Expandable adhesive sheet and stator for rotary electric machine

Abstract

To provide an expandable adhesive sheet in which front and rear of the expandable adhesive sheet can be discriminated not only when the sheet is in use but also even after assembled into a rotating machine.SOLUTION: An expandable adhesive sheet has a first adhesion layer, a substrate, and a second adhesion layer in this order, where the first adhesion layer and the second adhesion layer contain curable adhesive agent, at least one of the first adhesion layer and the second adhesion layer contains foaming agent, the first adhesion layer and the second adhesion layer have different properties from each other, a fiber layer is arranged on the side opposite to the substrate of the first adhesion layer or between the first adhesion layer and the substrate, and in the case where the fiber layer is arranged on the side opposite to the substrate of the first adhesion layer, the first adhesion layer contains the foaming agent.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a foamable adhesive sheet suitable for use in bonding a stator core and a coil of a stator for a rotating electric machine. [Background technology]

[0002] Generally, vehicles such as hybrid vehicles and electric vehicles include a rotating electric machine that can function as a motor and a generator. The rotating electric machine also generally includes a stator as a stationary part and a rotor as a rotor that rotates with a predetermined gap between them. The stator has a stator core and a plurality of coils wound around the stator core.

[0003] A stator core of a rotating electrical machine has slots formed therein, and coils are housed in the slots. In this case, an insulating layer must be disposed between the inner peripheral surface of the slot of the stator core and the coils to provide insulation.

[0004] Conventionally, insulating paper has been used as the insulating layer, and a method has been adopted in which the insulating paper is fixed between the stator core and the coil using a liquid adhesive.

[0005] On the other hand, in recent years, it has been proposed to use adhesive sheets containing a foaming agent (foamable adhesive sheets) instead of liquid adhesives. For example, Patent Document 1 discloses an adhesive sheet having 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. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2016 / 163514 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-236468 Summary of the Invention [Problem to be solved by the invention]

[0007] It has been proposed that, in a foam adhesive sheet used to bond a stator core and a coil, the adhesive layer arranged on the stator core side and the adhesive layer arranged on the coil side have different properties. For example, Patent Document 2 discloses an expandable sheet for a rotating electric machine in which a coil conductor is housed in a slot provided in the core, the expandable sheet being arranged between the core and the coil conductor in the slot and expanding when heated, with the coil conductor side expanding by a larger volume increase than the core side.

[0008] In a foam adhesive sheet, when the adhesive layer arranged on the stator core side and the adhesive layer arranged on the coil side have different properties, it is necessary to distinguish between the front and back of the foam adhesive sheet when using it. Using the foam adhesive sheet with the wrong front and back can cause malfunctions and even fatal accidents. One method for distinguishing between the front and back of a foam adhesive sheet is to check the product label. In this case, it is impossible to distinguish between the front and back after the product label is peeled off. Furthermore, it is difficult to distinguish between the front and back of an adhesive sheet after it has foamed and hardened after being installed in a rotating machine. Therefore, even if the malfunction was caused by the wrong front and back of the foam adhesive sheet, it is impossible to identify the cause of the malfunction.

[0009] The present disclosure has been made in consideration of the above-mentioned situation, and its main purpose is to provide a foamable adhesive sheet that makes it possible to distinguish between the front and back of the foamable adhesive sheet not only during use but also after it has been installed in a rotating machine. [Means for solving the problem]

[0010] One embodiment of the present disclosure provides a foamable adhesive sheet having, in this order, a first adhesive layer, a substrate, and a second adhesive layer, wherein the first adhesive layer and the second adhesive layer contain a curable adhesive, and at least one of the first adhesive layer and the second adhesive layer contains a foaming agent, the first adhesive layer and the second adhesive layer having different properties from each other, and a fiber layer is disposed on the side of the first adhesive layer opposite the substrate or between the first adhesive layer and the substrate, and when the fiber layer is disposed on the side of the first adhesive layer opposite the substrate, the first adhesive layer contains the foaming agent.

[0011] Another embodiment of the present disclosure provides a foamable adhesive sheet having, in this order, a first adhesive layer, a substrate, and a second adhesive layer, wherein the first adhesive layer and the second adhesive layer contain a curable adhesive, and at least one of the first adhesive layer and the second adhesive layer contains a foaming agent, the first adhesive layer and the second adhesive layer having different properties from each other, a first fiber layer disposed on the side of the first adhesive layer opposite the substrate, and a second fiber layer disposed on the side of the second adhesive layer opposite the substrate, or alternatively, a first fiber layer disposed between the first adhesive layer and the substrate and a second fiber layer disposed between the second adhesive layer and the substrate, the first fiber layer and the second fiber layer being different from each other, and in the case where the first fiber layer is disposed on the side of the first adhesive layer opposite the substrate, and the second fiber layer is disposed on the side of the second adhesive layer opposite the substrate, the first adhesive layer and the second adhesive layer contain the foaming agent.

[0012] Another embodiment of the present disclosure provides a foamable adhesive sheet having, in that order, a first adhesive layer, a substrate, and a second adhesive layer, wherein the first adhesive layer and the second adhesive layer contain a curable adhesive, and at least one of the first adhesive layer and the second adhesive layer contains a foaming agent, the first adhesive layer and the second adhesive layer have different properties, and the first adhesive layer and the second adhesive layer contain different amounts of filler.

[0013] Another embodiment of the present disclosure provides a foamable adhesive sheet having, in this order, a first adhesive layer, a substrate, and a second adhesive layer, wherein the first adhesive layer and the second adhesive layer contain a curable adhesive, and at least one of the first adhesive layer and the second adhesive layer contains a foaming agent, the first adhesive layer and the second adhesive layer have different properties from each other, and the first adhesive layer and the second adhesive layer contain different fillers from each other.

[0014] Another embodiment of the present disclosure provides a foamable adhesive sheet having a first adhesive layer, a substrate, and a second adhesive layer in this order, wherein the first adhesive layer and the second adhesive layer contain a curable adhesive, and at least one of the first adhesive layer and the second adhesive layer contains a foaming agent, and the first adhesive layer and the second adhesive layer have properties different from each other, and a pattern layer is disposed at least either between the first adhesive layer and the substrate and between the second adhesive layer and the substrate.

[0015] Another embodiment of the present disclosure provides a stator for a rotating electric machine, comprising a stator core having slots, a coil disposed in the slots, and an adhesive sheet disposed between the stator core and the coil, wherein the adhesive sheet is a foamed and cured product of the foamable adhesive sheet described above. [Effects of the Invention]

[0016] The foamable adhesive sheet of the present disclosure has the advantage that it is possible to distinguish between the front and back sides not only during use but also after the sheet has been installed in a rotating machine. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a schematic cross-sectional view showing an example of a foamable adhesive sheet according to the present disclosure. [Figure 2] FIG. 2 is a schematic cross-sectional view showing another example of a foamable adhesive sheet according to the present disclosure. [Figure 3] FIG. 2 is a schematic cross-sectional view showing another example of a foamable adhesive sheet according to the present disclosure. [Figure 4]FIG. 2 is a schematic cross-sectional view showing another example of a foamable adhesive sheet according to the present disclosure. [Figure 5] FIG. 2 is a schematic cross-sectional view showing another example of a foamable adhesive sheet according to the present disclosure. [Figure 6] FIG. 2 is a schematic cross-sectional view showing another example of a foamable adhesive sheet according to the present disclosure. [Figure 7] FIG. 2 is a schematic cross-sectional view showing another example of a foamable adhesive sheet according to the present disclosure. [Figure 8] FIG. 2 is a schematic cross-sectional view showing another example of a foamable adhesive sheet according to the present disclosure. [Figure 9] FIG. 2 is a schematic cross-sectional view showing another example of a foamable adhesive sheet according to the present disclosure. [Figure 10] FIG. 2 is a schematic cross-sectional view showing another example of a foamable adhesive sheet according to the present disclosure. [Figure 11] FIG. 2 is a schematic cross-sectional view showing another example of a foamable adhesive sheet according to the present disclosure. [Figure 12] FIG. 2 is a schematic cross-sectional view showing another example of a foamable adhesive sheet according to the present disclosure. [Figure 13] FIG. 2 is a schematic cross-sectional view showing another example of a foamable adhesive sheet according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0018] Embodiments of the present disclosure will be described below with reference to the drawings and the like. However, the present disclosure can be implemented in many different forms, and should not be construed as being limited to the description of the embodiments exemplified below. Furthermore, to clarify the explanation, the drawings may schematically depict the width, thickness, shape, etc. of each part compared to the actual form, but these are merely examples and are not intended to limit the interpretation of the present disclosure. Furthermore, in this specification and each drawing, elements similar to those previously described with reference to the preceding drawings will be designated by the same reference numerals, and detailed descriptions may be omitted as appropriate.

[0019] In this specification, when describing a mode in which another component is placed on a certain component, the term "above" or "below" is used, unless otherwise specified, to include both a case in which another component is placed directly above or below a certain component so as to be in contact with the component, and a case in which another component is placed above or below a certain component with another component interposed therebetween. Also, in this specification, when describing a mode in which another component is placed on the surface of a certain component, the term "on the surface" is used, unless otherwise specified, to include both a case in which another component is placed directly above or below a certain component so as to be in contact with the component, and a case in which another component is placed above or below a certain component with another component interposed therebetween.

[0020] In this specification, the term "sheet" also includes a member called a "film." The term "film" also includes a member called a "sheet."

[0021] The foamable adhesive sheet and the rotating electrical machine stator using the same according to the present disclosure will be described in detail below.

[0022] A. Foam adhesive sheet The foamable adhesive sheet of the present disclosure has a first adhesive layer, a substrate, and a second adhesive layer in this order, the first adhesive layer and the second adhesive layer containing a curable adhesive, at least one of the first adhesive layer and the second adhesive layer containing a foaming agent, and the first adhesive layer and the second adhesive layer having different properties from each other.

[0023] The foamable adhesive sheet of the present disclosure has five embodiments, each of which will be described below.

[0024] I. First embodiment A first embodiment of the foamable adhesive sheet of the present disclosure has, in this order, a first adhesive layer, a substrate, and a second adhesive layer, wherein the first adhesive layer and the second adhesive layer contain a curable adhesive, and at least one of the first adhesive layer and the second adhesive layer contains a foaming agent, the first adhesive layer and the second adhesive layer have different properties, and a fiber layer is disposed on the side of the first adhesive layer opposite the substrate or between the first adhesive layer and the substrate, and when the fiber layer is disposed on the side of the first adhesive layer opposite the substrate, the first adhesive layer contains the foaming agent.

[0025] The foamable adhesive sheet of this embodiment has two configurations: a first example in which a fiber layer is disposed on the surface of the first adhesive layer opposite the substrate, and a second example in which a fiber layer is disposed between the first adhesive layer and the substrate. Each configuration will be explained below.

[0026] 1. First Example of First Embodiment A first example of the first embodiment of the foamable adhesive sheet of the present disclosure has a first adhesive layer, a substrate, and a second adhesive layer in that order, the first adhesive layer and the second adhesive layer contain a curable adhesive, at least the first adhesive layer of the first adhesive layer and the second adhesive layer contains a foaming agent, the first adhesive layer and the second adhesive layer have different properties from each other, and a fiber layer is arranged on the side of the first adhesive layer opposite the substrate.

[0027] Fig. 1 is a schematic cross-sectional view illustrating an example of a foamable adhesive sheet of this embodiment. The foamable adhesive sheet 10 in Fig. 1 has a first adhesive layer 1a, a substrate 2, and a second adhesive layer 1b, in that order, with a fiber layer 3 disposed on the surface of first adhesive layer 1a opposite to substrate 2. First adhesive layer 1a and second adhesive layer 1b contain a curable adhesive, and of first adhesive layer 1a and second adhesive layer 1b, at least first adhesive layer 1a contains a foaming agent, and first adhesive layer 1a and second adhesive layer 1b have different properties.

[0028] In this embodiment, because the fiber layer is disposed on the side of the first adhesive layer opposite the substrate, it is easy to distinguish between the side facing the first adhesive layer and the side facing the second adhesive layer by, for example, visual or tactile observation, which prevents operational errors when using the foamable adhesive sheet.

[0029] Furthermore, in this embodiment, because a fiber layer is disposed on the side of the first adhesive layer opposite the substrate, after the foamable adhesive sheet of this embodiment is placed between the stator core and coil of a rotating electrical machine stator and foamed and cured to bond the stator core and coil, it is possible to easily distinguish between the side of the foamed and cured adhesive sheet facing the first adhesive layer and the side of the second adhesive layer by observing it visually, with an optical microscope, or with an electron microscope, for example. This makes it possible to identify the cause of a failure due to incorrectly positioning the foamable adhesive sheet on the front and back, and to discover such a failure cause early on.

[0030] In this manner, in this embodiment, it is possible to distinguish between the surface on the first adhesive layer side and the surface on the second adhesive layer side not only for the foamable adhesive sheet before it has foamed and hardened, but also for the adhesive sheet after it has foamed and hardened after being incorporated into a rotating electric machine.

[0031] In this embodiment, the fiber layer is disposed on the surface of the first adhesive layer opposite the substrate, making the surface on the first adhesive layer non-tacky (tack-free). This allows for a foamable adhesive sheet with good blocking resistance and slipperiness. This improves the handleability and workability of the foamable adhesive sheet. Specifically, the fiber layer is disposed on the surface of the first adhesive layer opposite the substrate, making the stickiness of the surface on the first adhesive layer lower than the stickiness of the surface on the second adhesive layer, thereby making the slipperiness of the surface on the first adhesive layer higher than the slipperiness of the surface on the second adhesive layer. For example, when placing a foam adhesive sheet in a slot of a stator core and then placing a coil in the slot of the stator core, by placing the foam adhesive sheet so that the surface on the first adhesive layer side faces the coil and the surface on the second adhesive layer side faces the stator core, when the foam adhesive sheet is placed in the slot of the stator core, the surface on the second adhesive layer side has better adhesion, making it less likely for the foam adhesive sheet to shift position relative to the stator core, and when placing a coil in the slot of the stator core, the surface on the first adhesive layer side is non-adhesive and has good slip properties, so the coil can be smoothly inserted into the narrower gap created by inserting the foam adhesive sheet into the slot of the stator core.

[0032] In this embodiment, the fiber layer allows the curable adhesive to penetrate or permeate the first adhesive layer when the first adhesive layer is foamed. Therefore, when the first adhesive layer is foamed, the curable adhesive can reach the outermost surface of the foamable adhesive sheet, allowing the surface on the first adhesive layer side to have adhesive strength. Therefore, even if a fiber layer is disposed on the side of the first adhesive layer opposite the substrate, it is possible to bond the stator core and coil. Furthermore, by disposing a fiber layer on the side of the first adhesive layer opposite the substrate, it is possible to prevent the first adhesive layer from spreading in the planar direction when foamed.

[0033] Each component of the foamable adhesive sheet of this embodiment will be described below.

[0034] (1) Fiber layer In this embodiment, the fibrous layer is disposed on the surface of the first adhesive layer opposite the substrate.

[0035] Examples of the form of the fiber layer include nonwoven fabric, paper, felt, knitted fabric, and woven fabric.

[0036] Examples of fibers that may be used to form the fiber layer include 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.

[0037] The density of the fiber layer is not particularly limited as long as it allows the hardening adhesive to pass through or penetrate when the first adhesive layer foams and expands, and may be, for example, 200 g / cm 3 less than or equal to 100 g / cm 3 It may be less than 50 g / cm 3 If the density of the fiber layer is too high, the voids in the fiber layer will be small, making it difficult for the curable adhesive to penetrate or permeate the first adhesive layer when it is foamed, and there is a possibility that sufficient adhesive strength will not be obtained after the first adhesive layer is foamed and cured. On the other hand, the density of the fiber layer may be, for example, 3 g / cm 3 More than 5g / cm 3 It may be more than 7 g / cm 3 If the density of the fiber layer is too low, it may be difficult to distinguish by touch.

[0038] Here, the density of the fiber layer (g / cm 3 ) is the basis weight of the fiber layer (g / cm 2 ) by the thickness of the fiber layer (cm).

[0039] The basis weight of the fiber layer can be measured by the following method. First, ten test pieces of the fiber layer, each measuring 100 mm x 100 mm, are taken, and the mass (g) of each test piece is measured. Next, the mass (g) of each test piece is multiplied by the area (cm) of each test piece.2 ) to obtain the basis weight (g / cm 2 ) is calculated. The average value of the basis weights of the 10 test pieces is calculated, and this average value is used as the basis weight.

[0040] The thickness of the fiber layer can be the average value of thicknesses measured at any 10 locations on a cross section of the foamable adhesive sheet in the thickness direction as observed with a transmission electron microscope (TEM), a scanning electron microscope (SEM), or a scanning transmission electron microscope (STEM).

[0041] The density of the fiber layer can be adjusted by the manufacturing method and manufacturing conditions of the fiber layer.

[0042] The thickness of the fiber layer is not particularly limited as long as it allows the curable adhesive to permeate or penetrate when the first adhesive layer foams and expands, and may be, for example, 100 μm or less, 80 μm or less, or 60 μm or less. If the fiber layer is too thick, the amount of curable adhesive that permeates or penetrates the first adhesive layer during foaming may be reduced, potentially reducing the adhesive strength of the first adhesive layer after foaming and curing. On the other hand, the thickness of the fiber layer may be, for example, 6 μm or more, 8 μm or more, or 10 μm or more. If the fiber layer is too thin, blocking may occur when the material is processed into a roll. Furthermore, it may be difficult to distinguish the thickness by cross-sectional observation.

[0043] Methods for placing a fiber layer on the side of the first adhesive layer opposite the substrate include, for example, a method of attaching the fiber layer by utilizing the adhesiveness of the first adhesive layer, a method of attaching the fiber layer to the first adhesive layer via a layer having adhesive properties different from the first adhesive layer, a method of applying a solvent-diluted adhesive composition onto the fiber layer and drying it, a method of heat-laminating the first adhesive layer and the fiber layer, or a combination of these methods.

[0044] (2) First adhesive layer and second adhesive layer In this embodiment, the first adhesive layer and the second adhesive layer contain a curable adhesive, and at least the first adhesive layer contains a foaming agent, and the first adhesive layer and the second adhesive layer have different properties.

[0045] (a) Materials for the first adhesive layer and the second adhesive layer (i) Foaming agent In this embodiment, of the first adhesive layer and the second adhesive layer, at least the first adhesive layer needs to contain a foaming agent; for example, only the first adhesive layer may contain a foaming agent, or both the first adhesive layer and the second adhesive layer may contain a foaming agent.

[0046] The foaming agent in this embodiment is not particularly limited and may be any foaming agent generally used in adhesive layers of foamable adhesive sheets, such as a foaming agent that undergoes a foaming reaction when exposed to heat.

[0047] The foaming initiation temperature of the foaming agent is preferably equal to or higher than the softening temperature of the base agent of the curable adhesive, such as an epoxy resin, and equal to or lower than the activation temperature of the curing reaction of the base agent of the curable adhesive, such as an epoxy resin. The foaming initiation temperature of the foaming agent is, for example, 70°C or higher, and may be 100°C or higher. If the foaming initiation temperature is too low, the reaction may start early, causing foaming to occur in a state where the flexibility and fluidity of the resin component are low, making it difficult to achieve uniform foaming. On the other hand, the foaming initiation temperature of the foaming agent is, for example, 210°C or lower. If the foaming initiation temperature is too high, the resin component may deteriorate.

[0048] The softening temperature of the base agent of a curable adhesive such as an epoxy resin can be measured using the ring and ball softening temperature test method specified in JIS K 2207.

[0049] The foaming agent may be, for example, a microcapsule type foaming agent, which preferably has a core made of a thermal expansion agent such as hydrocarbon and a shell made of a resin such as acrylonitrile copolymer.

[0050] In addition, organic blowing agents and inorganic blowing agents may be used as the blowing agent. Examples of organic blowing agents include azo blowing agents such as azodicarbonamide (ADCA), azobisformamide, and azobisisobutyronitrile; fluorinated alkane blowing agents such as trichloromonofluoromethane; hydrazine blowing agents such as paratoluenesulfonylhydrazide; semicarbazide blowing agents such as p-toluenesulfonylsemicarbazide; triazole blowing agents such as 5-morpholyl-1,2,3,4-thiatriazole; and N-nitroso blowing agents such as N,N-dinitrosoterephthalamide. On the other hand, examples of inorganic blowing agents include ammonium carbonate, ammonium bicarbonate, ammonium nitrite, ammonium borohydride, and azides.

[0051] The foaming agent may be used alone or in combination of two or more kinds.

[0052] The foaming agents contained in the first adhesive layer and the second adhesive layer may be the same or different from each other.

[0053] The content of the foaming agent is appropriately set depending on the desired expansion ratio and the strength and adhesive force required for the first adhesive layer and second adhesive layer after foaming and curing. The content of the foaming agent is, for example, 0.5 parts by mass or more, and may be 2 parts by mass or more, per 100 parts by mass of the resin component contained in the first adhesive layer or second adhesive layer. On the other hand, the content of the foaming agent is, for example, 25 parts by mass or less, or may be 20 parts by mass or less, or may be 15 parts by mass or less, per 100 parts by mass of the resin component contained in the first adhesive layer or second adhesive layer. Furthermore, the contents of the foaming agent in the first adhesive layer and the second adhesive layer may be the same or different from each other.

[0054] (ii) curable adhesive The curable adhesive contained in the adhesive layer in this embodiment is not particularly limited as long as it can bond the stator core and the coil, and any curable adhesive generally used in adhesive layers of foamable adhesive sheets can be used, such as a heat-curable adhesive.

[0055] Examples of curable adhesives include epoxy resin adhesives, acrylic resin adhesives, phenolic resin adhesives, unsaturated polyester resin adhesives, alkyd resin adhesives, urethane resin adhesives, and thermosetting polyimide resin adhesives.

[0056] Among them, the curable adhesive is preferably an epoxy resin adhesive. That is, the curable adhesive preferably contains an epoxy resin and a curing agent. Epoxy resin adhesives generally have excellent mechanical strength, heat resistance, insulating properties, chemical resistance, etc., and have little shrinkage upon curing, making them suitable for use in bonding stator cores and coils.

[0057] An example in which the curable adhesive is an epoxy resin adhesive will be described below.

[0058] (epoxy resin) The epoxy resin in this embodiment is a compound that has at least one epoxy group or glycidyl group and cures by crosslinking polymerization in combination with a curing agent. The epoxy resin also includes a monomer having at least one epoxy group or glycidyl group.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] The epoxy resins contained in the first adhesive layer and the second adhesive layer may be the same or different from each other.

[0063] (acrylic resin) When the curable adhesive is an epoxy-based adhesive, it may further contain an acrylic resin that is compatible with the epoxy resin. Because the acrylic resin is compatible with the epoxy resin, it is likely to improve the toughness of the adhesive layer. As a result, the adhesiveness after foaming and curing can be improved. Furthermore, the acrylic resin acts as a compatibilizer for the foaming agent (e.g., a foaming agent whose shell is an acrylonitrile copolymer resin), uniformly dispersing and foaming, which is thought to improve the adhesiveness after foaming and curing. The flexibility of the acrylic resin can be exhibited, improving the adhesion of the first adhesive layer and the second adhesive layer to the substrate. Furthermore, the compatibility of the acrylic resin with the epoxy resin can maintain high surface hardness of the first adhesive layer and the second adhesive layer. On the other hand, if the acrylic resin is incompatible with the epoxy resin, a flexible portion is formed on the surface of the first adhesive layer and the second adhesive layer, making the interface with the adherend less slippery and reducing workability.

[0064] Only one of the first adhesive layer and the second adhesive layer may contain an acrylic resin, or both may contain an acrylic resin.

[0065] The acrylic resin in this embodiment is compatible with the epoxy resin. The compatibility of the acrylic resin with the epoxy resin can be confirmed, for example, by observing the cross sections of the first and second adhesive layers of the foamable adhesive sheet with a scanning electron microscope (SEM) or a transmission electron microscope (TEM) and finding no micron-sized islands. More specifically, the average particle size of the islands is preferably 1 μm or less. In particular, the average particle size of the islands may be 0.5 μm or less, or even 0.3 μm or less. A large number of samples is preferred, for example, 100 or more. The area to be observed is within a range of 100 μm × 100 μm, or, if the thickness of the first and second adhesive layers is 100 μm or less, within a range of the thickness × 100 μm.

[0066] The acrylic resin may have a polar group, such as an epoxy group, a hydroxyl group, a carboxyl group, a nitrile group, or an amide group.

[0067] The acrylic resin is a homopolymer of an acrylic acid ester monomer, and may be a mixed component containing two or more of the above homopolymers, or may be a copolymer of two or more acrylic acid ester monomers and may be a component containing one or more copolymers. The acrylic resin may also be a mixed component of the above homopolymer and the above copolymer. The acrylic acid ester monomer "acrylic acid" also includes the concept of methacrylic acid. Specifically, the acrylic resin may be a mixture of a methacrylate polymer and an acrylate polymer, or may be an acrylic acid ester polymer such as acrylate-acrylate, methacrylate-methacrylate, or methacrylate-acrylate. In particular, the acrylic resin preferably contains a copolymer of two or more acrylic acid ester monomers (a (meth)acrylic acid ester copolymer).

[0068] Examples of the monomer component constituting the (meth)acrylic acid ester copolymer include the monomer components described in JP 2014-065889 A. The monomer component may have the polar group described above. Examples of the (meth)acrylic acid ester copolymer include an ethyl acrylate-butyl acrylate-acrylonitrile copolymer, an ethyl acrylate-acrylonitrile copolymer, and a butyl acrylate-acrylonitrile copolymer. Note that "acrylic acid" such as methyl acrylate and ethyl acrylate also includes "methacrylic acid" such as methyl methacrylate and ethyl methacrylate.

[0069] The (meth)acrylic acid ester copolymer is preferably a block copolymer, and more preferably an acrylic block copolymer such as a methacrylate-acrylate copolymer. Examples of (meth)acrylates constituting the acrylic block copolymer include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, and benzidyl acrylate. In these examples, "acrylic acid" also includes "methacrylic acid."

[0070] Specific examples of methacrylate-acrylate copolymers include acrylic copolymers such as methyl methacrylate-butyl acrylate-methyl methacrylate (MMA-BA-MMA) copolymer, which also includes block copolymers of polymethyl methacrylate-polybutyl acrylate-polymethyl methacrylate (PMMA-PBA-PMMA).

[0071] The acrylic copolymer may have no polar groups, or may be a modified product in which the above-mentioned polar groups have been partially introduced. The modified product is highly compatible with epoxy resins, thereby further improving adhesion.

[0072] Among these, the acrylic resin is preferably a (meth)acrylic acid ester copolymer having a first polymer portion having a glass transition temperature (Tg) of 10°C or lower and a second polymer portion having a glass transition temperature (Tg) of 20°C or higher. Such a (meth)acrylic acid ester copolymer has a first polymer portion that forms a soft segment and a second polymer portion that forms a hard segment. By adding such a copolymer, the toughness of the first adhesive layer and the second adhesive layer after curing can be improved, thereby further increasing the adhesive strength.

[0073] The manifestation of the above-mentioned effect can be presumed as follows: By using an acrylic resin having both a soft segment and a hard segment, such as the above-mentioned (meth)acrylic acid ester copolymer, the hard segment contributes to heat resistance, and the soft segment contributes to toughness or flexibility, so that a first adhesive layer and a second adhesive layer having good heat resistance, toughness, and flexibility can be obtained.

[0074] At least one of the first polymer portion and the second polymer portion contained in the (meth)acrylic acid ester copolymer has compatibility with epoxy resins. When the first polymer portion has compatibility with epoxy resins, flexibility can be increased. Furthermore, when the second polymer portion has compatibility with epoxy resins, cohesion and toughness can be increased.

[0075] The (meth)acrylic acid ester copolymer is preferably a block copolymer, and more preferably an ABA block copolymer in which a compatible portion is polymer block A and an incompatible portion is polymer block B. Furthermore, an ABA block copolymer in which a first polymer portion is an incompatible portion and a second polymer portion is a compatible portion, and in which the first polymer portion is polymer block B and the second polymer portion is polymer block A is more preferred.

[0076] The (meth)acrylic acid ester copolymer may be a modified product in which the above-mentioned polar group is introduced into a part of the first polymer segment or the second polymer segment.

[0077] A specific example of the (meth)acrylic acid ester copolymer having the first polymer portion and the second polymer portion is the MMA-BA-MMA copolymer.

[0078] The acrylic resins contained in the first adhesive layer and the second adhesive layer may be the same or different from each other.

[0079] The content of the acrylic resin may be, for example, 1 part by mass or more, 3 parts by mass or more, 5 parts by mass or more, 7 parts by mass or more, or 10 parts by mass or more, based on 100 parts by mass of the resin components contained in the first adhesive layer or the second adhesive layer. If the content of the acrylic resin is too low, the adhesiveness after foaming and curing and the adhesion of the first adhesive layer or the second adhesive layer to the substrate may be reduced. On the other hand, the content of the acrylic resin may be, for example, 60 parts by mass or less, 50 parts by mass or less, 40 parts by mass or less, 35 parts by mass or less, or 30 parts by mass or less, based on 100 parts by mass of the resin components contained in the first adhesive layer or the second adhesive layer. If the content of the acrylic resin is too high, the film strength may be reduced. Furthermore, the content of the acrylic resin in the first adhesive layer and the second adhesive layer may be the same or different from each other.

[0080] (hardening agent) The curing agent in this embodiment is not particularly limited and may be any curing agent that is generally used in epoxy resin adhesives.

[0081] The curing agent is preferably solid at 23°C. A curing agent that is solid at 23°C can have a longer storage stability (pot life) than a curing agent that is liquid at 23°C. The curing agent may be a latent curing agent. A curing agent that undergoes a curing reaction by heat can be used as the curing agent. One type of curing agent may be used alone, or two or more types may be used.

[0082] The reaction initiation temperature of the curing agent is, for example, 110°C or higher, and may be 130°C or higher. If the reaction initiation temperature is too low, the reaction will start early, and curing will occur with low flexibility and fluidity of the resin component, making it difficult to achieve uniform curing. On the other hand, the reaction initiation temperature of the curing agent is, for example, 200°C or lower. If the reaction initiation temperature is too high, the resin component may deteriorate. Note that when a highly heat-resistant resin such as a phenolic resin is used in addition to the epoxy resin, the resin component will deteriorate less, and the reaction initiation temperature of the curing agent may be, for example, 300°C or lower. The reaction initiation temperature of the curing agent can be determined by differential scanning calorimetry (DSC).

[0083] 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.

[0084] Examples of imidazole-based curing agents include imidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2-methylimidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole, 2-isopropylimidazole, and 2-phenylimidazole, as well as carboxylic acid salts of imidazole compounds and adducts with epoxy compounds. Furthermore, it is preferable that the imidazole-based curing agent has a hydroxyl group. Crystallization occurs due to hydrogen bonding between the hydroxyl groups, which tends to increase the reaction initiation temperature.

[0085] Examples of phenolic curing agents include phenolic resins. Further examples of phenolic resins include resol-type phenolic resins and novolac-type phenolic resins. From the viewpoint of adhesion of the adhesive layer to the substrate, phenolic-type novolac resins having a Tg of 110°C or less are particularly preferred. Furthermore, phenolic curing agents and imidazole-type curing agents may be used in combination. In this case, it is preferable to use an imidazole-type curing agent as a curing catalyst.

[0086] Examples of amine-based curing agents include aliphatic amines such as diethylenetriamine (DETA), triethylenetetramine (TETA), and metaxylylenediamine (MXDA); aromatic amines such as diaminodiphenylmethane (DDM), m-phenylenediamine (MPDA), and diaminodiphenylsulfone (DDS); alicyclic amines; and polyamidoamines. Furthermore, examples of amine-based curing agents that can be used include dicyandiamide-based curing agents such as dicyandiamide (DICY), organic acid dihydrazide-based curing agents, amine adduct-based curing agents, and ketimine-based curing agents.

[0087] Examples of acid anhydride curing agents include alicyclic acid anhydrides (liquid acid anhydrides) such as hexahydrophthalic anhydride (HHPA) and methyltetrahydrophthalic anhydride (MTHPA); and aromatic acid anhydrides such as trimellitic anhydride (TMA), pyromellitic anhydride (PMDA), and benzophenonetetracarboxylic acid (BTDA).

[0088] The isocyanate curing agent may, for example, be a blocked isocyanate.

[0089] Examples of thiol-based curing agents include ester-bonded thiol compounds, aliphatic ether-bonded thiol compounds, and aromatic ether-bonded thiol compounds.

[0090] The curing agents contained in the first adhesive layer and the second adhesive layer may be the same or different from each other.

[0091] The content of the curing agent is, for example, 1 part by mass or more and 40 parts by mass or less, based on 100 parts by mass of the resin component contained in the first adhesive layer or the second adhesive layer. For example, when an imidazole-based curing agent is used as the main curing agent, the content of the curing agent is preferably, for example, 1 part by mass or more and 15 parts by mass or less, based on 100 parts by mass of the resin component contained in the first adhesive layer or the second adhesive layer. On the other hand, when a phenol-based curing agent is used as the main curing agent, the content of the curing agent is preferably, for example, 5 parts by mass or more and 40 parts by mass or less, based on 100 parts by mass of the resin component contained in the first adhesive layer or the second adhesive layer. Note that using an imidazole-based curing agent or a phenol-based curing agent as the main curing agent means that the mass proportion of the imidazole-based curing agent or the phenol-based curing agent is the highest in the curing agent. Furthermore, the content of the curing agent in the first adhesive layer and the second adhesive layer may be the same or different.

[0092] (iii) Other ingredients In this embodiment, when the curable adhesive is an epoxy resin adhesive, the first adhesive layer and the second adhesive layer may further contain, as a resin component, a resin other than the above-mentioned epoxy resin and acrylic resin, such as a urethane resin.

[0093] The total proportion of epoxy resin and acrylic resin relative to the resin components contained in the first adhesive layer and the second adhesive layer is, for example, 70% by mass or more, or may be 80% by mass or more, or 90% by mass or more, or may be 100% by mass.

[0094] The content of the resin component contained in the first adhesive layer and the second adhesive layer is, for example, 60% by mass or more, or may be 70% by mass or more, or 80% by mass or more, or may be 90% by mass or more.

[0095] The first adhesive layer and the second adhesive layer may contain, as needed, for example, a silane coupling agent, a filler, an antioxidant, a light stabilizer, an ultraviolet absorber, a lubricant, a plasticizer, an antistatic agent, a crosslinking agent, and a colorant. Examples of silane coupling agents include epoxy-based silane coupling agents. Examples of antioxidants include phenol-based antioxidants and sulfur-based antioxidants. The filler will be described in detail in the third embodiment below.

[0096] (b) Characteristics of the first adhesive layer and the second adhesive layer In this embodiment, the first adhesive layer and the second adhesive layer have different properties. The different properties of the first adhesive layer and the second adhesive layer are appropriately selected depending on the properties required for the adhesive layer disposed on the stator core side and the adhesive layer disposed on the coil side, respectively. Specific examples include foaming properties such as foaming ratio and foaming initiation temperature of the foaming agent (including no foaming at all); surface properties such as adhesion, friction coefficient, and surface hardness; melt viscosity, pattern shape, and thickness.

[0097] The first adhesive layer and the second adhesive layer can be expanded at an expansion ratio of, for example, 1.5 to 15. The expansion ratio may be, for example, 3 to 10. The expansion ratios of the first adhesive layer and the second adhesive layer may be the same or different from each other.

[0098] Here, the expansion ratio can be calculated by the following formula. Foaming ratio (times) = adhesive layer thickness after foaming and hardening / adhesive layer thickness before foaming and hardening

[0099] The expansion ratio of the first adhesive layer and the second adhesive layer can be controlled, for example, by adjusting the composition of the first adhesive layer and the second adhesive layer. Specifically, the expansion ratio can be adjusted by appropriately selecting the type of foaming agent. The expansion ratio can also be increased by increasing the content of the foaming agent. The expansion ratio can also be increased by decreasing the melt viscosity of the resin, while the expansion ratio can be decreased by increasing the melt viscosity of the resin.

[0100] The adhesive strength of the first adhesive layer and the second adhesive layer is appropriately set according to the adhesiveness required for the adhesive layer disposed on the stator core side and the adhesive layer disposed on the coil side, respectively. In particular, the second adhesive layer is preferably substantially non-tacky (tack-free). In this case, it is preferable that the second adhesive layer is disposed as the outermost surface. In this embodiment, a fiber layer is disposed on the surface of the first adhesive layer opposite the substrate, so that the surface of the foamable adhesive sheet facing the fiber layer can be made non-tacky. Furthermore, since the second adhesive layer is substantially non-tacky, the surface of the foamable adhesive sheet facing the second adhesive layer can also be made non-tacky. This allows for a foamable adhesive sheet with good slip properties and blocking resistance. This improves the handleability and workability of the foamable adhesive sheet.

[0101] Here, non-tacky is generally used mainly to mean low adhesive strength, and in the present disclosure, "non-tacky" refers to a state in which the foamable adhesive sheet can be wound into a roll and then easily unwound without resistance.

[0102] When the second adhesive layer is substantially non-adhesive, specifically, the adhesive strength of the second adhesive layer is preferably 0 N / 25 mm or more and 0.1 N / 25 mm or less. By having the adhesive strength of the second adhesive layer within the above range, the second adhesive layer can be made substantially non-adhesive.

[0103] The adhesive strength of the second adhesive layer can be measured in accordance with JIS Z0237:2009 (Test methods for adhesive tapes and adhesive sheets) and Method 1 of the adhesive strength test method (a test method in which the tape or sheet is peeled off at an angle of 180° from a stainless steel test plate at a temperature of 23°C and a humidity of 50%).

[0104] The adhesive strength of the second adhesive layer can be adjusted to a predetermined value or less by, for example, adjusting the composition of the second adhesive layer. Specifically, the adhesiveness of the second adhesive layer can be reduced by using a base agent that is solid at room temperature or a curing agent that is solid at room temperature. The adhesiveness of the second adhesive layer can also be reduced by adding a base agent with a high softening temperature or a base agent with a low weight-average molecular weight. In the case of an epoxy resin-based adhesive, the adhesiveness of the second adhesive layer can be reduced by adding an acrylic resin that is compatible with the epoxy resin. The adhesiveness of the second adhesive layer can also be reduced by adding a filler.

[0105] The friction coefficients of the first and second adhesive layers are set appropriately according to the surface characteristics required for the adhesive layer disposed on the stator core side and the adhesive layer disposed on the coil side, respectively. The smaller the friction coefficient, the better the sliding and insertion properties can be.

[0106] The coefficient of friction of the surfaces of the first adhesive layer and the second adhesive layer can be controlled, for example, by adjusting the composition of the first adhesive layer and the second adhesive layer or by adjusting the surface hardness of the first adhesive layer and the second adhesive layer. Specifically, the coefficient of friction can be controlled by the average particle size and content of the foaming agent contained in the first adhesive layer and the second adhesive layer, and the average particle size and content of the filler contained in the first adhesive layer and the second adhesive layer. More specifically, the coefficient of friction tends to decrease as the average particle size of the foaming agent increases. Furthermore, the coefficient of friction tends to decrease as the foaming agent content increases. Furthermore, the coefficient of friction tends to decrease as the average particle size of the filler increases. Furthermore, the coefficient of friction tends to decrease as the filler content increases. Furthermore, the coefficient of friction also decreases as the surface hardness increases.

[0107] The surface hardness of the first adhesive layer and the second adhesive layer is set appropriately according to the surface characteristics required for the adhesive layer disposed on the stator core side and the adhesive layer disposed on the coil side, respectively. For example, pencil hardness can be used as the surface hardness. The higher the surface hardness, the better the sliding property and insertion property.

[0108] The surface hardness of the first adhesive layer and the second adhesive layer can be controlled, for example, by the composition of the first adhesive layer and the second adhesive layer. Specifically, the surface hardness can be controlled by the average particle size and content of the foaming agent, the average particle size and content of the filler, etc. More specifically, the surface hardness can be increased by increasing the average particle size of the foaming agent. The surface hardness can also be increased by increasing the content of the foaming agent. The surface hardness can also be increased by increasing the average particle size of the filler. The surface hardness can also be increased by increasing the content of the filler. Furthermore, the surface hardness can be increased, for example, by including a component having a rigid structure. Specifically, in the case of an epoxy resin-based adhesive, an example of a component having a rigid structure is a phenolic resin.

[0109] (c) Configuration of the first adhesive layer and the second adhesive layer The thickness of the first adhesive layer and the second adhesive layer is not particularly limited, but may be, for example, 10 μm or more, or 20 μm or more. If the first adhesive layer and the second adhesive layer are too thin, sufficient adhesion may not be obtained after foaming and curing. On the other hand, the thickness of the first adhesive layer and the second adhesive layer is, for example, 200 μm or less. Furthermore, the thickness of the first adhesive layer and the second adhesive layer may be the same or different from each other.

[0110] Here, the thickness of the first adhesive layer and the second adhesive layer can be the average value of thicknesses measured at any 10 locations on a cross section of the foamable adhesive sheet in the thickness direction observed with a transmission electron microscope (TEM), a scanning electron microscope (SEM), or a scanning transmission electron microscope (STEM). The same method can be used to measure the thickness of other layers of the foamable adhesive sheet.

[0111] The first adhesive layer and the second adhesive layer may be continuous or discontinuous. Examples of discontinuous layers include stripes and dots. The surfaces of the first adhesive layer and the second adhesive layer may have an uneven shape such as an embossed shape.

[0112] The first adhesive layer and the second adhesive layer can be formed, for example, by applying an adhesive composition containing the above-mentioned curable adhesive and a foaming agent, etc., and then removing the solvent. Examples of application methods include roll coating, reverse roll coating, transfer roll coating, gravure coating, gravure reverse coating, comma coating, rod coating, blade coating, bar coating, wire bar coating, die coating, lip coating, and dip coating.

[0113] The adhesive composition may or may not contain a solvent. In this specification, the term "solvent" is used in a broad sense to include not only a strict solvent (a solvent that dissolves a solute) but also a dispersion medium. The solvent contained in the adhesive composition is volatilized and removed when the adhesive composition is applied and dried to form an adhesive layer.

[0114] The adhesive composition can be obtained by mixing the above-mentioned components and kneading and dispersing them as necessary. As a mixing and dispersing method, a general kneading disperser, such as a two-roll mill, a three-roll mill, a pebble mill, a tron ​​mill, a Szegvari attritor, a high-speed impeller disperser, a high-speed stone mill, a high-speed impact mill, a desper, a high-speed mixer, a ribbon blender, a co-kneader, an intensive mixer, a tumbler, a blender, a desperzer, a homogenizer, or an ultrasonic disperser, can be used.

[0115] (3) Base material The substrate in this embodiment is a member that supports the first adhesive layer and the second adhesive layer.

[0116] The substrate preferably has insulating properties. The substrate is preferably in the form of a sheet. The substrate may have a single-layer structure or a multi-layer structure. The substrate may or may not have a porous structure inside.

[0117] Examples of the substrate include a resin substrate, a nonwoven fabric, paper, or a multi-layer thereof.

[0118] Examples of resins contained in the resin substrate include polyester resins such as polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate (PEN), and aromatic polyester; polycarbonate; polyarylate; polyurethane; polyamide resins such as polyamide and polyetheramide; polyimide resins such as polyimide, polyetherimide, and polyamideimide; polysulfone resins such as polysulfone and polyethersulfone; polyetherketone resins such as polyetherketone and polyetheretherketone; polyphenylene sulfide (PPS); and modified polyphenylene oxide. The glass transition temperature of the resin is, for example, 80°C or higher, or may be 140°C or higher, or even 200°C or higher. Furthermore, a liquid crystal polymer (LCP) may be used as the resin.

[0119] Examples of nonwoven fabrics 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.

[0120] The substrate may be surface-treated to enhance adhesion to the first adhesive layer and the second adhesive layer.

[0121] The thickness of the substrate is not particularly limited, but may be, for example, 2 μm or more, 5 μm or more, or 9 μm or more, and may be, for example, 200 μm or less, 100 μm or less, or 50 μm or less.

[0122] (4) First primer layer and second primer layer The foamable adhesive sheet of this embodiment may have a first primer layer between the substrate and the first adhesive layer, or may have a second primer layer between the substrate and the second adhesive layer. The presence of the first primer layer or the second primer layer can improve the adhesion of the first adhesive layer or the second adhesive layer to the substrate. Furthermore, the presence of the first primer layer or the second primer layer can, for example, reduce stress on the bent portion when the foamable adhesive sheet is folded, or reduce stress on the cut portion when the foamable adhesive sheet is cut. As a result, lifting or peeling of the first adhesive layer or the second adhesive layer from the substrate can be suppressed when the foamable adhesive sheet is bent or cut.

[0123] For example, in the foamable adhesive sheet 10 shown in Fig. 2, a first primer layer 4a is disposed between the substrate 2 and the first adhesive layer 1a, and a second primer layer 4b is disposed between the substrate 2 and the second adhesive layer 1b. Although the foamable adhesive sheet 10 in Fig. 2 has both the first primer layer 4a and the second primer layer 4b, it may have only one of them.

[0124] The first primer layer may be disposed only between the substrate and the first adhesive layer, the second primer layer may be disposed only between the substrate and the second adhesive layer, or the first primer layer may be disposed between the substrate and the first adhesive layer and the second primer layer may be disposed between the substrate and the second adhesive layer. Of these, it is preferable that the first primer layer be disposed between the substrate and the first adhesive layer and the second primer layer be disposed between the substrate and the second adhesive layer.

[0125] The materials contained in the first primer layer and the second primer layer are not particularly limited as long as they can increase the adhesion between the substrate and the first adhesive layer or the second adhesive layer and can relieve stress, and are appropriately selected depending on the materials of the substrate and the first adhesive layer or the second adhesive layer, etc. Examples include polyester, polyvinyl chloride, polyvinyl acetate, polyurethane, polymers obtained by copolymerizing at least two or more of these, crosslinked products thereof, and mixtures thereof.

[0126] The crosslinked product is a crosslinked product obtained by crosslinking the above resin with a curing agent. Examples of the curing agent include an isocyanate-based curing agent. Furthermore, for example, when the reactive group / NCO equivalent is 1, it is preferable to add the isocyanate-based curing agent in a ratio of 0.5% by mass or more to 20% by mass or less relative to the resin.

[0127] In particular, the first primer layer and the second primer layer preferably contain a crosslinked resin. A crosslinked resin refers to a resin that does not melt even at high temperatures. This improves adhesive strength at high temperatures, i.e., heat resistance. Furthermore, if the crosslinked resin is crosslinked with, for example, an isocyanate-based curing agent, the flexibility of the first primer layer and the second primer layer is improved, preventing cracking of the adhesive layer and lifting and peeling of the adhesive layer from the substrate when the foamable adhesive sheet is bent.

[0128] Examples of crosslinked resins include the crosslinked resins described above. Among these, the first primer layer and the second primer layer preferably contain a crosslinked polyester resin. When the first primer layer and the second primer layer contain a crosslinked polyester resin, the adhesion between the substrate and the first adhesive layer or the second adhesive layer tends to be enhanced.

[0129] The crosslinked polyester resin is a crosslinked product of polyester, a copolymer containing polyester, or a mixture containing polyester. Specifically, it is a crosslinked product obtained by crosslinking polyester, a copolymer containing polyester, or a mixture containing polyester with a curing agent. Examples of polyesters include polyester polyols. Examples of curing agents include isocyanate-based curing agents. The amount of curing agent added is as described above.

[0130] The thickness of the first primer layer and the second primer layer is not particularly limited, but may be, for example, 0.1 μm or more, 0.2 μm or more, or 0.5 μm or more. If the first primer layer or the second primer layer is too thin, the effect of suppressing peeling of the adhesive layer from the substrate when the foamable adhesive sheet is bent or cut may not be sufficiently obtained. On the other hand, the thickness of the first primer layer and the second primer layer is, for example, 10 μm or less. Since the first primer layer and the second primer layer themselves usually do not have high heat resistance, if the first primer layer or the second primer layer is too thick, heat resistance (adhesive strength at high temperatures) may be reduced.

[0131] The first primer layer and the second primer layer can be formed, for example, by applying a resin composition and removing the solvent. Examples of the application method include roll coating, reverse roll coating, transfer roll coating, gravure coating, gravure reverse coating, comma coating, rod coating, blade coating, bar coating, wire bar coating, die coating, lip coating, and dip coating.

[0132] (5) Foam adhesive sheet The thickness of the foamable adhesive sheet of this embodiment is, for example, 10 μm or more, and may be 20 μm or more, while the thickness of the foamable adhesive sheet is, for example, 1000 μm or less, and may be 500 μm or less.

[0133] The foamable adhesive sheet of this embodiment preferably has good shape retention. The bending moment based on JIS P 8125 is, for example, 40 gf·cm or more, and may be 50 gf·cm or more. On the other hand, the bending moment is, for example, 600 gf·cm or less, and may be 150 gf·cm or less.

[0134] The foamable adhesive sheet of this embodiment preferably has high adhesiveness after foaming and curing. The shear strength (adhesive strength) based on JIS K6850 at 23°C may be, for example, 2.10 MPa or more, 2.40 MPa or more, or 3.0 MPa or more. Furthermore, the shear strength (adhesive strength) at 200°C may be, for example, 0.28 MPa or more, or 0.30 MPa or more.

[0135] The foamable adhesive sheet of this embodiment preferably has high electrical insulation after foaming and curing. The breakdown voltage based on JIS C 2107 is preferably 3 kV or higher, more preferably 5 kV or higher. Furthermore, the foamable adhesive sheet after foaming and curing preferably has thermal conductivity of 0.1 W / mK or higher, more preferably 0.15 W / mK or higher.

[0136] The foamable adhesive sheet of this embodiment is used to bond the stator core and coil of a stator for a rotating electric machine. For example, the foamable adhesive sheet can be placed between the stator core and coil, and then foamed and cured to bond the stator core and coil.

[0137] In this embodiment, since a fiber layer is arranged on the side of the first adhesive layer opposite the substrate, it is preferable that the first adhesive layer be arranged on the coil side and the second adhesive layer be arranged on the stator core side.

[0138] There are no particular limitations on the method for producing the foamable adhesive sheet of this embodiment. For example, the first adhesive layer and the second adhesive layer may be formed sequentially or simultaneously.

[0139] 2. Second Example of First Embodiment A second example of the first embodiment of the foamable adhesive sheet of the present disclosure has a first adhesive layer, a substrate, and a second adhesive layer in that order, wherein the first adhesive layer and the second adhesive layer contain a curable adhesive, at least one of the first adhesive layer and the second adhesive layer contains a foaming agent, the first adhesive layer and the second adhesive layer have different properties from each other, and a fiber layer is disposed between the first adhesive layer and the substrate.

[0140] Fig. 3 is a schematic cross-sectional view illustrating an example of a foamable adhesive sheet of this embodiment. The foamable adhesive sheet 10 in Fig. 3 has a first adhesive layer 1a, a substrate 2, and a second adhesive layer 1b in this order, with a fiber layer 3 disposed between the first adhesive layer 1a and the substrate 2. The first adhesive layer 1a and the second adhesive layer 1b contain a curable adhesive, and at least one of the first adhesive layer 1a and the second adhesive layer 1b contains a foaming agent, and the first adhesive layer 1a and the second adhesive layer 1b have different properties.

[0141] In this embodiment, since a fiber layer is disposed between the first adhesive layer and the substrate, for example, if the first adhesive layer is transparent and the substrate is opaque, the fiber layer is visible from the side facing the first adhesive layer, making it easy to distinguish between the side facing the first adhesive layer and the side facing the second adhesive layer by visual observation. Furthermore, since the fiber layer is disposed between the first adhesive layer and the substrate, the unevenness of the fiber layer can be reflected in the first adhesive layer, making it easy to distinguish between the side facing the first adhesive layer and the side facing the second adhesive layer by observation, for example, with a white light interferometer, a laser microscope, or palpation. This prevents operational errors when using the foamable adhesive sheet.

[0142] Furthermore, in this embodiment, because a fiber layer is disposed between the first adhesive layer and the substrate, the foamable adhesive sheet of this embodiment can be placed between the stator core and coil of a rotating electrical machine stator, foamed and cured, and even after bonding the stator core and coil, the surface facing the first adhesive layer and the surface facing the second adhesive layer can be distinguished. For example, if the foamed and cured first adhesive layer is transparent and the substrate is opaque, the fiber layer can be seen through the surface facing the first adhesive layer. Therefore, by observing the surface facing the first adhesive layer and the surface facing the second adhesive layer in the foamed and cured adhesive sheet with the naked eye, an optical microscope, or an electron microscope, it is possible to easily distinguish the surface facing the first adhesive layer and the surface facing the second adhesive layer in the foamed and cured adhesive sheet. Furthermore, even if the foamed and cured first adhesive layer is not transparent, by observing the cross section of the foamable adhesive sheet at the slot opening with the naked eye or an optical microscope, it is possible to distinguish the surface facing the first adhesive layer and the surface facing the second adhesive layer in the foamed and cured adhesive sheet. This makes it possible to identify the cause of a failure due to incorrectly positioning the foamable adhesive sheet, and to discover such failures early.

[0143] In this manner, in this embodiment, it is possible to distinguish between the surface on the first adhesive layer side and the surface on the second adhesive layer side not only for the foamable adhesive sheet before it has foamed and hardened, but also for the adhesive sheet after it has foamed and hardened after being incorporated into a rotating electric machine.

[0144] Furthermore, in this embodiment, by disposing a fiber layer between the first adhesive layer and the substrate, the unevenness of the fiber layer can be reflected in the first adhesive layer, thereby roughening the surface of the first adhesive layer and reducing the contact area with the adherend, thereby reducing the adhesiveness of the first adhesive layer. This allows for a foamable adhesive sheet with good blocking resistance and slipperiness. This improves the handleability and workability of the foamable adhesive sheet. Specifically, by disposing a fiber layer between the first adhesive layer and the substrate, the adhesiveness of the first adhesive layer can be made lower than that of the second adhesive layer, thereby making the slipperiness of the first adhesive layer higher than that of the second adhesive layer. For example, when placing a foam adhesive sheet in a slot of a stator core and then placing a coil in the slot of the stator core, by placing the foam adhesive sheet so that the first adhesive layer is on the coil side and the second adhesive layer is on the stator core side, when the foam adhesive sheet is placed in the slot of the stator core, the second adhesive layer has better adhesion, making it less likely for the foam adhesive sheet to shift position relative to the stator core, and when placing a coil in the slot of the stator core, the first adhesive layer has better slip properties, making it possible to smoothly insert the coil into the narrower gap created by inserting the foam adhesive sheet into the slot of the stator core.

[0145] Furthermore, by disposing the fiber layer between the first adhesive layer and the substrate, it is possible to prevent the first adhesive layer from spreading in the planar direction when foaming.

[0146] In addition, in this embodiment, by disposing a fiber layer between the first adhesive layer and the substrate, it is possible to improve the adhesion between the first adhesive layer and the substrate.

[0147] Each component of the foamable adhesive sheet of this embodiment will be described below.

[0148] (1) Fiber layer In this embodiment, the fibrous layer is disposed between the first adhesive layer and the substrate.

[0149] The shape and material of the fiber layer may be the same as those of the fiber layer in the first example of the first embodiment.

[0150] The density, basis weight and thickness of the fiber layer are not particularly limited and may be set appropriately.

[0151] Methods for disposing a fiber layer on a substrate include, for example, dry lamination and thermal lamination.

[0152] (2) First adhesive layer and second adhesive layer In this embodiment, the first adhesive layer and the second adhesive layer contain a curable adhesive, and at least one of the first adhesive layer and the second adhesive layer contains a foaming agent, and the first adhesive layer and the second adhesive layer have different properties from each other.

[0153] In this embodiment, it is sufficient that at least one of the first adhesive layer and the second adhesive layer contains a foaming agent; for example, only the first adhesive layer may contain a foaming agent, only the second adhesive layer may contain a foaming agent, or both the first adhesive layer and the second adhesive layer may contain a foaming agent.

[0154] The materials for the first adhesive layer and the second adhesive layer can be the same as those for the first adhesive layer and the second adhesive layer in the first example of the first embodiment.

[0155] The adhesive strength of the first adhesive layer and the second adhesive layer is appropriately set according to the adhesiveness required for the adhesive layer disposed on the stator core side and the adhesive layer disposed on the coil side, respectively. It is particularly preferable that at least one of the first adhesive layer and the second adhesive layer is substantially non-tacky (tack-free). In this case, it is preferable that the adhesive layer exhibiting substantially non-tacky properties is disposed on the outermost surface. By making at least one of the first adhesive layer and the second adhesive layer substantially non-tacky, at least one surface of the foamable adhesive sheet can be made non-tacky. This allows for a foamable adhesive sheet with good slip properties and blocking resistance. This improves the handleability and workability of the foamable adhesive sheet.

[0156] Only one of the first adhesive layer and the second adhesive layer may be non-tacky, or both may be non-tacky.

[0157] When a foam adhesive sheet is placed between the stator core and the coil to bond them, for example, the foam adhesive sheet may be placed in the slot of the stator core, and then the coil may be placed in the slot of the stator core. In such a case, it is preferable that the adhesive layer placed on the coil side has good slip properties, and it is preferable that the adhesive layer placed on the stator core side has good adhesion to the stator core. Therefore, in this case, it is preferable that only one of the first adhesive layer and the second adhesive layer is non-sticky.

[0158] Furthermore, for example, when inserting a coil with a foam adhesive sheet placed on it into a slot in a stator core, it is preferable that the adhesive layer placed on the stator core side has good slip properties, and that the adhesive layer placed on the coil side has good adhesion to the coil. Therefore, in this case too, it is preferable that only one of the first adhesive layer and the second adhesive layer is non-sticky.

[0159] On the other hand, when a foam adhesive sheet is placed between the stator core and the coil to bond them, for example, after the coil is placed in the slot of the stator core, the foam adhesive sheet may be inserted into the gap between the stator core and the coil in the slot of the stator core. In such a case, it is preferable that both the adhesive layer placed on the stator core side and the adhesive layer placed on the coil side have good slip properties. Therefore, in this case, it is preferable that both the first adhesive layer and the second adhesive layer are non-sticky.

[0160] Furthermore, the first adhesive layer is preferably transparent. When the first adhesive layer is transparent, the fiber layer can be seen through the surface on the first adhesive layer side, making it easy to visually distinguish between the surface on the first adhesive layer side and the surface on the second adhesive layer side. The transparency of the first adhesive layer is sufficient as long as the fiber layer can be seen through the surface on the first adhesive layer side. Specifically, it is preferable that the haze of the first adhesive layer is 90% or less and the total light transmittance of the first adhesive layer is 20% or more. The haze of the first adhesive layer can be measured in accordance with JIS K7136. The total light transmittance of the first adhesive layer can be measured in accordance with JIS K7361-1.

[0161] Other characteristics of the first adhesive layer and the second adhesive layer can be the same as those of the first adhesive layer and the second adhesive layer in the first example of the first embodiment.

[0162] Furthermore, the thickness, shape, and forming method of the first adhesive layer and the second adhesive layer may be the same as those of the first adhesive layer and the second adhesive layer in the first example of the first embodiment.

[0163] (3) Base material The substrate in this embodiment is a member that supports the first adhesive layer and the second adhesive layer.

[0164] The substrate may be, for example, a resin substrate, and the material of the substrate may be the same as the material of the substrate in the first example of the first embodiment.

[0165] Furthermore, the substrate is preferably opaque. When the substrate is opaque and the first adhesive layer is transparent, the fiber layer can be made visible from the surface on the first adhesive layer side and invisible from the surface on the second adhesive layer side, making it easy to distinguish between the surface on the first adhesive layer side and the surface on the second adhesive layer side by visual inspection. The substrate needs to be opaque enough that the fiber layer cannot be seen from the surface of the substrate opposite the fiber layer, and it is sufficient that it can be determined whether the fiber layer is on the front or back of the substrate.

[0166] Other characteristics, shape, thickness, etc. of the substrate can be the same as those of the substrate in the first example of the first embodiment.

[0167] (4) First primer layer and second primer layer The foamable adhesive sheet of this embodiment may have a first primer layer between the fiber layer and the first adhesive layer, or a second primer layer between the substrate and the second adhesive layer. The presence of the first primer layer or the second primer layer can improve the adhesion of the first adhesive layer to the fiber layer and the adhesion of the second adhesive layer to the substrate. Furthermore, the presence of the first primer layer or the second primer layer can, for example, reduce stress on the bent portion when the foamable adhesive sheet is folded, or reduce stress on the cut portion when the foamable adhesive sheet is cut. As a result, lifting or peeling of the first adhesive layer or the second adhesive layer from the substrate can be suppressed when the foamable adhesive sheet is bent or cut.

[0168] For example, in the foamable adhesive sheet 10 shown in Fig. 4, a first primer layer 4a is disposed between the fiber layer 3 and the first adhesive layer 1a, and a second primer layer 4b is disposed between the substrate 2 and the second adhesive layer 1b. Although the foamable adhesive sheet 10 in Fig. 4 has both the first primer layer 4a and the second primer layer 4b, it may have only one of them.

[0169] The first primer layer may be disposed only between the fiber layer and the first adhesive layer, the second primer layer may be disposed only between the substrate and the second adhesive layer, or the first primer layer may be disposed between the fiber layer and the first adhesive layer and the second primer layer may be disposed between the substrate and the second adhesive layer. Of these, it is preferable that the first primer layer be disposed between the fiber layer and the first adhesive layer and the second primer layer be disposed between the substrate and the second adhesive layer.

[0170] Furthermore, the first primer layer is preferably transparent. When the first adhesive layer and the first primer layer are transparent, the fiber layer can be seen through from the surface on the first adhesive layer side, making it easy to visually distinguish between the surface on the first adhesive layer side and the surface on the second adhesive layer side. The transparency of the first primer layer is sufficient as long as the fiber layer can be seen through from the surface on the first adhesive layer side. Specifically, it is preferable that the haze of the first primer layer is 90% or less and the total light transmittance of the first primer layer is 20% or more. The haze of the first primer layer can be measured in accordance with JIS K7136. The total light transmittance of the first adhesive layer can be measured in accordance with JIS K7361-1.

[0171] The materials, thickness, formation method, etc. of the first primer layer and the second primer layer may be the same as those of the first primer layer and the second primer layer in the first example of the first embodiment.

[0172] (5) Foam adhesive sheet In this aspect, since the fiber layer is disposed between the first adhesive layer and the base material, it is preferable that the first adhesive layer be disposed on the coil side and the second adhesive layer be disposed on the stator core side.

[0173] The thickness, properties, production method, etc. of the foamable adhesive sheet of this embodiment can be the same as those of the foamable adhesive sheet of the first example of the first embodiment.

[0174] II. Second embodiment A second embodiment of the foamable adhesive sheet of the present disclosure has, in this order, a first adhesive layer, a substrate, and a second adhesive layer, wherein the first adhesive layer and the second adhesive layer contain a curable adhesive, and at least one of the first adhesive layer and the second adhesive layer contains a foaming agent, the first adhesive layer and the second adhesive layer have different properties, and a first fiber layer is arranged on the side of the first adhesive layer opposite the substrate, and a second fiber layer is arranged on the side of the second adhesive layer opposite the substrate, or a first fiber layer is arranged between the first adhesive layer and the substrate, and a second fiber layer is arranged between the second adhesive layer and the substrate, and the first fiber layer and the second fiber layer are different from each other, and when the first fiber layer is arranged on the side of the first adhesive layer opposite the substrate, and the second fiber layer is arranged on the side of the second adhesive layer opposite the substrate, the first adhesive layer and the second adhesive layer contain the foaming agent.

[0175] The foamable adhesive sheet of this embodiment has two configurations: a first example in which a first fiber layer is disposed on the surface of the first adhesive layer opposite the substrate, and a second fiber layer is disposed on the surface of the second adhesive layer opposite the substrate, and a second example in which a first fiber layer is disposed between the first adhesive layer and the substrate, and a second fiber layer is disposed between the second adhesive layer and the substrate. Each configuration will be explained separately below.

[0176] 1. First Example of the Second Embodiment A first example of the second embodiment of the foamable adhesive sheet of the present disclosure has a first adhesive layer, a substrate, and a second adhesive layer in that order, the first adhesive layer and the second adhesive layer containing a curable adhesive and a foaming agent, the first adhesive layer and the second adhesive layer having mutually different properties, a first fiber layer arranged on the side of the first adhesive layer opposite the substrate, and a second fiber layer arranged on the side of the second adhesive layer opposite the substrate, the first fiber layer and the second fiber layer being different from each other.

[0177] Fig. 5 is a schematic cross-sectional view illustrating an example of a foamable adhesive sheet according to this embodiment. The foamable adhesive sheet 10 in Fig. 5 comprises a first adhesive layer 1a, a substrate 2, and a second adhesive layer 1b, in that order. A first fiber layer 3a is disposed on the surface of the first adhesive layer 1a opposite the substrate 2, and a second fiber layer 3b is disposed on the surface of the second adhesive layer 1b opposite the substrate 2. The first adhesive layer 1a and the second adhesive layer 1b contain a curable adhesive and a foaming agent, and the first adhesive layer 1a and the second adhesive layer 1b have different properties. The first fiber layer 3a and the second fiber layer 3b are also different from each other.

[0178] In this embodiment, a first fiber layer is disposed on the surface of the first adhesive layer opposite the substrate, and a second fiber layer is disposed on the surface of the second adhesive layer opposite the substrate. Because the first fiber layer and the second fiber layer are different from each other, the surface facing the first adhesive layer and the surface facing the second adhesive layer can be distinguished. For example, if the densities of the first fiber layer and the second fiber layer are different from each other, the appearance and surface roughness of the first fiber layer and the second fiber layer can be made different from each other. This makes it easy to distinguish the surface facing the first adhesive layer and the surface facing the second adhesive layer by visual inspection, palpation, or observation with a white light interferometer. Furthermore, if the thicknesses of the first fiber layer and the second fiber layer are different from each other, the surface facing the first adhesive layer and the surface facing the second adhesive layer can be easily distinguished by measuring the thicknesses of the first fiber layer and the second fiber layer with a reflectance spectrometer or by observing the cross section of the foamable adhesive sheet. This prevents operational errors when using the foamable adhesive sheet.

[0179] In this embodiment, the first fiber layer is disposed on the surface of the first adhesive layer opposite the substrate, and the second fiber layer is disposed on the surface of the second adhesive layer opposite the substrate. Because the first fiber layer and the second fiber layer are different, the foamable adhesive sheet of this embodiment can be placed between a stator core and a coil of a rotating electric machine stator, foamed and cured, and the stator core and the coil can be bonded together. Even after the foamable adhesive sheet is placed between the stator core and the coil, foamed and cured, the first adhesive layer side and the second adhesive layer side can be easily distinguished. For example, if the densities of the first fiber layer and the second fiber layer are different, the appearances of the first fiber layer and the second fiber layer can be made different. The first adhesive layer side and the second adhesive layer side of the foamed and cured adhesive sheet can be easily distinguished by visual inspection, optical microscope, or electron microscope observation. Furthermore, if the thicknesses of the first fiber layer and the second fiber layer are different, the first adhesive layer side and the second adhesive layer side can be easily distinguished by observing the cross section of the foamed and cured adhesive sheet. Therefore, it is possible to identify the cause of a failure due to incorrectly placing the foamable adhesive sheet on the front and back, and to discover such a cause of failure at an early stage.

[0180] In this manner, in this embodiment, it is possible to distinguish between the surface on the first adhesive layer side and the surface on the second adhesive layer side not only for the foamable adhesive sheet before it has foamed and hardened, but also for the adhesive sheet after it has foamed and hardened after being incorporated into a rotating electric machine.

[0181] In this embodiment, the first fiber layer is disposed on the surface of the first adhesive layer opposite the substrate, and the second fiber layer is disposed on the surface of the second adhesive layer opposite the substrate, thereby making the surfaces facing the first adhesive layer and the second adhesive layer non-tacky (tack-free). This allows for a foamable adhesive sheet with good blocking resistance and slip properties. This improves the handleability and workability of the foamable adhesive sheet.

[0182] For example, when a foam adhesive sheet is placed in a slot of a stator core and then a coil is placed in the slot of the stator core, the surfaces on the first adhesive layer side and the second adhesive layer side are non-sticky and have good slip properties, so when the foam adhesive sheet is placed in the slot of the stator core, the foam adhesive sheet can be smoothly inserted into the slot of the stator core, and when a coil is placed in the slot of the stator core, the coil can be smoothly inserted into the narrower gap created by inserting the foam adhesive sheet into the slot of the stator core.

[0183] On the other hand, for example, when a coil is placed in a slot of a stator core and then a foam adhesive sheet is inserted into the gap between the stator core and the coil in the slot of the stator core, the surface on the first adhesive layer side and the surface on the second adhesive layer side are non-sticky and have good slip properties, so the foam adhesive sheet can be smoothly inserted into the gap between the stator core and the coil in the slot of the stator core.

[0184] In this embodiment, the first fiber layer allows the curable adhesive contained in the first adhesive layer to permeate or penetrate when the first adhesive layer is foamed, and the second fiber layer allows the curable adhesive contained in the second adhesive layer to permeate or penetrate when the second adhesive layer is foamed. Therefore, when the first and second adhesive layers are foamed, the curable adhesive can reach the outermost surface of the foamable adhesive sheet, thereby maintaining adhesive strength on the first adhesive layer side and the second adhesive layer side. Therefore, even when the first fiber layer is disposed on the side of the first adhesive layer opposite the substrate and the second fiber layer is disposed on the side of the second adhesive layer opposite the substrate, it is possible to bond the stator core and the coil. Furthermore, by disposing the first fiber layer on the side of the first adhesive layer opposite the substrate and the second fiber layer on the side of the second adhesive layer opposite the substrate, it is possible to prevent the first adhesive layer and the second adhesive layer from spreading in the planar direction when foamed.

[0185] In addition, in this embodiment, a first fiber layer is arranged on the side of the first adhesive layer opposite the substrate, and a second fiber layer is arranged on the side of the second adhesive layer opposite the substrate, thereby suppressing warping of the foamable adhesive sheet and improving the handleability and workability of the foamable adhesive sheet.

[0186] Each component of the foamable adhesive sheet of this embodiment will be described below.

[0187] (1) First fiber layer and second fiber layer In this embodiment, a first fiber layer is disposed on the surface of the first adhesive layer opposite the substrate, and a second fiber layer is disposed on the surface of the second adhesive layer opposite the substrate, and the first fiber layer and the second fiber layer are different from each other.

[0188] The shape, material, density, basis weight, and thickness of the first and second fiber layers may be the same as those of the fiber layers in the first example of the first embodiment.

[0189] The first fiber layer and the second fiber layer may differ from each other in any way that allows the surface facing the first adhesive layer and the surface facing the second adhesive layer to be distinguished, such as density, thickness, etc. In particular, it is preferable that the first fiber layer and the second fiber layer differ from each other in at least one of density and thickness.

[0190] When at least one of the densities and thicknesses of the first fiber layer and the second fiber layer is different from each other, as described above, it is possible to distinguish between the surface on the first adhesive layer side and the surface on the second adhesive layer side for both the foamable adhesive sheet before foaming and hardening and the adhesive sheet after foaming and hardening after being incorporated into a rotating electric motor.

[0191] Furthermore, when the densities of the first and second fiber layers are different, the surface roughness and coefficient of friction of the first and second fiber layers can be made different, thereby making it possible to make the slipperiness of the surface facing the first adhesive layer different from the surface facing the second adhesive layer. For example, when the density of the first fiber layer is higher than the density of the second fiber layer, the surface roughness of the first fiber layer tends to be smaller than the surface roughness of the second fiber layer, and the coefficient of friction of the surface of the first fiber layer tends to be larger than the coefficient of friction of the surface of the second fiber layer. In this case, the slipperiness of the surface facing the first adhesive layer tends to be lower than the slipperiness of the surface facing the second adhesive layer. In such a case, for example, when a foam adhesive sheet is placed in a slot of the stator core and then a coil is placed in the slot of the stator core, by placing the foam adhesive sheet so that the surface on the first adhesive layer side faces the stator core and the surface on the second adhesive layer side faces the coil, when the foam adhesive sheet is placed in the slot of the stator core, the surface on the first adhesive layer side has lower slipperiness, making it less likely for the foam adhesive sheet to shift position relative to the stator core; and when a coil is placed in the slot of the stator core, the surface on the second adhesive layer side has higher slipperiness, making it possible to smoothly insert the coil into the narrower gap created by inserting the foam adhesive sheet into the slot of the stator core.

[0192] The difference in density between the first fiber layer and the second fiber layer should be such that it is possible to distinguish between the surface on the first adhesive layer side and the surface on the second adhesive layer side, both for the foamable adhesive sheet before foaming and hardening, and for the adhesive sheet after foaming and hardening after being incorporated into a rotating electric motor.

[0193] Furthermore, the difference in thickness between the first fiber layer and the second fiber layer should be such that it is possible to distinguish between the surface on the first adhesive layer side and the surface on the second adhesive layer side, both for the foamable adhesive sheet before foaming and hardening and for the adhesive sheet after foaming and hardening after being incorporated into a rotating electric motor.

[0194] The first and second fiber layers may be arranged in the same manner as in the first example of the first embodiment.

[0195] (2) First adhesive layer and second adhesive layer In this embodiment, the first adhesive layer and the second adhesive layer contain a curable adhesive and a foaming agent, and have different properties from each other.

[0196] The material, characteristics, thickness, shape, forming method, etc. of the first adhesive layer and the second adhesive layer can be the same as those of the first adhesive layer and the second adhesive layer in the first example of the first embodiment described above.

[0197] (3) Base material The substrate in this embodiment is a member that supports the first adhesive layer and the second adhesive layer.

[0198] The material, characteristics, shape, thickness, etc. of the substrate may be the same as those of the substrate in the first example of the first embodiment.

[0199] (4) First primer layer and second primer layer The foamable adhesive sheet of this embodiment may have a first primer layer between the substrate and the first adhesive layer, and may also have a second primer layer between the substrate and the second adhesive layer.

[0200] For example, in the foamable adhesive sheet 10 shown in Fig. 6, a first primer layer 4a is disposed between the substrate 2 and the first adhesive layer 1a, and a second primer layer 4b is disposed between the substrate 2 and the second adhesive layer 1b. Although the foamable adhesive sheet 10 in Fig. 6 has both the first primer layer 4a and the second primer layer 4b, it may have only one of them.

[0201] The arrangement, material, thickness, formation method, etc. of the first primer layer and the second primer layer can be the same as those of the first primer layer and the second primer layer in the first example of the first embodiment.

[0202] (5) Foam adhesive sheet In this embodiment, for example, when the density of the first fiber layer is higher than the density of the second fiber layer, it is preferable that the first adhesive layer be disposed on the stator core side and the second adhesive layer be disposed on the coil side.

[0203] The thickness, properties, production method, etc. of the foamable adhesive sheet of this embodiment can be the same as those of the foamable adhesive sheet of the first example of the first embodiment.

[0204] 2. Second Example of Second Embodiment A second example of the second embodiment of the foamable adhesive sheet of the present disclosure has a first adhesive layer, a substrate, and a second adhesive layer in that order, the first adhesive layer and the second adhesive layer contain a curable adhesive, at least one of the first adhesive layer and the second adhesive layer contains a foaming agent, the first adhesive layer and the second adhesive layer have different properties from each other, a first fiber layer is disposed between the first adhesive layer and the substrate, and a second fiber layer is disposed between the second adhesive layer and the substrate, and the first fiber layer and the second fiber layer are different from each other.

[0205] Fig. 7 is a schematic cross-sectional view illustrating an example of a foamable adhesive sheet according to this embodiment. The foamable adhesive sheet 10 in Fig. 7 comprises a first adhesive layer 1a, a substrate 2, and a second adhesive layer 1b, in that order. A first fiber layer 3a is disposed between the first adhesive layer 1a and the substrate 2, and a second fiber layer 3b is disposed between the second adhesive layer 1b and the substrate 2. The first adhesive layer 1a and the second adhesive layer 1b contain a curable adhesive, and at least one of the first adhesive layer 1a and the second adhesive layer 1b contains a foaming agent. The first adhesive layer 1a and the second adhesive layer 1b have different properties. The first fiber layer 3a and the second fiber layer 3b are also different from each other.

[0206] In this embodiment, a first fiber layer is disposed between the first adhesive layer and the substrate, and a second fiber layer is disposed between the second adhesive layer and the substrate. Because the first fiber layer and the second fiber layer are different from each other, it is possible to distinguish between the surface facing the first adhesive layer and the surface facing the second adhesive layer. For example, if the densities of the first fiber layer and the second fiber layer are different from each other, the appearances of the first fiber layer and the second fiber layer can be made different from each other. Therefore, if the first adhesive layer and the second adhesive layer are transparent and the substrate is opaque, the first fiber layer can be seen through from the surface facing the first adhesive layer, and the second fiber layer can be seen through from the surface facing the second adhesive layer. Therefore, it is easy to distinguish between the surface facing the first adhesive layer and the surface facing the second adhesive layer by visual observation. Furthermore, by disposing a fiber layer between the first adhesive layer and the substrate and disposing a second fiber layer between the second adhesive layer and the substrate, the unevenness caused by the first fiber layer can be reflected in the first adhesive layer, and the unevenness caused by the second fiber layer can be reflected in the second adhesive layer. Therefore, for example, if the densities of the first and second fiber layers are different, the surface roughness of the surface facing the first adhesive layer and the surface facing the second adhesive layer can be made different, and the surface facing the first adhesive layer and the surface facing the second adhesive layer can be easily distinguished by visual inspection, palpation, observation with a white light interferometer, or laser microscope. Furthermore, if the thicknesses of the first and second fiber layers are different, the surface facing the first adhesive layer and the surface facing the second adhesive layer can be easily distinguished by measuring the thicknesses of the first and second fiber layers with a reflectance spectroscopic film thickness meter or by observing the cross section of the foamable adhesive sheet. This prevents operational errors when using the foamable adhesive sheet.

[0207] In this embodiment, a first fiber layer is disposed between the first adhesive layer and the substrate, and a second fiber layer is disposed between the second adhesive layer and the substrate, and the first fiber layer and the second fiber layer are different from each other. Therefore, even after the foamable adhesive sheet of this embodiment is placed between a stator core and a coil of a rotating electric machine stator and foamed and cured to bond the stator core and the coil, the surface facing the first adhesive layer and the surface facing the second adhesive layer can be distinguished. For example, if the densities of the first fiber layer and the second fiber layer are different from each other, the appearances of the first fiber layer and the second fiber layer can be made different. Therefore, if the first adhesive layer and the second adhesive layer are transparent after foaming and curing and the substrate is opaque, the first fiber layer can be seen through from the surface facing the first adhesive layer, and the second fiber layer can be seen through from the surface facing the second adhesive layer. Therefore, the surface facing the first adhesive layer and the surface facing the second adhesive layer of the foamed and cured adhesive sheet can be easily distinguished by observation with the naked eye, an optical microscope, or an electron microscope. Furthermore, even if the first adhesive layer and the second adhesive layer are not transparent after foaming and curing, the side of the foamed and cured adhesive sheet facing the first adhesive layer and the side facing the second adhesive layer can be distinguished by visually observing the cross section of the foamed adhesive sheet at the slot opening or by using an optical microscope. Furthermore, for example, if the first fiber layer and the second fiber layer have different thicknesses, the side of the foamed and cured adhesive sheet facing the first adhesive layer and the side facing the second adhesive layer can be easily distinguished by observing the cross section of the foamed and cured adhesive sheet. This makes it possible to identify the cause of a failure due to incorrectly positioning the foamed adhesive sheet on the front and back, enabling early detection of such failures.

[0208] In this manner, in this embodiment, it is possible to distinguish between the surface on the first adhesive layer side and the surface on the second adhesive layer side not only for the foamable adhesive sheet before it has foamed and hardened, but also for the adhesive sheet after it has foamed and hardened after being incorporated into a rotating electric machine.

[0209] In this embodiment, a first fiber layer is disposed between the first adhesive layer and the substrate, and a second fiber layer is disposed between the second adhesive layer and the substrate. This allows the unevenness of the first fiber layer to be reflected in the first adhesive layer, and the unevenness of the second fiber layer to be reflected in the second adhesive layer. This roughens the surfaces of the first adhesive layer and the second adhesive layer, reducing the contact area with the adherend and reducing the adhesiveness of the first adhesive layer and the second adhesive layer. This results in a foamable adhesive sheet with good blocking resistance and slipperiness. This improves the handleability and workability of the foamable adhesive sheet.

[0210] For example, when a foam adhesive sheet is placed in a slot of a stator core and then a coil is placed in the slot of the stator core, the first adhesive layer and the second adhesive layer have low adhesion and good slip properties, so when the foam adhesive sheet is placed in the slot of the stator core, the foam adhesive sheet can be smoothly inserted into the slot of the stator core, and when a coil is placed in the slot of the stator core, the coil can be smoothly inserted into the narrower gap created by inserting the foam adhesive sheet into the slot of the stator core.

[0211] On the other hand, for example, when a coil is placed in a slot of a stator core and then a foam adhesive sheet is inserted into the gap between the stator core and the coil in the slot of the stator core, the first adhesive layer and the second adhesive layer have low adhesion and good slip properties, so the foam adhesive sheet can be smoothly inserted into the gap between the stator core and the coil in the slot of the stator core.

[0212] In addition, in this embodiment, a first fiber layer is disposed between the first adhesive layer and the substrate, and a second fiber layer is disposed between the second adhesive layer and the substrate, thereby suppressing warping of the foamable adhesive sheet and improving the handleability and workability of the foamable adhesive sheet.

[0213] In addition, by arranging a first fiber layer between the first adhesive layer and the substrate and a second fiber layer between the second adhesive layer and the substrate, it is possible to prevent the first adhesive layer and the second adhesive layer from spreading in the planar direction when foaming.

[0214] In addition, in this embodiment, by arranging a first fiber layer between the first adhesive layer and the substrate and a second fiber layer between the second adhesive layer and the substrate, the adhesion between the first adhesive layer and the substrate and the adhesion between the second adhesive layer and the substrate can also be improved.

[0215] Each component of the foamable adhesive sheet of this embodiment will be described below.

[0216] (1) First fiber layer and second fiber layer In this embodiment, a first fiber layer is disposed between the first adhesive layer and the substrate, and a second fiber layer is disposed between the second adhesive layer and the substrate, and the first fiber layer and the second fiber layer are different from each other.

[0217] The shape and material of the first and second fiber layers may be the same as those of the fiber layers in the first example of the first embodiment.

[0218] The density, basis weight, and thickness of the first and second fiber layers are not particularly limited and may be set appropriately.

[0219] The first fiber layer and the second fiber layer may differ from each other in any way that allows the surface facing the first adhesive layer and the surface facing the second adhesive layer to be distinguished, such as density, thickness, etc. In particular, it is preferable that the first fiber layer and the second fiber layer differ from each other in at least one of density and thickness.

[0220] When at least one of the densities and thicknesses of the first fiber layer and the second fiber layer is different from each other, as described above, it is possible to distinguish between the surface on the first adhesive layer side and the surface on the second adhesive layer side for both the foamable adhesive sheet before foaming and hardening and the adhesive sheet after foaming and hardening after being incorporated into a rotating electric motor.

[0221] Furthermore, if the first and second fiber layers have different densities, the unevenness of the first fiber layer can be reflected in the first adhesive layer, and the unevenness of the second fiber layer can be reflected in the second adhesive layer, making it possible to make the surface roughness of the first adhesive layer side and the surface roughness of the second adhesive layer side different from each other, thereby making the adhesiveness of the first adhesive layer side and the surface roughness of the second adhesive layer side different from each other, and as a result, making the slipperiness of the first adhesive layer side and the surface roughness of the second adhesive layer side different from each other.

[0222] For example, when the density of the first fiber layer is higher than the density of the second fiber layer, the surface roughness of the surface facing the first adhesive layer tends to be smaller than the surface roughness of the surface facing the second adhesive layer. In this case, the adhesiveness of the surface facing the first adhesive layer tends to be higher than the adhesiveness of the surface facing the second adhesive layer, and the slipperiness of the surface facing the first adhesive layer tends to be lower than the slipperiness of the surface facing the second adhesive layer. In such a case, for example, when a foam adhesive sheet is placed in a slot of a stator core and then a coil is placed in the slot of the stator core, by placing the foam adhesive sheet so that the surface facing the first adhesive layer faces the stator core and the surface facing the second adhesive layer faces the coil, when the foam adhesive sheet is placed in the slot of the stator core, the surface facing the first adhesive layer has better adhesiveness, making it less likely for the foam adhesive sheet to shift position relative to the stator core. When a coil is placed in the slot of the stator core, the surface facing the second adhesive layer has better slipperiness, making it possible to smoothly insert the coil into the narrower gap created by inserting the foam adhesive sheet into the slot of the stator core.

[0223] The difference in density between the first fiber layer and the second fiber layer should be such that it is possible to distinguish between the surface on the first adhesive layer side and the surface on the second adhesive layer side, both for the foamable adhesive sheet before foaming and hardening, and for the adhesive sheet after foaming and hardening after being incorporated into a rotating electric motor.

[0224] Furthermore, the difference in thickness between the first fiber layer and the second fiber layer should be such that it is possible to distinguish between the surface on the first adhesive layer side and the surface on the second adhesive layer side, both for the foamable adhesive sheet before foaming and hardening and for the adhesive sheet after foaming and hardening after being incorporated into a rotating electric motor.

[0225] The first and second fiber layers may be arranged in the same manner as in the second example of the first embodiment.

[0226] (2) First adhesive layer and second adhesive layer In this embodiment, the first adhesive layer and the second adhesive layer contain a curable adhesive, and at least one of the first adhesive layer and the second adhesive layer contains a foaming agent, and the first adhesive layer and the second adhesive layer have different properties from each other.

[0227] The first adhesive layer and the second adhesive layer may also be transparent. When the first adhesive layer and the second adhesive layer are transparent, the first fiber layer can be seen through from the surface facing the first adhesive layer, and the second fiber layer can be seen through from the surface facing the second adhesive layer, making it easy to visually distinguish between the surface facing the first adhesive layer and the surface facing the second adhesive layer. The transparency of the first adhesive layer and the second adhesive layer may be such that the first fiber layer can be seen through from the surface facing the first adhesive layer, and the second fiber layer can be seen through from the surface facing the second adhesive layer. Specifically, the transparency of the first adhesive layer and the second adhesive layer can be the same as that of the first adhesive layer in the second example of the first embodiment described above.

[0228] Preferably, at least one of the first adhesive layer and the second adhesive layer is substantially tack-free. The adhesiveness of the first adhesive layer and the second adhesive layer can be the same as that of the first adhesive layer and the second adhesive layer in the second example of the first embodiment.

[0229] The materials, other characteristics, thickness, shape, formation method, etc. of the first adhesive layer and the second adhesive layer can be the same as those of the first adhesive layer and the second adhesive layer in the first example of the first embodiment described above.

[0230] (3) Base material The substrate in this embodiment is a member that supports the first adhesive layer and the second adhesive layer.

[0231] The substrate may also be opaque. When the substrate is opaque and the first adhesive layer and the second adhesive layer are transparent, the first fiber layer can be seen through from the surface facing the first adhesive layer and the first fiber layer can be hidden from the surface facing the second adhesive layer, and the second fiber layer can be seen through from the surface facing the second adhesive layer and the second fiber layer can be hidden from the surface facing the first adhesive layer, so that the surface facing the first adhesive layer and the surface facing the second adhesive layer can be easily distinguished visually. The opacity of the substrate needs to be such that the first fiber layer is not visible from the surface of the substrate opposite the first fiber layer and the second fiber layer is not visible from the surface of the substrate opposite the second fiber layer.

[0232] The material, other properties, shape, thickness, etc. of the substrate may be the same as those of the substrate in the second example of the first embodiment.

[0233] (4) First primer layer and second primer layer The foamable adhesive sheet of this embodiment may have a first primer layer between the first fiber layer and the first adhesive layer, and may also have a second primer layer between the second fiber layer and the second adhesive layer.

[0234] For example, in the foamable adhesive sheet 10 shown in Fig. 8, a first primer layer 4a is disposed between the first fiber layer 3a and the first adhesive layer 1a, and a second primer layer 4b is disposed between the second fiber layer 3b and the second adhesive layer 1b. Although the foamable adhesive sheet 10 in Fig. 8 has both the first primer layer 4a and the second primer layer 4b, it may have only one of them.

[0235] Furthermore, the first primer layer and the second primer layer preferably have transparency. When the first adhesive layer, the second adhesive layer, the first primer layer, and the second primer layer are transparent, the first fiber layer can be seen through from the side facing the first adhesive layer, and the second fiber layer can be seen through from the side facing the second adhesive layer, making it easy to visually distinguish between the side facing the first adhesive layer and the side facing the second adhesive layer. The transparency of the first primer layer and the second primer layer may be such that the first fiber layer can be seen through from the side facing the first adhesive layer, and the second fiber layer can be seen through from the side facing the second adhesive layer. Specifically, the transparency of the first primer layer and the second primer layer can be the same as that of the first primer layer in the second example of the first embodiment described above.

[0236] The arrangement, material, thickness, formation method, etc. of the first primer layer and the second primer layer can be the same as those of the first primer layer and the second primer layer in the first example of the first embodiment.

[0237] (5) Foam adhesive sheet In this embodiment, for example, when the density of the first fiber layer is higher than the density of the second fiber layer, it is preferable that the first adhesive layer be disposed on the stator core side and the second adhesive layer be disposed on the coil side.

[0238] The thickness, properties, production method, etc. of the foamable adhesive sheet of this embodiment can be the same as those of the foamable adhesive sheet of the first example of the first embodiment.

[0239] III. Third embodiment A third embodiment of the foamable adhesive sheet of the present disclosure has, in that order, a first adhesive layer, a substrate, and a second adhesive layer, wherein the first adhesive layer and the second adhesive layer contain a curable adhesive, and at least one of the first adhesive layer and the second adhesive layer contains a foaming agent, the first adhesive layer and the second adhesive layer have different properties, and the first adhesive layer and the second adhesive layer contain different amounts of filler.

[0240] Fig. 9 is a schematic cross-sectional view illustrating a foamable adhesive sheet according to this embodiment. The foamable adhesive sheet 10 in Fig. 9 comprises a first adhesive layer 1a, a substrate 2, and a second adhesive layer 1b, in that order. The first adhesive layer 1a and the second adhesive layer 1b contain a curable adhesive, and at least one of the first adhesive layer 1a and the second adhesive layer 1b contains a foaming agent. The first adhesive layer 1a and the second adhesive layer 1b have different properties. The first adhesive layer 1a and the second adhesive layer 1b also contain different amounts of filler.

[0241] In this embodiment, the first adhesive layer and the second adhesive layer contain different amounts of filler, which allows the first adhesive layer and the second adhesive layer to have different surface roughness, hardness, and whiteness. Therefore, for example, by visually observing or palpating the first adhesive layer and the second adhesive layer, or by measuring the hardness of the first adhesive layer and the second adhesive layer with a hardness tester, it is easy to distinguish between the first adhesive layer side and the second adhesive layer side. This prevents operational errors when using the foamable adhesive sheet.

[0242] Furthermore, in this embodiment, because the first adhesive layer and the second adhesive layer contain different amounts of filler, after the foamable adhesive sheet of this embodiment is placed between the stator core and coil of a rotating electrical machine stator and foamed and cured to bond the stator core and coil, it is possible to easily distinguish between the surface of the foamed and cured adhesive sheet facing the first adhesive layer and the surface of the foamed and cured adhesive sheet facing the second adhesive layer by, for example, performing qualitative or quantitative analysis of the elements contained in the filler using a scanning electron microscope and energy dispersive X-ray spectroscopy (SEM-EDX), or by observing the cross section of the foamed and cured adhesive sheet. This makes it possible to identify the cause of failure due to incorrect placement of the foamable adhesive sheet, and to discover such failure causes early on.

[0243] In this manner, in this embodiment, it is possible to distinguish between the surface on the first adhesive layer side and the surface on the second adhesive layer side not only for the foamable adhesive sheet before it has foamed and hardened, but also for the adhesive sheet after it has foamed and hardened after being incorporated into a rotating electric machine.

[0244] Furthermore, in this embodiment, by differentiating the amounts of filler contained in the first adhesive layer and the second adhesive layer, the surface properties of the first adhesive layer and the second adhesive layer, such as adhesion, friction coefficient, surface hardness, etc., can be made different from each other. Therefore, by differentiating the amounts of filler contained in the first adhesive layer and the second adhesive layer, the properties of the first adhesive layer and the second adhesive layer can be made different from each other, and at the same time, it is possible to distinguish between the surface on the first adhesive layer side and the surface on the second adhesive layer side.

[0245] In this embodiment, at least one of the first adhesive layer and the second adhesive layer contains a filler. An adhesive layer containing a filler can increase the surface roughness and hardness of the adhesive layer. In this case, the adhesive layer tends to have a reduced tackiness and a tendency to have improved slipperiness. Therefore, by including a filler in at least one of the first adhesive layer and the second adhesive layer, a foamable adhesive sheet with good blocking resistance and slipperiness can be obtained. This can improve the handleability and workability of the foamable adhesive sheet.

[0246] For example, if the first adhesive layer and the second adhesive layer contain a filler, the first adhesive layer and the second adhesive layer have low stickiness and good slipperiness, so when a foam adhesive sheet is placed in a slot of the stator core and then a coil is placed in the slot of the stator core, the foam adhesive sheet can be smoothly inserted into the slot of the stator core when placing the foam adhesive sheet in the slot of the stator core, and when a coil is placed in the slot of the stator core, the coil can be smoothly inserted into the narrower gap created by inserting the foam adhesive sheet into the slot of the stator core.

[0247] Furthermore, in the above case, since the first adhesive layer and the second adhesive layer have low adhesion and good slipperiness, for example, when a coil is placed in a slot of the stator core and then a foam adhesive sheet is inserted into the gap between the stator core and the coil in the slot of the stator core, the foam adhesive sheet can be smoothly inserted into the gap between the stator core and the coil in the slot of the stator core.

[0248] In this embodiment, the first adhesive layer and the second adhesive layer contain different amounts of filler, which allows the first adhesive layer and the second adhesive layer to have different surface roughnesses and hardnesses. Specifically, when the first adhesive layer contains a filler and the second adhesive layer does not, the surface roughness of the first adhesive layer can be made greater than the surface roughness of the second adhesive layer, and the hardness of the first adhesive layer can be made greater than the hardness of the second adhesive layer. In this case, the stickiness of the first adhesive layer tends to be lower than the stickiness of the second adhesive layer, and the slipperiness of the first adhesive layer tends to be higher than the slipperiness of the second adhesive layer. In such a case, for example, when a foam adhesive sheet is placed in a slot of the stator core and then a coil is placed in the slot of the stator core, by placing the foam adhesive sheet so that the first adhesive layer is on the coil side and the second adhesive layer is on the stator core side, when the foam adhesive sheet is placed in the slot of the stator core, the second adhesive layer has better adhesion, so the foam adhesive sheet is less likely to shift position relative to the stator core, and when a coil is placed in the slot of the stator core, the first adhesive layer has better slip properties, so the coil can be inserted smoothly into the narrower gap created by inserting the foam adhesive sheet into the slot of the stator core.

[0249] Each component of the foamable adhesive sheet of this embodiment will be described below.

[0250] 1. First adhesive layer and second adhesive layer In this embodiment, the first adhesive layer and the second adhesive layer contain a curable adhesive, and at least one of the first adhesive layer and the second adhesive layer contains a foaming agent. The first adhesive layer and the second adhesive layer have different properties. The first adhesive layer and the second adhesive layer contain different amounts of filler.

[0251] (1) Materials for the first adhesive layer and the second adhesive layer (a) Filler The filler in this embodiment is not particularly limited as long as it has insulating properties, and for example, both inorganic fillers and organic fillers can be used. Among them, inorganic fillers are preferred from the viewpoints of heat dissipation, hardness, heat resistance, etc.

[0252] The inorganic filler may be any inorganic filler that has insulating properties, and may be any inorganic filler that is generally used in adhesives.For example, inorganic fillers such as silica, alumina, titanium oxide, zirconium oxide, magnesium oxide, antimony oxide, aluminum nitride, boron nitride, calcium carbonate, magnesium carbonate, barium sulfate, aluminum hydroxide, magnesium hydroxide, aluminum borate, zinc borate, barium titanate, strontium titanate, calcium titanate, magnesium titanate, bismuth titanate, potassium titanate, barium zirconate, calcium zirconate, glass, talc, clay, mica, molybdenum compounds, and natural minerals may be mentioned.

[0253] The organic filler may be any organic filler that has insulating properties, and may be any organic filler that is generally used in adhesives. Examples include acrylic, polystyrene, urethane, polyamide, polyimide, polyester, and polyethylene organic fillers. The filler may be in the form of particles or fibers.

[0254] The filler may be used alone or in combination of two or more kinds.

[0255] The fillers contained in the first adhesive layer and the second adhesive layer may be the same or different from each other.

[0256] The average particle size of the filler is, for example, 0.1 μm or more, or may be 0.2 μm or more, or 0.3 μm or more. When the average particle size of the filler is large, the coefficient of friction on the surfaces of the first adhesive layer and the second adhesive layer tends to decrease, thereby increasing the slipperiness of the first adhesive layer and the second adhesive layer. Furthermore, fillers with too small an average particle size are difficult to manufacture and may cause aggregation. On the other hand, the average particle size of the filler is, for example, 100 μm or less, or may be 80 μm or less, or may be 50 μm or less. When the average particle size of the filler is too large, the adhesion between the first adhesive layer and the second adhesive layer and the substrate may decrease, or the adhesive strength of the first adhesive layer and the second adhesive layer after foaming and curing may decrease.

[0257] Here, the average particle size of the filler refers to the average value of the top 5 largest particle sizes out of 50 particles observed in a transmission electron microscope (TEM) photograph of the cross section of the first adhesive layer or the second adhesive layer.

[0258] The first adhesive layer and the second adhesive layer contain different amounts of filler. As the filler content increases, the surface roughness of the adhesive layer tends to increase and the hardness of the adhesive layer tends to increase, which in turn tends to reduce the adhesive layer's adhesion and reduce the coefficient of friction of the adhesive layer's surface, increasing its slipperiness. Therefore, by differing the amounts of filler contained in the first adhesive layer and the second adhesive layer, the surface roughness and hardness of the first adhesive layer and the second adhesive layer can be made different from each other. This allows the adhesiveness, coefficient of friction, and slipperiness of the first adhesive layer and the second adhesive layer to be made different from each other.

[0259] The amounts of filler contained in the first adhesive layer and the second adhesive layer may differ from each other, so at least one of the first adhesive layer and the second adhesive layer may contain a filler. That is, one of the first adhesive layer and the second adhesive layer may contain a filler and the other may not, or both may contain a filler.

[0260] The content of the filler is appropriately set depending on the desired surface roughness, hardness, and coefficient of friction, as well as the strength and adhesive force required for the first adhesive layer and second adhesive layer after foaming and curing. The content of the filler is, for example, 200 parts by mass or less, or alternatively 150 parts by mass or less, or even 100 parts by mass or less, per 100 parts by mass of the resin component contained in the first adhesive layer or second adhesive layer. If the content of the filler is too high, foaming of the first adhesive layer or second adhesive layer may be inhibited.

[0261] The difference in the amount of filler contained in the first adhesive layer and the second adhesive layer should be such that it is possible to distinguish between the surface on the first adhesive layer side and the surface on the second adhesive layer side, both for the foamable adhesive sheet before foaming and hardening, and for the adhesive sheet after foaming and hardening after being incorporated into a rotating electric motor.

[0262] (b) curable adhesives, foaming agents, and other ingredients The curable adhesive, foaming agent, and other components contained in the first adhesive layer and second adhesive layer in this embodiment can be the same as those in the first adhesive layer and second adhesive layer in the first example of the first embodiment above.

[0263] (2) Characteristics and configuration of the first adhesive layer and the second adhesive layer The adhesiveness of the first adhesive layer and the second adhesive layer in this embodiment can be the same as the adhesiveness of the first adhesive layer and the second adhesive layer in the second example of the first embodiment. In addition, other properties of the first adhesive layer and the second adhesive layer in this embodiment can be the same as the properties of the first adhesive layer and the second adhesive layer in the first example of the first embodiment.

[0264] Furthermore, the thickness, shape, and forming method of the first adhesive layer and the second adhesive layer may be the same as those of the first adhesive layer and the second adhesive layer in the first example of the first embodiment.

[0265] 2. Base material The substrate in this embodiment is a member that supports the first adhesive layer and the second adhesive layer.

[0266] The material, characteristics, shape, thickness, etc. of the substrate may be the same as those of the substrate in the first example of the first embodiment.

[0267] 3. First primer layer and second primer layer The foamable adhesive sheet of this embodiment may have a first primer layer between the substrate and the first adhesive layer, and may also have a second primer layer between the substrate and the second adhesive layer.

[0268] For example, in the foamable adhesive sheet 10 shown in Fig. 10, a first primer layer 4a is disposed between the substrate 2 and the first adhesive layer 1a, and a second primer layer 4b is disposed between the substrate 2 and the second adhesive layer 1b. Although the foamable adhesive sheet 10 in Fig. 10 has both the first primer layer 4a and the second primer layer 4b, it may have only one of them.

[0269] The arrangement, material, thickness, formation method, etc. of the first primer layer and the second primer layer can be the same as those of the first primer layer and the second primer layer in the first example of the first embodiment.

[0270] 4.Foam adhesive sheet In this embodiment, for example, when the amount of filler contained in the first adhesive layer is greater than the amount of filler contained in the second adhesive layer, it is preferable that the first adhesive layer be positioned on the coil side and the second adhesive layer be positioned on the stator core side.

[0271] The thickness, characteristics, manufacturing method, etc. of the foamable adhesive sheet of this embodiment can be the same as those of the foamable adhesive sheet of the first example of the first embodiment.

[0272] IV. Fourth Embodiment A fourth embodiment of the foamable adhesive sheet of the present disclosure has, in that order, a first adhesive layer, a substrate, and a second adhesive layer, wherein the first adhesive layer and the second adhesive layer contain a curable adhesive, and at least one of the first adhesive layer and the second adhesive layer contains a foaming agent, the first adhesive layer and the second adhesive layer have different properties, and the first adhesive layer and the second adhesive layer contain different fillers.

[0273] Fig. 9 is a schematic cross-sectional view illustrating a foamable adhesive sheet according to this embodiment. The foamable adhesive sheet 10 in Fig. 9 comprises a first adhesive layer 1a, a substrate 2, and a second adhesive layer 1b, in that order. The first adhesive layer 1a and the second adhesive layer 1b contain a curable adhesive, and at least one of the first adhesive layer 1a and the second adhesive layer 1b contains a foaming agent. The first adhesive layer 1a and the second adhesive layer 1b have different properties. The first adhesive layer 1a and the second adhesive layer 1b also contain different fillers.

[0274] In this embodiment, the first adhesive layer and the second adhesive layer contain different fillers, which allows the first adhesive layer and the second adhesive layer to have different surface roughness, hardness, or whiteness. Therefore, for example, by visually observing or palpating the first adhesive layer and the second adhesive layer, or by measuring the hardness of the first adhesive layer and the second adhesive layer with a hardness tester, it is easy to distinguish between the first adhesive layer side and the second adhesive layer side. This prevents operational errors when using the foamable adhesive sheet.

[0275] Furthermore, in this embodiment, because the first adhesive layer and the second adhesive layer contain different fillers, the foamable adhesive sheet of this embodiment is placed between the stator core and coil of a stator for a rotating electrical machine and foamed and cured. After bonding the stator core and coil, for example, by observing the cross section of the foamed and cured adhesive sheet, it is easy to distinguish between the side facing the first adhesive layer and the side facing the second adhesive layer. This makes it possible to identify the cause of a failure due to incorrectly positioning the foamable adhesive sheet, and to discover such a failure early on.

[0276] In this manner, in this embodiment, it is possible to distinguish between the surface on the first adhesive layer side and the surface on the second adhesive layer side not only for the foamable adhesive sheet before it has foamed and hardened, but also for the adhesive sheet after it has foamed and hardened after being incorporated into a rotating electric machine.

[0277] Furthermore, in this embodiment, by containing different fillers in the first adhesive layer and the second adhesive layer, the surface properties such as adhesion, friction coefficient, surface hardness, etc. of the first adhesive layer and the second adhesive layer can be made different from each other. Therefore, by containing different fillers in the first adhesive layer and the second adhesive layer, the properties of the first adhesive layer and the second adhesive layer can be made different from each other, and at the same time, it is possible to distinguish between the surface on the first adhesive layer side and the surface on the second adhesive layer side.

[0278] Furthermore, in this embodiment, by including a filler in the first adhesive layer and the second adhesive layer, the surface roughness of the first adhesive layer and the second adhesive layer can be increased, and the hardness of the first adhesive layer and the second adhesive layer can be increased. In this case, the tackiness of the first adhesive layer and the second adhesive layer tends to be reduced, which tends to improve the slipperiness of the first adhesive layer and the second adhesive layer. Therefore, by including a filler in the first adhesive layer and the second adhesive layer, a foamable adhesive sheet with good blocking resistance and slipperiness can be obtained. This can improve the handleability and workability of the foamable adhesive sheet.

[0279] For example, when a foam adhesive sheet is placed in a slot of a stator core and then a coil is placed in the slot of the stator core, the first adhesive layer and the second adhesive layer have low adhesion and good slip properties, so when the foam adhesive sheet is placed in the slot of the stator core, the foam adhesive sheet can be smoothly inserted into the slot of the stator core, and when a coil is placed in the slot of the stator core, the coil can be smoothly inserted into the narrower gap created by inserting the foam adhesive sheet into the slot of the stator core.

[0280] On the other hand, for example, when a coil is placed in a slot of a stator core and then a foam adhesive sheet is inserted into the gap between the stator core and the coil in the slot of the stator core, the first adhesive layer and the second adhesive layer have low adhesion and good slip properties, so the foam adhesive sheet can be smoothly inserted into the gap between the stator core and the coil in the slot of the stator core.

[0281] Each component of the foamable adhesive sheet of this embodiment will be described below.

[0282] 1. First adhesive layer and second adhesive layer In this embodiment, the first adhesive layer and the second adhesive layer contain a curable adhesive, and at least one of the first adhesive layer and the second adhesive layer contains a foaming agent. The first adhesive layer and the second adhesive layer have different properties. The first adhesive layer and the second adhesive layer contain different fillers.

[0283] (1) Materials for the first adhesive layer and the second adhesive layer (a) Filler The first adhesive layer and the second adhesive layer contain different fillers. The difference between the fillers contained in the first adhesive layer and the second adhesive layer may be any difference that allows the surface on the first adhesive layer side and the surface on the second adhesive layer side to be distinguished, and examples of such differences include average particle size and refractive index. In particular, it is preferable that the average particle size of the fillers contained in the first adhesive layer and the second adhesive layer be different from each other.

[0284] For example, if the average particle diameters of the fillers contained in the first adhesive layer and the second adhesive layer are different, the surface roughness, hardness, or whiteness of the first adhesive layer and the second adhesive layer can be made different. Therefore, for example, by visually observing or palpating the adhesive, or by measuring the hardness of the first adhesive layer and the second adhesive layer with a hardness tester, the first adhesive layer side and the second adhesive layer side can be easily distinguished. Furthermore, after the foamable adhesive sheet of this embodiment is placed between the stator core and the coil of a rotating electric machine stator and foamed and cured to bond the stator core and the coil, for example, by observing the cross section of the foamed and cured adhesive sheet, the first adhesive layer side and the second adhesive layer side of the foamed and cured adhesive sheet can be easily distinguished. Therefore, the first adhesive layer side and the second adhesive layer side can be easily distinguished for both the foamable adhesive sheet before foaming and curing and the foamed and cured adhesive sheet after being incorporated into a rotating electric machine.

[0285] Furthermore, as the average particle size of the filler increases, the surface roughness of the adhesive layer tends to increase, the hardness of the adhesive layer tends to increase, and the coefficient of friction of the surface of the adhesive layer tends to decrease, which tends to decrease the stickiness of the adhesive layer and increase the slipperiness of the adhesive layer. Therefore, when the average particle sizes of the filler contained in the first adhesive layer and the second adhesive layer are different from each other, the surface roughness, hardness, and coefficient of friction of the first adhesive layer and the second adhesive layer can be made different from each other. This allows the stickiness and slipperiness of the first adhesive layer and the second adhesive layer to be made different from each other.

[0286] For example, if the average particle size of the filler contained in the first adhesive layer is larger than the average particle size of the filler contained in the second adhesive layer, the surface roughness of the first adhesive layer can be made larger than the surface roughness of the second adhesive layer, the hardness of the first adhesive layer can be made larger than the hardness of the second adhesive layer, and the coefficient of friction of the surface of the first adhesive layer can be made smaller than the coefficient of friction of the surface of the second adhesive layer. In this case, the stickiness of the first adhesive layer tends to be lower than the stickiness of the second adhesive layer, and the slipperiness of the first adhesive layer tends to be higher than the slipperiness of the second adhesive layer. In such a case, for example, when a foam adhesive sheet is placed in a slot of the stator core and then a coil is placed in the slot of the stator core, by placing the foam adhesive sheet so that the first adhesive layer is on the coil side and the second adhesive layer is on the stator core side, when the foam adhesive sheet is placed in the slot of the stator core, the second adhesive layer has better adhesion, so the foam adhesive sheet is less likely to shift position relative to the stator core, and when a coil is placed in the slot of the stator core, the first adhesive layer has better slip properties, so the coil can be inserted smoothly into the narrower gap created by inserting the foam adhesive sheet into the slot of the stator core.

[0287] The average particle size of the filler can be the same as the average particle size of the filler contained in the first adhesive layer and the second adhesive layer in the third embodiment.

[0288] The difference in the average particle size of the filler contained in the first adhesive layer and the second adhesive layer should be such that it is possible to distinguish between the surface on the first adhesive layer side and the surface on the second adhesive layer side, both for the foamable adhesive sheet before foaming and hardening, and for the adhesive sheet after foaming and hardening after being incorporated into a rotating electric motor.

[0289] Furthermore, for example, when the refractive indexes of the fillers contained in the first adhesive layer and the second adhesive layer are different, the transparency and whiteness of the first adhesive layer and the second adhesive layer can be made different. Therefore, for example, by visual observation, it is easy to distinguish between the surface facing the first adhesive layer and the surface facing the second adhesive layer. Furthermore, when the refractive indexes of the fillers contained in the first adhesive layer and the second adhesive layer are different, for example, when the fillers contained in the first adhesive layer and the second adhesive layer are inorganic fillers and the compositions of the inorganic fillers are different, the foamable adhesive sheet of this embodiment is placed between the stator core and coil of a stator for a rotating electrical machine, foamed and cured, and the stator core and coil are bonded together. After that, for example, qualitative or quantitative analysis of the elements contained in the filler is performed using a scanning electron microscope and energy dispersive X-ray spectroscopy (SEM-EDX), making it easy to distinguish between the surface facing the first adhesive layer and the surface facing the second adhesive layer of the foamed and cured adhesive sheet. Therefore, it is possible to distinguish between the surface on the first adhesive layer side and the surface on the second adhesive layer side for both the foamable adhesive sheet before foaming and curing and the adhesive sheet after foaming and curing after being incorporated into a rotating electrical machine.

[0290] The refractive index of the filler is appropriately selected depending on the refractive index of the resin components contained in the first adhesive layer and the second adhesive layer.

[0291] The difference in refractive index between the filler contained in the first adhesive layer and the second adhesive layer should be such that the surface of the foamable adhesive sheet before foaming and curing can be distinguished from the surface of the first adhesive layer side and the surface of the second adhesive layer side.

[0292] Furthermore, when the refractive indices of the fillers contained in the first adhesive layer and the second adhesive layer are different from each other, it is preferable that the filler is an inorganic filler and that the compositions of the inorganic fillers contained in the first adhesive layer and the second adhesive layer are different from each other.

[0293] The filler content is appropriately set depending on the desired surface roughness, hardness, and coefficient of friction, as well as the strength and adhesive force required for the first adhesive layer and the second adhesive layer after foaming and curing. The filler content is, for example, 200 parts by mass or less, or may be 150 parts by mass or less, or may be 100 parts by mass or less, relative to 100 parts by mass of the resin component contained in the first adhesive layer or the second adhesive layer. If the filler content is too high, foaming of the first adhesive layer or the second adhesive layer may be inhibited. On the other hand, the filler content is, for example, 1 part by mass or more, or may be 5 parts by mass or more, or may be 10 parts by mass or more, relative to 100 parts by mass of the resin component contained in the first adhesive layer or the second adhesive layer. For example, when performing qualitative or quantitative analysis using SEM-EDX, if the filler content is too low, the analysis may become difficult.

[0294] The material of the filler in this embodiment can be the same as the material of the filler contained in the first adhesive layer and the second adhesive layer in the third embodiment.

[0295] (b) curable adhesives, foaming agents, and other ingredients The curable adhesive, foaming agent, and other components contained in the first adhesive layer and second adhesive layer in this embodiment can be the same as those in the first adhesive layer and second adhesive layer in the first example of the first embodiment above.

[0296] (2) Characteristics and configuration of the first adhesive layer and the second adhesive layer The adhesiveness of the first adhesive layer and the second adhesive layer in this embodiment can be the same as the adhesiveness of the first adhesive layer and the second adhesive layer in the second example of the first embodiment. In addition, other properties of the first adhesive layer and the second adhesive layer in this embodiment can be the same as the properties of the first adhesive layer and the second adhesive layer in the first example of the first embodiment.

[0297] Furthermore, the thickness, shape, and forming method of the first adhesive layer and the second adhesive layer may be the same as those of the first adhesive layer and the second adhesive layer in the first example of the first embodiment.

[0298] 2. Base material The substrate in this embodiment is a member that supports the first adhesive layer and the second adhesive layer.

[0299] The material, characteristics, shape, thickness, etc. of the substrate may be the same as those of the substrate in the first example of the first embodiment.

[0300] 3. First primer layer and second primer layer The foamable adhesive sheet of this embodiment may have a first primer layer between the substrate and the first adhesive layer, and may also have a second primer layer between the substrate and the second adhesive layer.

[0301] The arrangement, material, thickness, formation method, etc. of the first primer layer and the second primer layer can be the same as those of the first primer layer and the second primer layer in the first example of the first embodiment.

[0302] 4.Foam adhesive sheet In this embodiment, for example, if the average particle size of the filler contained in the first adhesive layer is larger than the average particle size of the filler contained in the second adhesive layer, it is preferable that the first adhesive layer be positioned on the coil side and the second adhesive layer be positioned on the stator core side.

[0303] The thickness, characteristics, manufacturing method, etc. of the foamable adhesive sheet of this embodiment can be the same as those of the foamable adhesive sheet of the first example of the first embodiment.

[0304] V. Fifth embodiment A fifth embodiment of the foamable adhesive sheet of the present disclosure has a first adhesive layer, a substrate, and a second adhesive layer in this order, the first adhesive layer and the second adhesive layer containing a curable adhesive, at least one of the first adhesive layer and the second adhesive layer containing a foaming agent, the first adhesive layer and the second adhesive layer having properties different from each other, and a pattern layer disposed between the first adhesive layer and the substrate and at least one of the second adhesive layer and the substrate.

[0305] The foamable adhesive sheet of this embodiment has two configurations: a first example in which a design layer is disposed either between the first adhesive layer and the substrate or between the second adhesive layer and the substrate, and a second example in which a design layer is disposed both between the first adhesive layer and the substrate and between the second adhesive layer and the substrate. Each configuration will be explained below.

[0306] 1. First Example of Fifth Embodiment A first example of the fifth embodiment of the foamable adhesive sheet of the present disclosure has a first adhesive layer, a substrate, and a second adhesive layer in this order, the first adhesive layer and the second adhesive layer containing a curable adhesive, at least one of the first adhesive layer and the second adhesive layer containing a foaming agent, the first adhesive layer and the second adhesive layer having properties different from each other, and a pattern layer disposed either between the first adhesive layer and the substrate or between the second adhesive layer and the substrate.

[0307] FIG. 11 is a schematic cross-sectional view illustrating an example of a foamable adhesive sheet according to this embodiment. The foamable adhesive sheet 10 in FIG. 11 comprises a first adhesive layer 1a, a substrate 2, and a second adhesive layer 1b, in this order. The first adhesive layer 1a and the second adhesive layer 1b contain a curable adhesive, and at least one of the first adhesive layer 1a and the second adhesive layer 1b contains a foaming agent. The first adhesive layer 1a and the second adhesive layer 1b have different properties. A design layer 5 is disposed between the first adhesive layer 1a and the substrate 2. While the design layer 5 is disposed only between the first adhesive layer 1a and the substrate 2 in FIG. 11, the design layer may be disposed only between the second adhesive layer and the substrate.

[0308] In this embodiment, since a design layer is disposed either between the first adhesive layer and the substrate or between the second adhesive layer and the substrate, the design layer can be made visible from either the surface facing the first adhesive layer or the surface facing the second adhesive layer, making it easy to distinguish between the surface facing the first adhesive layer and the surface facing the second adhesive layer by visual observation, for example. For example, when a design layer is disposed between the first adhesive layer and the substrate, the design layer can be made visible from the surface facing the first adhesive layer but not from the surface facing the second adhesive layer, making it easy to distinguish between the surface facing the first adhesive layer and the surface facing the second adhesive layer by visual observation. This prevents operational errors when using the foamable adhesive sheet.

[0309] Furthermore, in this embodiment, because a pattern layer is disposed either between the first adhesive layer and the substrate or between the second adhesive layer and the substrate, the foamable adhesive sheet of this embodiment is disposed between the stator core and coil of a rotating electrical machine stator, foamed and cured, and even after the stator core and coil are bonded together, it is easy to distinguish between the side of the adhesive sheet facing the first adhesive layer and the side facing the second adhesive layer by, for example, visually observing the appearance of the pattern layer from both sides. This makes it possible to identify the cause of a failure due to incorrectly positioning the foamable adhesive sheet on the front and back, and to detect such failures early on.

[0310] In this manner, in this embodiment, it is possible to distinguish between the surface on the first adhesive layer side and the surface on the second adhesive layer side not only for the foamable adhesive sheet before it has foamed and hardened, but also for the adhesive sheet after it has foamed and hardened after being incorporated into a rotating electric machine.

[0311] In this embodiment, a design layer is disposed either between the first adhesive layer and the substrate or between the second adhesive layer and the substrate, thereby improving the adhesion between the first adhesive layer or the second adhesive layer and the substrate. Furthermore, the presence of a design layer can, for example, reduce stress on the bent portion when the foamable adhesive sheet is folded, or reduce stress on the cut portion when the foamable adhesive sheet is cut. As a result, lifting or peeling of the first adhesive layer or the second adhesive layer from the substrate can be suppressed when the foamable adhesive sheet is bent or cut.

[0312] Each component of the foamable adhesive sheet of this embodiment will be described below.

[0313] (1) Picture layer In this embodiment, the design layer is disposed either between the first adhesive layer and the substrate or between the second adhesive layer and the substrate.

[0314] The design layer has any design such as a picture, a photograph, a letter, a number, a symbol, a figure, or a pattern.

[0315] Examples of the design layer include a print layer and a concavo-convex layer having a concavo-convex shape.

[0316] The printed layer can be formed using a common ink. A common printing method can be used to form the printed layer. In addition, the printed layer may be monochromatic or multicolored. In particular, chromatic colors such as red, blue, yellow, and green are preferred.

[0317] The uneven layer has an uneven shape on its surface. The uneven shape is not particularly limited as long as it can form any pattern, and the height and pitch of the uneven shape are set as appropriate. The pitch of the uneven shape may be regular or irregular. The material for the uneven layer is not particularly limited as long as it can form an uneven layer having an uneven shape on its surface, and examples thereof include curable resins such as thermosetting resins and photocurable resins, and photosensitive resins. The method for forming the uneven layer is appropriately selected depending on the material, and examples thereof include a molding method and a photolithography method.

[0318] The design layer is preferably disposed over the entire surface of the substrate. When the design layer is disposed over the entire surface of the substrate, it can also serve as a primer layer, as will be described later.

[0319] The design layer preferably also serves as a primer layer. In this case, the design layer can improve adhesion between the first adhesive layer or the second adhesive layer and the substrate. Furthermore, the design layer can, for example, reduce stress on the bent portion when the foamable adhesive sheet is folded, or reduce stress on the cut portion when the foamable adhesive sheet is cut. As a result, lifting or peeling of the first adhesive layer or the second adhesive layer from the substrate can be suppressed when the foamable adhesive sheet is bent or cut.

[0320] (2) First adhesive layer and second adhesive layer In this embodiment, the first adhesive layer and the second adhesive layer contain a curable adhesive, and at least one of the first adhesive layer and the second adhesive layer contains a foaming agent, and the first adhesive layer and the second adhesive layer have different properties from each other.

[0321] The material, thickness, shape, formation method, etc. of the first adhesive layer and second adhesive layer in this embodiment can be the same as those of the first adhesive layer and second adhesive layer in the first example of the first embodiment above.

[0322] The adhesiveness of the first adhesive layer and the second adhesive layer in this embodiment can be the same as the adhesiveness of the first adhesive layer and the second adhesive layer in the second example of the first embodiment. In addition, other properties of the first adhesive layer and the second adhesive layer in this embodiment can be the same as the properties of the first adhesive layer and the second adhesive layer in the first example of the first embodiment.

[0323] (3) Base material The substrate in this embodiment is a member that supports the first adhesive layer and the second adhesive layer.

[0324] The opacity of the substrate can be the same as that of the substrate in the second example of the first embodiment. The material, other properties, shape, thickness, etc. of the substrate can be the same as that of the substrate in the first example of the first embodiment.

[0325] (4) Primer layer In this embodiment, as described above, it is preferable that the design layer also serves as a primer layer. In this case, when the design layer is disposed between the substrate and the first adhesive layer, a primer layer may be disposed between the substrate and the second adhesive layer. On the other hand, when the design layer is disposed between the substrate and the second adhesive layer, a primer layer may be disposed between the substrate and the first adhesive layer.

[0326] For example, in the foamable adhesive sheet 10 shown in Fig. 12, a pattern layer 5 is disposed between the substrate 2 and the first adhesive layer 1a, and a primer layer 4 is disposed between the substrate 2 and the second adhesive layer 1b. Note that in Fig. 12, the pattern layer 5 is disposed between the substrate 2 and the first adhesive layer 1a, and the primer layer 4 is disposed between the substrate 2 and the second adhesive layer 1b, but the pattern layer may be disposed between the substrate and the second adhesive layer, and the primer layer may be disposed between the substrate and the first adhesive layer.

[0327] The arrangement, material, thickness, formation method, etc. of the primer layer may be the same as those of the first primer layer and the second primer layer in the first example of the first embodiment.

[0328] (5) Foam adhesive sheet The thickness, properties, production method, etc. of the foamable adhesive sheet of this embodiment can be the same as those of the foamable adhesive sheet of the first example of the first embodiment.

[0329] 2. Second Example of Fifth Embodiment A second example of the fifth embodiment of the foamable adhesive sheet of the present disclosure has a first adhesive layer, a substrate, and a second adhesive layer in this order, the first adhesive layer and the second adhesive layer contain a curable adhesive, at least one of the first adhesive layer and the second adhesive layer contains a foaming agent, the first adhesive layer and the second adhesive layer have different properties, a first pattern layer is disposed between the first adhesive layer and the substrate, a second pattern layer is disposed between the second adhesive layer and the substrate, and the patterns of the first pattern layer and the second pattern layer are different from each other.

[0330] Fig. 13 is a schematic cross-sectional view illustrating an example of a foamable adhesive sheet according to this embodiment. The foamable adhesive sheet 10 in Fig. 13 comprises a first adhesive layer 1a, a substrate 2, and a second adhesive layer 1b, in that order. The first adhesive layer 1a and the second adhesive layer 1b contain a curable adhesive, and at least one of the first adhesive layer 1a and the second adhesive layer 1b contains a foaming agent. The first adhesive layer 1a and the second adhesive layer 1b have different properties. A first design layer 5a is disposed between the first adhesive layer 1a and the substrate 2, and a second design layer 5b is disposed between the second adhesive layer 1b and the substrate 2. The designs of the first design layer 5a and the second design layer 5b are different from each other.

[0331] In this embodiment, a first pattern layer is disposed between the first adhesive layer and the substrate, and a second pattern layer is disposed between the second adhesive layer and the substrate. This allows the first pattern layer to be seen through from the side facing the first adhesive layer, and the second pattern layer to be seen through from the side facing the second adhesive layer. Furthermore, because the patterns of the first and second pattern layers are different from each other, it is easy to distinguish between the side facing the first adhesive layer and the side facing the second adhesive layer, for example, by visual observation. This prevents operational errors when using the foamable adhesive sheet.

[0332] Furthermore, in this embodiment, since the first pattern layer is disposed between the first adhesive layer and the substrate, and the second pattern layer is disposed between the second adhesive layer and the substrate, the foamable adhesive sheet of this embodiment is placed between the stator core and coil of a rotating electrical machine stator and foamed and cured, and even after the stator core and coil are bonded together, it is easy to distinguish between the side of the adhesive sheet facing the first adhesive layer and the side facing the second adhesive layer by, for example, visually observing the patterns on the first and second pattern layers. This makes it possible to identify the cause of a failure due to incorrectly positioning the foamable adhesive sheet on the front and back, and to detect such failures early on.

[0333] In this manner, in this embodiment, it is possible to distinguish between the surface on the first adhesive layer side and the surface on the second adhesive layer side not only for the foamable adhesive sheet before it has foamed and hardened, but also for the adhesive sheet after it has foamed and hardened after being incorporated into a rotating electric machine.

[0334] In this embodiment, the first pattern layer is disposed between the first adhesive layer and the substrate, and the second pattern layer is disposed between the second adhesive layer and the substrate. The first and second pattern layers improve the adhesion between the first and second adhesive layers and the substrate. Furthermore, the presence of the first and second pattern layers can, for example, reduce stress on the bent portion when the foamable adhesive sheet is folded, or reduce stress on the cut portion when the foamable adhesive sheet is cut. As a result, lifting or peeling of the first and second adhesive layers from the substrate can be suppressed when the foamable adhesive sheet is bent or cut.

[0335] Each component of the foamable adhesive sheet of this embodiment will be described below.

[0336] (1) First and second pattern layers In this embodiment, a first pattern layer is disposed between the first adhesive layer and the substrate, and a second pattern layer is disposed between the second adhesive layer and the substrate, and the patterns of the first pattern layer and the second pattern layer are different from each other.

[0337] The first and second design layers may have different designs, such as pictures, photographs, letters, numbers, symbols, figures, patterns, etc.

[0338] The first and second design layers may be similar to the design layers in the first example of the fifth embodiment.

[0339] (2) First adhesive layer and second adhesive layer In this embodiment, the first adhesive layer and the second adhesive layer contain a curable adhesive, and at least one of the first adhesive layer and the second adhesive layer contains a foaming agent, and the first adhesive layer and the second adhesive layer have different properties from each other.

[0340] The material, thickness, shape, formation method, etc. of the first adhesive layer and second adhesive layer in this embodiment can be the same as those of the first adhesive layer and second adhesive layer in the first example of the first embodiment above.

[0341] The adhesiveness of the first adhesive layer and the second adhesive layer in this embodiment can be the same as the adhesiveness of the first adhesive layer and the second adhesive layer in the second example of the first embodiment. In addition, other properties of the first adhesive layer and the second adhesive layer in this embodiment can be the same as the properties of the first adhesive layer and the second adhesive layer in the first example of the first embodiment.

[0342] (3) Base material The substrate in this embodiment is a member that supports the first adhesive layer and the second adhesive layer.

[0343] The material, characteristics, shape, thickness, etc. of the substrate may be the same as those of the substrate in the first example of the first embodiment.

[0344] (4) Foam adhesive sheet The thickness, properties, production method, etc. of the foamable adhesive sheet of this embodiment can be the same as those of the foamable adhesive sheet of the first example of the first embodiment.

[0345] B. Stators for rotating electrical machines The stator for a rotating electric machine in the present disclosure comprises a stator core having slots, a coil arranged in the slots, and an adhesive sheet arranged between the stator core and the coil, wherein the adhesive sheet is a foamed and cured product of the foamable adhesive sheet described above.

[0346] In the present disclosure, because the adhesive sheet is a foamed and cured product of the foamable adhesive sheet described above, it is possible to distinguish between the side of the adhesive sheet facing the first adhesive layer and the side of the adhesive sheet facing the second adhesive layer after the adhesive sheet has been incorporated into a rotating electrical machine. This makes it possible to identify the cause of a malfunction due to incorrectly positioning the foamable adhesive sheet on the front and back before it has been foamed and cured, and to discover such a malfunction at an early stage.

[0347] The configuration of the stator for the rotating electrical machine can be the same as that of a general stator for a rotating electrical machine, and therefore a description thereof will be omitted here.

[0348] A method for manufacturing a stator for a rotating electric machine can include an arrangement step of arranging the above-mentioned foamable adhesive sheet between the stator core and the coil, and an adhesion step of foaming and hardening the foamable adhesive sheet to adhere the stator core and the coil.

[0349] The method for placing the foam adhesive sheet between the stator core and the coil is not particularly limited, and examples include a method in which a foam adhesive sheet is placed in the slot of the stator core, and then a coil is inserted into the gap left after placing the foam adhesive sheet in the slot of the stator core, or a method in which a coil is placed in the slot of the stator core, and then a foam adhesive sheet is inserted into the gap between the stator core and the coil.

[0350] An example of a method for foaming and curing the foamable adhesive sheet is heating. Heating conditions are appropriately set depending on the type of curable adhesive and foaming agent contained in the first and second adhesive layers of the foamable adhesive sheet, the type of substrate, and other factors. The heating temperature can be, for example, 130°C or higher and 200°C or lower. The heating time can be, for example, 3 minutes or higher and 3 hours or lower.

[0351] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical idea described in the claims of the present disclosure and that provides similar effects is included within the technical scope of the present disclosure. [Explanation of symbols]

[0352] 1a…first adhesive layer 1b…Second adhesive layer 2...Base material 3...fiber layer 3a ... First fiber layer 3b…Second fiber layer 4... Primer layer 4a ... First primer layer 4b: Second primer layer 5...Picture layer 5a ... First pattern layer 5b ... Second pattern layer 10...Foam adhesive sheet

Claims

1. A first adhesive layer, a substrate, and a second adhesive layer in this order, the first adhesive layer and the second adhesive layer contain a curable adhesive; At least one of the first adhesive layer and the second adhesive layer contains a foaming agent; the first adhesive layer and the second adhesive layer have different properties; A foamable adhesive sheet, wherein the first adhesive layer and the second adhesive layer contain different amounts of filler.

2. A first adhesive layer, a substrate, and a second adhesive layer in this order, the first adhesive layer and the second adhesive layer contain a curable adhesive; At least one of the first adhesive layer and the second adhesive layer contains a foaming agent; the first adhesive layer and the second adhesive layer have different properties; A foamable adhesive sheet, wherein the first adhesive layer and the second adhesive layer contain different fillers.

3. The foamable adhesive sheet according to claim 2 , wherein the filler contained in the first adhesive layer and the second adhesive layer have different average particle sizes.

4. A first adhesive layer, a substrate, and a second adhesive layer in this order, the first adhesive layer and the second adhesive layer contain a curable adhesive; At least one of the first adhesive layer and the second adhesive layer contains a foaming agent; the first adhesive layer and the second adhesive layer have different properties; A foamable adhesive sheet, wherein a pattern layer is disposed at least either between the first adhesive layer and the substrate or between the second adhesive layer and the substrate.

5. The foamable adhesive sheet according to claim 4 , wherein the design layer is a printed layer or a concavo-convex layer having a concavo-convex shape.

6. 6. The foamable adhesive sheet according to claim 4, wherein the design layer also serves as a primer layer.

7. a stator core having slots; a coil disposed within the slot; an adhesive sheet disposed between the stator core and the coil; 7. A stator for a rotating electric machine, comprising: a foamed and cured adhesive sheet according to claim 1;

Images