Foaming adhesive sheet and method for producing article

Abstract

To provide a foaming adhesive sheet that can be used in gaps of members or between members and has excellent insertability and adhesiveness.SOLUTION: A foaming adhesive sheet comprising a base material and an adhesive layer disposed on at least one surface side of the base material, in which the adhesive layer contains a curable adhesive agent and a foaming agent, the adhesive layer is disposed on a topmost layer, the adhesive layer has an adhesive force of 0 N / 25 mm or more and 0.1 N / 25 mm or less, a static friction coefficient of a surface of the adhesive layer opposite to the base material is 0.30 or less, and a pencil hardness of the surface of the adhesive layer opposite to the base material is F or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

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

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

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

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

[0006] Such foamable adhesive sheets are desired to be easy to insert, for example, into gaps between components or between components, or when placing a foamable adhesive sheet on one component and then inserting the other component into the gap.

[0007] Furthermore, it is desirable for such foamable adhesive sheets to have good adhesive properties after foaming and curing. However, when the gap between members is relatively large, adhesive properties may be reduced.

[0008] The present disclosure has been made in consideration of the above-mentioned circumstances, and has as its first object to provide a foamable adhesive sheet that exhibits good insertability and ease of insertion of components. The second object of the present disclosure is to provide a foamable adhesive sheet that exhibits good adhesion even when the gap between components is relatively wide. [Means for solving the problem]

[0009] One embodiment of the present disclosure provides a foamable adhesive sheet having a substrate and an adhesive layer disposed on at least one surface of the substrate, wherein the adhesive layer contains a curable adhesive and a foaming agent, the adhesive layer is disposed on the outermost surface, the adhesive layer has an adhesive strength of 0 N / 25 mm or more and 0.1 N / 25 mm or less, the static friction coefficient of the adhesive layer on the surface opposite the substrate is 0.30 or less, and the pencil hardness of the adhesive layer on the surface opposite the substrate is F or more.

[0010] Another embodiment of the present disclosure provides a foamable adhesive sheet having a substrate and an adhesive layer disposed on at least one side of the substrate, wherein the adhesive layer contains a curable adhesive and a foaming agent, and the average particle size of the foaming agent is 10 μm or more and 24 μm or less.

[0011] Another embodiment of the present disclosure provides a method for manufacturing an article, comprising: a placement step of placing the above-mentioned foamable adhesive sheet between a first member and a second member; and a bonding step of foaming and curing the foamable adhesive sheet to bond the first member and the second member together. [Effects of the Invention]

[0012] The foamable adhesive sheet of the present disclosure exhibits the advantage of good insertability of the foamable adhesive sheet and of the member insertability, and also exhibits the advantage of good adhesion even when the gap between members is relatively wide. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a schematic cross-sectional view showing an example of a foamable adhesive sheet according to the present disclosure. [Figure 2] FIG. 2 is a schematic cross-sectional view showing another example of a foamable adhesive sheet according to the present disclosure. [Figure 3] FIG. 2 is a schematic cross-sectional view showing another example of a foamable adhesive sheet according to the present disclosure. [Figure 4] FIG. 1 is a schematic perspective view showing another example of a foamable adhesive sheet according to the present disclosure. [Figure 5] 1 is a schematic cross-sectional view showing an example of a method for manufacturing an article according to the present disclosure. [Figure 6] FIG. 1 is a schematic cross-sectional view illustrating a method for testing adhesiveness. DETAILED DESCRIPTION OF THE INVENTION

[0014] Embodiments of the present disclosure will be described below with reference to the drawings and the like. However, the present disclosure can be implemented in many different forms, and should not be construed as being limited to the description of the embodiments exemplified below. Furthermore, to clarify the explanation, the drawings may schematically depict the width, thickness, shape, etc. of each part compared to the actual form, but these are merely examples and are not intended to limit the interpretation of the present disclosure. Furthermore, in this specification and each drawing, elements similar to those previously described with reference to the preceding drawings will be designated by the same reference numerals, and detailed descriptions may be omitted as appropriate.

[0015] In this specification, when describing a mode in which another component is placed on a certain component, the terms "above" or "below" are used, unless otherwise specified, to include both a case in which another component is placed directly above or below a certain component so as to be in contact with the component, and a case in which another component is placed above or below a certain component with another component interposed therebetween. Also, in this specification, when describing a mode in which another component is placed on the surface of a certain component, the terms "on the surface side" or "on the surface" are used, unless otherwise specified, to include both a case in which another component is placed directly above or below a certain component so as to be in contact with the component, and a case in which another component is placed above or below a certain component with another component interposed therebetween.

[0016] In this specification, the term "sheet" also includes a member called a "film." In addition, the term "film" also includes a member called a "sheet." In addition, the numerical ranges in this specification are ranges of average values.

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

[0018] A. Foam adhesive sheet The foamable adhesive sheet of the present disclosure will be described in a first embodiment and a second embodiment.

[0019] I. First embodiment A first embodiment of the foamable adhesive sheet of the present disclosure will be described in detail.

[0020] The foamable adhesive sheet in this embodiment has a substrate and an adhesive layer arranged on at least one side of the substrate, the adhesive layer containing a curable adhesive and a foaming agent, the adhesive layer being arranged on the outermost surface, the adhesive layer having an adhesive strength of 0 N / 25 mm or more and 0.1 N / 25 mm or less, a static friction coefficient of the adhesive layer on the side opposite the substrate of 0.30 or less, and a pencil hardness of the adhesive layer on the side opposite the substrate of F or more.

[0021] 1 and 2 are schematic cross-sectional views illustrating an example of a foamable adhesive sheet according to this embodiment. Foamable adhesive sheet 10 in FIG. 1 has a substrate 2 and an adhesive layer 1 disposed on one side of substrate 2. Foamable adhesive sheet 10 in FIG. 2 has a substrate 2 and a first adhesive layer 1a disposed on one side of substrate 2 and a second adhesive layer 1b disposed on the other side of substrate 2. Adhesive layer 1, first adhesive layer 1a, and second adhesive layer 1b contain a curable adhesive and a foaming agent and are disposed on the outermost surface of foamable adhesive sheet 10. In foamable adhesive sheet 10 in FIG. 1, adhesive layer 1 has a predetermined adhesive strength, and the static friction coefficient and pencil hardness of the surface of adhesive layer 1 opposite substrate 2 are also within predetermined ranges. In foamable adhesive sheet 10 in FIG. 2, adhesive strength of first adhesive layer 1a and second adhesive layer 1b are also within predetermined ranges, and the static friction coefficient and pencil hardness of the surface of first adhesive layer 1a and second adhesive layer 1b opposite substrate 2 are also within predetermined ranges.

[0022] When the foamable adhesive sheet has adhesive layers on both sides, it is preferable that the adhesive strength of both adhesive layers be within a predetermined range and that the static friction coefficient and pencil hardness of the side of both adhesive layers opposite the substrate be within a predetermined range. However, since the foamable adhesive sheet in this embodiment may be usable by paying attention to the direction in which the surfaces are facing, it is sufficient that the adhesive strength of either one of the adhesive layers be within a predetermined range and that the static friction coefficient and pencil hardness of the side of either adhesive layer opposite the substrate be within a predetermined range.

[0023] In this embodiment, the adhesive layer has an adhesive strength of a predetermined value or less, making it substantially non-tacky (tack-free). The static friction coefficient of the surface of the adhesive layer opposite the substrate is a predetermined value or less, making the adhesive layer exhibit low friction. Furthermore, the pencil hardness of the surface of the adhesive layer opposite the substrate is a predetermined value or more, making the adhesive layer exhibit high hardness. The adhesive layer is disposed on the outermost surface. Therefore, a foamable adhesive sheet with excellent sliding properties and insertability can be obtained. Specifically, because the adhesive strength of the adhesive layer is a predetermined value or less and the static friction coefficient of the surface of the adhesive layer opposite the substrate is a predetermined value or less, when a foamable adhesive sheet is disposed between components to bond them together, the foamable adhesive sheet can be smoothly inserted into gaps between components or between components, or one component can be smoothly inserted into the gap after the foamable adhesive sheet has been disposed between the components. Furthermore, because the pencil hardness of the surface of the adhesive layer opposite the substrate is equal to or greater than a predetermined value, when inserting a foamable adhesive sheet into a gap between components or between components, or when inserting a component into the gap after placing the foamable adhesive sheet on one component, the edge of the component can be prevented from digging into the adhesive layer. This makes it less likely for the adhesive layer to get caught on the burrs on the edge of the component, especially if there are burrs on the edge of the component. Furthermore, because the pencil hardness of the surface of the adhesive layer opposite the substrate is equal to or greater than a predetermined value, when inserting a foamable adhesive sheet into a gap between components or between components, or when inserting a component into the gap after placing the foamable adhesive sheet on one component, the edge or surface of the adhesive layer can be prevented from wearing down. This improves the ease of inserting the foamable adhesive sheet into a gap between components or between components, and the ease of inserting a component into the gap after placing the foamable adhesive sheet on one component.

[0024] Furthermore, as described above, the foamable adhesive sheet of this embodiment has good sliding properties and insertion properties. Furthermore, the foamable adhesive sheet of this embodiment has good blocking resistance because the adhesive strength of the adhesive layer is below a predetermined value and the adhesive layer is substantially non-adhesive (tack-free). Therefore, the handleability and workability of the foamable adhesive sheet can be improved.

[0025] Furthermore, in this embodiment, the adhesive strength of the adhesive layer is below a predetermined value, the static friction coefficient of the surface of the adhesive layer opposite the substrate is below a predetermined value, and the adhesive layer is particularly non-sticky and slippery.Therefore, when a foamable adhesive sheet is placed between components to bond them together, when one component is moved relative to the other component to align them, the one component can be moved smoothly relative to the other component while they are overlapping each other.

[0026] Furthermore, for example, Patent Document 1 discloses providing a release agent layer on the surface of an expandable adhesive layer. However, if a release agent layer is provided on the surface of the adhesive layer, the adhesiveness of the adhesive layer after foaming and curing may be reduced. In contrast, in the foamable adhesive sheet of the present embodiment, the adhesive layer has a tackiness within a predetermined range, so there is no need to provide a release layer or release sheet for the purpose of imparting blocking resistance or slip properties, and the adhesive layer can be provided on the outermost surface. This allows for a foamable adhesive sheet with good adhesiveness of the adhesive layer after foaming and curing.

[0027] Here, "adhesion" is a concept that is included in "bonding." The two are sometimes distinguished in that "adhesion" is used to mean a temporary adhesive phenomenon, while "bonding" is used to mean a substantially permanent adhesive phenomenon (Iwanami Shoten Physics and Chemistry Dictionary, 5th Edition). "Adhesion" and "adhesive strength" refer to the property of adhering through pressure and the adhesive strength at that time.

[0028] In this specification, unless otherwise specified, the terms "adhesion of the adhesive layer" and "adhesion strength of the adhesive layer" refer to the adhesion and adhesive strength of the adhesive layer before foaming and curing. In addition, in this specification, unless otherwise specified, the terms "adhesion of the adhesive layer" and "adhesion strength of the adhesive layer" refer to the adhesion and adhesive strength of the adhesive layer after foaming and curing.

[0029] Hereinafter, each component of the foamable adhesive sheet in this embodiment will be described.

[0030] 1. Characteristics of foam adhesive sheets In the foamable adhesive sheet of this embodiment, the adhesive layer has an adhesive strength of 0 N / 25 mm or more and 0.1 N / 25 mm or less, or may be 0.05 N / 25 mm or less, or may be 0.02 N / 25 mm or less. When the adhesive strength of the adhesive layer is within the above range, the adhesive layer can be made substantially non-sticky (tack-free), and a foamable adhesive sheet with good sliding properties, insertability, and blocking resistance can be obtained.

[0031] When adhesive layers are disposed on both sides of the substrate, the adhesive strength of at least one adhesive layer should be within the above range. For example, when a foamable adhesive sheet is disposed between components to bond them together, the foamable adhesive sheet may be first disposed on one component, and then the other component may be inserted into the gap after the foamable adhesive sheet has been disposed on the other component. In such cases, when inserting the other component into the gap after the foamable adhesive sheet has been disposed on one component, it is sufficient that the surface of the foamable adhesive sheet that comes into contact with the other component has good slip properties. Therefore, the adhesive strength of at least one adhesive layer should be within the above range.

[0032] When adhesive layers are disposed on both sides of the substrate, for example, the adhesive strength of either one of the adhesive layers may be within the above range, or the adhesive strength of both adhesive layers may be within the above range, but it is particularly preferable that the adhesive strength of both adhesive layers be within the above range.

[0033] The adhesive strength of the adhesive layer can be measured in accordance with JIS Z0237:2009 (Test method for adhesive tapes and adhesive sheets), which was created based on ISO 29862, and Method 1 of the adhesive strength test method (a test method in which the tape or sheet is peeled off at an angle of 180° from a stainless steel test plate at a temperature of 23°C and humidity of 50%). Details of the method for measuring the adhesive strength of the adhesive layer are described in the Examples section below.

[0034] In this embodiment, the adhesive strength of the adhesive layer can be adjusted to a predetermined value or less by, for example, adjusting the composition of the adhesive layer. Specifically, the adhesive layer containing an epoxy resin and a curing agent can have a lower adhesive strength by using an epoxy resin that is solid at room temperature or a curing agent that is solid at room temperature. The adhesive layer can also have a lower adhesive strength by adding an epoxy resin with a high softening temperature or an epoxy resin with a high weight-average molecular weight to the adhesive layer. For example, the adhesive layer can have a lower adhesive strength by adding multiple epoxy resins with different softening temperatures. For example, when the adhesive layer contains one epoxy resin, the adhesive layer can have a lower adhesive strength by adding another epoxy resin with a softening temperature of 25°C or higher and 10°C or higher than the softening temperature of the epoxy resin. Furthermore, for example, the adhesive layer can be made to contain multiple epoxy resins with different weight-average molecular weights. That is, when the adhesive layer contains one epoxy resin, the adhesive layer can be made to contain another epoxy resin with a weight-average molecular weight of 370 or more that is 300 or more greater than the weight-average molecular weight of the epoxy resin. More specifically, in an adhesive layer containing an epoxy resin and a curing agent, the adhesive layer can be made to contain a first epoxy resin with a low softening temperature and low molecular weight and a second epoxy resin with a high softening temperature and high molecular weight, as described below. Furthermore, in an adhesive layer containing an epoxy resin and a curing agent, the adhesive layer can be made to contain an acrylic resin that is compatible with the epoxy resin, as described below.

[0035] In the foamable adhesive sheet of this embodiment, the surface of the adhesive layer opposite the substrate has a pencil hardness of F or higher. Having a pencil hardness of the surface of the adhesive layer within the above range allows for a foamable adhesive sheet with good sliding properties and insertability. Specifically, when the pencil hardness of the surface of the adhesive layer is within the above range, frictional resistance tends to be low. Furthermore, the pencil hardness may be, for example, 2H or less. If the pencil hardness is too high, the adhesive layer may have poor adhesion to the substrate.

[0036] When adhesive layers are disposed on both sides of the substrate, the pencil hardness of at least one of the adhesive layers on the side opposite the substrate may be within the above range. For example, the pencil hardness of either one of the adhesive layers on the side opposite the substrate may be within the above range, or the pencil hardness of both adhesive layers on the side opposite the substrate may be within the above range. In particular, it is preferable that the pencil hardness of both adhesive layers on the side opposite the substrate be within the above range.

[0037] The pencil hardness can be determined in accordance with JIS K5600, which corresponds to ISO 15184. Details of the method for measuring pencil hardness will be described in the Examples section below.

[0038] In this embodiment, the pencil hardness of the surface of the adhesive layer can be controlled, for example, by the composition of the adhesive layer. Specifically, the pencil hardness can be controlled by the average particle size and content of the foaming agent contained in the adhesive layer. More specifically, the pencil hardness can be increased by increasing the average particle size of the foaming agent. Furthermore, the pencil hardness can be increased by increasing the content of the foaming agent. Furthermore, the pencil hardness can be increased, for example, by including an inorganic filler in the adhesive layer. Furthermore, the pencil hardness can be increased, for example, by including a component having a rigid structure in the adhesive layer. Specifically, in an adhesive layer containing an epoxy resin and a curing agent, an example of the component having a rigid structure is a phenolic resin.

[0039] In the foamable adhesive sheet of this embodiment, the static friction coefficient of the adhesive layer on the surface opposite the substrate is 0.30 or less, and may be 0.26 or less. Having the static friction coefficient of the adhesive layer surface within this range allows for a foamable adhesive sheet with good sliding properties and insertability. The static friction coefficient may also be, for example, 0.16 or more.

[0040] When adhesive layers are disposed on both sides of the substrate, the static friction coefficient of at least one adhesive layer on the side opposite the substrate may be within the above range. For example, the static friction coefficient of either adhesive layer on the side opposite the substrate may be within the above range, or the static friction coefficients of both adhesive layers on the sides opposite the substrate may be within the above range. In particular, it is preferable that the static friction coefficients of both adhesive layers on the sides opposite the substrate be within the above range.

[0041] The static friction coefficient can be determined in accordance with JIS K7125, which corresponds to ISO 8295. Details of the method for measuring the static friction coefficient will be described in the Examples section below.

[0042] In this embodiment, the static friction coefficient of the surface of the adhesive layer can be controlled, for example, by adjusting the composition of the adhesive layer or by adjusting the pencil hardness of the surface of the adhesive layer. Specifically, the static friction coefficient can be controlled by the average particle size and content of the foaming agent contained in the adhesive layer. More specifically, as the average particle size of the foaming agent increases, the static friction coefficient of the surface of the adhesive layer tends to decrease. Furthermore, as the content of the foaming agent increases, the static friction coefficient of the surface of the adhesive layer tends to decrease.

[0043] The foamable adhesive sheet of this embodiment preferably has good shape retention. The bending moment based on JIS P8125, which corresponds to ISO 2493, is, for example, 3 gf·cm or more, and may be 5 gf·cm or more. On the other hand, the bending moment may be, for example, less than 40 gf·cm, and may be less than 30 gf·cm. Conventionally, foamable adhesive sheets typically have a high bending moment to improve their shape retention and ease of insertion into narrow gaps. In contrast, the inventors of the present disclosure have discovered that shape retention can be ensured by modifying the shape, and that a high bending moment has other drawbacks. Taking other characteristics into consideration, it is preferable that the bending moment be within the above range. If the bending moment is smaller than the above range, shape retention may be difficult even with measures such as folding. Furthermore, if the bending moment is larger than the above range, the sheet will return to its original shape after folding, requiring heating or creases during folding. Heating reduces the sheet life, and creases can reduce the insulating properties of those areas. In addition, the foamable adhesive sheet of this embodiment has a high surface hardness, so the surface will not be damaged even if it is inserted at high speed.

[0044] The foamable adhesive sheet of this embodiment preferably has high adhesiveness after foaming and curing. The shear strength (adhesive strength) based on JIS K6850, which corresponds to ISO 4587, may be, for example, 2.10 MPa or more, 2.40 MPa or more, or 3.0 MPa or more at 23°C. Furthermore, 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. For example, a high-strength acrylic foam adhesive tape that does not require heating has a shear strength (adhesive strength) of approximately 1 MPa to 2 MPa at room temperature and is not heat-resistant at 200°C. Therefore, if the shear strength (adhesive strength) is within the above range at 23°C, it has advantages in terms of strength. Furthermore, if the shear strength (adhesive strength) is within the above range at 200°C, it can be used in applications requiring heat resistance such as around automobile engines.

[0045] The foamable adhesive sheet of this embodiment preferably has high electrical insulation after foaming and curing. The breakdown voltage based on JIS C2107, which corresponds to IEC 60454-2, is preferably, for example, 3 kV or higher, more preferably 5 kV or higher. Having the breakdown voltage within the above range enables application for rust prevention and around copper wires. Furthermore, the adhesive sheet after foaming and curing preferably has a thermal conductivity of, for example, 0.1 W / mK or higher, more preferably 0.15 W / mK or higher. Having the thermal conductivity within the above range allows for miniaturization of components and promotes the curing reaction during heating.

[0046] 2.Adhesive layer The adhesive layer in this embodiment is disposed on at least one surface of the substrate, and contains a curable adhesive and a foaming agent.

[0047] (1) Adhesive layer material (a) Hardening adhesive The curable adhesive contained in the adhesive layer in this embodiment can be a curable adhesive generally used in the adhesive layer of a foamable adhesive sheet. Examples of curable adhesives include heat-curable adhesives and light-curable adhesives. Of these, heat-curable adhesives are preferred. Heat-curable adhesives can be applied even to components that do not have transparency, such as metal components.

[0048] The curable adhesive is preferably an epoxy resin adhesive. That is, the curable adhesive preferably contains an epoxy resin and a curing agent. In general, epoxy resin adhesives are excellent in mechanical strength, heat resistance, insulating properties, chemical resistance, etc., and have little shrinkage upon curing, making them suitable for a wide range of applications.

[0049] An example in which the curable adhesive is an epoxy resin adhesive will be described below.

[0050] (i) Epoxy resin The epoxy resin in this embodiment is a compound that has at least one epoxy group or glycidyl group and cures by a crosslinking polymerization reaction when used in combination with a curing agent. The epoxy resin also includes a monomer having at least one epoxy group or glycidyl group.

[0051] The epoxy resin can be any epoxy resin commonly used in the adhesive layer of a foamable adhesive sheet. In particular, the curable adhesive preferably contains a first epoxy resin having a softening temperature of 50°C or higher and an epoxy equivalent of 5,000 g / eq or less, and a second epoxy resin having a softening temperature higher than that of the first epoxy resin and a weight-average molecular weight of 20,000 or more. Using a combination of the first and second epoxy resins can reduce the adhesiveness (tackiness) of the adhesive layer, resulting in a foamable adhesive sheet with excellent slip properties. Furthermore, a foamable adhesive sheet with excellent blocking resistance and adhesion after foaming and curing can be obtained.

[0052] For example, if the only goal is to improve adhesiveness after foaming and curing, it is more effective to use a low-molecular-weight (low-epoxy equivalent) epoxy resin than a high-molecular-weight (high-epoxy equivalent) epoxy resin. However, if a low-molecular-weight (low-epoxy equivalent) epoxy resin is used, for example, when the foamable adhesive sheet is wound into a roll, the low-molecular-weight (low-epoxy equivalent) epoxy resins tend to assimilate with each other, making blocking more likely to occur.

[0053] In contrast, when a first epoxy resin having a relatively low softening temperature (relatively high crystallinity) and a low molecular weight (low epoxy equivalent weight) is used, the first epoxy resin rapidly melts and changes into a low-viscosity liquid when heated to a temperature above its softening temperature. This facilitates improved adhesiveness after foaming and curing. Meanwhile, because the first epoxy resin has relatively high crystallinity, it can suppress blocking compared to epoxy resins with relatively low crystallinity or no crystallinity. However, using only the first epoxy resin may result in insufficient blocking suppression or excessive tackiness of the adhesive layer. Therefore, by further using a second epoxy resin having a relatively high softening temperature (relatively low crystallinity) and a high molecular weight, it is possible to improve the blocking suppression effect and reduce the tackiness of the adhesive layer.

[0054] (i-1) First epoxy resin The first epoxy resin has a softening temperature of 50°C or higher and an epoxy equivalent of 5000 g / eq or lower. The first epoxy resin has a relatively low softening temperature (relatively high crystallinity) compared to the second epoxy resin described below. The first epoxy resin has relatively high crystallinity and a low molecular weight, which makes it easy to improve adhesion and blocking resistance after foaming and curing. Furthermore, the first epoxy resin has a low molecular weight, which makes it possible to increase the crosslink density, resulting in an adhesive layer with good mechanical strength, chemical resistance, and curing properties. Furthermore, the first epoxy resin is preferably an epoxy resin that is solid at room temperature (23°C).

[0055] The softening temperature of the first epoxy resin is usually 50° C. or higher, and may be 55° C. or higher, or 60° C. or higher. On the other hand, the softening temperature of the first epoxy resin is, for example, 150° C. or lower. The softening temperature can be measured by the ring and ball method in accordance with JIS K7234.

[0056] The epoxy equivalent of the first epoxy resin is, for example, 5000 g / eq or less, and may be 3000 g / eq or less, 1000 g / eq or less, or 600 g / eq or less. On the other hand, the epoxy equivalent of the first epoxy resin is, for example, 90 g / eq or more, 100 g / eq or more, or 110 g / eq or more. The epoxy equivalent can be measured by a method in accordance with JIS K7236, which corresponds to ISO 3001 (Plastics - Epoxy compounds - Determination of epoxy equivalent), and is the number of grams of resin containing 1 gram equivalent of epoxy groups.

[0057] The first epoxy resin may be a monofunctional epoxy resin, a difunctional epoxy resin, a trifunctional epoxy resin, or a tetrafunctional or higher functional epoxy resin.

[0058] The weight-average molecular weight (Mw) of the first epoxy resin is usually smaller than the weight-average molecular weight (Mw) of the second epoxy resin described below. The Mw of the first epoxy resin is, for example, 6,000 or less, and may be 4,000 or less, or 3,000 or less. On the other hand, the Mw of the first epoxy resin is, for example, 400 or more. Mw is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

[0059] The melt viscosity of the first epoxy resin at 150°C is, for example, 0.005 Pa·s or more, or may be 0.015 Pa·s or more, 0.03 Pa·s or more, 0.05 Pa·s or more, or 0.1 Pa·s or more. If the melt viscosity is too low, good foaming properties may not be obtained. Furthermore, if the melt viscosity of the first epoxy resin is too low (if the crystallinity of the first epoxy resin is too high), the resulting adhesive layer may have high tackiness. This is presumably because if the melt viscosity of the first epoxy resin is too low (if the crystallinity of the first epoxy resin is too high), its crystallinity is significantly reduced when it is mixed with the second epoxy resin or the acrylic resin, resulting in a decrease in the Tg of the entire adhesive composition. On the other hand, the melt viscosity of the first epoxy resin at 150°C is, for example, 10 Pa·s or less, or may be 5 Pa·s or less, or 2 Pa·s or less. If the melt viscosity is too high, the resulting adhesive layer may have poor uniformity. The melt viscosity can be determined in accordance with JIS K6862, which corresponds to ISO 2555 (Resins in the liquid state or as emulsions or dispersions—Determination of Brookfield RV viscosity), by measurement using a Brookfield-type single-cylinder rotational viscometer and a thermocell for heating the solution.

[0060] Next, the composition of the first epoxy resin will be described. Examples of the first epoxy resin include aromatic epoxy resins, aliphatic epoxy resins, alicyclic epoxy resins, and heterocyclic epoxy resins. Specific examples of the first epoxy resin include bisphenol-type epoxy resins such as bisphenol A-type epoxy resins and bisphenol F-type epoxy resins; novolac-type epoxy resins such as bisphenol A novolac-type epoxy resins and cresol novolac-type epoxy resins; and modified epoxy resins such as urethane-modified epoxy resins and rubber-modified epoxy resins. Other specific examples include biphenyl-type epoxy resins, stilbene-type epoxy resins, triphenolmethane-type epoxy resins, alkyl-modified triphenolmethane-type epoxy resins, triazine nucleus-containing epoxy resins, dicyclopentadiene-modified phenol-type epoxy resins, naphthalene-type epoxy resins, glycol-type epoxy resins, and pentaerythritol-type epoxy resins. The first epoxy resin may be one type or two or more types.

[0061] Bisphenol A epoxy resins can exist in a liquid state or a solid state at room temperature depending on the number of repeating units in the bisphenol skeleton. Bisphenol A epoxy resins having, for example, 2 to 10 bisphenol skeletons in the main chain are solid at room temperature. Bisphenol A epoxy resins are particularly preferred because they can improve heat resistance.

[0062] In particular, the first epoxy resin is preferably a bisphenol A novolac epoxy resin represented by the following general formula (1).

[0063] [ka]

[0064] In general formula (1), R 1 is C m H 2m (m is 1 or more and 3 or less), and R 2 and R 3are each independently, C p H 2p+1 (p is 1 or more and 3 or less), and n is 0 or more and 10 or less.

[0065] In general formula (1), R 1 m in is 1, that is, R 1 is preferably -CH2-. Similarly, R 2 and R 3 p in is 1, that is, R 2 and R 3 is preferably —CH 3 . Furthermore, the hydrogen bonded to the benzene ring in general formula (1) may be substituted with other elements or other groups.

[0066] The content of the first epoxy resin, based on 100 parts by mass of the resin components contained in the adhesive layer, may be, for example, 1 part by mass or more, 3 parts by mass or more, 5 parts by mass or more, 10 parts by mass or more, 15 parts by mass or more, or 25 parts by mass or more. If the content of the first epoxy resin is too low, the adhesiveness and blocking resistance after foaming and curing may be reduced. On the other hand, the content of the first epoxy resin, based on 100 parts by mass of the resin components contained in the adhesive layer, may be, for example, 90 parts by mass or less, 80 parts by mass or less, 70 parts by mass or less, 60 parts by mass or less, 50 parts by mass or less, or 40 parts by mass or less. If the content of the first epoxy resin is too high, the contents of the second epoxy resin and acrylic resin may be relatively low, which may make it difficult to achieve a balance between non-stickiness, adhesion of the adhesive layer to the substrate, blocking resistance, and adhesiveness after foaming and curing.

[0067] (i-2) Second epoxy resin The second epoxy resin has a softening temperature higher than that of the first epoxy resin and a weight-average molecular weight of 20,000 or more. The second epoxy resin has a relatively high softening temperature (relatively low crystallinity) compared to the first epoxy resin. The second epoxy resin has relatively low crystallinity and a high molecular weight, which makes it easy to improve blocking resistance. Furthermore, the second epoxy resin has relatively low crystallinity and a high molecular weight, which can suppress an increase in adhesion (tackiness) caused by the first epoxy resin. Furthermore, the second epoxy resin is preferably an epoxy resin that is solid at room temperature (23°C).

[0068] The weight average molecular weight (Mw) of the second epoxy resin is usually larger than the weight average molecular weight (Mw) of the first epoxy resin. The Mw of the second epoxy resin is usually 20,000 or more, and may be 30,000 or more, or even 35,000 or more. On the other hand, the Mw of the second epoxy resin is, for example, 100,000 or less.

[0069] The epoxy equivalent of the second epoxy resin may be greater than, less than, or the same as the epoxy equivalent of the first epoxy resin. The epoxy equivalent of the second epoxy resin is, for example, 4000 g / eq or more, 5000 g / eq or more, or even 6000 g / eq or more. On the other hand, the epoxy equivalent of the second epoxy resin is, for example, 20000 g / eq or less.

[0070] The second epoxy resin may be a monofunctional epoxy resin, a difunctional epoxy resin, a trifunctional epoxy resin, or a tetrafunctional or higher functional epoxy resin.

[0071] The softening temperature of the second epoxy resin is usually higher than that of the first epoxy resin. The difference between the two temperatures is, for example, 10°C or higher, and may be 20°C or higher, or even 30°C or higher. The softening temperature of the second epoxy resin is, for example, 80°C or higher, and may be 90°C or higher. On the other hand, the softening temperature of the second epoxy resin is, for example, 180°C or lower.

[0072] The constitution of the second epoxy resin is the same as that of the first epoxy resin described above, and therefore description thereof will be omitted here.

[0073] The content of the second epoxy resin, based on 100 parts by mass of the resin components contained in the adhesive layer, may be, for example, 10 parts by mass or more, 15 parts by mass or more, 20 parts by mass or more, 25 parts by mass or more, 30 parts by mass or more, 35 parts by mass or more, 40 parts by mass or more, or 45 parts by mass or more. If the content of the second epoxy resin is too low, the adhesiveness may be high and the blocking resistance may be reduced. On the other hand, the content of the second epoxy resin, based on 100 parts by mass of the resin components contained in the adhesive layer, may be, for example, 90 parts by mass or less, 85 parts by mass or less, 80 parts by mass or less, or 75 parts by mass or less. If the content of the second epoxy resin is too high, the contents of the first epoxy resin and acrylic resin may be relatively low, which may make it difficult to achieve a balance between non-stickiness, adhesion of the adhesive layer to the substrate, blocking resistance, and adhesion after foaming and curing.

[0074] The proportion of the first epoxy resin relative to the total of the first epoxy resin and the second epoxy resin is, for example, 5% by mass or more, or alternatively 10% by mass or more, or 15% by mass or more, or even 20% by mass or more, while the proportion of the first epoxy resin is, for example, 80% by mass or less, or alternatively 75% by mass or less, or alternatively 60% by mass or less.

[0075] Furthermore, the total proportion of the first epoxy resin and the second epoxy resin to all epoxy resins contained in the adhesive layer is, for example, 50% by mass or more, or may be 70% by mass or more, or 90% by mass or more, or may be 100% by mass.

[0076] (ii) Acrylic resin The acrylic resin in this embodiment is a resin compatible with epoxy resin. Because the acrylic resin is compatible with epoxy resin, it is easy to improve the toughness of the adhesive layer. As a result, the adhesiveness after foaming and curing can be improved. Furthermore, it is believed that the acrylic resin acts as a compatibilizer for the foaming agent (for example, a foaming agent whose shell is an acrylonitrile copolymer resin), uniformly dispersing and foaming, thereby improving the adhesiveness after foaming and curing. Furthermore, the flexibility of the acrylic resin can be exhibited, improving the adhesion of the adhesive layer to the substrate. Furthermore, the compatibility of the acrylic resin with the epoxy resin can maintain high hardness on the surface of the adhesive layer. On the other hand, if the acrylic resin is incompatible with the epoxy resin, a soft portion is formed on the surface of the adhesive layer, making the interface with the adherend less slippery and reducing workability.

[0077] The acrylic resin in this embodiment is compatible with the epoxy resin. The compatibility of the acrylic resin with the epoxy resin can be confirmed, for example, by observing the cross section of the adhesive layer of the foamable adhesive sheet with a scanning electron microscope (SEM) or a transmission electron microscope (TEM) and finding no micron-sized islands. More specifically, the average particle size of the islands is preferably 1 μm or less. In particular, the average particle size of the islands may be 0.5 μm or less, or even 0.3 μm or less. A large number of samples is preferably used, for example, 100 or more. The area to be observed is within a range of 100 μm × 100 μm, or, if the average thickness of the adhesive layer is 100 μm or less, within a range of the average thickness × 100 μm.

[0078] The weight-average molecular weight (Mw) of the acrylic resin is, for example, 50,000 or more, or may be 70,000 or more, or even 100,000 or more. The first epoxy resin has relatively high crystallinity, which can result in a low melt viscosity (or dynamic viscoelasticity) when heated, potentially causing shrinkage during curing after foaming (between the time when the foaming agent finishes foaming and the time when the adhesive composition cures). However, by using an acrylic resin with a certain molecular weight, it is possible to prevent the melt viscosity from becoming too low, making it less likely for shrinkage to occur during curing after foaming. Meanwhile, the Mw of the acrylic resin is, for example, 1,500,000 or less. The weight-average molecular weight of the acrylic resin can be measured by GPC (eluent: THF, standard: PS, sample: 20 μL, flow rate: 1 mL / min, column temperature: 40°C).

[0079] 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 K7121, which corresponds to ISO 3146.

[0080] Acrylic resin has a storage modulus (E') of 1 x 10 at the foaming initiation temperature. 6 A low E' at the foaming initiation temperature can improve fluidity and provide good foaming properties. On the other hand, E' at the foaming initiation temperature can be, for example, 1 x 10 5 The foaming initiation temperature is equal to or higher than 100 Pa. The foaming initiation temperature varies depending on the type of foaming agent. When two or more foaming agents are used, the foaming initiation temperature is the temperature at which the main foaming reaction begins.

[0081] Acrylic resin has a storage modulus (E') of 1 x 10 at the curing initiation temperature. 5The viscosity may be 100 Pa or more. As mentioned above, shrinkage may occur during curing after foaming (between the time when the foaming of the foaming agent is completed and the time when the adhesive composition is cured). However, if E' at the curing initiation temperature is large, shrinkage can be suppressed and good shape retention can be obtained. The curing initiation temperature varies depending on the type of curing agent. When two or more curing agents are used as the curing agent, the initiation temperature of the main curing reaction is taken as the curing initiation temperature.

[0082] In addition, the average storage modulus (E') of acrylic resin at temperatures between 0°C and 100°C is 1 x 10 6 The storage modulus (E') may be 1 x 10 Pa or more. A high average value of E' before foaming can provide good non-stickiness and blocking resistance. On the other hand, the average value of the storage modulus (E') at temperatures between 0°C and 100°C can be, for example, 1 x 10 8 Pa or less.

[0083] The acrylic resin may have a polar group, such as an epoxy group, a hydroxyl group, a carboxyl group, a nitrile group, or an amide group.

[0084] The acrylic resin is a homopolymer of an acrylic acid ester monomer, and may be a mixed component containing two or more of the above homopolymers, or may be a copolymer of two or more acrylic acid ester monomers and may be a component containing one or more copolymers. The acrylic resin may also be a mixed component of the above homopolymer and the above copolymer. The acrylic acid ester monomer "acrylic acid" also includes the concept of methacrylic acid. Specifically, the acrylic resin may be a mixture of a methacrylate polymer and an acrylate polymer, or may be an acrylic acid ester polymer such as acrylate-acrylate, methacrylate-methacrylate, or methacrylate-acrylate. In particular, the acrylic resin preferably contains a copolymer of two or more acrylic acid ester monomers (a (meth)acrylic acid ester copolymer).

[0085] Examples of the monomer component constituting the (meth)acrylic acid ester copolymer include the monomer components described in JP 2014-065889 A. The monomer component may have the polar group described above. Examples of the (meth)acrylic acid ester copolymer include an ethyl acrylate-butyl acrylate-acrylonitrile copolymer, an ethyl acrylate-acrylonitrile copolymer, and a butyl acrylate-acrylonitrile copolymer. Note that "acrylic acid" such as methyl acrylate and ethyl acrylate also includes "methacrylic acid" such as methyl methacrylate and ethyl methacrylate.

[0086] The (meth)acrylic acid ester copolymer is preferably a block copolymer, and more preferably an acrylic block copolymer such as a methacrylate-acrylate copolymer. Examples of (meth)acrylates constituting the acrylic block copolymer include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, and benzidyl acrylate. In these examples, "acrylic acid" also includes "methacrylic acid."

[0087] Specific examples of methacrylate-acrylate copolymers include acrylic copolymers such as methyl methacrylate-butyl acrylate-methyl methacrylate (MMA-BA-MMA) copolymer, which also includes block copolymers of polymethyl methacrylate-polybutyl acrylate-polymethyl methacrylate (PMMA-PBA-PMMA).

[0088] The acrylic copolymer may have no polar groups, or may be a modified product in which the above-mentioned polar groups have been partially introduced. The modified product is highly compatible with epoxy resins, thereby further improving adhesion.

[0089] Among these, the acrylic resin is preferably a (meth)acrylic acid ester copolymer having a first polymer portion having a glass transition temperature (Tg) of 10° C. or lower and a second polymer portion having a glass transition temperature (Tg) of 20° C. or higher. Such a (meth)acrylic acid ester copolymer has the first polymer portion that becomes a soft segment and the second polymer portion that becomes a hard segment.

[0090] The manifestation of the above-mentioned effect can be presumed as follows: By using an acrylic resin having both a soft segment and a hard segment, such as the above-mentioned (meth)acrylic acid ester copolymer, the hard segment contributes to heat resistance, and the soft segment contributes to toughness or flexibility, so that an adhesive layer having good heat resistance, toughness, and flexibility can be obtained.

[0091] At least one of the first polymer portion and the second polymer portion contained in the (meth)acrylic acid ester copolymer has compatibility with epoxy resins. When the first polymer portion has compatibility with epoxy resins, flexibility can be increased. Furthermore, when the second polymer portion has compatibility with epoxy resins, cohesion and toughness can be increased.

[0092] When either the first polymer portion or the second polymer portion is incompatible with the epoxy resin, the (meth)acrylic acid ester copolymer has a compatible portion, which is a polymer portion that is compatible with the epoxy resin, and an incompatible portion, which is a polymer portion that is incompatible with the epoxy resin. In this case, when the (meth)acrylic acid ester copolymer is added to an adhesive composition, the compatible portion is compatible with the epoxy resin, and the incompatible portion is incompatible with the epoxy resin, causing fine phase separation. As a result, a fine sea-island structure is formed. The sea-island structure varies depending on the type of (meth)acrylic acid ester copolymer, the compatibility of the first polymer portion and the second polymer portion contained in the (meth)acrylic acid ester copolymer, and whether or not modification by introduction of polar groups has been performed, and examples include a sea-island structure in which the compatible portions of the cured epoxy resin and the (meth)acrylic acid ester copolymer are the sea and the incompatible portions of the (meth)acrylic acid ester copolymer are the islands, a sea-island structure in which the incompatible portions of the (meth)acrylic acid ester copolymer are the sea and the compatible portions of the cured epoxy resin and the (meth)acrylic acid ester copolymer are the islands, and a sea-island structure in which the (meth)acrylic acid ester copolymer is the sea and the cured epoxy resin is the islands. Such a sea-island structure makes it easier to disperse stress, thereby preventing interfacial failure and achieving excellent adhesion after foaming and curing.

[0093] The (meth)acrylic acid ester copolymer is preferably a block copolymer, and particularly preferably an ABA block copolymer having a polymer block A as the compatible portion and a polymer block B as the incompatible portion. Furthermore, an ABA block copolymer having a first polymer portion as the incompatible portion and a second polymer portion as the compatible portion, polymer block B as the first polymer portion, and polymer block A as the second polymer portion, is preferred. By using such an ABA block copolymer as the acrylic resin, the island portions can be reduced in a case where a sea-island structure is formed in which the compatible portions of the cured epoxy resin and the (meth)acrylic acid ester copolymer are the sea and the incompatible portions of the (meth)acrylic acid ester copolymer are the islands. Furthermore, the sea portions can be reduced in a case where a sea-island structure is formed in which the incompatible portions of the (meth)acrylic acid ester copolymer are the sea and the compatible portions of the cured epoxy resin and the (meth)acrylic acid ester copolymer are the islands, or in a case where the (meth)acrylic acid ester copolymer is the sea and the cured epoxy resin is the islands.

[0094] The (meth)acrylic acid ester copolymer may be a modified product in which the above-mentioned polar group is introduced into a part of the first polymer segment or the second polymer segment.

[0095] The Tg of the first polymer portion contained in the (meth)acrylic acid ester copolymer is 10°C or less, and can be in the range of -150°C or more and 10°C or less, particularly in the range of -130°C or more and 0°C or less, and particularly in the range of -110°C or more and -10°C or less.

[0096] The Tg of the first polymer portion can be calculated using the following formula based on the Tg(K) of each homopolymer described in "POLYMERHANDBOOK, Third Edition" (published by John Wiley & Sons, Inc.). 1 / Tg(K)=W1 / Tg1+W2 / Tg2+····+W n / Tg n W n ; mass fraction of each monomer Tgn This is the Tg (K) of the homopolymer of each monomer, and publicly available values ​​such as those in the Polymer Handbook (3rd Ed., J. Brandrup and E.H. Immergut, Wiley Interscience) may be used. The same applies to the Tg of the second polymer portion described below.

[0097] The first polymer portion contained in the (meth)acrylic acid ester copolymer may be either a homopolymer or a copolymer, but is preferably a homopolymer. The monomer and polymer components constituting the first polymer portion may be any monomer and polymer components capable of obtaining a first polymer portion having a Tg within a predetermined range, and examples thereof include acrylate monomers such as butyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate, and methyl acrylate, other monomers such as vinyl acetate, acetal, and urethane, polar group-containing monomers containing the above-mentioned polar groups, and copolymers such as EVA.

[0098] The Tg of the second polymer portion contained in the (meth)acrylic acid ester copolymer is 20°C or higher, and can be within the range of 20°C or higher and 150°C or lower, particularly within the range of 30°C or higher and 150°C or lower, and particularly within the range of 40°C or higher and 150°C or lower.

[0099] The second polymer portion contained in the (meth)acrylic acid ester copolymer may be either a homopolymer or a copolymer, but is preferably a homopolymer. The monomer component constituting the second polymer portion may be any monomer component capable of obtaining a second polymer portion having a Tg within a predetermined range, and examples thereof include acrylic acid ester monomers such as methyl methacrylate, other monomers such as acrylamide, styrene, vinyl chloride, amide, acrylonitrile, cellulose acetate, phenol, urethane, vinylidene chloride, methylene chloride, and methacrylonitrile, and polar group-containing monomers containing the above-mentioned polar groups.

[0100] A specific example of the (meth)acrylic acid ester copolymer having the first polymer portion and the second polymer portion is the MMA-BA-MMA copolymer.

[0101] The content of the acrylic resin, based on 100 parts by mass of the resin components contained in the adhesive layer, may be, for example, 1 part by mass or more, 3 parts by mass or more, 5 parts by mass or more, 7 parts by mass or more, or 10 parts by mass or more. If the content of the acrylic resin is too low, the adhesion of the adhesive layer to the substrate and the adhesion after foaming and curing may be reduced. On the other hand, the content of the acrylic resin, based on 100 parts by mass of the resin components contained in the adhesive layer, may be, for example, 60 parts by mass or less, 50 parts by mass or less, 40 parts by mass or less, 35 parts by mass or less, or 30 parts by mass or less. If the content of the acrylic resin is too high, the contents of the first epoxy resin and the second epoxy resin may be relatively low, which may make it impossible to achieve a balance between non-stickiness, adhesion of the adhesive layer to the substrate, blocking resistance, and adhesion after foaming and curing. Furthermore, if the content of the acrylic resin is too high, the film strength may be reduced.

[0102] (iii) hardener The curing agent in this embodiment may be a curing agent generally used in epoxy resin adhesives. The curing agent is preferably solid at 23°C. A curing agent that is solid at 23°C can have a longer storage stability (pot life) than a curing agent that is liquid at 23°C. The curing agent may also be a latent curing agent. The curing agent may also be a curing agent that undergoes a curing reaction when heated, or a curing agent that undergoes a curing reaction when exposed to light. In the present disclosure, a single curing agent may be used, or two or more types of curing agents may be used.

[0103] The reaction initiation temperature of the curing agent is, for example, 110°C or higher, and may be 130°C or higher. If the reaction initiation temperature is too low, the reaction will start early, and curing will occur with low flexibility and fluidity of the resin component, making it difficult to achieve uniform curing. On the other hand, the reaction initiation temperature of the curing agent is, for example, 200°C or lower. If the reaction initiation temperature is too high, the resin component may deteriorate. Note that when a highly heat-resistant resin such as a phenolic resin is used in addition to the epoxy resin, the resin component will deteriorate less, and the reaction initiation temperature of the curing agent may be, for example, 300°C or lower. The reaction initiation temperature of the curing agent can be determined by differential scanning calorimetry (DSC).

[0104] Specific examples of the curing agent include imidazole-based curing agents, phenol-based curing agents, amine-based curing agents, acid anhydride-based curing agents, isocyanate-based curing agents, and thiol-based curing agents.

[0105] Examples of imidazole-based curing agents include imidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2-methylimidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole, 2-isopropylimidazole, and 2-phenylimidazole, as well as carboxylic acid salts of imidazole compounds and adducts with epoxy compounds. Furthermore, it is preferable that the imidazole-based curing agent has a hydroxyl group. Crystallization occurs due to hydrogen bonding between the hydroxyl groups, which tends to increase the reaction initiation temperature.

[0106] Examples of phenolic curing agents include phenolic resins. Further examples of phenolic resins include resol-type phenolic resins and novolac-type phenolic resins. From the viewpoint of adhesion of the adhesive layer to the substrate, phenolic-type novolac resins having a Tg of 110°C or less are particularly preferred. Furthermore, phenolic curing agents and imidazole-type curing agents may be used in combination. In this case, it is preferable to use an imidazole-type curing agent as a curing catalyst.

[0107] Examples of amine-based curing agents include aliphatic amines such as diethylenetriamine (DETA), triethylenetetramine (TETA), and metaxylylenediamine (MXDA); aromatic amines such as diaminodiphenylmethane (DDM), m-phenylenediamine (MPDA), and diaminodiphenylsulfone (DDS); alicyclic amines; and polyamidoamines. Furthermore, examples of amine-based curing agents that can be used include dicyandiamide-based curing agents such as dicyandiamide (DICY), organic acid dihydrazide-based curing agents, amine adduct-based curing agents, and ketimine-based curing agents.

[0108] Examples of acid anhydride curing agents include alicyclic acid anhydrides (liquid acid anhydrides) such as hexahydrophthalic anhydride (HHPA) and methyltetrahydrophthalic anhydride (MTHPA); and aromatic acid anhydrides such as trimellitic anhydride (TMA), pyromellitic anhydride (PMDA), and benzophenonetetracarboxylic acid (BTDA).

[0109] The isocyanate curing agent may, for example, be a blocked isocyanate.

[0110] Examples of thiol-based curing agents include ester-bonded thiol compounds, aliphatic ether-bonded thiol compounds, and aromatic ether-bonded thiol compounds.

[0111] The content of the curing agent is, for example, 1 part by mass or more and 40 parts by mass or less, based on 100 parts by mass of the resin component contained in the adhesive layer. For example, when an imidazole-based curing agent is used as the main component of the curing agent, the content of the curing agent is preferably, for example, 1 part by mass or more and 15 parts by mass or less, based on 100 parts by mass of the resin component contained in the adhesive layer. On the other hand, when a phenol-based curing agent is used as the main component of the curing agent, the content of the curing agent is preferably, for example, 5 parts by mass or more and 40 parts by mass or less, based on 100 parts by mass of the resin component contained in the adhesive layer. Note that using an imidazole-based curing agent or a phenol-based curing agent as the main component of the curing agent means that the mass proportion of the imidazole-based curing agent or the phenol-based curing agent is the highest in the curing agent.

[0112] (b) Foaming agent The foaming agent in this embodiment may be a foaming agent generally used in the adhesive layer of a foamable adhesive sheet. The foaming agent may be a foaming agent that undergoes a foaming reaction when exposed to heat or light.

[0113] The foaming initiation temperature of the foaming agent is preferably equal to or higher than the softening temperature of the base of the curable adhesive, such as an epoxy resin, and equal to or lower than the activation temperature of the curing reaction of the base of the curable adhesive, such as an epoxy resin. The foaming initiation temperature of the foaming agent is, for example, 70°C or higher, and may be 100°C or higher. If the reaction initiation temperature is too low, the reaction may start early, causing foaming to occur in a state where the flexibility and fluidity of the resin component are low, making it difficult to achieve uniform foaming. On the other hand, the reaction initiation temperature of the foaming agent is, for example, 210°C or lower. If the reaction initiation temperature is too high, the resin component may deteriorate.

[0114] The softening temperature of the base agent of a curable adhesive such as an epoxy resin can be measured using the ring and ball softening temperature test method specified in JIS K7234.

[0115] The foaming agent may be, for example, a microcapsule type foaming agent, which preferably has a core made of a thermal expansion agent such as hydrocarbon and a shell made of a resin such as acrylonitrile copolymer.

[0116] In addition, organic or inorganic blowing agents may be used as the blowing agent. Examples of organic blowing agents include azo blowing agents such as azodicarbonamide (ADCA), azobisformamide, and azobisisobutyronitrile; fluorinated alkane blowing agents such as trichloromonofluoromethane; hydrazine blowing agents such as paratoluenesulfonylhydrazide; semicarbazide blowing agents such as p-toluenesulfonylsemicarbazide; triazole blowing agents such as 5-morpholyl-1,2,3,4-thiatriazole; and N-nitroso blowing agents such as N,N-dinitrosoterephthalamide. Examples of inorganic blowing agents include ammonium carbonate, ammonium bicarbonate, ammonium nitrite, ammonium borohydride, and azides.

[0117] The average particle size of the foaming agent may be, for example, 10 μm or more, 13 μm or more, or 17 μm or more. By having the average particle size of the foaming agent within the above range, the pencil hardness of the surface of the adhesive layer can be increased, and the static friction coefficient of the surface of the adhesive layer can be reduced, resulting in a foamable adhesive sheet with good slip properties and insertability. Furthermore, the average particle size of the foaming agent is preferably equal to or less than the average thickness of the adhesive layer, and may be, for example, 44 μm or less, 30 μm or less, or 24 μm or less.

[0118] The average particle size of the foaming agent is the particle size at 50% of the cumulative value in the particle size distribution determined by laser diffraction scattering. To measure the average particle size of the foaming agent, the adhesive layer is dissolved in a solvent to separate the foaming agent. The solvent is not particularly limited as long as it can dissolve components other than the foaming agent contained in the adhesive layer. It is appropriately selected depending on the type of curable adhesive contained in the adhesive layer, and for example, a solvent used in the adhesive composition used to form the adhesive layer can be used. Specific examples include methyl ethyl ketone, ethyl acetate, and toluene.

[0119] The content of the foaming agent is, for example, 0.5 parts by mass or more, 2 parts by mass or more, 3 parts by mass or more, 4 parts by mass or more, or 5 parts by mass or more, based on 100 parts by mass of the resin component contained in the adhesive layer. On the other hand, the content of the foaming agent is, for example, 25 parts by mass or less, 20 parts by mass or less, or 15 parts by mass or less, based on 100 parts by mass of the resin component contained in the adhesive layer. If the content of the foaming agent is too low, the static friction coefficient of the surface of the adhesive layer may increase or the pencil hardness of the surface of the adhesive layer may decrease. Furthermore, if the content of the foaming agent is too high, the content of the curable adhesive may be relatively low, which may result in a decrease in adhesion after foaming and curing.

[0120] (c) Other ingredients In the present embodiment, when the curable adhesive is an epoxy resin adhesive, the adhesive layer may contain only an epoxy resin and an acrylic resin as resin components, or may further contain other resins, such as urethane resins.

[0121] The total proportion of the first epoxy resin, the second epoxy resin, and the acrylic resin relative to the resin components contained in the adhesive layer is, for example, 70% by mass or more, or may be 80% by mass or more, or 90% by mass or more, or may be 100% by mass.

[0122] The content of the resin component in the adhesive layer is, for example, 60% by mass or more, optionally 70% by mass or more, optionally 80% by mass or more, or optionally 90% by mass or more.

[0123] The adhesive layer may contain, as needed, for example, a silane coupling agent, a filler, an antioxidant, a light stabilizer, an ultraviolet absorber, a lubricant, a plasticizer, an antistatic agent, a crosslinking agent, and a colorant. Examples of the silane coupling agent include epoxy-based silane coupling agents. Examples of the filler include inorganic fillers such as calcium carbonate, aluminum hydroxide, magnesium hydroxide, antimony trioxide, zinc borate, molybdenum compounds, and titanium dioxide. Examples of the antioxidant include phenol-based antioxidants and sulfur-based antioxidants.

[0124] (2) Structure of the adhesive layer The adhesive layer can be foamed at an expansion ratio of, for example, 1.5 times or more and 15 times or less. The expansion ratio may be, for example, 3.5 times or more, 4 times or more, or 4.5 times or more. The expansion ratio may be, for example, 9 times or less, 8.5 times or less, or 8 times or less. If the expansion ratio is too small or too large, the adhesiveness after foaming and curing may be reduced.

[0125] Here, the expansion ratio can be calculated by the following formula. Foaming ratio (times) = adhesive layer thickness after foaming and hardening / adhesive layer thickness before foaming and hardening

[0126] The average thickness of the adhesive layer is not particularly limited, but is preferably equal to or greater than the average particle size of the foaming agent, for example, 10 μm or more, or 15 μm or more, or even 20 μm or more. If the adhesive layer is too thin, it may be difficult to obtain sufficient adhesion to the substrate and adhesion after foaming and curing. On the other hand, the average thickness of the adhesive layer is, for example, 200 μm or less, or may be 150 μm or less, or may be 100 μm or less. If the adhesive layer is too thick, the surface quality may deteriorate or the pencil hardness may decrease.

[0127] Here, the average thickness of the adhesive layer is a value measured from a cross section of the foamable adhesive sheet in the thickness direction as observed with a transmission electron microscope (TEM), a scanning electron microscope (SEM), or a scanning transmission electron microscope (STEM), and can be the average value of thicknesses at 10 randomly selected locations. The same method can be used to measure the average thickness of other layers of the foamable adhesive sheet.

[0128] The adhesive layer may be a continuous layer or a discontinuous layer. Examples of discontinuous layers include stripes and dots. The surface of the adhesive layer may have an uneven shape such as an embossed shape.

[0129] The adhesive layer can be formed, for example, by applying an adhesive composition containing the above-mentioned curable adhesive and a foaming agent, etc., and then removing the solvent. Examples of application methods include roll coating, reverse roll coating, transfer roll coating, gravure coating, gravure reverse coating, comma coating, rod coating, blade coating, bar coating, wire bar coating, die coating, lip coating, and dip coating.

[0130] The adhesive composition may or may not contain a solvent. In this specification, the term "solvent" is used in a broad sense to include not only a strict solvent (a solvent that dissolves a solute) but also a dispersion medium. The solvent contained in the adhesive composition is volatilized and removed when the adhesive composition is applied and dried to form an adhesive layer.

[0131] The adhesive composition can be obtained by mixing the above-mentioned components and kneading and dispersing them as necessary. As a mixing and dispersing method, a general kneading disperser, such as a two-roll mill, a three-roll mill, a pebble mill, a tron ​​mill, a Szegvari attritor, a high-speed impeller disperser, a high-speed stone mill, a high-speed impact mill, a desper, a high-speed mixer, a ribbon blender, a co-kneader, an intensive mixer, a tumbler, a blender, a desperzer, a homogenizer, or an ultrasonic disperser, can be used.

[0132] 3.Base material The substrate in this embodiment may be, for example, a support substrate that supports the adhesive layer, or a separator that protects the adhesive layer.

[0133] (1) Supporting base material The supporting substrate in this embodiment preferably has insulating properties. The supporting substrate is preferably in the form of a sheet. The supporting substrate may have a single-layer structure or a multi-layer structure. The supporting substrate may or may not have a porous structure inside.

[0134] Examples of the supporting substrate include a resin substrate and a nonwoven fabric.

[0135] Examples of resins contained in the resin substrate include polyester resins such as polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate (PEN), and aromatic polyester; polycarbonate; polyarylate; polyurethane; polyamide resins such as polyamide and polyetheramide; polyimide resins such as polyimide, polyetherimide, and polyamideimide; polysulfone resins such as polysulfone and polyethersulfone; polyetherketone resins such as polyetherketone and polyetheretherketone; polyphenylene sulfide (PPS); and modified polyphenylene oxide. The glass transition temperature of the resin is, for example, 80°C or higher, or may be 140°C or higher, or even 200°C or higher. Furthermore, a liquid crystal polymer (LCP) may be used as the resin.

[0136] Examples of nonwoven fabrics include nonwoven fabrics containing fibers such as cellulose fibers, polyester fibers, nylon fibers, aramid fibers, polyphenylene sulfide fibers, liquid crystal polymer fibers, glass fibers, metal fibers, and carbon fibers.

[0137] The surface of the supporting substrate on which the adhesive layer is to be disposed may be subjected to a surface treatment in order to enhance adhesion to the adhesive layer.

[0138] The average thickness of the supporting substrate is not particularly limited, but may be, for example, 2 μm or more, 5 μm or more, or 9 μm or more, and may be, for example, 200 μm or less, 100 μm or less, or 50 μm or less.

[0139] (2) Separator The separator in this embodiment is not particularly limited as long as it can be peeled from the adhesive layer, and it can have a strength sufficient to protect the adhesive layer. Examples of such separators include release films and release papers. The separator may have a single-layer structure or a multi-layer structure.

[0140] An example of a separator having a single layer structure is a fluororesin film.

[0141] Further, examples of multilayer separators include laminates having a release layer on one or both sides of a substrate layer. Examples of substrate layers include resin films such as polypropylene, polyethylene, and polyethylene terephthalate, as well as paper such as fine paper, coated paper, and impregnated paper. The material for the release layer is not particularly limited as long as it has releasability, and examples include silicone compounds, organic compound-modified silicone compounds, fluorine compounds, aminoalkyd compounds, melamine compounds, acrylic compounds, polyester compounds, and long-chain alkyl compounds. These compounds can be emulsion-type, solvent-type, or solventless.

[0142] 4. Other configurations In the present embodiment, when the substrate is a support substrate, the foamable adhesive sheet may have an intermediate layer between the substrate and the adhesive layer. The presence of the intermediate layer can improve the adhesion of the adhesive layer to the substrate. Furthermore, the presence of the intermediate layer can, for example, reduce stress on the bent portion when the foamable adhesive sheet is folded, or reduce stress on the cut portion when the foamable adhesive sheet is cut. As a result, lifting or peeling of the adhesive layer from the substrate can be suppressed when the foamable adhesive sheet is bent or cut.

[0143] For example, in the foamable adhesive sheet 10 shown in Fig. 3, a substrate 2, an intermediate layer 3, and an adhesive layer 1 are arranged in this order in the thickness direction. In the foamable adhesive sheet 10 shown in Fig. 4, a first adhesive layer 1a is arranged on one side of the substrate 2, a second adhesive layer 1b is arranged on the other side of the substrate 2, a first intermediate layer 3a is arranged between the substrate 2 and the first adhesive layer 1a, and a second intermediate layer 3b is arranged between the substrate 2 and the second adhesive layer 1b. Note that, although the foamable adhesive sheet 10 in Fig. 4 has both the first intermediate layer 3a and the second intermediate layer 3b, it may have only one of them.

[0144] When adhesive layers are disposed on both sides of the substrate, it is sufficient that an intermediate layer is disposed between the substrate and at least one of the adhesive layers, and for example, an intermediate layer may be disposed between the substrate and only one of the adhesive layers, or an intermediate layer may be disposed between the substrate and both adhesive layers. Of these, it is preferable that an intermediate layer is disposed between the substrate and both adhesive layers.

[0145] The material contained in the intermediate layer is not particularly limited as long as it can increase the adhesion between the substrate and the adhesive layer and relieve stress, and is appropriately selected depending on the materials of the substrate and the adhesive layer, etc. Examples include polyester, polyvinyl chloride, polyvinyl acetate, polyurethane, copolymers of at least two of these, crosslinked products thereof, and mixtures thereof.

[0146] The crosslinked product is a crosslinked product obtained by crosslinking the above resin with a curing agent. Examples of the curing agent include an isocyanate-based curing agent. Furthermore, for example, when the reactive group / NCO equivalent is 1, it is preferable to add the isocyanate-based curing agent in a ratio of 0.5% by mass or more to 20% by mass or less relative to the resin.

[0147] In particular, the intermediate layer preferably contains a crosslinked resin. Note that a crosslinked resin is one that does not melt even at high temperatures. This improves adhesive strength at high temperatures, i.e., heat resistance.

[0148] The average thickness of the intermediate layer is not particularly limited, but may be, for example, 0.1 μm or more, 0.5 μm or more, or even 1 μm or more. If the intermediate layer is too thin, the effect of suppressing peeling of the adhesive layer from the substrate when the foamable adhesive sheet is bent or cut may not be sufficiently obtained. On the other hand, the average thickness of the intermediate layer may be, for example, 4 μm or less, or 3.5 μm or less. Since the intermediate layer itself usually does not have high heat resistance, if the intermediate layer is too thick, heat resistance (adhesive strength at high temperatures) may be reduced.

[0149] The intermediate layer can be formed, for example, by applying a resin composition and removing the solvent. Examples of the application method include roll coating, reverse roll coating, transfer roll coating, gravure coating, gravure reverse coating, comma coating, rod coating, blade coating, bar coating, wire bar coating, die coating, lip coating, and dip coating.

[0150] 5.Foam adhesive sheet The average thickness of the foamable adhesive sheet in this embodiment is, for example, 10 μm or more, and may be 20 μm or more, while the average thickness of the foamable adhesive sheet is, for example, 1000 μm or less, and may be 200 μm or less.

[0151] The use of the foamable adhesive sheet of this embodiment is not particularly limited. For example, the foamable adhesive sheet of this embodiment can be used when bonding components together by placing the foamable adhesive sheet between components and then foaming and curing the foamable adhesive sheet.

[0152] 6. Manufacturing method of foam adhesive sheet The method for producing the foamable adhesive sheet in this embodiment is not particularly limited. For example, an adhesive layer can be formed by applying the above-mentioned adhesive composition to one side of a substrate and drying it. When a first adhesive layer is formed on one side of the substrate and a second adhesive layer is formed on the other side of the substrate, the first adhesive layer and the second adhesive layer can be formed sequentially or simultaneously.

[0153] II. Second embodiment A second embodiment of the foamable adhesive sheet of the present disclosure will now be described in detail.

[0154] The inventors of the present disclosure have focused on the average particle size of the foaming agent contained in the adhesive layer of a foamable adhesive sheet and conducted extensive research into the adhesive properties after foaming and curing. They found that when the average particle size of the foaming agent is relatively small, adhesion is good when the gap between components is relatively narrow, but adhesion may decrease when the gap between components is relatively wide. They also found that when the average particle size of the foaming agent is relatively large, adhesion may decrease when the gap between components is relatively narrow. Surprisingly, they found that when the average particle size of the foaming agent is within a predetermined range, adhesion is good not only when the gap between components is relatively narrow, but also when the gap between components is relatively wide. This embodiment is based on these findings.

[0155] The foamable adhesive sheet in this embodiment has a substrate and an adhesive layer arranged on at least one side of the substrate, the adhesive layer containing a curable adhesive and a foaming agent, and the average particle size of the foaming agent is 10 μm or more and 24 μm or less.

[0156] 1 and 2 are schematic cross-sectional views illustrating an example of a foamable adhesive sheet according to this embodiment. The details of FIGS. 1 and 2 are the same as those described in the first embodiment. The adhesive layer 1, the first adhesive layer 1a, and the second adhesive layer 1b contain a curable adhesive and a foaming agent, and the foaming agent has an average particle size within a predetermined range.

[0157] In the foamable adhesive sheet of this embodiment, the average particle size of the foaming agent contained in the adhesive layer is within a predetermined range, thereby achieving good adhesion even when the gap between components is relatively wide. The reason for this is unclear, but is presumed to be as follows: If the average particle size of the foaming agent is too small, the expansion ratio of the adhesive layer tends to be small. Therefore, even if good adhesion is obtained when the gap between components is narrow, adhesion may decrease when the gap between components is wide. Furthermore, if the average particle size of the foaming agent is small, the expansion ratio of the adhesive layer can be increased by increasing the foaming agent content. However, increasing the foaming agent content results in a relatively low content of curable adhesive, which leads to thinner walls between bubbles in the adhesive layer after foaming and curing, a decrease in cohesive force, and a decrease in adhesion when the gap between components is wide. On the other hand, if the average particle size of the foaming agent is too large, the expansion ratio of the adhesive layer increases, but the bubbles in the adhesive layer after foaming and curing become larger, which leads to thinner walls between bubbles and a decrease in cohesive force, resulting in a decrease in adhesion both when the gap between components is narrow and when the gap between components is wide. In contrast, when the average particle size of the foaming agent is within a specified range, the foaming ratio of the adhesive layer is not too small, so that the gaps between the components can be sufficiently filled, and the bubbles in the adhesive layer after foaming and hardening are not too large, so that the walls between the bubbles become thicker, and the contact area between the walls between the bubbles in the adhesive layer after foaming and hardening and the components can be increased.As a result, it is thought that good adhesion can be obtained not only when the gaps between the components are narrow, but also when the gaps between the components are wide.

[0158] Therefore, when components are bonded together by placing a foam adhesive sheet between them, for example, the gap between the components can be widened, making it easier to insert the foam adhesive sheet into the gap between the components, or to insert one component into the gap after placing the foam adhesive sheet on the other component. Furthermore, by using the foam adhesive sheet of this embodiment, for example, even if tolerances occur in the components, the components can be bonded together well regardless of the tolerances.

[0159] Hereinafter, each component of the foamable adhesive sheet in this embodiment will be described.

[0160] 1.Adhesive layer The adhesive layer in this embodiment is disposed on at least one surface of the substrate, and contains a curable adhesive and a foaming agent.

[0161] (1) Adhesive layer material (a) Foaming agent The average particle size of the foaming agent in this embodiment is, for example, 10 μm or more, or may be 13 μm or more, or 17 μm or more. The average particle size of the foaming agent is, for example, 24 μm or less, or may be 21 μm or less, or may be 20 μm or less. By having the average particle size of the foaming agent within the above range, good adhesion can be obtained both when the gap between the components is relatively narrow and when the gap between the components is relatively wide.

[0162] The method for measuring the average particle size of the foaming agent is the same as in the first embodiment.

[0163] The foaming agent is not particularly limited as long as it has a predetermined average particle size, and foaming agents generally used in adhesive layers of foamable adhesive sheets can be used. The type of foaming agent and foaming initiation temperature can be the same as those described in the first embodiment above.

[0164] The content of the foaming agent is, for example, 3 parts by mass or more, 4 parts by mass or more, or even 5 parts by mass or more, based on 100 parts by mass of the resin component contained in the adhesive layer. On the other hand, the content of the foaming agent is, for example, 25 parts by mass or less, 20 parts by mass or less, or even 15 parts by mass or less, based on 100 parts by mass of the resin component contained in the adhesive layer. If the content of the foaming agent is too low, the expansion ratio of the adhesive layer will be small, which may result in reduced adhesion when the gap between the components is large. Furthermore, if the content of the foaming agent is too high, the content of the curable adhesive will be relatively low, which may result in thinner walls between bubbles in the adhesive layer after foaming and curing, reduced cohesive force, and reduced adhesion.

[0165] (b) Hardening adhesive The curable adhesive may be the same as the curable adhesive described in the first embodiment. Examples of the curable adhesive include epoxy resin adhesives, acrylic resin adhesives, phenol resin adhesives, unsaturated polyester resin adhesives, alkyd resin adhesives, urethane resin adhesives, and thermosetting polyimide resin adhesives. Of these, the curable adhesive is preferably an epoxy resin adhesive.

[0166] An example in which the curable adhesive is an epoxy resin adhesive will be described below.

[0167] (i) Epoxy resin The definition of the epoxy resin may be the same as that of the epoxy resin described in the first embodiment above, and the type of the epoxy resin may be the same as that of the first epoxy resin described in the first embodiment above.

[0168] (ii) Acrylic resin When the curable adhesive is an epoxy adhesive, it may further contain an acrylic resin that is compatible with the epoxy resin. The acrylic resin may be the same as the acrylic resin described in the first embodiment.

[0169] (iii) hardener The curing agent may be the same as the curing agent described in the first embodiment.

[0170] (c) Other ingredients In the present embodiment, when the curable adhesive is an epoxy resin adhesive, the adhesive layer may further contain, as a resin component, a resin other than the above-described epoxy resin and acrylic resin, such as a urethane resin.

[0171] The total proportion of epoxy resin and acrylic resin relative to the resin components contained in the adhesive layer is, for example, 70% by mass or more, or may be 80% by mass or more, or 90% by mass or more, or may be 100% by mass.

[0172] The content of the resin component contained in the adhesive layer can be the same as in the first embodiment.

[0173] The adhesive layer may contain additives as needed, which may be the same as those described in the first embodiment.

[0174] (2) Structure of the adhesive layer The adhesive layer in this embodiment can be expanded at an expansion ratio of, for example, 3.5 times or more and 9 times or less. The expansion ratio may be, for example, 4 times or more, or 4.5 times or more. The expansion ratio may be, for example, 8.5 times or less, or 8 times or less. When the expansion ratio is within the above range, adhesion tends to be high when the gap between the members is wide. On the other hand, if the expansion ratio is too small, adhesion may decrease when the gap between the members is wide. Furthermore, if the expansion ratio is too large, adhesion may decrease even when the gap between the members is narrow. The method for determining the expansion ratio is the same as in the first embodiment.

[0175] The adhesive layer in this embodiment is preferably substantially non-tacky (tack-free). By making the adhesive layer substantially non-tacky (tack-free), the foamable adhesive sheet can have good sliding properties and blocking resistance. This improves the handleability and workability of the foamable adhesive sheet. Specifically, when a foamable adhesive sheet is placed between components to bond them together, the foamable adhesive sheet can be smoothly inserted into gaps between or between components, or after a foamable adhesive sheet is placed on one component, the other component can be smoothly inserted into the gap.

[0176] Here, non-tacky is generally used mainly to mean low adhesive strength, and in the present disclosure, "non-tacky" refers to a state in which the foamable adhesive sheet can be wound into a roll and then easily unwound without resistance.

[0177] The adhesive strength of the adhesive layer when the adhesive layer is substantially non-adhesive can be the same as that of the adhesive layer described in the first embodiment above. Furthermore, the adhesive strength of the adhesive layer when adhesive layers are disposed on both sides of the substrate can also be the same as that described in the first embodiment above. The method for measuring the adhesive strength of the adhesive layer is the same as that of the first embodiment above.

[0178] The average thickness, shape, and method of forming the adhesive layer can be the same as those described in the first embodiment.

[0179] 2. Base material The substrate may be the same as the substrate described in the first embodiment.

[0180] 3. Other configurations When the foamable adhesive sheet of this embodiment uses the substrate as a support substrate, it may have an intermediate layer between the substrate and the adhesive layer, which may be the same as the intermediate layer described in the first embodiment.

[0181] 4.Foam adhesive sheet The average thickness and uses of the foamable adhesive sheet in this embodiment can be the same as those described in the first embodiment above.

[0182] The foamable adhesive sheet of this embodiment preferably has high adhesiveness after foaming and curing. The shear strength (adhesive strength) based on JIS K6850, which corresponds to ISO 4587, at 23°C is preferably 2.10 MPa or higher, more preferably 2.40 MPa or higher, and even more preferably 3.0 MPa or higher. Furthermore, the shear strength (adhesive strength) at 200°C is preferably 0.55 MPa or higher, more preferably 0.58 MPa or higher. As mentioned above, for example, high-strength acrylic foam adhesive tapes that do not require heating have shear strengths (adhesive strengths) of approximately 1 MPa to 2 MPa at room temperature and lack heat resistance at 200°C. Therefore, if the shear strength (adhesive strength) is within the above range at 23°C, it has advantages in terms of strength. Furthermore, if the shear strength (adhesive strength) is within the above range at 200°C, it can be used in applications requiring heat resistance such as around automobile engines.

[0183] The foamable adhesive sheet of this embodiment preferably has good shape retention. The bending moment can be the same as in the first embodiment.

[0184] The foamable adhesive sheet of this embodiment preferably has high electrical insulation properties after foaming and curing. The breakdown voltage and thermal conductivity can be the same as those of the first embodiment.

[0185] B. How the Article is Manufactured The method for manufacturing an article according to the present disclosure includes a placement step of placing the above-mentioned foamable adhesive sheet between a first member and a second member, and a bonding step of foaming and curing the foamable adhesive sheet to bond the first member and the second member together.

[0186] Fig. 5 is a process diagram showing an example of a method for manufacturing an article according to the present disclosure. First, as shown in Fig. 5(a), a foamable adhesive sheet 10 is placed between a first member 20a and a second member 20b. Next, as shown in Fig. 5(b), the foamable adhesive sheet 10 is foamed and cured, for example, by heating. The foamed and cured adhesive sheet 11 adheres (bonds) the first member 20a and the second member 20b. This results in an article 100 in which the adhesive sheet 11 is placed between the first member 20a and the second member 20b.

[0187] In the method for manufacturing an article according to the present disclosure, when the foamable adhesive sheet of the first embodiment described above is used, the foamable adhesive sheet can be smoothly inserted into a gap between one member or two members, or one member can be smoothly inserted into the gap after the foamable adhesive sheet has been placed on the other member. Furthermore, the use of the foamable adhesive sheet described above allows for accurate alignment of the two members.

[0188] Furthermore, in the method for manufacturing an article according to the present disclosure, when the foamable adhesive sheet of the second embodiment described above is used, good adhesion can be obtained both when the gap between the members is narrow and when the gap between the members is wide, and therefore an article can be obtained in which the first and second members have good adhesion.

[0189] The method for manufacturing the article according to the present disclosure will now be described.

[0190] 1.Foam adhesive sheet In the method for producing an article according to the present disclosure, the foamable adhesive sheet used is the foamable adhesive sheet described above.

[0191] When the substrate in the foamable adhesive sheet is the support substrate, the foamable adhesive sheet can have an adhesive layer and a substrate arranged in this order. In this case, if the foamable adhesive sheet is the foamable adhesive sheet of the first embodiment described above, the foamable adhesive sheet can have an adhesive layer with a predetermined adhesive strength and a static friction coefficient and pencil hardness within predetermined ranges on the surface of the adhesive layer opposite the substrate. Alternatively, the foamable adhesive sheet can have a first adhesive layer and a second adhesive layer as adhesive layers, with the first adhesive layer, substrate, and second adhesive layer arranged in this order in the thickness direction. In this case, if the foamable adhesive sheet is the foamable adhesive sheet of the first embodiment described above, the adhesive strength of either the first adhesive layer or the second adhesive layer can be within a predetermined range, and the static friction coefficient and pencil hardness of either adhesive layer opposite the substrate can be within a predetermined range.

[0192] On the other hand, when the substrate of the foamable adhesive sheet is a separator, the substrate is peeled off from the foamable adhesive sheet when the foamable adhesive sheet is disposed between the first member and the second member.

[0193] Details of the foamable adhesive sheet are described above in the section "A. Foamable adhesive sheet," so further description will be omitted here.

[0194] 2.Placement process In the placement step of the present disclosure, the method for placing the foamable adhesive sheet between the first member and the second member is not particularly limited, and examples include a method of inserting the foamable adhesive sheet into the gap between the first member and the second member, or a method of placing the foamable adhesive sheet on the first member and then inserting the second member into the gap after placing the foamable adhesive sheet on the first member.

[0195] 3.Gluing process In the bonding step of the present disclosure, examples of the method for foaming and curing the foamable adhesive sheet include heating and light irradiation. Among these, it is preferable to foam and cure the foamable adhesive sheet by heating. The heating method is also applicable even when the first and second members are not transparent, such as when the first and second members are made of metal.

[0196] The heating conditions are appropriately set depending on the types of curable adhesive and foaming agent contained in the adhesive layer, the type of substrate, etc. The heating temperature can be, for example, 130° C. or higher and 200° C. or lower. The heating time can be, for example, 3 minutes or higher and 3 hours or lower.

[0197] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical idea described in the claims of the present disclosure and that provides similar effects is included within the technical scope of the present disclosure. [Example]

[0198] [Examples 1-1 to 1-11, Comparative Examples 1-1 to 1-4] The foamable adhesive sheet of the first embodiment will be described with reference to examples and comparative examples.

[0199] First, an adhesive composition was prepared having the composition (mass %) shown in Table 1 below. Details of each material listed in Table 1 are shown below.

[0200] Acrylic resin: PMMA-PBuA-PMMA (partially contains acrylamide groups), Tg: -20°C, 120°C, Mw: 150,000 Epoxy resin A: Bisphenol A novolac type, solid at room temperature, softening temperature: 70°C, epoxy equivalent: 210 g / eq, Mw: 1300, melt viscosity at 150°C: 0.5 Pa·s Epoxy resin B: BPA phenoxy type, solid at room temperature, softening temperature: 110°C, epoxy equivalent: 8000g / eq, Mw: 50,000 Hardener 1: α-(hydroxy(or dihydroxy)phenylmethyl)-ω-hydropoly[biphenyl-4,4'-diylmethylene(hydroxy(or dihydroxy)phenylenemethylene)] Curing agent 2: 2-phenyl-4,5-dihydroxymethylimidazole, average particle size: 3 μm, melting point: 230°C, reaction initiation temperature: 145°C to 155°C, active temperature range: 155°C to 173°C (Shikoku Chemicals Corporation, 2PHZ-PW) Hardener 3: Dicyandiamide, particle size: 10 μm or less, melting point: 209°C (manufactured by Evonik Degussa, DYHARD100SH)

[0201] Thermal blowing agent 1: Thermal expansion microcapsules, average particle size 7μm, expansion start temperature 120~145℃, maximum expansion temperature 155~175℃, core: hydrocarbon, shell: thermoplastic polymer Thermal blowing agent 2: Thermal expansion microcapsules, average particle size 13 μm, expansion start temperature 123-133°C, maximum expansion temperature 168-178°C, core: hydrocarbon, shell: thermoplastic polymer Thermal blowing agent 3: Thermally expandable microcapsules, average particle size 17 μm, expansion start temperature 120-130°C, maximum expansion temperature 160-170°C, core: hydrocarbon, shell: acrylonitrile copolymer Thermal blowing agent 4: Thermal expansion microcapsules, average particle size 20 μm, expansion start temperature 115-125°C, maximum expansion temperature 155-165°C, core: hydrocarbon, shell: thermoplastic polymer Thermal blowing agent 5: Thermally expandable microcapsules, average particle size 21 μm, expansion start temperature 130-140°C, maximum expansion temperature 160-170°C, core: hydrocarbon, shell: acrylonitrile copolymer Thermal blowing agent 6: Thermal expansion microcapsules, average particle size 25 μm, expansion start temperature 125-135°C, maximum expansion temperature 165-180°C, core: hydrocarbon, shell: thermoplastic polymer Thermal blowing agent 7: Thermally expandable microcapsules, average particle size 30 μm, expansion start temperature 120-130°C, maximum expansion temperature 160-170°C, core: hydrocarbon, shell: acrylonitrile copolymer Thermal blowing agent 8: Thermally expandable microcapsules, average particle size 41 μm, expansion start temperature 115-125°C, maximum expansion temperature 165-175°C, core: hydrocarbon, shell: acrylonitrile copolymer Solvent: Methyl ethyl ketone

[0202] Next, a highly insulating polyphenylene sulfide film (PPS film, manufactured by Toray Industries, Inc., Torelina 115-3F00, thickness 115 μm) was used as the substrate. Furthermore, 15 parts by mass of a curing agent (polyisocyanate) and 0.3 parts by mass of a catalyst (trisdimethylaminomethylphenol) were blended with 100 parts by mass of polyester polymer, and the resulting mixture was diluted with methyl ethyl ketone (MEK) to a solids content of 15% by mass to prepare a resin composition. The resin composition was applied to one side of the substrate using a bar coater and dried in an oven at 100°C for 1 minute to form a first intermediate layer with a thickness of 2 μm. Furthermore, a second intermediate layer was formed on the other side of the substrate in the same manner as the first intermediate layer.

[0203] Next, the adhesive composition was applied to the surface of the first intermediate layer opposite the substrate using an applicator so that the thickness after application was 38 μm. This was then dried in an oven at 100°C for 3 minutes to form a first adhesive layer. Furthermore, a second adhesive layer was formed on the surface of the second intermediate layer opposite the substrate in the same manner as the first adhesive layer. This resulted in a foamable adhesive sheet in which the first adhesive layer, first intermediate layer, substrate, second intermediate layer, and second adhesive layer were arranged in this order.

[0204] [Rating 1] (Adhesive strength) The foam adhesive sheet was cut to a width of 24 mm and a length of 300 mm, and the first adhesive layer of the foam adhesive sheet was attached to a stainless steel plate (SUS304) using a manual roller. The adhesive strength (N / 25 mm) to the stainless steel plate was then measured using a tensile tester (A&D Corporation, Tensilon RTF1150) under conditions (pulling speed: 300 mm / min, peel distance: 150 mm, peel angle: 180°) in accordance with JIS Z0237:2009 (Testing Methods for Adhesive Tapes and Sheets), which was based on ISO 29862, and Method 1 of the adhesive strength test method (temperature: 23°C, humidity: 50%, peeling test method in which tapes and sheets are peeled at an angle of 180° from a stainless steel test plate).

[0205] (coefficient of friction) The dynamic and static coefficients of friction between the first adhesive layer of a foam adhesive sheet and a metal plate were measured in accordance with JIS K7125, which corresponds to ISO 8295. First, the foam adhesive sheet was cut into 80 mm x 200 mm pieces. Next, the foam adhesive sheet was placed on a horizontally placed rectangular metal plate. A sliding piece (63 mm x 63 mm, 200 g weight, felt base) was placed on the first adhesive layer of the foam adhesive sheet. The friction force was measured at 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 and static coefficients of friction were calculated. A Toyo Seiki Co., Ltd. Friction Tester TR-2 friction tester was used. The stainless steel plate used as the metal plate was made of SUS304 and had a surface roughness Ra of 0.05 μm.

[0206] (Pencil hardness) An A4-sized foamable adhesive sheet was prepared and placed on a glass plate. The pencil hardness of the first adhesive layer of the foamable adhesive sheet was measured using a pencil hardness tester (with a level) in accordance with JIS K5600, which corresponds to ISO 15184. The measurement conditions were a pencil angle of 45° from the horizontal, a load of 750 g, a test speed of 1 mm / sec, a test length of 20 mm, and a temperature of 23°C. The maximum pencil hardness that did not visually scratch the first adhesive layer of the foamable adhesive sheet was recorded as the pencil hardness. The pencil hardness tester used was a TQC KT-VF2378-12.

[0207] (Insertion weight) Two foam adhesive sheets cut to 5.5 cm x 6.0 cm were prepared, along with a hollow cylinder 1 with an outer diameter of 22 mm, a thickness of 1.5 mm, and a length of 60 mm, and a hollow cylinder 2 with an outer diameter of 18 mm, a thickness of 1.0 mm, and a length of 80 mm. The two foam adhesive sheets were stacked and rolled up with the first adhesive layer side facing inward, and then placed inside cylinder 1. Cylinder 2 was then pre-inserted about 1 mm into the gap inside the foam adhesive sheets in cylinder 1. A weight was then placed on cylinder 2, and the weight of the weight was measured when cylinder 2 was completely inserted into the gap inside the foam adhesive sheets in cylinder 1. This weight was taken as the insertion weight. The smaller the insertion weight, the better the insertion ability.

[0208] [Table 1]

[0209] As shown in Table 1, Example 1-3 had a smaller static friction coefficient and dynamic friction coefficient and a higher pencil hardness than Comparative Examples 1-1, 1-2, and 1-4, resulting in a smaller insertion weight. This suggests that the friction coefficient and hardness of the adhesive layer surface contribute to insertion performance. The evaluation results for the first adhesive layer and the second adhesive layer of the foamable adhesive sheet were nearly identical.

[0210] [Examples 2-1 to 2-9, Comparative Examples 2-1 to 2-5] The foamable adhesive sheet of the second embodiment will be described with reference to examples and comparative examples.

[0211] A foamable adhesive sheet was produced in the same manner as in Example 1-1.

[0212] Details of curing agents 4 and 5 shown in Table 2 below are shown below. Curing agent 4: 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanuric acid adduct, average particle size: 2 μm, melting point: 260°C, reaction initiation temperature: 120°C to 130°C, active region: 130°C to 146°C (Shikoku Chemicals Corporation, 2MAOK-PW) Hardener 5: Aliphatic dimethylurea compound, powder fine particles, melting point: 175°C (San-Apro Co., Ltd., UCAT-3513N)

[0213] [Rating 2] (Expansion ratio) The foamable adhesive sheet was cut into 50mm x 50mm pieces, hung lengthwise in a hot air dryer, and foam-cured at 180°C or 150°C for 30 minutes, then cooled at room temperature for 2 hours to obtain a foam-cured adhesive sheet. The thickness of the foam-cured adhesive sheet was then measured using a thickness gauge according to JIS Z0237. The expansion ratio was calculated using the following formula: Foaming ratio (times) = {thickness of adhesive sheet after foaming and curing - (thickness of base material + thickness of first intermediate layer + thickness of second intermediate layer)} / (total thickness of the first adhesive layer and second adhesive layer of the foamable adhesive sheet before foaming and curing)

[0214] (Adhesiveness) As shown in Figures 6(a) and 6(b), two metal plates 31 (cold-rolled steel plate SPCC-SD) with a thickness of 1.6 mm, width of 25 mm, and length of 100 mm were prepared. A spacer 32 (Kapton tape) was placed at a predetermined distance from one end of one of the metal plates 31. The spacer thickness was approximately 280 μm, approximately 350 μm, or approximately 420 μm (the thickness of four, five, or six layers of Kapton Tape P-221 manufactured by Nitto Denko Corporation). Next, a foam adhesive sheet 10 cut to a size of 12.5 mm x 25 mm was placed between the spacers 32, and the other metal plate 31 was placed so that one end overlapped.

[0215] 6(a), a test piece was obtained by placing a support 33, the thickness of which was the same as the total thickness of the metal plate 31 and the spacer 32, on the other end of each of the two metal plates 31. The test piece was then placed in a heat press and heated at 150°C for 8 minutes with a press load of 500 kgf, thereby curing the foamable adhesive sheet 10.

[0216] The remainder was fixed with clips to obtain a test piece, which was then placed in a heating oven and heated at 180° C. for 30 minutes to cure the foamable adhesive sheet 10.

[0217] The shear strength (adhesion strength) of the heated test pieces was measured using a tensile tester Tensilon RTF1350 (manufactured by A&D Co., Ltd.) in accordance with JIS K6850, which corresponds to ISO 4587. The measurement conditions were a tensile speed of 10 mm / min and a temperature of 200°C.

[0218] [Table 2]

[0219] As shown in Table 2, in Comparative Examples 2-1 to 2-2, the average particle size of the foaming agent was small, so the adhesive strength was good when the gap was about 280 μm, but the adhesive strength decreased when the gap was about 350 μm. In Comparative Examples 2-3 to 2-5, the average particle size of the foaming agent was large, so the adhesive strength decreased when the gap was about 280 μm. In Comparative Examples 2-6 and 2-8, the average particle size of the foaming agent was small, so the adhesive strength was good when the gap was about 280 μm or about 350 μm, but the adhesive strength decreased when the gap was about 420 μm. In Comparative Examples 2-7 and 2-9, the average particle size of the foaming agent was large, so the expansion ratio was high and the adhesive strength decreased regardless of the gap width. In contrast, in Examples 2-1 to 2-9, the average particle size of the foaming agent was within the specified range, so the adhesive strength was good both when the gap was about 280 μm and when the gap was about 350 μm. Furthermore, in Examples 2-10 to 2-13, the average particle size of the foaming agent was within a predetermined range, and therefore the adhesive strength was good when the gap was approximately 280 μm, approximately 350 μm, or approximately 420 μm. This suggests that when the average particle size of the foaming agent is within a predetermined range, the adhesiveness is good not only when the gap between the components is relatively narrow, but also when the gap between the components is relatively wide. [Explanation of symbols]

[0220] 1 … Adhesive layer 2...Base material 3. Middle class 10...Foam adhesive sheet 11... Adhesive sheet after foaming and hardening 20a ... First member 20b ... Second member 100 … Goods

Claims

1. A foamable adhesive sheet having a substrate and an adhesive layer disposed on at least one surface of the substrate, The adhesive layer contains a curable adhesive and a foaming agent, the curable adhesive contains an epoxy resin and a curing agent, and the curable adhesive contains, as the epoxy resin, an epoxy resin that is solid at room temperature; The adhesive layer is disposed on the outermost surface, The adhesive strength of the adhesive layer to a stainless steel plate, measured in accordance with Method 1 of the adhesive strength testing method of JIS Z0237:2009, is 0 N / 25 mm or more and 0.1 N / 25 mm or less; A foamable adhesive sheet, wherein the static friction coefficient of the surface of the adhesive layer opposite to the substrate is 0.26 or less.

2. A foamable adhesive sheet having a substrate and an adhesive layer disposed on at least one surface of the substrate, The adhesive layer contains a curable adhesive and a foaming agent, the curable adhesive contains an epoxy resin and a curing agent, and the curable adhesive contains, as the epoxy resin, an epoxy resin that is solid at room temperature; The adhesive layer is disposed on the outermost surface, The adhesive strength of the adhesive layer to a stainless steel plate, measured in accordance with Method 1 of the adhesive strength testing method of JIS Z0237:2009, is 0 N / 25 mm or more and 0.1 N / 25 mm or less; A foamable adhesive sheet having an insertion weight of 320 g or less, as measured by the following insertion weight measurement method. (Method of measuring insertion weight) (1) Prepare two 5.5 cm x 6.0 cm foamable adhesive sheets, a hollow cylinder 1 having an outer diameter of 22 mm, a thickness of 1.5 mm, and a length of 60 mm, and a hollow cylinder 2 having an outer diameter of 18 mm, a thickness of 1.0 mm, and a length of 80 mm. (2) The two foamable adhesive sheets are placed inside the cylinder 1 in a rolled-up state with the adhesive layer side facing inward. (3) The cylinder 2 is inserted into the gap inside the foamable adhesive sheet in the cylinder 1 by about 1 mm in advance. (4) Place a weight on the cylinder 2 and measure the weight of the weight when the cylinder 2 is completely inserted into the gap inside the foamable adhesive sheet inside the cylinder 1. The minimum weight of the weight at this time is taken as the insertion weight.

3. 3. The foamable adhesive sheet according to claim 1, wherein the bending moment is 3 gf·cm or more and less than 40 gf·cm.

4. a placement step of placing the foamable adhesive sheet according to any one of claims 1 to 3 between a first member and a second member; a bonding step of foaming and curing the foamable adhesive sheet to bond the first member and the second member together; A method for manufacturing an article, comprising:

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