Foaming Adhesive Sheet and Method for Manufacturing an 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 foaming adhesive sheet and a method for manufacturing an article using the same.

Background Art

[0002] Adhesives for bonding members are used in various fields, and many bonding methods are known.

[0003] For example, Patent Documents 1 and 2 disclose adhesive sheets (foaming adhesive sheets) containing a foaming agent. Patent Document 1 discloses an adhesive sheet having an expandable adhesive layer containing an epoxy resin containing a polyfunctional epoxy resin, a phenolic resin as a curing agent, an imidazole-based compound as a curing catalyst, and a thermosensitive foaming agent on both sides or one side of a base material, and a release agent is applied to the surface of at least one expandable adhesive layer. Further, Patent Document 2 discloses an adhesive sheet including a base material, thermally expandable adhesive layers provided on both sides of the base material, and an adhesive permeable layer provided on the surface of each adhesive layer and permeable to the adhesive when the adhesive thermally expands.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] As a method of using a foaming adhesive sheet, for example, a method of arranging a foaming adhesive sheet between members and then foaming and curing the foaming adhesive sheet to bond the members together is known.

[0006] When the foaming adhesive sheet has an adhesive layer on one or both sides of the base material, when the foaming adhesive sheet is bent, or in a processing step such as cutting the foaming adhesive sheet, the adhesive layer may float or peel off from the base material. Also, when there are burrs on the member, when inserting the foaming adhesive sheet into the gap between the members or between the members, or when inserting the other member into the gap after arranging the foaming adhesive sheet on one member, the foaming adhesive sheet may catch on the burrs of the member, resulting in the floating or peeling of the adhesive layer from the base material. Therefore, in the foaming adhesive sheet, further improvement in the adhesion of the adhesive layer to the base material is desired.

[0007] However, in the foaming adhesive sheet, since the adhesive layer contains a foaming agent, the adhesion of the adhesive layer tends to decrease compared to an adhesive layer that does not contain a foaming agent. Also, for improving handling properties and workability, it is desirable that the adhesive layer before foaming and curing is non-tacky (tack-free), but in that case, the adhesion of the adhesive layer tends to decrease. Also, for example, when the adhesive layer is foamed and cured by heating, a heat-resistant base material is used, but generally many heat-resistant base materials have low adhesion.

[0008] The present disclosure has been made in view of the above circumstances, and the main object is to provide a foaming adhesive sheet having excellent adhesion of the adhesive layer to the base material.

Means for Solving the Problems

[0009] One embodiment of the present disclosure is a foaming adhesive sheet having a base material and an adhesive layer disposed on at least one surface side of the base material, wherein the adhesive layer contains a curable adhesive and a foaming agent, and the peeling force on the surface side where the adhesive layer is disposed, measured by the SAICAS method, is 2.0 N or more. Hereinafter, Surface And Interfacial Cutting Analysis System is abbreviated as SAICAS.

[0010] Other embodiments of the present disclosure provide a method for manufacturing an article, which includes an arranging step of disposing the above-described foaming adhesive sheet between a first member and a second member, and an adhering step of foaming and curing the foaming adhesive sheet to adhere the first member and the second member.

Advantages of the Invention

[0011] The foaming adhesive sheet in the present disclosure has an effect of excellent adhesion to the base material of the adhesive layer.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings and the like. However, the present disclosure can be implemented in many different modes and is not to be construed as limited to the description of the embodiments exemplified below. Also, for the purpose of making the description clearer, the drawings may schematically represent the width, thickness, shape, etc. of each part compared to the actual form, but this is merely an example and does not limit the interpretation of the present disclosure. Further, in this specification and each drawing, elements similar to those described above with respect to the previously presented drawings may be denoted by the same reference numerals, and detailed descriptions may be omitted as appropriate.

[0014] In this specification, when expressing the manner of arranging one member on another member, if simply denoted as "on" or "under", unless otherwise specified, it shall include both the case where another member is arranged directly above or below so as to be in contact with a certain member, and the case where another member is arranged above or below a certain member with yet another member interposed therebetween. Further, in this specification, when expressing the manner of arranging one member on the surface of another member, if simply denoted as "on the surface side" or "on the surface", unless otherwise specified, it shall include both the case where another member is arranged directly above or below so as to be in contact with a certain member, and the case where another member is arranged above or below a certain member with yet another member interposed therebetween.

[0015] Also, in this specification, "sheet" includes a member called "film". Further, "film" includes a member called "sheet". Also, the numerical ranges in this specification are ranges of average values.

[0016] The inventors of the present disclosure have intensively studied the adhesion of the adhesive layer to the base material in the foaming adhesive sheet having the adhesive layer on one or both sides of the base material. For example, Patent Document 1 discloses an evaluation of the adhesion of the adhesive layer to the base material by an L-shaped bending test in which the foaming adhesive sheet is bent at 90° into an L shape once. However, as described above, in the foaming adhesive sheet, since the required level for the adhesion of the adhesive layer to the base material is high, it has been found that simply satisfying the adhesion by the L-shaped bending test is not sufficient and it may not withstand practical use. Further, as a result of repeated studies by the inventors of the present disclosure, it has been found that in order to obtain a foaming adhesive sheet that can withstand practical use, it is necessary to satisfy the adhesion in an adhesion test under conditions more severe than the L-shaped bending test, specifically, the adhesion by a cross-bending test in which the foaming adhesive sheet is bent twice at 180° into a cross shape as described later. And, in the foaming adhesive sheet, by setting the peel force of the surface on the adhesive layer side measured by the SAICAS method to a predetermined value or more, it is possible to satisfy not only the adhesion by the L-shaped bending test but also the adhesion by the cross-bending test, and it has been found that a foaming adhesive sheet that can withstand practical use can be obtained. The present disclosure is based on such findings.

[0017] Hereinafter, the foaming adhesive sheet and the method for manufacturing an article using the same in the present disclosure will be described in detail.

[0018] A. Foaming adhesive sheet The foaming adhesive sheet in the present disclosure has a base material and an adhesive layer disposed on at least one surface side of the base material, the adhesive layer contains a curable adhesive and a foaming agent, and the peel force of the surface side on which the adhesive layer is disposed, measured by the SAICAS method, is 2.0 N or more.

[0019] Figs. 1 and 2 are schematic cross-sectional views illustrating the foaming adhesive sheet in the present disclosure. The foaming adhesive sheet 10 in Fig. 1 has a base material 2 and an adhesive layer 1 disposed on one surface side of the base material 2. The foaming adhesive sheet 10 in Fig. 2 has a base material 2, a first adhesive layer 1a disposed on one surface side of the base material 2, and a second adhesive layer 1b disposed on the other surface side of the base material 2. The adhesive layer 1, the first adhesive layer 1a, and the second adhesive layer 1b contain a curable adhesive and a foaming agent. In the foaming adhesive sheet 10 in Fig. 1, the peel strength on the surface side where the adhesive layer 1 is disposed, measured by the SAICAS method, is a predetermined value or more. Further, in the foaming adhesive sheet 10 in Fig. 2, the peel strength on the surface side where the first adhesive layer 1a is disposed and the peel strength on the surface side where the second adhesive layer 1b is disposed, both measured by the SAICAS method, are a predetermined value or more. Note that when the foaming adhesive sheet has adhesive layers on both surface sides, it is preferable that the peel strengths on both surface sides are a predetermined value or more. However, since the foaming adhesive sheet in the present disclosure may 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 one of the surface sides is a predetermined value or more.

[0020] In the foaming adhesive sheet in the present disclosure, since the peel strength on the surface side where the adhesive layer is disposed, measured by the SAICAS method, is a predetermined value or more, a foaming adhesive sheet excellent in adhesion of the adhesive layer to the base material can be obtained. Specifically, as will be described later, the foaming adhesive sheet in the present disclosure can satisfy not only the adhesion by the L-shaped bending test but also the adhesion by the cross-shaped bending test. Therefore, for example, when disposing the foaming adhesive sheet between members, even when the foaming adhesive sheet is bent, the occurrence of lifting or peeling of the adhesive layer from the base material can be suppressed. Further, when disposing the foaming adhesive sheet between members, even when there are burrs on the members, the occurrence of lifting or peeling of the adhesive layer from the base material can be suppressed. Thus, a foaming adhesive sheet that can withstand practical use can be provided.

[0021] Hereinafter, each component of the foaming adhesive sheet in the present disclosure will be described.

[0022] 1. Characteristics of the Foamable Adhesive Sheet In the foamable adhesive sheet according to the present disclosure, the peel strength on the side where the adhesive layer is disposed, measured by the SAICAS method, is 2.0 N or more, may be 3.0 N or more, may be 3.5 N or more, or may be 4.0 N or more. Further, the peel strength on the side where the adhesive layer of the foamable adhesive sheet is disposed is, for example, 6.0 N or less, may be 5.5 N or less, or may be 5.0 N or less. By the peel strength on the side where the adhesive layer of the foamable adhesive sheet is disposed being within the above range, a foamable adhesive sheet excellent in adhesion of the adhesive layer to the base material can be obtained.

[0023] When adhesive layers are disposed on both sides of the base material, as described above, it is sufficient that the peel strength on either one side of the foamable adhesive sheet is within the above range, and it is preferable that the peel strengths on both sides of the foamable adhesive sheet are within the above range.

[0024] The peel strength on the side where the adhesive layer of the foamable adhesive sheet is disposed can be measured based on the SAICAS method. The SAICAS method is also referred to as a surface interface cutting method or the like. When measuring the peel strength on the side where the adhesive layer of the foamable adhesive sheet is disposed by the SAICAS method, first, a cutting edge is brought into contact with the surface on the adhesive layer side of the foamable adhesive sheet, and the cutting edge is relatively moved at a constant speed simultaneously in the horizontal direction and the vertical direction with respect to the foamable adhesive sheet to perform cutting. That is, the adhesive layer is obliquely cut by the cutting edge. Next, when the cutting edge reaches a predetermined depth equal to or greater than the thickness of the adhesive layer from the surface on the adhesive layer side of the foamable adhesive sheet, a large change is seen in the force applied to the cutting edge, and the horizontal force applied to the cutting edge decreases. At this point, the cutting edge is relatively moved with respect to the foamable adhesive sheet only in the horizontal direction to perform cutting. The horizontal force applied to the cutting edge when the cutting edge is relatively moved with respect to the foamable adhesive sheet only in the horizontal direction corresponds to the peel strength on the side where the adhesive layer of the foamable adhesive sheet is disposed. In the present disclosure, this peel strength is set to 2.0 N or more.

[0025] In the foaming adhesive sheet disclosed in the present disclosure, for example, the adhesive layer may be directly disposed on the base material, or an intermediate layer may be disposed between the base material and the adhesive layer as described later. However, in any case, after the cutting blade is relatively moved at a constant speed simultaneously in the horizontal and vertical directions with respect to the foaming adhesive sheet for cutting, first, when a large change is observed in the force applied to the cutting blade and the horizontal force applied to the cutting blade decreases, the cutting blade is relatively moved only in the horizontal direction with respect to the foaming adhesive sheet for cutting. In this case, the interface when the cutting blade is relatively moved only in the horizontal direction with respect to the foaming adhesive sheet for cutting is the interface between the adhesive layer and the layer adjacent to the adhesive layer, or the interface located between the adhesive layer and the base material, and that interface is likely to be a peeling interface.

[0026] Details of the method for measuring the peel force on the surface side where the adhesive layer of the foaming adhesive sheet is disposed by the SAICAS method will be described in the section of the examples described later.

[0027] In the present disclosure, the peel force on the surface side where the adhesive layer of the foaming adhesive sheet is disposed as measured by the SAICAS method can be set to a predetermined value or more, for example, by disposing an intermediate layer between the base material and the adhesive layer, performing surface treatment on the surface of the base material where 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 the materials of the base material, intermediate layer, and adhesive layer.

[0028] For example, as described later, by disposing an intermediate layer between the base material and the adhesive layer, or performing surface treatment on the surface of the base material where the adhesive layer is disposed, the adhesion of the adhesive layer to the base material can be improved, and the above peel force can be increased.

[0029] Also, when adjusting the composition of the adhesive layer, for example, in an adhesive layer containing an epoxy resin and a curing agent, by incorporating a polymer component having a flexible structure, the flexibility and toughness of the adhesive layer can be enhanced, the adhesion of the adhesive layer to the substrate can be improved, and the above-mentioned peel force can be increased. Specifically, as the polymer component having the above flexible structure, an acrylic resin compatible with the epoxy resin can be cited, as will be described later. Further, for example, in an adhesive layer containing an epoxy resin and a curing agent, by not containing a component that reduces toughness, a decrease in the toughness of the adhesive layer can be suppressed, the adhesion of the adhesive layer to the substrate can be improved, and the above-mentioned peel force can be increased. Specifically, as the component that reduces toughness, a phenolic resin can be cited, as will be described later. Also, 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 enhanced, the adhesion of the adhesive layer to the substrate can be improved, and the above-mentioned peel force can be increased. Specifically, in an adhesive layer containing an epoxy resin and a curing agent, the molecular weight of at least one of the epoxy resin and the curing agent is increased, or in an adhesive layer containing an epoxy resin, an acrylic resin, and a curing agent, a method of increasing the molecular weight of at least one of the epoxy resin, the acrylic resin, and the curing agent can be cited.

[0030] Also, when adjusting the average thickness of the adhesive layer, for example, as will be described later, by increasing the average thickness of the adhesive layer, the adhesion of the adhesive layer to the substrate can be improved, and the above-mentioned peel force can be increased.

[0031] Also, when adjusting the combination of materials of the substrate, the intermediate layer, and the adhesive layer, for example, as will be described later, when the substrate contains polyphenylene sulfide or polyethylene, the intermediate layer contains a crosslinked polyester resin, and the adhesive layer contains an epoxy resin and a curing agent, the adhesion of the adhesive layer to the substrate tends to be high, and the above-mentioned peel force can be increased.

[0032] In the foaming adhesive sheet according to the present disclosure, it is preferable that the adhesive layer is substantially non-tacky. In this case, it is preferable that the adhesive layer is disposed on the outermost surface. Since the adhesive layer is substantially non-tacky, a foaming adhesive sheet having good slipperiness and anti-blocking properties can be obtained. Therefore, the handleability and workability of the foaming adhesive sheet can be improved. Specifically, when the foaming adhesive sheet is disposed between members to bond the members together, the foaming adhesive sheet can be smoothly inserted into the gap between the members or the gap between the members, or after the foaming adhesive sheet is disposed on one member, the other member can be smoothly inserted into the gap.

[0033] Here, non-tackiness is generally used mainly in the sense that the adhesive force is low. In the present disclosure, "being non-tacky" means a state in which the foaming adhesive sheet is wound into a roll and then can be easily unwound without resistance.

[0034] When the adhesive layer is substantially non-tacky, specifically, the adhesive force of the adhesive layer is preferably 0 N / 25 mm or more and 0.1 N / 25 mm or less, may be 0.05 N / 25 mm or less, or may be 0.02 N / 25 mm or less. Since the adhesive force of the adhesive layer is within the above range, the adhesive layer can be made substantially non-tacky, and a foaming adhesive sheet having good slipperiness and anti-blocking properties 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 disposed on the surface of the adhesive layer, the adhesiveness of the adhesive layer after foaming and curing may decrease. On the other hand, in the foaming adhesive sheet in which the adhesive layer is substantially non-tacky, it is not necessary to dispose a release layer or a release sheet for the purpose of imparting anti-blocking properties and slipperiness, and the adhesive layer can be disposed on the outermost surface. Therefore, a foaming adhesive sheet having good adhesiveness of the adhesive layer after foaming and curing can be obtained.

[0036] When an adhesive layer is disposed on both sides of the base material, it is sufficient that the adhesive strength of at least one of the adhesive layers is within the above range. For example, when a foaming adhesive sheet is disposed between members to bond the members together, first, the foaming adhesive sheet is disposed on one member, and then, the other member may be inserted into the gap after the foaming adhesive sheet is disposed on one member. In such a case, when the other member is inserted into the gap after the foaming adhesive sheet is disposed on one member, it is sufficient that the slidability of the surface of the foaming adhesive sheet in contact with the other member is good. Therefore, it is sufficient that the adhesive strength of at least one of the adhesive layers is within the above range.

[0037] When an adhesive layer is disposed on both sides of the base material, for example, the adhesive strength of either one of the adhesive layers may be within the above range, or the adhesive strengths of both adhesive layers may be within the above range. Among them, it is preferable that the adhesive strengths of both adhesive layers are 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 test method for adhesive strength (test method of peeling at 180° with respect to a stainless steel test plate at a temperature of 23°C and a humidity of 50%). The details of the measurement method of the adhesive strength of the adhesive layer will be described in the section of Examples described later.

[0039] In the present disclosure, the adhesive strength of the adhesive layer can be made equal to or less than a predetermined value, for example, by adjusting the composition of the adhesive layer. Specifically, in the adhesive layer containing an epoxy resin and a curing agent, the adhesiveness of the adhesive layer can be reduced by using an epoxy resin that is solid at room temperature or a curing agent that is solid at room temperature. Further, in the adhesive layer containing an epoxy resin and a curing agent, the adhesiveness of the adhesive layer can be reduced by including an epoxy resin having a high softening temperature or an epoxy resin having a small weight average molecular weight. More specifically, in the adhesive layer containing an epoxy resin and a curing agent, as will be described later, the adhesiveness of the adhesive layer can be reduced by including a first epoxy resin having a low softening temperature and a low molecular weight and a second epoxy resin having a high softening temperature and a high molecular weight as the epoxy resin. Further, in the adhesive layer containing an epoxy resin and a curing agent, as will be described later, the adhesiveness of the adhesive layer can be reduced by including an acrylic resin compatible with the epoxy resin.

[0040] In the foaming adhesive sheet in the present disclosure, the pencil hardness of the surface on the adhesive layer side may be, for example, HB or higher, or F or higher. When the pencil hardness of the surface on the adhesive layer side of the foaming adhesive sheet in the present disclosure is F or higher, the slipperiness and insertability can be further improved. Specifically, when the pencil hardness of the surface on the adhesive layer side of the foaming adhesive sheet is within the above range, the frictional resistance tends to be small, and the slipperiness can be improved. Also, when inserting the foaming adhesive sheet into the gap between members or between members, or when inserting the other member into the gap after arranging the foaming adhesive sheet on one member, when the above pencil hardness is within the above range, it is possible to suppress the end face of the member from digging into the adhesive layer. In particular, when there is a burr on the end face of the member, it is possible to make it difficult for the adhesive layer to catch on the burr on the end face of the member, and the insertability can be improved. Therefore, for example, when arranging a foaming adhesive sheet between members to bond the members together, it is possible to smoothly insert the foaming adhesive sheet into the gap between members or between members, or smoothly insert the other member into the gap after arranging the foaming adhesive sheet on one member. Also, when the above pencil hardness is within the above range, it is possible to suppress the surface on the adhesive layer side of the foaming adhesive sheet from being worn when arranging the foaming adhesive sheet between members. Also, the above pencil hardness may be, for example, 2H or lower. If the above pencil hardness is too high, the adhesion to the base material of the adhesive layer may decrease.

[0041] When adhesive layers are arranged on both sides of the base material, at least one of the surfaces on both sides of the foaming adhesive sheet may have a pencil hardness within the above range. 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. Among them, it is preferable that the pencil hardness of both surfaces of the foaming adhesive sheet is within the above range.

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

[0043] In the foaming adhesive sheet of the present disclosure, the pencil hardness of the surface on the adhesive layer side can be controlled, for example, by the composition of the adhesive layer or the like. Specifically, the pencil hardness can be controlled by the average particle diameter, content, etc. of the foaming agent contained in the adhesive layer. More specifically, by increasing the average particle diameter of the foaming agent, the pencil hardness can be increased. Also, by increasing the content of the foaming agent, the pencil hardness can be increased. Further, for example, by including an inorganic filler in the adhesive layer, the pencil hardness can be increased. Also, for example, by including a component having a rigid structure in the adhesive layer, the pencil hardness can be increased. Specifically, in an adhesive layer containing an epoxy resin and a curing agent, examples of the component having a rigid structure include phenolic resins.

[0044] In the foaming adhesive sheet of the present disclosure, the coefficient of static friction of the surface on the adhesive layer side may be, for example, 0.34 or less, 0.30 or less, or 0.26 or less. Also, the coefficient of static friction may be, for example, 0.16 or more. When the coefficient of static friction of the surface on the adhesive layer side of the foaming adhesive sheet in the present disclosure is 0.30 or less, the slipperiness and insertability can be further improved. Thus, for example, when a foaming adhesive sheet is disposed between members to bond the members together, the foaming adhesive sheet can be smoothly inserted into the gaps between the members or between the members, or the other member can be smoothly inserted into the gap after the foaming adhesive sheet is disposed on one member.

[0045] When adhesive layers are disposed on both sides of the base material, it is sufficient that the coefficient of static friction of at least one of the two surfaces of the foaming adhesive sheet is within the above range. For example, the coefficient of static friction of either one of the surfaces may be within the above range, or the coefficients of static friction of both surfaces may be within the above range. Among these, it is preferable that the coefficients of static friction of both surfaces of the foaming adhesive sheet are within the above range.

[0046] The coefficient of static friction can be determined in accordance with JIS K7125. Details of the method for measuring the coefficient of static friction will be described in the section of Examples below.

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

[0048] The foaming adhesive sheet in 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 foaming adhesive sheet in the present disclosure preferably has high adhesiveness after foaming and curing. The shear strength (adhesive strength) based on JIS K6850 may be, for example, 2.10 MPa or more, 2.40 MPa or more, or 3.0 MPa or more at 23°C. Also, the shear strength (adhesive strength) may be, for example, 0.27 MPa or more, 0.55 MPa or more, or 0.58 MPa or more at 200°C.

[0050] The foaming adhesive sheet in the present disclosure preferably has high electrical insulation 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. Also, the adhesive sheet after foaming and curing preferably has a 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 side of the base material and contains a curable adhesive and a foaming agent.

[0052] (1) Materials of the adhesive layer (a) Curable adhesive As the curable adhesive contained in the adhesive layer in the present disclosure, a curable adhesive generally used for the adhesive layer of a foaming adhesive sheet can be used. Examples of the curable adhesive include a heat-curable adhesive and a photo-curable adhesive. Among them, a heat-curable adhesive is preferable. The heat-curable adhesive is applicable even when the member does not have transparency, such as a member made of metal.

[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, an epoxy resin-based adhesive has a hard and tough cured film and is suitable for adhering to hard material members such as metal or glass members. Since burrs are likely to occur in the processing process of metal members, for example, when inserting a foaming adhesive sheet into the gap between members or inserting the other member into the gap after disposing the foaming adhesive sheet on one member, there is a concern that the foaming adhesive sheet may be caught by the burrs of the metal member, resulting in the lifting or peeling of the adhesive layer from the base material. In contrast, in the present disclosure, since the adhesion of the adhesive layer to the base material is excellent, the occurrence of lifting or peeling of the adhesive layer from the base material as described above can be suppressed. Therefore, when using an epoxy resin-based adhesive, the present disclosure is useful. In addition, epoxy resin-based adhesives generally have excellent heat resistance, insulation properties, chemical resistance, etc., have a small curing shrinkage, and can be used in a wide range of applications.

[0054] Further, when the curable adhesive is an epoxy resin-based adhesive, the curable adhesive preferably further contains an acrylic resin compatible with the epoxy resin. By further using an acrylic resin compatible with the epoxy resin, the toughness of the adhesive layer can be increased, and the adhesion of the adhesive layer to the base material can be improved.

[0055] (i) Epoxy resin The epoxy resin in the present disclosure is a compound having at least one or more epoxy groups or glycidyl groups, which undergoes a cross-linking polymerization reaction and cures when used in combination with a curing agent. The epoxy resin also includes monomers having at least one or more epoxy groups or glycidyl groups.

[0056] As the epoxy resin, an epoxy resin generally used for the adhesive layer of a foaming adhesive sheet can be used. Among them, a curable adhesive preferably contains, as the epoxy resin, a first epoxy resin having a softening temperature of 50 °C or higher and an epoxy equivalent of 5000 g / eq or less, and a second epoxy resin having a softening temperature higher than that of the first epoxy resin and a weight average molecular weight of 20,000 or more. By using the first epoxy resin and the second epoxy resin in combination, a foaming adhesive sheet having good blocking resistance and adhesiveness after foaming and curing can be obtained. Furthermore, the tackiness of the adhesive layer can be reduced, and a foaming adhesive sheet having good slipperiness can be obtained.

[0057] For example, when only improving the adhesiveness after foaming and curing, it is effective to use an epoxy resin with a lower molecular weight (lower epoxy equivalent) than a high molecular weight (high epoxy equivalent) epoxy resin. However, when an epoxy resin with a lower molecular weight (lower epoxy equivalent) is used, for example, when the foaming adhesive sheet is wound into a roll, the epoxy resins with a lower molecular weight (lower epoxy equivalent) assimilate with each other, and blocking is likely to occur.

[0058] On the other hand, when using a first epoxy resin with a relatively low softening temperature (relatively high crystallinity) and a low molecular weight (low epoxy equivalent), the first epoxy resin rapidly melts and changes into a low-viscosity liquid state when the temperature reaches or exceeds the softening temperature. Therefore, it is easy to improve the adhesiveness after foam curing. On the other hand, since the first epoxy resin has a relatively high crystallinity, compared with an epoxy resin having a relatively low crystallinity or an epoxy resin having no crystallinity, the occurrence of blocking can be suppressed. However, when only the first epoxy resin is used, there is a possibility that the effect of suppressing the occurrence of blocking is insufficient, or the tackiness of the adhesive layer may become too high. Therefore, by further using a second epoxy resin with a relatively high softening temperature (relatively low crystallinity) and a high molecular weight, the effect of suppressing the occurrence of blocking can be improved, and the tackiness of the adhesive layer can be kept low.

[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 less. The first epoxy resin has a relatively low softening temperature (relatively high crystallinity) compared with the second epoxy resin described later. Since the first epoxy resin has a relatively high crystallinity and a low molecular weight, it is easy to improve the adhesiveness and blocking resistance after foam curing. In addition, since the first epoxy resin has a low molecular weight, the crosslinking density can be increased, and an adhesive layer with good mechanical strength, chemical resistance, and curability can be obtained. Further, 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 may be 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 JIS K 7234.

[0061] The epoxy equivalent of the first epoxy resin is, for example, 5,000 g / eq or less, may be 3,000 g / eq or less, may be 1,000 g / eq or less, or may be 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, may be 100 g / eq or more, or may be 110 g / eq or more. The epoxy equivalent can be measured by a method conforming to 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 bifunctional epoxy resin, a trifunctional epoxy resin, or a tetrafunctional or higher-functional epoxy resin.

[0063] Also, 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 later. The Mw of the first epoxy resin is, for example, 6,000 or less, may be 4,000 or less, or may be 3,000 or less. On the other hand, the Mw of the first epoxy resin is, for example, 400 or more. Mw is a value in terms of polystyrene when measured by gel permeation chromatography (GPC).

[0064] The first epoxy resin has a melt viscosity at 150°C of, for example, 0.005 Pa·s or more, and 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 foamability may not be obtained. Also, if the melt viscosity of the first epoxy resin is too low (if the crystallinity of the first epoxy resin is too high), the tackiness of the resulting adhesive layer may increase. The reason is presumably that when the melt viscosity of the first epoxy resin is too low (when the crystallinity of the first epoxy resin is too high), its crystallinity significantly decreases when it is compatible with the second epoxy resin or acrylic resin, resulting in a decrease in the Tg of the entire adhesive composition. On the other hand, the first epoxy resin has a melt viscosity at 150°C of, for example, 10 Pa·s or less, and may be 5 Pa·s or less, or 2 Pa·s or less. If the melt viscosity is too high, the uniformity of the resulting adhesive layer may decrease. The melt viscosity can be determined by measuring it in accordance with JIS K6862 using a Brookfield 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 resin and bisphenol F-type epoxy resin, novolak-type epoxy resins such as bisphenol A novolak-type epoxy resin and cresol novolak-type epoxy resin, and modified epoxy resins such as urethane-modified epoxy resin and rubber-modified epoxy resin. Other specific examples include biphenyl-type epoxy resin, stilbene-type epoxy resin, triphenolmethane-type epoxy resin, alkyl-modified triphenolmethane-type epoxy resin, triazine nucleus-containing epoxy resin, dicyclopentadiene-modified phenol-type epoxy resin, naphthalene-type epoxy resin, glycol-type epoxy resin, and pentaerythritol-type epoxy resin. The first epoxy resin may be one type or two or more types.

[0066] The bisphenol A-type epoxy resin can exist in a liquid state at room temperature or a solid state at room temperature depending on the number of repeating units of the bisphenol skeleton. The bisphenol A-type epoxy resin in which the bisphenol skeleton of the main chain is, for example, 2 or more and 10 or less is solid at room temperature. In particular, the bisphenol A-type epoxy resin is preferable in terms of improving heat resistance.

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

[0068]

Chemical formula

[0069] In general formula (1), R 1 is a group represented by C m H 2m (m is 1 or more and 3 or less), R 2 and R 3is, independently of each other, a group represented by C p H 2p+1 (where p is from 1 to 3), and n is from 0 to 10.

[0070] In general formula (1), m in R 1 is preferably 1, that is, R 1 is preferably -CH2-. Similarly, p in R 2 and R 3 is preferably 1, that is, R 2 and R 3 are preferably -CH3. Also, the hydrogen bonded to the benzene ring of general formula (1) may be substituted with other elements or other groups.

[0071] When the resin component contained in the adhesive layer is 100 parts by mass, the content of the first epoxy resin is, for example, 1 part by mass or more, and may be 3 parts by mass or more, 5 parts by mass or more, 10 parts by mass or more, 15 parts by mass or more, 25 parts by mass or more. If the content of the first epoxy resin is too small, the adhesiveness and blocking resistance after foam curing may decrease. On the other hand, when the resin component contained in the adhesive layer is 100 parts by mass, the content of the first epoxy resin is, for example, 90 parts by mass or less, and may be 80 parts by mass or less, 70 parts by mass or less, 60 parts by mass or less, 50 parts by mass or less, 40 parts by mass or less. If the content of the first epoxy resin is too large, the contents of the second epoxy resin and the acrylic resin will be relatively small, and it may not be possible to balance the adhesiveness to the base material of the adhesive layer, the blocking resistance, and the adhesiveness after foam 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. Compared with the above-described first epoxy resin, the second epoxy resin has a relatively high softening temperature (relatively low crystallinity). Since the second epoxy resin has relatively low crystallinity and a high molecular weight, it is easy to improve the blocking resistance. Furthermore, since the second epoxy resin has relatively low crystallinity and a high molecular weight, it can suppress an increase in the adhesiveness (tackiness) due to the first epoxy resin. Also, 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, may be 30,000 or more, and may be 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 larger, smaller, or the same as compared with the epoxy equivalent of the first epoxy resin. The epoxy equivalent of the second epoxy resin is, for example, 4000 g / eq or more, may be 5000 g / eq or more, and may be 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 bifunctional 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 the softening temperature of the first epoxy resin. The difference between the two is, for example, 10°C or more, may be 20°C or more, and may be 30°C or more. The softening temperature of the second epoxy resin is, for example, 80°C or more, and may be 90°C or more. On the other hand, the softening temperature of the second epoxy resin is, for example, 180°C or less.

[0077] The composition of the second epoxy resin is the same as that of the first epoxy resin described above, so the description here is omitted.

[0078] When the resin components contained in the adhesive layer are 100 parts by mass, the content of the second epoxy resin is, for example, 10 parts by mass or more, and may be 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 small, the blocking resistance may decrease. On the other hand, when the resin components contained in the adhesive layer are 100 parts by mass, the content of the second epoxy resin is, for example, 90 parts by mass or less, and may be 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 large, the contents of the first epoxy resin and the acrylic resin will be relatively small, and it may not be possible to balance the adhesion of the adhesive layer to the substrate, the blocking resistance, and the adhesiveness after foaming and curing.

[0079] The ratio of the first epoxy resin to the total of the first epoxy resin and the second epoxy resin is, for example, 5% by mass or more, and may be 10% by mass or more, 15% by mass or more, or 20% by mass or more. On the other hand, the above ratio of the first epoxy resin is, for example, 80% by mass or less, and may be 75% by mass or less, or 60% by mass or less.

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

[0081] (ii) Acrylic resin The acrylic resin in the present disclosure is a resin compatible with an epoxy resin. Since the acrylic resin is compatible with the epoxy resin, it is easy to improve the toughness of the adhesive layer. As a result, the adhesion of the adhesive layer to the substrate can be improved. In addition, by improving the toughness of the adhesive layer, the adhesiveness after foam curing can be improved. Furthermore, it is considered that the acrylic resin acts as a compatibilizer for a foaming agent (for example, a foaming agent whose shell part is a resin of acrylonitrile copolymer), and the adhesiveness after foam curing is improved by uniformly dispersing and foaming. In addition, since the acrylic resin is compatible with the epoxy resin, the hardness of the surface of the adhesive layer can be kept high. On the other hand, if the acrylic resin is incompatible with the epoxy resin, soft parts are formed on the surface of the adhesive layer, so the interface with the adherend becomes less slippery, and the workability may decrease.

[0082] The acrylic resin in the present disclosure is compatible with the epoxy resin. Here, the fact that the acrylic resin is compatible with the epoxy resin can be confirmed, for example, when observing a cross-section of the adhesive layer of the foaming adhesive sheet with a scanning electron microscope (SEM) or a transmission electron microscope (TEM), no micron-sized islands are generated. More specifically, it is preferable that the average particle size of the islands is 1 μm or less. Among them, the average particle size of the islands may be 0.5 μm or less, or may be 0.3 μm or less. It is preferable that the number of samples is large, for example, 100 or more. The observation area is in the range of 100 μm × 100 μm, or when the average thickness of the adhesive layer is 100 μm or less, it is performed in the 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, may be 70,000 or more, and may be 100,000 or more. The first epoxy resin has relatively high crystallinity, and the melt viscosity (or dynamic viscoelasticity) during heating becomes too low, and shrinkage may occur during curing after foaming (from the end of foaming of the foaming agent until the adhesive composition cures). However, by using an acrylic resin having a certain molecular weight, it is possible to suppress the melt viscosity from becoming too low, and shrinkage is less likely to occur during curing after foaming. On the other hand, the Mw of the acrylic resin is, for example, 1,500,000 or less. The weight average molecular weight of the acrylic resin can be measured by GPC (eluent: THF, standard substance: PS, sample: 20 μL, flow rate: 1 mL / min, column temperature: 40 °C).

[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] The acrylic resin may have a storage modulus (E') of 1×10 6 Pa or less at the foaming start temperature. When E' at the start of foaming is low, the fluidity is improved, and good foamability can be obtained. On the other hand, E' at the foaming start temperature is, for example, 1×10 5 Pa or more. The foaming start temperature is a temperature that varies depending on the type of foaming agent. Also, when using two or more types of foaming agents as the foaming agent, the start temperature of the main foaming reaction is defined as the foaming start temperature.

[0086] The acrylic resin has a storage modulus (E') of 1×10 5It may also be Pa or higher. As described above, shrinkage may occur during curing after foaming (from the end of foaming of the foaming agent until the adhesive composition cures). However, since E’ at the curing start temperature is large, shrinkage can be suppressed and good shape retention can be obtained. Note that the curing start temperature is a temperature that varies depending on the type of curing agent. Further, when two or more types of curing agents are used as the curing agent, the start temperature of the main curing reaction is taken as the curing start temperature.

[0087] In addition, the acrylic resin may have an average value of the storage elastic modulus (E’) at 0°C or higher and 100°C or lower of 1×10 6 Pa or higher. By having a high average value of E’ before foaming, good blocking resistance can be obtained. On the other hand, the average value of the storage elastic modulus (E’) at 0°C or higher and 100°C or lower is, for example, 1×10 8 Pa or lower.

[0088] The acrylic resin may have a polar group. Examples of the polar group include an epoxy group, a hydroxyl group, a carboxyl group, a nitrile group, and an amide group.

[0089] The acrylic resin is a homopolymer of an acrylate monomer, may be a mixed component containing two or more of the above homopolymers, may be a copolymer of two or more acrylate monomers, or may be a component containing one or more copolymers. Further, the acrylic resin may be a mixed component of the above homopolymer and the above copolymer. The “acrylic acid” of the acrylate monomer also includes the concept of methacrylic acid. Specifically, the acrylic resin may be a mixture of a polymer of methacrylate and a polymer of acrylate, or may be an acrylate polymer such as acrylate-acrylate, methacrylate-methacrylate, or methacrylate-acrylate. Among them, it is preferable that the acrylic resin contains a copolymer of two or more acrylate monomers ((meth)acrylate copolymer).

[0090] Examples of the monomer components constituting the (meth)acrylate copolymer include, for example, the monomer components described in JP-A-2014-065889. The above monomer components may have the polar groups described above. Examples of the (meth)acrylate 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] As the above (meth)acrylate copolymer, a block copolymer is preferable, and an acrylic block copolymer such as a methacrylate-acrylate copolymer is more preferable. Examples of the (meth)acrylate constituting the acrylic block copolymer include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, and benzyl acrylate. These "acrylic acids" also include "methacrylic acid".

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

[0093] The acrylic copolymer may not have a polar group, or may be a modified product in which a part of the above-described polar group is introduced. Since the above modified product is easily compatible with the epoxy resin, the adhesiveness is further improved.

[0094] Among them, the acrylic resin is preferably a (meth)acrylic acid ester copolymer having a first polymer portion with a glass transition temperature (Tg) of 10°C or lower and a second polymer portion with a glass transition temperature (Tg) of 20°C or higher. Such a (meth)acrylic acid ester copolymer has a first polymer portion that becomes a soft segment and a second polymer portion that becomes a hard segment.

[0095] The manifestation of the above effects can be estimated as follows. By using an acrylic resin having both a soft segment and a hard segment, such as the above (meth)acrylic acid ester copolymer, the hard segment contributes to heat resistance, and the soft segment contributes to toughness or flexibility, so an adhesive layer with 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 above (meth)acrylic acid ester copolymer has compatibility with the epoxy resin. When the first polymer portion has compatibility with the epoxy resin, the flexibility can be enhanced. Also, when the second polymer portion has compatibility with the epoxy resin, the cohesiveness and toughness can be enhanced.

[0097] When one of the first polymer part or the second polymer part has no compatibility with the epoxy resin, the (meth)acrylic acid ester copolymer has a compatible part which is a polymer part having compatibility with the epoxy resin and a non-compatible part which is a polymer part having no compatibility with the epoxy resin. In this case, when the above (meth)acrylic acid ester copolymer is added to the adhesive composition, since the compatible part is compatible with the epoxy resin and the non-compatible part is not compatible with the epoxy resin, fine phase separation occurs. As a result, a fine sea-island structure is formed. The sea-island structure varies depending on the type of the (meth)acrylic acid ester copolymer, the compatibility of the first polymer part and the second polymer part contained in the (meth)acrylic acid ester copolymer, and the presence or absence of modification by introducing a polar group. For example, a sea-island structure in which the cured product of the epoxy resin and the compatible part of the (meth)acrylic acid ester copolymer are the sea and the non-compatible part of the (meth)acrylic acid ester copolymer is the island, a sea-island structure in which the non-compatible part of the (meth)acrylic acid ester copolymer is the sea and the cured product of the epoxy resin and the compatible part of the (meth)acrylic acid ester copolymer are the island, and a sea-island structure in which the (meth)acrylic acid ester copolymer is the sea and the cured product of the epoxy resin is the island can be mentioned. By having such a sea-island structure, it is possible to easily disperse stress, so that interfacial failure can be avoided and excellent adhesiveness can be obtained after foam curing.

[0098] Among these, the (meth)acrylic acid ester copolymer is preferably a block copolymer, and particularly preferably an A-B-A block copolymer having a polymer block A as a compatible part and a polymer block B as an incompatible part. Further, it is preferable that the first polymer part is an incompatible part, the second polymer part is a compatible part, and it is an A-B-A block copolymer having the first polymer part as a polymer block B and the second polymer part as a polymer block A. By using such an A-B-A block copolymer as the acrylic resin, in the case of a sea-island structure in which the cured product of the epoxy resin and the compatible part of the (meth)acrylic acid ester copolymer are the sea and the incompatible part of the (meth)acrylic acid ester copolymer is the island, the island part can be made smaller. Also, in the case of a sea-island structure in which the incompatible part of the (meth)acrylic acid ester copolymer is the sea, the cured product of the epoxy resin and the compatible part of the (meth)acrylic acid ester copolymer are the island, or in the case of a sea-island structure in which the (meth)acrylic acid ester copolymer is the sea and the cured product of the epoxy resin is the island, the sea part can be made smaller.

[0099] Further, 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 part or the second polymer part.

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

[0101] Note that the Tg of the first polymer part can be obtained by calculation using the following formula based on the Tg (K) of each homopolymer described in "POLYMER HANDBOOK 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 generally published 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 part described later.

[0102] The first polymer part contained in the above (meth)acrylate copolymer may be a homopolymer or a copolymer, but among them, a homopolymer is preferably used. The monomer components and polymer components constituting the first polymer part may be any monomer components and polymer components that can obtain a first polymer part with a Tg within a predetermined range. For example, acrylate monomers such as butyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate, methyl acrylate, and other monomers such as vinyl acetate, acetal, urethane, polar group-containing monomers containing the above-mentioned polar groups, and copolymers such as EVA can be mentioned.

[0103] The Tg of the second polymer part contained in the above (meth)acrylate 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 especially within the range of 40 °C or higher and 150 °C or lower.

[0104] Also, the second polymer part contained in the above (meth)acrylate copolymer may be a homopolymer or a copolymer, but among them, a homopolymer is preferably used. The monomer component constituting the second polymer part may be any monomer component that can obtain a second polymer part with a Tg within a predetermined range. For example, acrylate monomers such as methyl methacrylate, and other monomers such as acrylamide, styrene, vinyl chloride, amide, acrylonitrile, cellulose acetate, phenol, urethane, vinylidene chloride, methylene chloride, methacrylonitrile, and polar group-containing monomers containing the above-mentioned polar groups can be mentioned.

[0105] Specific examples of the (meth)acrylic acid ester copolymer having the above-mentioned first polymer part and second polymer part include the above-mentioned MMA-BA-MMA copolymer.

[0106] When the resin component contained in the adhesive layer is 100 parts by mass, the content of the acrylic resin is, for example, 1 part by mass or more, and may be 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 small, the adhesion of the adhesive layer to the base material and the adhesiveness after foam curing may decrease. On the other hand, when the resin component contained in the adhesive layer is 100 parts by mass, the content of the acrylic resin is, for example, 60 parts by mass or less, and may be 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 large, the contents of the first epoxy resin and the second epoxy resin will be relatively small, and it may not be possible to balance the adhesion of the adhesive layer to the base material, the blocking resistance, and the adhesiveness after foam curing.

[0107] (iii) Curing agent In the present disclosure, the curing agent is appropriately selected according to the type of the curable adhesive. When the curable adhesive is, for example, an epoxy resin-based adhesive, as the curing agent, a curing agent generally used for epoxy resin-based adhesives can be used. 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) compared to a curing agent that is liquid at 23°C. Further, the curing agent may be a latent curing agent. Also, the curing agent may be a curing agent in which a curing reaction occurs by heat, or a curing agent in which a curing reaction occurs by light. In the present disclosure, the curing agent may be used alone or in combination of two or more.

[0108] The reaction start temperature of the curing agent is, for example, 110°C or higher, and may be 130°C or higher. If the reaction start temperature is too low, the reaction may start prematurely, and curing may occur in a state where the flexibility and fluidity of the resin component are low, making it difficult to achieve uniform curing. On the other hand, the reaction start temperature of the curing agent is, for example, 200°C or lower. If the reaction start temperature is too high, the resin component may deteriorate. In addition, when using a resin with high heat resistance such as a phenolic resin in addition to the epoxy resin, since the deterioration of the resin component is less, the reaction start temperature of the curing agent may be, for example, 300°C or lower. The reaction start temperature of the curing agent can be determined by differential scanning calorimetry (DSC).

[0109] Specific examples of the curing agent include imidazole-based curing agents, phenolic 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, 2-phenylimidazole, carboxylates of imidazole compounds, and adducts with epoxy compounds. Further, the imidazole-based curing agent preferably has a hydroxyl group. Since it crystallizes by hydrogen bonding between hydroxyl groups, the reaction start temperature tends to be high.

[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 to the base material of the adhesive layer, etc., a phenolic novolac resin with a Tg of 110°C or lower is particularly preferred. In addition, a phenolic curing agent and an imidazole-based curing agent may be used in combination. In that case, it is preferable to use the imidazole-based curing agent as a curing catalyst.

[0112] In the adhesive layer, heat resistance can be improved by containing a phenol resin. However, on the other hand, toughness decreases, and there is concern that the adhesive layer may lift or peel off from the base material when, for example, the foamed adhesive sheet is bent or cut. In contrast, in the present disclosure, since the adhesion of the adhesive layer to the base material is excellent, even when the adhesive layer contains a phenol resin, it is possible to suppress the occurrence of lifting or peeling of the adhesive layer from the base material during bending. As a result, it is possible to obtain a foamed adhesive sheet that achieves both an improvement in heat resistance and suppression of lifting or peeling of the adhesive layer from the base material during bending.

[0113] From the viewpoint of heat resistance, a biphenyl type is preferable for the phenol resin. Further, the phenol resin may be a resin in which the phenol nucleus is modified. By modifying the phenol nucleus, for example, heat resistance can be further improved.

[0114] On the other hand, when the adhesive layer does not contain a phenol resin, it is possible to effectively suppress the occurrence of lifting or peeling of the adhesive layer from the base material during bending or cutting, and it is possible to improve the adhesion of the adhesive layer to the base material.

[0115] Examples of the amine-based curing agent 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 polyamideamines. Further, as the amine-based curing agent, dicyandiamide-based curing agents such as dicyandiamide (DICY), organic acid dihydrazide-based curing agents, amine adduct-based curing agents, and ketimine-based curing agents can be used.

[0116] Examples of the acid anhydride-based curing agent 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] Examples of the isocyanate-based curing agent include blocked isocyanate.

[0118] Examples of the thiol-based curing agent include ester bond type thiol compounds, aliphatic ether bond type thiol compounds, and aromatic ether bond type thiol compounds.

[0119] When the content of the curing agent is based on 100 parts by mass of the resin component contained in the adhesive layer, it is, for example, 1 part by mass or more and 40 parts by mass or less. For example, when an imidazole-based curing agent is mainly used as the curing agent, it is preferable that the content of the curing agent is 1 part by mass or more and 15 parts by mass or less when the resin component contained in the adhesive layer is 100 parts by mass. On the other hand, when a phenol-based curing agent is mainly used as the curing agent, it is preferable that the content of the curing agent is 5 parts by mass or more and 40 parts by mass or less when the resin component contained in the adhesive layer is 100 parts by mass. Note that using an imidazole-based curing agent or a phenol-based curing agent as the main component of the curing agent means that the mass ratio of the imidazole-based curing agent or the phenol-based curing agent in the curing agent is the highest.

[0120] (b) Foaming agent As the foaming agent in the present disclosure, a foaming agent generally used in the adhesive layer of a foamable adhesive sheet can be used. Further, the foaming agent may be a foaming agent that causes a foaming reaction by heat or a foaming agent that causes a foaming reaction by light.

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

[0122] Incidentally, the softening temperature of the main component of a curable adhesive such as an epoxy resin can be measured using the ring and ball softening temperature test method defined in JIS K 2207.

[0123] Examples of the foaming agent include organic foaming agents and inorganic foaming agents. Examples of the organic foaming agent include azo foaming agents such as azodicarbonamide (ADCA), azobisformamide, and azobisisobutyronitrile, fluorinated alkane-based foaming agents such as trichloromonofluoromethane, hydrazine-based foaming agents such as paratoluenesulfonyl hydrazide, semicarbazide-based foaming agents such as p-toluenesulfonyl semicarbazide, triazole-based foaming agents such as 5-morpholyl-1,2,3,4-thiatriazole, and N-nitroso-based foaming agents such as N,N-dinitrosoterephthalamide. On the other hand, examples of the inorganic foaming agent include ammonium carbonate, ammonium bicarbonate, ammonium nitrite, ammonium borohydride, and azides.

[0124] Also, a microcapsule-type foaming agent may be used as the foaming agent. The microcapsule-type foaming agent preferably has a heat-expandable agent such as a hydrocarbon as the core and a resin such as an acrylonitrile copolymer as the shell.

[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 surface on the adhesive layer side of the foamable adhesive sheet can be increased, and the coefficient of static friction of the surface on the adhesive layer side of the foamable adhesive sheet can be decreased, 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 be, for example, 13 μm or more, or may be 17 μm or more. Also, the average particle size of the foaming agent may be, for example, 21 μm or less, or may be 20 μm or less. When the average particle size of the foaming agent is within the above range, the adhesiveness can be enhanced even when the gap between the members is relatively wide. The reason for this is not clear, but it is presumed as follows. That is, when the average particle size of the foaming agent is too small, the expansion ratio of the adhesive layer tends to be small. Therefore, good adhesiveness can be obtained when the gap between the members is narrow, whereas the adhesiveness may decrease when the gap between the members is wide. Also, when the average particle size of the foaming agent is small, increasing the content of the foaming agent can increase the expansion ratio of the adhesive layer. However, when the content of the foaming agent is increased, the content of the curable adhesive relatively decreases. Therefore, in the adhesive layer after foaming and curing, the wall between the bubbles becomes thin, the cohesive force decreases, and it is considered that the adhesiveness decreases when the gap between the members is wide. On the other hand, when the average particle size of the foaming agent is too large, the bubbles after foaming become large. Therefore, in the adhesive layer after foaming and curing, the wall between the bubbles becomes thin, the cohesive force decreases, and it is considered that the adhesiveness decreases even when the gap between the members is narrow. In contrast, when the average particle size of the foaming agent is within the above range, the expansion ratio of the adhesive layer is not too small, so the gap between the members can be sufficiently filled. Also, since the bubbles after foaming are not too large, the wall between the bubbles in the adhesive layer after foaming and curing becomes thick, and the contact area between the wall between the bubbles and the members in the adhesive layer after foaming and curing can be increased. As a result, it is presumed that good adhesiveness can be obtained not only when the gap between the members is narrow but also when the gap between the members is wide.

[0127] The average particle size of the foaming agent is the particle size at the 50% integrated value in the particle size distribution determined by the laser diffraction scattering method. When measuring the average particle size of the foaming agent, the adhesive layer is dissolved in a solvent to separate the foaming agent. The solvent is not particularly limited as long as it can dissolve components other than the foaming agent contained in the adhesive layer, and is appropriately selected according to the type of curable adhesive contained in the adhesive layer, etc. For example, the 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] When the resin component contained in the adhesive layer is 100 parts by mass, the content of the foaming agent is, for example, 0.5 parts by mass or more, and may be 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. On the other hand, the content of the foaming agent is, for example, 25 parts by mass or less, and may be 20 parts by mass or less, 15 parts by mass or less, with respect to 100 parts by mass of the resin component contained in the adhesive layer. If the content of the foaming agent is too small, the coefficient of static friction of the surface on the adhesive layer side of the foaming adhesive sheet may increase, or the pencil hardness of the surface on the adhesive layer side of the foaming adhesive sheet may decrease, resulting in a possible decrease in slipperiness and insertability. Also, if the content of the foaming agent is too small, the foaming ratio of the adhesive layer may be small, and the adhesiveness may decrease when the gap between members is wide. On the other hand, if the content of the foaming agent is too large, the content of the curable adhesive will be relatively small, so the wall between bubbles in the adhesive layer after foaming and curing will be thin, and the cohesive force will decrease, resulting in a possible decrease in adhesiveness. When the average particle size of the foaming agent is 10 μm or more and 24 μm or less, by setting the content of the foaming agent to 3 parts by mass or more and 25 parts by mass or less with respect to 100 parts by mass of the resin component contained in the adhesive layer, the adhesiveness in the case where the gap between members is narrow and in the case where the gap between members is wide can be further improved.

[0129] (c) Other components In the present disclosure, when the curable adhesive in the adhesive layer is an epoxy resin-based adhesive, for example, as the resin component, it may contain only an epoxy resin and an acrylic resin, or may further contain other resins. Examples of the other resins include urethane resins.

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

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

[0132] The adhesive layer may optionally contain, 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, or 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 phenolic antioxidants and sulfur-based antioxidants.

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

[0134] Here, the foaming ratio can be obtained by the following formula. Foaming ratio (times) = Thickness of the adhesive layer after foaming and curing / Thickness of the adhesive layer before foaming and curing

[0135] The average thickness of the adhesive layer is not particularly limited, but it is preferably equal to or greater than the average particle diameter of the foaming agent, for example, 10 μm or more, may be 15 μm or more, or may be 20 μm or more. If the adhesive layer is too thin, it may not be possible to sufficiently obtain the adhesion to the base material and the adhesiveness after foaming and curing. On the other hand, the average thickness of the adhesive layer is, for example, 200 μm or less, may be 150 μm or less, or may be 100 μm or less.

[0136] Here, the average thickness of the adhesive layer can be the average value of the thicknesses of any 10 locations obtained by measuring from the cross-section in the thickness direction of the foaming adhesive sheet observed by a transmission electron microscope (TEM), a scanning electron microscope (SEM), or a scanning transmission electron microscope (STEM). Note that the same can be applied to the measurement method of the average thickness of other layers of the foaming adhesive sheet.

[0137] The adhesive layer may be a continuous layer or a discontinuous layer. Examples of the discontinuous layer include patterns such as stripes and dots. Also, the surface of the adhesive layer may have an uneven shape such as an emboss.

[0138] The subsequent layer can be formed, for example, by applying an adhesive composition containing the above-mentioned curable adhesive and foaming agent, etc., and removing the solvent. Examples of the coating method include roll coating, reverse roll coating, transfer roll coating, gravure coating, gravure reverse coating, comma coating, rod coating, blade coating, bar coating, wire bar coating, die coating, lip coating, dip coating, etc.

[0139] The adhesive composition may or may not contain a solvent. In addition, the solvent in this specification has a broad meaning including not only a strict solvent (a solvent that dissolves a solute) but also a dispersion medium. Further, the solvent contained in the adhesive composition volatilizes and is 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 respective components and kneading and dispersing them as necessary. As the mixing and dispersing methods, general kneading and dispersing machines, for example, two-roll mills, three-roll mills, pebble mills, trommel mills, Szegvari attritors, high-speed impeller dispersers, high-speed stone mills, high-speed impact mills, despers, high-speed mixers, ribbon blenders, coneyders, intensive mixers, tumblers, blenders, dispersers, homogenizers, ultrasonic dispersers can be applied.

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

[0142] Examples of the substrate include a resin substrate and a non-woven fabric.

[0143] Examples of the resin contained in the resin substrate include polyester resins such as polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate (PEN), and aromatic polyesters; polycarbonate; polyarylate; polyurethane; polyamide resins such as polyamide and polyether amide; polyimide resins such as polyimide, polyether imide, and polyamide imide; polysulfone resins such as polysulfone and polyether sulfone; polyether ketone resins such as polyether ketone and polyether ether ketone; polyphenylene sulfide (PPS); modified polyphenylene oxide, etc. The glass transition temperature of the resin is, for example, 80°C or higher, may be 140°C or higher, and may be 200°C or higher. Also, a liquid crystal polymer (LCP) may be used as the resin.

[0144] Examples of the nonwoven fabric include nonwoven fabrics containing fibers such as cellulose fibers, polyester fibers, nylon fibers, aramid fibers, polyphenylene sulfide fibers, liquid crystal polymer fibers, glass fibers, metal fibers, and carbon fibers.

[0145] Among them, it is preferable that the substrate 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 foaming adhesive sheet by heating. Also, polyphenylene sulfide and polyethylene naphthalate have high insulation properties, and for example, members can be insulated from each other by the adhesive sheet after foaming and curing. Also, polyphenylene sulfide and polyethylene naphthalate generally have poor wettability with adhesives and poor adhesion to the adhesive layer, but in the present disclosure, the adhesion of the adhesive layer to the substrate can be improved. Therefore, a foaming adhesive sheet with balanced heat resistance, insulation properties, and adhesion between the substrate and the adhesive layer can be obtained.

[0146] In order to enhance the adhesion to the adhesive layer, the surface of the base material on which the adhesive layer is disposed may be subjected to surface treatment. Examples of the surface treatment include corona treatment, blast treatment, plasma treatment, flame treatment, ito treatment, hydrophilization treatment with fluorine gas, and the like. Among these surface treatments, blast treatment is preferable. When the adhesive layer penetrates into the fine irregularities on the blasted surface of the base material, the adhesion between the base material and the adhesive layer is increased, that is, an anchor effect is obtained. In addition, the blast treatment is a roughening treatment, and it is considered that the adhesion between the base material and the adhesive layer is more stable compared to surface activation treatments such as corona treatment.

[0147] Further, a surface treatment layer may be disposed on the surface of the base material on which the adhesive layer is disposed. Examples of the surface treatment layer include a silicon oxide film and the like. Examples of the method for forming the surface treatment layer include CVD method, PVD method, and the like.

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

[0149] 4. Intermediate layer The foamable adhesive sheet in the present disclosure preferably has an intermediate layer between the base material and the adhesive layer. By disposing the intermediate layer, the adhesion of the adhesive layer to the base material can be further improved. Furthermore, by disposing the intermediate layer, for example, when the foamable adhesive sheet is bent, the stress applied to the bent portion can be relaxed, or when the foamable adhesive sheet is cut, the stress applied to the cut portion can be relaxed. As a result, peeling or lifting of the adhesive layer from the base material can be effectively suppressed not only when the foamable adhesive sheet is bent but also when it is cut.

[0150] For example, in the foaming adhesive sheet 10 shown in FIG. 3, the base material 2, the intermediate layer 3, and the adhesive layer 1 are arranged in this order in the thickness direction. Further, in the foaming adhesive sheet 10 shown in FIG. 4, the first adhesive layer 1a is arranged on one surface side of the base material 2, and the second adhesive layer 1b is arranged on the other surface side of the base material 2. A first intermediate layer 3a is arranged between the base material 2 and the first adhesive layer 1a, and a second intermediate layer 3b is arranged between the base material 2 and the second adhesive layer 1b. In FIG. 4, the foaming adhesive sheet 10 has both the first intermediate layer 3a and the second intermediate layer 3b, but it may have only one of them.

[0151] When adhesive layers are arranged on both surfaces of the base material, an intermediate layer may be arranged between the base material and at least one of the adhesive layers. For example, the intermediate layer may be arranged only between the base material and one of the adhesive layers, or the intermediate layer may be arranged between the base material and both of the adhesive layers. Among them, it is preferable that the intermediate layer is arranged between the base material and both of the adhesive layers.

[0152] The material contained in the intermediate layer is not particularly limited as long as it can enhance the adhesion between the base material and the adhesive layer and can relieve stress, and is appropriately selected according to the materials of the base material and the adhesive layer, etc. For example, polyester, polyvinyl chloride, polyvinyl acetate, polyurethane, a polymer obtained by copolymerizing at least two or more of them, a crosslinked product thereof, and a mixture thereof, etc. may be mentioned.

[0153] The crosslinked product is a crosslinked product obtained by crosslinking the above resin with a curing agent. Examples of the curing agent include isocyanate-based curing agents. Further, for example, when the reaction group / NCO equivalent is 1, it is preferable to add the isocyanate-based curing agent to the resin at a ratio of 0.5% by mass or more and 20% by mass or less.

[0154] Among them, the intermediate layer preferably contains a crosslinked resin. The crosslinked resin refers to a resin that does not melt even at high temperatures. Thereby, the adhesive strength at high temperatures, that is, the heat resistance, can be improved. Further, when the crosslinked resin is crosslinked by, for example, an isocyanate-based curing agent, the flexibility of the intermediate layer becomes good, and cracking of the adhesive layer, lifting, and peeling of the adhesive layer from the base material during bending of the foaming adhesive sheet can be suppressed.

[0155] Examples of the crosslinked resin include the above-mentioned crosslinked products. Among them, the intermediate layer preferably contains a crosslinked polyester resin. When the intermediate layer contains a crosslinked polyester resin, the adhesion between the base material and the adhesive layer tends to be high. In particular, when the base material contains polyphenylene sulfide (PPS) or polyethylene naphthalate (PEN), and the adhesive layer contains an epoxy resin-based adhesive as a curable adhesive, the adhesion between the base material and the adhesive layer can be improved by the intermediate layer containing a crosslinked polyester resin.

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

[0157] The average thickness of the intermediate layer is not particularly limited as long as the peel strength on the side where the adhesive layer of the foaming adhesive sheet measured by the SAICAS method can be made a predetermined value or more. For example, it is 0.1 μm or more, and it may be 0.5 μm or more, or may be 1 μm or more. If the intermediate layer is too thin, the effect of suppressing the peeling of the adhesive layer from the base material during bending and cutting of the foaming adhesive sheet may not be sufficiently obtained. On the other hand, the average thickness of the intermediate layer is, for example, 4 μm or less, and may be 3.5 μm or less. Since the intermediate layer itself usually does not have high heat resistance, if the intermediate layer is too thick, the heat resistance (adhesive strength at high temperature) may decrease. When using a base material with relatively high heat resistance such as polyethylene naphthalate (PEN) or polyphenylene sulfide (PPS), by setting the average thickness of the intermediate layer to 0.5 μm or more and 4 μm or less, the adhesion and heat resistance can be further improved.

[0158] The intermediate layer can be formed, for example, by applying a resin composition and removing the solvent. Examples of the coating method include roll coating, reverse roll coating, transfer roll coating, gravure coating, gravure reverse coating, comma coating, rod coating, blade coating, bar coating, wire bar coating, die coating, lip coating, and dip coating.

[0159] 5. Foaming Adhesive Sheet The average thickness of the foaming adhesive sheet in the present disclosure is, for example, 10 μm or more, and may be 20 μm or more. On the other hand, the average thickness of the foaming adhesive sheet is, for example, 1000 μm or less, and may be 200 μm or less.

[0160] The use of the foaming adhesive sheet in the present disclosure is not particularly limited. The foaming adhesive sheet in the present disclosure can be used, for example, when an foaming adhesive sheet is disposed between members and then the foaming adhesive sheet is foamed and cured to bond the members together. Further, in the present disclosure, when the foaming adhesive sheet is disposed between members, even if there are burrs on the members, the occurrence of lifting or peeling of the adhesive layer from the base material can be suppressed. Therefore, it can be used when bonding metal members or resin members that are likely to generate burrs during processing. Among them, the foaming adhesive sheet in the present disclosure can be preferably used when the foaming adhesive sheet is disposed between metal members to bond the members together.

[0161] 6. Method for manufacturing the foaming adhesive sheet The method for manufacturing the foaming adhesive sheet in the present disclosure is not particularly limited. For example, a method of forming an adhesive layer by applying and drying the above-described adhesive composition on one surface side of the base material can be mentioned. When forming a first adhesive layer on one surface side of the base material and a second adhesive layer on the other surface side of the base material, the first adhesive layer and the second adhesive layer may be formed sequentially or simultaneously. By forming the second adhesive layer after forming the first adhesive layer, the first adhesive layer can be further dried, and the peeling force on the surface side of the first adhesive layer of the foaming adhesive sheet can be made higher than the peeling force on the surface side of the second adhesive layer.

[0162] B. Method for manufacturing an article The method for manufacturing an article in the present disclosure includes an arranging step of arranging the above-described foaming adhesive sheet between a first member and a second member, and an adhering step of foaming and curing the foaming adhesive sheet to bond the first member and the second member.

[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 foaming adhesive sheet 10 is disposed between a first member 20a and a second member 20b. Next, as shown in FIG. 5(b), the foaming adhesive sheet 10 is foamed and cured, for example, by heating. The first member 20a and the second member 20b are adhered (joined) by the adhesive sheet 11 after foaming and curing. Thereby, an article 100 in which the adhesive sheet 11 is disposed between the first member 20a and the second member 20b is obtained.

[0164] In the method for manufacturing an article according to the present disclosure, since the above-described foaming adhesive sheet is used, the adhesion to the base material of the adhesive layer is excellent, and even when there is a burr on at least one of the first member and the second member, when inserting the foaming adhesive sheet into the gap of one member or the gap between two members, or when inserting the other member into the gap after disposing the foaming adhesive sheet on one member, it is possible to suppress the lifting or peeling of the adhesive layer from the base material. Further, when disposing the foaming adhesive sheet between the first member and the second member, even when the foaming adhesive sheet is bent in advance, it is also possible to suppress the lifting or peeling of the adhesive layer from the base material. Therefore, an article having good adhesion between the first member and the second member can be obtained.

[0165] Hereinafter, the method for manufacturing an article according to the present disclosure will be described.

[0166] 1. Foaming Adhesive Sheet In the method for manufacturing an article according to the present disclosure, as the foaming adhesive sheet, the above-described foaming adhesive sheet is used, in which the adhesive layer and the base material are arranged in this order, and the peel force measured by the SAICAS method on the surface side where the adhesive layer is arranged is 2.0 N or more can be used. Further, as the foaming adhesive sheet, one having a first adhesive layer and a second adhesive layer as the adhesive layer, and the first adhesive layer, the base material, and the second adhesive layer are arranged in this order in the thickness direction can be used. In this case, it is sufficient that the peel force of at least one of the surface side where the first adhesive layer of the foaming adhesive sheet is arranged and the surface side where the second adhesive layer is arranged measured by the SAICAS method is 2.0 N or more.

[0167] Note that since the details of the foaming adhesive sheet are described in the section of "A. Foaming Adhesive Sheet" above, the description here is omitted.

[0168] 2. Arrangement step In the arrangement step in the present disclosure, the method of arranging the foaming adhesive sheet between the first member and the second member is not particularly limited. For example, a method of inserting the foaming adhesive sheet into the gap between the first member and the second member, or a method of arranging the foaming adhesive sheet on the first member and then inserting the second member into the gap after arranging the foaming adhesive sheet on the first member can be mentioned.

[0169] 3. Adhesion step In the adhesion step in the present disclosure, examples of the method of foaming and curing the foaming adhesive sheet include heating or light irradiation. Among them, it is preferable to foam and cure the foaming adhesive sheet by heating. The method by heating is applicable even when the first member and the second member do not have transparency, such as in the case of a member made of metal.

[0170] The heating conditions are appropriately set according to the type of the curable adhesive and the foaming agent contained in the adhesive layer, the type of the base material, etc. The heating temperature can be, for example, 130°C or higher and 200°C or lower. Also, the heating time can be, for example, 3 minutes or longer and 3 hours or shorter.

[0171] Note that the present disclosure is not limited to the above embodiments. The above embodiments are examples, and those having a configuration substantially the same as the technical idea described in the claims in the present disclosure and exhibiting the same operational effects are included in the technical scope of the present disclosure regardless of what they are.

Example

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

[0173] Also, as the base material, a polyphenylene sulfide film (PPS film, manufactured by Toray Industries, Inc., Trellina 100-3A30, thickness 100 μm) with high insulation was used, and corona treatment was performed so that the surface tension would be 70 dynes or more. On one surface of this base material, the above adhesive composition was applied using an applicator so that the thickness after coating would be 45 μm. Then, it was dried in an oven at 100°C for 3 minutes to form a first adhesive layer. Further, in the same manner as the first adhesive layer, a second adhesive layer was formed on the other surface of the base material. Thereby, a foaming adhesive sheet having a first adhesive layer and a second adhesive layer formed on both surfaces of the base material was obtained.

[0174] [Example 2] A foaming adhesive sheet was produced in the same manner as in Example 1, except that the base material was subjected to blasting treatment so that the arithmetic mean roughness would be Ra 0.64 μm.

[0175] [Comparative Example 1] A foaming 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 foaming 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 as the base material, a polyphenylene sulfide film (PPS film, thickness 100 μm, arithmetic mean roughness Ra 0.64 μm) subjected to the same blasting treatment as in Example 2 was used.

[0177] [Example 4] As the base material, a highly insulating polyphenylene sulfide film (PPS film, thickness 100 μm) similar to that of Example 1 was prepared. Also, 2 parts by mass of a curing agent (polyisocyanate) was blended with 100 parts by mass of a mixture of polyester and polyvinyl chloride, and further diluted with methyl ethyl ketone (MEK) so that the solid content became 15% by mass to prepare a resin composition. The resin composition was applied to one surface of the base material with 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. Further, a second intermediate layer was formed on the other surface of the base material 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. As a result, a foaming adhesive sheet in which the first adhesive layer, the first intermediate layer, the base material, the second intermediate layer, and the second adhesive layer were arranged in this order was obtained.

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

[0180] [Example 5] Using the same adhesive composition as in Example 3, and as the base material, a highly insulating polyethylene naphthalate film (PEN film, thickness 100 μm) similar to that of Comparative Example 2 was used, and a foaming adhesive sheet was produced in the same manner as in Example 1, except that blasting treatment was performed so that the arithmetic mean roughness Ra became 0.77 μm.

[0181] [Example 6] A foaming adhesive sheet was produced in the same manner as in Example 4, except that a highly insulating polyethylene naphthalate film (PEN film, thickness 100 μm) similar to that of Comparative Example 2 was used as the base material.

[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] As the base material, a polyphenylene sulfide film (PPS film, manufactured by Toray Industries, Inc., Torelina 115-3F00, thickness 115 μm) with high insulation was used. Further, 15 parts by mass of a curing agent (polyisocyanate) and 0.3 parts by mass of a catalyst (trisdimethylaminomethylphenol) were blended with respect to 100 parts by mass of the polyester polymer, and further diluted with methyl ethyl ketone (MEK) so that the solid content became 15% by mass to prepare a resin composition. The resin composition was applied to one surface of the base material with 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. Further, a second intermediate layer was formed on the other surface of the base material 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 to the base material using an applicator so that the thickness after coating was 38 μm. Then, it was dried in an oven at 100°C for 3 minutes to form a first adhesive layer. Further, a second adhesive layer was formed on the surface of the second intermediate layer opposite to the base material in the same manner as the first adhesive layer. Thus, a foamable adhesive sheet in which the first adhesive layer, the first intermediate layer, the base material, the second intermediate layer, and the second adhesive layer were arranged in this order was obtained.

[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] [Evaluation 1] (Peeling force) The peeling force on the side where the first adhesive layer of the foaming adhesive sheet is disposed and the peeling force on the side where the second adhesive layer is disposed were each measured using a surface interface cutting test apparatus. First, the foaming adhesive sheet was cut into 5 cm × 5 cm, and this foaming adhesive sheet was fixed to a vacuum holder, and the adhesive layer was cut with a cutting blade. Specifically, first, after cutting the adhesive layer obliquely from one surface of the foaming adhesive sheet with a cutting blade, when the force applied to the cutting blade changed greatly and the horizontal force applied to the cutting blade decreased for the first time, cutting was performed only in the horizontal direction with respect to the foaming adhesive sheet. Then, the horizontal force applied to the cutting blade during cutting was measured. The horizontal force applied to the cutting blade when the cutting blade is cutting only in the horizontal direction with respect to the foaming adhesive sheet corresponds to the above peeling force. The measurement of the above peeling force was performed on the surface on the first adhesive layer side and the surface on the second adhesive layer side of the foaming adhesive sheet, respectively. As the surface interface cutting test apparatus, SAICAS DN-GS type manufactured by DYNAFLOW WINTERS was used. As the cutting blade, a cutting blade made of a boron nitride alloy, having a blade width of 1.0 mm, a rake angle of 20°, and a clearance angle of 10° was used. Also, the measurement conditions were as follows. Measurement mode: Constant speed mode Horizontal speed: 2 μm / sec Vertical speed: 0.1 μm / sec Temperature: 23°C

[0188] (L-shaped bending test) The foaming adhesive sheet was cut out into 3 cm × 3 cm, and this foaming adhesive sheet was bent at 90° in half so that the surface on which the adhesive layer to be tested was disposed was inside and the size became 3 cm × 1.5 cm. Then, it was confirmed whether or not the adhesive layer floated from the base material. The adhesion by the L-shaped bending test was evaluated according to the following criteria. A: There is no floating in the bent part B: There is floating in the bent part

[0189] (Cross-shaped bending test) The foaming adhesive sheet was cut into pieces of 3 cm × 3 cm. This foaming adhesive sheet was folded 180° in half so that the surface on which the adhesive layer to be tested was located faced inward and the size became 3 cm × 1.5 cm. Subsequently, the foaming adhesive sheet in this state was further folded 180° in half so that the size became 1.5 cm × 1.5 cm. Then, it was confirmed whether the adhesive layer floated from the base material. The adhesion by the cross-folding test was evaluated according to the following criteria. A: There is no lifting at the folding part B: There is lifting at the folding part

[0190] (Cutter cutting test) The surface of the foaming adhesive sheet on which the adhesive layer to be tested was located was cut at a speed of 20 mm / s or more and 100 mm / s or less for a length of 100 mm with a cutter (manufactured by Alpha Corporation, cutter knife A plus). It was confirmed whether the adhesive layer floated from the base material on the cut surface. The adhesion by the cutter cutting test was evaluated according to the following criteria. A: There is no lifting at the cut surface at all B: There is some lifting at the cut surface C: There is complete lifting at the cut surface

[0191] (Adhesive force) The foaming adhesive sheet was cut into a width of 24 mm and a length of 300 mm. One side of the adhesive layer surface of this foaming adhesive sheet was bonded to a stainless steel plate (SUS304) using a manual roller. Then, using a tensile testing machine (manufactured by A&D Company, Tensilon RTF1150), under the conditions compliant with JIS Z0237:2009 (Test methods for adhesive tapes and adhesive sheets) and Method 1 of the test method for adhesive force (temperature 23°C, humidity 50%, test method of peeling the tape and sheet at 180° with respect to the stainless steel test plate) (tensile speed: 300 mm / min, peeling distance: 150 mm, peeling angle: 180°), the adhesive force (N / 25 mm) with respect to the stainless steel plate surface was measured.

[0192]

Table 1

[0193]

Table 2

[0194] As shown in Table 1, in Examples 1 to 9, both the adhesion by the L-bending test and the adhesion by the cross-bending test were good. Further, in Examples 2, 3, 5, and 7, since the base material was subjected to a blasting treatment, the adhesion by the cutter cutting test was also good. Furthermore, in Examples 4, 6, 8, and 9, since an intermediate layer was disposed between the base material and the adhesive layer, the adhesion by the cutter cutting test was excellent. On the other hand, in Comparative Examples 1 to 3, since the peel force measured by the SAICAS method was small, both the adhesion by the L-bending test and the adhesion by the cross-bending test were inferior. Incidentally, the test results on the surface side of the first adhesive layer and the test results on the surface side of the second adhesive layer of the foaming adhesive sheet were the same.

[0195] [Examples 10 to 23] First, an adhesive composition having the composition (mass %) shown in Table 3 below was prepared. Details of each material other than the foaming agent described in Table 3 are as shown in Table 2. As the foaming agent, the following thermal foaming agents 1 to 8 were used. · Thermal foaming agent 1: Thermally expandable microcapsules, average particle diameter 7 μm, expansion start temperature 120 to 145°C, maximum expansion temperature 155 to 175°C, core: hydrocarbon, shell: thermoplastic polymer · Thermal foaming agent 2: Thermally expandable microcapsules, average particle diameter 13 μm, expansion start temperature 123 to 133°C, maximum expansion temperature 168 to 178°C, core: hydrocarbon, shell: thermoplastic polymer · Thermal foaming agent 3: Thermally expandable microcapsules, average particle diameter 17 μm, expansion start temperature 120 to 130°C, maximum expansion temperature 160 to 170°C, core: hydrocarbon, shell: acrylonitrile copolymer · Thermal foaming agent 4: Thermally expandable microcapsules, average particle diameter 20 μm, expansion start temperature 115 to 125°C, maximum expansion temperature 155 to 165°C, core: hydrocarbon, shell: thermoplastic polymer · Thermal foaming 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 foaming agent 6: Thermally expandable microcapsules, average particle size 25 μm, expansion start temperature 125 - 135 °C, maximum expansion temperature 165 - 180 °C, core: hydrocarbon, shell: thermoplastic polymer · Thermal foaming 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 foaming 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] As the base material, a polyphenylene sulfide film (PPS film, manufactured by Toray Industries, Inc., Torelina 115 - 3F00, thickness 115 μm) with high insulation properties was used. Also, 15 parts by mass of a curing agent (polyisocyanate) and 0.3 parts by mass of a catalyst (tris(dimethylaminomethyl)phenol) were blended with respect to 100 parts by mass of the polyester polymer, and further diluted with methyl ethyl ketone (MEK) so that the solid content became 15% by mass to prepare a resin composition. The resin composition was applied to one surface of the base material 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. Further, a second intermediate layer was formed on the other surface of the base material 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 to the base material using an applicator so that the thickness after coating was 38 μm. Then, it was dried in an oven at 100 °C for 3 minutes to form a first adhesive layer. Further, a second adhesive layer was formed on the surface of the second intermediate layer opposite to the base material in the same manner as the first adhesive layer. Thus, a foaming adhesive sheet in which the first adhesive layer, the first intermediate layer, the base material, the second intermediate layer, and the second adhesive layer were arranged in this order was obtained.

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

[0199] [Evaluation 2] (Peel strength) In the same manner as in Example 1, the peel strength on the side where the first adhesive layer of the foaming adhesive sheet was disposed and the peel strength on the side where the second adhesive layer was disposed were measured respectively.

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

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

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

[0203] (Adhesive force) In the same manner as in Example 1, the adhesive force was measured.

[0204] (Coefficient of friction) In accordance with JIS K7125, the dynamic friction coefficient and the static friction coefficient between the surface on which the adhesive layer to be tested of the foaming adhesive sheet was disposed and a metal plate were measured. First, the foaming adhesive sheet was cut into 80 mm × 200 mm. Next, the foaming adhesive sheet was placed on a rectangular metal plate (cold-rolled steel sheet SPCC) placed horizontally, and a sliding piece (63 mm × 63 mm, weight 200 g, bottom surface: felt) was placed on the surface on which the adhesive layer to be tested of the foaming adhesive sheet was disposed. Then, the frictional force was measured under the conditions of a test speed of 100 mm / min, a test length of 50 mm, a load cell of 10 N, and a temperature of 23°C, and the dynamic friction coefficient and the static friction coefficient were calculated. As the apparatus, a friction measuring machine FRICTION TESTER TR-2 manufactured by Toyo Seiki Seisakusho was used.

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

[0206] (Insertion weight) Two foaming adhesive sheets cut to 5.5 cm × 6.0 cm, one hollow cylinder 1 with an outer diameter of 22 mm, a thickness of 1.5 mm, and a length of 60 mm, and one hollow cylinder 2 with an outer diameter of 18 mm, a thickness of 1.0 mm, and a length of 80 mm were prepared. The two foaming adhesive sheets were overlapped with the surfaces where the adhesive layers to be tested were located facing inward and rolled up, and then placed inside cylinder 1. Next, cylinder 2 was inserted into the inner gap of the foaming adhesive sheet in cylinder 1 by about 1 mm in advance. Then, a weight was placed on cylinder 2, and the weight of the weight when cylinder 2 was completely inserted into the inner gap of the foaming adhesive sheet in cylinder 1 was measured. The weight of the weight at this time was taken as the insertion weight. The smaller the insertion weight, the better the insertability.

[0207] (Expansion ratio) The foaming adhesive sheet was cut into a size of 5 cm × 5 cm, hung vertically in a hot air dryer, and foamed and cured under the conditions of 180°C or 150°C for 30 minutes, and then cooled at room temperature for 2 hours to obtain a foamed and cured adhesive sheet. Then, the thickness of the foamed and cured adhesive sheet was measured using a thickness gauge in accordance with the method specified in JIS Z0237. The expansion ratio was calculated by the following formula. Expansion ratio (times) = {Thickness of the foamed and cured adhesive sheet - (Thickness of the base material + Thickness of the first intermediate layer + Thickness of the second intermediate layer)} / (Total thickness of the first adhesive layer and the second adhesive layer of the foaming adhesive sheet before foaming and curing)

[0208] (Adhesiveness) As shown in FIGS. 6(a) and 6(b), two metal plates 31 (cold-rolled steel sheet SPCC-SD) with a thickness of 1.6 mm, a width of 25 mm, and a length of 100 mm were prepared. A spacer 32 (Kapton tape) was arranged at a predetermined interval at one end of one of the metal plates 31. The thickness of the spacer was about 280 μm or about 350 μm (the thickness obtained by stacking 4 or 5 sheets of Kapton tape P-221 manufactured by Nitto Denko Corporation). An expandable adhesive sheet 10 cut into 12.5 mm × 25 mm was placed between the spacers 32, and the other metal plate 31 was arranged such that one end overlapped.

[0209] For a part, as shown in FIG. 6(a), supports 33 having the same thickness as the total thickness of the metal plate 31 and the spacer 32 were respectively arranged at the other ends of the two metal plates 31 to obtain test pieces. Then, the test pieces were placed in a hot press machine and heated at 150 °C for 8 minutes under a pressing load of 500 kgf to cure the expandable adhesive sheet 10.

[0210] For the rest, they were fixed with clips to obtain test pieces. Then, the test pieces were placed in a hot oven and heated at 180 °C for 30 minutes to cure the expandable adhesive sheet 10.

[0211] The shear strength (adhesive strength) of the heated test pieces was measured using a tensile testing machine Tensilon RTF1350 (manufactured by A&D Company Limited) in accordance with JIS K6850. The measurement conditions were a tensile 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, since an intermediate layer was arranged between the base material and the adhesive layer, both the adhesion by the L-shaped bending test and the adhesion by the cross-bending test were good, and the adhesion by the cutter cutting test was also good. The test results on the surface side of the first adhesive layer and the surface side of the second adhesive layer of the expandable adhesive sheet were the same.

[0214] Also, as shown in Table 3, as the average particle size of the foaming agent increased, the static friction coefficient and the dynamic friction coefficient decreased, and the pencil hardness increased. Further, in Example 15, compared with Examples 10 and 12, the average particle size of the foaming agent was large, the static friction coefficient and the dynamic friction coefficient were small, the pencil hardness was high, and the insertion weight was small. Thus, it was suggested that when the average particle size of the foaming agent is equal to or greater than a predetermined value, the slipperiness and the insertability are improved. Also, it was suggested that the friction coefficient and the hardness of the surface on the adhesive layer side of the foaming adhesive sheet contributed to the insertability. Note that Table 3 shows the evaluation results on the surface side of the first adhesive layer of the foaming adhesive sheet, and the evaluation results on the surface side of the first adhesive layer of the foaming adhesive sheet and the evaluation results on the second adhesive layer were almost the same.

[0215] Also, as shown in Table 3, in Examples 10 to 11 where the average particle size of the foaming agent was 7 μm, the adhesive strength when the gap was about 280 μm exceeded 0.51 MPa and was good, but the adhesive strength when the gap was about 350 μm decreased. On the other hand, in Examples 12 to 20 where the average particle size of the foaming agent was 13 μm to 21 μm, the adhesive strength exceeded 0.51 MPa and was good both when the gap was about 280 μm and when the gap was about 350 μm. Further, in Examples 21 to 23 where the average particle size of the foaming agent was 25 μm to 41 μm, the adhesive strength when the gap was about 280 μm decreased. Thus, it was suggested that when the average particle size of the foaming agent is within a predetermined range, both the adhesiveness when the gap between members is relatively narrow and the adhesiveness when the gap between members is relatively wide are improved.

Explanation of Reference Numerals

[0216] 1 … Adhesive layer 2 … Base material 3 … Intermediate layer 10 … Foaming adhesive sheet 11 … Adhesive sheet after foaming and curing 20a … First member 20b … Second member 100 … Article

Claims

1. A foaming adhesive sheet having a base material and an adhesive layer disposed on at least one surface side of the base material, wherein the adhesive layer contains a curable adhesive and a foaming agent, the curable adhesive contains an epoxy resin and a curing agent, the base material contains a resin having a glass transition temperature of 80°C or higher, an intermediate layer containing a crosslinked polyester resin is disposed between the base material and the adhesive layer, a foaming adhesive sheet, wherein the peeling force on the surface side where the adhesive layer is disposed, measured by the SAICAS (Surface And Interfacial Cutting Analysis System) method using a cutting edge with a blade width of 1.0 mm, is 2.0 N or more.

2. A foaming adhesive sheet having a base material and an adhesive layer disposed on at least one surface side of the base material, wherein the adhesive layer contains a curable adhesive and a foaming agent, the curable adhesive contains an epoxy resin and a curing agent, the base material contains a resin having a glass transition temperature of 80°C or higher, the surface of the base material on which the adhesive layer is disposed is subjected to a blasting treatment, a foaming adhesive sheet, wherein the peeling force on the surface side where the adhesive layer is disposed, measured by the SAICAS (Surface And Interfacial Cutting Analysis System) method using a cutting edge with a blade width of 1.0 mm, is 2.0 N or more.

3. A foaming adhesive sheet having a base material and an adhesive layer disposed on at least one surface side of the base material, wherein the adhesive layer contains a curable adhesive and a foaming agent, the curable adhesive contains an epoxy resin, an acrylic resin compatible with the epoxy resin, and a curing agent, the surface of the base material on which the adhesive layer is disposed is subjected to a corona treatment or a blasting treatment, or an intermediate layer containing a crosslinked polyester resin is disposed between the base material and the adhesive layer, the base material is a polyphenylene sulfide film or a polyethylene naphthalate film, a foaming adhesive sheet, wherein the peeling force on the surface side where the adhesive layer is disposed, measured by the SAICAS (Surface And Interfacial Cutting Analysis System) method using a cutting edge with a blade width of 1.0 mm, is 2.0 N or more.

4. The foaming adhesive sheet according to claim 3, wherein the average thickness of the intermediate layer is 0.5 μm or more and 4 μm or less.

5. The foamable adhesive sheet according to claim 1 or claim 2, wherein the curable adhesive contains an acrylic resin compatible with the epoxy resin.

6. The foamable adhesive sheet according to any one of claims 3 to 5, wherein the weight average molecular weight of the acrylic resin is 50,000 or more.

7. The foamable adhesive sheet according to any one of claims 1 to 6, wherein the curable adhesive contains an epoxy resin having a weight average molecular weight of 20,000 or more as the epoxy resin.

8. The foamable adhesive sheet according to any one of claims 1 to 7, wherein the average thickness of the adhesive layer is 10 μm or more and 200 μm or less.

9. An arrangement step of arranging the foamable adhesive sheet according to any one of claims 1 to 8 between a first member and a second member; An adhesion step of foaming and curing the foamable adhesive sheet to adhere the first member and the second member; A method for manufacturing an article having the above steps.

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