Adhesive sheet, cured foam and motor

Abstract

Provided is an adhesive sheet having an expandable adhesive layer having a foaming agent and having excellent thermal conductivity after foaming and curing. The adhesive sheet includes a substrate, a first adhesive layer disposed on one surface of the substrate, and a second adhesive layer disposed on the other side of the substrate. The first adhesive layer contains an adhesive (A), a thermally conductive filler (B) having an average short side length of 1 [mu] m or more, and a foaming agent (C). The thermally conductive filler (B) has an aspect ratio of 1.3 or more and includes a filler (B-1). The second adhesive layer contains an adhesive (A '), a thermally conductive filler (B') having an average short side length of 1 [mu] m or more, and a foaming agent (C '), and the thermally conductive filler (B') includes a filler (B '-1) having an aspect ratio of 1.3 or more.

Description

Technical Field

[0001] The present invention relates to an electric motor, which includes an adhesive sheet, a cured foam of the adhesive sheet, and a cured foam of the adhesive sheet. Background Art

[0002] Conventionally, adhesive sheets have been used to bond objects to be adhered, and adhesive sheets with various structures have been studied according to the application of the adhesive sheet, required properties, etc.

[0003] For example, WO 2016 / 163514 discloses an epoxy resin which contains a polyfunctional epoxy resin, a phenolic resin as a curing agent, an imidazole compound as a curing catalyst, and an adhesive sheet having an expanded adhesive layer formed by including a thermosensitive foaming agent as an adhesive sheet for fixing a stator core and a winding. Summary of the Invention

[0004] An expandable adhesive layer is useful because it can fill the gap between objects to be adhered, but it is difficult to obtain sufficient thermal conductivity after expansion because voids appear in the adhesive layer as it expands.

[0005] The present disclosure relates to an adhesive sheet having an expandable adhesive layer which has a foaming agent and has excellent thermal conductivity after foaming and curing. Further, the present disclosure relates to a foamed and cured product having an adhesive sheet and having high thermal conductivity. Further, the present disclosure relates to an electric motor which includes a cured foam and has a stator with good heat dissipation.

[0006] One aspect of the present disclosure relates to an adhesive sheet which includes a base, a first adhesive layer provided on one surface of the base, and a second adhesive layer provided on the other surface of the base. The first adhesive layer contains an adhesive (A), a heat conductive filler (B) having an average short side length of 1 μm or more, and a foaming agent (C), and the content of the heat conductive filler (B) is 1% by volume or more and 37% by volume or less based on the total volume of the first adhesive layer. The heat conductive filler (B) includes a filler (B-1) having an aspect ratio of 1.3 or more. The second adhesive layer contains an adhesive (A'), a heat conductive filler (B') having an average short side length of 1 μm or more, and a foaming agent (C'), and the content of the heat conductive filler (B') is 1% by volume or more and 37% by volume or less based on the total volume of the second adhesive layer, and the heat conductive filler (B') includes a filler (B'-1) having an aspect ratio of 1.3 or more.

[0007] Since the first adhesive layer and the second adhesive layer are expanded by arranging such an adhesive sheet between objects to be adhered and then heating them, the objects to be adhered can be bonded to each other when filled between the objects to be adhered. In addition, since the first adhesive layer and the second adhesive layer have expandability, the thickness of the adhesive sheet can be thinner than the gap between the objects to be adhered. Therefore, the adhesive sheet can be easily arranged between the objects to be adhered.

[0008] In addition, in the adhesive sheet, the first adhesive layer and the second adhesive layer contain a predetermined amount of thermally conductive filler, and the aspect ratio of at least a part of the thermally conductive filler is 1.3 or more. One of the reasons for achieving such an effect is that the aspect ratio of the filler is high. Therefore, even if the space between the bubbles generated during expansion is narrow, it is considered that a heat conduction path from one surface side to the other side of the adhesive layer is easily formed. In the adhesive sheet, due to the formation of such a heat conduction path, even when foaming and curing are performed at a high expansion ratio (for example, 1.4 times or more), a cured foam body having a high thermal conductivity can be obtained.

[0009] Another aspect of the present disclosure relates to an electric motor including a stator. The stator includes a stator core having at least one slot, a winding, and an adhesive layer for adhering the stator core and the winding, and at least a part of the winding is accommodated in the slot. The adhesive layer contains a cured foam body of the above-mentioned adhesive sheet.

[0010] The adhesive sheet of the present disclosure includes an expandable adhesive layer having a foaming agent and has excellent thermal conductivity after foaming and curing. In addition, the foaming and curing product of the present disclosure is the foaming and curing product of the adhesive sheet and has a high thermal conductivity. In addition, the electric motor of the present disclosure includes a cured foam body and includes a stator with good heat dissipation. Description of the Drawings

[0011] Figure 1 is a cross-sectional view showing one aspect of the adhesive sheet.

[0012] Figure 2 is a cross-sectional view showing another aspect of the adhesive sheet.

[0013] Figure 3 is a cross-sectional view showing one aspect of the foamed and cured body. Detailed Description

[0014] Hereinafter, with reference to the drawings, preferred embodiments of the present invention will be described. In the description of the drawings, the same elements are denoted by the same numerals, and repeated descriptions are omitted. In addition, for ease of understanding, a part of the drawings is enlarged, and the dimensional ratio is not limited to that described in the drawings.

[0015] The adhesive sheet of the present embodiment includes a base, a first adhesive layer provided on one surface of the base, and a second adhesive layer provided on the other surface of the base.

[0016] The first adhesive layer contains an adhesive (A), a heat conductive filler (B) having an average short side length of 1 μm or more, and a foaming agent (C). The second adhesive layer contains an adhesive (A'), a heat conductive filler (B') having an average short side length of 1 μm or more, and a foaming agent (C').

[0017] The content of the heat conductive filler (B) is 1% by volume or more and 37% by volume or less based on the total volume of the first adhesive layer, and the heat conductive filler (B) includes a filler (B-1) having an aspect ratio of 1.3 or more.

[0018] The content of the heat conductive filler (B') is 1% by volume or more and 37% by volume or less based on the total volume of the second adhesive layer, and the heat conductive filler (B') includes a filler (B'-1) having an aspect ratio of 1.3 or more.

[0019] In this specification, the aspect ratio represents the ratio of the average long side length to the average short side length. The average short side length is the average length of the short side of the smallest bounding rectangle (the smallest bounding rectangle) of the particle projection image observed by transmission electron microscopy. In addition, the average long side length represents the average length of the long side of the smallest circumscribed rectangle (the smallest bounding rectangle) of the particle projection image observed by transmission electron microscopy. The average lengths of the short side and the long side are obtained by obtaining at least three observation images of transmission electron microscopy for one type of filler and measuring the short sides and long sides of a total of 50 or more fillers (10 to 30 for each image).

[0020] Since the adhesive sheet of the present embodiment is expanded by placing the first adhesive layer and the second adhesive layer between the objects to be adhered and then heating them, the adhesive sheet can bond the objects to be adhered to each other when filled between the objects to be adhered. In addition, since the adhesive sheet of the present embodiment has the expanded first adhesive layer and the second adhesive layer, it can be thinner than the gap between the objects to be adhered and is easily arranged between the objects to be adhered.

[0021] In addition, in the adhesive sheet of the present embodiment, the first adhesive layer and the second adhesive layer contain a predetermined amount of a heat-conductive filler, and at least a part of the heat-conductive filler has an aspect ratio. Since it is a filler having an aspect ratio of 1.3 or more, a cured foam having a high thermal conductivity can be formed after foam curing. One of the reasons for achieving such an effect is that the filler has a high aspect ratio, and even when the space between the bubbles generated during expansion is narrow, it is easy to form a heat conduction path from one side to the other side of the adhesive layer. In the adhesive sheet of the present embodiment, due to the formation of such a heat conduction path, even when foam curing is performed at a high expansion ratio (for example, 1.4 times or more), a cured foam having a high thermal conductivity can be obtained.

[0022] The adhesive sheet of the present embodiment may further include a first adhesive-permeable layer disposed on the first adhesive layer. In addition, the adhesive sheet of the present embodiment may further include a second adhesive-permeable layer provided on the second adhesive layer. The first adhesive-permeable layer is a layer that can permeate the adhesive (A) when the first adhesive foams, and the second adhesive-permeable layer is a layer that can permeate the adhesive (A') when the second adhesive foams.

[0023] When the adhesive sheet of the present embodiment includes the first adhesive-permeable layer and the second adhesive-permeable layer, when the adhesive sheet is placed between the objects to be adhered and then heated, the first adhesive layer and the second adhesive layer start to thermally expand, and the adhesive (A) oozes out onto the outer surface of the first adhesive-permeable layer, and the adhesive (A') oozes out onto the outer surface of the second adhesive-permeable layer. Thus, the adhesive can reach the outside of the first adhesive-permeable layer and the second adhesive-permeable layer that were in the outermost layer before heating, and can bond the objects to be adhered to each other. Before heating the adhesive sheet, that is, when the adhesive sheet is positioned relative to the objects to be adhered, the first adhesive-permeable layer and the second adhesive-permeable layer are disposed on the outermost layer of the adhesive sheet.

[0024] In addition, the first adhesive-permeable layer and the second adhesive-permeable layer can also function as members that suppress the spreading of the adhesives (A) and (A') in the surface direction when the first adhesive layer and the second adhesive layer expand.

[0025] Hereinafter, each structure of the adhesive sheet of the present embodiment will be described in detail.

[0026] substrate

[0027] The base is a base portion for forming the first adhesive layer and the second adhesive layer, and it is a member that substantially defines the size of the adhesive surface of the adhesive sheet.

[0028] The base functions as a base for forming the first adhesive layer and the second adhesive layer during the manufacturing stage of the adhesive sheet. Therefore, the material constituting the base is strong enough to support the first adhesive layer and the second adhesive layer, and any material can be used as long as the adhesive strength is not reduced during the expansion of the first adhesive layer and the second adhesive layer (for example, when heated).

[0029] In addition, when the adhesive sheet of the present embodiment is used in applications that require electrical insulation, the adhesive sheet can be easily given electrical insulation properties by selecting an insulating base as the base.

[0030] The material constituting the base is not particularly limited, but from the viewpoints of excellent strength, heat resistance, and electrical insulation, and being particularly useful as a slot liner of a stator core of an electric motor, polyester resins (for example, polyethylene naphthalate (PEN), polyethylene terephthalate (PET)), polycarbonate resins, polyimide resins (for example, polyetherimide (PEI), polyamideimide, etc.), polyamide resins (for example, polyetheramide, polyaramide, nylon, etc.), acrylic resins, polysulfone resins (polysulfone, polyethersulfone, etc.), polyetherketone resins (polyetherketone, polyetheretherketone, etc.), modified polyphenylene ether, etc. are preferred. The base may contain only one of these substances, or may contain two or more.

[0031] The thickness of the base can be appropriately adjusted according to the interval between the objects to be adhered. When the gap between the objects to be adhered is large, it is easy to fill the gap by increasing the thickness of the base. The thickness of the base can be, for example, 2 μm or more, and from the viewpoint of possibly increasing the breakdown voltage, the thickness can be 3 μm or more, 5 μm or more, 7 μm or more, 9 μm or more, or 11 μm or more. In addition, from the viewpoint of the flexibility of the adhesive sheet, the thickness of the base can be, for example, 200 μm or less, 150 μm or less, 100 μm or less, or 90 μm or less.

[0032] first adhesive layer

[0033] The first adhesive layer is provided on one surface of the base, and contains an adhesive (A), a heat-conductive filler (B) having an average short-side length of 1 μm or more, and a foaming agent (C). Since the first adhesive layer contains the foaming agent (C), the first adhesive layer expands when the objects to be adhered to each other can fill the gap between the objects to be adhered.

[0034] As the adhesive (A), for example, a material that is substantially solid at room temperature, can flow by heating, and can be cured by further continuing heating can be used. That is, the adhesive (A) can be a thermosetting adhesive. Examples of such adhesives include epoxy resin adhesives.

[0035] The binder (A) may include a thermosetting resin. For example, when the binder (A) is an epoxy resin binder, the binder (A) may include a thermosetting epoxy resin.

[0036] Examples of the thermosetting epoxy resin include bisphenol type epoxy resins (e.g., bisphenol A type epoxy resin, bisphenol F type epoxy resin, etc.), aliphatic epoxy resins (e.g., hexanediol diglycidyl ether, etc.), glycidylamine epoxy resins (e.g., triglycidyl aminophenol, etc.), novolac epoxy resins (e.g., phenol novolac epoxy resin, cresol novolac epoxy resin, etc.), alicyclic epoxy resins (e.g., 3,4-epoxycyclohexylmethyl, 3,4-epoxycyclohexanecarboxylate), bis(3,4-epoxycyclohexylmethyl adipate), brominated epoxy resins (e.g., tetrabromobisphenol A diglycidyl ether, etc.), polyfunctional epoxy resins (e.g., tris(hydroxyphenyl)methane triglycidyl ether, sorbitol polyglycidyl ether, tetraglycidyl diaminodiphenylmethane, etc.), crystalline epoxy resins (e.g., tetramethyl bisphenol F diglycidyl ether, tetramethyl bisphenol diglycidyl ether, etc.). These may be used alone, or two or more of them may be used in combination.

[0037] The binder (A) may further include a curing agent. The curing agent may be any curing agent capable of curing the thermosetting resin, and may be appropriately selected from known curing agents. As the curing agent, latent curing agents are preferred from the viewpoint of avoiding curing before the blowing agent (C) is blown.

[0038] When the binder (A) is an epoxy resin binder, the curing agent includes, for example, dicyandiamide, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanuric acid adduct, etc.

[0039] The content of the curing agent may be appropriately adjusted according to the type of the thermosetting resin and the type of the curing agent. With respect to 100 parts by mass of the thermosetting resin, the content of the curing agent may be, for example, 1 part by mass or more, 2 parts by mass or more, 3 parts by mass or more, 4 parts by mass or more, or 5 parts by mass or more. With respect to 100 parts by mass of the thermosetting resin, the content of the curing agent may be, for example, 20 parts by mass or less, 18 parts by mass or less, 16 parts by mass or less, 14 parts by mass or less, 12 parts by mass or less, or 10 parts by mass or less.

[0040] The binder (A) may further include a curing accelerator. The curing accelerator only needs to be able to promote the curing with the thermosetting resin curing agent, and may be appropriately selected from known curing accelerators.

[0041] When the binder (A) is an epoxy resin binder, the curing accelerator includes, for example, an imidazole curing accelerator (e.g., 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine, etc.), a urea curing accelerator (e.g., 4,4'-methylenebis(phenyl dimethylurea), 3-(3,4-dichlorophenyl)-1,1-dimethylurea, etc.), and the like.

[0042] The content of the curing accelerator can be appropriately adjusted according to the type of the thermosetting resin and the type of the curing agent. The content of the curing accelerator can be, for example, 0.1 part by mass or more, 0.2 part by mass or more, 0.3 part by mass or more, 0.4 part by mass or more, or 0.5 part by mass or more. With respect to 100 parts by mass of the thermosetting resin, the content of the curing accelerator can be, for example, 10 parts by mass or less, 8 parts by mass or less, 6 parts by mass or less, 4 parts by mass or less, or 2 parts by mass or less.

[0043] The binder (A) may further include a thermoplastic resin.

[0044] The binder (A) may further include other components other than those described above. The other components include a silane coupling agent and the like.

[0045] The heat-conductive filler (B) is a filler having an average short-side length of 1 μm or more.

[0046] A filler having an average short-side length of less than 1 μm contributes less to the thermal conductivity and is difficult to function as a heat-conductive filler. The average short-side length of the heat-conductive filler (B) is 1 μm or more, and from the viewpoint of greater contribution to the thermal conductivity, it can be 1.5 μm or more or 2 μm or more. The average short-side length of the heat-conductive filler (B) can be, for example, 100 μm or less, 90 μm or less, 80 μm or less, or 70 μm or less.

[0047] The content of the heat-conductive filler (B) is 1% by volume or more based on the total volume of the first binder layer, and from the viewpoint of further increasing the thermal conductivity of the foam-cured product, the content can be 3% by volume or more, 5% by volume or more, or 10% by volume or more. The content of the heat-conductive filler (B) is 37% by volume or less based on the total volume of the first binder layer, and from the viewpoint of further increasing the adhesion strength to the adherend, the content can be 35% by volume or less or 33% by volume or less.

[0048] In addition, when the adhesive sheet has a first adhesive-permeable layer, the adhesive (A) easily penetrates the first adhesive-permeable layer, and from the viewpoint of high adhesive strength with an easily obtainable object, the content of the heat-conductive filler (B) is 30% by volume or less, 27% by mass or less, 25% by mass or less, 23% by mass or less, 21% by mass or less, 19% by mass or less. The content may be 17% by mass or less or 15% by mass or less.

[0049] The material of the heat-conductive filler (B) is not particularly limited and may be appropriately selected from known heat-conductive fillers. The heat-conductive filler (B) may include, for example, at least one selected from the group consisting of, for example, boron nitride, aluminum nitride, alumina, magnesia, anhydrous magnesium carbonate, magnesium hydroxide, silica, and silicon nitride.

[0050] The heat-conductive filler (B) may include a filler (B-1) having an aspect ratio of 1.3 or more. Since such a filler (B-1) has a high aspect ratio, even when the space between bubbles generated during expansion is narrow, it is easy to form a heat conduction path from one side to the other side of the adhesive layer. Therefore, according to the filler (B-1), even when foaming and curing are performed at a high expansion ratio (for example, 1.4 times or more), a foamed and cured product having high thermal conductivity can be obtained.

[0051] The shape of the filler (B-1) is not particularly limited as long as it satisfies the aspect ratio, but it may be, for example, flaky, whisker-like, agglomerated, or the like.

[0052] From the viewpoint of more significantly exhibiting the above effects, the aspect ratio of the filler (B-1) may be, for example, 1.4 or more, 1.5 or more, or 1.6 or more.

[0053] The aspect ratio of the filler (B-1) may be, for example, 200 or less, 150 or less, or 100 or less.

[0054] When the filler (B-1) is flaky or agglomerated, the aspect ratio of the filler (B-1) may be, for example, 50 or less, 30 or less, 10 or less, 5 or less, or 3 or less. When the filler (B-1) is whisker-like, the aspect ratio of the filler (B-1) may be, for example, greater than 50, 60 or more, 70 or more, 80 or more, or 90 or more.

[0055] The average short-side length of the filler (B-1) may be the same as the average short-side length of the heat-conductive filler (B).

[0056] In the present embodiment, a heat conduction path is effectively formed between bubbles by the filler (B-1) having a high aspect ratio. The heat-conductive filler (B) may be at least a part of the filler (B-1) and may be entirely the filler (B-1).

[0057] From the viewpoint of forming more heat conduction paths, the content of the filler (B-1) may be, for example, 0.01% by volume or more, 0.05% by volume or more, 0.1% by volume or more, or 0.15% by volume or more based on the total volume of the first adhesive layer.

[0058] The heat conductive filler (B) may further include a filler (B-2) having an aspect ratio of less than 1.3. That is, the heat conductive filler (B) may include a filler (B-1) having an aspect ratio of 1.3 or more and a filler (B-2) having an aspect ratio of less than 1.3.

[0059] The ratio of the filler (B-1) to the heat conductive filler (B) may be, for example, 0.1% by volume or more based on the total volume of the heat conductive filler (B), and from the viewpoint of more efficiently forming heat conduction paths, the ratio may be 0.3% by volume or more, 0.5% by volume or more, 0.7% by volume or more, or 1% by volume or more.

[0060] When the aspect ratio of the filler (B-1) exceeds 50 (for example, when the filler (B-1) is whisker-shaped), the ratio of the filler (B-1) to the heat conductive filler (B) is, for example, 100% by volume or less, 50% by volume or less, 30% by volume or less based on the total volume of the heat conductive filler (B). The ratio may be 10% by volume or less, 5% by volume or less, or 3% by volume or less.

[0061] When the aspect ratio of the filler (B-1) is 50 or less (for example, when the filler (B-1) is flake-shaped or an aggregate), the ratio of the filler (B-1) to the heat conductive filler (B) is 10% by volume or more, 30% by volume or more, 50% by volume or more. The ratio may be 70% by volume or more, 90% by volume or more, or may be 100% by volume.

[0062] The foaming agent (C) may be any foaming agent that foams when adhered to the object to be adhered and can expand the adhesive layer. The foaming agent (C) is preferably a temperature-sensitive foaming agent.

[0063] Examples of the foaming agent (C) include inorganic foaming agents such as ammonium carbonate, ammonium bicarbonate, ammonium nitrite, ammonium borohydride, and azides; alkane fluorides such as trichlorofluoromethane; azo compounds such as azobisisobutyronitrile; hydrazine compounds such as p-toluenesulfonylhydrazide; semicarbazide compounds such as p-toluenesulfonyl semicarbazide; triazole compounds such as 5-morpholino-1,2,3,4-thiatriazole; N,N-organic foaming agents such as N-nitroso compounds such as dinitrosoterephthalamide; thermally expandable microcapsules obtained by microencapsulating a thermal fermenting agent (e.g., hydrocarbon compound), etc. Among them, from the viewpoint of not easily inhibiting the curing of the adhesive (A), the thermally expandable particles (C-1) are preferred.

[0064] The thermally expandable particles (C-1) may include, for example, a thermoplastic shell and a blowing agent (e.g., a liquid hydrocarbon) encapsulated in the shell. Examples of the thermally expandable particles (C-1) include Matsumoto Microsphere (registered trademark) of each series (manufactured by Matsumoto Yushi-Seiyaku Co., Ltd) and the like.

[0065] The foaming start temperature (Tc) of the foaming agent (C) may be, for example, 90°C or higher, and from the viewpoint of tending to start foaming after the adhesive (A) becomes sufficiently soft, it may be 95°C or higher or 100°C or higher. Further, the foaming start temperature (Tc) of the foaming agent (C) may be, for example, 140°C or lower, and from the viewpoint of easily obtaining a sufficient expansion ratio before curing the adhesive (A), it may be 135°C or lower or 130°C or lower.

[0066] The content of the foaming agent (C) may be a content that can achieve the expansion ratio described later. With respect to 100 parts by mass of the thermosetting resin, the content of the foaming agent (C) may be, for example, 0.5 part by mass or more, 1 part by mass or more, 3 parts by mass or more, or 5 parts by mass or more. The content of the foaming agent (C) may be, for example, 30 parts by mass or less, 25 parts by mass or less, or 20 parts by mass or less.

[0067] The first adhesive layer is foamed and cured by heating. The foaming ratio of the first adhesive layer is not particularly limited and may be appropriately determined according to the thermal conductivity and adhesive strength required for the foamed and cured product, the distance between the objects to be adhered, and the like. The foaming ratio of the first adhesive layer may be, for example, 1.5 times or more, 2 times or more, 2.5 times or more, or 3 times or more. Further, the foaming ratio of the first adhesive layer may be, for example, 10 times or less, 9 times or less, 8 times or less, or 7 times or less. The larger the foaming ratio, the more voids are generated by foaming, and the lower the thermal conductivity after foaming and curing. In the present specification, the foaming ratio of the first adhesive layer is a value obtained as the ratio of the thickness of the first adhesive layer before and after foaming and curing.

[0068] The foaming ratio of the first adhesive layer can be appropriately adjusted, for example, by the content of the foaming agent (C) and the like.

[0069] The first adhesive layer may further contain other components in addition to the adhesive (A), the heat conductive filler (B), and the foaming agent (C). Other components include, for example, a thickener, an impact resistance improver, and the like.

[0070] Examples of the thickener include pyrogenic silica and the like.

[0071] The content of the thickener is not particularly limited. The first adhesive layer can be formed by applying a coating solution containing an adhesive (A), a heat-conductive filler (B), a foaming agent (C), and a solvent and drying the same. The thickener can be blended so that the viscosity of the coating solution becomes a viscosity suitable for application, and the content of the thickener is the viscosity of the coating solution. The content of the thickener can be, for example, 5% by mass or less, 3% by mass or less, 2.5% by mass or less, or the content can be 2% by mass or less based on the total amount of the components of the first adhesive layer other than the heat-conductive filler (B). Further, the content of the thickener can be, for example, 0.1% by mass or more, 0.3% by mass or more, 0.5% by mass or more based on the total amount of the components of the first adhesive layer other than the heat-conductive filler (B). The content can be 0.7% by mass or more or 1% by mass or more.

[0072] Examples of the impact modifier include core-shell type impact modifiers. Examples of the core-shell type impact modifiers include core-shell rubbers.

[0073] The core-shell rubber contains different materials for the core part and the shell part, respectively. The glass transition temperature (Tg) of the shell part is preferably higher than the Tg of the core part. The Tg of the core part can be, for example, from -110°C to -30°C, and the Tg of the shell part can be, for example, from 0°C to 200°C. In the present specification, the Tg of the core part and the shell part is defined as the temperature of the peak of tanδ in the dynamic viscoelasticity measurement. The impact resistance is improved by the core part of the core-shell rubber serving as a stress concentration point, and the shell part suppresses the undesired aggregation between the core-shell rubbers so that the core-shell rubbers are uniformly distributed.

[0074] The core-shell rubber is, for example, a polymer of a conjugated diene such as butadiene, isoprene, 1,3-pentadiene, cyclopentadiene, dicyclopentadiene; a polymer of a non-conjugated diene such as 1,4-hexadiene, ethylidene norbornene; a copolymer of a conjugated diene or non-conjugated diene and a monofunctional monomer (e.g., an aromatic vinyl compound such as styrene, vinyltoluene, and α-methylstyrene, an unsaturated nitrile compound such as acrylonitrile and methacrylonitrile, a (meth)acrylate such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, etc.); an acrylic rubber such as polybutyl acrylate; a silicone rubber; an IPN-type composite rubber composed of silicone and an alkyl polyacrylate; a core-shell graft copolymer can be provided, which contains a core part such as a rubber component and a shell part formed by copolymerizing a (meth)acrylate around the core part. As the core part, polybutadiene, a butadiene-styrene copolymer, and an acrylic / butadiene rubber-styrene copolymer can be advantageously used, and as the shell part, a shell part formed by copolymerizing methyl (meth)acrylate can be advantageously used. The shell part can be layered and can be composed of one layer or multiple layers. As the core-shell rubber, two or more types of core-shell rubbers can be used in combination.

[0075] Examples of the core-shell rubber include a methyl methacrylate-butadiene copolymer, a methyl methacrylate-butadiene-styrene copolymer, a methyl methacrylate-acrylonitrile-butadiene-styrene copolymer, a methyl methacrylate-acrylic rubber copolymer, a methyl methacrylate-acrylic rubber-styrene copolymer, a methyl methacrylate-acrylic / butadiene rubber copolymer, a methyl methacrylate-acrylic / butadiene rubber-styrene copolymer, a methyl methacrylate-(acrylic / silicone IPN rubber) copolymer, etc. Among them, a methyl methacrylate-butadiene copolymer, a methyl methacrylate-butadiene-styrene copolymer, and a methyl methacrylate-acrylic-butadiene rubber-styrene copolymer can be advantageously used as the core-shell rubber.

[0076] The average value (mass average particle size) of the original particle size of the core-shell rubber can be, for example, 0.05 μm or larger, or can be 0.1 μm or larger. In addition, the average value (mass average particle size) of the original particle size of the core-shell rubber can be, for example, 5 μm or smaller, and can be 3 μm or smaller or 1 μm or smaller. The average value of the original particle size of the core-shell rubber is calculated from the value obtained by ζ potential particle size distribution measurement.

[0077] The content of the impact modifier is not particularly limited, and may be, for example, 20% by mass or less, 15% by mass or less, or 10% based on the total amount of the components other than the heat conductive filler (B) in the first adhesive layer. In addition, the content of the impact modifier may be, for example, 1% by mass or more based on the total amount of the components other than the heat conductive filler (B) in the first adhesive layer, and may be 2% by mass or more, or 3 parts by mass or more.

[0078] The first adhesive layer can be formed by applying a first coating solution containing each of the above components and a solvent on a substrate and drying it.

[0079] The solvent is not particularly limited, and the adhesive (A) can be dissolved, and a solvent that can be removed without curing the adhesive (A) can be used. Examples of such solvents include methyl ethyl ketone, acetone, toluene, and the like.

[0080] The thickness of the first adhesive layer is not particularly limited, and may be, for example, 5 μm or more, 10 μm or more, or 15 μm or more. In addition, the thickness of the first adhesive layer is not particularly limited. For example, it may be 200 μm or less, and from the viewpoint of good processability, the thickness may be 100 μm or less, 80 μm or less, or 60 μm or less.

[0081] second adhesive layer

[0082] The second adhesive layer is provided on the opposite surface of the substrate and contains an adhesive (A'), a heat conductive filler (B') having an average short side length of 1 μm or more, and a foaming agent (C'). Since the second adhesive layer contains the foaming agent (C'), when the objects to be adhered to each other can fill the gap between the objects to be adhered, the second adhesive layer expands.

[0083] Each structure of the second adhesive layer can be similar to each structure of the first adhesive layer.

[0084] For example, the adhesive (A') can be exemplified as the same as the adhesive (A).

[0085] Examples of the heat conductive filler (B') are the same as those of the heat conductive filler (B). The heat conductive filler (B') may include a filler (B'-1) having an aspect ratio of 1.3 or more, and may include a filler (B'-2) having an aspect ratio of less than 1.3. Examples of the filler (B'-1) and the filler (B'-2) are the same as those of the filler (B-1) and the filler (B-2).

[0086] Examples of the foaming agent (C) are the same as those of the foaming agent (C'). The foaming agent (C') may include thermally expandable particles (C'-1). Examples of the thermally expandable particles (C'-1) are the same as those of the thermally expandable particles (C-1).

[0087] The content of each component in the second adhesive layer may be the same as the content of each component in the first adhesive layer.

[0088] first adhesive permeable layer

[0089] When the first adhesive layer expands (foams), the first adhesive permeable layer allows the adhesive (A) to pass from one major surface side of the first adhesive permeable layer to the other major surface side.

[0090] The first adhesive permeable layer may have a plurality of holes penetrating from one major surface to the other major surface. In this case, when the first adhesive layer in contact with only one major surface of the first adhesive permeable layer expands (foams), the adhesive (A) can reach the other major surface of the first adhesive permeable layer through the holes.

[0091] The material constituting the first adhesive permeable layer is not particularly limited and may be a material that can maintain the shape for permeating the adhesive (A) at the curing start temperature of the adhesive (A).

[0092] The first adhesive permeable layer may be, for example, a nonwoven fabric composed of natural fibers, chemical fibers, or a mixture thereof. Since the nonwoven fabric has a large number of through holes inside, the above effects can be significantly obtained.

[0093] The weight of the first adhesive permeable layer may be, for example, 10 g / m 2 or more, and may be 11 g / m 2 or more. The upper limit of the weight limit of the first adhesive permeable layer is not particularly limited and may be within the range that satisfies, for example, the thickness range of the first adhesive permeable layer described later.

[0094] The thickness of the first adhesive permeable layer may be, for example, 55 μm or less, and from the viewpoint of obtaining the amount of the adhesive (A) exuding on the surface when the first adhesive layer expands and a higher adhesive strength, the thickness may be 50 μm or less or 47 μm or less. The lower limit of the thickness of the first adhesive permeable layer is not particularly limited and may be within the range that satisfies, for example, the weight range of the first adhesive permeable layer described above.

[0095] second adhesive permeable layer

[0096] When the second adhesive layer expands (foams), the second adhesive permeable layer allows the adhesive (A') to pass through from one major surface side of the second adhesive permeable layer to the other major surface side.

[0097] Each configuration of the second adhesive permeable layer can be the same as each configuration of the first adhesive permeable layer.

[0098] Figure 1 is a cross-sectional view showing one aspect of the adhesive sheet. Figure 1 The illustrated adhesive sheet 1 includes a substrate 3, a first adhesive layer 5 provided on one surface of the substrate 3, and a second adhesive layer 5' provided on the other side of the substrate 3.

[0099] Figure 1 The illustrated adhesive sheet 1 has adhesive strength on both surfaces of the adhesive sheet 1 because the first adhesive layer 5 and the second adhesive layer 5' are in the outermost layers. By disposing the adhesive sheet 1 between objects to be adhered and heating them to cause the first adhesive layer 5 and the second adhesive layer 5' to expand, the objects to be adhered to each other can be bonded when filling the gap between the objects to be adhered.

[0100] Figure 2 is a cross-sectional view showing another aspect of the adhesive sheet. Figure 2 The illustrated adhesive sheet 11 includes a substrate 13, a first adhesive layer 15 provided on one surface of the substrate 13, a second adhesive layer 15' provided on the other side of the substrate 13, a first adhesive permeable layer 17 provided on the surface of the first adhesive layer 15 opposite to the substrate 13, and a second adhesive permeable layer 17' provided on the surface of the second adhesive layer 15' opposite to the substrate 13.

[0101] Figure 2 The illustrated adhesive sheet 11 can be said to be non-tacky because the first adhesive permeable layer 17 and the second adhesive permeable layer 17' are in the outermost layers. By placing the adhesive sheet 11 between objects to be adhered and heating to cause the first adhesive layer 15 and the second adhesive layer 15' to expand, the adhesive oozes out outside the first adhesive permeable layer 17 and the second adhesive permeable layer 17'. As a result, the adhesive exists between the first adhesive permeable layer 17 and the object to be adhered and between the second adhesive permeable layer 17' and the object to be adhered, and exhibits adhesive force. Then, by curing the adhesive, the objects to be adhered to each other can be bonded.

[0102] By heating the adhesive sheet of the present embodiment, a cured foam of the adhesive sheet can be obtained.

[0103] The cured foam of the present embodiment includes a substrate, a first foam layer formed by foaming and curing a first adhesive layer, and a second foam layer formed by foaming and curing a second adhesive layer.

[0104] In the cured foam of the present embodiment, a first adhesive permeable layer may be embedded in the first foam layer. Further, the cured foam of this embodiment may have a second adhesive permeable layer embedded in the second foam layer.

[0105] The expansion ratio of the adhesive sheet of the present embodiment is not particularly limited and can be appropriately determined according to the thermal conductivity and adhesive strength required for the foamed and cured product, the spacing between the adhesives, and the like. The expansion ratio of the adhesive sheet may be, for example, 1.3 times or more, 1.35 times or more, or 1.4 times or more. Further, the expansion ratio of the adhesive sheet may be, for example, 6.5 times or less, 5.8 times or less, 5.3 times or less, or 4.6 times or less. In the present specification, the expansion ratio of the adhesive sheet is a value obtained as the ratio between the thickness of the adhesive sheet and the thickness of the cured foam in which the adhesive sheet is foamed and cured.

[0106] Figure 3 is a cross-sectional view showing one aspect of the cured foam. Figure 3 The cured foam 21 shown includes a substrate 23, a first foam layer 25, and a second foam layer 25'. A first adhesive permeable layer 27 is encapsulated in the first foam layer 25, and a second adhesive permeable layer 27' is encapsulated in the second foam layer 25'.

[0107] In Figure 3 it, the outer surfaces of the first foam layer 25 and the second foam layer 25' are described as being smooth, but the first foam layer 25 and the second foam layer 25' may have shapes corresponding to the shapes of the objects to be adhered with which they are in contact.

[0108] The use of the adhesive sheet of the present embodiment is not particularly limited and can be used in various applications for adhering objects to each other. Since the adhesive sheet of the present embodiment has excellent thermal conductivity after foaming and curing, it can be suitably used in applications that require properties such as thermal conductivity and heat dissipation.

[0109] Further, since the adhesive sheet of the present embodiment is expandable, it can conform to the surface shape of the objects to be adhered and can fill the space between the objects to be adhered. Further, even if unintentional unevenness appears on the surfaces of the objects to be adhered, the objects to be adhered can be suitably bonded to each other. Therefore, when the surfaces of the objects to be adhered are uneven or when it is necessary to fill the gap between the objects to be adhered, the adhesive sheet of the present embodiment can be suitably used.

[0110] The adhesive sheet of the present embodiment can be suitably used, for example, as a slot liner of a stator core in an electric motor. That is, the adhesive sheet of the present embodiment can be used to bond a stator core and a winding, for example, by arranging it between the stator core and the winding.

[0111] The electric motor of the present embodiment may include a stator including a stator core having at least one slot, a winding at least partially received in the slot, and an adhesive layer for bonding the stator core and the winding.

[0112] The adhesive layer may be a layer formed by foaming and curing the adhesive sheet. That is, the adhesive layer may be a layer including a cured foam of the adhesive sheet.

[0113] In the electric motor of the present embodiment, each structure other than the adhesive layer is not particularly limited and may be the same as each structure in a known electric motor.

[0114] As described above, although the preferred embodiments of the present invention have been described, the present invention is not limited to the above embodiments.

[0115] The present invention may relate to, for example, the following forms.

[0116] [1] An adhesive sheet, the adhesive sheet comprising;

[0117] A base;

[0118] A first adhesive layer provided on one surface of the base, and

[0119] A second adhesive layer provided on the other surface of the base, wherein

[0120] The first adhesive layer contains an adhesive (A), a heat-conductive filler (B) having an average short-side length of 1 μm or more, and a foaming agent (C),

[0121] The content of the heat-conductive filler (B) is 1% by volume or more and 37% by volume or less based on the total volume of the first adhesive layer,

[0122] The heat-conductive filler (B) includes a filler (B-1) having an aspect ratio of 1.3 or more,

[0123] The second adhesive layer contains an adhesive (A'), a heat-conductive filler (B') having an average short-side length of 1 μm or more, and a foaming agent (C'),

[0124] The content of the heat-conductive filler (B') is 1% by volume or more and 37% by volume or less based on the total volume of the second adhesive layer, and

[0125] The heat-conductive filler (B') includes a filler (B'-1) having an aspect ratio of 1.3 or greater.

[0126] [2] The adhesive sheet according to [1], wherein

[0127] The content of the filler (B-1) is 0.1% by volume or greater based on the total volume of the first adhesive layer,

[0128] The content of the filler (B'-1) is 0.1% by volume or greater based on the total volume of the second adhesive layer.

[0129] [3] The adhesive sheet according to [1] or [2], further comprising;

[0130] A first adhesive-permeable layer, the first adhesive-permeable layer being provided on the first adhesive layer and capable of permeating the adhesive (A) when the first adhesive layer foams, and

[0131] A second adhesive-permeable layer, the second adhesive-permeable layer being provided on the second adhesive layer and capable of permeating the adhesive (A') when the second adhesive layer foams. [4] The adhesive sheet according to [3], wherein

[0132] The content of the heat-conductive filler (B) is 1% by volume or greater and 30% by volume or less based on the total volume of the first adhesive layer, and

[0133] The content of the heat-conductive filler (B') is 1% by volume or greater and 30% by volume or less based on the total volume of the second adhesive layer.

[0134] [5] The adhesive sheet according to any one of [1] to [4], wherein

[0135] The heat-conductive filler (B) contains at least one selected from the group consisting of boron nitride, aluminum nitride, and aluminum oxide, and

[0136] The heat-conductive filler (B') contains at least one selected from the group consisting of boron nitride, aluminum nitride, and aluminum oxide.

[0137] [6] The adhesive sheet according to any one of [1] to [5], wherein

[0138] The filler (B-1) is flaky, whisker-shaped, or agglomerated, and

[0139] The filler (B'-1) is flaky, whisker-shaped, or agglomerated.

[0140] [7] The adhesive sheet according to any one of [1] to [6], wherein

[0141] The foaming agent (C) includes thermally expandable particles (C-1), and

[0142] the foaming agent (C’) includes thermally expandable particles (C’-1).

[0143] [8] The adhesive sheet according to any one of [1] to [7], wherein the adhesive sheet is a slot liner of a stator core of an electric motor.

[0144] [9] A cured foam of the adhesive sheet according to any one of [1] to [8].

[0145]

[10] An electric motor, the electric motor including a stator, wherein

[0146] the stator includes;

[0147] a stator core having at least one slot;

[0148] a winding at least partially received in the slot, and

[0149] an adhesive layer for bonding the stator core and the winding, wherein

[0150] the adhesive layer contains a cured foam of the adhesive sheet according to any one of [1] to [8].

[0151] Example

[0152] Hereinafter, the present invention will be described in more detail with reference to embodiments, but the present invention is not limited to these embodiments.

[0153] Preparation of Adhesive Composition (1)

[0154] Prepare the materials shown in Table 1.

[0155] [Table 1]

[0156]

[0157]

[0158] Mix BTA731 (core-shell impact modifier) and NPPN442 (trifunctional epoxy resin), then add the other materials shown in Table 1 and mix with a mixer to obtain an adhesive composition (1). The amount of each material is shown in Table 2. The blending amount of YP-50EK35 (MEK solution of phenoxy resin, solid content concentration 35 mass%) represents the amount containing the solvent (MEK).

[0159] [Table 2]

[0160]

[0161] Preparation of Thermal Conductive Filler

[0162] Prepare the thermal conductive fillers shown in Table 3.

[0163] [Table 3]

[0164]

[0165] Obtain the average short side length, average long side length, and aspect ratio of each thermal conductive filler by the following method. The results are shown in Table 4.

[0166] Measurement of Filler Size

[0167] Sprinkle the fillers on the conductive double-sided adhesive tape attached to the sample stage, and remove the excess fillers with a blower. Next, coat the fillers with osmium using an osmium plasma coater (OPC80N, Japan Laser Electronics Co., Ltd.), and conduct electricity treatment on the samples.

[0168] Use a scanning electron microscope (S3400N, Hitachi High-Tech) to obtain secondary electron images of the fillers at an acceleration voltage of 10 kV, a working distance of 10 mm, and an observation magnification range of 100 to 3000 times. From the obtained images, confirm the smallest rectangle (minimum circumscribed rectangle) that can cover the fillers visually and by image analysis, and determine the long side and short side of the rectangle as the long side or short side of the fillers.

[0169] For each type of filler, obtain at least three images, measure the long sides and short sides of 10 to 30 fillers, a total of 50 or more fillers, and the average values are the average long side length and average short side length of the fillers.

[0170] [Table 4]

[0171]

[0172]

[0173] Preparation of Substrate

[0174] As the substrate, prepare a 75-μm-thick PEN film (trade name: Theonex Q51, manufactured by Teijin Film Solution Co., Ltd.).

[0175] Example 1-1

[0176] 100 parts by mass of the adhesive composition (1) prepared by the above method and 24.9 parts by mass of the heat-conductive filler (1) (content in the adhesive layer: 13.9% by volume) were mixed to obtain a coating solution for forming an adhesive layer. The coating solution was applied to one side of a substrate and dried at 65°C for 3 minutes and then dried at 90°C for 3 minutes to form a first adhesive layer. The thickness of the first adhesive layer was 35.5 μm. The thickness of the first adhesive layer was obtained by measuring the thickness of any three points in the A4-sized area of the sample after forming the first adhesive layer using a bench micrometer, and subtracting the average thickness from the thickness of the substrate.

[0177] Next, a nonwoven fabric sheet (PET, basis weight 23 g / m2) was laminated, heated, and pressed at a roll temperature of 60°C using a roll laminator to obtain a laminated structure composed of a substrate, a first adhesive layer, and a first adhesive-permeable layer.

[0178] Next, the coating solution was applied to the other side of the substrate and dried at 65°C for 3 minutes and then dried at 90°C for 3 minutes to form a second adhesive layer. The thickness of the second adhesive layer was 35.2 μm. The thickness of the second adhesive layer was measured for the A4-sized area of the sample before and after forming the second adhesive layer using a bench micrometer, and the average value of the measured values after forming the second adhesive layer was subtracted from the average value of the measured values before forming the second adhesive layer.

[0179] Then, a nonwoven fabric sheet (PET, basis weight 23 g / m 2 ) was laminated on the second adhesive layer, and a roll laminator was used to heat and press at a roll temperature of 60°C to obtain an adhesive sheet having a thickness (T1) of 190 μm.

[0180] On the obtained adhesive sheet, the measurement of test objects, expansion ratio, thermal conductivity measurement, and shear strength were measured by the following methods. The results are shown in Table 5.

[0181] Preparation of Test Specimens

[0182] (1) Preparation of Specimens for Measuring Thermal Conductivity

[0183] Cut the adhesive sheet into 50 mm × 50 mm. Prepare two fluororesin sheets (Alam Co., Ltd., thickness 0.2 mm). Place the adhesive sheet and a spacer with a thickness of 400 μm around the entire outer periphery of the adhesive sheet on one fluororesin sheet, and place the other fluororesin sheet on the adhesive sheet. Place it on the spacer and hot press at 160 °C for 10 minutes to obtain a foamed and cured product with a thickness (T2) of 360 μm. Use this cured foam as a test body for measuring thermal conductivity. When measuring the thermal conductivity described later, use the thickness measurement function of the thermal conductivity measuring instrument to measure the thickness (T2) of the cured foam.

[0184] (2) Preparation of Specimens for Shear Test

[0185] Cut the adhesive sheet into 12.5 mm × 25 mm. Prepare two SPCC plates (100 mm × 25 mm × 1.6 mm (conforming to JIS G 3141)) with surfaces cleaned with methyl ethyl ketone, and sequentially place the adhesive sheet and a spacer with a thickness of 400 μm on one SPCC plate from the end side. Place the other SPCC plate on the adhesive sheet and the spacer and hot press at 160 °C for 10 minutes to obtain a shear specimen (conforming to JIS K6850) containing a foamed and cured product with a thickness (T3) of 380 μm. Obtain the thickness (T3) of the cured foam product by measuring the thickness of the entire specimen for the shear test and subtracting the thickness equivalent to two SPCC plates (3200 μm) from the measured value.

[0186] Measurement of Expansion Ratio

[0187] (1) Measurement of Expansion Ratio of Cured Foam in Specimens for Measuring Thermal Conductivity

[0188] Obtain the expansion ratio by T2 / T1 using the thickness (T1) of the adhesive sheet and the thickness (T2) of the cured foam.

[0189] (2) Measurement of Expansion Ratio of Cured Foam in Specimens for Shear Test

[0190] Determine the expansion ratio by T3 / T1 using the thickness (T1) of the adhesive sheet and the thickness (T3) of the cured foam in the shear specimen.

[0191] Measurement of Thermal Conductivity

[0192] Use a thermal conductivity measuring device (Analysis Tech Inc., Thermal Interface Material Tester TIM Tester Model 1300) to measure the thermal conductivity of the specimen for measuring thermal conductivity according to ASTM D5470.

[0193] Shear Strength Measurement

[0194] Use a material testing machine equipped with a constant temperature testing device (RTC-1325A manufactured by ORIENTEC). Allow the measurement sample (shear specimen) to stand in the material testing machine heated to 200 °C for 10 minutes and heat it sufficiently. Then, measure the shear strength at a shear tensile rate of 5 mm / min at 200 °C.

[0195] Example 1-2

[0196] Change the thermal conductive filler (1) to 24.9 parts by mass of thermal conductive filler (2) (content in the adhesive layer is 13.9% by volume), and the thickness of the first adhesive layer is 49 μm.

[0197] Regarding the obtained adhesive sheet, perform measurement of specimens, measurement of expansion ratio, measurement of thermal conductivity, and measurement of shear strength in the same manner as in Example 1-1. The results are shown in Table 5.

[0198] Example 1-3

[0199] Change the thermal conductive filler (1) to 2.0 parts by mass of thermal conductive filler (4) and 34.2 parts by mass of thermal conductive filler (5) (total content of (4) and (5) in the adhesive layer is 13.9% by volume), the thickness of the first adhesive layer is 45 μm, and the thickness of the second adhesive layer. Prepare an adhesive sheet with a thickness (T1) of 225 μm in the same manner as in Example 1-1 except that the frame is set to 30 μm.

[0200] For the obtained adhesive sheet, perform measurement of specimens for measurement, measurement of expansion ratio, measurement of thermal conductivity, and measurement of shear strength in the same manner as in Example 1-1 except that the thickness of the spacer is changed to 440 μm. The results are shown in Table 5.

[0201] Example 1-4

[0202] Change the thermal conductive filler (1) to 23.5 parts by mass of thermal conductive filler (1) and 2.0 parts by mass of thermal conductive filler (4) (total content of (1) and (4) in the adhesive layer is 13.9% by volume), and the thickness of the first adhesive layer is 55 μm. Prepare an adhesive sheet with a thickness (T1) of 260 μm in the same manner as in Example 1-1 except that the frame is set to 60 μm.

[0203] For the obtained adhesive sheet, perform measurement of specimens for measurement, measurement of expansion ratio, measurement of thermal conductivity, and measurement of shear strength in the same manner as in Example 1-1 except that the thickness of the spacer is changed to 440 μm. The results are shown in Table 5.

[0204] Comparative Example 1-1

[0205] Same as Example 1-1 except that the thermally conductive filler (1) is not blended, the thickness of the first adhesive layer is 35 μm, and the thickness of the second adhesive layer is 38.3 μm. An adhesive sheet having a thickness (T1) of 210 μm was prepared.

[0206] Regarding the obtained adhesive sheet, measurement specimens, expansion ratio, thermal conductivity measurement, and shear strength measurement were carried out in the same manner as in Example 1-1. The results are shown in Table 5.

[0207] Comparative Example 1-2

[0208] The thermally conductive filler (1) was changed to 24.9 parts by mass of the thermally conductive filler (3) (content in the adhesive layer: 13.9% by volume), the thickness of the first adhesive layer was 43 μm, and the thickness of the second adhesive layer was 42 μm. An adhesive sheet having a thickness (T1) of 220 μm was prepared in the same manner as in Example 1-1.

[0209] Regarding the obtained adhesive sheet, measurement specimens, expansion ratio, thermal conductivity measurement, and shear strength measurement were carried out in the same manner as in Example 1-1. The results are shown in Table 5.

[0210] Comparative Example 1-3

[0211] The thermally conductive filler (1) was changed to 36.2 parts by mass of the thermally conductive filler (5) (content in the adhesive layer: 13.9% by volume), the thickness of the first adhesive layer was 39 μm, and the thickness of the second adhesive layer was 36 μm. An adhesive sheet having a thickness (T1) of 190 μm was prepared in the same manner as in Example 1-1.

[0212] Regarding the obtained adhesive sheet, measurement specimens, expansion ratio, thermal conductivity measurement, and shear strength measurement were carried out in the same manner as in Example 1-1. The results are shown in Table 5.

[0213] Comparative Example 1-4

[0214] The thermally conductive filler (1) was changed to 40.4 parts by mass of the thermally conductive filler (6) (content in the adhesive layer: 13.9% by volume), and the thickness of the first adhesive layer was 30 μm and the thickness of the second adhesive layer was 33.3 μm. Otherwise, an adhesive sheet having a thickness (T1) of 200 μm was prepared in the same manner as in Example 1-1.

[0215] Regarding the obtained adhesive sheet, measurement specimens, expansion ratio, thermal conductivity measurement, and shear strength measurement were carried out in the same manner as in Example 1-1. The results are shown in Table 5.

[0216] [Table 5]

[0217]

[0218] Example 2-1

[0219] The amount of the heat-conductive filler (1) was changed to 50.0 parts by mass (content in the adhesive layer: 24.5% by volume), the thickness of the first adhesive layer was 39 μm, and the thickness of the second adhesive layer was 44.3 μm. An adhesive sheet having a thickness (T1) of 190 μm was prepared in the same manner as in Example 1-1.

[0220] Regarding the obtained adhesive sheet, measurement specimens, expansion ratio, thermal conductivity measurement, and shear strength measurement were carried out in the same manner as in Example 1-1. The results are shown in Table 6.

[0221] Example 2-2

[0222] The heat-conductive filler (1) was changed to 49.5 parts by mass of the heat-conductive filler (2) (content in the adhesive layer: 24.3% by volume), the thickness of the first adhesive layer was 48 μm, and the thickness of the second adhesive layer was 57 μm. Otherwise, an adhesive sheet having a thickness (T1) of 220 μm was prepared in the same manner as in Example 1-1.

[0223] Regarding the obtained adhesive sheet, measurement specimens, expansion ratio, thermal conductivity measurement, and shear strength measurement were carried out in the same manner as in Example 1-1. The results are shown in Table 6.

[0224] Comparative Example 2-1

[0225] The heat-conductive filler (1) was changed to 49.5 parts by mass of the heat-conductive filler (3) (content in the adhesive layer: 24.3% by volume), the thickness of the first adhesive layer was 85 μm, and the thickness of the second adhesive layer was 95 μm. Otherwise, an adhesive sheet having a thickness (T1) of 290 μm was prepared in the same manner as in Example 1-1.

[0226] For the obtained adhesive sheet, measurement test specimens, expansion ratio measurement, thermal conductivity measurement, and shear strength measurement were carried out in the same manner as in Example 1-1, except that the thickness of the spacer was changed to 480 μm. The results are shown in Table 6.

[0227] [Table 6]

[0228]

[0229]

[0230] Example 3-1

[0231] The amount of the heat conductive filler (1) was changed to 5.0 parts by mass (content in the adhesive: 3.1% by volume), the thickness of the first adhesive layer was 31 μm, and the thickness of the second adhesive layer was 35.7 μm.

[0232] For the obtained adhesive sheet, except that the thickness of the spacer was changed to 440 μm, measurement specimens, expansion ratio measurement, thermal conductivity measurement, and shear strength measurement were carried out in the same manner as in Example 1-1. The results are shown in Table 7.

[0233] Example 3-2

[0234] The amount of the heat conductive filler (1) was changed to 5.0 parts by mass (content in the adhesive: 3.1% by volume), the thickness of the first adhesive layer was 33 μm, and the thickness of the second adhesive layer was 38.7 μm. An adhesive sheet having a thickness (T1) of 190 μm was prepared.

[0235] Regarding the obtained adhesive sheet, measurement specimens, expansion ratio measurement, thermal conductivity measurement, and shear strength measurement were carried out in the same manner as in Example 1-1. The results are shown in Table 7.

[0236] Example 3-3

[0237] The amount of the heat conductive filler (1) was changed to 10.0 parts by mass (content in the adhesive: 6.1% by volume), the thickness of the first adhesive layer was 36 μm, and the thickness of the second adhesive layer was 40.7 μm. An adhesive sheet having a thickness (T1) of 190 μm was prepared.

[0238] Regarding the obtained adhesive sheet, measurement specimens, expansion ratio, thermal conductivity measurement, and shear strength measurement were carried out in the same manner as in Example 1-1. The results are shown in Table 7.

[0239] Example 3-4

[0240] The amount of the heat conductive filler (1) was changed to 10.0 parts by mass (content in the adhesive: 6.1% by volume), and the thickness of the first adhesive layer was 55 μm and the thickness of the second adhesive layer was 50 μm. Except for this, in the same manner as in Example 1-1, an adhesive sheet having a thickness (T1) of 205 μm was prepared.

[0241] For the obtained adhesive sheet, except that the thickness of the spacer was changed to 360 μm, measurement specimens, expansion ratio measurement, thermal conductivity measurement, and shear strength measurement were carried out in the same manner as in Example 1-1. The results are shown in Table 7.

[0242] Reference Example 1

[0243] Except that the amount of the heat-conductive filler (1) was changed to 74.5 parts by mass (content in the adhesive: 32.5% by volume), the thickness of the first adhesive layer was 55 μm, and the thickness of the second adhesive layer was 50 μm. An adhesive sheet having a thickness (T1) of 250 μm was prepared in the same manner as in Example 1-1.

[0244] An attempt was made to prepare a measurement test object from the obtained adhesive sheet in the same manner as in Example 1-1, but in the adhesive sheet of Reference Example 1, even when heated, the adhesive oozed out from the adhesive-permeable layer (nonwoven fabric sheet).

[0245] Comparative Example 3-1

[0246] Except that the amount of the heat-conductive filler (1) was changed to 104.0 parts by mass (content in the adhesive: 40.2% by volume), an attempt was made to coat the solution in the same manner as in Example 1-1. However, in Comparative Example 3-1, the kneading of the coating solution became difficult and it was difficult to form an adhesive layer.

[0247] [Table 7]

[0248]

[0249] Example 4-1

[0250] 100 parts by mass of the adhesive composition (1) prepared by the above method and 74.5 parts by mass of the heat-conductive filler (1) (content in the adhesive layer: 32.5% by volume) were mixed to obtain a coating solution for forming an adhesive layer. The coating solution was applied to one side of a substrate, dried at 65 °C for 3 minutes and then dried at 90 °C for 3 minutes, and a first adhesive layer was formed by drying. The thickness of the first adhesive layer was 55 μm. The thickness of the first adhesive layer was obtained by measuring the thickness of any three points in the A4-size area of the sample after forming the first adhesive layer using a bench micrometer.

[0251] Next, the coating solution was applied onto the other surface of the substrate and dried at 65 °C for 3 minutes and then at 90 °C for 3 minutes to form a second adhesive layer, and an adhesive sheet having a thickness (T1) of 215 μm was obtained. The thickness of the second adhesive layer was 51.7 μm. The thickness of the second adhesive layer was measured for the A4-sized area of the sample before and after forming the second adhesive layer using a bench micrometer, and the average value of the measured values after forming the second adhesive layer was subtracted from the average value of the measured values before forming the second adhesive layer value.

[0252] For the obtained adhesive sheet, except that the thickness of the spacer was set to 360 μm, the measurement of the test object, the measurement of the expansion ratio, the measurement of the thermal conductivity, and the measurement of the shear strength were carried out in the same manner as in Example 1-1. The results are shown in Table 8.

[0253] Example 4-2

[0254] Except that the amount of the thermal conductive filler (1) was changed to 90.0 parts by mass (content in the adhesive was 36.8 vol%), the thickness of the first adhesive layer was 45 μm, and the thickness of the second adhesive layer was 40 μm. In the same manner as in Example 4-1, an adhesive sheet having a thickness (T1) of 210 μm was prepared.

[0255] For the obtained adhesive sheet, except that the thickness of the spacer was changed to 360 μm, the measurement of the measurement specimen, the measurement of the expansion ratio, the measurement of the thermal conductivity, and the measurement of the shear strength were carried out in the same manner as in Example 1-1. The results are shown in Table 8.

[0256] Comparative Example 4-1

[0257] Except that the amount of the thermal conductive filler (1) was changed to 95.0 parts by mass (content in the adhesive was 38.1 vol%), the coating solution was tried in the same manner as in Example 4-1. However, in Comparative Example 4-1, the kneading of the coating solution became difficult and it was difficult to form an adhesive layer.

[0258] Comparative Example 4-2

[0259] Except that the amount of the thermal conductive filler (1) was changed to 104.0 parts by mass (content in the adhesive was 40.2 vol%), the coating solution was tried in the same manner as in Example 4-1. However, in Comparative Example 4-1, the kneading of the coating solution became difficult and it was difficult to form an adhesive layer.

[0260] [Table 8]

[0261]

[0262] Explanation of Reference Numerals

[0263] 1, 11... adhesive sheet, 3, 13, 23... substrate, 5, 15... first adhesive layer, 5', 15'... second adhesive layer, 17, 27... first adhesive permeable layer, 17', 27'... second adhesive permeable layer, 21... cured foam, 23... substrate, 25... first foam, 25'... second foam.

Claims

1. An adhesive sheet, the adhesive sheet comprising; A substrate; A first adhesive layer disposed on one surface of the substrate, and A second adhesive layer disposed on the other surface of the substrate, wherein The first adhesive layer contains an adhesive (A), a heat conductive filler (B) having an average short side length of 1 μm or more, and a foaming agent (C), The content of the heat conductive filler (B) is 1% by volume or more and 37% by volume or less based on the total volume of the first adhesive layer, The heat conductive filler (B) includes a filler (B-1) having an aspect ratio of 1.3 or more, the second adhesive layer contains an adhesive (A'), a heat conductive filler (B') having an average short side length of 1 μm or more, and a foaming agent (C'), The content of the heat conductive filler (B') is 1% by volume or more and 37% by volume or less based on the total volume of the second adhesive layer, and The heat conductive filler (B') includes a filler (B'-1) having an aspect ratio of 1.3 or more.

2. The adhesive sheet according to claim 1, wherein The content of the filler (B-1) is 0.1% by volume or more based on the total volume of the first adhesive layer, The content of the filler (B'-1) is 0.1% by volume or more based on the total volume of the second adhesive layer.

3. The adhesive sheet according to claim 1, further comprising; A first adhesive permeable layer disposed on the first adhesive layer and capable of permeating the adhesive (A) when the first adhesive layer foams, and A second adhesive permeable layer disposed on the second adhesive layer and capable of permeating the adhesive (A') when the second adhesive layer foams.

4. The adhesive sheet according to claim 3, wherein The content of the heat conductive filler (B) is 1% by volume or more and 30% by volume or less based on the total volume of the first adhesive layer, and The content of the heat conductive filler (B') is 1% by volume or more and 30% by volume or less based on the total volume of the second adhesive layer.

5. The adhesive sheet according to claim 1, wherein The heat conductive filler (B) contains at least one selected from the group consisting of boron nitride, aluminum nitride, and alumina, and The heat conductive filler (B') contains at least one selected from the group consisting of boron nitride, aluminum nitride, and alumina.

6. The adhesive sheet according to claim 1, wherein The filler (B-1) is flaky, whisker-like, or agglomerated, and The filler (B'-1) is flaky, whisker-like, or agglomerated.

7. The adhesive sheet according to claim 1, wherein The foaming agent (C) includes thermally expandable particles (C-1), and The foaming agent (C') includes thermally expandable particles (C'-1).

8. The adhesive sheet is a slot liner of a stator core of an electric motor.

9. A cured foam of the adhesive sheet according to any one of claims 1 to 8.

10. A motor, the motor comprising a stator, wherein the stator comprises; a stator core having at least one slot; a winding at least partially received in the slot, and an adhesive layer for bonding the stator core and the winding, wherein the adhesive layer comprises a cured foam of the adhesive sheet according to any one of claims 1 to 8.

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