Adhesive sheet and method for manufacturing the same, article, and method for manufacturing article

Abstract

To provide an adhesive sheet that can ensure favorable ease of insertion even when inserted into a narrow space in use, and can also favorably exhibit various characteristics during or after heating.SOLUTION: An adhesive sheet includes: a first adhesive layer formed of an adhesive composition containing an epoxy resin having a softening point of 50°C or higher and a thermal curing agent; and a second adhesive layer that has tackiness and is foamed and cured by heat. An outermost layer of the adhesive sheet is formed of the first adhesive layer, and the adhesive sheet has a plurality of convex structures on a surface on a side of the outermost layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an adhesive sheet and a method for manufacturing the same, an article, and a method for manufacturing an article. [Background technology]

[0002] Adhesive sheets have traditionally been used to bond objects together. The performance required of adhesive sheets varies depending on the application. For example, adhesive sheets that are inserted into narrow spaces such as the slots of EV motors must not only provide sufficiently high adhesion after bonding, but also be easy to insert.

[0003] In response to this, for example, Patent Document 1 proposes a thermosetting thermally expandable adhesive sheet as an adhesive sheet to be inserted into a slot in the rotor core of an IPM (Interior Permanent Magnet) motor and to bond the rotor core to a magnet. The adhesive sheet has a base material having a first surface and a second surface opposite the first surface and having a communication opening, and a first adhesive layer formed on the first surface of the base material and containing a thermosetting thermally expandable epoxy adhesive, and when heated, the thermosetting thermally expandable epoxy adhesive passes through the communication opening in the base material to form a second adhesive layer on the second surface of the base material.

[0004] Furthermore, for example, Patent Document 2 proposes a heat-expandable adhesive sheet that is inserted into a slot in the stator body of a motor to bond the stator and coil, and that includes a base material, two heat-expandable adhesive layers provided on both sides of the base material, and two adhesive-permeable layers provided on the surface of each of the two adhesive layers, through which the adhesive can pass when the adhesive thermally expands. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-23559 [Patent Document 2] Special issue 2019-203062 publication Summary of the Invention [Problem to be solved by the invention]

[0006] The substrate and adhesive permeable layer having the above-mentioned communication openings are not so-called adhesives and do not contribute to adhesive strength, etc. Even in adhesive sheets that are inserted into narrow spaces as described above, there is hope for improved adhesive performance, and there is room for improvement in performance in terms of making effective use of the narrow spaces.

[0007] The present inventors have attempted to develop an adhesive sheet that can be inserted into such narrow spaces by using a method different from that disclosed in the above-mentioned Patent Documents 1 and 2. However, if one were to simply use, for example, a thermosetting adhesive that is substantially non-tacky at room temperature (e.g., an adhesive containing a thermosetting resin with a softening point of 50°C or higher) in order to ensure good ease of insertion, this would impose restrictions on the selection of various components, and could continue to restrict the expression of various properties required of an adhesive sheet during or after heating, such as reactivity, foaming property, and adhesive strength.

[0008] An object of the present disclosure is to provide an adhesive sheet that can ensure good ease of insertion even when inserted into a narrow space and that exhibits good properties during or after heating, and a method for manufacturing the same. A further object of the present disclosure is to provide an article that includes such an adhesive sheet, and a method for manufacturing an article that uses such an adhesive sheet. [Means for solving the problem]

[0009] The present disclosure provides the following [1] to

[11] .

[0010] [1] An adhesive sheet comprising: a first adhesive layer made of an adhesive composition containing an epoxy resin having a softening point of 50°C or higher and a thermosetting agent; and a second adhesive layer that is adhesive and foams and hardens when heated, wherein at least one of the outermost layers is made of the first adhesive layer and has a plurality of convex structures on the surface of the outermost layer made of the first adhesive layer.

[0011] [2] The adhesive sheet according to [1], wherein the outermost layer, which is the first adhesive layer, is made of a molded product of the adhesive composition.

[0012] [3] The adhesive sheet according to [1], wherein the outermost layer of the first adhesive layer is a deposit of the powdery adhesive composition.

[0013] [4] The adhesive sheet according to any one of [1] to [3], wherein the height of the convex structures is 2 to 200 μm.

[0014] [5] The adhesive sheet according to any one of [1] to [4], further comprising a substrate layer as an intermediate layer.

[0015] [6] The adhesive sheet according to any one of [1] to [5], wherein one outermost layer is the second adhesive layer.

[0016] [7] The adhesive sheet according to any one of [1] to [5], wherein both outermost layers are made of the first adhesive layer and have a plurality of the convex structures on both surfaces.

[0017] [8] An article comprising the adhesive sheet according to any one of [1] to [7] and an adherend to which the adhesive sheet is attached.

[0018] [9] A method for manufacturing an adhesive sheet having a plurality of convex structures on its surface, comprising the steps of: applying a solution containing an epoxy resin having a softening point of 50°C or higher and a thermosetting agent to the surface of a mold having a plurality of concave structures on its surface, and solidifying the solution to form a first adhesive layer; and providing a second adhesive layer, which has adhesiveness and foams and hardens when heated, on the side of the first adhesive layer opposite the mold.

[0019]

[10] A method for manufacturing an adhesive sheet having a plurality of convex structures on its surface, comprising the steps of: forming an adhesive layer that has adhesiveness and that expands and hardens when heated on the surface of a mold having a plurality of concave structures on its surface, thereby forming a plurality of convex structures on the surface of the adhesive layer; and depositing a powdered adhesive composition on the surface of the adhesive layer, the powdered adhesive composition including an epoxy resin having a softening point of 50°C or higher and a thermosetting agent.

[0020]

[11] A method for manufacturing an article comprising a first element, a second element, and a filling portion that fills the space between the first element and the second element, the method comprising the steps of: placing an adhesive sheet described in any one of [1] to [7] between the first element and the second element; and heating the adhesive sheet to thermally expand and harden it to form the filling portion. [Effects of the Invention]

[0021] According to the present disclosure, it is possible to provide an adhesive sheet and a method for manufacturing the same that can ensure good ease of insertion even when inserted into a narrow space and that can exhibit various properties well during or after heating. Furthermore, according to the present disclosure, it is possible to provide an article including such an adhesive sheet and a method for manufacturing an article using such an adhesive sheet. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a perspective view of an adhesive sheet according to one embodiment. [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Figure 3] FIG. 10 is a cross-sectional view showing an example of a convex structure. [Figure 4] FIG. 10 is a cross-sectional view showing an example of a convex structure. [Figure 5] 2 is a cross-sectional view illustrating a method for manufacturing the adhesive sheet of FIG. 1. FIG. [Figure 6] 2 is a cross-sectional view showing an article including the adhesive sheet of FIG. 1. [Figure 7] FIG. 10 is a cross-sectional view showing an adhesive sheet according to another embodiment. [Figure 8] FIG. 10 is a cross-sectional view showing an adhesive sheet according to another embodiment. [Figure 9] 9A to 9C are cross-sectional views illustrating a method for manufacturing the adhesive sheet of FIG. 8. [Figure 10] FIG. 10 is a cross-sectional view showing an adhesive sheet according to another embodiment. [Figure 11] FIG. 10 is a cross-sectional view showing an adhesive sheet according to another embodiment. [Figure 12] FIG. 10 is a cross-sectional view showing an adhesive sheet according to another embodiment. [Figure 13] FIG. 1 is a diagram showing a mold (sheet) used in the examples. [Figure 14] FIG. 1 is a diagram showing a mold (sheet) used in the examples. [Figure 15] 1(a) is a laser microscope image of the adhesive sheet of Example 1, and FIG. 1(b) is an optical microscope image showing the adhesive surface between the adhesive sheet of Example 1 and a glass substrate. [Figure 16] 1(a) is a laser microscope image of the adhesive sheet of Example 2, and FIG. 1(b) is an optical microscope image showing the adhesive surface between the adhesive sheet of Example 2 and the glass substrate. [Figure 17] 1(a) is a laser microscope image of the adhesive sheet of Example 3, and FIG. 1(b) is an optical microscope image showing the adhesive surface between the adhesive sheet of Example 3 and a glass substrate. [Figure 18] FIG. 1 is a cross-sectional view illustrating a method for preparing a sample for measuring shear strength. DETAILED DESCRIPTION OF THE INVENTION

[0023] In this specification, a numerical range indicated using "to" indicates a range that includes the numerical values before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this specification, the upper or lower limit of a numerical range in a certain stage may be replaced with the upper or lower limit of a numerical range in another stage. Furthermore, in the numerical ranges described in this specification, the upper or lower limit of the numerical range may be replaced with a value shown in the Examples. Furthermore, the upper and lower limits individually described can be combined in any way. Furthermore, in this specification, "(meth)acrylate" means at least one of acrylate and the corresponding methacrylate.

[0024] In one embodiment, the adhesive sheet comprises at least one first adhesive layer and at least one second adhesive layer. When there are multiple first adhesive layers, the multiple first adhesive layers may be the same or different. When there are multiple second adhesive layers, the multiple second adhesive layers may be the same or different.

[0025] At least one of the first adhesive layers constitutes the outermost layer of the adhesive sheet. In other words, at least one of the two outermost layers of the adhesive sheet consists of the first adhesive layer. The other outermost layer may be the first adhesive layer or a layer other than the first adhesive layer (for example, a second adhesive layer). In this specification, the "outermost layer" refers to the layer located on the outermost side of the adhesive sheet and that first comes into contact with the object when the adhesive sheet of the present disclosure approaches the object. The adhesive sheet has a plurality of convex structures on the surface of the outermost layer side consisting of the first adhesive layer.

[0026] (First adhesive layer) The first adhesive layer is made of a first adhesive composition containing an epoxy resin and a thermosetting agent. The first adhesive composition has thermosetting properties because it contains an epoxy resin and a thermosetting agent.

[0027] The softening point of the epoxy resin contained in the first adhesive layer is 50°C or higher. Therefore, the first adhesive layer is substantially non-tacky. Here, "the first adhesive layer is substantially non-tacky" means that even when the first adhesive layer is brought into contact with SPCC-SB (cold-rolled steel plate) at room temperature (e.g., 25°C), the first adhesive layer does not stick to SPCC-SB. The presence of such properties of the first adhesive layer can be confirmed, for example, by measuring the dynamic friction coefficient of the surface of the first adhesive layer. The dynamic friction coefficient is measured in accordance with JIS K7125 "Testing Method for Friction Coefficient of Plastics and Films." The dynamic friction coefficient of the surface of the first adhesive layer is, for example, 0.8 μd or less. The upper limit of the softening point of the epoxy resin is not particularly limited, but is preferably below the activation temperature of the thermosetting agent, e.g., 150°C or less. The softening point of the epoxy resin is measured using the ring and ball softening point test method specified in JIS K 2207.

[0028] Examples of epoxy resins include those obtained from epoxy compounds (monomer epoxy compounds or polymer epoxy compounds) having at least one oxirane ring polymerizable by a ring-opening reaction. The epoxy compounds may be aliphatic, alicyclic, aromatic, or heterocyclic. The epoxy compounds may have preferably at least two, and more preferably 2 to 4, polymerizable epoxy groups per molecule. The average epoxy equivalent of the epoxy resin may be 80 to 1,000 or 90 to 600, from the viewpoint of obtaining better adhesive strength. The average epoxy equivalent is a value determined in accordance with JIS K 7236.

[0029] Examples of epoxy resins include bisphenol epoxy resins such as bisphenol A epoxy resin, dimer acid-modified bisphenol A epoxy resin, and bisphenol F resin, epoxy resins having an aliphatic skeleton such as hexanediol glycidyl ether, glycidylamine epoxy resins such as p-aminophenol triglycidyl, novolac epoxy resins such as phenol novolac epoxy resin and cresol novolac epoxy resin, brominated epoxy resins, alicyclic epoxy resins, and mixtures thereof. In a preferred embodiment, the epoxy resin is a bisphenol epoxy resin, a glycidylamine epoxy resin, or a novolac epoxy resin.

[0030] To adjust the softening point of the epoxy resin, a mixture of multiple epoxy resins may be used. In this case, the softening point of the mixture of multiple epoxy resins is 50°C or higher. The first adhesive layer may contain an epoxy resin with a softening point of less than 50°C, as long as the effects of the present invention are not impaired, i.e., in an amount such that the softening point of the mixed epoxy resin is 50°C or higher.

[0031] The content of the epoxy resin may be 30% by mass or more, 50% by mass or more, or 70% by mass or more, based on the total mass of the first adhesive composition, from the viewpoint of obtaining better adhesive strength. The content of the epoxy resin may be 70% by mass or less, 50% by mass or less, or 30% by mass or less, based on the total mass of the first adhesive composition, from the viewpoint of obtaining the advantages of the other contained components. From these viewpoints, the content of the epoxy resin may be 30 to 70% by mass, based on the total mass of the first adhesive composition.

[0032] The thermal curing agent can be any of a variety of thermal curing agents known in the art to be usable as a thermal curing agent for epoxy resins. Examples of thermal curing agents include compounds that react with the oxirane ring of an epoxide to substantially crosslink the epoxide and form a crosslinked polymer network. These compounds contain at least one nucleophilic or electrophilic moiety (e.g., an active hydrogen atom) that initiates the crosslinking reaction. As will be understood by those skilled in the art, thermal curing agents and curing accelerators are often not distinguished from each other. Therefore, the thermal curing agent of the present disclosure also encompasses a curing accelerator. In a preferred embodiment, the thermal curing agent includes a curing accelerator to enhance the epoxide curing reaction rate. In a typical embodiment, the curing accelerator is a polyfunctional compound.

[0033] The heat curing agent is, for example, a latent curing agent that is inactive near room temperature and activated by heat. Examples of latent curing agents include dicyandiamide and its derivatives, hydrazide compounds, boron trifluoride-amine complexes, and reaction products of amine compounds with isocyanate compounds or urea compounds (urea derivatives). A latent curing accelerator may be used in combination with the epoxy resin curing agent. Examples of curing accelerators include imidazole compounds, reaction products of amine compounds with epoxy compounds (amine-epoxy adducts), and urea derivatives. Preferably, the heat curing agent is dicyandiamide.

[0034] The content of the thermosetting agent may be 0.1 to 80 parts by mass, 1 to 60 parts by mass, or 3 to 50 parts by mass relative to 100 parts by mass of the epoxy resin, from the viewpoint of realizing a good crosslinking reaction of the epoxy resin and obtaining better adhesive strength.

[0035] The first adhesive composition may further contain optional components other than the above components, such as a plasticizer, a core-shell toughening agent, and a filler.

[0036] The total thickness of the first adhesive layer can be set by the width of the space (slot) into which the adhesive sheet is inserted and the corresponding total thickness of the second adhesive layer, etc. The total thickness of the first adhesive layer is, for example, 2 to 400 μm, and may be 5 to 200 μm.

[0037] (Second adhesive layer) The second adhesive layer is a layer that has adhesive properties and foams and hardens when heated. The adhesive properties of the second adhesive layer mean that when the second adhesive layer is brought into contact with SPCC-SB (cold-rolled steel plate) at room temperature (e.g., 25°C), the second adhesive layer adheres to SPCC-SB. Therefore, when the tack evaluation (described later) is evaluated as 1, it can be said that the second adhesive layer has adhesive properties.

[0038] The second adhesive layer is composed of a second adhesive composition containing, for example, an adhesive component and a thermal foaming agent. The adhesive component may be composed of components that impart tackiness and thermosetting properties to the second adhesive layer. While the first adhesive layer is required to be substantially non-tacky (i.e., have a low surface dynamic friction coefficient at room temperature), the second adhesive layer does not have such a requirement, and there are fewer restrictions on the selection of various components when developing high adhesive strength through thermal curing. Therefore, the second adhesive layer typically has superior adhesive strength after thermal curing (e.g., shear strength when using SPCC-SB as an adherend, as evaluated by the method described in the Examples) than the first adhesive layer. The adhesive component may, for example, contain an epoxy resin, a (meth)acrylate polymer, and a thermosetting agent.

[0039] Examples of epoxy resins include the compounds exemplified as the epoxy resin contained in the first adhesive composition (first adhesive layer). The softening point of the epoxy resin in the second adhesive composition does not need to be 50°C or higher, and may be lower than 50°C (for example, higher than 0°C and lower than 50°C).

[0040] The content of the epoxy resin may be 20% by mass or more, 30% by mass or more, 35% by mass or more, or 40% by mass or more, based on the total mass of the second adhesive composition, from the viewpoint of obtaining better adhesive strength. The content of the epoxy resin may be 60% by mass or less, 55% by mass or less, or 50% by mass or less, based on the total mass of the second adhesive composition, from the viewpoint of obtaining the advantages of the other contained components. From these viewpoints, the content of the epoxy resin may be 20 to 60% by mass or 30 to 60% by mass, based on the total mass of the second adhesive composition.

[0041] The (meth)acrylate polymer is a polymer containing units ((meth)acrylate units) derived from (meth)acrylate monomers. The (meth)acrylate polymer preferably contains alicyclic (meth)acrylate units and glycidyl (meth)acrylate units. Examples of the alicyclic (meth)acrylate units include dicyclopentanyl (meth)acrylate and cyclohexyl (meth)acrylate.

[0042] The (meth)acrylate polymer preferably contains a total of 50% by mass or more, or 70% by mass or more, of units derived from (meth)acrylate monomers having a solubility parameter value (SP value) of less than 10. In this specification, the solubility parameter value refers to the Fedors solubility parameter at 25°C (see Fedors, Polym. Eng. And Sci., 14, 147 (1974)). In a preferred embodiment, the (meth)acrylate polymer is derived substantially only from (meth)acrylate monomers having a solubility parameter value of less than 10. (Meth)acrylate monomers having a solubility parameter value of less than 10 tend to have low hygroscopicity, and are therefore advantageous in terms of reducing the hygroscopicity of the adhesive.

[0043] Examples of (meth)acrylate monomers having a solubility parameter value of less than 10 include glycidyl methacrylate (solubility parameter value: 9.79), dicyclopentanyl acrylate (solubility parameter value: 9.66), dicyclopentanyl methacrylate (solubility parameter value: 9.60), dicyclopentenyl acrylate (solubility parameter value: 9.71), tetrahydrofurfuryl acrylate (solubility parameter value: 9.51), tetrahydrofurfuryl methacrylate (solubility parameter value: 9.45), cyclic trimethylpropane formal acrylate (solubility parameter value: 9.35), and cyclohexyl acrylate (solubility parameter value: 9.26).

[0044] From the viewpoint of ease of handling of the adhesive sheet, the content of the (meth)acrylate polymer may be 12% by mass or more, 15% by mass or more, or 18% by mass or more, based on the total mass of the second adhesive composition. From the viewpoint of facilitating setting of viscosity at the curing temperature, the content of the (meth)acrylate polymer may be 35% by mass or less, 30% by mass or less, or 25% by mass or less, based on the total mass of the second adhesive composition. From these viewpoints, the content of the (meth)acrylate polymer may be 12 to 35% by mass, based on the total mass of the second adhesive composition.

[0045] Examples of the thermosetting agent include the compounds exemplified as the thermosetting agent contained in the first adhesive composition (first adhesive layer). The content of the thermosetting agent in the second adhesive composition may be selected from the range exemplified as the content of the thermosetting agent in the first adhesive composition.

[0046] As the thermal foaming agent, various materials that generate foam when heated can be used. As will be understood by those skilled in the art, thermal foaming agents and thermal expansion materials are often not distinguished from each other. Therefore, the thermal foaming agent also includes materials that are generally called thermal expansion materials. By adding a thermal foaming agent to the second adhesive composition, thermal foaming properties can be imparted to the second adhesive layer.

[0047] Examples of thermal foaming agents include chemical foaming agents, encapsulated thermal expansion materials, expandable graphite, etc. From the viewpoint of effectively preventing deterioration of the adherend by preventing gas or liquid from permeating through the adhesive during and after curing, encapsulated thermal expansion materials are preferred.

[0048] Encapsulated thermally expansive materials typically include a thermoplastic polymer shell and a liquefied gas encapsulated within the shell. Examples of thermoplastic polymers include vinylidene chloride polymers, acrylonitrile copolymers, and acrylic polymers. Examples of liquefied gases include trichlorofluoromethane and hydrocarbons (e.g., n-pentane, isopentane, neopentane, butane, isobutane, etc.). The typical behavior of encapsulated thermally expansive materials when heated is as follows: When heated, the capsule expands due to softening of the shell and an increase in internal pressure caused by gasification of the liquefied gas. As the temperature increases, the capsule expands (i.e., a balloon is formed). After the capsule volume reaches its maximum, further increase in temperature causes the shell to thin, allowing the gas inside the capsule to diffuse through and the capsule volume to begin to decrease (i.e., the capsule shrinks). Typically, the material and dimensions of encapsulated thermally expansive materials are appropriately designed to control the temperature at which the capsule volume reaches its maximum.

[0049] The ratio of the maximum capsule volume to the minimum capsule volume when the temperature of the encapsulated thermal expansion material is varied is preferably 2 or more or 3 or more from the viewpoint of imparting good thermal expansion performance to the adhesive, and is preferably 100 or less or 50 or less from the viewpoint of avoiding inconveniences such as the adhesive overflowing from the adherend due to an excessive increase in volume.

[0050] The temperature at which the volume of the encapsulated thermally expandable material changes when heated (also referred to as the expansion initiation temperature in this disclosure) may be 70°C or higher, 80°C or higher, or 90°C or higher, in order to avoid shrinkage before the adhesive is completely cured, and may be 160°C or lower, 150°C or lower, or 140°C or lower, in order to cause expansion during curing heating.

[0051] The average particle size of the encapsulated expanding material is, for example, 1 to 50 μm, and may be 3 to 30 μm or 5 to 20 μm. The average particle size of the encapsulated expanding material is a value measured by laser diffraction.

[0052] The encapsulated thermal expansion material may be a commercially available product, and examples thereof include FN-80GSD, FN-100SD, and FN-100MD (all available from Matsumoto Yushi Seiyaku Co., Ltd.), EML101 and EMH204 (all available from Sekisui Chemical Co., Ltd.), 461DU40, and 920DU40 (all available from AczoNobel).

[0053] The content of the thermal blowing agent may be 0.1 mass % or more, 0.3 mass % or more, or 0.5 mass % or more, based on the total mass of the second adhesive composition, from the viewpoint of improving the space-filling properties due to foaming of the second adhesive layer. The content of the thermal blowing agent may be 20 mass % or less, 15 mass % or less, or 10 mass % or less, based on the total mass of the second adhesive composition, from the viewpoint of suppressing a decrease in adhesive strength due to excessive expansion. From these viewpoints, the content of the thermal blowing agent may be 0.1 to 20 mass %, based on the total mass of the second adhesive composition.

[0054] The second adhesive composition preferably further comprises a core-shell toughening agent. As the core-shell toughening agent, various core-shell rubber modifiers generally known in the art can be used. Core-shell toughening agents typically have an inner core and an outer shell made of different materials.

[0055] The core material is, for example, a rubbery polymer with a glass transition temperature below room temperature. Specific examples include acrylic polymers made from butyl acrylate, butadiene polymers, butadiene-styrene copolymers, and silicone rubber, as well as crosslinked products thereof. The shell material is, for example, a polymer (non-rubber-like at room temperature) with a glass transition temperature above room temperature. Specific examples include methyl methacrylate polymers and copolymers thereof, as well as crosslinked products thereof, and products modified with functional groups such as carboxyl, hydroxyl, epoxy, cyanate, amino, and thiol that can react with epoxy components.

[0056] The core-shell toughening agent may be a commercially available product, and examples thereof include MX217, BTA751, BTA731 (all available from The Dow Chemical Company), AC-3355 (available from Aica Kogyo Co., Ltd.), and the like.

[0057] The content of the core-shell toughener may be 10% by mass or more, 12% by mass or more, or 15% by mass or more, based on the total mass of the second adhesive composition, from the viewpoint of further improving the physical properties of the adhesive. The content of the core-shell toughener may be 50% by mass or less, 30% by mass or less, 25% by mass or less, or 20% by mass or less, based on the total mass of the second adhesive composition, from the viewpoint of effectively obtaining the advantages of the other contained components. From these viewpoints, the content of the core-shell toughener may be 10 to 50% by mass or 10 to 30% by mass, based on the total mass of the second adhesive composition.

[0058] In the second adhesive composition, the total amount of the epoxy resin and the core-shell toughening agent may be 40% by mass or more or 50% by mass or more, based on the total mass of the second adhesive composition, from the viewpoint of obtaining good physical properties, and may be 80% by mass or less, 75% by mass or less, or 70% by mass or less, from the viewpoint of obtaining good effects of other components in the adhesive.

[0059] The second adhesive composition may further contain optional components other than the above components, such as thermoplastic resins, fillers, flame retardants, impact modifiers, heat stabilizers, processing aids, lubricants, reinforcing agents, colorants, photopolymerization initiators, crosslinking agents, chain transfer agents, and silane coupling agents.

[0060] The second adhesive composition may be, for example, a photocured product of a precursor composition containing a foaming agent, an epoxy resin, a thermosetting agent, a (meth)acrylate monomer, a photopolymerization initiator, and optionally a chain transfer agent. The precursor composition is irradiated with light to activate the photopolymerization initiator, thereby polymerizing the (meth)acrylate monomer, thereby producing a (meth)acrylate polymer. The (meth)acrylate monomer is a monomer exemplified as a monomer unit of the (meth)acrylate polymer.

[0061] As the photopolymerization initiator, a cleavage type or a hydrogen abstraction type is effective. Examples of the cleavage type photopolymerization initiator include benzoethyl ether, diethoxyacetophenone, 2,2-dimethoxy-1,2-diphenylethan-1-one, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]-phenyl}-2-methyl-propan-1-one, 2-methyl-1-[4-(methyl Examples of the hydrogen abstraction type photopolymerization initiator include benzophenone and 2,4-diethylthioxanthone.

[0062] Examples of chain transfer agents include carbon tetrabromide, mercapto compounds, etc. Examples of mercapto compounds include ethanethiol, butanethiol, dodecanethiol, mercaptoethanol (thioglycol), 3-mercaptopropanol, thioglycerin (mercaptoglycerin), thioglycolic acid (mercaptoacetic acid), 2-mercaptopropionic acid (thiolactic acid), 3-mercaptopropionic acid, α-mercaptoisobutyric acid, methyl mercaptopropionate, and ethyl mercaptopropionate.

[0063] The total thickness of the second adhesive layer can be set according to the width of the space (slot) into which the adhesive sheet is inserted. For example, if the slot width is 200 μm, the total thickness of the adhesive sheet that can be inserted will be thinner than 200 μm. If the total thickness of the adhesive sheet is set to about 150 μm, a 50 μm gap will be created. The total thickness of the second adhesive layer is set taking into account the expansion ratio due to foaming and the required adhesive strength so that this gap can be filled by foaming the second adhesive layer. For example, if the gap is 50 μm, the total thickness of the second adhesive layer is 20 to 200 μm, or may be 50 to 150 μm.

[0064] The adhesive sheet may further include a layer other than the first and second adhesive layers, such as a substrate layer (a layer made of a substrate).

[0065] The substrate layer is usually a layer provided as an intermediate layer (a layer other than the outermost layer). The substrate constituting the substrate layer preferably has heat resistance to such an extent that it does not deteriorate at the heating temperature used when curing the first adhesive layer and the second adhesive layer. A polyethylene naphthalate (PEN) film, for example, is preferably used as the substrate. The substrate may have insulating properties. When the adhesive sheet is used for insulating purposes, an insulating substrate is preferably used.

[0066] The thickness of the substrate layer is, for example, 1 to 200 μm, and may be 2 to 150 μm or 5 to 100 μm.

[0067] The adhesive sheet described above can be used in a method for manufacturing an article, which includes, for example, the steps of placing the adhesive sheet between a first element and a second element, and heating the adhesive sheet to thermally expand and harden it to form a filling portion, and is particularly suitable for use when the space between the two elements (the first element and the second element) is narrow, for the following reasons.

[0068] First, because the second adhesive layer of the adhesive sheet is foamable, it has a thickness that allows insertion at room temperature, yet can foam and expand upon heat curing. Therefore, by placing the adhesive sheet in the space between the adherend elements and then heating it, the space can be filled. Furthermore, because the adhesive sheet is composed of a first adhesive layer with at least one surface that is substantially non-tacky, insertion is easier than using conventional adhesives such as liquid adhesives or adhesives with tacky surfaces. Furthermore, the adhesive sheet includes, in addition to the first adhesive layer, a second adhesive layer with fewer restrictions on various components than the first adhesive layer. Therefore, the adhesive sheet is less likely to be restricted in its ability to exhibit the various properties required of the adhesive sheet during or after heating, and can exhibit these properties well. In particular, because the adhesive sheet has multiple convex structures on the surface of the outermost layer, which is made up of the first adhesive layer, it tends to be able to adhere to the adherend with improved shear strength after heat curing.

[0069] The reason why the multiple convex structures provide improved shear strength is unclear, but is presumed to be as follows. First, when multiple convex structures are present on the surface of the outermost layer of the first adhesive layer, it is presumed that the first adhesive layer and the second adhesive layer are more likely to mix well together after heating and before curing is complete, compared to when the outermost layer of the first adhesive layer is flat. As described above, the first adhesive layer and the second adhesive layer have different constraints on the selection of various components, and the adhesive strength of the second adhesive layer after heat curing tends to be higher than the adhesive strength of the first adhesive layer after heat curing. Therefore, it is presumed that the mixing of the first adhesive layer and the second adhesive layer makes it easier to exert the high adhesive strength derived from the second adhesive layer, resulting in improved shear strength.

[0070] In one example, the first element is a rotor core of an EV motor (e.g., an IPM motor), and the second element is a magnet. In this example, one surface of the adhesive sheet is adhesive. For example, one outermost layer of the adhesive sheet is made of a second adhesive layer. In this example, the adhesive sheet is first attached to the magnet from the surface opposite the surface having the multiple convex structures to create a laminate of the magnet and the adhesive sheet (an article including the adhesive sheet). Next, the laminate is inserted into a slot in the rotor core, thereby placing the adhesive sheet between the rotor core (first element) and the magnet (second element).

[0071] In another example, the first element is a stator of an EV motor, and the second element is a coil. In this example, the adhesive sheet has both surfaces with a plurality of convex structures (the surface of the outermost layer made of the first adhesive layer), and in addition to the first and second adhesive layers, it also includes an insulating base layer. In this example, the adhesive sheet is positioned between the stator (first element) and the coil (second element) by inserting it into a slot in the stator.

[0072] The heating conditions for the adhesive sheet are appropriately adjusted from the viewpoint of thermally foaming the second adhesive layer and thermally curing the first and second adhesive layers. The heating temperature is, for example, 150 to 200°C, and the heating time is, for example, 1 to 30 minutes.

[0073] According to the above method, an article is provided that includes a first element, a second element, and a filler portion that fills the space between the first element and the second element.

[0074] The adhesive sheet of the present disclosure will be described in more detail below with reference to the accompanying drawings. In the description of the drawings, the same or equivalent elements are designated by the same reference numerals, and duplicated explanations will be omitted. The drawings show an XYZ Cartesian coordinate system as necessary.

[0075] Fig. 1 is a perspective view of an adhesive sheet according to one embodiment, and Fig. 2 is a cross-sectional view taken along line II-II in Fig. 1. The adhesive sheet 10 shown in Figs. 1 and 2 includes a surface 10a and a surface 10b. The surface 10a is the surface on the side of the first outermost layer 11, and the surface 10b is the surface on the side of the second outermost layer 12. The surfaces 10a and 10b extend along a plane (e.g., the XY plane) perpendicular to the thickness direction (e.g., the Z-axis direction) of the adhesive sheet 10.

[0076] The adhesive sheet 10 has a microstructure 5 on the surface 10a, and no microstructure 5 on the surface 10b. The microstructure 5 includes a plurality of convex structures 4 (convex bodies). In this specification, a "convex structure" generally refers to a three-dimensional figure having an arbitrary planar figure as the base and formed by connecting all points on the sides of the base with all points on the sides of another arbitrary planar figure or straight line (top) that is not on the same plane. Preferably, the area of the top of the convex structure is smaller than the area of the base. More preferably, the convex structure has a shape that tapers from the base to the top.

[0077] The plurality of convex structures 4 may be arranged regularly or irregularly on a plane. In the example of Figures 1 and 2, the plurality of convex structures 4 are arranged in a grid pattern along the X-axis direction and the Y-axis direction on the surface 10a.

[0078] Each convex structure 4 has a bottom surface 1, an apex 2, and a plurality of side surfaces 3 connecting the edge of the bottom surface 1 and the apex 2. The bottom surface 1 has any planar shape such as a circle (including an ellipse) or a polygon (triangle, square, hexagon). In the example of Figures 1 and 2, the convex structure 4 is a pyramidal structure having a square pyramid shape, and the bottom surface 1 has a square shape.

[0079] 1 and 2, the convex structure 4 is a cone structure, but the convex structure 4 may be a frustum structure or a rib structure. The convex structure 4 may be a combination of two or more of a cone structure, a frustum structure, and a rib structure.

[0080] 3 and 4 are cross-sectional views showing examples of the convex structure 4. FIG. 3 is a cross-sectional view of the convex structure 4 having a cone structure or a rib structure, and FIG. 4 is a cross-sectional view of the convex structure 4 having a frustum structure or a rib structure. The cross section of the convex structure 4 may have a triangular shape as shown in FIG. 3(a), or may have distorted side surfaces as shown in (b) to (d), or may have a shape in which the apex is positioned off-center from the base as shown in (e), or may have distorted side surfaces and a shape in which the apex is positioned off-center from the base as shown in (f). The cross section of the convex structure 4 may have a trapezoidal shape as shown in FIG. 4(a), or may have distorted side surfaces as shown in (b) to (c), or may have a distorted top surface as shown in (d) to (e), or may have distorted side surfaces and a distorted top surface as shown in (f). That is, the top surface of the convex structure 4 (frustum structure and rib structure) does not have to be parallel to the bottom surface, and does not have to be flat. When the convex structure 4 is a cone structure or a frustum structure, the cross sections passing through the apex of the convex structure 4 (the apex of the cone structure or the apex of the cone corresponding to the frustum structure) do not necessarily all have the same shape, and each cross section may have a different shape.

[0081] The area of the convex structure 4 projected onto a plane perpendicular to the height direction of the convex structure 4 (the area of the bottom surface 1 of the convex structure 4) may be 10 square μm or more, or 10,000 square μm or less.

[0082] The width (α in FIG. 2) of the bottom surface 1 of the convex structure 4 in the arrangement direction of the convex structure 4 (for example, the X-axis direction) may be 2 mm or less, 1 mm or less, 500 μm or less, 300 μm or less, 100 μm or less, or 50 μm or less.

[0083] The height of the convex structure 4 (H in FIG. 2) can be set according to the width of the space (slot) into which the adhesive sheet is inserted. From the viewpoint of reducing the coefficient of dynamic friction of the surface, it may be 2 μm or more, 5 μm or more, or 10 μm or more. From the viewpoint of facilitating mixing of the second adhesive layer and the first adhesive layer when the second adhesive layer is foamed, the height of the convex structure 4 may be 200 μm or less, 100 μm or less, 75 μm or less, 50 μm or less, or 25 μm or less. From these viewpoints, the height of the convex structure 4 may be 2 to 200 μm. The height of the convex structure 4 is based on the normal direction (Z-axis direction) of the bottom surface 1 of the convex structure 4.

[0084] The side surface of the convex structure 4 may have various shapes. The angle θ formed between the side surface 3 and the bottom surface 1 in a cross section (XZ plane) including the apex of the convex structure 4 and the arrangement direction of the convex structures 4 is greater than 0° and less than 180°, and may be 5° or more, 10° or more, 15° or more, 20° or more, 25° or more, or 30° or more, or may be less than 90°, 85° or less, 80° or less, or 70° or less.

[0085] The shapes of the multiple convex structures 4 may be the same or different. The multiple convex structures 4 preferably have substantially the same height (for example, a difference within ±5%, ±3%, or ±1%), and more preferably all have substantially the same shape. When convex structures 4 with different shapes are present, the microstructure 5 is preferably composed of 10 or less, 9 or less, 8 or less, 7 or less, 6 or less, 5 or less, 4 or less, 3 or less, or 2 or less types of convex structures.

[0086] The center-to-center distance between two adjacent convex structures 4 may be 10 μm or more, 20 μm or more, or 30 μm or more to facilitate mixing of the second adhesive layer and the first adhesive layer as the second adhesive layer foams and expands. Alternatively, the center-to-center distance may be 2 mm or less, 1 mm or less, 500 μm or less, 300 μm or less, or 200 μm or less to maintain a low coefficient of dynamic friction at room temperature. The center of the convex structure 4 refers to the apex of the convex structure 4 (e.g., the apex of a cone structure or the apex of a cone corresponding to a frustum structure). The center-to-center distance between two adjacent convex structures 4 corresponds to the sum (α + β) of the width α of the base 1 of the convex structure 4 and the spacing β between the bases 1 of adjacent convex structures 4. In the example of FIG. 2, the spacing β is 0.

[0087] The number of convex structures 4 is determined based on the surface area of the adhesive sheet 10 per 1 cm from the viewpoint of achieving both high adhesiveness and a low coefficient of dynamic friction. 2 Preferably, there are 25 or more, 36 or more, 49 or more, 64 or more, 81 or more, or 100 or more convex structures 4 per unit area. The number of convex structures 4 corresponds to the number of centers of convex structures 4 present within a unit area. From the viewpoint of manufacturing stability, the number of convex structures 4 is preferably about 1000 or less.

[0088] The adhesive sheet 10 has a base 6 below the plurality of convex structures 4. The base 6 is joined to or continuous with the bottom surfaces 1 of the convex structures 4 of the microstructures 5. The thickness of the base 6 can be set arbitrarily depending on the desired thickness of the adhesive sheet 10.

[0089] The adhesive sheet 10 has one outermost layer (first outermost layer 11) made of a first adhesive layer, and the other outermost layer (second outermost layer 12) made of a second adhesive layer. The first outermost layer 11 is a molded product of the first adhesive composition, and constitutes the entire convex structure 4 and part of the base 6. The second outermost layer 12 constitutes the other part of the base 6.

[0090] The thickness of the first outermost layer 11 (first adhesive layer) may be 1 μm or more, 2.5 μm or more, 5 μm or more, or 10 μm or more, and may be 200 μm or less, 100 μm or less, or 50 μm or less, or may be 1 to 200 μm, 2.5 to 100 μm, 5 to 50 μm, or 10 to 50 μm. The thickness of the first outermost layer 11 refers to the distance between the highest part of the convex structure 4 and the surface opposite to the surface 10 a (the surface overlapping with the interface 10 c), based on the normal direction (Z-axis direction) of the bottom surface 1 of the convex structure 4.

[0091] The thickness of the second outermost layer 12 (second adhesive layer) may be 10 μm or more, 25 μm or more, or 50 μm or more, and may be 200 μm or less, or 150 μm or less, or may be 10 to 200 μm, 25 to 150 μm, or 50 to 150 μm.

[0092] The thickness of the adhesive sheet 10 can be set according to the width of the space (slot) into which the adhesive sheet is inserted. That is, it can be set arbitrarily according to the width of the space (slot) into which the adhesive sheet is inserted, the gap to be filled, the foaming ratio, the required adhesive strength, and the like. As an example, the thickness of the adhesive sheet 10 may be, for example, 15 μm to 1 mm, or 50 μm to 300 μm. The thickness of the adhesive sheet 10 refers to the distance between the highest part of the convex structure 4 and the surface 10b opposite to the surface 10a having the microstructure 5, based on the normal direction of the bottom surface 1 of the convex structure 4.

[0093] The dynamic friction coefficient of the surface 10a of the adhesive sheet 10 having the microstructures 5 is, for example, 0.8 μd or less (e.g., 0 to 0.8 μd), and can also be reduced to 0.5 μd or less by changing the composition of the first adhesive layer and the shape and arrangement of the convex structures 4. The dynamic friction coefficient is a value measured in accordance with JIS K7125 "Testing method for the coefficient of friction of plastics and films."

[0094] Fig. 5 is a cross-sectional view illustrating one example of a method for manufacturing the adhesive sheet 10. The method for manufacturing the adhesive sheet 10 includes, for example, the steps of preparing a mold 20 having a plurality of recessed structures 21 (concave bodies) on a surface 20a (Fig. 5(a)), applying a solution (a solution of a first adhesive composition) containing an epoxy resin having a softening point of 50°C or higher and a thermosetting agent to the surface 20a of the mold 20 and allowing it to solidify, thereby forming a first adhesive layer (a first outermost layer 11) (Fig. 5(b)), and providing a second adhesive layer (a second outermost layer 12) on the side of the first adhesive layer (first outermost layer 11) opposite the mold 20 (Fig. 5(c)).

[0095] The mold 20 has a microstructure 22 on its surface 20a, which includes multiple recessed structures 21. The recessed structure 21 has a top surface 23, a bottom 24, and multiple side surfaces 25 connecting the edge of the top surface 23 and the bottom 24. The top surface 23 is a virtual surface that corresponds to the surface 20a when the recessed structures 21 are not present on the surface 20a. The microstructure 22 substantially corresponds to the microstructure 5 of the adhesive sheet. That is, the protruding structures 4 of the adhesive sheet 10 and the recessed structures 21 of the mold 20 have substantially the same shape and are arranged in substantially the same arrangement. The mold 20 can be produced, for example, by processing a flat plate made of a material such as metal or resin using a diamond cutter, laser, or the like. The difference in size between the protruding structures 4 and the recessed structures 21 is preferably within ±5%, ±3%, or ±1%.

[0096] Examples of methods for applying the solution include hand coating and die coating. The solution may contain the above-mentioned components that may be contained in the first adhesive composition, in addition to the epoxy resin and thermosetting agent. The solution may contain a solvent. The solvent is not particularly limited as long as it can dissolve the components that may be contained in the first adhesive composition, and examples include methyl ethyl ketone, ethyl acetate, and methyl isobutyl ketone. The solution may be solidified, for example, by heating the solution. The heating conditions may be set appropriately depending on the type of solvent in the solution, etc.

[0097] The step of providing the second adhesive layer (second outermost layer 12) may be, for example, a step of providing a layer made of a precursor composition of the second adhesive composition on the first adhesive layer (first outermost layer 11) and then photocuring the precursor composition. The layer made of the precursor composition may be formed on the first adhesive layer, or may be provided by first forming a layer made of the precursor composition and then laminating the layer to the first adhesive layer. The layer made of the precursor composition can be obtained, for example, by applying a solution containing the components of the precursor composition onto the first adhesive layer or onto a release substrate and then solidifying the solution by heating or the like.

[0098] The adhesive sheet 10 described above is used by adhering the surface 10b (the surface on the second adhesive layer side) of the adhesive sheet 10 to an adherend 15, for example, as shown in Fig. 6. That is, one embodiment of the present disclosure provides an article 16 comprising the adhesive sheet 10 and an adherend 15 to which the adhesive sheet 10 is adhered. An example of the adherend 15 is a magnet inserted into a slot in the rotor core of an IPM (Interior Permanent Magnet) motor.

[0099] The adhesive sheet of the present disclosure has been described in detail above using adhesive sheet 10 according to one embodiment as an example, but the adhesive sheet of the present disclosure is not limited to the above embodiment. Other embodiments of the adhesive sheet of the present disclosure will be described below. Note that in the following description, explanations of content that overlaps with the above embodiment will be omitted.

[0100] FIG. 7 is a cross-sectional view of an adhesive sheet according to another embodiment. The adhesive sheet 30 shown in FIG. 7 includes a first outermost layer 31 made of a first adhesive layer and a second outermost layer 32 made of a second adhesive layer. In the examples of FIGS. 1 and 2, two adjacent convex structures 4 are adjacent to each other and share one side of the bottom surface 1, but the multiple convex structures 4 of the adhesive sheet 30 are arranged with a spacing β greater than 0 between the bottom surfaces 1 of adjacent convex structures 4. The spacing β is 0 μm or more and may be 1 μm or more. The spacing β may be 100 μm or less, 50 μm or less, 15 μm or less, or 10 μm or less.

[0101] Fig. 8 is a cross-sectional view of an adhesive sheet according to another embodiment. The adhesive sheet 40 shown in Fig. 8 has a first outermost layer 41 made of a first adhesive layer, which is made of a deposit of a powdery first adhesive composition. A second outermost layer 42 adjacent to the first outermost layer 41 has a microstructure 425 including a plurality of convex structures 424 on a surface 42a in contact with the first outermost layer 41. The plurality of convex structures 424 has a bottom surface 421, an apex 422, and a plurality of side surfaces 423 connecting the edge of the bottom surface 421 and the apex 422. The first outermost layer 41 is formed by depositing the powdery first adhesive composition on the surface 42a, and therefore has a structure that follows the microstructure 425. That is, the microstructure 5 on the surface 40a of the adhesive sheet 40 has a structure that follows the microstructure 425. When the adhesive sheet 40 includes an intermediate layer, the intermediate layer adjacent to the first outermost layer 41 may have the above-described microstructure.

[0102] The above embodiment in which the first outermost layer of the first adhesive layer is a deposit of the powdery first adhesive composition offers the advantage of eliminating the need for a solvent and the drying time required to form the first outermost layer, compared to the embodiment in which the first outermost layer is a molded product of the first adhesive composition. On the other hand, the embodiment in which the first outermost layer of the first adhesive layer is a molded product of the first adhesive composition offers the advantage of more stably adhering the first outermost layer to an adjacent layer, compared to the embodiment in which the first outermost layer is a deposit of the powdery first adhesive composition.

[0103] 9 is a cross-sectional view illustrating an example of a method for manufacturing the adhesive sheet 40 of the above embodiment. The adhesive sheet 40 includes, for example, steps of forming a second adhesive layer (second outermost layer 42) on the surface 20a of a mold 20 having a plurality of recessed structures 21 on the surface 20a, thereby forming a plurality of protruding structures 424 on the surface 42a of the second adhesive layer (second outermost layer 42) ((a) and (b) of FIG. 9), and a step of depositing a powdery first adhesive composition on the surface 42a of the second adhesive layer (second outermost layer 42) ((c) of FIG. 9). Details of the mold 20 are the same as those of the above embodiment, and therefore will not be repeated here.

[0104] The second adhesive layer (second outermost layer 42) may be formed, for example, by providing a layer made of a precursor composition of the second adhesive composition on the surface 20a of the mold 20 and then photocuring the precursor composition. The layer made of the precursor composition may be formed on the surface 20a of the mold 20, or may be provided by first forming a layer made of the precursor composition and then bonding the layer to the mold 20. As a result, a microstructure 425 is formed on the surface 42a of the second adhesive layer (second outermost layer 42). The microstructure 425 includes convex structures 424 having substantially the same shape as the concave structures 21 of the mold 20, in substantially the same arrangement as the mold 20.

[0105] In this embodiment, the first adhesive composition can be deposited on the surface 42a of the second adhesive layer (second outermost layer 42) by, for example, sprinkling the first adhesive composition onto the surface 42a. The first adhesive composition contains, for example, a particulate epoxy resin having an average particle diameter of 1 to 100 μm as an epoxy resin having a softening point of 50°C or higher. The larger the average particle diameter of the epoxy resin, the greater the distance between the adherend and the second adhesive layer can be, while the smaller the average particle diameter, the smaller the center-to-center distance between particles can be. Within the above range, these tend to be well balanced. The average particle diameter of the epoxy resin is a value measured by laser diffraction.

[0106] Figure 10 is a cross-sectional view of an adhesive sheet of another embodiment. The adhesive sheet 50 shown in Figure 10(a) comprises a first outermost layer 51 made of a first adhesive layer and a second outermost layer 52 made of a second adhesive layer. The adhesive sheet 60 shown in Figure 10(b) comprises a first outermost layer 61 made of a first adhesive layer and a second outermost layer 62 made of a second adhesive layer. In the examples of Figures 2 and 8, the entire convex structure is made of the first adhesive layer, but in the adhesive sheets 50 and 60 shown in Figures 10(a) and 10(b), only a portion of the convex structure 4 (a portion including the apex 2 of the convex structure 4) is made of the first adhesive layer (first outermost layers 51 and 61). The first outermost layer 51 (first adhesive layer) shown in FIG. 10(a) can be obtained by molding a first adhesive composition in the same manner as the first outermost layer 11 (first adhesive layer) of the adhesive sheet 10 shown in FIG. 2. The first outermost layer 61 (first adhesive layer) shown in FIG. 10(b) can be obtained by depositing a powdery first adhesive composition in the same manner as the first outermost layer 41 (first adhesive layer) of the adhesive sheet 40 shown in FIG. 8. In the adhesive sheet shown in FIG. 10(a), the first outermost layer 51 is discontinuously present in a portion on the adjacent second outermost layer 52, and structures having such shapes are also included in the term "layer" in this specification. In other words, the term "layer" in this specification includes not only structures that are continuously formed over the entire surface when observed in a plan view, but also structures that are discontinuously formed in a portion.

[0107] Figure 11 is a cross-sectional view of an adhesive sheet of another embodiment. The adhesive sheet 70 shown in Figure 11 includes an intermediate layer in addition to a first outermost layer 71 and a second outermost layer 72. The intermediate layers include a first intermediate layer 73 and a second intermediate layer 74. The first intermediate layer 73 is a layer adjacent to the first outermost layer 71, and is, for example, a second adhesive layer. The second intermediate layer 74 is a layer adjacent to the second outermost layer 72, and is, for example, the base material layer described above.

[0108] Figure 12 is a cross-sectional view of an adhesive sheet of another embodiment. In the adhesive sheet 80 shown in Figure 12, both outermost layers (a first outermost layer 81 and a second outermost layer 82) are made of a first adhesive layer, and both surfaces 80a, 80b have microstructures 5a, 5b. The details of the microstructures 5a, 5b (including the details of the convex structures 4a, 4b) are the same as those of the microstructure 5 of the adhesive sheet 10 described above. The microstructure 5a on one surface 80a may be the same as or different from the microstructure 5b on the other surface 80b.

[0109] The intermediate layer 83 of the adhesive sheet 80 includes a second adhesive layer. In addition to the second adhesive layer, the intermediate layer 83 preferably includes the above-mentioned base layer (for example, a layer made of an insulating base material). The adhesive sheet 80 may have a structure in which a first adhesive layer, a second adhesive layer, a base layer, a second adhesive layer, and a first adhesive layer are laminated in this order, for example. Such an adhesive sheet 80 can be suitably used for bonding the stator and coil of an EV motor. [Example]

[0110] The contents of the present disclosure will be explained in detail below using experimental examples, but the present disclosure is not limited to the following experimental examples.

[0111] <Material preparation> The following materials were prepared:

[0112] [Table 1]

[0113] 13(a) is an enlarged plan view of the mold 1, and FIG. 13(b) is a cross-sectional view taken along line b1-b1 in FIG. 13(a). As shown in FIGS. 13(a) and 13(b), protrusions 90 are formed in a lattice pattern on the surface of the mold 1, and a square pyramidal recess 91 is formed in the center of each square surrounded by the protrusions 90. The depth of the recess 91 (corresponding to h1 in FIG. 13(b)) is 10 μm, the opening width of the recess 91 (corresponding to w1 in FIG. 13(b)) is 38 μm, the bottom width of the protrusion 90 (corresponding to w2 in FIG. 13(b)) is 20 μm, the top width of the protrusion 90 (corresponding to w3 in FIG. 13(b)) is 3 μm, and the pitch between adjacent protrusions (corresponding to w4 in FIG. 13(b)) is 197 μm.

[0114] 14(a) is an enlarged plan view of the mold 2, and (b) is a cross-sectional view taken along line b2-b2 in (a). As shown in (a) and (b) of FIG. 14, square pyramidal recesses 92 are formed on the surface of the mold 2 and arranged in a lattice pattern. The depth of the recesses 92 (corresponding to h2 in (b) of FIG. 14) is 13 μm, and the opening width between adjacent recesses 92 (corresponding to w5 in (b) of FIG. 14) is 197 μm.

[0115] <Experimental Example 1> The materials shown in Table 2 were mixed with MEK (methyl ethyl ketone) in the proportions shown in Table 2 to obtain a mixed solution (solid content: 50% by mass). The resulting mixed solution was applied to a substrate film (PET film) and dried to form a coating film. Next, mold 1 was pressed against the coating film so that the surface of the coating film opposite the substrate film was in contact with the surface of mold 1 (the surface on which the microstructure was formed). The coating film was then cured by irradiating it with UV light to form a thermosetting adhesive layer (second adhesive layer, thickness: 120 μm).

[0116] Next, mold 1 was removed from the laminate of the base film, adhesive layer, and mold 1 obtained above, and then Scotchkote TM 206N was sprinkled on the surface of the adhesive layer (the surface to which mold 1 had been attached) and uniformly applied and deposited on the surface. TMA surface layer (first adhesive layer, thickness: 31 μm) consisting of a deposit of 206N was formed. Through the above operations, an adhesive sheet consisting of a pressure-sensitive adhesive layer (second adhesive layer) and a surface layer (first adhesive layer) was obtained. The surface of the surface layer side of the adhesive sheet was observed using a laser microscope, and it was confirmed that multiple convex structures had been formed on the surface. Furthermore, a glass substrate was placed on the surface layer of the adhesive sheet, and the contact state between the adhesive sheet and the glass substrate was observed using an optical microscope (magnification: 10x). The observed laser microscope image and optical microscope image are shown in Figure 15 (a) and (b), respectively.

[0117] [Table 2]

[0118] <Experimental Example 2> Scotchkote TM 206N was dissolved in MEK to obtain a solution of an adhesive composition (solid content: 30% by mass). The obtained solution was applied to the surface of mold 1 (the surface on which the microstructure was formed) using a hand coater and then dried. As a result, an adhesive layer (first adhesive layer, thickness: 30 μm) made of the adhesive composition was formed on mold 1.

[0119] Next, a mixed solution was obtained in the same manner as in Experimental Example 1, and the mixed solution obtained was applied to a substrate film (PET film) and dried to form a coating film. Thereafter, the coating film was cured by irradiating it with light under the same conditions as in Experimental Example 1 to form a thermosetting adhesive layer (second adhesive layer, thickness: 120 μm).

[0120] Next, the laminate of the adhesive layer and mold 1 obtained above was laminated onto the pressure-sensitive adhesive layer from the adhesive layer side, forming a surface layer consisting of the first adhesive layer on the pressure-sensitive adhesive layer. Through the above operations, an adhesive sheet consisting of a pressure-sensitive adhesive layer (second adhesive layer) and a surface layer (first adhesive layer) was obtained. After removing mold 1, the surface of the surface layer side of the adhesive sheet (the surface to which mold 1 was attached) was observed using a laser microscope, and it was confirmed that multiple convex structures had been formed on this surface. Furthermore, a glass substrate was placed on the surface layer of the adhesive sheet, and the contact state between the adhesive sheet and the glass substrate was observed using an optical microscope (magnification: 10x). The observed laser microscope image and optical microscope image are shown in Figure 16(a) and (b), respectively.

[0121] <Experimental Example 3> An adhesive sheet consisting of a pressure-sensitive adhesive layer (second adhesive layer) and a surface layer (first adhesive layer) was obtained in the same manner as in Experimental Example 2, except that mold 2 was used instead of mold 1. After removing mold 2, the surface of the surface layer side of the adhesive sheet (the surface to which mold 2 was attached) was observed using a laser microscope, and it was confirmed that multiple convex structures were formed on this surface. In addition, a glass substrate was placed on the surface layer of the adhesive sheet, and the contact state between the adhesive sheet and the glass substrate was observed using an optical microscope (magnification: 10x). The observed laser microscope image and optical microscope image are shown in Figure 17(a) and (b), respectively.

[0122] <Experimental Example 4> Except for changing the amount of coating so that the thickness was 150 μm, a thermosetting adhesive layer was formed on a base film (PET film) in the same manner as in Experimental Example 2. In Experimental Example 4, the adhesive layer thus obtained was used as an adhesive sheet.

[0123] <Experimental Example 5> A thermosetting adhesive layer was formed on a substrate film (PET film) in the same manner as in Experimental Example 2, except that the coating amount was changed so that the thickness was 110 μm. The obtained adhesive layer was then laminated on a PET nonwoven fabric, and a surface layer made of PET nonwoven fabric was formed on the adhesive layer. In Experimental Example 5, the laminate of the adhesive layer and surface layer thus obtained was used as an adhesive sheet.

[0124] <Experimental Example 6> A thermosetting adhesive layer was formed on a substrate film (PET film) in the same manner as in Experimental Example 2, except that the coating amount was changed so that the thickness was 121 μm. Next, a solution of the adhesive composition was obtained in the same manner as in Experimental Example 2, and the obtained solution was then applied to the surface of the adhesive layer using a hand coater and dried. This resulted in a surface layer (thickness: 30 μm) made of the adhesive composition on the adhesive layer. In Experimental Example 6, the laminate of the adhesive layer and surface layer obtained in this manner was used as an adhesive sheet.

[0125] <Evaluation> (Ease of insertion evaluation) The ease of insertion was evaluated based on the tackiness and dynamic friction coefficient of the surface of the adhesive sheet. The evaluation method is shown below, and the evaluation results are shown in Table 3. In this evaluation, the laminate of the adhesive sheet and the base film obtained in the experimental example was used.

[0126] [Tack Rating] An SPCC-SB (cold-rolled steel sheet) was prepared, and the surface (adhesion surface) of the SPCC-SB was cleaned with MEK. Then, a laminate was placed on the SPCC-SB so that the surface (adhesion surface) of the SPCC-SB was in contact with the surface of the adhesive sheet opposite the base film. The tackiness of the adhesive sheet surface was evaluated according to the following criteria. Evaluation 1: The test sample stuck to the SPCC-SB Rating 2: The test sample did not stick to the SPCC-SB and slid smoothly over the second adherend (however, the test sample did stick to the SPCC-SB when pressed). Evaluation 3: The test sample does not stick to the SPCC-SB even when pressed. The above evaluation was carried out at room temperature (25° C.), and the pressure applied was 1 MPa.

[0127] [Dynamic friction coefficient measurement] The dynamic friction coefficient of the adhesive sheet surface (the surface opposite the base film) in the laminate was measured in accordance with JIS K7125 "Testing method for coefficient of friction of plastics and films." The dynamic friction coefficient was calculated using the following formula: Formula:μ D= F D / F P [In the formula, μ D denotes the coefficient of kinetic friction, and F D indicates the kinetic friction force, and F P indicates the normal force (1.96N) from the load cell.]

[0128] (shear strength evaluation) The adhesive sheet of the experimental example was cut into a size of 12.5 mm x 25 mm to serve as a test sample. Two SPCC-SB (cold-rolled steel plates, size: 1.6 mm x 25 mm x 50 mm) were prepared as adherends. The surface of the SPCC-SB (adhesion surface) was pre-cleaned with MEK.

[0129] A test sample was sandwiched between two adherends (SPCC-SB) to obtain a laminate (first adherend / adhesive sheet / second adherend). The laminate was then sandwiched between a pair of hot plates and heated at 180°C for 15 minutes under a pressure of 100 kN to cure the adhesive sheet. Specifically, as shown in FIG. 18, the laminate (first adherend 93a / adhesive sheet 94 / second adherend 93b) was placed on a lower hot plate 99 via a jig 95 and a thermocouple 98. A spacer 96 (thickness: 0.35 mm) was used to fix the gap, and a cover plate 97 was then placed on the laminate. An upper hot plate (not shown) was then placed on the cover plate 97 to heat the laminate from above and below. During heating, the heating temperature was monitored using the thermocouple 98, and pressure was applied to the laminate by moving the lower hot plate 99 upward.

[0130] The heated laminate was used as a shear strength measurement sample, and the shear strength (overlap shear strength) of the measurement sample was measured using a Tensilon universal testing machine. Specifically, the Tensilon oven was first preheated to 150°C. The measurement sample was then placed in the jaws and preheated in the oven for 5 minutes. The shear strength was then measured when the first adherend and the second adherend were pulled in opposite directions at a crosshead speed of 50 mm / min. The measured values are shown in Table 3. In this experimental example, a shear strength of more than 5 MPa was considered to be sufficiently high.

[0131] [Table 3]

[0132] As shown in Table 3 above, it was confirmed that the adhesive sheets of Experimental Examples 1 to 3 had reduced surface tack, a sufficiently small coefficient of dynamic friction on the surface, and good ease of insertion, and had improved adhesiveness compared to Experimental Example 6. Comparing Experimental Example 1 with Experimental Examples 2 and 3, in Experimental Example 1, Scotchkote TM In contrast to the possibility of powder falling off of 206N, in Experimental Examples 2 and 3, the first adhesive layer constituting the surface layer is a molded product of the adhesive composition, and therefore is stably fixed to the second adhesive layer, which is the adhesive layer. From this perspective, it can be said that Experimental Examples 2 and 3 are easier to handle than Experimental Example 1. [Explanation of symbols]

[0133] 1,421...bottom surface, 2,422...top, 3,423...side, 4,424...convex structure, 5,5a,5b,425...microstructure, 6...base, 10,30,40,50,60,70...adhesive sheet, 10a,10b...surface, 11,31,41,51,61,71,81...first outermost layer (first adhesive layer), 12,32,42,52,62,72,82...second outermost layer, 15...adherend (magnet), 16...article, 20...mold, 21...concave structure, 22...microstructure, 73...first intermediate layer (second adhesive layer), 74...second intermediate layer (substrate layer).

Claims

1. a first adhesive layer made of an adhesive composition containing an epoxy resin having a softening point of 50°C or higher and a thermosetting agent; a second adhesive layer that has adhesiveness and expands and hardens when heated; At least one outermost layer is made of the first adhesive layer, An adhesive sheet having a plurality of convex structures on the surface of the outermost layer side consisting of the first adhesive layer.

2. The adhesive sheet according to claim 1 , wherein the outermost layer formed of the first adhesive layer is formed of a molded product of the adhesive composition.

3. The adhesive sheet according to claim 1 , wherein the outermost layer of the first adhesive layer is a deposit of the adhesive composition in powder form.

4. The adhesive sheet according to any one of claims 1 to 3, wherein the height of the convex structures is 2 to 200 µm.

5. The adhesive sheet according to any one of claims 1 to 4, further comprising a substrate layer as an intermediate layer.

6. The adhesive sheet according to any one of claims 1 to 5, wherein one outermost layer comprises the second adhesive layer.

7. Both outermost layers are made of the first adhesive layer, The adhesive sheet according to any one of claims 1 to 5, having a plurality of said convex structures on both surfaces.

8. The adhesive sheet according to any one of claims 1 to 7; and an adherend to which the adhesive sheet is attached.

9. A method for producing an adhesive sheet having a plurality of convex structures on a surface thereof, comprising: A step of applying a solution containing an epoxy resin having a softening point of 50°C or higher and a thermosetting agent to a surface of a mold having a plurality of recessed structures on the surface, and solidifying the solution to form a first adhesive layer; and providing a second adhesive layer on the side of the first adhesive layer opposite the mold, the second adhesive layer having adhesive properties and foaming and hardening when heated.

10. A method for producing an adhesive sheet having a plurality of convex structures on a surface thereof, comprising: forming a tacky adhesive layer that foams and hardens when heated on a surface of a mold having a plurality of concave structures on the surface of the mold, thereby forming a plurality of convex structures on the surface of the adhesive layer; and depositing a powdered adhesive composition on the surface of the adhesive layer, the powdered adhesive composition including an epoxy resin having a softening point of 50°C or higher and a thermosetting agent.

11. A method for manufacturing an article comprising a first element, a second element, and a filling portion that fills a space between the first element and the second element, the method comprising: placing the adhesive sheet according to any one of claims 1 to 7 between the first element and the second element; and heating the adhesive sheet to thermally expand and harden it to form the filling portion.

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