Laminate and electrical insulation sheet for motors

Abstract

The purpose of the present invention is to provide a laminate with excellent adhesiveness and thermal conductivity. Provided is a laminate obtained by laminating a first layer which is provided with voids and a second layer which includes a base material, wherein: the first layer contains at least an epoxy resin, an acrylic resin, and an inorganic filler; the inorganic filler includes at least one type of particles selected from the group consisting of aluminum oxide particles, boron nitride particles, and aluminum nitride particles; the void ratio in the first layer is 50-80%; and the content of the inorganic filler is 60-85 mass% with respect to the total mass of the first layer.

Description

Laminate and electrical insulating sheet for motors

[0001] The present invention relates to a laminate and an electrical insulating sheet for a motor.

[0002] Drive motors for electric and hybrid vehicles, as well as compressor motors (for commercial, residential, and in-car air conditioners), consist of a stator and a rotor that rotates with a predetermined gap relative to the stator. The stator has a stator core and multiple coils wound around it. The stator core has slots formed in it, and the coils are housed in the slots. An insulating material is provided between the inner circumferential surface of the slots in the stator core and the coils for insulation. A liquid adhesive has traditionally been used to secure the stator core, coils, and insulating material together.

[0003] On the other hand, in recent years, it has been proposed to use an adhesive sheet containing a foaming agent instead of a liquid adhesive. For example, Patent Documents 1 and 2 disclose adhesive sheets containing a foaming agent instead of the insulating material, which have an expandable adhesive layer on one or both sides of a substrate, the adhesive layer containing an epoxy resin including a multifunctional epoxy resin, a phenolic resin as a curing agent, an imidazole compound as a curing catalyst, and a temperature-sensitive foaming agent.

[0004] JP 2020-34889 A JP 2019-203062 A

[0005] In recent years, drive motors for electric and hybrid vehicles have become smaller and more powerful, resulting in increased drive voltages, and in order to suppress heat generation in the motors, adhesive sheets containing the insulating materials and foaming agents described above are required to have high thermal conductivity and adhesive properties equivalent to those of conventional liquid adhesives.

[0006] The adhesive sheets containing the foaming agents described in Patent Documents 1 and 2 are useful in that they have excellent adhesiveness, but there is a need to develop a laminate that has excellent heat dissipation properties without reducing thermal conductivity even though it contains voids due to the foaming agent.

[0007] In response to such demands, an object of the present invention is to provide a laminate having excellent adhesiveness and thermal conductivity.

[0008] In order to solve the above problems, one preferred aspect of the present invention has the following configuration: (1) A laminate comprising a first layer having voids and a second layer including a substrate, wherein the first layer contains at least an epoxy resin, an acrylic resin, and an inorganic filler, the inorganic filler includes at least one kind selected from the group consisting of aluminum oxide particles, boron nitride particles, and aluminum nitride particles, the porosity of the first layer is 50% or more and 80% or less, and the content of the inorganic filler is 60% by mass or more and 85% by mass or less with respect to the total mass of the first layer. (2) The laminate according to (1), wherein the first layer has voids and solid portions, the solid portions contain a first inorganic filler having an aspect ratio of 1 to 2 and a second inorganic filler having an aspect ratio of 4 to 20, the content of the first inorganic filler being 40% to 60% and the content of the second inorganic filler being 5% to 20%. (3) The laminate according to (2), wherein, when the average particle diameter of the first inorganic filler is a and the average particle diameter of the second inorganic filler is b, b / a is 0.03 to 0.40. (4) The laminate according to any one of (1) to (3), wherein the thickness of the first layer is 100 μm to 400 μm. (5) The laminate according to any one of (1) to (3), wherein the substrate is a film made of a thermoplastic resin, and the thickness of the substrate is 50 μm or more and 200 μm or less. (6) The laminate according to any one of (1) to (3), wherein the thermal conductivity of the laminate is 0.5 W / (m·K) or more, and the shear adhesive strength according to JIS Z 1541 (2009) is 0.4 MPa or more. (7) An electrical insulating sheet for a motor, comprising the laminate according to any one of (1) to (3).

[0009] According to the present invention, a laminate having excellent thermal conductivity and adhesiveness can be obtained.

[0010] 1 is a side view of a laminate of the present invention, a side view of a sample for measuring shear adhesive strength in the laminate of the present invention, and a plan view of a sample for measuring shear adhesive strength in the laminate of the present invention.

[0011] The laminate of the present invention will now be described.

[0012] The laminate of the present invention is a laminate formed by laminating a first layer having voids and a second layer including a substrate. The laminate of the present invention will be described with reference to Figure 1. Figure 1 is a side view of the laminate of the present invention, and is formed by laminating a first layer having voids 1 and a second layer including a substrate 2 in this order. Although not shown, the laminate of the present invention may also have a configuration in which the first layer having voids is laminated on both sides of the second layer including a substrate.

[0013] The first layer contains at least an epoxy resin, an acrylic resin, and an inorganic filler.

[0014] The epoxy resin is a compound having at least one epoxy group or glycidyl group, and is cured by a cross-linking polymerization reaction when used in combination with a curing agent. The epoxy resin also includes a monomer having at least one epoxy group or glycidyl group.

[0015] Examples of epoxy resins include aromatic epoxy resins, aliphatic epoxy resins, alicyclic epoxy resins, and heterocyclic epoxy resins. Specific examples of epoxy resins include bisphenol-type epoxy resins such as bisphenol A-type epoxy resins and bisphenol F-type epoxy resins, novolac-type epoxy resins such as bisphenol A novolac-type epoxy resins and cresol novolac-type epoxy resins, and modified epoxy resins such as urethane-modified epoxy resins and rubber-modified epoxy resins. Other specific examples include biphenyl-type epoxy resins, stilbene-type epoxy resins, triphenolmethane-type epoxy resins, alkyl-modified triphenolmethane-type epoxy resins, triazine-nucleus-containing epoxy resins, dicyclopentadiene-modified phenol-type epoxy resins, naphthalene-type epoxy resins, glycol-type epoxy resins, and pentaerythritol-type epoxy resins. The epoxy resins may be one type or two or more types.

[0016] Bisphenol A epoxy resins can exist in a liquid state or a solid state at room temperature depending on the number of repeating units in the bisphenol skeleton. Bisphenol A epoxy resins having, for example, 2 to 10 bisphenol skeletons in the main chain are solid at room temperature. Bisphenol A epoxy resins are particularly preferred because they can improve heat resistance.

[0017] The epoxy resin may be a monofunctional epoxy resin, a difunctional epoxy resin, a trifunctional epoxy resin, or a tetrafunctional or higher functional epoxy resin.

[0018] The epoxy resin preferably contains a curing agent from the viewpoint of improving heat resistance and adhesion. As the curing agent, a curing agent generally used in epoxy resin adhesives can be used, and is not particularly limited. Specific examples of the curing agent include imidazole-based curing agents, phenol-based curing agents, amine-based curing agents, acid anhydride-based curing agents, isocyanate-based curing agents, and thiol-based curing agents.

[0019] The acrylic resin is obtained by polymerizing the following monomer components. From the viewpoint of excellent heat resistance, the monomer components preferably include (meth)acrylic acid ester-based monomers such as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, stearyl (meth)acrylate, phenyl (meth)acrylate, isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate, and nitrile-based monomers such as acrylonitrile, methacrylonitrile, and fumaronitrile. Note that (meth)acrylic means acrylic or methacrylic.

[0020] A preferred method for forming the voids in the first layer is to use a thermally expandable capsule. A preferred example of a thermally expandable capsule is a spherical capsule with an outer shell made of the acrylic resin and containing a liquid hydrocarbon. When the thermally expandable capsule is heated, the acrylic resin in the outer shell softens, and the encapsulated liquid hydrocarbon vaporizes, increasing the volume and causing the capsule to expand. The capsule expands, forming a first layer, which increases the contact area with the coil and stator core, thereby improving adhesion.

[0021] The inorganic filler includes at least one type selected from the group consisting of aluminum oxide particles, boron nitride particles, and aluminum nitride particles. Two or more types of inorganic fillers may be mixed together as long as the effects of the present invention are not impaired. The shape of the filler is not particularly limited, and spherical, globular, scale-like, flake-like, foil-like, fibrous, needle-like, and other shapes can be used. The inclusion of the inorganic filler can suppress a decrease in thermal conductivity due to voids in the first layer, thereby improving heat dissipation.

[0022] It is important that the void ratio of the voids is 50% or more and 80% or less. In the present invention, the term "voids" refers to the spaces present in the first layer in a cross section obtained by cutting the laminate perpendicular to the thickness direction (hereinafter referred to as a "thickness direction cross section"). The void ratio refers to the area ratio of the voids in the cross section of the first layer in the laminate, and can be determined by calculating the ratio of the total area of ​​the voids to the total area of ​​the first layer from an enlarged image of the thickness direction cross section (described below). If the void ratio is less than 50%, the contact area between the first layer and the coil or stator core may decrease, resulting in poor adhesion to the coil or stator. If the void ratio is greater than 80%, the cohesive force of the first layer may decrease, resulting in poor adhesion. Furthermore, a large number of voids may reduce thermal conductivity, resulting in insufficient heat dissipation.

[0023] From the viewpoint of adhesiveness and thermal conductivity, it is important that the content of the inorganic filler is 60% by mass or more and 85% by mass or less with respect to the total mass of the first layer. Adhesion and thermal conductivity are in a trade-off relationship with respect to the content of the inorganic filler. By setting the content to 60% by mass or more and 85% by mass or less, the amount of inorganic filler required for heat transfer can be secured while maintaining the proportion of the resin component required for adhesion, thereby imparting sufficient thermal conductivity. The content of the inorganic filler was calculated using the ash measurement method described below.

[0024] The thermal conductivity of the laminate of the present invention is preferably 0.5 W / (m·K) or more, and the shear adhesive strength in accordance with JIS Z 1541 (2009) is preferably 0.4 MPa or more. When the thermal conductivity of the laminate of the present invention is 0.5 W / (m·K) or more and the shear adhesive strength is 0.4 MPa or more, it is easy to obtain a laminate that has sufficient thermal conductivity for heat dissipation of the coil and excellent adhesion to the coil and stator core.

[0025] The second layer is a member that forms the framework of the laminate. The second layer may have a single-layer structure or a laminate structure. The total thickness of the second layer is, for example, 1 to 300 μm, preferably 5 to 250 μm, and more preferably 50 to 200 μm.

[0026] The second layer in the present invention includes a substrate, which is preferably insulating, such as a resin, nonwoven fabric, paper, mesh sheet, or a multilayer thereof, and a resin-impregnated nonwoven fabric, paper, or mesh woven fabric. When the substrate is a resin substrate, examples of the resin include polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and aromatic polyester; polycarbonate; polyarylate; polyurethane; polyamide resins such as polyamide and polyetheramide; polyimide resins such as polyimide, polyetherimide, and polyamideimide; polysulfone resins such as polysulfone and polyethersulfone; polyetherketone resins such as polyetherketone and polyetheretherketone; polyphenylene sulfide (PPS); modified polyphenylene oxide; and the like. The glass transition temperature of the resin is, for example, 80°C or higher, or may be 140°C or higher, or 200°C or higher.

[0027] Examples of the nonwoven fabric include nonwoven fabrics containing fibers such as basalt fibers, vinylon fibers, polyarylate fibers, polyethylene fibers, polypropylene fibers, silicon carbide fibers, cellulose fibers, polyester fibers, nylon fibers, aramid fibers, polyphenylene sulfide fibers, liquid crystal polymer fibers, and glass fibers.

[0028] The mesh sheet refers to a sheet woven from cotton, hemp, aramid fiber, cellulose fiber, nylon fiber, polyolefin fiber, polyphenylene sulfide fiber, or the like, and having square openings of a predetermined size.

[0029] The thermal conductivity of the second layer is preferably 0.5 W / (m·K) or more. To achieve a thermal conductivity of 0.5 W / (m·K) or more for the laminate, it is preferable that both the first layer and the second layer have a thermal conductivity of 0.5 W / (m·K) or more. To increase the thermal conductivity of the second layer, it is preferable that the second layer contains the same inorganic filler as the first layer.

[0030] The method for producing the laminate of the present invention will be exemplified below.

[0031] A coating liquid is obtained by adding a solvent to the epoxy resin, thermally expandable capsules having an acrylic resin shell and a liquid hydrocarbon encapsulated therein, and inorganic filler, as exemplified above, to dissolve and disperse them to a viscosity suitable for application by the coating method described below. The coating liquid is applied to the second layer, as exemplified above, by a coating method such as die coating, roll coating, gravure roll coating, or kiss coating, or by a printing method, and then dried to obtain a coating film. Hereinafter, the second layer and the coating film laminated thereon may be referred to as an adhesive sheet. After foaming, the coating film becomes the first layer, and after foaming, the adhesive sheet becomes the laminate of the present invention.

[0032] Next, the temperature is raised to a temperature at which the thermally expandable capsules can expand, and the thermally expandable capsules are expanded to form voids, thereby expanding the coating film. The thickness of the coating film before expansion is preferably 10 to 200 μm, and the thickness of the first layer, which is the coating film after expansion, is preferably 100 to 400 μm. By setting the thickness within this range, the contact area with the coil and stator core increases during expansion, resulting in excellent adhesive strength and thermal conductivity. If the expansion is too large, the increase in voids may reduce thermal conductivity and the cohesive force of the coating film, which may result in reduced adhesiveness.

[0033] By using the above-mentioned laminate as an electrical insulating sheet for a motor, it is possible to provide a smaller, higher-output motor, as it has sufficient adhesion to the coil and stator core even when subjected to vibrations during motor operation, and also has excellent thermal conductivity.

[0034] In the laminate of the present invention, the first layer has voids and solid portions, and the solid portions contain a first inorganic filler having an aspect ratio of 1 or more and 2 or less and a second inorganic filler having an aspect ratio of 4 or more and 20 or less, and it is preferable that the content of the first inorganic filler is 40% or more and 60% or less, and the content of the second inorganic filler is 5% or more and 20% or less.

[0035] In the present invention, the solid portion refers to the portion of the first layer other than the voids.

[0036] In the present invention, the aspect ratio means the ratio between the maximum length and the minimum length of an inorganic filler. The maximum length and the minimum length of each of the first inorganic filler and the second inorganic filler are determined using a scanning electron microscope by the method described below, and the aspect ratio is calculated from the obtained values ​​by dividing the maximum length by the minimum length.

[0037] In the laminate of the present invention, when voids are formed due to an increase in the volume of the thermally expandable capsule, the second inorganic filler particles having a high aspect ratio tend to overlap with each other in the long side direction. Therefore, while the inorganic fillers tend to come into contact with each other, improving thermal conductivity, excessive overlapping can lead to cleavage between the inorganic fillers, reducing the cohesive strength of the first layer and resulting in poor adhesion. By combining the first and second inorganic fillers described above, the thermal conductivity is improved by the overlapping of the second inorganic filler particles, while the inclusion of the first inorganic filler prevents excessive overlapping, suppressing cleavage and ensuring adhesion.

[0038] In the laminate of the present invention, when the average particle size of the first inorganic filler is a and the average particle size of the second inorganic filler is b, it is preferable that b / a is 0.03 to 0.40. By setting b / a to 0.03 to 0.40, it is possible to prevent excessive overlapping of the second inorganic filler and to fill the gaps formed between the first inorganic fillers with the second inorganic filler, resulting in excellent thermal conductivity. b / a is 0.03 to 0.40, preferably 0.04 to 0.30, and more preferably 0.05 to 0.20.

[0039] The average particle diameters of the first and second inorganic fillers were calculated based on the maximum length and minimum length of each inorganic filler by the method described below, using the formula (maximum length + minimum length) / 2.

[0040] [Methods for measuring physical properties] The configuration and effects of the present invention will be explained in more detail below using examples. However, the present invention is not limited to the following examples. Before describing each example, methods for measuring various physical properties will be described.

[0041] (1) Shear Adhesion Strength The shear adhesive strength was measured as follows according to the test method described in JIS Z 1541 (2009). An SPCC plate (manufactured by Iwata Seisakusho, model number TF50-100-01, 0.1 mm thick, 50 × 100 mm) was used as the adherend. The sample area was 10 × 10 mm, and the tensile speed during measurement was 200 mm / min. First, as shown in Figure 2 , a 10 × 100 mm cut-out of the adhesive sheet was placed on SPCC plate 3, and then another SPCC plate 4 was placed on it via two spacers 5. The height of spacers 5 was adjusted so that the clearance between SPCC plate 4 and the adhesive sheet was 50 μm. This sample was heat-treated at 200°C for 7 minutes and then attached to a tensile tester to measure the shear adhesive strength between the laminate and the SPCC plate.

[0042] (2) Thermal Conductivity The laminate was cut into a size of 10 × 10 mm, and the thermal diffusivity was measured using a laser flash thermal diffusivity measuring device LFA447 manufactured by Netsch Co., Ltd. The specific gravity of the laminate was measured by the Archimedes method, and the specific heat of the cured product was measured by the DSC method, and the thermal conductivity was calculated by the formula: thermal diffusivity × specific gravity × specific heat.

[0043] (3) Inorganic Filler Content The inorganic filler content can be measured by a general ash measurement method. 10 mg of the first layer alone was sampled from the laminate, and the residual content was calculated before and after the test according to JIS K7120:1987.

[0044] (4) Porosity The laminate was cut using a microtome in a plane perpendicular to the thickness of the laminate. The cut surface thus obtained was observed using a Hitachi S-800 field emission scanning electron microscope (FE-SEM) at the maximum magnification at which the first layer could be observed, and the image was imported into an electronic device. The obtained image was then imported into an image analyzer (Nireco Corporation: "Luzex (registered trademark)" IID), and the area of ​​the voids in each layer was measured using a binarization process. The ratio of this area to the area of ​​the portion corresponding to the laminate in the observed image was calculated. Measurements were performed on five images taken at any five locations, and the average of the measured values ​​was taken as the porosity.

[0045] (5) Aspect Ratio A cross section obtained in the same manner as in "(4) Porosity" was observed at the maximum magnification, including the solid portion, using a Hitachi S-800 field emission scanning electron microscope (FE-SEM). The image was then imported into an electronic device. The obtained image was then imported into an image analyzer (developed by the National Institutes of Health (NIH), image processing software "ImageJ"), and the maximum and minimum lengths of the inorganic filler in the solid portion were measured, and (maximum length) ÷ (minimum length) was calculated. Next, 50 inorganic fillers were observed for each of the first and second inorganic fillers, and the (maximum length) ÷ (minimum length) was calculated individually. The average value was used as the aspect ratio of the first and second inorganic fillers.

[0046] (6) Contents of First and Second Inorganic Fillers Using the same method as in "(5) Aspect Ratio," images of the solid portions were imported into an image analyzer (developed by the National Institutes of Health (NIH), image processing software "ImageJ"), and the areas of the solid portions, the first inorganic filler, and the second inorganic filler were measured. Similar processing was performed on images of 10 solid portions, and the ratio of the area occupied by the inorganic filler in the solid portions was taken as the content of the inorganic filler. The value obtained by multiplying the average value of (area of ​​the first inorganic filler) ÷ (area of ​​the solid portions) by 100 was taken as the content of the first inorganic filler, and the value obtained by multiplying the average value of (area of ​​the second inorganic filler) ÷ (area of ​​the solid portions) by 100 was taken as the content of the second inorganic filler.

[0047] (7) Average particle diameter In the same manner as in "(5) Aspect ratio", an image of the solid portion was imported into an imaging analyzer (developed by the National Institutes of Health (NIH), image processing software "ImageJ"), and the maximum and minimum lengths of the first and second inorganic fillers were measured, and (maximum length + minimum length) / 2 was calculated. Next, 50 inorganic fillers for each of the first and second inorganic fillers were observed, and (maximum length + minimum length) / 2 was calculated for each, and the average value was used as the average particle diameter of the first and second inorganic fillers.

[0048] [Materials used for each layer] 1. First layer (coating liquids a to ac) The types of raw materials used for the first layer are as follows. The following products were used as the raw materials. Coating liquids a to ac, which would become the first layer, were prepared according to the formulations shown in Table 1. 1: Epoxy resin "jER 828" bisphenol A type, epoxy equivalent 225 g / eq (manufactured by Mitsubishi Chemical Corporation) 2: Epoxy resin "EPICLON EXA-4850-150" bisphenol A type, epoxy equivalent 432 g / eq (manufactured by DIC Corporation) 3: Epoxy resin "YSLV-120TE" thioether type, epoxy equivalent 246 g / eq (manufactured by Nippon Steel Chemical & Material Co., Ltd.) 4: Curing agent "Seikacure-S" 4,4'-diaminodiphenyl sulfone (manufactured by Seika Corporation) 5: Curing catalyst "IS-1000" imidazole silane coupling agent (manufactured by JX Nippon Mining & Metals Corporation) 6: Thermally expandable capsule with acrylic resin outer shell and liquid hydrocarbon encapsulated inside "FN-180SS" particle size: 20 μm maximum expansion temperature: 165 to 180°C (manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd.) 7: Inorganic filler "HFS-50" aluminum nitride (manufactured by Tokuyama Corporation) 8: Inorganic filler "CB-A50S" aluminum oxide (manufactured by Resonac Corporation) 9: Inorganic filler "CB-A20S" aluminum oxide (manufactured by Resonac Corporation) 10: Inorganic filler "CB-P10" aluminum oxide (manufactured by Resonac Corporation) 11: Inorganic filler "BMB-B" aluminum oxide (manufactured by Kawai Lime Industry Co., Ltd.) 12: Inorganic filler "BMT" aluminum oxide (manufactured by Kawai Lime Industry Co., Ltd.) 13: Inorganic filler "BMF" aluminum oxide (manufactured by Kawai Lime Industry Co., Ltd.) 14: Inorganic filler "BMT" aluminum oxide (manufactured by Kawai Lime Industry Co., Ltd.) 15: Inorganic filler "Al-43-KT" aluminum oxide (manufactured by Resonac Corporation) 16: Inorganic filler "BMI" aluminum oxide (manufactured by Kawai Lime Industry Co., Ltd.) 17: Inorganic filler "UHP-S2" boron nitride (manufactured by Resonac Co., Ltd.) 18: Inorganic filler "UHP-1K" boron nitride (manufactured by Resonac Co., Ltd.) 19: Inorganic filler "UHP-2" boron nitride (manufactured by Resonac Co., Ltd.)

[0049]

[0050]

[0051] 2. Film (PPS-A) made of polyphenylene sulfide (hereinafter referred to as PPS) As the second layer, a PPS film "TORELINA (registered trademark)" manufactured by Toray Industries, Inc. was used as a film made of PPS. The thickness of the film was 50 μm.

[0052] 3. Mesh sheet made of resin-impregnated PPS fibers (PPS-B) A mesh sheet made of PPS fibers with a fiber diameter of 55 μm, mesh openings of 200 μm, 100 mesh, and a thickness of 100 μm was coated on both sides with a coating liquid prepared according to the formulation shown in Table 2 using a comma coater, followed by drying at 100°C for 3 minutes. The mesh sheet was then heat-treated at 150°C for 1 hour to obtain a PPS-B with a total thickness of 200 μm. The raw materials shown in Table 2 were the same as those used in 1. First Layer, 1. to 5. Furthermore, the inorganic filler used was aluminum oxide "CB-A20S" manufactured by Resonac, Inc., with a particle size of 21 μm.

[0053]

[0054] (Examples 1 to 25, Comparative Examples 1 to 4) A coating solution was applied to the second layer shown in Table 3 using a Baker-type applicator, and the sheet was dried at 100°C for 3 minutes to obtain an adhesive sheet in which a coating film (which would become the first layer after expansion) was laminated on the second layer. The sheet was then heated at 200°C for 7 minutes to expand the coating film, yielding a laminate. The types of coating solution, first layer, and second layer are as shown in the table. The results of the characteristic evaluation are shown in Table 3. The laminates of Examples 1 to 25 have good adhesion and thermal conductivity due to the adjustment of the porosity and the amount of inorganic filler. In Comparative Example 3, the porosity of the first layer was low, preventing sufficient expansion, resulting in an insufficient adhesive area with the SPCC plate and low shear adhesion strength.

[0055] The laminates of Examples 10 and 23 have the first and / or second inorganic filler content, aspect ratio, and b / a in a more preferred range than the laminates of Examples 13, 14, 18, and 20 to 22, and therefore are free of inorganic filler filling or cleavage of the second inorganic filler, and have better thermal conductivity and shear adhesive strength.

[0056]

[0057] According to the present invention, it is possible to provide a laminate that has excellent adhesiveness and thermal conductivity even while containing voids. The laminate of the present invention can be suitably used as electrical insulation for motors.

[0058] 1: First layer 2: Second layer 3: SPCC plate 3 4: SPCC plate 4 5: Spacer 6: First layer before expansion

Claims

1. A laminate comprising a first layer having a void and a second layer including a substrate, the first layer containing at least an epoxy resin, an acrylic resin and an inorganic filler, the inorganic filler containing at least one type selected from the group consisting of aluminum oxide particles, boron nitride particles and aluminum nitride particles, the porosity of the first layer being 50% or more and 80% or less, and the content of the inorganic filler being 60% by mass or more and 85% by mass or less relative to the total mass of the first layer.

2. The laminate described in claim 1, wherein the first layer has voids and a solid portion, the solid portion contains a first inorganic filler having an aspect ratio of 1 or more and 2 or less and a second inorganic filler having an aspect ratio of 4 or more and 20 or less, the content of the first inorganic filler is 40% or more and 60% or less, and the content of the second inorganic filler is 5% or more and 20% or less.

3. The laminate according to claim 2, wherein when the average particle size of the first inorganic filler is a and the average particle size of the second inorganic filler is b, b / a is 0.03 or more and 0.40 or less.

4. A laminate according to any one of claims 1 to 3, wherein the first layer has a thickness of 100 μm or more and 400 μm or less.

5. A laminate according to any one of claims 1 to 3, wherein the substrate is a film made of a thermoplastic resin, and the thickness of the substrate is 50 µm or more and 200 µm or less.

6. A laminate according to any one of claims 1 to 3, having a thermal conductivity of 0.5 W / (m·K) or more and a shear adhesive strength according to JIS Z 1541 (2009) of 0.4 MPa or more.

7. An electrical insulating sheet for a motor, comprising the laminate according to any one of claims 1 to 3.

Images