Foamable adhesive sheet, article, stator for rotary electric machine, and rotor for rotary electric machine

Abstract

The present disclosure provides a foamable adhesive sheet having a first adhesive layer, a first gas barrier layer, a substrate, and a second gas barrier layer in this order, wherein the first adhesive layer contains a curable adhesive and a foaming agent, and the foaming agent comprises thermally expandable microcapsules.

Description

Foamable adhesive sheet, article, stator for rotating electric machine, and rotor for rotating electric machine

[0001] The present disclosure relates to a foamable adhesive sheet, and to an article, a stator for a rotating electric machine, and a rotor for a rotating electric machine using the foamable adhesive sheet.

[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).

[0004] JP 2017-203114 A International Publication No. 2016 / 163514

[0005] One known method for using a foamable adhesive sheet is to place the foamable adhesive sheet between two components and then allow the foamable adhesive sheet to foam and harden to bond the two components. Since the adhesive layer of such a foamable adhesive sheet contains a curable adhesive, high storage stability is desirable. However, when the foamable adhesive sheet is stored under high temperature and humidity, its foaming properties can deteriorate. In this case, depending on the size of the gap between the two components, the foamable adhesive sheet after foaming and hardening cannot fill the gap between the two components, resulting in reduced adhesive strength after foaming and hardening. Furthermore, when using a foamable adhesive sheet to bond two components, it is expected that the environment in which it is used will be high temperatures, so high adhesive durability is also desirable.

[0006] The present disclosure has been made in view of the above circumstances, and has as its main object to provide a foamable adhesive sheet that has excellent foaming properties and adhesive durability.

[0007] One embodiment of the present disclosure provides a foamable adhesive sheet having, in this order, a first adhesive layer, a first gas barrier layer, a substrate, and a second gas barrier layer, wherein the first adhesive layer contains a curable adhesive and a foaming agent, and the foaming agent is thermally expandable microcapsules.

[0008] Another embodiment of the present disclosure provides an article having a first member, a second member, and an adhesive member disposed between the first member and the second member, wherein the adhesive member has a first cured adhesive layer, a first gas barrier layer, a substrate, and a second gas barrier layer, in this order, the first cured adhesive layer contains a foamed, cured product of an adhesive composition comprising a curable adhesive and a foaming agent, and the foaming agent is a thermally expandable microcapsule.

[0009] Another embodiment of the present disclosure provides a stator for a rotating electric machine having a stator core, coils arranged in slots of the stator core, and an adhesive member arranged between the stator core and the coils, wherein the adhesive member has a first cured adhesive layer, a first gas barrier layer, a substrate, and a second gas barrier layer, in this order, the first cured adhesive layer contains a foamed cured product of an adhesive composition including a curable adhesive and a foaming agent, and the foaming agent is a thermally expandable microcapsule.

[0010] Another embodiment of the present disclosure provides a rotor for a rotating electric machine having a rotor core, a permanent magnet or a coil arranged in a slot of the rotor core, and an adhesive member arranged between the rotor core and the permanent magnet or the coil, wherein the adhesive member has a first cured adhesive layer, a first gas barrier layer, a substrate, and a second gas barrier layer, in this order, the first cured adhesive layer contains a foamed cured product of an adhesive composition including a curable adhesive and a foaming agent, and the foaming agent is a thermally expandable microcapsule.

[0011] The foamable adhesive sheet of the present disclosure exhibits the effects of excellent foaming properties and adhesive durability.

[0012] FIG. 1 is a schematic cross-sectional view illustrating an example of a foamable adhesive sheet according to the present disclosure. FIG. 2 is a schematic perspective view illustrating an example of a foamable adhesive sheet according to the present disclosure. FIG. 3 is a schematic cross-sectional view illustrating an example of a foamable adhesive sheet according to the present disclosure. FIG. 4 is a schematic cross-sectional view illustrating an example of a foamable adhesive sheet according to the present disclosure. FIG. 5 is a schematic cross-sectional view illustrating an example of a foamable adhesive sheet according to the present disclosure. FIG. 6 is a schematic cross-sectional view illustrating an example of an article according to the present disclosure. FIG. 7 is a schematic cross-sectional view illustrating an example of a stator for a rotating electric machine according to the present disclosure. FIG. 8 is a schematic cross-sectional view illustrating an example of a rotor for a rotating electric machine according to the present disclosure. FIG.

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

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

[0015] In this specification, the term "sheet" also includes a member called a "film."

[0016] Furthermore, the numerical ranges in this specification are ranges of average values.

[0017] The foamable adhesive sheet according to the present disclosure, as well as articles using the same, a stator for a rotating electric machine, and a rotor for a rotating electric machine, will be described in detail below.

[0018] A. Foamable Adhesive Sheet The foamable adhesive sheet according to the present disclosure comprises a first adhesive layer, a first gas barrier layer, a substrate, and a second gas barrier layer, in this order, wherein the first adhesive layer contains a curable adhesive and a foaming agent, and the foaming agent is thermally expandable microcapsules.

[0019] 1 is a schematic cross-sectional view showing an example of a foamable adhesive sheet according to the present disclosure. The foamable adhesive sheet 10 in FIG. 1 includes a first adhesive layer 1, a first gas barrier layer 2, a substrate 3, and a second gas barrier layer 4, and is arranged in a thickness direction D. Ｔ The first adhesive layer 1 contains a curable adhesive and a foaming agent, and the foaming agent is a thermally expandable microcapsule.

[0020] In the present disclosure, the foaming agent is a thermally expandable microcapsule, in which a thermal expansion agent such as hydrocarbon is encapsulated within a resin shell. The inventors of the present application conducted extensive research into the storage environment of foamable adhesive sheets and found that storing foamable adhesive sheets under high humidity conditions reduces the expansion ratio. This is believed to be due to the loss of the thermal expansion agent from the thermally expandable microcapsules under high humidity conditions. When a foamable adhesive sheet is used to bond a first member and a second member, a decrease in expansion ratio prevents the foamable adhesive sheet from sufficiently filling the gap between the first member and the second member after foaming and curing, resulting in reduced adhesive strength after foaming and curing. Therefore, moisture must be prevented when storing foamable adhesive sheets.

[0021] Here, the foamable adhesive sheet may be manufactured using a roll-to-roll production line, which is advantageous in terms of productivity. In this roll-to-roll production line, the foamable adhesive sheet is wound around a core in the form of a roll. The foamable adhesive sheet is often stored in a rolled state. Therefore, to prevent moisture, the rolled foamable adhesive sheet needs to be stored in a moisture-proof bag or in a low-humidity environment.

[0022] In contrast, in the present disclosure, when the foamable adhesive sheet 10 is wound into a roll as shown in Fig. 2 , and when the foamable adhesive sheet 10 is wound into a roll as shown in Fig. 3( a) so that the surface of the second gas barrier layer 4 of the foamable adhesive sheet 10 is on the outside and the surface of the first adhesive layer 1 is on the inside, the first adhesive layer 1 is located more inner than the first gas barrier layer 2 and the second gas barrier layer 4, thereby preventing moisture from penetrating from the outside into the first adhesive layer 1. Furthermore, when the foamable adhesive sheet 10 is wound into a roll as shown in Fig. 3( b) so that the surface of the first adhesive layer 1 of the foamable adhesive sheet 10 is on the outside and the surface of the second gas barrier layer 4 is on the inside, the first adhesive layer 1 of the foamable adhesive sheet 10B, which is located more inner than the outermost foamable adhesive sheet 10A, is located more inner than the first gas barrier layer 2 and the second gas barrier layer 4 of the foamable adhesive sheet 10A, thereby preventing moisture from penetrating from the outside into the first adhesive layer 1. The relationship between the foamable adhesive sheet 10B and the foamable adhesive sheet 10C is the same as the relationship between the foamable adhesive sheet 10A and the foamable adhesive sheet 10B described above.

[0023] Therefore, in the present disclosure, by winding up the foamable adhesive sheet into a roll, the first adhesive layer can be protected from moisture. This prevents a decrease in the expansion ratio of the first adhesive layer due to moisture, thereby achieving stable foaming characteristics and improving adhesiveness after foaming and curing. Furthermore, precise humidity control is not required for the foamable adhesive sheet, making it easy to handle.

[0024] Furthermore, the inventors of the present application conducted extensive research into the use environment of a foamed and cured foamable adhesive sheet and discovered that when the foamed and cured foamable adhesive sheet is used at high temperatures, the thickness of the foamed and cured foamable adhesive sheet decreases. One possible reason for this is that, at high temperatures, the substrate tends to be oxidatively decomposed, resulting in a decrease in the thickness of the substrate. When a foamed and cured foamable adhesive sheet is used to bond a first component and a second component, if the thickness of the foamed and cured foamable adhesive sheet decreases, the gap between the first and second components cannot be sufficiently filled with the foamed and cured foamable adhesive sheet, resulting in reduced adhesion. Furthermore, if the substrate has insulating properties, the substrate hardens upon oxidative decomposition, making it more susceptible to cracking. As a result, the adhesive properties and the insulating properties of the substrate decrease.

[0025] When a foamable adhesive sheet is used to bond a first member and a second member, a portion of the foamable adhesive sheet may be exposed. For example, when bonding a stator core and a coil in a rotating electric machine stator, it is preferable to place the foamable adhesive sheet between the stator core and the coil so that the foamable adhesive sheet protrudes from the edge of the stator core to suppress creeping discharge. In rotating electric machines, heat is generated when current flows through the coil. In this case, a portion of the foamable adhesive sheet is exposed after foaming and curing, and the foamable adhesive sheet is exposed to high temperatures, raising concerns about oxidative decomposition of the substrate. Furthermore, depending on the material of the first member or second member, for example, when the first member or second member contains a thermoplastic resin or rubber, the oxygen permeability of the first member or second member may increase at high temperatures. In this case, too, oxidative decomposition of the substrate is a concern.

[0026] In contrast, the foamable adhesive sheet of the present disclosure has a first gas barrier layer and a second gas barrier layer disposed on both sides of the substrate, thereby preventing oxygen from entering the substrate from the outside. This prevents oxidative decomposition of the substrate. As a result, when a first member and a second member are bonded using the foamable adhesive sheet, the thickness of the foamable adhesive sheet after foaming and curing can be maintained, thereby maintaining adhesion. Furthermore, it prevents a decrease in adhesion due to oxidative decomposition and hardening of the substrate. Therefore, when a first member and a second member are bonded using the foamable adhesive sheet, it improves adhesion durability. Furthermore, when the substrate has insulating properties, it prevents a decrease in the insulating properties of the substrate due to oxidative decomposition of the substrate. Therefore, when the foamable adhesive sheet is used to manufacture electrical appliances such as rotating electrical machines, it improves the insulation durability of the electrical appliances.

[0027] 4 is a schematic cross-sectional view showing another example of a foamable adhesive sheet according to the present disclosure. The foamable adhesive sheet 10 in FIG. 4 includes a first adhesive layer 1, a first gas barrier layer 2, a substrate 3, a second gas barrier layer 4, and a second adhesive layer 5, and is arranged in a thickness direction D. Ｔ The first adhesive layer 1 contains a curable adhesive and a foaming agent, the foaming agent being a thermally expandable microcapsule. The second adhesive layer 5 contains a curable adhesive and may further contain a foaming agent, the foaming agent being a thermally expandable microcapsule.

[0028] When the foamable adhesive sheet 10 is wound into a roll as shown in Fig. 2 , and when the foamable adhesive sheet 10 is wound into a roll as shown in Fig. 5 so that the surface of the second adhesive layer 5 of the foamable adhesive sheet 10 is on the outside and the surface of the first adhesive layer 1 is on the inside, the first adhesive layer 1 is located inside the first gas barrier layer 2 and the second gas barrier layer 4, thereby preventing moisture from penetrating from the outside into the first adhesive layer 1. Furthermore, in the foamable adhesive sheet 10B located inside the outermost foamable adhesive sheet 10A, the second adhesive layer 5 of the foamable adhesive sheet 10B is located inside the first gas barrier layer 2 and the second gas barrier layer 4 of the foamable adhesive sheet 10A, thereby preventing moisture from penetrating from the outside into the second adhesive layer 5. The relationship between the foamable adhesive sheet 10B and the foamable adhesive sheet 10C is the same as the relationship between the foamable adhesive sheet 10A and the foamable adhesive sheet 10B described above. Furthermore, although not shown, when the foamable adhesive sheet 10 is wound into a roll so that the surface of the first adhesive layer 1 of the foamable adhesive sheet 10 is on the outside and the surface of the second adhesive layer 5 is on the inside, the same effect is achieved as when the foamable adhesive sheet 10 is wound into a roll so that the surface of the second adhesive layer 5 of the foamable adhesive sheet 10 is on the outside and the surface of the first adhesive layer 1 is on the inside.

[0029] Therefore, by winding the foamable adhesive sheet into a roll, the first adhesive layer and the second adhesive layer can be protected from moisture. This prevents a decrease in the expansion ratio of the first adhesive layer and the second adhesive layer due to moisture, thereby achieving stable foaming characteristics and improving adhesion after foaming and curing. Furthermore, precise humidity control is not required for the foamable adhesive sheet, making it easy to handle.

[0030] In addition, the foamable adhesive sheet shown in Fig. 2 has a first gas barrier layer and a second gas barrier layer disposed on both sides of the substrate, similar to the foamable adhesive sheet shown in Fig. 1. Therefore, it has the same effects as the foamable adhesive sheet shown in Fig. 1.

[0031] In this way, the same effect can be obtained whether the foamable adhesive sheet 10 has, in this order, a first adhesive layer 1, a first gas barrier layer 2, a substrate 3, and a second gas barrier layer 4 as shown in Figure 1, or whether the foamable adhesive sheet 10 has, in this order, a first adhesive layer 1, a first gas barrier layer 2, a substrate 3, a second gas barrier layer 4, and a second adhesive layer 5 as shown in Figure 2.

[0032] Hereinafter, each component of the foamable adhesive sheet according to the present disclosure will be described.

[0033] 1. First Gas Barrier Layer and Second Gas Barrier Layer In the present disclosure, the first gas barrier layer is disposed on the first surface of the substrate and between the substrate and the first adhesive layer, and the second gas barrier layer is disposed on the second surface of the substrate.

[0034] The first gas barrier layer and the second gas barrier layer have gas barrier properties. Specifically, as described below, the oxygen permeability and water vapor permeability of the foamable adhesive sheet are preferably within predetermined ranges. The first gas barrier layer and the second gas barrier layer may or may not be transparent.

[0035] The first and second gas barrier layers are not particularly limited as long as they have the desired gas barrier properties, and examples thereof include inorganic films and organic-inorganic composite films. Furthermore, the first and second gas barrier layers may each comprise a plurality of inorganic films, a plurality of organic-inorganic composite films, or a combination of an inorganic film and an organic-inorganic composite film. Among these, the first and second gas barrier layers are preferably inorganic films. Since inorganic films can be formed by vapor deposition, their thickness can be reduced while maintaining gas barrier properties. Therefore, the overall thickness of the foamable adhesive sheet can be reduced, making the foamable adhesive sheet applicable even when the gap between the first and second members is narrow.

[0036] (1) Inorganic Film: Inorganic materials constituting the inorganic film include metals and inorganic compounds. Examples of metals include aluminum, stainless steel, titanium, nickel, iron, copper, and other metals, as well as alloys containing these metals. Examples of inorganic compounds include one or more inorganic compounds selected from inorganic oxides, inorganic oxynitrides, inorganic nitrides, inorganic oxycarbides, inorganic oxycarbonitrides, and silicon-zinc oxides. Specific examples include inorganic compounds containing one or more atoms selected from silicon, aluminum, magnesium, calcium, potassium, tin, sodium, titanium, boron, yttrium, zirconium, cerium, and zinc. More specific examples include silicon oxide, aluminum oxide, magnesium oxide, titanium oxide, tin oxide, silicon-zinc alloy oxide, indium alloy oxide, silicon nitride, aluminum nitride, titanium nitride, and silicon oxide nitride. Aluminum oxide (alumina) and silicon oxide (silica) are particularly preferred. The inorganic compounds may be used alone or in combination. Of these, aluminum, aluminum oxide, or silicon oxide is preferred, and aluminum is more preferred.

[0037] The inorganic film may be a vapor-deposited film formed by a vapor deposition method, or a coated film formed by a coating method. Among these, a vapor-deposited film is preferred from the viewpoint of good adhesion to the substrate and exhibiting high gas barrier properties. The vapor-deposited film may be formed by a single vapor deposition, or may be formed by multiple vapor depositions. That is, one inorganic film may be a single film formed by a single vapor deposition, or may have a laminated structure formed by multiple vapor depositions.

[0038] (2) Organic-inorganic composite film Examples of the organic-inorganic composite film include a layer containing a resin and an inorganic layered compound, a layer containing a reaction product of a polycarboxylic acid polymer and a polyvalent metal compound, a layer containing a reaction product of a metal oxide and a phosphorus compound, and a layer containing a sol-gel compound.

[0039] In the layer containing a resin and an inorganic layered compound, examples of the resin include polyvinyl alcohol (PVA), ethylene-vinyl alcohol copolymer (EVOH), polyvinylidene chloride (PVDC), polyacrylonitrile (PAN), polysaccharides, polyacrylic acid and its esters, and examples of the inorganic layered compound include clay minerals such as smectite, kaolin, mica, hydrotalcite, and chlorite.

[0040] The layer containing the reaction product of a polycarboxylic acid polymer and a polyvalent metal compound has crosslinks formed between carboxyl groups of the polycarboxylic acid polymer by polyvalent metal ions. The reaction product is a polyvalent metal salt of the polycarboxylic acid polymer. Examples of polyvalent metal salts of the polycarboxylic acid polymer include zinc acrylate. The layer containing the reaction product of the polycarboxylic acid polymer and a polyvalent metal compound can be formed, for example, by reacting a carboxylic acid resin film such as polyacrylic acid with a coating film in which fine particles of a polyvalent metal compound such as zinc oxide are dispersed.

[0041] The layer containing the reaction product of a metal oxide and a phosphorus compound has an M-O-P bond. M represents a metal atom, O represents an oxygen atom, and P represents a phosphorus atom. Examples of metal oxides include oxides of metals with a valence of two or more. Specific examples include oxides of metals such as Group 2 metals in the periodic table (e.g., magnesium and calcium), Group 12 metals in the periodic table (e.g., zinc), Group 13 metals in the periodic table (e.g., aluminum), Group 14 metals in the periodic table (e.g., silicon), and transition metals such as titanium and zirconium. Among these, aluminum oxide (alumina) is preferred. Examples of phosphorus compounds include phosphoric acid, polyphosphoric acid, phosphorous acid, phosphonic acid, and derivatives thereof. Specific examples of reaction products of metal oxides and phosphorus compounds are similar to those disclosed in, for example, JP 2011-226644 A.

[0042] The layer containing the sol-gel compound may be, for example, a compound represented by the general formula R １ ｎ M (OR ２ ) ｍand a hydrophilic group-containing resin, and further, the liquid material is obtained by polycondensation by a sol-gel method. １ , R ２ represents an organic group having 1 to 8 carbon atoms, M represents a metal atom, n represents an integer of 0 or greater, m represents an integer of 1 or greater, and n + m represents the atomic valence of M. Examples of the metal atom M in the alkoxide represented by the above general formula include silicon, zirconium, titanium, and aluminum. Of these, silicon is preferred. A preferred silicon alkoxide is tetraethyl orthosilicate (TEOS). Furthermore, examples of hydrophilic group-containing resins include resins containing hydrophilic groups, and specific examples include polyvinyl alcohol, ethylene-vinyl alcohol copolymers, polyacrylic acid, methyl cellulose, carboxymethyl cellulose, cellulose nanofibers, and polysaccharides. Of these, polyvinyl alcohol is preferred.

[0043] The sol-gel compound is a mixed compound containing a metal element, an oxygen element, and a hydrophilic group-containing resin, and has a C-O-M bond via oxygen (O) between a carbon atom (C) in the hydrophilic group-containing resin and a metal atom (M) in the metal alkoxide. Among these, the sol-gel compound is preferably a polycondensate of tetraethyl orthosilicate (TEOS) and polyvinyl alcohol. The polycondensate of tetraethyl orthosilicate (TEOS) and polyvinyl alcohol is similar to that disclosed in, for example, Japanese Patent No. 5,568,897.

[0044] The organic-inorganic composite film can be formed, for example, by a coating method.

[0045] (3) Thickness: The thickness of the first gas barrier layer and the thickness of the second gas barrier layer are each, for example, 1 nm or more, 5 nm or more, or 10 nm or more. Although depending on the materials of the first gas barrier layer and the second gas barrier layer, the desired gas barrier properties are easily obtained if the thicknesses are within the above ranges. On the other hand, the thicknesses of the first gas barrier layer and the second gas barrier layer are each, for example, preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 3 μm or less. When the thicknesses are within the above ranges, the thickness of the foamable adhesive sheet can be reduced. Therefore, the foamable adhesive sheet can be used even when the gap between the first and second members is narrow. Specifically, the thicknesses of the first gas barrier layer and the second gas barrier layer are each 1 nm or more and 10 μm or less, or 5 nm or more and 5 μm or less, or 10 nm or more and 3 μm or less. Note that when the first gas barrier layer has multiple layers, the above thickness refers to the thickness of the entire first gas barrier layer. Similarly, when the second gas barrier layer has multiple layers, the above thickness refers to the thickness of the entire second gas barrier layer.

[0046] 2. First Adhesive Layer In the present disclosure, the first adhesive layer is disposed on the side of the first gas barrier layer opposite the substrate, and contains a curable adhesive and a foaming agent.

[0047] (1) Material of the First Adhesive Layer (a) Curable Adhesive The curable adhesive contained in the first adhesive layer in the present disclosure can be a curable adhesive generally used for adhesive layers. The curable adhesive is not particularly limited, but a thermosetting adhesive is preferably used. The thermosetting adhesive can be applied even when the component does not have transparency, such as a metal component.

[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 produce hard and tough cured films, making them suitable for bonding hard material components such as metal and glass components. In addition, epoxy resin adhesives generally have excellent heat resistance, insulating properties, chemical resistance, etc., and have little shrinkage upon curing, making them suitable for a wide range of applications.

[0049] Furthermore, when the curable adhesive is an epoxy resin-based adhesive, the curable adhesive preferably further contains an acrylic resin that is compatible with the epoxy resin. By using an acrylic resin that is compatible with the epoxy resin, the toughness of the first adhesive layer can be increased, and the adhesion of the first adhesive layer to the first gas barrier layer can be improved.

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

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

[0052] For example, when only improving adhesiveness after foaming and curing is desired, 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, when 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, resulting in blocking.

[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, the first epoxy resin has relatively high crystallinity, which 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 suppression of blocking, or excessive tackiness of the first adhesive layer. Therefore, by further using a second epoxy resin having a relatively high softening temperature (relatively low crystallinity) and a high molecular weight, the effect of suppressing blocking can be improved and the tackiness of the first adhesive layer can be reduced.

[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 allows for a high crosslink density, resulting in a first adhesive layer with excellent 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 is measured by the ring and ball method in accordance with JIS K7234:1986.

[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 is measured by a method in accordance with JIS K7236, which corresponds to ISO 3001 (Plastics - Epoxy compounds - Determination of epoxy equivalent). The epoxy equivalent 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 first epoxy resin has a melt viscosity at 150°C of, 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. When the melt viscosity is within the above range, good foaming properties can be obtained. Furthermore, when the melt viscosity is within the above range, the tackiness (tackiness) of the first adhesive layer can be prevented from becoming too high. 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 will be significantly reduced when it is miscible with the second epoxy resin or the acrylic resin, resulting in a decrease in the Tg of the entire adhesive composition. Meanwhile, the first epoxy resin has a melt viscosity at 150°C of, for example, 10 Pa·s or less, or may be 5 Pa·s or less, or 2 Pa·s or less. When the melt viscosity is within the above range, the uniformity of the first adhesive layer is likely to be good. The melt viscosity is measured in accordance with JIS K6862:1984, which corresponds to ISO 2555 (Resins in the liquid state or as emulsions or dispersions—Determination of Brookfield RV viscosity), 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]

[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 ３ are 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 Ha-CH ２ Similarly, R ２ and R ３ p in is 1, that is, R ２ and R ３ Ha-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, relative to 100 parts by mass of the resin component contained in the first 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. When the content of the first epoxy resin is within the above range, the adhesive properties and blocking resistance after foaming and curing are likely to be good. On the other hand, when the content of the resin component contained in the first adhesive layer is 100 parts by mass, the content of the first epoxy resin 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. When the content of the first epoxy resin is within the above range, the contents of the second epoxy resin and the acrylic resin are prevented from becoming relatively small, thereby achieving a balance between blocking resistance and adhesive properties 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 described above. 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. In addition, 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, or may be 30,000 or more, or may be 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 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 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, relative to 100 parts by mass of the resin component contained in the first 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. When the content of the second epoxy resin is within the above range, blocking resistance is likely to be good. On the other hand, when the content of the resin component contained in the first adhesive layer is 100 parts by mass, the content of the second epoxy resin 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. When the content of the second epoxy resin is within the above range, the contents of the first epoxy resin and the acrylic resin are prevented from becoming relatively small, thereby achieving a balance between 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 alternatively 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 first 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 the present disclosure is a resin compatible with epoxy resin. Because acrylic resin is compatible with epoxy resin, it is easy to improve the toughness of the first adhesive layer. As a result, the adhesion of the first adhesive layer can be improved. Furthermore, improved toughness of the first adhesive layer can improve adhesion after foaming and curing. Furthermore, it is believed that the acrylic resin acts as a compatibilizer for the foaming agent (e.g., a foaming agent whose shell portion is an acrylonitrile copolymer resin), uniformly dispersing and foaming, thereby improving adhesion after foaming and curing. Furthermore, the compatibility of the acrylic resin with the epoxy resin can maintain high hardness on the surface of the first adhesive layer. On the other hand, if the acrylic resin is incompatible with the epoxy resin, a flexible portion is formed on the surface of the first adhesive layer, making the interface with the adherend less slippery and reducing workability.

[0077] The acrylic resin in the present disclosure is compatible with the epoxy resin. The compatibility of the acrylic resin with the epoxy resin can be confirmed, for example, by observing the cross section of the first 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 thickness of the first adhesive layer is 100 μm or less, within a range of the 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 end of foaming of the foaming agent and the curing of the adhesive composition). 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 is 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 is measured by a differential scanning calorimeter (DSC) in accordance with JIS K7121:2012, which corresponds to ISO 3146.

[0080] The 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 a temperature that 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] The acrylic resin has a storage modulus (E') of 1 x 10 at the curing initiation temperature. ５Pa or more. As described above, shrinkage may occur during curing after foaming (from the time when foaming of the foaming agent is completed until 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] The acrylic resin has an average storage modulus (E') of 1 x 10 at temperatures between 0°C and 100°C. ６ The average value of E' before foaming may be high, which allows for good blocking resistance. On the other hand, the average value of the storage modulus (E') at temperatures of 0°C or higher and 100°C or lower may 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 may be a homopolymer of an acrylic acid ester monomer, a mixed component containing two or more of the above homopolymers, or a copolymer of two or more acrylic acid ester monomers, 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" acrylic acid ester monomer also includes the concept of methacrylic acid. Specifically, the acrylic resin may be a mixture of a methacrylate polymer and an acrylate polymer, or an acrylic acid ester polymer such as acrylate-acrylate, methacrylate-methacrylate, or methacrylate-acrylate. Of these, it is preferable that the acrylic resin contain 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 benzyl 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 a first 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. The presence of 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 A-B-A block copolymer in which a compatible portion is polymer block A and an incompatible portion is polymer block B. Furthermore, an A-B-A block copolymer in which a first polymer portion is an incompatible portion and a second polymer portion is a compatible portion, with the first polymer portion being polymer block B and the second polymer portion being polymer block A, is preferred. By using such an A-B-A block copolymer as the acrylic resin, in a case where a sea-island structure is formed in which the compatible portion of the cured epoxy resin and the (meth)acrylic acid ester copolymer is a sea and the incompatible portion of the (meth)acrylic acid ester copolymer is an island, the island portions can be made smaller. Furthermore, in a case where a sea-island structure is formed in which the incompatible portion of the (meth)acrylic acid ester copolymer is a sea and the compatible portion of the cured epoxy resin and the (meth)acrylic acid ester copolymer is an island, or in a case where the (meth)acrylic acid ester copolymer is a sea and the cured epoxy resin is an island, the sea portions can be made smaller.

[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 set within a range of -150°C or more and 10°C or less, particularly within a range of -130°C or more and 0°C or less, and particularly within a 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 "POLYMER HANDBOOK, Third Edition" (published by John Wiley & Sons, Inc.): 1 / Tg(K)=W １ / Tg １ +W ２ / Tg ２ +...+W ｎ / Tg ｎ W ｎ : mass fraction of each monomer Tg ｎ: 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 component and polymer component constituting the first polymer portion may be any monomer component and polymer component that can give 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 set within a range of 20°C or higher and 150°C or lower, particularly within a range of 30°C or higher and 150°C or lower, and particularly within a 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 above-mentioned MMA-BA-MMA copolymer.

[0101] The content of the acrylic resin, relative to 100 parts by mass of the resin component contained in the first 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. When the content of the acrylic resin is within the above range, the adhesiveness after foaming and curing is likely to be good. On the other hand, when the content of the resin component contained in the first adhesive layer is 100 parts by mass, the content of the acrylic resin 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. When the content of the acrylic resin is within the above range, the contents of the first epoxy resin and the second epoxy resin are prevented from becoming relatively small, thereby achieving a balance between blocking resistance and adhesiveness after foaming and curing.

[0102] (iii) Curing Agent The curing agent in the present disclosure is appropriately selected depending on the type of curable adhesive. When the curable adhesive is, for example, an epoxy resin adhesive, a curing agent generally used in epoxy resin adhesives can be used as the curing agent. The curing agent is preferably solid at 23°C. A curing agent that is solid at 23°C can extend storage stability (pot life) compared to 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 due to heat or a curing agent that undergoes a curing reaction due to light. In the present disclosure, a single curing agent may be used, or two or more types 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 within the above range, the reaction starts early, preventing curing from occurring in a state where the flexibility and fluidity of the resin component are low, making it easier 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 within the above range, deterioration of the resin component can be suppressed. Note that when a resin with high heat resistance, such as a phenolic resin, is used in addition to the epoxy resin, deterioration of the resin component is small, so the reaction initiation temperature of the curing agent may be, for example, 300°C or lower. The reaction initiation temperature of the curing agent is 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, 2-phenylimidazole, 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 hydroxy groups, so the reaction initiation temperature tends to be high.

[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 first adhesive layer, phenolic novolac resins having a Tg of 110°C or less are particularly preferred. Furthermore, a phenolic curing agent and an imidazole-type curing agent may be used in combination. In this case, it is preferable to use an imidazole-type curing agent as a curing catalyst. From the viewpoint of heat resistance, biphenyl-type phenolic resins are preferred. Furthermore, the phenolic resin may be a resin in which the phenol nucleus has been modified. By modifying the phenol nucleus, for example, heat resistance can be further improved.

[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 anhydride (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 first 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 first 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 first 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) Blowing Agent The blowing agent in the present disclosure is a thermally expandable microcapsule.

[0113] The thermally expandable microcapsules preferably have a core made of a thermal expansion agent such as hydrocarbon and a shell made of a resin such as acrylonitrile copolymer.

[0114] 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 foaming initiation temperature is within the above range, the reaction starts early, preventing foaming from occurring in a state where the flexibility and fluidity of the resin component are low, and uniform foaming is more likely to be obtained. On the other hand, the foaming initiation temperature of the foaming agent is, for example, 210°C or lower. If the foaming initiation temperature is within the above range, deterioration of the resin component can be prevented.

[0115] The softening temperature of the base resin of the curable adhesive such as epoxy resin is measured by the ring and ball method in accordance with JIS K7234:1986.

[0116] The average particle size of the foaming agent may be, for example, 10 μm or more, 13 μm or more, or 17 μm or more. The average particle size of the foaming agent is preferably equal to or less than the thickness of the first adhesive layer of the foamable adhesive sheet, and may be, for example, 44 μm or less, 30 μm or less, or 24 μm or less.

[0117] 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 first 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 first adhesive layer. It is appropriately selected depending on the type of curable adhesive contained in the first adhesive layer. For example, a solvent used in the adhesive composition used to form the first adhesive layer can be used. Specifically, methyl ethyl ketone, ethyl acetate, toluene, etc. can be used.

[0118] 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, 5 parts by mass or more, 13 parts by mass or more, or 15 parts by mass or more, relative to 100 parts by mass of the resin component in the first adhesive layer. If the content of the foaming agent is within the above range, sufficient adhesiveness of the first adhesive layer after foaming and curing can be obtained. On the other hand, the content of the foaming agent is, for example, 30 parts by mass or less, 25 parts by mass or less, or 20 parts by mass or less, relative to 100 parts by mass of the resin component in the first adhesive layer. If the content of the foaming agent is within the above range, the content of the thermosetting resin can be prevented from becoming relatively small, and sufficient adhesiveness of the first adhesive layer after foaming and curing can be obtained. Specifically, the content of the foaming agent is, for example, 0.5 parts by mass or more and 30 parts by mass or less, or may be 2 parts by mass or more and 30 parts by mass or less, or may be 3 parts by mass or more and 25 parts by mass or less, or may be 4 parts by mass or more and 25 parts by mass or less, or may be 5 parts by mass or more and 25 parts by mass or less, or may be 13 parts by mass or more and 20 parts by mass or less, or may be 15 parts by mass or more and 20 parts by mass or less, relative to 100 parts by mass of the resin component in the first adhesive layer.

[0119] (c) Other Components In the present disclosure, for example, when the curable adhesive is an epoxy resin adhesive, the first 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.

[0120] The total ratio of the first epoxy resin, the second epoxy resin and the acrylic resin to the resin components contained in the first 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.

[0121] The content of the resin component contained in the first adhesive layer is, for example, 60% by mass or more, or may be 70% by mass or more, or 80% by mass or more, or may be 90% by mass or more.

[0122] The first 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.

[0123] (2) Form of First Adhesive Layer The first 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 also 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.

[0124] Here, the expansion ratio can be calculated by the following formula: Expansion ratio (times) = thickness of first adhesive layer after foaming and curing / thickness of first adhesive layer before foaming and curing

[0125] The thickness of the first 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 20 μm or more. If the thickness of the first adhesive layer is within the above range, sufficient adhesion and adhesiveness after foam curing can be obtained. On the other hand, the thickness of the first adhesive layer is, for example, 200 μm or less, or 150 μm or less, or 100 μm or less. If the thickness of the first adhesive layer is within the above range, deterioration of surface quality can be suppressed. Specifically, the thickness of the first adhesive layer is 10 μm or more and 200 μm or less, or 15 μm or more and 150 μm or less, or 20 μm or more and 100 μm or less.

[0126] The thickness of the first adhesive layer is a value measured from a cross section of the foamable adhesive sheet in the thickness direction observed with a scanning electron microscope (SEM), and is the average value of thicknesses measured at 10 randomly selected locations. The same applies to the method for measuring the thickness of each layer.

[0127] The first adhesive layer may be a continuous layer or a discontinuous layer. Examples of discontinuous layers include stripes and dots. The surface of the first adhesive layer may have an uneven shape such as an embossed shape.

[0128] The first 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.

[0129] 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 the first adhesive layer.

[0130] The adhesive composition can be obtained by mixing the above-mentioned components and, if necessary, kneading and dispersing them. 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.

[0131] 3. Second Adhesive Layer: In the foamable adhesive sheet of the present disclosure, a second adhesive layer is preferably disposed on the side of the second gas barrier layer opposite the substrate. The second adhesive layer can protect the second gas barrier layer. Therefore, for example, when the foamable adhesive sheet is disposed between the first member and the second member, peeling of the second gas barrier layer can be suppressed.

[0132] The second adhesive layer contains a curable adhesive. The curable adhesive is the same as the curable adhesive described in the above section "2. First Adhesive Layer." The curable adhesive contained in the first adhesive layer and the curable adhesive contained in the second adhesive layer may be the same or different.

[0133] The second adhesive layer may further contain a foaming agent. When both the first adhesive layer and the second adhesive layer contain a curable adhesive and a foaming agent, the adhesiveness of the first adhesive layer after foaming and curing and the adhesiveness of the second adhesive layer after foaming and curing can be improved. The foaming agent is the same as the foaming agent described in the above section "2. First Adhesive Layer." The foaming agent contained in the first adhesive layer and the foaming agent contained in the second adhesive layer may be the same or different.

[0134] Other components contained in the second adhesive layer, the foaming ratio of the second adhesive layer, the thickness of the second adhesive layer, the method of forming the second adhesive layer, etc. are the same as those described in the above section ``2. First adhesive layer.''

[0135] 4. Substrate The substrate in the present disclosure is preferably in the form of a sheet. The substrate may have a single-layer structure or a multi-layer structure. Furthermore, the substrate may or may not have a porous structure inside.

[0136] Examples of the substrate include a resin substrate and a nonwoven fabric.

[0137] Examples of resins contained in the resin substrate include polyester resin, polycarbonate, polyarylate, polyurethane, polyamide resin, polyimide resin, polysulfone resin, polyether ketone resin, polyolefin resin, polyphenylene sulfide (PPS), and modified polyphenylene oxide. Examples of polyester resins include polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate (PEN), and aromatic polyester. Examples of polyamide resins include polyamide and polyether amide. Examples of polyimide resins include polyimide, polyether imide, and polyamide imide. Examples of polysulfone resins include polysulfone and polyether sulfone. Examples of polyether ketone resins include polyether ketone and polyether ether ketone. Examples of polyolefin resins include polyethylene and polypropylene. Liquid crystal polymers (LCPs) may also be used as the resin. The glass transition temperature of the resin is, for example, 80°C or higher, or may be 140°C or higher, or 200°C or higher.

[0138] 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.

[0139] In particular, the substrate preferably has heat resistance and insulating properties, and more preferably has good adhesion to the first gas barrier layer and the second gas barrier layer. Good adhesion between the substrate and the first gas barrier layer and the second gas barrier layer eliminates the need for a primer layer to improve adhesion, as described below, and the overall thickness of the foamable adhesive sheet can be reduced. As such a substrate, a substrate containing at least one selected from the group consisting of polyester resin, polyamide resin, polyimide resin, polypropylene, and polyethylene is preferably used. In particular, the substrate preferably contains a polyester resin, and more preferably contains polyethylene naphthalate (PEN).

[0140] The substrate may be subjected to a surface treatment to enhance adhesion to the first gas barrier layer or the second gas barrier layer.

[0141] The thickness of the substrate is not particularly limited, and may be, for example, 2 μm or more and 200 μm or less, 5 μm or more and 100 μm or less, or 9 μm or more and 50 μm or less.

[0142] 5. Other Configurations (1) Primer Layer A primer layer may be disposed between the substrate and the first gas barrier layer, between the substrate and the second gas barrier layer, between the first gas barrier layer and the first adhesive layer, or between the second gas barrier layer and the second adhesive layer in order to enhance adhesion.

[0143] (2) Separator The foamable adhesive sheet in the present disclosure may have a first separator on the side of the first adhesive layer opposite the substrate, and may have a second separator on the side of the second adhesive layer opposite the substrate.

[0144] When the foamable adhesive sheet has a separator, the separator is peeled off from the foamable adhesive sheet when the foamable adhesive sheet is disposed between the first member and the second member.

[0145] The separator 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.

[0146] An example of a separator having a single layer structure is a fluororesin film.

[0147] 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.

[0148] The first separator and the second separator may be the same or different. In particular, when the first adhesive layer is substantially non-adhesive and the second adhesive layer is adhesive, it is preferable that the first separator have heavy releasability and the second separator have light releasability. For example, when a foamable adhesive sheet is placed on a second member and then the second member on which the foamable adhesive sheet is placed is inserted into a hole in the first member, the second adhesive layer of the foamable adhesive sheet is attached to the second member with the first adhesive layer of the foamable adhesive sheet facing outward, thereby improving the adhesion between the second member and the foamable adhesive sheet during insertion and the ease of inserting the second member on which the foamable adhesive sheet is placed. In this case, the first separator will peel from the second separator, so having the first separator have heavy releasability and the second separator have light releasability can make the second separator easier to peel than the first separator.

[0149] Light peeling and heavy peeling refer to the degree of force required to peel the first separator and the second separator from the first adhesive layer and the second adhesive layer, respectively, and light peeling means that the peeling force is smaller than that of heavy peeling.

[0150] (3) Protective Layer As shown in FIG. 1, when the foamable adhesive sheet 10 has a first adhesive layer 1, a first gas barrier layer 2, a substrate 3, and a second gas barrier layer 4 in this order, but does not have a second adhesive layer 5, a protective layer (not shown) for protecting the second gas barrier layer may be disposed on the surface of the second gas barrier layer 4 opposite the substrate 3.

[0151] 6. Physical Properties of the Foamable Adhesive Sheet (1) Oxygen Permeability The foamable adhesive sheet of the present disclosure has an oxygen permeability of 2 cc / (m ２ ·day·atm) or less, and 1.5 cc / (m ２ ·day·atm) or less is more preferable, and 1 cc / (m ２ When the oxygen permeability is in the above range, oxidative decomposition of the substrate at high temperatures can be further suppressed.

[0152] The oxygen permeability is measured in accordance with JIS K7126:2006 using an oxygen permeability measuring device under measurement conditions of 23°C and 90% RH. The oxygen permeability measuring device that can be used is an "OX-TRAN" manufactured by Mocon. When measuring the oxygen permeability, if the foamable adhesive sheet has a separator, the separator is peeled off before the measurement.

[0153] (2) Water Vapor Permeability The foamable adhesive sheet of the present disclosure has a water vapor permeability of 1.6 g / (m ２ ·day) or less, and 1.3 g / (m ２ ·day) or less is more preferable, and 1.0 g / (m ２ If the water vapor permeability is within the above range, by winding the foamable adhesive sheet into a roll, the first adhesive layer and the second adhesive layer can be protected from moisture, and deterioration of the foaming properties can be further suppressed.

[0154] The water vapor permeability is measured in accordance with JIS K7129-2:2019 using a water vapor permeability measuring device under measurement conditions of 40°C and 100% RH. A "Permatran" manufactured by Mocon Co., Ltd. can be used as the water vapor permeability measuring device. When measuring the water vapor permeability, if the foamable adhesive sheet has a separator, the separator is peeled off before the measurement.

[0155] (3) Tack In the foamable adhesive sheet of the present disclosure, it is preferred that both the first adhesive layer and the second adhesive layer are substantially non-tacky (tack-free), or that one of the first adhesive layer and the second adhesive layer is substantially non-tacky (tack-free) and the other is tacky (tacky).

[0156] When both the first adhesive layer and the second adhesive layer are 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, the foamable adhesive sheet can be smoothly inserted into the gap between the first and second members. Furthermore, if the first member has a hole or groove, the second member can be smoothly inserted into the gap after the foamable adhesive sheet has been placed in the hole or groove of the first member.

[0157] On the other hand, when one of the first adhesive layer and the second adhesive layer is substantially non-tacky (tack-free) and the other is tacky (tacky), for example, when the first adhesive layer is substantially non-tacky (tack-free) and the second adhesive layer is tacky (tacky), the second adhesive layer can have good adhesion to the second member. Specifically, when the second adhesive layer surface of the foamable adhesive sheet is attached to the second member and the second member to which the foamable adhesive sheet is attached is inserted into a hole, groove, or the like of the first member, the tackiness of the second adhesive layer allows the second adhesive layer surface of the foamable adhesive sheet to be attached to the second member by utilizing the tackiness of the second adhesive layer, thereby improving the adhesion of the second adhesive layer to the second member. This prevents the foamable adhesive sheet from peeling off or shifting when the second member to which the foamable adhesive sheet is attached is inserted into a hole, groove, or the like of the first member.

[0158] In the above case, the second adhesive layer has adhesiveness, which allows the second adhesive layer to have good reworkability, and therefore, for example, when the adhesiveness of the second adhesive layer is used to attach the second adhesive layer surface of the foamable adhesive sheet to the second member as described above, misalignment of the foamable adhesive sheet can be corrected.

[0159] Furthermore, in the above case, the non-tacky nature of the first adhesive layer allows the first adhesive layer to have good slip properties. Therefore, for example, when inserting a second component with a foamable adhesive sheet attached into a hole, groove, or the like of a first component as described above, the second component with the foamable adhesive sheet attached can be inserted smoothly, improving insertability. This prevents the foamable adhesive sheet from peeling off or shifting out of position. Furthermore, when moving the second component relative to the first component to align the first and second components, the second component can be moved smoothly relative to the first component while the second component is inserted into a hole, groove, or the like of the first component, facilitating alignment.

[0160] Furthermore, in the above case, as described above, the second adhesive layer has excellent adhesion to the second member, and the first adhesive layer has excellent slipperiness, which prevents peeling or misalignment of the foamable adhesive sheet, thereby preventing a decrease in the adhesive strength of the foamable adhesive sheet after foaming and curing due to peeling or misalignment of the foamable adhesive sheet, and reducing variations in the adhesive strength of the foamable adhesive sheet after foaming and curing due to peeling or misalignment of the foamable adhesive sheet.

[0161] In the above case, the second adhesive layer having adhesiveness can suppress lifting of the second adhesive layer, for example, when the second adhesive layer is formed by a transfer method. Furthermore, as will be described later, when a second separator is disposed on the side of the second adhesive layer opposite the first adhesive layer, the second separator can be easily peeled off, thereby improving workability.

[0162] When both the first adhesive layer and the second adhesive layer are substantially non-tacky, specifically, the tack of the first adhesive layer and the tack of the second adhesive layer are each preferably less than 0.1 N, and may be 0.05 N or less, or may be 0.02 N or less. By having the tack of the first adhesive layer and the tack of the second adhesive layer within the above ranges, the first adhesive layer and the second adhesive layer can be made substantially non-tacky, and a foamable adhesive sheet with good sliding properties and blocking resistance can be obtained. The lower limits of the tack of the first adhesive layer and the tack of the second adhesive layer are not particularly limited, and may be 0 N.

[0163] Furthermore, when the first adhesive layer is substantially non-adhesive (tack-free) and the second adhesive layer is adhesive (tacky), specifically, the tackiness of the first adhesive layer is preferably less than 0.1 N, and the tackiness of the second adhesive layer is preferably 0.1 N or more and 5 N or less.

[0164] In the above case, the tackiness of the first adhesive layer is preferably less than 0.1 N, and may be 0.05 N or less, or even 0.02 N or less. By having the tackiness of the first adhesive layer within the above range, the first adhesive layer can be made substantially non-sticky, and a foamable adhesive sheet with good slip properties and blocking resistance can be obtained. The lower limit of the tackiness of the first adhesive layer is not particularly limited, and may be 0 N.

[0165] In the above case, the tackiness of the second adhesive layer is preferably 0.1 N or more, and may be 0.3 N or more, or 0.5 N or more. The tackiness of the second adhesive layer is preferably 5 N or less, and may be 4 N or less, or may be 3 N or less. Having the tackiness of the second adhesive layer within the above range enhances adhesion between the second adhesive layer and the second component when the tackiness of the second adhesive layer is used to attach the second adhesive layer surface of the foamable adhesive sheet to the second component. This prevents the foamable adhesive sheet from peeling or shifting due to poor adhesion between the second adhesive layer and the second component when inserting the second component with the foamable adhesive sheet attached into a hole or groove in the first component. As a result, the adhesion between the first adhesive layer and the second adhesive layer after foaming and curing is prevented from decreasing, and variations in adhesive strength are prevented. Having the tackiness of the second adhesive layer within the above range also improves the reworkability of the second adhesive layer.

[0166] Here, the tackiness of the adhesive layer is measured by a probe tack test. Specifically, a cylindrical stainless steel probe with a diameter of 5 mm is pressed against the surface of the adhesive layer of the foamable adhesive sheet at a temperature of 25°C under a load of 10.0 gf and a speed of 30 mm / min, and after holding for 1.0 second, it is peeled off at a speed of 30 mm / min, and the load at the time of peeling is measured. This measurement is performed five times, and the average value is taken as the tackiness. As a probe tackiness tester, for example, a tackiness tester "TAC-II" manufactured by RHESCA can be used.

[0167] One example of a method for controlling the tackiness of an adhesive layer is to adjust 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. On the other hand, the adhesive layer tends to have a higher adhesive strength when an epoxy resin that is liquid at room temperature or a curing agent that is liquid at room temperature is used in an adhesive layer containing an epoxy resin and a curing agent. The adhesive strength of an adhesive layer can also be reduced 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 including multiple epoxy resins with different softening temperatures, i.e., by including one epoxy resin and another epoxy resin with a softening temperature of 25°C or higher and 10°C or higher than the softening temperature of the first epoxy resin. Furthermore, for example, the adhesive layer can contain multiple epoxy resins with different weight-average molecular weights. That is, the adhesive layer can contain one epoxy resin and another epoxy resin with a weight-average molecular weight of 370 or more and 300 or more greater than that of the first epoxy resin, thereby reducing the adhesiveness of the adhesive layer. More specifically, in an adhesive layer containing an epoxy resin and a curing agent, the adhesive layer can be reduced by containing 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 above. On the other hand, in an adhesive layer containing an epoxy resin and a curing agent, the adhesiveness of the adhesive layer tends to increase when an epoxy resin with a low softening temperature or an epoxy resin with a small weight-average molecular weight is contained. In an adhesive layer containing an epoxy resin and a curing agent, the adhesiveness of the adhesive layer can be reduced by containing an acrylic resin compatible with the epoxy resin, as described above. In addition, the adhesive layer can be reduced by adding a tackifier to the adhesive layer.In addition, when a curing agent that is liquid at room temperature is used, the adhesiveness tends to increase, but storage stability may decrease. Therefore, it is preferable to adjust the tackiness of the adhesive layer by adjusting the properties and type of components other than the curing agent, such as the epoxy resin.

[0168] Here, "adhesion" is a concept 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 Dictionary of Physics and Chemistry, 5th Edition). "Adhesion" and "adhesive strength" refer to the property of adhering by pressure and the adhesive strength at that time.

[0169] 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 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 curing.

[0170] (4) Shape Retention: The foamable adhesive sheet of the present disclosure preferably has good shape retention. The bending moment based on JIS P8125-2:2017, which corresponds to ISO 2493, is, for example, 0.1 gf·cm or more, and may be 1 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 found that shape retention can be ensured by devising the shape, and that a high bending moment has other drawbacks. Therefore, 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 greater than the above range, the sheet will return to its original shape after bending, so it is necessary to heat the sheet or to score the folds during bending. Heating reduces the sheet life, and scoring can reduce the insulation properties of the scored areas.

[0171] (5) Adhesion: The foamable adhesive sheet of the present disclosure preferably has high adhesiveness after foaming and curing. The tensile shear adhesive strength (adhesive strength) based on JIS K6850:1999, which corresponds to ISO 4587:1995, may be, for example, 1.50 MPa or more, 1.80 MPa or more, or 2.10 MPa or more at 23°C. Furthermore, the tensile shear adhesive strength (adhesive strength) may be, for example, 0.50 MPa or more, 0.75 MPa or more, or 1.00 MPa or more at 130°C. For example, a high-strength acrylic foam adhesive tape that does not require heating has a tensile shear adhesive strength (adhesive strength) of approximately 1 MPa or more to 2 MPa or less at room temperature and is not heat resistant at 200°C. Therefore, if the tensile shear adhesive strength (adhesive strength) is within the above range at 23°C, it has advantages in terms of strength. Furthermore, if the tensile shear adhesive strength (adhesive strength) is within the above range at 130° C., the composition can be used in applications requiring heat resistance such as around automobile engines.

[0172] (6) Insulation: The foamable adhesive sheet according to the present disclosure preferably has high electrical insulation properties after foaming and curing. After foaming and curing, the foamable adhesive sheet preferably has a breakdown voltage of 3 kV or more, more preferably 5 kV or more, based on JIS C2107:2011, which corresponds to IEC 60454-2. Having a breakdown voltage within the above range allows for rust prevention and application around copper wires. Furthermore, after foaming and curing, the foamable adhesive sheet preferably has a thermal conductivity of 0.1 W / mK or more, more preferably 0.15 W / mK or more. Having a thermal conductivity within the above range allows for the miniaturization of components and accelerates the curing reaction during heating.

[0173] 7. Other Features of the Foamable Adhesive Sheet The thickness of the foamable adhesive sheet according to the present disclosure is, for example, 10 μm or more and 1000 μm or less, and may be 20 μm or more and 200 μm or less.

[0174] The uses of the foamable adhesive sheet of the present disclosure are not particularly limited. The foamable adhesive sheet of the present disclosure can be used, for example, when bonding two components by placing the foamable adhesive sheet between them and then heating to foam and harden the foamable adhesive sheet. In particular, the foamable adhesive sheet of the present disclosure is preferably used when bonding metal components together.

[0175] B. Article The article according to the present disclosure is an article having a first member, a second member, and an adhesive member disposed between the first member and the second member, wherein the adhesive member has a first cured adhesive layer, a first gas barrier layer, a substrate, and a second gas barrier layer, in this order, and the first cured adhesive layer contains a foamed, cured product of an adhesive composition containing a curable adhesive and a blowing agent, and the blowing agent is thermally expandable microcapsules.

[0176] Fig. 6(a) is a process diagram showing an example of an article according to the present disclosure. The article 20 shown in Fig. 6(a) includes a first member 21, a second member 22, and an adhesive member 23 disposed between the first member 21 and the second member 22. The adhesive member 23 includes, in this order, a first cured adhesive layer 11, a first gas barrier layer 2, a substrate 3, and a second gas barrier layer 4. The first cured adhesive layer 11 contains a foamed, cured product of an adhesive composition containing a curable adhesive and a blowing agent, where the blowing agent is thermally expandable microcapsules.

[0177] Fig. 6(b) is a process diagram showing another example of an article according to the present disclosure. The article 20 shown in Fig. 6(a) includes a first member 21, a second member 21, and an adhesive member 23 disposed between the first member 21 and the second member 22. The adhesive member 23 includes, in this order, a first cured adhesive layer 11, a first gas barrier layer 2, a substrate 3, a second gas barrier layer 4, and a second cured adhesive layer 15. The first cured adhesive layer 11 and the second cured adhesive layer 15 each contain a foamed, cured product of an adhesive composition containing a curable adhesive and a blowing agent, where the blowing agent is thermally expandable microcapsules.

[0178] The article according to the present disclosure can be produced using the foamable adhesive sheet described above, and the article according to the present disclosure exhibits the same effects as the foamable adhesive sheet described above.

[0179] The article in this disclosure will be described below.

[0180] 1. Adhesive Member The adhesive member according to the present disclosure is disposed between a first member and a second member, and includes, in this order, a first cured adhesive layer, a first gas barrier layer, a substrate, and a second gas barrier layer. Alternatively, the adhesive member may include, in this order, a first cured adhesive layer, a first gas barrier layer, a substrate, a second gas barrier layer, and a second adhesive layer.

[0181] In the adhesive member, the adhesive layer located on the first member side may be the first adhesive layer or the second adhesive layer. Similarly, in the adhesive member, the adhesive layer located on the second member side may be the first adhesive layer or the second adhesive layer.

[0182] (1) Substrate The substrate is the same as that described above in the section "A. Foamable adhesive sheet 4. Substrate."

[0183] (2) First Gas Barrier Layer and Second Gas Barrier Layer The first gas barrier layer and second gas barrier layer are the same as those described above in the section "A. Foamable Adhesive Sheet 1. First Gas Barrier Layer and Second Gas Barrier Layer."

[0184] (3) First Cured Adhesive Layer The first cured adhesive layer is disposed on the side of the first gas barrier layer opposite the substrate, and contains a foamed, cured product of an adhesive composition containing a curable adhesive and a foaming agent. The materials contained in the adhesive composition are the same as those for the first adhesive layer described above in the section "A. Foamable Adhesive Sheet 2. First Adhesive Layer."

[0185] The thickness of the first cured adhesive layer is not particularly limited and is appropriately set depending on the application. The thickness of the first cured adhesive layer is, for example, 10 μm to 1000 μm, or may be 20 μm to 900 μm, or may be 30 μm to 800 μm. If the thickness of the first cured adhesive layer is within the above range, sufficient adhesiveness can be obtained.

[0186] The first cured adhesive layer may be a continuous layer or a discontinuous layer.

[0187] (4) Second Cured Adhesive Layer The adhesive member may have a second cured adhesive layer on the side of the second gas barrier layer opposite the substrate. The second cured adhesive layer contains a cured product of an adhesive composition containing a curable adhesive. The second cured adhesive layer may also contain a foamed cured product of an adhesive composition containing a curable adhesive and a foaming agent. The materials contained in the adhesive composition are the same as the materials for the second adhesive layer described above in the section "A. Foamable Adhesive Sheet 3. Second Adhesive Layer."

[0188] The other aspects of the second cured adhesive layer are the same as those of the first adhesive layer.

[0189] When the adhesive composition used in the second cured adhesive layer does not contain a foaming agent, the thickness of the second cured adhesive layer is not particularly limited and is set appropriately depending on the application, but may be, for example, 10 μm or more and 200 μm or less, 15 μm or more and 150 μm or less, or 20 μm or more and 100 μm or less.

[0190] (5) Other Components The adhesive member may have other components as needed in addition to the above-described substrate, first gas barrier layer, second gas barrier layer, first cured adhesive layer, and second cured adhesive layer. The other components are the same as those described above in the section "A. Foamable Adhesive Sheet 5. Other Components."

[0191] 2. First Member and Second Member The first member and second member in the present disclosure are appropriately selected depending on the application of the article, etc. The material and shape of the first member and second member are not particularly limited. Examples of the first member and second member include metal members, resin members, and ceramic members. In particular, the first member and second member are preferably members that require adhesion and insulation. Examples include components of electrical and electronic devices, specifically, stator cores and coils of stators for rotating electric machines, rotor cores and coils of rotors for rotating electric machines, and rotor cores and permanent magnets of rotors for rotating electric machines.

[0192] 3. Article Manufacturing Method The article manufacturing method according to the present disclosure includes, for example, an arrangement step of arranging the foamable adhesive sheet described above between a first member and a second member, and an adhesion step of foaming and curing the foamable adhesive sheet to adhere the first member and the second member to each other.

[0193] The method for disposing the foamable adhesive sheet between the first and second members is appropriately selected depending on the types of the first and second members. Examples include inserting the foamable adhesive sheet into the gap between the first and second members, or disposing the foamable adhesive sheet in a hole or groove in the first member, and then inserting the second member into the gap. Furthermore, when the first member has a hole or groove and the second member is to be disposed in the hole or groove, examples include a method of attaching the surface of the second adhesive layer of the foamable adhesive sheet to the second member using the tack of the second adhesive layer of the foamable adhesive sheet, and then disposing the second member with the foamable adhesive sheet attached in the hole or groove of the first member, or a method of disposing the foamable adhesive sheet in the hole or groove of the first member, and then attaching the surface of the second adhesive layer of the foamable adhesive sheet to the hole or groove of the first member using the tack of the second adhesive layer of the foamable adhesive sheet, and then disposing the second member in the hole or groove of the first member with the foamable adhesive sheet attached.

[0194] Heating is a preferred method for foaming and curing the foamable adhesive sheet. Heating methods are applicable even when the first and second members are not transparent, such as metal members. Heating conditions are appropriately set depending on the type of curable adhesive and foaming agent used to form the first and second cured adhesive layers, the type of substrate, and other factors. The heating temperature is, for example, 130°C or higher and 200°C or lower. The heating time is, for example, 3 minutes or higher and 3 hours or shorter.

[0195] C. Stator for Rotating Electric Machine A stator for a rotating electric machine according to the present disclosure includes a stator core, coils disposed in slots of the stator core, and an adhesive member disposed between the stator core and the coils, wherein the adhesive member includes a first cured adhesive layer, a first gas barrier layer, a substrate, and a second gas barrier layer, in this order, and the first cured adhesive layer contains a foamed, cured product of an adhesive composition containing a curable adhesive and a foaming agent, and the foaming agent is thermally expandable microcapsules.

[0196] Fig. 7(a) is a schematic plan view illustrating a stator for a rotating electric machine according to the present disclosure, and Figs. 7(b) and 7(c) are partially enlarged views of Fig. 7(a). As shown in Figs. 7(a) to 7(c), a stator 30 for a rotating electric machine includes a stator core 31, coils 33 disposed in slots 32 of the stator core 31, and an adhesive member 34 disposed between the stator core 31 and the coils 33. The adhesive member 34 includes, in this order, a first cured adhesive layer 11, a first gas barrier layer 2, a substrate 3, a second gas barrier layer 4, and a second cured adhesive layer 15. The first cured adhesive layer 11 and the second cured adhesive layer 15 each contain a foamed, cured product of an adhesive composition containing a curable adhesive and a blowing agent, where the blowing agent is thermally expandable microcapsules. In FIG. 7( c ), the adhesive member 34 has a first cured adhesive layer 11, a first gas barrier layer 2, a substrate 3, a second gas barrier layer 4, and a second cured adhesive layer 15 in this order; however, although not shown, the adhesive member 34 may also have a first cured adhesive layer 11, a first gas barrier layer 2, a substrate 3, and a second gas barrier layer 4 in this order.

[0197] The stator for a rotating electric machine according to the present disclosure can be manufactured using the foamable adhesive sheet described above, and the article according to the present disclosure achieves the same effects as the foamable adhesive sheet described above.

[0198] The configuration of a stator for a rotating electric machine according to the present disclosure will be described below.

[0199] 1. Adhesive Member The adhesive member is the same as that described above in the section "B. Article 1. Adhesive Member."

[0200] 2. Stator Core The stator core has slots into which coils are inserted. The stator core is similar to a general stator core, so a detailed description will be omitted here.

[0201] 3. Coil The coil is similar to a general coil, so a description of it will be omitted here.

[0202] 4. Other Features of the Rotating Electric Machine Stator A manufacturing method for a rotating electric machine stator according to the present disclosure includes, for example, an arrangement step of arranging a foamable adhesive sheet between a stator core and a coil, and an adhesion step of foaming and curing the foamable adhesive sheet to adhere the coil to the stator core.

[0203] Methods for placing a foam adhesive sheet between the stator core and the coil include placing a foam adhesive sheet around the coil and then inserting the coil and foam adhesive sheet into the slot of the stator core, inserting a foam adhesive sheet into the slot of the stator core and then inserting the coil into the slot of the stator core, and inserting a coil into the slot of the stator core and then inserting a foam adhesive sheet into the slot of the stator core.

[0204] Heating can be used as a method for foaming and curing the foamable adhesive sheet. The heating conditions are the same as those described above in the section "B. Article 3. Method for manufacturing an article."

[0205] D. Rotor for a Rotating Electric Machine A rotor for a rotating electric machine according to the present disclosure is a rotor for a rotating electric machine having a rotor core, permanent magnets or coils arranged in slots of the rotor core, and an adhesive member arranged between the rotor core and the permanent magnets or the coils, wherein the adhesive member has a first cured adhesive layer, a first gas barrier layer, a substrate, and a second gas barrier layer, in this order, and the first cured adhesive layer contains a foamed, cured product of an adhesive composition containing a curable adhesive and a blowing agent, and the blowing agent is thermally expandable microcapsules.

[0206] Fig. 8(a) is a schematic plan view illustrating a rotor for a rotating electric machine according to the present disclosure, and Figs. 8(b) and 8(c) are partially enlarged views of Fig. 8(a). As shown in Figs. 8(a) to 8(c), a rotor 40 for a rotating electric machine includes a rotor core 41, permanent magnets 43 disposed in slots 42 of the rotor core 41, and an adhesive member 45 disposed between the rotor core 41 and the permanent magnets 43. The adhesive member 45 includes, in this order, a first cured adhesive layer 11, a first gas barrier layer 2, a substrate 3, a second gas barrier layer 4, and a second cured adhesive layer 15. The first cured adhesive layer 11 and the second cured adhesive layer 15 each contain a foamed, cured product of an adhesive composition containing a curable adhesive and a blowing agent, where the blowing agent is thermally expandable microcapsules. In FIG. 8( c ), adhesive member 45 has first cured adhesive layer 11, first gas barrier layer 2, substrate 3, second gas barrier layer 4, and second cured adhesive layer 15 in this order; however, although not shown, adhesive member 45 may also have first cured adhesive layer 11, first gas barrier layer 2, substrate 3, and second gas barrier layer 4 in this order.

[0207] Fig. 9(a) is a schematic plan view illustrating a rotor for a rotating electric machine according to the present disclosure, and Figs. 9(b) and 9(c) are partially enlarged views of Fig. 9(a). As shown in Figs. 9(a) to 9(c), a rotor 40 for a rotating electric machine includes a rotor core 41, coils 44 disposed in slots 42 of the rotor core 41, and an adhesive member 45 disposed between the rotor core 41 and the coils 44. The adhesive member 45 includes, in this order, a first cured adhesive layer 11, a first gas barrier layer 2, a substrate 3, a second gas barrier layer 4, and a second cured adhesive layer 15. The first cured adhesive layer 11 and the second cured adhesive layer 15 each contain a foamed, cured product of an adhesive composition containing a curable adhesive and a blowing agent, where the blowing agent is thermally expandable microcapsules. In FIG. 9( c), adhesive member 45 has first cured adhesive layer 11, first gas barrier layer 2, substrate 3, second gas barrier layer 4, and second cured adhesive layer 15 in this order; however, although not shown, adhesive member 45 may also have first cured adhesive layer 11, first gas barrier layer 2, substrate 3, and second gas barrier layer 4 in this order.

[0208] The rotor for a rotating electric machine according to the present disclosure can be manufactured using the foamable adhesive sheet described above, and the article according to the present disclosure exhibits the same effects as the foamable adhesive sheet described above.

[0209] The configuration of the rotor for a rotating electric machine according to the present disclosure will be described below.

[0210] 1. Adhesive Member The adhesive member is the same as that described above in the section "B. Article 1. Adhesive Member."

[0211] 2. Rotor Core The rotor core has slots into which coils are inserted. The rotor is similar to a rotor core generally used in a wound-field motor, so a detailed description will be omitted here.

[0212] 3. Coil The coil is similar to a general coil, so a description of it will be omitted here.

[0213] 4. Other Aspects of the Rotor for a Rotating Electric Machine The rotor for a rotating electric machine in the present disclosure is, for example, a rotor for a rotating electric machine used in an interior permanent magnet motor or a rotor for a rotating electric machine used in a wound field motor.

[0214] The manufacturing method of a rotor for a rotating electric machine in the present disclosure includes an arrangement step of arranging a foam adhesive sheet between a rotor core and a coil, and an adhesion step of foaming and hardening the foam adhesive sheet to adhere the coil to the rotor core.

[0215] The steps in the method for manufacturing a rotor for a rotating electric machine are the same as the steps in the method for manufacturing a stator for a rotating electric machine described above.

[0216] 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.

[0217] [Reference Example 1] Polyethylene naphthalate (PEN film, manufactured by Toyobo Film Solutions Co., Ltd., Teonex Q51, thickness 100 μm) was used as the substrate. Alumina vapor deposition films with a thickness of 10 nm were formed on both sides of the substrate as a first gas barrier layer and a second gas barrier layer, respectively. This resulted in a barrier film having the first gas barrier layer, the substrate, and the second gas barrier layer in this order.

[0218] Reference Example 2 The substrate used in the above Reference Example 1 was used.

[0219] [Evaluation 1] For the barrier film of Reference Example 1 and the substrate of Reference Example 2, dumbbell-shaped test pieces of the No. 3 dumbbell shape described in JIS K6251:2017 were prepared. The test pieces were subjected to the following durability test. The test pieces before and after the durability test were subjected to the following tensile test to measure the tensile strength and elongation. Five test pieces were used for each test, and the average values ​​of the tensile test results were calculated.

[0220] <Durability test> Test environment: 200°C, 500 hours Equipment: Yamato Scientific "DN610"

[0221] <Tensile test> Equipment: A&D tensile testing machine (Tensilon RTF1150-H), contact extensometer (U-4310D) Tensile speed: 15 mm / min Gauge distance (distance between extensometer clamps): 20 mm Chuck distance: 60 mm

[0222]

[0223] When gas barrier layers were not disposed on both sides of the substrate, as in Reference Example 2, the elongation of the substrate after the durability test was very small. This was because the substrate was oxidatively decomposed and hardened at high temperatures. When the elongation of the substrate after the durability test was very small, cracks were more likely to occur. Cracking can cause a decrease in the insulating properties of the substrate and a decrease in the adhesiveness of the foamable adhesive sheet. In contrast, when gas barrier layers were disposed on both sides of the substrate, as in Reference Example 1, the elongation of the substrate after the durability test was small, but not as small as in Reference Example 2. Specifically, the elongation of the substrate after the durability test in Reference Example 1 was approximately 1.8 times that of the substrate after the durability test in Reference Example 2. This is thought to be because the gas barrier layer suppressed oxidative decomposition of the substrate.

[0224] Example 1 First, an adhesive composition having the following composition was prepared. <Composition of Adhesive Composition> Acrylic resin: PMMA-PBuA-PMMA (containing a portion of acrylamide groups), Tg: -20°C, 120°C, Mw: 150,000, 13 parts by mass; 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, 40 parts by mass; Epoxy resin B: BPA phenoxy type, solid at room temperature, softening temperature: 110°C, epoxy equivalent: 8000 g / eq, Mw: 50,000, 42 parts by mass; Curing agent A: α-(hydroxy(or dihydroxy)phenylmethyl)-ω-hydropoly[biphenyl-4,4'-diylmethylene(hydroxy(or dihydroxy)phenylenemethylene)] 6 parts by weight of curing catalyst: 2-phenyl-4,5-dihydroxymethylimidazole, average particle size: 3 μm, melting point: 230°C, reaction start temperature: 145°C to 155°C, active region: 155°C to 173°C (Shikoku Chemical Industry Co., Ltd., 2PHZ-PW) 8 parts by weight of foaming agent: thermally expandable microcapsules, average particle size: 10 μm to 16 μm, expansion start temperature: 123°C to 133°C, maximum expansion temperature: 168°C to 178°C, core: hydrocarbon, shell: thermoplastic polymer 13.5 parts by weight of solvent: methyl ethyl ketone 150 parts by weight

[0225] Polyethylene naphthalate (PEN film, manufactured by Toyobo Film Solutions Co., Ltd., Teonex Q51, thickness 100 μm) was used as the substrate. A 10 nm thick alumina vapor-deposited film was formed on each side of the substrate as a first gas barrier layer and a second gas barrier layer. Next, the adhesive composition was applied to the first gas barrier layer using an applicator to a thickness of 45 μm after application. This was then dried in an oven at 100°C for 3 minutes to form a first adhesive layer. Next, the adhesive composition was applied to the second gas barrier layer using an applicator to a thickness of 45 μm after application. This was then dried in an oven at 100°C for 3 minutes to form a second adhesive layer. This resulted in a foamable adhesive sheet in which the first adhesive layer, first gas barrier layer, substrate, second gas barrier layer, and second adhesive layer were arranged in this order.

[0226] The present disclosure provides, for example, the following inventions. [1] A foamable adhesive sheet having a first adhesive layer, a first gas barrier layer, a substrate, and a second gas barrier layer in this order, wherein the first adhesive layer contains a curable adhesive and a foaming agent, and the foaming agent is thermally expandable microcapsules. [2] The foamable adhesive sheet according to [1], having a second adhesive layer on the side of the second gas barrier layer opposite the substrate, the second adhesive layer containing a curable adhesive. [3] The foamable adhesive sheet according to [2], wherein the second adhesive layer contains a foaming agent, and the foaming agent is thermally expandable microcapsules. [4] The foamable adhesive sheet has an oxygen permeability of 2 cc / (m ２ [5] The foamable adhesive sheet according to any one of [1] to [3], wherein the water vapor permeability of the foamable adhesive sheet is 1.6 g / (m ２

[0033] The foamable adhesive sheet according to any one of [1] to [4], wherein the first gas barrier layer and the second gas barrier layer each have a thickness of 1 nm or more and 10 μm or less. [6] The foamable adhesive sheet according to any one of [1] to [5], wherein the first gas barrier layer and the second gas barrier layer each have a thickness of 1 nm or more and 10 μm or less. [7] The foamable adhesive sheet according to any one of [1] to [6], wherein the foamable adhesive sheet is wound into a roll. [8] An article having a first member, a second member, and an adhesive member disposed between the first member and the second member, wherein the adhesive member has a first cured adhesive layer, a first gas barrier layer, a substrate, and a second gas barrier layer, in this order, the first cured adhesive layer containing a foamed, cured product of an adhesive composition comprising a curable adhesive and a blowing agent, and the blowing agent is a thermally expandable microcapsule. [9] The article according to [8], wherein the adhesive member has a second cured adhesive layer on the side of the second gas barrier layer opposite the substrate, and the second cured adhesive layer contains a cured product of an adhesive composition comprising a curable adhesive.

[10] The article according to [9], wherein the second cured adhesive layer contains a foamed, cured product of an adhesive composition comprising the curable adhesive and a blowing agent, and the blowing agent is a thermally expandable microcapsule.

[11] The article according to [8] or [9], wherein the thickness of the first gas barrier layer and the thickness of the second gas barrier layer are each 1 nm or more and 10 μm or less.

[12] A stator for a rotating electric machine having a stator core, coils arranged in slots of the stator core, and an adhesive member arranged between the stator core and the coil, wherein the adhesive member has a first cured adhesive layer, a first gas barrier layer, a substrate, and a second gas barrier layer, in this order, the first cured adhesive layer contains a foamed, cured product of an adhesive composition comprising the curable adhesive and a blowing agent, and the blowing agent is a thermally expandable microcapsule.

[13] The stator for a rotating electric machine according to

[12] , wherein the adhesive member has a second cured adhesive layer on a surface of the second gas barrier layer opposite the substrate, and the second cured adhesive layer contains a cured product of an adhesive composition including a curable adhesive.

[14] The stator for a rotating electric machine according to

[13] , wherein the second cured adhesive layer contains a foamed, cured product of an adhesive composition containing the curable adhesive and a foaming agent, and the foaming agent is a thermally expandable microcapsule.

[15] A rotor for a rotating electric machine having a rotor core, permanent magnets or coils arranged in slots of the rotor core, and an adhesive member arranged between the rotor core and the permanent magnets or the coil, wherein the adhesive member has a first cured adhesive layer, a first gas barrier layer, a substrate, and a second gas barrier layer, in this order, the first cured adhesive layer contains a foamed, cured product of an adhesive composition containing the curable adhesive and a foaming agent, and the foaming agent is a thermally expandable microcapsule.

[16] The rotor for a rotating electric machine according to

[15] , wherein the adhesive member has a second cured adhesive layer on a surface of the second gas barrier layer opposite the substrate, the second cured adhesive layer containing a cured product of an adhesive composition containing the curable adhesive.

[17] The rotor for a rotating electric machine according to

[16] , wherein the second cured adhesive layer contains a foamed, cured product of an adhesive composition comprising the curable adhesive and a foaming agent, and the foaming agent is a thermally expandable microcapsule.

[0227] DESCRIPTION OF SYMBOLS 1... First adhesive layer 2... First gas barrier layer 3... Substrate 4... Second gas barrier layer 5... Second adhesive layer 10... Foamable adhesive sheet 11... First cured adhesive layer 15... Second cured adhesive layer 20... Article 21... First member 22... Second member 23... Adhesive member 30... Stator for rotating electric machine 31... Stator core 32... Slot 33... Coil 34... Adhesive member 40... Rotor for rotating electric machine 41... Rotor core 42... Slot 43... Permanent magnet 44... Coil 45... Adhesive member

Claims

1. A foamable adhesive sheet having, in this order, a first adhesive layer, a first gas barrier layer, a substrate, and a second gas barrier layer, wherein the first adhesive layer contains a curable adhesive and a foaming agent, and the foaming agent is thermally expandable microcapsules.

2. The foamable adhesive sheet according to claim 1, further comprising a second adhesive layer on the side of the second gas barrier layer opposite the substrate, the second adhesive layer containing a curable adhesive.

3. The foamable adhesive sheet according to claim 2, wherein the second adhesive layer contains a foaming agent, and the foaming agent is a thermally expandable microcapsule.

4. The oxygen permeability of the foamable adhesive sheet is 2 cc / (m ２ 2. The foamable adhesive sheet according to claim 1, wherein the viscosity is 1000 kJ / min.

5. The water vapor permeability of the foamable adhesive sheet is 1.6 g / (m ２ 2. The foamable adhesive sheet according to claim 1, wherein the adhesive strength is 1000 times or less.

6. The foamable adhesive sheet according to claim 1, wherein the thickness of the first gas barrier layer and the thickness of the second gas barrier layer are each 1 nm or more and 10 μm or less.

7. The foamable adhesive sheet according to claim 1, wherein the foamable adhesive sheet is wound into a roll.

8. An article having a first member, a second member, and an adhesive member disposed between the first member and the second member, wherein the adhesive member has a first cured adhesive layer, a first gas barrier layer, a substrate, and a second gas barrier layer, in this order, and the first cured adhesive layer contains a foamed, cured product of an adhesive composition comprising a curable adhesive and a foaming agent, and the foaming agent is a thermally expandable microcapsule.

9. The article according to claim 8, wherein the adhesive member has a second cured adhesive layer on the side of the second gas barrier layer opposite the substrate, and the second cured adhesive layer contains a cured product of an adhesive composition including a curable adhesive.

10. The article of claim 9, wherein the second cured adhesive layer comprises a foamed, cured product of an adhesive composition comprising the curable adhesive and a foaming agent, the foaming agent being thermally expandable microcapsules.

11. The article according to claim 8, wherein the thickness of the first gas barrier layer and the thickness of the second gas barrier layer are each 1 nm or more and 10 μm or less.

12. A stator for a rotating electric machine having a stator core, coils arranged in slots of the stator core, and an adhesive member arranged between the stator core and the coils, wherein the adhesive member has a first cured adhesive layer, a first gas barrier layer, a substrate, and a second gas barrier layer, in this order, the first cured adhesive layer contains a foamed, cured product of an adhesive composition comprising a curable adhesive and a foaming agent, and the foaming agent is a thermally expandable microcapsule.

13. A stator for a rotating electric machine according to claim 12, wherein the adhesive member has a second cured adhesive layer on the side of the second gas barrier layer opposite the substrate, and the second cured adhesive layer contains a cured product of an adhesive composition including a curable adhesive.

14. A stator for a rotating electric machine according to claim 13, wherein the second cured adhesive layer contains a foamed, cured product of an adhesive composition comprising the curable adhesive and a foaming agent, and the foaming agent is a thermally expandable microcapsule.

15. A rotor for a rotating electric machine having a rotor core, a permanent magnet or a coil arranged in a slot of the rotor core, and an adhesive member arranged between the rotor core and the permanent magnet or the coil, wherein the adhesive member has a first cured adhesive layer, a first gas barrier layer, a substrate, and a second gas barrier layer, in this order, the first cured adhesive layer contains a foamed, cured product of an adhesive composition containing a curable adhesive and a foaming agent, and the foaming agent is a thermally expandable microcapsule.

16. A rotor for a rotating electric machine according to claim 15, wherein the adhesive member has a second cured adhesive layer on the side of the second gas barrier layer opposite the substrate, and the second cured adhesive layer contains a cured product of an adhesive composition including a curable adhesive.

17. A rotor for a rotating electric machine according to claim 16, wherein the second cured adhesive layer contains a foamed, cured product of an adhesive composition comprising the curable adhesive and a foaming agent, and the foaming agent is a thermally expandable microcapsule.

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