of the acrylic resin, based on 100 parts by mass of the resin components contained in the adhesive layer, may be, 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. If the content of the acrylic resin is too high, the contents of the first epoxy resin and the second epoxy resin may be relatively low, which may make it difficult to achieve a balance between the adhesion of the adhesive layer to the substrate, the blocking resistance, and the adhesion after foaming and curing.

[0107] (iii) hardener The curing agent in the present disclosure is appropriately selected depending on the type of curable adhesive. When the curable adhesive is, for example, an epoxy resin adhesive, a curing agent generally used for epoxy resin adhesives can be used as the curing agent. The curing agent is preferably solid at 23°C. A curing agent that is solid at 23°C can have a longer storage stability (pot life) than a curing agent that is liquid at 23°C. The curing agent may also be a latent curing agent. The curing agent may also be a curing agent that undergoes a curing reaction by heat or a curing agent that undergoes a curing reaction by light. In the present disclosure, a single curing agent may be used, or two or more types may be used.

[0108] The reaction initiation temperature of the curing agent is, for example, 110°C or higher, and may be 130°C or higher. If the reaction initiation temperature is too low, the reaction will start early, and curing will occur with low flexibility and fluidity of the resin component, making it difficult to achieve uniform curing. On the other hand, the reaction initiation temperature of the curing agent is, for example, 200°C or lower. If the reaction initiation temperature is too high, the resin component may deteriorate. Note that when a highly heat-resistant resin such as a phenolic resin is used in addition to the epoxy resin, the resin component will deteriorate less, and the reaction initiation temperature of the curing agent may be, for example, 300°C or lower. The reaction initiation temperature of the curing agent can be determined by differential scanning calorimetry (DSC).

[0109] Specific examples of the curing agent include imidazole-based curing agents, phenol-based curing agents, amine-based curing agents, acid anhydride-based curing agents, isocyanate-based curing agents, and thiol-based curing agents.

[0110] 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, and 2-phenylimidazole, as well as carboxylic acid salts of imidazole compounds and adducts with epoxy compounds. Furthermore, it is preferable that the imidazole-based curing agent has a hydroxyl group. Crystallization occurs due to hydrogen bonding between the hydroxyl groups, which tends to increase the reaction initiation temperature.

[0111] Examples of phenolic curing agents include phenolic resins. Further examples of phenolic resins include resol-type phenolic resins and novolac-type phenolic resins. From the viewpoint of adhesion of the adhesive layer to the substrate, phenolic-type novolac resins having a Tg of 110°C or less are particularly preferred. Furthermore, phenolic curing agents and imidazole-type curing agents may be used in combination. In this case, it is preferable to use an imidazole-type curing agent as a curing catalyst.

[0112] In addition, by including a phenolic resin in the adhesive layer, heat resistance can be improved, but on the other hand, toughness is reduced, and there is a concern that the adhesive layer may lift or peel off from the substrate, for example, when the foamable adhesive sheet is folded or cut. In contrast, in the present disclosure, because the adhesive layer has excellent adhesion to the substrate, even when the adhesive layer contains a phenolic resin, the adhesive layer can be prevented from lifting or peeling off from the substrate when bent. As a result, a foamable adhesive sheet can be obtained that achieves both improved heat resistance and prevention of the adhesive layer from lifting or peeling off from the substrate when bent.

[0113] The phenolic resin is preferably a biphenyl type from the viewpoint of heat resistance. The phenolic resin may also be a resin in which the phenol nucleus is modified. By modifying the phenol nucleus, for example, it is possible to further improve heat resistance.

[0114] On the other hand, when the adhesive layer does not contain a phenolic resin, the adhesive layer can be effectively prevented from lifting or peeling off from the substrate when bent or cut, and the adhesion of the adhesive layer to the substrate can be improved.

[0115] Examples of amine-based curing agents 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. Furthermore, examples of amine-based curing agents that can be used include dicyandiamide-based curing agents such as dicyandiamide (DICY), organic acid dihydrazide-based curing agents, amine adduct-based curing agents, and ketimine-based curing agents.

[0116] 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).

[0117] The isocyanate curing agent may, for example, be a blocked isocyanate.

[0118] Examples of thiol-based curing agents include ester-bonded thiol compounds, aliphatic ether-bonded thiol compounds, and aromatic ether-bonded thiol compounds.

[0119] The content of the curing agent is, for example, 1 part by mass or more and 40 parts by mass or less, based on 100 parts by mass of the resin component contained in the adhesive layer. For example, when an imidazole-based curing agent is used as the main component of 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, based on 100 parts by mass of the resin component contained in the adhesive layer. On the other hand, when a phenol-based curing agent is used as the main component of 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, based on 100 parts by mass of the resin component contained in the adhesive layer. Note that using an imidazole-based curing agent or a phenol-based curing agent as the main component of the curing agent means that the mass proportion of the imidazole-based curing agent or the phenol-based curing agent is the highest in the curing agent.

[0120] (b) Foaming agent The foaming agent in the present disclosure may be any foaming agent generally used in the adhesive layer of a foamable adhesive sheet. The foaming agent may be one that undergoes a foaming reaction when exposed to heat or light.

[0121] The foaming initiation temperature of the foaming agent is preferably equal to or higher than the softening temperature of the base of the curable adhesive, such as an epoxy resin, and equal to or lower than the activation temperature of the curing reaction of the base of the curable adhesive, such as an epoxy resin. The foaming initiation temperature of the foaming agent is, for example, 70°C or higher, and may be 100°C or higher. If the reaction initiation temperature is too low, the reaction may start early, causing foaming to occur in a state where the flexibility and fluidity of the resin component are low, making it difficult to achieve uniform foaming. On the other hand, the reaction initiation temperature of the foaming agent is, for example, 210°C or lower. If the reaction initiation temperature is too high, the resin component may deteriorate.

[0122] The softening temperature of the base agent of a curable adhesive such as an epoxy resin can be measured using the ring and ball softening temperature test method specified in JIS K 2207.

[0123] Examples of the blowing agent include organic blowing agents and inorganic blowing agents. Examples of the organic blowing agent 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 the inorganic blowing agent include ammonium carbonate, ammonium hydrogencarbonate, ammonium nitrite, ammonium borohydride, and azides.

[0124] Alternatively, a microcapsule type foaming agent may be used as the foaming agent. The microcapsule type foaming agent preferably has a core made of a thermal expansion agent such as hydrocarbon and a shell made of a resin such as acrylonitrile copolymer.

[0125] The average particle size of the foaming agent may be, for example, 7 μm or more, 10 μm or more, 13 μm or more, or 17 μm or more. When the average particle size of the foaming agent is 10 μm or more, the pencil hardness of the adhesive layer side of the foamable adhesive sheet can be increased, and the static friction coefficient of the adhesive layer side of the foamable adhesive sheet can be reduced, further improving the slipperiness and insertability. On the other hand, the average particle size of the foaming agent is preferably equal to or less than the average thickness of the adhesive layer.

[0126] Furthermore, the average particle size of the foaming agent is preferably, for example, 10 μm or more and 24 μm or less. The average particle size of the foaming agent may, for example, be 13 μm or more or 17 μm or more. The average particle size of the foaming agent may, for example, be 21 μm or less or 20 μm or less. By having the average particle size of the foaming agent within the above range, adhesion can be improved even when the gap between the components is relatively wide. The reason for this is unclear, but is presumed to be as follows. That is, if the average particle size of the foaming agent is too small, the expansion ratio of the adhesive layer tends to be small. Therefore, good adhesion can be obtained when the gap between the components is narrow, but adhesion may decrease when the gap between the components is wide. Furthermore, when the average particle size of the foaming agent is small, the expansion ratio of the adhesive layer can be increased by increasing the content of the foaming agent. However, increasing the content of the foaming agent relatively reduces the content of the curable adhesive. This is thought to result in thinner walls between bubbles in the adhesive layer after foaming and curing, a decrease in cohesive force, and therefore poor adhesion when the gap between the components is wide. On the other hand, if the average particle size of the foaming agent is too large, the bubbles after foaming will be large, so the walls between the bubbles in the adhesive layer after foaming and curing will be thin, and the cohesive force will be reduced, which is thought to result in reduced adhesiveness even when the gap between the components is narrow.In contrast, if the average particle size of the foaming agent is within the above range, the expansion ratio of the adhesive layer will not be too small, so that the gap between the components can be sufficiently filled, and the bubbles after foaming and curing will not be too large, so that the walls between the bubbles in the adhesive layer after foaming and curing will be thick, and the contact area between the walls between the bubbles in the adhesive layer after foaming and curing and the components can be increased.As a result, it is thought that good adhesiveness can be obtained not only when the gap between the components is narrow, but also when the gap between the components is wide.

[0127] The average particle size of the foaming agent is the particle size at 50% of the cumulative value in the particle size distribution determined by laser diffraction scattering. To measure 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 can dissolve components other than the foaming agent contained in the adhesive layer. It is appropriately selected depending on the type of curable 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.

[0128] The content of the foaming agent 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, based on 100 parts by mass of the resin component contained in the adhesive layer. On the other hand, the content of the foaming agent is, 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 content of the foaming agent is too low, the static friction coefficient of the adhesive layer side of the foamable adhesive sheet may increase, or the pencil hardness of the adhesive layer side of the foamable adhesive sheet may decrease, resulting in reduced slippage and insertion properties. Furthermore, if the content of the foaming agent is too low, the expansion ratio of the adhesive layer may decrease, potentially reducing adhesion when the gap between components is large. On the other hand, if the content of the foaming agent is too high, the content of the curable adhesive may decrease relatively, resulting in thinner walls between bubbles in the adhesive layer after foaming and curing, reduced cohesive force, and potentially reducing adhesion. In addition, when the average particle size of the foaming agent is 10 μm or more and 24 μm or less, the content of the foaming agent can be set to 3 parts by mass or more and 25 parts by mass or less per 100 parts by mass of the resin component contained in the adhesive layer, thereby further improving the adhesion when the gap between the components is narrow and when the gap between the components is wide.

[0129] (c) Other ingredients In the adhesive layer of the present disclosure, for example, when the curable adhesive is an epoxy resin adhesive, the resin components may consist of only an epoxy resin and an acrylic resin, or may further contain other resins, such as urethane resins.

[0130] The total proportion of the first epoxy resin, the second epoxy resin, and the acrylic resin relative to the resin components contained in the adhesive layer is, for example, 70% by mass or more, or may be 80% by mass or more, or 90% by mass or more, or may be 100% by mass.

[0131] The content of the resin component in the adhesive layer is, for example, 60% by mass or more, optionally 70% by mass or more, optionally 80% by mass or more, or optionally 90% by mass or more.

[0132] The adhesive layer may contain, as needed, for example, a silane coupling agent, a filler, an antioxidant, a light stabilizer, an ultraviolet absorber, a lubricant, a plasticizer, an antistatic agent, a crosslinking agent, and a colorant. Examples of the silane coupling agent include epoxy-based silane coupling agents. Examples of the filler include inorganic fillers such as calcium carbonate, aluminum hydroxide, magnesium hydroxide, antimony trioxide, zinc borate, molybdenum compounds, and titanium dioxide. Examples of the antioxidant include phenol-based antioxidants and sulfur-based antioxidants.

[0133] (2) Structure of the adhesive layer The adhesive layer can be expanded at an expansion ratio of, for example, 1.5 times or more and 15 times or less. The expansion ratio may be, for example, 3.5 times or more, 4 times or more, or 4.5 times or more. The expansion ratio may be, for example, 9 times or less, 8.5 times or less, or 8 times or less. When the average particle size of the foaming agent is within a predetermined range, an expansion ratio of 3.5 times or more and 9 times or less tends to increase adhesiveness when the gap between the components is wide. On the other hand, if the expansion ratio is too small, adhesiveness may decrease when the gap between the components is wide. If the expansion ratio is too large, adhesiveness may decrease even when the gap between the components is narrow.

[0134] Here, the expansion ratio can be calculated by the following formula. Foaming ratio (times) = adhesive layer thickness after foaming and hardening / adhesive layer thickness before foaming and hardening

[0135] The average 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, for example, 10 μm or more, or 15 μm or more, or even 20 μm or more. If the adhesive layer is too thin, it may be difficult to obtain sufficient adhesion to the substrate and adhesion after foaming and curing. On the other hand, the average thickness of the adhesive layer may be, for example, 200 μm or less, or 150 μm or less, or even 100 μm or less.

[0136] Here, the average thickness of the adhesive layer can be the average value of thicknesses measured at any 10 locations on a cross section of the foamable adhesive sheet in the thickness direction as observed with a transmission electron microscope (TEM), a scanning electron microscope (SEM), or a scanning transmission electron microscope (STEM). The same method can be used to measure the average thickness of other layers of the foamable adhesive sheet.

[0137] 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.

[0138] The adhesive layer can be formed, for example, by applying an adhesive composition containing the above-mentioned curable adhesive and a foaming agent, etc., and then 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.

[0139] 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.

[0140] 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 disperser, 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 desper, a high-speed mixer, a ribbon blender, a co-kneader, an intensive mixer, a tumbler, a blender, a desperzer, a homogenizer, or an ultrasonic disperser, can be used.

[0141] 3.Base material The substrate in the present disclosure preferably has insulating properties. The substrate is preferably in the form of a sheet. The substrate sheet may have a single-layer structure or a multi-layer structure. The substrate sheet may or may not have a porous structure inside.

[0142] Examples of the substrate include a resin substrate and a nonwoven fabric.

[0143] 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, or may be 140°C or higher, or even 200°C or higher. Furthermore, a liquid crystal polymer (LCP) may be used as the resin.

[0144] 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.

[0145] Among these, the substrate preferably contains polyphenylene sulfide (PPS) or polyethylene naphthalate (PEN). Polyphenylene sulfide and polyethylene naphthalate have high heat resistance and are suitable for foaming and curing the foamable adhesive sheet by heating. Furthermore, polyphenylene sulfide and polyethylene naphthalate have high insulating properties, and for example, the adhesive sheet after foaming and curing can insulate components from each other. Furthermore, polyphenylene sulfide and polyethylene naphthalate generally have poor wettability with adhesives and poor adhesion to the adhesive layer. However, the present disclosure can improve the adhesion of the adhesive layer to the substrate. Therefore, a foamable adhesive sheet can be obtained that balances heat resistance, insulating properties, and adhesion between the substrate and the adhesive layer.

[0146] The substrate may be subjected to a surface treatment on the surface on which the adhesive layer is to be disposed to enhance adhesion with the adhesive layer. Examples of surface treatments include corona treatment, blast treatment, plasma treatment, flame treatment, Itro treatment, and hydrophilization treatment using fluorine gas. Among the above surface treatments, blast treatment is preferred. The adhesive layer penetrates into the fine irregularities on the blast-treated surface of the substrate, thereby enhancing adhesion between the substrate and the adhesive layer, i.e., achieving an anchor effect. Furthermore, blast treatment is a surface roughening treatment, and is thought to stabilize adhesion between the substrate and the adhesive layer compared to surface activation treatments such as corona treatment.

[0147] A surface treatment layer may be disposed on the surface of the substrate on which the adhesive layer is disposed. Examples of the surface treatment layer include a silicon oxide film. Examples of methods for forming the surface treatment layer include a CVD method and a PVD method.

[0148] The average thickness of the substrate is not particularly limited, but may be, for example, 2 μm or more, 5 μm or more, or 9 μm or more, and may be, for example, 200 μm or less, 100 μm or less, or 50 μm or less.

[0149] 4. Middle class The foamable adhesive sheet of the present disclosure preferably has an intermediate layer between the substrate and the adhesive layer. The presence of the intermediate layer can further improve the adhesion of the adhesive layer to the substrate. Furthermore, the presence of the intermediate layer can, for example, alleviate stress at the bent portion when the foamable adhesive sheet is folded, or at the cut portion when the foamable adhesive sheet is cut. As a result, lifting or peeling of the adhesive layer from the substrate can be effectively suppressed not only when the foamable adhesive sheet is bent but also when it is cut.

[0150] For example, in the foamable adhesive sheet 10 shown in Fig. 3, a substrate 2, an intermediate layer 3, and an adhesive layer 1 are arranged in this order in the thickness direction. In the foamable adhesive sheet 10 shown in Fig. 4, a first adhesive layer 1a is arranged on one side of the substrate 2, a second adhesive layer 1b is arranged on the other side of the substrate 2, a first intermediate layer 3a is arranged between the substrate 2 and the first adhesive layer 1a, and a second intermediate layer 3b is arranged between the substrate 2 and the second adhesive layer 1b. Note that, although the foamable adhesive sheet 10 in Fig. 4 has both the first intermediate layer 3a and the second intermediate layer 3b, it may have only one of them.

[0151] When adhesive layers are disposed on both sides of the substrate, it is sufficient that an intermediate layer is disposed between the substrate and at least one of the adhesive layers, and for example, an intermediate layer may be disposed between the substrate and only one of the adhesive layers, or an intermediate layer may be disposed between the substrate and both adhesive layers. Of these, it is preferable that an intermediate layer is disposed between the substrate and both adhesive layers.

[0152] The material contained in the intermediate layer is not particularly limited as long as it can increase the adhesion between the substrate and the adhesive layer and relieve stress, and is appropriately selected depending on the materials of the substrate and the adhesive layer, etc. Examples include polyester, polyvinyl chloride, polyvinyl acetate, polyurethane, copolymers of at least two of these, crosslinked products thereof, and mixtures thereof.

[0153] The crosslinked product is a crosslinked product obtained by crosslinking the above resin with a curing agent. Examples of the curing agent include an isocyanate-based curing agent. Furthermore, 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 to 20% by mass or less relative to the resin.

[0154] In particular, the intermediate layer preferably contains a crosslinked resin. A crosslinked resin refers to a resin that does not melt even at high temperatures. This improves adhesive strength at high temperatures, i.e., heat resistance. Furthermore, if the crosslinked resin is crosslinked with, for example, an isocyanate-based curing agent, the flexibility of the intermediate layer is improved, and cracking of the adhesive layer and lifting and peeling of the adhesive layer from the substrate when the foamable adhesive sheet is bent can be suppressed.

[0155] Examples of crosslinked resins include the crosslinked bodies described above. Among these, the intermediate layer preferably contains a crosslinked polyester resin. When the intermediate layer contains a crosslinked polyester resin, the adhesion between the substrate and the adhesive layer tends to be enhanced. In particular, when the substrate contains polyphenylene sulfide (PPS) or polyethylene naphthalate (PEN) and the adhesive layer contains an epoxy resin adhesive as a curable adhesive, the adhesion between the substrate and the adhesive layer can be improved by including a crosslinked polyester resin in the intermediate layer.

[0156] The crosslinked polyester resin is a crosslinked product of polyester, a copolymer containing polyester, or a mixture containing polyester. Specifically, it is a crosslinked product obtained by crosslinking polyester, a copolymer containing polyester, or a mixture containing polyester with a curing agent. Examples of polyesters include polyester polyols. Examples of curing agents include isocyanate-based curing agents. The amount of curing agent added is as described above.

[0157] The average thickness of the intermediate layer is not particularly limited as long as it can maintain a predetermined peel strength of the adhesive layer side of the foamable adhesive sheet as measured by the SAICAS method. It can be, for example, 0.1 μm or more, 0.5 μm or more, or even 1 μm or more. If the intermediate layer is too thin, it may not be effective enough to prevent the adhesive layer from peeling from the substrate when the foamable adhesive sheet is bent or cut. On the other hand, the average thickness of the intermediate layer can be, for example, 4 μm or less, or even 3.5 μm or less. Since the intermediate layer itself usually does not have high heat resistance, if the intermediate layer is too thick, its heat resistance (adhesive strength at high temperatures) may be reduced. When using a substrate with relatively high heat resistance, such as polyethylene naphthalate (PEN) or polyphenylene sulfide (PPS), the adhesion and heat resistance can be further improved by setting the average thickness of the intermediate layer to 0.5 μm or more and 4 μm or less.

[0158] The intermediate layer can be formed, for example, by applying a resin composition and removing the solvent. Examples of the application method 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.

[0159] 5.Foam adhesive sheet The average thickness of the foamable adhesive sheet of the present disclosure is, for example, 10 μm or more, and may be 20 μm or more, while the average thickness of the foamable adhesive sheet is, for example, 1000 μm or less, and may be 200 μm or less.

[0160] The use of the foamable adhesive sheet of the present disclosure is not particularly limited. The foamable adhesive sheet of the present disclosure can be used, for example, when bonding components together by placing a foamable adhesive sheet between components and then foaming and curing the foamable adhesive sheet. Furthermore, when placing a foamable adhesive sheet between components, even if the components have burrs, the foamable adhesive sheet of the present disclosure can suppress the adhesive layer from lifting or peeling from the substrate. Therefore, the foamable adhesive sheet of the present disclosure can be used when bonding metal or resin components that are prone to burrs during processing. In particular, the foamable adhesive sheet of the present disclosure is preferably used when bonding metal components together by placing a foamable adhesive sheet between them.

[0161] 6. Manufacturing method of foam adhesive sheet The method for producing the foamable adhesive sheet of the present disclosure is not particularly limited. For example, an adhesive layer can be formed by applying and drying the above-described adhesive composition to one side of a substrate. When a first adhesive layer is formed on one side of a substrate and a second adhesive layer is formed on the other side of the substrate, the first adhesive layer and the second adhesive layer can be formed sequentially or simultaneously. By forming the second adhesive layer after forming the first adhesive layer, the first adhesive layer can be dried more thoroughly, and the peel strength of the foamable adhesive sheet on the side of the first adhesive layer can be made higher than the peel strength of the side of the second adhesive layer.

[0162] B. How the Article is Manufactured The method for manufacturing an article according to the present disclosure includes a placement step of placing the above-mentioned foamable adhesive sheet between a first member and a second member, and a bonding step of foaming and curing the foamable adhesive sheet to bond the first member and the second member together.

[0163] Fig. 5 is a process diagram showing an example of a method for manufacturing an article according to the present disclosure. First, as shown in Fig. 5(a), a foamable adhesive sheet 10 is placed between a first member 20a and a second member 20b. Next, as shown in Fig. 5(b), the foamable adhesive sheet 10 is foamed and cured, for example, by heating. The foamed and cured adhesive sheet 11 adheres (bonds) the first member 20a and the second member 20b. This results in an article 100 in which the adhesive sheet 11 is placed between the first member 20a and the second member 20b.

[0164] In the method for manufacturing an article according to the present disclosure, the foamable adhesive sheet described above is used, resulting in excellent adhesion of the adhesive layer to the substrate. Even if at least one of the first and second components has burrs, lifting or peeling of the adhesive layer from the substrate can be prevented when inserting the foamable adhesive sheet into a gap between one of the components or a gap between two components, or when inserting one component into the gap after placing the foamable adhesive sheet on the other component. Furthermore, even when the foamable adhesive sheet is folded in advance when placing it between the first and second components, lifting or peeling of the adhesive layer from the substrate can be prevented. Therefore, an article can be obtained in which the first and second components have excellent adhesion.

[0165] The method for manufacturing the article according to the present disclosure will now be described.

[0166] 1.Foam adhesive sheet In the method for manufacturing an article according to the present disclosure, the foamable adhesive sheet may be the foamable adhesive sheet described above, in which an adhesive layer and a substrate are arranged in this order, and the peel strength of the surface on which the adhesive layer is arranged, measured by the SAICAS method, is 2.0 N or greater. Alternatively, the foamable adhesive sheet may have a first adhesive layer and a second adhesive layer as adhesive layers, in which the first adhesive layer, the substrate, and the second adhesive layer are arranged in this order in the thickness direction. In this case, it is sufficient that the peel strength of at least one of the surface on which the first adhesive layer and the surface on which the second adhesive layer are arranged, measured by the SAICAS method, is 2.0 N or greater.

[0167] Details of the foamable adhesive sheet are described above in the section "A. Foamable adhesive sheet," so further description will be omitted here.

[0168] 2.Placement process In the placement step of the present disclosure, the method for placing the foamable adhesive sheet between the first member and the second member is not particularly limited, and examples include a method of inserting the foamable adhesive sheet into the gap between the first member and the second member, or a method of placing the foamable adhesive sheet on the first member and then inserting the second member into the gap after placing the foamable adhesive sheet on the first member.

[0169] 3.Gluing process In the bonding step of the present disclosure, examples of the method for foaming and curing the foamable adhesive sheet include heating and light irradiation. Among these, it is preferable to foam and cure the foamable adhesive sheet by heating. The heating method is also applicable even when the first and second members are not transparent, such as when the first and second members are made of metal.

[0170] The heating conditions are appropriately set depending on the types of curable adhesive and foaming agent contained in the adhesive layer, the type of substrate, etc. The heating temperature can be, for example, 130° C. or higher and 200° C. or lower. The heating time can be, for example, 3 minutes or higher and 3 hours or lower.

[0171] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical idea described in the claims of the present disclosure and that provides similar effects is included within the technical scope of the present disclosure. [Example]

[0172] [Example 1] First, an adhesive composition was prepared having the composition (mass %) shown in Table 1 below. Details of each material listed in Table 1 are shown in Table 2.

[0173] Furthermore, a highly insulating polyphenylene sulfide film (PPS film, manufactured by Toray Industries, Inc., Torelina 100-3A30, thickness 100 μm) was used as the substrate, and corona treatment was performed to achieve a surface tension of 70 dynes or more. The adhesive composition described above was applied to one side of this substrate using an applicator so that the thickness after application was 45 μm. This was then dried in an oven at 100°C for 3 minutes to form a first adhesive layer. Furthermore, a second adhesive layer was formed on the other side of the substrate in the same manner as the first adhesive layer described above. This resulted in a foamable adhesive sheet in which a first adhesive layer and a second adhesive layer were formed on both sides of the substrate, respectively.

[0174] [Example 2] A foamable adhesive sheet was produced in the same manner as in Example 1, except that the substrate was subjected to a blast treatment so that the arithmetic mean roughness Ra was 0.64 μm.

[0175] [Comparative Example 1] A foamable adhesive sheet was produced in the same manner as in Example 1, except that an adhesive composition having the composition (mass %) shown in Table 1 below was used.

[0176] [Example 3] A foamable adhesive sheet was produced in the same manner as in Example 1, except that an adhesive composition having the composition (mass %) shown in Table 1 below was used, and a highly insulating polyphenylene sulfide film (PPS film, thickness 100 μm, arithmetic mean roughness Ra 0.64 μm) that had been subjected to the same blast treatment as in Example 2 was used as the substrate.

[0177] [Example 4] A highly insulating polyphenylene sulfide film (PPS film, 100 μm thick) similar to that used in Example 1 was prepared as a substrate. A curing agent (polyisocyanate) was blended in a ratio of 2 parts by mass to 100 parts by mass of a mixture of polyester and polyvinyl chloride, and the resulting mixture was diluted with methyl ethyl ketone (MEK) to a solids content of 15% by mass to prepare a resin composition. The resin composition was applied to one side of the substrate using a bar coater and dried in an oven at 120°C for 3 minutes to form a first intermediate layer with a thickness of 2 μm. A second intermediate layer was then formed on the other side of the substrate in the same manner as the first intermediate layer.

[0178] Next, using the same adhesive composition as in Example 3, a first adhesive layer and a second adhesive layer were formed on the first intermediate layer and the second intermediate layer, respectively, in the same manner as in Example 1. This resulted in a foamable adhesive sheet in which the first adhesive layer, first intermediate layer, substrate, second intermediate layer, and second adhesive layer were arranged in this order.

[0179] Comparative Example 2 A foamable adhesive sheet was prepared in the same manner as in Comparative Example 1, except that a highly insulating polyethylene naphthalate film (PEN film, manufactured by Toyobo Film Solutions Co., Ltd., Teonex Q51-100, thickness 100 μm) was used as the substrate and corona treatment was performed so that the surface tension was 70 dynes or more.

[0180] [Example 5] A foamable adhesive sheet was produced in the same manner as in Example 1, except that the same adhesive composition as in Example 3 was used, and the same highly insulating polyethylene naphthalate film (PEN film, thickness 100 μm) as in Comparative Example 2 was used as the substrate, and blast treatment was performed so that the arithmetic mean roughness Ra was 0.77 μm.

[0181] [Example 6] A foamable adhesive sheet was produced in the same manner as in Example 4, except that the same highly insulating polyethylene naphthalate film (PEN film, thickness 100 μm) as in Comparative Example 2 was used as the substrate.

[0182] Comparative Example 3 A foamable adhesive sheet was produced in the same manner as in Example 1, except that an adhesive composition having the composition (mass %) shown in Table 1 below was used.

[0183] [Example 7] A foamable adhesive sheet was produced in the same manner as in Example 2, except that an adhesive composition having the composition (mass %) shown in Table 1 below was used.

[0184] [Example 8] A highly insulating polyphenylene sulfide film (PPS film, manufactured by Toray Industries, Inc., Torelina 115-3F00, thickness 115 μm) was used as the substrate. A resin composition was prepared by blending 15 parts by mass of a curing agent (polyisocyanate) and 0.3 parts by mass of a catalyst (trisdimethylaminomethylphenol) with 100 parts by mass of polyester polymer, and then diluting with methyl ethyl ketone (MEK) to a solids content of 15% by mass. The resin composition was applied to one side of the substrate using a bar coater and dried in an oven at 100°C for 1 minute to form a first intermediate layer with a thickness of 2 μm. A second intermediate layer was then formed on the other side of the substrate in the same manner as the first intermediate layer.

[0185] Next, an adhesive composition having the composition (mass%) shown in Table 1 below was applied to the surface of the first intermediate layer opposite the substrate using an applicator so that the thickness after application was 38 μm. This was then dried in an oven at 100°C for 3 minutes to form a first adhesive layer. Furthermore, a second adhesive layer was formed on the surface of the second intermediate layer opposite the substrate in the same manner as the first adhesive layer. This resulted in a foamable adhesive sheet in which the first adhesive layer, first intermediate layer, substrate, second intermediate layer, and second adhesive layer were arranged in this order.

[0186] [Example 9] A foamable adhesive sheet was produced in the same manner as in Example 8, except that an adhesive composition having the composition (mass %) shown in Table 1 below was used.

[0187] [Rating 1] (peel force) The peel force of the foam adhesive sheet on the side with the first adhesive layer and the side with the second adhesive layer was measured using a surface and interface cutting tester. First, the foam adhesive sheet was cut into 5 cm x 5 cm pieces, fixed to a vacuum holder, and the adhesive layer was cut using a cutting blade. Specifically, the adhesive layer was first cut diagonally from one side of the foam adhesive sheet using a cutting blade. After the force applied to the cutting blade initially changed significantly, and the horizontal force applied to the cutting blade decreased, cutting was continued only in the horizontal direction relative to the foam adhesive sheet. The horizontal force applied to the cutting blade during cutting was then measured. The horizontal force applied to the cutting blade when cutting only in the horizontal direction relative to the foam adhesive sheet corresponds to the peel force. The peel force measurements were performed on the side of the foam adhesive sheet with the first adhesive layer and the side with the second adhesive layer. The surface and interface cutting tester was a SAICAS DN-GS model manufactured by Daipla Wintes. The cutting edge was made of a borazon alloy and had a cutting width of 1.0 mm, a rake angle of 20°, and a clearance angle of 10°. The measurement conditions were as follows: Measurement mode: Constant speed mode Horizontal speed: 2μm / sec Vertical speed: 0.1μm / sec Temperature: 23℃

[0188] (L-shaped bending test) The foamable adhesive sheet was cut into a 3cm x 3cm piece, and this foamable adhesive sheet was folded in half by 90° so that the side with the adhesive layer to be tested was facing inward, resulting in a 3cm x 1.5cm piece. It was then checked to see if the adhesive layer was lifting off the substrate. The adhesion in the L-shaped bending test was evaluated according to the following criteria. A: There is no lift at the folded part. B: There is a gap at the bend

[0189] (Cross bending test) The foamable adhesive sheet was cut into a 3 cm x 3 cm piece, and this foamable adhesive sheet was folded in half 180° to a size of 3 cm x 1.5 cm, with the side containing the adhesive layer to be tested facing inward. The foamable adhesive sheet was then folded again 180° to a size of 1.5 cm x 1.5 cm. It was then checked to see if the adhesive layer was lifting off the substrate. The adhesion in the cross-bending test was evaluated according to the following criteria: A: There is no lift at the folded part. B: There is a gap at the bend

[0190] (Cutter cutting test) The surface of the foamable adhesive sheet on which the adhesive layer to be tested was located was cut with a cutter (OLFA Cutter Knife A Plus) at a speed of 20 mm / s to 100 mm / s to a length of 100 mm, and the cut surface was checked to see if the adhesive layer was floating away from the substrate. The adhesion in the cutter cutting test was evaluated according to the following criteria. A: There is absolutely no lift on the cut surface. B: There is some lift on the cut surface C: The cut surface is completely lifted

[0191] (Adhesive strength) The foam adhesive sheet was cut to a width of 24 mm and a length of 300 mm, and one adhesive layer of the foam adhesive sheet was attached to a stainless steel plate (SUS304) using a manual roller. The adhesive strength (N / 25 mm) to the stainless steel plate was then measured using a tensile tester (A&D Co., Ltd., Tensilon RTF1150) under conditions (pulling speed: 300 mm / min, peel distance: 150 mm, peel angle: 180°) in accordance with JIS Z0237:2009 (Testing Methods for Adhesive Tapes and Adhesive Sheets) and Method 1 of the Adhesion Test Method (temperature: 23°C, humidity: 50%, peeling tape or sheet at an angle of 180° to the stainless steel test plate).

[0192] [Table 1]

[0193] [Table 2]

[0194] As shown in Table 1, in Examples 1 to 9, the adhesion in both the L-shaped bending test and the cross bending test was good. Furthermore, in Examples 2, 3, 5, and 7, the substrate was blast-treated, and therefore the adhesion in the cutter cutting test was also good. Furthermore, in Examples 4, 6, 8, and 9, an intermediate layer was disposed between the substrate and the adhesive layer, and therefore the adhesion in the cutter cutting test was excellent. In contrast, in Comparative Examples 1 to 3, the peel force measured by the SAICAS method was small, and therefore the adhesion in both the L-shaped bending test and the cross bending test was poor. The test results for the surface of the first adhesive layer of the foamable adhesive sheet were the same as those for the surface of the second adhesive layer.

[0195] [Examples 10 to 23] First, adhesive compositions were prepared with the compositions (mass %) shown in Table 3 below. Details of the materials other than the foaming agents shown in Table 3 are as shown in Table 2. The following thermal foaming agents 1 to 8 were used as foaming agents. Thermal blowing agent 1: Thermal expansion microcapsules, average particle size 7μm, expansion start temperature 120~145℃, maximum expansion temperature 155~175℃, core: hydrocarbon, shell: thermoplastic polymer Thermal blowing agent 2: Thermal expansion microcapsules, average particle size 13 μm, expansion start temperature 123-133°C, maximum expansion temperature 168-178°C, core: hydrocarbon, shell: thermoplastic polymer Thermal blowing agent 3: Thermally expandable microcapsules, average particle size 17 μm, expansion start temperature 120-130°C, maximum expansion temperature 160-170°C, core: hydrocarbon, shell: acrylonitrile copolymer Thermal blowing agent 4: Thermal expansion microcapsules, average particle size 20 μm, expansion start temperature 115-125°C, maximum expansion temperature 155-165°C, core: hydrocarbon, shell: thermoplastic polymer Thermal blowing agent 5: Thermally expandable microcapsules, average particle size 21 μm, expansion start temperature 130-140°C, maximum expansion temperature 160-170°C, core: hydrocarbon, shell: acrylonitrile copolymer Thermal blowing agent 6: Thermal expansion microcapsules, average particle size 25 μm, expansion start temperature 125-135°C, maximum expansion temperature 165-180°C, core: hydrocarbon, shell: thermoplastic polymer Thermal blowing agent 7: Thermally expandable microcapsules, average particle size 30 μm, expansion start temperature 120-130°C, maximum expansion temperature 160-170°C, core: hydrocarbon, shell: acrylonitrile copolymer Thermal blowing agent 8: Thermally expandable microcapsules, average particle size 41 μm, expansion start temperature 115-125°C, maximum expansion temperature 165-175°C, core: hydrocarbon, shell: acrylonitrile copolymer

[0196] A highly insulating polyphenylene sulfide film (PPS film, manufactured by Toray Industries, Inc., Torelina 115-3F00, thickness 115 μm) was used as the substrate. A resin composition was prepared by blending 15 parts by mass of a curing agent (polyisocyanate) and 0.3 parts by mass of a catalyst (trisdimethylaminomethylphenol) with 100 parts by mass of polyester polymer, and then diluting with methyl ethyl ketone (MEK) to a solids content of 15% by mass. The resin composition was applied to one side of the substrate using a bar coater and dried in an oven at 100°C for 1 minute to form a first intermediate layer with a thickness of 2 μm. A second intermediate layer was then formed on the other side of the substrate in the same manner as the first intermediate layer.

[0197] Next, the adhesive composition was applied to the surface of the first intermediate layer opposite the substrate using an applicator so that the thickness after application was 38 μm. This was then dried in an oven at 100°C for 3 minutes to form a first adhesive layer. Furthermore, a second adhesive layer was formed on the surface of the second intermediate layer opposite the substrate in the same manner as the first adhesive layer. This resulted in a foamable adhesive sheet in which the first adhesive layer, first intermediate layer, substrate, second intermediate layer, and second adhesive layer were arranged in this order.

[0198] [Reference example] An adhesive sheet containing no foaming agent was prepared in the same manner as in Example 10, except that the adhesive composition having the composition (mass %) shown in Table 3 below was used.

[0199] [Rating 2] (peel force) In the same manner as in Example 1, the peel strength of the surface of the foamable adhesive sheet on which the first adhesive layer was disposed and the peel strength of the surface on which the second adhesive layer was disposed were measured.

[0200] (L-shaped bending test) In the same manner as in Example 1, the adhesion was evaluated by an L-shaped bending test.

[0201] (Cross bending test) In the same manner as in Example 1, the adhesion was evaluated by a cross bending test.

[0202] (Cutter cutting test) In the same manner as in Example 1, the adhesion was evaluated by a cutter cutting test.

[0203] (Adhesive strength) The adhesive strength was measured in the same manner as in Example 1.

[0204] (coefficient of friction) The dynamic and static friction coefficients between the surface of the foam adhesive sheet on which the adhesive layer to be tested was located and a metal plate were measured in accordance with JIS K7125. First, the foam adhesive sheet was cut into 80mm x 200mm pieces. Next, the foam adhesive sheet was placed on a horizontally placed rectangular metal plate (cold-rolled SPCC steel plate). A sliding piece (63mm x 63mm, weight 200g, felt base) was placed on the surface of the foam adhesive sheet on which the adhesive layer to be tested was located. The friction force was measured at a test speed of 100mm / min, a test length of 50mm, a load cell of 10N, and a temperature of 23°C, and the dynamic and static friction coefficients were calculated. The friction tester, a Toyo Seiki Co., Ltd. friction tester, TR-2, was used.

[0205] (Pencil hardness) An A4-sized foamable adhesive sheet was prepared and placed on a glass plate. In accordance with JIS K5600, the pencil hardness of the surface of the foamable adhesive sheet on which the adhesive layer to be tested was located was measured using a pencil hardness tester (with a level). The measurement conditions were a pencil angle of 45° from the horizontal, a load of 750 g, a test speed of 1 mm / sec, a test length of 20 mm, and a temperature of 23°C. The maximum pencil hardness at which the foamable adhesive sheet was not scratched by visual observation was taken as the pencil hardness. The pencil hardness tester used was a TQC KT-VF2378-12.

[0206] (Insertion weight) Two foam adhesive sheets cut to 5.5 cm x 6.0 cm were prepared, along with a hollow cylinder 1 measuring 22 mm in outer diameter, 1.5 mm in thickness, and 60 mm in length, and a hollow cylinder 2 measuring 18 mm in outer diameter, 1.0 mm in thickness, and 80 mm in length. The two foam adhesive sheets were placed inside cylinder 1 in a rolled-up state, with the adhesive layer to be tested facing inward. Cylinder 2 was then inserted approximately 1 mm into the gap between the foam adhesive sheets in cylinder 1. A weight was then placed on cylinder 2, and the weight of the weight was measured when cylinder 2 was completely inserted into the gap between the foam adhesive sheets in cylinder 1. This weight was taken as the insertion weight. The smaller the insertion weight, the better the insertion ability.

[0207] (Expansion ratio) The foamable adhesive sheet was cut into 5cm x 5cm pieces, hung lengthwise in a hot air dryer, and foam-cured at 180°C or 150°C for 30 minutes, then cooled at room temperature for 2 hours to obtain a foam-cured adhesive sheet. The thickness of the foam-cured adhesive sheet was then measured using a thickness gauge according to JIS Z0237. The expansion ratio was calculated using the following formula: Foaming ratio (times) = {thickness of adhesive sheet after foaming and curing - (thickness of base material + thickness of first intermediate layer + thickness of second intermediate layer)} / (total thickness of the first adhesive layer and second adhesive layer of the foamable adhesive sheet before foaming and curing)

[0208] (Adhesiveness) As shown in Figures 6(a) and 6(b), two metal plates 31 (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 32 (Kapton tape) was placed at a predetermined distance from one end of one of the metal plates 31. The spacer thickness was approximately 280 µm or 350 µm (the thickness of four or five layers of Kapton Tape P-221 manufactured by Nitto Denko Corporation). A foam adhesive sheet 10 cut to a size of 12.5 mm x 25 mm was placed between the spacers 32, and the other metal plate 31 was placed so that one end overlapped.

[0209] 6(a), a test piece was obtained by placing a support 33, the thickness of which was the same as the total thickness of the metal plate 31 and the spacer 32, on the other end of each of the two metal plates 31. The test piece was then placed in a heat press and heated at 150°C for 8 minutes with a press load of 500 kgf, thereby curing the foamable adhesive sheet 10.

[0210] The remainder was fixed with clips to obtain a test piece, which was then placed in a heating oven and heated at 180° C. for 30 minutes to cure the foamable adhesive sheet 10.

[0211] The shear strength (adhesion strength) of the heated test piece was measured in accordance with JIS K6850 using a tensile tester Tensilon RTF1350 (manufactured by A&D Co., Ltd.) under the measurement conditions of a pulling speed of 10 mm / min and a temperature of 200°C.

[0212] [Table 3]

[0213] As shown in Table 3, in Examples 10 to 23, an intermediate layer was disposed between the substrate and the adhesive layer, and therefore the adhesion in both the L-shaped bending test and the cross bending test was good, and the adhesion in the cutter cutting test was also good. Note that the test results for the surface side of the first adhesive layer of the foamable adhesive sheet were the same as the test results for the surface side of the second adhesive layer.

[0214] As shown in Table 3, the larger the average particle size of the foaming agent, the smaller the static and dynamic friction coefficients and the higher the pencil hardness. Furthermore, in Example 15, compared to Examples 10 and 12, the average particle size of the foaming agent was larger, the static and dynamic friction coefficients were smaller, the pencil hardness was higher, and the insertion weight was smaller. This suggests that when the average particle size of the foaming agent is above a certain value, the slipperiness and insertion ability are improved. It also suggests that the friction coefficient and hardness of the adhesive layer side of the foamable adhesive sheet contribute to insertion ability. Table 3 shows the evaluation results for the first adhesive layer side of the foamable adhesive sheet, but the evaluation results for the first adhesive layer side and the second adhesive layer side of the foamable adhesive sheet were nearly identical.

[0215] Furthermore, as shown in Table 3, in Examples 10 and 11, in which the average particle size of the foaming agent was 7 μm, the adhesive strength was good, exceeding 0.51 MPa, when the gap was approximately 280 μm, but decreased when the gap was approximately 350 μm. On the other hand, in Examples 12 to 20, in which the average particle size of the foaming agent was 13 μm to 21 μm, the adhesive strength was good, exceeding 0.51 MPa, when the gap was both approximately 280 μm and approximately 350 μm. Furthermore, in Examples 21 to 23, in which the average particle size of the foaming agent was 25 μm to 41 μm, the adhesive strength decreased when the gap was approximately 280 μm. This suggests that when the average particle size of the foaming agent is within a specified range, the adhesive strength is improved both when the gap between the components is relatively narrow and when the gap between the components is relatively wide. [Explanation of symbols]

[0216] 1 … Adhesive layer 2...Base material 3. Middle class 10...Foam adhesive sheet 11... Adhesive sheet after foaming and hardening 20a ... First member 20b ... Second member 100 … Goods

Claims

1. A foamable adhesive sheet having a substrate and an adhesive layer disposed on at least one surface of the substrate, The adhesive layer contains a curable adhesive and a foaming agent, the peel strength of the surface on which the adhesive layer is disposed is 2.0 N or more, as measured by the SAICAS (Surface and Interfacial Cutting Analysis System) method; The adhesive strength of the adhesive layer is 0 N / 25 mm or more and 0.1 N / 25 mm or less, the coefficient of static friction of the surface of the foamable adhesive sheet facing the adhesive layer is 0.26 or less; The adhesive layer is disposed on the outermost surface, a surface of the substrate on which the adhesive layer is to be disposed is subjected to a corona treatment or a blast treatment, or an intermediate layer is disposed between the substrate and the adhesive layer; The foamable adhesive sheet, wherein the curable adhesive contains an epoxy resin, a curing agent, and a polymer component having a flexible structure.

2. A foamable adhesive sheet having a substrate and an adhesive layer disposed on at least one surface of the substrate, The adhesive layer contains a curable adhesive and a foaming agent, the peel strength of the surface on which the adhesive layer is disposed is 2.0 N or more, as measured by the SAICAS (Surface and Interfacial Cutting Analysis System) method; The adhesive strength of the adhesive layer is 0 N / 25 mm or more and 0.1 N / 25 mm or less, The insertion weight measured by the following insertion weight measurement method is 320 g or less, The adhesive layer is disposed on the outermost surface, a surface of the substrate on which the adhesive layer is to be disposed is subjected to a corona treatment or a blast treatment, or an intermediate layer is disposed between the substrate and the adhesive layer; The foamable adhesive sheet, wherein the curable adhesive contains an epoxy resin, a curing agent, and a polymer component having a flexible structure. (Method of measuring insertion weight) (1) Prepare two 5.5 cm x 6.0 cm foamable adhesive sheets, a hollow cylinder 1 having an outer diameter of 22 mm, a thickness of 1.5 mm, and a length of 60 mm, and a hollow cylinder 2 having an outer diameter of 18 mm, a thickness of 1.0 mm, and a length of 80 mm. (2) The two foamable adhesive sheets are placed inside the cylinder 1 in a rolled-up state with the adhesive layer side facing inward. (3) The cylinder 2 is inserted into the gap inside the foamable adhesive sheet in the cylinder 1 by about 1 mm in advance. (4) Place a weight on the cylinder 2 and measure the weight of the weight when the cylinder 2 is completely inserted into the gap inside the foamable adhesive sheet inside the cylinder 1. The minimum weight of the weight at this time is taken as the insertion weight.

3. A foamable adhesive sheet having a substrate and an adhesive layer disposed on at least one surface of the substrate, The adhesive layer contains a curable adhesive and a foaming agent, the peel strength of the surface on which the adhesive layer is disposed is 2.0 N or more, as measured by the SAICAS (Surface and Interfacial Cutting Analysis System) method; The adhesive strength of the adhesive layer is 0 N / 25 mm or more and 0.1 N / 25 mm or less, The adhesive layer is disposed on the outermost surface, a surface of the substrate on which the adhesive layer is to be disposed is subjected to a corona treatment or a blast treatment, or an intermediate layer is disposed between the substrate and the adhesive layer; The curable adhesive contains an epoxy resin, a curing agent, and a polymer component having a flexible structure; The foamable adhesive sheet, wherein the polymer component having a flexible structure is an acrylic resin (excluding core-shell polymers), and the weight-average molecular weight of the acrylic resin is 50,000 or more.

4. 4. The foamable adhesive sheet according to claim 1, wherein the intermediate layer has an average thickness of 0.5 μm or more and 4 μm or less.

5. The foamable adhesive sheet according to claim 1 , wherein the intermediate layer contains a crosslinked resin.

6. 6. The foamable adhesive sheet according to claim 1, wherein the foaming agent has an average particle size of 10 μm or more and 24 μm or less.

7. The foamable adhesive sheet according to claim 6 , wherein the average thickness of the adhesive layer is equal to or greater than the average particle size of the foaming agent.

8. The foamable adhesive sheet according to claim 7 , wherein the adhesive layer has an average thickness of 10 μm or more and 200 μm or less.

9. 9. The foamable adhesive sheet according to claim 6, wherein the content of the foaming agent is 3 parts by mass or more and 25 parts by mass or less, relative to 100 parts by mass of the resin component contained in the adhesive layer.

10. 10. The foamable adhesive sheet according to claim 6, wherein the adhesive layer is foamable at an expansion ratio of 3.5 to 9 times.

11. a placement step of placing the foamable adhesive sheet according to any one of claims 1 to 10 between a first member and a second member; a bonding step of foaming and curing the foamable adhesive sheet to bond the first member and the second member together; A method for manufacturing an article having the following structure:

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