Rotary electric machine stator, rotary electric machine rotor, foamable adhesive sheet, method for manufacturing rotary electric machine stator, and method for manufacturing rotary electric machine rotor

Abstract

The present invention provides a rotary electric machine stator. The rotary electric machine stator has: a stator core; a coil disposed in a slot of the stator core; and an adhesive sheet disposed between the stator core and the coil. The adhesive sheet has a foam layer and a non-foam layer. The ratio of the thickness of the foam layer to the thickness of the non-foam layer is 1 to 29, inclusive. The adhesive sheet is disposed such that the non-foam layer faces the coil side and the foam layer faces the stator core side.

Description

Stator for rotating electric machine, rotor for rotating electric machine, foamable adhesive sheet, method for manufacturing stator for rotating electric machine, and method for manufacturing rotor for rotating electric machine

[0001] The present disclosure relates to a stator for a rotating electric machine, a rotor for a rotating electric machine, a foamable adhesive sheet, a method for manufacturing a stator for a rotating electric machine, and a method for manufacturing a rotor for a rotating electric machine.

[0002] Generally, vehicles such as hybrid vehicles and electric vehicles include a rotating electric machine that can function as a motor and a generator. In addition, the rotating electric machine generally includes a stator as a fixed part and a rotor as a rotor that rotates with a predetermined gap between them.

[0003] In the stator, coils are inserted into slots in the stator core, and an insulating sheet is disposed between the inner peripheral surface of the slots of the stator core and the coils for insulation.

[0004] In addition, in the rotor of a wound field motor, coils are wound around the teeth of the rotor core, or coils are inserted between the teeth of the rotor core, i.e., into the slots of the rotor core, and an insulating sheet is placed between the teeth of the rotor core and the coils for insulation.

[0005] Conventionally, insulating paper has been used as the insulating sheet, and a method has been adopted in which the insulating paper is fixed between the stator core or rotor core and the coil using a liquid adhesive.

[0006] Meanwhile, in recent years, the use of adhesive sheets containing a foaming agent (foam adhesive sheets) instead of liquid adhesives has been proposed. For example, Patent Document 1 discloses a motor in which magnets are fixed to a rotor core using a heat-expanding adhesive tape, although this is not a technology for fixing coils to a stator core or rotor core. For example, Patent Document 2 discloses a stator in which coils are fixed to a stator core using insulating paper with foam layers on both sides. For example, Patent Document 3 discloses an insulating sheet for fixing coils to a stator core, the insulating sheet having an insulating base, a foamed resin layer, and a non-foamed resin layer, and the insulating sheet is folded so that the non-foamed resin layer faces the wall surface of the stator core.

[0007] Japanese Patent No. 6274540 Japanese Patent Application Laid-Open No. 2022-135608 Japanese Patent Application Laid-Open No. 2021-197888

[0008] In rotating electrical machines, heat is generated when a current flows through the coil. Generally, foam layers have low thermal conductivity and heat insulating properties. Therefore, when a coil is fixed to a stator core or rotor core using a foam adhesive sheet, heat dissipation may be reduced. In particular, heat dissipation is impaired when the foam layer is in contact with the coil.

[0009] The present disclosure has been made in consideration of the above-described circumstances, and has as its main object to provide a stator for a rotating electric machine and a rotor for a rotating electric machine that have good heat dissipation properties for heat generated from a coil.

[0010] One embodiment of the present disclosure provides a stator for a rotating electric machine having a stator core, coils arranged in slots of the stator core, and an adhesive sheet arranged between the stator core and the coil, wherein the adhesive sheet has a foam layer and a non-foam layer, the ratio of the thickness of the foam layer to the thickness of the non-foam layer is 1 or more and 29 or less, and the adhesive sheet is arranged so that the non-foam layer faces the coil side and the foam layer faces the stator core side.

[0011] Another embodiment of the present disclosure provides a rotor for a rotating electric machine having a rotor core, a coil arranged in a slot of the rotor core, and an adhesive sheet arranged between the rotor core and the coil, wherein the adhesive sheet has a foam layer and a non-foam layer, the ratio of the thickness of the foam layer to the thickness of the non-foam layer is 1 or more and 29 or less, and the adhesive sheet is arranged so that the non-foam layer faces the coil side and the foam layer faces the rotor core side.

[0012] Another embodiment of the present disclosure provides a foamable adhesive sheet used to fix a coil to a slot in a stator core or rotor core of a rotating electric machine, the foamable adhesive sheet having a first adhesive layer containing a curable adhesive and a foaming agent, and a second adhesive layer containing a curable adhesive but not a foaming agent, wherein the ratio of the thickness of the first adhesive layer to the thickness of the second adhesive layer is 1 or more and 8 or less, and the second adhesive layer is arranged so as to face the coil side, and the first adhesive layer is arranged so as to face the stator core side or the rotor core side.

[0013] Another embodiment of the present disclosure provides a manufacturing method for a stator for a rotating electric machine that fixes a coil in a slot of a stator core, the manufacturing method including: a preparation step of preparing a foamable adhesive sheet having a first adhesive layer containing a curable adhesive and a foaming agent, and a second adhesive layer containing the curable adhesive but not a foaming agent; an arrangement step of arranging the foamable adhesive sheet between the stator core and the coil so that the second adhesive layer faces the coil and the first adhesive layer faces the stator core; and an adhesion step of foaming and curing the foamable adhesive sheet and adhering the coil to the stator core, wherein the foamable adhesive sheet has a thickness ratio of the first adhesive layer to the second adhesive layer of 1 or more and 8 or less.

[0014] Another embodiment of the present disclosure provides a method for manufacturing a rotor for a rotating electric machine that fixes a coil in a slot of a rotor core, the method comprising: a preparation step of preparing a foamable adhesive sheet having a first adhesive layer containing a curable adhesive and a foaming agent, and a second adhesive layer containing a curable adhesive but not a foaming agent; an arrangement step of arranging the foamable adhesive sheet between the rotor core and the coil so that the second adhesive layer faces the coil and the first adhesive layer faces the rotor core; and an adhesion step of foaming and curing the foamable adhesive sheet and adhering the coil to the rotor core, wherein the foamable adhesive sheet has a ratio of the thickness of the first adhesive layer to the thickness of the second adhesive layer of 1 or more and 8 or less.

[0015] The present disclosure has the effect of improving the heat dissipation performance of heat generated from the coil.

[0016] FIG. 1 is a schematic plan view illustrating a stator for a rotating electric machine according to the present disclosure. FIG. 2 is a schematic plan view illustrating a stator for a rotating electric machine according to the present disclosure. FIG. 3 is a schematic plan view illustrating a stator for a rotating electric machine according to the present disclosure. FIG. 4 is a graph illustrating a stress-strain curve. FIG. 5 is a schematic plan view illustrating a rotor for a rotating electric machine according to the present disclosure. FIG. 6 is a schematic cross-sectional view illustrating a foamable adhesive sheet according to the present disclosure. FIG. 7 is a schematic cross-sectional view illustrating a foamable adhesive sheet according to the present disclosure. FIG. 8 is a schematic cross-sectional view illustrating a method for testing the tensile shear bond strength of the second adhesive layer after curing. FIG. 9 is a schematic cross-sectional view illustrating a method for testing the tensile shear bond strength of the first adhesive layer after foaming and curing. FIG. 10 is a schematic cross-sectional view illustrating a method for testing the tensile shear bond strength of the first adhesive layer after foaming and curing. FIG. 11 is a schematic cross-sectional view illustrating a method for testing the tensile shear bond strength of the foamable adhesive sheet after foaming and curing.

[0017] Embodiments of the present disclosure will be described below with reference to the drawings and the like. However, the present disclosure can be implemented in many different forms and should not be construed as being limited to the description of the embodiments exemplified below. Furthermore, to clarify the explanation, the drawings may show the width, thickness, shape, etc. of each part schematically compared to the actual form, but these are merely examples and do not limit the interpretation of the present disclosure. Furthermore, in this specification and each drawing, elements similar to those described above with reference to the previous drawings may be designated by the same reference numerals, and detailed descriptions may be omitted as appropriate.

[0018] In this specification, when describing a mode in which another component is placed on a certain component, the term "above" or "below" is used, unless otherwise specified, to include both a case in which another component is placed directly above or below a certain component so as to be in contact with the component, and a case in which another component is placed above or below a certain component with another component interposed therebetween. Also, in this specification, when describing a mode in which another component is placed on the surface of a certain component, the term "on the surface side" or "on the surface" is used, unless otherwise specified, to include both a case in which another component is placed directly above or below a certain component so as to be in contact with the component, and a case in which another component is placed above or below a certain component with another component interposed therebetween.

[0019] In this specification, the term "sheet" also includes a member called a "film." The term "film" also includes a member called a "sheet."

[0020] The stator for a rotating electric machine, the rotor for a rotating electric machine, the foamable adhesive sheet, the method for manufacturing a stator for a rotating electric machine, and the method for manufacturing a rotor for a rotating electric machine according to the present disclosure will be described in detail below.

[0021] A. Stator for a Rotating Electric Machine A stator for a rotating electric machine according to the present disclosure includes a stator core, coils disposed in slots of the stator core, and an adhesive sheet disposed between the stator core and the coils, wherein the adhesive sheet has a foam layer and a non-foam layer, the ratio of the thickness of the foam layer to the thickness of the non-foam layer being equal to or greater than 1 and equal to or less than 29, and the adhesive sheet is disposed such that the non-foam layer faces the coils and the foam layer faces the stator core.

[0022] Fig. 1(a) is a schematic plan view illustrating a stator for a rotating electric machine according to the present disclosure, and Figs. 1(b) and 1(c) are partially enlarged views of Fig. 1(a). As shown in Figs. 1(a) to 1(c), a stator 10 for a rotating electric machine includes a stator core 1, coils 3 disposed in slots 2 of the stator core 1, and an adhesive sheet 4 disposed between the stator core 1 and the coils 3. The adhesive sheet 4 includes a foam layer 11 and a non-foam layer 12. In the adhesive sheet 4, the ratio of the thickness of the foam layer 11 to the thickness of the non-foam layer 12 is within a predetermined range. The adhesive sheet 4 is disposed so that the non-foam layer 12 faces the coils 3 and the foam layer 11 faces the stator core 1.

[0023] Generally, a foam layer has low thermal conductivity and heat insulation properties. Therefore, if a coil is fixed to a stator core using a foam adhesive sheet, heat dissipation may be reduced. In particular, heat dissipation is impaired when the foam layer is in contact with the coil. On the other hand, a non-foam layer has a higher thermal conductivity than a foam layer because it is substantially free of bubbles caused by a foaming agent. In the present disclosure, the adhesive sheet is arranged so that the non-foam layer faces the coil, thereby conducting heat generated from the coil through the non-foam layer. This improves heat dissipation.

[0024] As illustrated in FIG. 1( b ), multiple coils 3 may be arranged in the slots 2 of the stator core 1. In this case, if there are gaps between the coils, the gaps become air gaps, allowing heat generated from the coils to be conducted through the air gaps. A foam layer adhesive composition containing a foaming agent is used for the foam layer. When the coils are fixed to the stator core, the foam layer adhesive composition foams and hardens. Therefore, if the adhesive sheet is arranged so that the foam layer faces the coils, the gaps between the coils are filled with the foam layer, eliminating the air gaps and resulting in reduced heat dissipation. On the other hand, a non-foam layer adhesive composition not containing a foaming agent is used for the non-foam layer. When the coils are fixed to the stator core, the non-foam layer adhesive composition hardens but does not foam. In the present disclosure, the adhesive sheet is arranged so that the non-foam layer faces the coils, ensuring sufficient gaps between the coils. Therefore, heat generated from the coils is conducted through the air gaps, improving heat dissipation.

[0025] Therefore, in the present disclosure, by arranging the adhesive sheet so that the non-foamed layer faces the coil, it is possible to improve the dissipation of heat generated from the coil.

[0026] The foam layer uses a foam layer adhesive composition containing a foaming agent. Therefore, the foam layer before foaming and curing may have unevenness due to the foaming agent. In this case, the unevenness due to the foaming agent tends to lower the coefficient of friction of the foam layer before foaming and curing, and improve the slipperiness of the foam layer before foaming and curing. Since the adhesive sheet is arranged so that the foam layer faces the stator core, the adhesive sheet before foaming and curing can be easily inserted into the slot of the stator core.

[0027] On the other hand, a non-foamed layer adhesive composition that does not contain a foaming agent is used for the non-foamed layer. Therefore, the non-foamed layer before curing does not have unevenness due to the foaming agent. Since the adhesive sheet is arranged so that the non-foamed layer faces the coil, when a coil is inserted into a slot of a stator core into which the adhesive sheet before foaming and curing has been inserted, the coil is prevented from getting caught on the surface of the non-foamed layer before curing. Therefore, it is possible to prevent the foaming agent from falling off and the non-foamed layer before curing from being scraped when inserting the coil. Therefore, the wear resistance of the adhesive sheet before foaming and curing can be improved.

[0028] Furthermore, in the present disclosure, by arranging the adhesive sheet so that the foam layer faces the stator core, the gap between the stator core and the adhesive sheet is filled with the foam layer, thereby improving the adhesion between the stator core and the adhesive sheet. In the adhesive sheet, the foam layer has a relatively weak cohesive force, while the non-foam layer has a relatively strong cohesive force. Furthermore, as illustrated in FIG. 1B , when multiple coils 3 are arranged in the slots 2 of the stator core 1, gaps exist between the coils, resulting in a small adhesive area on the coil side and a large adhesive area on the stator core side. Therefore, by arranging the adhesive sheet so that the foam layer, which has a relatively weak cohesive force, contacts the stator core, which allows for a large adhesive area, and the non-foam layer, which has a relatively strong cohesive force, contacts the coil, which allows for a small adhesive area, the coil can be firmly fixed to the stator core.

[0029] Furthermore, when the pre-foamed and cured adhesive sheet is inserted into the slot of the stator core in a folded state, a portion of the pre-foamed and cured foam layer located on the stator core side may come into contact with the wall surface or corner of the slot of the stator core and be scraped off. In contrast, in the present disclosure, the thickness of the foam layer is equal to or greater than the thickness of the non-foamed layer, and the ratio of the thickness of the foam layer to the thickness of the non-foamed layer is within a predetermined range, thereby preventing a decrease in foamability even if a portion of the pre-foamed and cured foam layer is scraped off. Furthermore, when the pre-foamed and cured adhesive sheet is inserted into the slot of the stator core in a folded state, tensile stress acts on the pre-foamed and cured foam layer located on the stator core side at the bent portion, causing the pre-foamed and cured foam layer to become thinner. In contrast, in the present disclosure, the thickness of the foam layer is equal to or greater than the thickness of the non-foamed layer, and the ratio of the thickness of the foam layer to the thickness of the non-foamed layer is within a predetermined range, thereby preventing a decrease in foamability even if the thickness of the pre-foamed and cured foam layer becomes thinner due to tensile stress at the bent portion. Therefore, sufficient foamability can be ensured.

[0030] The configuration of a stator for a rotating electric machine according to the present disclosure will be described below.

[0031] 1. Adhesive Sheet The adhesive sheet in the present disclosure has a foam layer and a non-foam layer, and is disposed between the stator core and the coil so that the non-foam layer faces the coil and the foam layer faces the stator core. In the present disclosure, the adhesive sheet is disposed between the stator core and the coil so that the non-foam layer contacts the coil and the foam layer contacts the stator core.

[0032] (1) Foam Layer The foam layer in the present disclosure is a layer containing bubbles.

[0033] (a) Material of Foam Layer The foam layer contains a foamed and cured product of an adhesive composition containing a curable adhesive and a foaming agent.

[0034] (i) Curable Adhesive The curable adhesive used in the foam layer of the present disclosure may be any curable adhesive generally used in the adhesive layer of a foamable adhesive sheet. Examples of the curable adhesive include thermosetting adhesives.

[0035] Examples of thermosetting 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.

[0036] Among them, the thermosetting adhesive is preferably an epoxy resin adhesive. That is, the thermosetting adhesive preferably contains an epoxy resin and a curing agent. In general, epoxy resin adhesives are excellent in mechanical strength, heat resistance, insulating properties, chemical resistance, etc., and have little shrinkage upon curing, making them suitable for a wide range of applications.

[0037] An example in which the curable adhesive is an epoxy resin adhesive will be described below.

[0038] (i-1) Epoxy Resin The epoxy resin in the present disclosure is a compound that has at least one epoxy group or glycidyl group and cures by a crosslinking polymerization reaction when used in combination with a curing agent. The epoxy resin also includes a monomer having at least one epoxy group or glycidyl group.

[0039] As the epoxy resin, an epoxy resin generally used in an epoxy resin adhesive can be used.

[0040] In particular, the thermosetting adhesive preferably contains, as epoxy resins, a first epoxy resin having a softening temperature of 50°C or higher and an epoxy equivalent of 5,000 g / eq or lower, and a second epoxy resin having a softening temperature higher than that of the first epoxy resin and a weight-average molecular weight of 20,000 or higher. By using a combination of the first epoxy resin and the second epoxy resin, the adhesive layer formed from the adhesive composition can be reduced in tackiness and can have good slip properties. Furthermore, the adhesive composition can have good blocking resistance and good adhesion after foaming and curing.

[0041] For example, when only improving adhesiveness after foaming and curing is desired, it is more effective to use a low molecular weight (low epoxy equivalent) epoxy resin than a high molecular weight (high epoxy equivalent) epoxy resin, but using a low molecular weight (low epoxy equivalent) epoxy resin is more likely to cause blocking.

[0042] In contrast, when a first epoxy resin having a relatively low softening temperature (relatively high crystallinity) and a low molecular weight (low epoxy equivalent weight) is used, the first epoxy resin rapidly melts and changes to a low-viscosity liquid when heated to a temperature above its softening temperature. This facilitates improved adhesiveness after foaming and curing. Meanwhile, the first epoxy resin has relatively high crystallinity, which can suppress blocking compared to epoxy resins having relatively low crystallinity or no crystallinity. However, when the first epoxy resin is used alone, the blocking suppression effect may be insufficient, or the adhesive layer formed from the adhesive composition may become too tacky. Therefore, by further using a second epoxy resin having a relatively high softening temperature (relatively low crystallinity) and a high molecular weight, the blocking suppression effect can be improved and the adhesive layer formed from the adhesive composition can be kept low in tackiness.

[0043] (i-1-1) First Epoxy Resin The first epoxy resin has a softening temperature of 50°C or higher and an epoxy equivalent of 5000 g / eq or lower. The first epoxy resin has a relatively low softening temperature (relatively high crystallinity) compared to the second epoxy resin described below. The first epoxy resin has relatively high crystallinity and a low molecular weight, which makes it easy to improve adhesion and blocking resistance after foaming and curing. Furthermore, the first epoxy resin has a low molecular weight, which makes it possible to increase the crosslink density, resulting in an adhesive layer with good mechanical strength, chemical resistance, and curing properties. Furthermore, the first epoxy resin is preferably an epoxy resin that is solid at room temperature (23°C).

[0044] The softening temperature of the first epoxy resin is usually 50° C. or higher, and may be 55° C. or higher, or 60° C. or higher. On the other hand, the softening temperature of the first epoxy resin is, for example, 150° C. or lower. The softening temperature is measured by the ring and ball method in accordance with JIS K7234:1986.

[0045] The epoxy equivalent of the first epoxy resin is, for example, 5000 g / eq or less, and may be 3000 g / eq or less, 1000 g / eq or less, or 600 g / eq or less. On the other hand, the epoxy equivalent of the first epoxy resin is, for example, 90 g / eq or more, 100 g / eq or more, or 110 g / eq or more. The epoxy equivalent is the number of grams of resin containing 1 gram equivalent of epoxy groups. The epoxy equivalent is measured by a method in accordance with JIS K7236:2009, which corresponds to ISO 3001 (Plastics - Epoxy compounds - Determination of epoxy equivalent).

[0046] The first epoxy resin may be a monofunctional epoxy resin, a difunctional epoxy resin, a trifunctional epoxy resin, or a tetrafunctional or higher functional epoxy resin.

[0047] The weight-average molecular weight (Mw) of the first epoxy resin is usually smaller than the weight-average molecular weight (Mw) of the second epoxy resin described below. The Mw of the first epoxy resin is, for example, 6,000 or less, and may be 4,000 or less, or 3,000 or less. On the other hand, the Mw of the first epoxy resin is, for example, 400 or more. Mw is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

[0048] The melt viscosity of the first epoxy resin at 150°C is, for example, 0.005 Pa·s or more, or may be 0.015 Pa·s or more, 0.03 Pa·s or more, 0.05 Pa·s or more, or 0.1 Pa·s or more. If the melt viscosity is too low, good foaming properties may not be obtained. Furthermore, if the melt viscosity of the first epoxy resin is too low (if the crystallinity of the first epoxy resin is too high), the adhesive layer formed from the adhesive composition may have high tackiness. This is presumably because if the melt viscosity of the first epoxy resin is too low (if the crystallinity of the first epoxy resin is too high), its crystallinity is significantly reduced when it is miscible with the second epoxy resin or acrylic resin, resulting in a decrease in the Tg of the adhesive layer. On the other hand, the melt viscosity of the first epoxy resin at 150°C is, for example, 10 Pa·s or less, or may be 5 Pa·s or less, or 2 Pa·s or less. If the melt viscosity is too high, the uniformity of the adhesive layer formed from the adhesive composition may be reduced. The melt viscosity is measured in accordance with JIS K6862:1984, which corresponds to ISO 2555 (Resins in the liquid state or as emulsions or dispersions—Determination of Brookfield RV viscosity), using a Brookfield-type single-cylinder rotational viscometer and a thermocell for heating the solution.

[0049] Next, the composition of the first epoxy resin will be described. Examples of the first epoxy resin include aromatic epoxy resins, aliphatic epoxy resins, alicyclic epoxy resins, and heterocyclic epoxy resins. Specific examples of the first epoxy resin include bisphenol-type epoxy resins such as bisphenol A-type epoxy resins and bisphenol F-type epoxy resins, novolac-type epoxy resins such as bisphenol A novolac-type epoxy resins and cresol novolac-type epoxy resins, and modified epoxy resins such as urethane-modified epoxy resins and rubber-modified epoxy resins. Other specific examples include biphenyl-type epoxy resins, stilbene-type epoxy resins, triphenolmethane-type epoxy resins, alkyl-modified triphenolmethane-type epoxy resins, triazine-nucleus-containing epoxy resins, dicyclopentadiene-modified phenol-type epoxy resins, naphthalene-type epoxy resins, glycol-type epoxy resins, and pentaerythritol-type epoxy resins. The first epoxy resin may be one type or two or more types.

[0050] Bisphenol A epoxy resins 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.

[0051] In particular, the first epoxy resin is preferably a bisphenol A novolac epoxy resin represented by the following general formula (1).

[0052]

[0053] In general formula (1), R １ is C ｍ H ２ｍ (m is 1 or more and 3 or less), and R ２ and R ３ are each independently C ｐ H ２ｐ＋１ (p is 1 or more and 3 or less), and n is 0 or more and 10 or less.

[0054] In general formula (1), R １ m in is 1, that is, R １ Ha-CH ２ Similarly, R ２ and R ３ p in is 1, that is, R ２ and R ３ Ha-CH ３ Furthermore, the hydrogen bonded to the benzene ring in general formula (1) may be substituted with other elements or other groups.

[0055] (i-1-2) Second Epoxy Resin The second epoxy resin has a softening temperature higher than that of the first epoxy resin and a weight-average molecular weight of 20,000 or more. The second epoxy resin has a relatively high softening temperature (relatively low crystallinity) compared to the first epoxy resin described above. The second epoxy resin has relatively low crystallinity and a high molecular weight, which makes it easy to improve blocking resistance. Furthermore, the second epoxy resin has relatively low crystallinity and a high molecular weight, which can suppress an increase in adhesion (tackiness) caused by the first epoxy resin. In addition, the second epoxy resin is preferably an epoxy resin that is solid at room temperature (23°C).

[0056] The weight average molecular weight (Mw) of the second epoxy resin is usually larger than the weight average molecular weight (Mw) of the first epoxy resin. The Mw of the second epoxy resin is usually 20,000 or more, or may be 30,000 or more, or may be 35,000 or more. On the other hand, the Mw of the second epoxy resin is, for example, 100,000 or less.

[0057] The epoxy equivalent of the second epoxy resin may be greater than, less than, or the same as the epoxy equivalent of the first epoxy resin. The epoxy equivalent of the second epoxy resin is, for example, 4000 g / eq or more, 5000 g / eq or more, or 6000 g / eq or more. On the other hand, the epoxy equivalent of the second epoxy resin is, for example, 20000 g / eq or less.

[0058] The second epoxy resin may be a monofunctional epoxy resin, a difunctional epoxy resin, a trifunctional epoxy resin, or a tetrafunctional or higher functional epoxy resin.

[0059] The softening temperature of the second epoxy resin is usually higher than that of the first epoxy resin. The difference between the two temperatures is, for example, 10°C or higher, and may be 20°C or higher, or 30°C or higher. The softening temperature of the second epoxy resin is, for example, 80°C or higher, and may be 90°C or higher. On the other hand, the softening temperature of the second epoxy resin is, for example, 180°C or lower.

[0060] The constitution of the second epoxy resin is the same as that of the first epoxy resin described above, and therefore description thereof will be omitted here.

[0061] (i-2) Acrylic Resin When the thermosetting adhesive is an epoxy resin-based adhesive, the adhesive composition may further contain an acrylic resin compatible with the epoxy resin. The acrylic resin is a resin compatible with the epoxy resin. Because the acrylic resin is compatible with the epoxy resin, it is easy to improve toughness. As a result, the adhesive properties 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 adhesive properties after foaming and curing. In addition, the flexibility of the acrylic resin can be exerted, improving adhesion to the substrate after foaming and curing and crack resistance after foaming and curing. Furthermore, the compatibility of the acrylic resin with the epoxy resin can maintain high hardness of the surface of the adhesive layer composed of the adhesive composition. On the other hand, if the acrylic resin is incompatible with the epoxy resin, a soft portion is formed on the surface of the adhesive layer, making the interface with the stator core less slippery and reducing workability.

[0062] The acrylic resin in the present disclosure is compatible with the epoxy resin. The compatibility of the acrylic resin with the epoxy resin can be confirmed by observing the cross section of an adhesive layer made of the adhesive composition with a scanning electron microscope (SEM) or a transmission electron microscope (TEM) to see if micron-sized islands are present. The average particle size of the islands is preferably 1 μm or less, and may be 0.5 μm or less, or may be 0.3 μm or less. A large number of samples is preferably used, for example, 100 or more. The area to be observed is a range of 100 μm × 100 μm, or, if the thickness of the adhesive layer is 100 μm or less, a range of the thickness × 100 μm.

[0063] The weight-average molecular weight (Mw) of the acrylic resin is, for example, 50,000 or more, or may be 70,000 or more, or even 100,000 or more. The first epoxy resin has relatively high crystallinity, which can result in a low melt viscosity (or dynamic viscoelasticity) when heated, potentially causing shrinkage during curing after foaming (between the end of foaming of the foaming agent and the curing of the adhesive composition). However, by using an acrylic resin with a certain molecular weight, it is possible to prevent the melt viscosity from becoming too low, making it less likely for shrinkage to occur during curing after foaming. Meanwhile, the Mw of the acrylic resin is, for example, 1,500,000 or less. The weight-average molecular weight of the acrylic resin is measured by GPC (eluent: THF, standard: PS, sample: 20 μL, flow rate: 1 mL / min, column temperature: 40°C).

[0064] The glass transition temperature (Tg) of the acrylic resin is, for example, 90° C. or higher, and may be 100° C. or higher. On the other hand, the Tg of the acrylic resin is, for example, 180° C. or lower. Tg is measured by a differential scanning calorimeter (DSC) in accordance with JIS K7121:2012, which corresponds to ISO 3146.

[0065] The acrylic resin has a storage modulus (E') of 1 x 10 at the foaming initiation temperature. ６ A low E' at the foaming initiation temperature can improve fluidity and provide good foaming properties. On the other hand, E' at the foaming initiation temperature can be, for example, 1 x 10 ５The foaming initiation temperature is a temperature that varies depending on the type of foaming agent. When two or more foaming agents are used, the foaming initiation temperature is the temperature at which the main foaming reaction begins.

[0066] The acrylic resin has a storage modulus (E') of 1 x 10 at the curing initiation temperature. ５ Pa or more. As described above, shrinkage may occur during curing after foaming (from the time when foaming of the foaming agent is completed until the adhesive composition is cured). However, if E' at the curing initiation temperature is large, shrinkage can be suppressed and good shape retention can be obtained. The curing initiation temperature varies depending on the type of curing agent. When two or more curing agents are used as the curing agent, the initiation temperature of the main curing reaction is taken as the curing initiation temperature.

[0067] The acrylic resin has an average storage modulus (E') of 1 x 10 at temperatures between 0°C and 100°C. ６ The average value of E' before foaming may be high, which allows for good non-stickiness and blocking resistance. On the other hand, the average value of the storage modulus (E') at temperatures from 0°C to 100°C may be, for example, 1 x 10 ８ Pa or less.

[0068] 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.

[0069] The acrylic resin may be a homopolymer of an acrylic acid ester monomer, a mixed component containing two or more of the above homopolymers, or a copolymer of two or more acrylic acid ester monomers, a component containing one or more copolymers. The acrylic resin may also be a mixed component of the above homopolymer and the above copolymer. The "acrylic acid" acrylic acid ester monomer also includes the concept of methacrylic acid. Specifically, the acrylic resin may be a mixture of a methacrylate polymer and an acrylate polymer, or an acrylic acid ester polymer such as acrylate-acrylate, methacrylate-methacrylate, or methacrylate-acrylate. Of these, it is preferable that the acrylic resin contain a copolymer of two or more acrylic acid ester monomers (a (meth)acrylic acid ester copolymer).

[0070] 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.

[0071] 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."

[0072] 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).

[0073] 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. Such modified products are more compatible with epoxy resins, thereby further improving adhesiveness.

[0074] Among these, the acrylic resin is preferably a (meth)acrylic acid ester copolymer having a first polymer portion having a glass transition temperature (Tg) of 10° C. or lower and a second polymer portion having a glass transition temperature (Tg) of 20° C. or higher. Such a (meth)acrylic acid ester copolymer has the first polymer portion that becomes a soft segment and the second polymer portion that becomes a hard segment.

[0075] The manifestation of the above-mentioned effects 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 the heat resistance, toughness, and flexibility can be improved.

[0076] 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.

[0077] When either the first polymer portion or the second polymer portion is incompatible with the epoxy resin, the (meth)acrylic acid ester copolymer has a compatible portion, which is a polymer portion that is compatible with the epoxy resin, and an incompatible portion, which is a polymer portion that is incompatible with the epoxy resin. In this case, when the (meth)acrylic acid ester copolymer is added, the compatible portion becomes compatible with the epoxy resin, and the incompatible portion becomes incompatible with the epoxy resin, causing fine phase separation. As a result, a fine sea-island structure is formed. The sea-island structure varies depending on the type of (meth)acrylic acid ester copolymer, the compatibility of the first polymer portion and the second polymer portion contained in the (meth)acrylic acid ester copolymer, and whether or not modification by introduction of polar groups has been performed, and examples include a sea-island structure in which the compatible portions of the cured epoxy resin and the (meth)acrylic acid ester copolymer are the sea and the incompatible portions of the (meth)acrylic acid ester copolymer are the islands, a sea-island structure in which the incompatible portions of the (meth)acrylic acid ester copolymer are the sea and the compatible portions of the cured epoxy resin and the (meth)acrylic acid ester copolymer are the islands, and a sea-island structure in which the (meth)acrylic acid ester copolymer is the sea and the cured epoxy resin is the islands. The presence of such a sea-island structure makes it easier to disperse stress, thereby preventing interfacial failure and achieving excellent adhesion after foaming and curing.

[0078] The (meth)acrylic acid ester copolymer is preferably a block copolymer, and particularly preferably an A-B-A block copolymer in which a compatible portion is polymer block A and an incompatible portion is polymer block B. Furthermore, an A-B-A block copolymer in which a first polymer portion is an incompatible portion and a second polymer portion is a compatible portion, with the first polymer portion being polymer block B and the second polymer portion being polymer block A, is preferred. By using such an A-B-A block copolymer as the acrylic resin, in a case where a sea-island structure is formed in which the compatible portion of the cured epoxy resin and the (meth)acrylic acid ester copolymer is a sea and the incompatible portion of the (meth)acrylic acid ester copolymer is an island, the island portions can be made smaller. Furthermore, in a case where a sea-island structure is formed in which the incompatible portion of the (meth)acrylic acid ester copolymer is a sea and the compatible portion of the cured epoxy resin and the (meth)acrylic acid ester copolymer is an island, or in a case where the (meth)acrylic acid ester copolymer is a sea and the cured epoxy resin is an island, the sea portions can be made smaller.

[0079] 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.

[0080] The Tg of the first polymer portion contained in the (meth)acrylic acid ester copolymer is 10°C or lower, in the range of -150°C or higher and 10°C or lower, particularly in the range of -130°C or higher and 0°C or lower, and particularly in the range of -110°C or higher and -10°C or lower.

[0081] The Tg of the first polymer portion is calculated using the following formula based on the Tg(K) of each homopolymer described in "POLYMER HANDBOOK, Third Edition" (published by John Wiley & Sons, Inc.): 1 / Tg(K)=W １ / Tg １ +W ２ / Tg ２ +...+W ｎ / Tg ｎ W ｎ ; Mass fraction of each monomer Tg ｎTg (K) of the homopolymer of each monomer, and publicly available values ​​such as those in the Polymer Handbook (3rd Ed., J. Brandrup and E. H. Immergut, Wiley Interscience) may be used. The same applies to the Tg of the second polymer portion described below.

[0082] The first polymer portion contained in the (meth)acrylic acid ester copolymer may be either a homopolymer or a copolymer, but is preferably a homopolymer. The monomer component and polymer component constituting the first polymer portion may be any monomer component and polymer component that can give a first polymer portion having a Tg within a predetermined range, and examples thereof include acrylate monomers such as butyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate, and methyl acrylate, other monomers such as vinyl acetate, acetal, and urethane, polar group-containing monomers containing the above-mentioned polar groups, and copolymers such as EVA.

[0083] The Tg of the second polymer portion contained in the (meth)acrylic acid ester copolymer is 20°C or higher, and is within the range of 20°C or higher and 150°C or lower, particularly within the range of 30°C or higher and 150°C or lower, and particularly within the range of 40°C or higher and 150°C or lower.

[0084] The second polymer portion contained in the (meth)acrylic acid ester copolymer may be either a homopolymer or a copolymer, but is preferably a homopolymer. The monomer component constituting the second polymer portion may be any monomer component capable of obtaining a second polymer portion having a Tg within a predetermined range, and examples thereof include acrylic acid ester monomers such as methyl methacrylate, other monomers such as acrylamide, styrene, vinyl chloride, amide, acrylonitrile, cellulose acetate, phenol, urethane, vinylidene chloride, methylene chloride, and methacrylonitrile, and polar group-containing monomers containing the above-mentioned polar groups.

[0085] A specific example of the (meth)acrylic acid ester copolymer having the first polymer portion and the second polymer portion is the above-mentioned MMA-BA-MMA copolymer.

[0086] (i-3) Curing Agent As the curing agent in the present disclosure, a curing agent generally used in an epoxy resin adhesive can be used. The curing agent is a curing agent that undergoes a curing reaction by heat. The curing agent is preferably solid at room temperature (23°C). A curing agent that is solid at room temperature can extend storage stability (pot life) compared to a curing agent that is liquid at room temperature. The curing agent may also be a latent curing agent. Furthermore, a single curing agent may be used, or two or more types may be used.

[0087] 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 is measured using a differential scanning calorimeter (DSC).

[0088] 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.

[0089] Examples of imidazole-based curing agents include imidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2-methylimidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole, 2-isopropylimidazole, 2-phenylimidazole, carboxylic acid salts of imidazole compounds, and adducts with epoxy compounds. Furthermore, it is preferable that the imidazole-based curing agent has a hydroxyl group. Crystallization occurs due to hydrogen bonding between the hydroxy groups, so the reaction initiation temperature tends to be high.

[0090] 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 viewpoints of adhesion to the substrate after foaming and curing and crack resistance after foaming and curing, phenolic 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.

[0091] 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.

[0092] 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 dianhydride (BTDA).

[0093] The isocyanate curing agent may, for example, be a blocked isocyanate.

[0094] Examples of thiol-based curing agents include ester-bonded thiol compounds, aliphatic ether-bonded thiol compounds, and aromatic ether-bonded thiol compounds.

[0095] (ii) Foaming Agent The foaming agent used in the foam layer of the present disclosure may be any foaming agent that is generally used in the adhesive layer of a foamable adhesive sheet. The foaming agent is a foaming agent that undergoes a foaming reaction when exposed to heat.

[0096] 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.

[0097] Furthermore, organic or 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.

[0098] The foaming initiation temperature of the foaming agent is preferably equal to or higher than the softening temperature of the base of the thermosetting adhesive, such as an epoxy resin, and equal to or lower than the activation temperature of the curing reaction of the base of the thermosetting 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 reaction initiation temperature is too high, the resin component may deteriorate.

[0099] The softening temperature is measured by the ring and ball method in accordance with JIS K7234:1986.

[0100] The average particle size of the foaming agent may be, for example, 10 μm or more, 13 μm or more, or 17 μm or more. When the average particle size of the foaming agent is within the above range, the static friction coefficient of the surface of the adhesive layer formed from the adhesive composition can be reduced, and slip properties can be improved. Furthermore, the average particle size of the foaming agent is preferably equal to or less than the thickness of the adhesive layer formed from the adhesive composition, and may be, for example, 44 μm or less, 30 μm or less, or 24 μm or less.

[0101] The average particle size of the foaming agent is the particle size at 50% of the cumulative value in the particle size distribution determined by laser diffraction scattering. Furthermore, when measuring the average particle size of the foaming agent, the adhesive composition is dissolved in a solvent to separate the foaming agent. The solvent is not particularly limited as long as it is capable of dissolving components other than the foaming agent contained in the adhesive composition, and is appropriately selected depending on the type of thermosetting adhesive, etc. For example, a solvent used in the adhesive composition can be used. Specifically, methyl ethyl ketone, ethyl acetate, or toluene can be used.

[0102] The expansion ratio of the foaming agent at the maximum foaming temperature is, for example, 1.5 times or more, and may be 2 times or more. On the other hand, the expansion ratio of the foaming agent at the maximum foaming temperature is, for example, 15 times or less, and may be 10 times or less. The expansion ratio of the foaming agent is the ratio of the diameter of the foaming agent after foaming to the diameter of the foaming agent before foaming.

[0103] (iii) Other Components In the adhesive composition used in the foam layer of the present disclosure, for example, when the curable adhesive is an epoxy resin adhesive, the adhesive composition may contain only an epoxy resin and an acrylic resin as resin components, or may further contain other resins, such as urethane resins.

[0104] The adhesive composition may contain additives such as 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, as necessary. Examples of the silane coupling agent include an epoxy-based silane coupling agent. Examples of the filler include inorganic fillers such as calcium carbonate, aluminum hydroxide, magnesium hydroxide, antimony trioxide, zinc borate, a molybdenum compound, and titanium dioxide. Examples of the antioxidant include a phenol-based antioxidant and a sulfur-based antioxidant.

[0105] (b) Thickness of Foam Layer In the present disclosure, the ratio of the thickness of the foam layer to the thickness of the non-foam layer is 1 or more, or may be 3 or more, or 5.5 or more. By having the thickness ratio within the above range, sufficient foamability can be ensured, as described above. On the other hand, the ratio of the thickness of the foam layer to the thickness of the non-foam layer is 29 or less, or may be 20 or less, or may be 13 or less. When the thickness ratio is within the above range, the thickness of the non-foam layer does not become too thin, thereby suppressing a decrease in adhesive strength. Specifically, the ratio of the thickness of the foam layer to the thickness of the non-foam layer is 1 or more and 29 or less, or may be 3 or more and 20 or less, or may be 5.5 or more and 13 or less.

[0106] The thickness of the foam layer is not particularly limited as long as it satisfies the above thickness relationship, and is appropriately set depending on the application. The thickness of the foam layer is, for example, 30 μm or more, or may be 40 μm or more, or 50 μm or more. The thickness of the foam layer is, for example, 1000 μm or less, or may be 900 μm or less, or may be 800 μm or less. That is, the thickness of the foam layer is, for example, 30 μm or more and 1000 μm or less, or may be 40 μm or more and 900 μm or less, or may be 50 μm or more and 800 μm or less. If the foam layer is too thin, sufficient adhesion may not be obtained. If the foam layer is too thick, the surface quality may be deteriorated.

[0107] (c) Other Points of the Foam Layer The foam layer may be a continuous layer or a discontinuous layer. Examples of discontinuous layers include patterns such as stripes and dots.

[0108] The foam layer contains a foamed and cured product of the adhesive composition. Examples of a method for foaming and curing the adhesive composition include heating.

[0109] (2) Non-foamed Layer The non-foamed layer in the present disclosure is a layer that is substantially free of bubbles derived from the foaming agent.

[0110] (a) Material of Non-Foamed Layer The non-foamed layer in the present disclosure contains a curable adhesive and a cured product of an adhesive composition that does not contain a foaming agent.

[0111] (i) Curable Adhesive The curable adhesive used in the non-foamed layer in the present disclosure is the same as the curable adhesive used in the foamed layer. The curable adhesive used in the foamed layer and the curable adhesive used in the non-foamed layer may be the same or different.

[0112] (ii) Foaming Agent The adhesive composition used in the non-foamed layer of the present disclosure does not contain a foaming agent. Here, "the adhesive composition does not contain a foaming agent" means that the content of the foaming agent in the adhesive composition is 2.0% by mass or less. The content of the foaming agent in the adhesive composition is preferably 1.0% by mass or less, and more preferably 0% by mass.

[0113] (iii) Other Components Other components contained in the adhesive composition used in the non-foamed layer in the present disclosure are the same as the other components contained in the adhesive composition used in the foamed layer.

[0114] (b) Thickness of the Non-Foamed Layer The thickness of the non-foamed layer is not particularly limited as long as it satisfies the above-mentioned thickness relationship and can be appropriately set depending on the application. The thickness of the non-foamed layer is, for example, 10 μm or more, 15 μm or more, or 20 μm or more. The thickness of the non-foamed layer is, for example, 200 μm or less, 150 μm or less, or 100 μm or less. That is, the thickness of the non-foamed layer is, for example, 10 μm or more to 200 μm or less, 15 μm or more to 150 μm or less, or 20 μm or more to 100 μm or less. If the non-foamed layer is too thin, sufficient adhesiveness may not be obtained. If the non-foamed layer is too thick, the thickness of the foamed layer becomes relatively thin, making it difficult to fill the gap between the stator core and the coil with the adhesive sheet, which may result in reduced adhesiveness.

[0115] (c) Other Points of the Non-Foamed Layer The non-foamed layer may be a continuous layer or a discontinuous layer. The surface of the non-foamed layer may have an uneven shape such as an embossed shape.

[0116] The non-foamed layer contains a cured product of the adhesive composition. The adhesive composition can be cured by heating.

[0117] (3) Substrate The adhesive sheet of the present disclosure may have a substrate between the foam layer and the non-foam layer. When a substrate is disposed between the foam layer and the non-foam layer, the insulating properties of the adhesive sheet can be improved. Furthermore, the adhesive sheet before foaming and curing can be made easier to handle and work with. On the other hand, when no substrate is disposed between the foam layer and the non-foam layer, the overall thickness of the adhesive sheet before foaming and curing can be reduced, allowing the adhesive sheet before foaming and curing to be inserted into narrow gaps.

[0118] For example, in the adhesive sheet 4 shown in Fig. 2, a substrate 13 is disposed between the foam layer 11 and the non-foam layer 12. On the other hand, in the adhesive sheet 4 shown in Fig. 1(c), for example, a substrate 13 is not disposed between the foam layer 11 and the non-foam layer 12.

[0119] 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.

[0120] Examples of the substrate include a resin substrate and a nonwoven fabric.

[0121] Examples of resins contained in the resin substrate include polyester resin, polycarbonate, polyarylate, polyurethane, polyamide resin, polyimide resin, polysulfone resin, polyether ketone resin, polyphenylene sulfide (PPS), and modified polyphenylene oxide. Examples of polyester resins include polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate (PEN), and aromatic polyester. Examples of polyamide resins include polyamide and polyether amide. Examples of polyimide resins include polyimide, polyether imide, and polyamide imide. Examples of polysulfone resins include polysulfone and polyether sulfone. Examples of polyether ketone resins include polyether ketone and polyether ether ketone. Liquid crystal polymers (LCPs) may also be used as the resin. The glass transition temperature of the resin is, for example, 80°C or higher, or may be 140°C or higher, or may be 200°C or higher.

[0122] Examples of nonwoven fabrics include nonwoven fabrics containing fibers such as cellulose fibers, polyester fibers, nylon fibers, aramid fibers, polyphenylene sulfide fibers, liquid crystal polymer fibers, glass fibers, metal fibers, and carbon fibers.

[0123] The substrate may be surface-treated to enhance adhesion to the foamed layer and the non-foamed layer.

[0124] 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.

[0125] (4) First Intermediate Layer and Second Intermediate Layer The adhesive sheet of the present disclosure may have a first intermediate layer between the substrate and the foam layer. The adhesive sheet of the present disclosure may also have a second intermediate layer between the substrate and the non-foam layer. The presence of the first intermediate layer or second intermediate layer can improve the adhesion of the foam layer or non-foam layer to the substrate. Furthermore, the presence of the first intermediate layer or second intermediate layer can reduce stress on the bent portion of the adhesive sheet. As a result, lifting or peeling of the foam layer or non-foam layer from the substrate can be suppressed.

[0126] For example, in the adhesive sheet 4 shown in Fig. 3, a first intermediate layer 14 is disposed between the substrate 13 and the foam layer 11, and a second intermediate layer 15 is disposed between the substrate 13 and the non-foam layer 12. Although the adhesive sheet 4 in Fig. 3 has both the first intermediate layer 14 and the second intermediate layer 15, it may have only one of them.

[0127] The adhesive sheet may have at least one of a first intermediate layer and a second intermediate layer, and may, for example, have only the first intermediate layer disposed between the substrate and the foam layer, or may have only the second intermediate layer disposed between the substrate and the non-foam layer, or may have both the first intermediate layer disposed between the substrate and the foam layer and the second intermediate layer disposed between the substrate and the non-foam layer. Of these, it is preferable that the first intermediate layer be disposed between the substrate and the foam layer, and the second intermediate layer be disposed between the substrate and the non-foam layer.

[0128] The materials contained in the first intermediate layer and the second intermediate layer are not particularly limited as long as they can improve adhesion between the substrate and the foamed layer or non-foamed layer and can relieve stress, and can be appropriately selected depending on the materials of the substrate, foamed layer, and non-foamed layer, etc. Examples include polyester, polyvinyl chloride, polyvinyl acetate, polyurethane, copolymers of at least two of these, crosslinked products thereof, and mixtures thereof.

[0129] The crosslinked product is a crosslinked product obtained by crosslinking the above-mentioned 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 mass % to 20 mass % relative to the resin.

[0130] In particular, the first intermediate layer and the second intermediate layer preferably contain a crosslinked resin. Note that 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.

[0131] The thickness of the first intermediate layer and the second intermediate layer is not particularly limited, but may be, for example, 0.1 μm or more, 0.5 μm or more, or 1 μm or more. If the first intermediate layer or the second intermediate layer is too thin, the effect of suppressing peeling of the foamed layer or the non-foamed layer from the substrate at the bent portion of the adhesive sheet may not be sufficiently obtained. On the other hand, the thickness of the first intermediate layer and the second intermediate layer may be, for example, 4 μm or less, or 3.5 μm or less. Since the first intermediate layer and the second intermediate layer themselves usually do not have high heat resistance, if the first intermediate layer or the second intermediate layer is too thick, the heat resistance (adhesive strength at high temperatures) may be reduced.

[0132] The first intermediate layer and the second intermediate layer can be formed, for example, by applying a resin composition and 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.

[0133] (5) Characteristics of the Adhesive Sheet (a) Electrical Insulation The adhesive sheet of the present disclosure preferably has high electrical insulation. The breakdown voltage of the adhesive sheet based on JIS C2107:2011, which corresponds to IEC 60454-2, is preferably 3 kV or more, and more preferably 5 kV or more. Having the breakdown voltage within the above range enables application to rotating electrical machines. Furthermore, the adhesive sheet preferably has a thermal conductivity of 0.05 W / mK or more, and more preferably 0.10 W / mK or more. Having the thermal conductivity within the above range allows for miniaturization of components and promotes the curing reaction during heating.

[0134] (b) Stress-strain curve (i) Stress-strain curve of non-foamed layer In the adhesive sheet of the present disclosure, in the stress-strain curve obtained when the tensile shear adhesive strength test method is performed on the non-foamed layer, the slope of the approximation line in the section from 3% strain to 5% strain is preferably 0.20 MPa or less, may be 0.15 MPa or less, or may be 0.10 MPa or less.

[0135] In adhesive sheets, the non-foamed layer tends to be harder and more brittle than the foamed layer. Therefore, when an adhesive sheet has a substrate between a foamed layer and a non-foamed layer, the non-foamed layer is likely to peel off from the substrate, which could result in the generation of foreign matter. Furthermore, when shear stress is applied to an adhesive sheet, excessive load is placed on layers other than the non-foamed layer, leading to destruction. Here, for a non-foamed layer, if the slope of the approximate line is large, the non-foamed layer tends to be hard, while if the slope of the approximate line is small, the non-foamed layer tends to be soft. For a non-foamed layer, if the slope of the approximate line is below a predetermined value, the non-foamed layer will have an appropriate hardness. Therefore, the difference between the hardness of the non-foamed layer and the hardness of the foamed layer can be reduced. Therefore, in an adhesive sheet, the adhesion of the non-foamed layer to the substrate can be improved, thereby preventing the generation of foreign matter. Furthermore, when shear stress is applied to an adhesive sheet, excessive load is prevented from being placed on layers other than the non-foamed layer, improving the durability of the adhesive sheet.

[0136] On the other hand, the slope of the approximation curve is, for example, 0.05 MPa or more, or may be 0.07 MPa or more, or 0.10 MPa or more. If the slope of the approximation curve for the non-foamed layer is below a predetermined value, the non-foamed layer may become too soft, which may result in a decrease in adhesiveness of the non-foamed layer. If the slope of the approximation curve is within the above range, the non-foamed layer will have an appropriate hardness, thereby ensuring the adhesiveness of the non-foamed layer.

[0137] Specifically, the gradient of the approximation curve may be 0.05 MPa or more and 0.20 MPa or less, or 0.07 MPa or more and 0.15 MPa or less.

[0138] (ii) Stress-strain curves of the foam layer and the non-foam layer In the adhesive sheet of the present disclosure, the difference between the slope of the approximate line in the section from 3% to 5% strain in the stress-strain curve obtained when the foam layer is subjected to the tensile shear adhesive strength test method and the slope of the approximate line in the section from 3% to 5% strain in the stress-strain curve obtained when the non-foam layer is subjected to the tensile shear adhesive strength test method is preferably 0.20 MPa or less, and may be 0.15 MPa or less, or may be 0.10 MPa or less. When the difference in the slope of the approximate curve is within the above range, the difference in hardness between the non-foam layer and the foam layer is small. Therefore, when the adhesive sheet has a substrate between the foam layer and the non-foam layer, peeling of the non-foam layer from the substrate can be suppressed, thereby suppressing the generation of foreign matter. Furthermore, excessive load on layers other than the non-foam layer can be suppressed in the adhesive sheet, improving the durability of the adhesive sheet. On the other hand, the difference in the slope of the approximation curve is, for example, 0.05 MPa or more, or may be 0.07 MPa or more, or may be 0.10 MPa or more. If the difference in slope is within the above range, the non-foamed layer will have an appropriate hardness, thereby ensuring the adhesiveness of the non-foamed layer. Specifically, the difference in slope of the approximation curve may be 0.05 MPa or more and 0.20 MPa or less, or may be 0.07 MPa or more and 0.15 MPa or less.

[0139] (iii) Stress-Strain Curve Measurement Method When performing the tensile shear adhesive strength test on a non-foamed layer, a non-foamed layer is prepared before curing. For example, if the adhesive sheet before foaming and curing is known and the adhesive composition or its composition used in the non-foamed layer is known, the adhesive composition or an adhesive composition with that composition is prepared to form the non-foamed layer before curing. The tensile shear adhesive strength test on the non-foamed layer is performed in the same manner as when performing the tensile shear adhesive strength test on the second adhesive layer after curing in a foamable adhesive sheet, as described below. In this case, the thickness of the non-foamed layer before curing is the thickness of the non-foamed layer before curing in the adhesive sheet before foaming and curing.

[0140] Furthermore, when performing the tensile shear adhesive strength test on the foam layer, a foam layer before foaming and curing is prepared. For example, if the adhesive sheet before foaming and curing is known and the adhesive composition or its composition used for the foam layer is known, the adhesive composition or an adhesive composition with that composition is prepared to form the foam layer before foaming and curing. The tensile shear adhesive strength test on the foam layer is performed in the same manner as when performing the tensile shear adhesive strength test on the first adhesive layer after foaming and curing in the foamable adhesive sheet described below. In this case, the thickness of the foam layer before foaming and curing is the thickness of the foam layer on the adhesive sheet before foaming and curing. Furthermore, the thickness of the spacer is the distance between the inner walls facing each other circumferentially in the slot of the stator core. If there is a manufacturing tolerance, the thickness of the spacer is the maximum allowable value.

[0141] The stress-strain curve is a plot of the relationship between shear stress and strain obtained in the above-mentioned tensile shear bond strength test method, with strain (%) on the horizontal axis and shear stress (MPa) on the vertical axis, as shown in Figures 4(a) and (b). The strain is the increase in the distance between the grippers divided by the length of the foamed or non-foamed layer, i.e., 12.5 mm. Figure 4(b) is a partially enlarged view of Figure 4(a).

[0142] In the stress-strain curve obtained by the above-mentioned tensile shear bond strength test method, the approximate straight line in the section from 3% strain to 5% strain is obtained by linearly approximating the curve in the section from 3% strain to 5% strain using the least squares method. The slope of the approximate straight line is then calculated. The above-mentioned tensile shear bond strength test method is performed three times, and the average value of the three measurements is used as the slope of the approximate straight line.

[0143] In the stress-strain curve obtained by the above-mentioned tensile shear bond strength test method, the initial slope is the slope in the elastic region. Therefore, in the present disclosure, the initial slope is adopted. Furthermore, in the stress-strain curve, shear stress tends to be unstable in the section below 3% strain. Therefore, in the present disclosure, the slope in the section from 3% strain to 5% strain is adopted as the initial slope.

[0144] For the non-foamed layer, examples of methods for controlling the slope of the approximate straight line include adjusting the composition of the adhesive composition used in the non-foamed layer and adjusting the drying conditions when forming the non-foamed layer.

[0145] In a method for adjusting the composition of the adhesive composition used in the non-foamed layer, as described below, by adding soft particles to the adhesive composition, the hardness of the non-foamed layer tends to decrease and the slope of the above-mentioned approximate straight line tends to decrease. Furthermore, in an adhesive composition containing an epoxy resin and a curing agent, if the number of functional groups of the epoxy resin is the same, by reducing the molecular weight of the epoxy resin, the hardness of the non-foamed layer tends to decrease and the slope of the above-mentioned approximate straight line tends to decrease. Furthermore, in an adhesive composition containing an epoxy resin and a curing agent, by reducing the content of a multifunctional epoxy resin, the crosslink density after curing decreases, and therefore the hardness of the non-foamed layer tends to decrease and the slope of the above-mentioned approximate straight line tends to decrease.

[0146] 2. Stator Core The stator core has slots into which coils are inserted. The stator core is similar to a general stator core, so a detailed description will be omitted here.

[0147] 3. Coil The coil is similar to a general coil, so a description thereof will be omitted here.

[0148] 4. Other aspects of the stator for a rotating electric machine The manufacturing method for the stator for a rotating electric machine will be described later.

[0149] B. Rotor for a Rotating Electric Machine A rotor for a rotating electric machine in the present disclosure is a rotor for a rotating electric machine having a rotor core, coils arranged in slots of the rotor core, and an adhesive sheet arranged between the rotor core and the coil, wherein the adhesive sheet has a foam layer and a non-foam layer, the ratio of the thickness of the foam layer to the thickness of the non-foam layer being equal to or greater than 1 and equal to or less than 29, and the adhesive sheet is arranged so that the non-foam layer faces the coil and the foam layer faces the rotor core.

[0150] Fig. 5(a) is a schematic plan view illustrating a rotor for a rotating electric machine according to the present disclosure, and Figs. 5(b) and 5(c) are partially enlarged views of Fig. 5(a). As shown in Figs. 5(a) to 5(c), a rotor 20 for a rotating electric machine includes a rotor core 21, coils 23 disposed in slots 22 of the rotor core 21, and an adhesive sheet 4 disposed between the rotor core 21 and the coils 23. The adhesive sheet 4 includes a foam layer 11 and a non-foam layer 12. In the adhesive sheet 4, the ratio of the thickness of the foam layer 11 to the thickness of the non-foam layer 12 is within a predetermined range. The adhesive sheet 4 is disposed so that the non-foam layer 12 faces the coils 23 and the foam layer 11 faces the rotor core 21.

[0151] In the present disclosure, the adhesive sheet is arranged so that the non-foamed layer faces the coil, so that heat generated from the coil is conducted via the non-foamed layer. Furthermore, by arranging the adhesive sheet so that the non-foamed layer faces the coil, a gap between the coils can be secured. Therefore, the heat generated from the coil is conducted via an air layer. Therefore, in the present disclosure, by arranging the adhesive sheet so that the non-foamed layer faces the coil, the heat dissipation performance of the heat generated from the coil can be improved.

[0152] Furthermore, as described above in "A. Stator for a rotating electric machine," the unevenness caused by the foaming agent tends to lower the coefficient of friction of the foam layer before foaming and curing, improving the slipperiness of the foam layer before foaming and curing. Since the adhesive sheet is arranged so that the foam layer faces the rotor core, the adhesive sheet before foaming and curing can be easily inserted into the slots of the rotor core.

[0153] Furthermore, as described above in "A. Stator for Rotating Electric Machine," the non-foamed layer before curing does not have any irregularities caused by the foaming agent. Since the adhesive sheet is arranged so that the non-foamed layer faces the coil, when inserting a coil into a slot of a rotor core into which the adhesive sheet before foaming and curing has been inserted, the coil is prevented from getting caught on the surface of the non-foamed layer before curing. This prevents the foaming agent from falling off and the non-foamed layer before curing from being scraped off when inserting the coil. This improves the wear resistance of the adhesive sheet before foaming and curing.

[0154] In addition, in the present disclosure, by arranging the adhesive sheet so that the foam layer faces the rotor core, the gap between the rotor core and the adhesive sheet is filled with the foam layer, thereby improving the adhesion between the rotor core and the adhesive sheet. Also, by arranging the adhesive sheet so that the foam layer, which has a relatively weak cohesive force, is in contact with the rotor core, which allows for a large adhesive area, and the non-foam layer, which has a relatively strong cohesive force, is in contact with the coil, which has a smaller adhesive area, the coil can be firmly fixed to the rotor core.

[0155] Furthermore, when the pre-foamed and cured adhesive sheet is inserted into the rotor core slot in a folded state, a portion of the pre-foamed and cured foam layer located on the rotor core side may come into contact with the wall surface or corner of the slot and be scraped off. In contrast, in the present disclosure, the thickness of the foam layer is equal to or greater than the thickness of the non-foamed layer, and the ratio of the thickness of the foam layer to the thickness of the non-foamed layer is within a predetermined range, thereby preventing a decrease in foamability even if a portion of the pre-foamed and cured foam layer is scraped off. Furthermore, when the pre-foamed and cured adhesive sheet is inserted into the rotor core slot in a folded state, tensile stress acts on the pre-foamed and cured foam layer located on the rotor core side at the bent portion, causing the pre-foamed and cured foam layer to become thinner. In contrast, in the present disclosure, the thickness of the foam layer is equal to or greater than the thickness of the non-foamed layer, and the ratio of the thickness of the foam layer to the thickness of the non-foamed layer is within a predetermined range, thereby preventing a decrease in foamability even if the thickness of the pre-foamed and cured foam layer becomes thinner due to tensile stress at the bent portion. Therefore, sufficient foamability can be ensured.

[0156] The configuration of the rotor for a rotating electric machine according to the present disclosure will be described below.

[0157] 1. Adhesive Sheet The adhesive sheet in the present disclosure has a foam layer and a non-foam layer, and is disposed between the rotor core and the coil so that the non-foam layer faces the coil and the foam layer faces the rotor core. In the present disclosure, the adhesive sheet is disposed between the rotor core and the coil so that the non-foam layer contacts the coil and the foam layer contacts the rotor core.

[0158] The adhesive sheet in the present disclosure is similar to the adhesive sheet in the stator for a rotating electric machine described above, and therefore a description thereof will be omitted here.

[0159] 2. Rotor Core The rotor core has slots into which coils are inserted. The rotor is similar to rotor cores generally used in wound-field motors, so a detailed description will be omitted here.

[0160] 3. Coil The coil is similar to a general coil, so a description thereof will be omitted here.

[0161] 4. Other Features of the Rotor for a Rotating Electric Machine The rotor for a rotating electric machine according to the present disclosure is a rotor for a rotating electric machine used in, for example, a wound field motor.

[0162] The method for manufacturing the rotor for a rotating electrical machine will be described later.

[0163] C. Foamable Adhesive Sheet The foamable adhesive sheet according to the present disclosure is a foamable adhesive sheet used to secure a coil to a slot in a stator core or rotor core of a rotating electric machine, the foamable adhesive sheet having a first adhesive layer containing a curable adhesive and a foaming agent, and a second adhesive layer containing a curable adhesive but no foaming agent, the ratio of the thickness of the first adhesive layer to the thickness of the second adhesive layer being equal to or greater than 1 and equal to or less than 8, and the second adhesive layer being arranged so as to face the coil, and the first adhesive layer being arranged so as to face the stator core or rotor core.

[0164] Fig. 6 is a schematic cross-sectional view illustrating an example of a foamable adhesive sheet according to the present disclosure. As shown in Fig. 6, foamable adhesive sheet 30 has a first adhesive layer 31 containing a curable adhesive and a foaming agent, and a second adhesive layer 32 containing a curable adhesive but not a foaming agent. The ratio of the thickness T1 of first adhesive layer 31 to the thickness T2 of second adhesive layer 32 is within a predetermined range. Foamable adhesive sheet 30 is arranged so that the second adhesive layer faces the coil side and the first adhesive layer faces the stator core side or the rotor core side.

[0165] The first adhesive layer contains a foaming agent and becomes a foamed layer after foaming and curing. Generally, foamed layers have low thermal conductivity and thermal insulation properties. Therefore, when a coil is fixed to a stator core using a foamed adhesive sheet, heat dissipation may be reduced. In particular, heat dissipation is impaired when the foamed layer is in contact with the coil. On the other hand, the second adhesive layer does not contain a foaming agent and becomes a non-foamed layer after curing. The non-foamed layer does not have bubbles caused by the foaming agent and therefore has a higher thermal conductivity than the foamed layer. In the present disclosure, the foamed adhesive sheet is arranged so that the second adhesive layer faces the coil, allowing heat generated from the coil to be conducted through the non-foamed layer. This improves heat dissipation.

[0166] Furthermore, if there is a gap between the coils, the gap becomes an air layer, and heat generated from the coil is conducted through the air layer. Because the first adhesive layer contains a foaming agent, the first adhesive layer foams and hardens when the coil is fixed to the stator core or rotor core. Therefore, if the foamable adhesive sheet is arranged so that the first adhesive layer faces the coil, the gap between the coils is filled with the foam layer, eliminating the air layer and reducing heat dissipation. On the other hand, because the second adhesive layer does not contain a foaming agent, the second adhesive layer hardens but does not foam when the coil is fixed to the stator core or rotor core. In the present disclosure, by arranging the foamable adhesive sheet so that the second adhesive layer faces the coil, gaps between the coils can be secured. Therefore, heat generated from the coil is conducted through the air layer, improving heat dissipation.

[0167] Therefore, in the present disclosure, by arranging the foamable adhesive sheet so that the second adhesive layer faces the coil side, it is possible to improve the dissipation of heat generated from the coil.

[0168] The first adhesive layer contains a foaming agent, and therefore may have irregularities due to the foaming agent. In this case, the irregularities due to the foaming agent tend to lower the coefficient of friction of the first adhesive layer and improve the slipperiness of the first adhesive layer. Because the foamable adhesive sheet is arranged so that the first adhesive layer faces the stator core or rotor core, the foamable adhesive sheet can be easily inserted into the slots of the stator core or rotor core.

[0169] On the other hand, the second adhesive layer does not contain a foaming agent and therefore does not have the irregularities caused by the foaming agent. Since the foamable adhesive sheet is arranged so that the second adhesive layer faces the coil, it is possible to prevent the coil from getting caught on the surface of the second adhesive layer when inserting the coil into a slot in a stator core or rotor core into which the foaming adhesive sheet has been inserted. This prevents the foaming agent from falling off and the second adhesive layer from being scraped off when the coil is inserted. This improves the abrasion resistance of the foamable adhesive sheet.

[0170] In addition, in the present disclosure, by arranging the foamable adhesive sheet so that the first adhesive layer faces the stator core or rotor core, the gap between the stator core or rotor core and the foamable adhesive sheet can be filled with the first adhesive layer after foaming and curing, thereby improving the adhesion between the stator core or rotor core and the foamable adhesive sheet after foaming and curing. Also, by arranging the foamable adhesive sheet so that the first adhesive layer, which has a relatively weak cohesive force, contacts the stator core or rotor core, which has a large adhesive area, and the second adhesive layer, which has a relatively strong cohesive force, contacts the coil, which has a small adhesive area, the coil can be firmly fixed to the stator core or rotor core.

[0171] Furthermore, when a foamable adhesive sheet is inserted into a slot of a stator core or rotor core in a folded state, a portion of the first adhesive layer disposed on the stator core or rotor core side may come into contact with the wall surface or corner of the slot of the stator core or rotor core and be scraped off. In contrast, in the present disclosure, the thickness of the first adhesive layer is equal to or greater than the thickness of the second adhesive layer, and the ratio of the thickness of the first adhesive layer to the thickness of the second adhesive layer is within a predetermined range, thereby preventing a decrease in foamability even if a portion of the first adhesive layer is scraped off. Furthermore, when a foamable adhesive sheet is inserted into a slot of a stator core or rotor core in a folded state, tensile stress acts on the first adhesive layer disposed on the stator core or rotor core side at the bent portion, causing the thickness of the first adhesive layer to become thinner. In contrast, in the present disclosure, the thickness of the first adhesive layer is equal to or greater than the thickness of the second adhesive layer, and the ratio of the thickness of the first adhesive layer to the thickness of the second adhesive layer is within a predetermined range, thereby preventing a decrease in foamability even if the thickness of the first adhesive layer becomes thinner due to tensile stress at the bent portion. Therefore, sufficient foamability can be ensured.

[0172] Hereinafter, each component of the foamable adhesive sheet according to the present disclosure will be described.

[0173] 1. First Adhesive Layer (1) Materials for the First Adhesive Layer The first adhesive layer in the present disclosure contains a curable adhesive and a foaming agent.

[0174] The material of the first adhesive layer is the same as the material used for the foam layer in the stator for a rotating electric machine described above, and therefore, a description thereof will be omitted here.

[0175] When the thermosetting adhesive is an epoxy resin-based adhesive and contains a first epoxy resin and a second epoxy resin as described above, the content of the first epoxy resin is, for example, 1 part by mass or more, 3 parts by mass or more, 5 parts by mass or more, 10 parts by mass or more, 15 parts by mass or more, or 25 parts by mass or more, relative to 100 parts by mass of the resin component contained in the first adhesive layer. If the content of the first epoxy resin is too low, the adhesiveness and blocking resistance after foaming and curing may be reduced. On the other hand, the content of the first epoxy resin is, for example, 90 parts by mass or less, 80 parts by mass or less, 70 parts by mass or less, 60 parts by mass or less, 50 parts by mass or less, or 40 parts by mass or less, relative to 100 parts by mass of the resin component contained in the first adhesive layer. If the content of the first epoxy resin is too high, the contents of the second epoxy resin and the acrylic resin will be relatively low, and it may not be possible to achieve a balance between non-stickiness, blocking resistance, adhesion to the substrate after foaming and curing, cracking resistance after foaming and curing, and adhesiveness after foaming and curing.

[0176] In the above case, the content of the second epoxy resin may be, for example, 10 parts by mass or more, 15 parts by mass or more, 20 parts by mass or more, 25 parts by mass or more, 30 parts by mass or more, 35 parts by mass or more, 40 parts by mass or more, or 45 parts by mass or more, relative to 100 parts by mass of the resin component contained in the first adhesive layer. If the content of the second epoxy resin is too low, the adhesion may be high and the blocking resistance may be reduced. On the other hand, the content of the second epoxy resin may be, for example, 90 parts by mass or less, 85 parts by mass or less, 80 parts by mass or less, or 75 parts by mass or less, relative to 100 parts by mass of the resin component contained in the first adhesive layer. If the content of the second epoxy resin is too high, the contents of the first epoxy resin and the acrylic resin may be relatively low, which may make it difficult to achieve a balance between non-stickiness, blocking resistance, adhesion to the substrate after foaming and curing, cracking resistance after foaming and curing, and adhesion after foaming and curing.

[0177] The proportion of the first epoxy resin relative to the total of the first epoxy resin and the second epoxy resin is, for example, 5% by mass or more, or alternatively 10% by mass or more, or 15% by mass or more, or alternatively 20% by mass or more, while the proportion of the first epoxy resin is, for example, 80% by mass or less, or alternatively 75% by mass or less, or alternatively 60% by mass or less.

[0178] Furthermore, the total proportion of the first epoxy resin and the second epoxy resin to all epoxy resins contained in the first adhesive layer is, for example, 50% by mass or more, or may be 70% by mass or more, or 90% by mass or more, or may be 100% by mass.

[0179] When the first adhesive layer and the second adhesive layer are substantially non-tacky and the curable adhesive is an epoxy resin-based adhesive, it is preferable that the first adhesive layer contains a first epoxy resin and a second epoxy resin as described above.

[0180] Furthermore, when the first adhesive layer is substantially non-adhesive and the second adhesive layer is adhesive, and the curable adhesive is an epoxy resin-based adhesive, it is preferable that the first adhesive layer contains a first epoxy resin and a second epoxy resin as described above.

[0181] On the other hand, when the first adhesive layer is adhesive and the second adhesive layer is substantially non-adhesive, and the curable adhesive is an epoxy resin-based adhesive, it is preferable that the first adhesive layer contains an epoxy resin that is liquid at room temperature, such as bisphenol A type epoxy resin or bisphenol F type epoxy resin, or an epoxy resin with a low softening point.

[0182] When the thermosetting adhesive is an epoxy resin-based adhesive and the first adhesive layer further contains an acrylic resin compatible with the epoxy resin, 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, relative to 100 parts by mass of the resin components contained in the first adhesive layer. If the content of the acrylic resin is too low, the adhesion to the substrate after foaming and curing, the cracking resistance after foaming and curing, and the adhesiveness after foaming and curing 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, relative to 100 parts by mass of the resin components contained in the first adhesive layer. If the content of the acrylic resin is too high, the contents of the first epoxy resin and the second epoxy resin will be relatively low, and it may be impossible to achieve a balance between non-stickiness, blocking resistance, adhesion to the substrate after foaming and curing, cracking resistance after foaming and curing, and adhesiveness after foaming and curing. Moreover, if the content of the acrylic resin is too high, the strength of the film may decrease.

[0183] The total ratio of epoxy resin and acrylic resin to the resin components contained in the first adhesive layer is, for example, 70% by mass or more, or may be 80% by mass or more, or 90% by mass or more, or may be 100% by mass.

[0184] The content of the resin component contained in the first adhesive layer is, for example, 60% by mass or more, or may be 70% by mass or more, or 80% by mass or more, or may be 90% by mass or more.

[0185] The content of the curing agent is, for example, 1 part by mass or more and 40 parts by mass or less per 100 parts by mass of the resin component contained in the first adhesive layer. Furthermore, when an imidazole-based curing agent is used as the main component of the curing agent, the content of the curing agent is preferably, for example, 1 part by mass or more and 15 parts by mass or less per 100 parts by mass of the resin component contained in the first adhesive layer. On the other hand, when a phenol-based curing agent is used as the main component of the curing agent, the content of the curing agent is preferably, for example, 5 parts by mass or more and 40 parts by mass or less per 100 parts by mass of the resin component contained in the first adhesive layer. Using an imidazole-based curing agent or a phenol-based curing agent as the main component of the curing agent means that the mass proportion of the imidazole-based curing agent or the phenol-based curing agent is the highest in the curing agent.

[0186] The content of the foaming agent is, for example, 0.5 parts by mass or more, 2 parts by mass or more, 3 parts by mass or more, 4 parts by mass or more, or 5 parts by mass or more, relative to 100 parts by mass of the resin component contained in the adhesive layer. On the other hand, the content of the foaming agent is, for example, 25 parts by mass or less, 20 parts by mass or less, or 15 parts by mass or less, relative to 100 parts by mass of the resin component contained in the adhesive layer. If the content of the foaming agent is too high, the content of the curable adhesive will be relatively low, which may result in a decrease in adhesion after foaming and curing.

[0187] (2) Thickness of the First Adhesive Layer In the present disclosure, the thickness of the first adhesive layer is equal to or greater than the thickness of the second adhesive layer. As described above, by making the thickness of the first adhesive layer equal to or greater than the thickness of the second adhesive layer, sufficient foaming properties can be ensured.

[0188] The ratio of the thickness of the first adhesive layer to the thickness of the second adhesive layer is 1 or more, and may be 1.2 or more, or 1.4 or more. By having the thickness ratio within the above range, sufficient foaming properties can be ensured, as described above. On the other hand, the ratio of the thickness of the first adhesive layer to the thickness of the second adhesive layer is 8 or less, and may be 6.6 or less, or 4.8 or less. When the thickness ratio is within the above range, the thickness of the second adhesive layer does not become too thin, thereby suppressing a decrease in adhesive strength. Specifically, the ratio of the thickness of the first adhesive layer to the thickness of the second adhesive layer is 1 or more and 8 or less, and may be 1.2 or more and 6.6 or less, or 1.4 or more and 4.8 or less.

[0189] The thickness of the first adhesive layer preferably satisfies the above thickness relationship and is equal to or greater than the average particle size of the foaming agent. The thickness of the first adhesive layer is, for example, 10 μm or more, or may be 15 μm or more, or 20 μm or more. If the first adhesive layer is too thin, it may be difficult to obtain sufficient adhesion to the substrate and adhesion after foam curing. On the other hand, the thickness of the first adhesive layer is, for example, 200 μm or less, or may be 150 μm or less, or may be 100 μm or less. If the first adhesive layer is too thick, the surface quality may be deteriorated. Specifically, the thickness of the first adhesive layer is 10 μm or more to 200 μm or less, or may be 15 μm or more to 150 μm or less, or may be 20 μm or more to 100 μm or less.

[0190] (3) Other Points of the First Adhesive Layer The first adhesive layer can be foamed at an expansion ratio of, for example, 1.5 times or more and 15 times or less. The expansion ratio may be, for example, 3.5 times or more, 4 times or more, or 4.5 times or more. The expansion ratio may also be, for example, 15 times or less, 14 times or less, or 13 times or less. If the expansion ratio is too small or too large, the adhesiveness after foaming and curing may be reduced.

[0191] Here, the expansion ratio is calculated by the following formula: Expansion ratio (times) = thickness of first adhesive layer after foaming and curing / thickness of first adhesive layer before foaming and curing

[0192] The first adhesive layer may be a continuous layer or a discontinuous layer. Examples of discontinuous layers include stripes and dots. The surface of the first adhesive layer may have an uneven shape such as an embossed shape.

[0193] The first adhesive layer can be formed, for example, by applying an adhesive composition containing the above-mentioned curable adhesive and a foaming agent, etc., and then removing the solvent. Examples of application methods include roll coating, reverse roll coating, transfer roll coating, gravure coating, gravure reverse coating, comma coating, rod coating, blade coating, bar coating, wire bar coating, die coating, lip coating, and dip coating.

[0194] 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.

[0195] The adhesive composition can be obtained by mixing the above-mentioned components and, if necessary, kneading and dispersing them. As a mixing and dispersing method, a general kneading disperser, such as a two-roll mill, a three-roll mill, a pebble mill, a tron ​​mill, a Szegvari attritor, a high-speed impeller disperser, a high-speed stone mill, a high-speed impact mill, a desper, a high-speed mixer, a ribbon blender, a co-kneader, an intensive mixer, a tumbler, a blender, a desperzer, a homogenizer, or an ultrasonic disperser can be used.

[0196] 2. Second Adhesive Layer (1) Material of Second Adhesive Layer The second adhesive layer in the present disclosure contains a curable adhesive and does not contain a foaming agent.

[0197] Here, the term "the second adhesive layer does not contain a foaming agent" means that the content of the foaming agent in the second adhesive layer is 2.0% by mass or less, preferably 1.0% by mass or less, and more preferably 0% by mass.

[0198] The material of the second adhesive layer is the same as the material used for the non-foamed layer in the stator for a rotating electric machine described above, and therefore, a description thereof will be omitted here.

[0199] When the first adhesive layer and the second adhesive layer are substantially non-tacky and the curable adhesive is an epoxy resin-based adhesive, it is preferable that the second adhesive layer contains the first epoxy resin and the second epoxy resin as described above.

[0200] Furthermore, when the first adhesive layer is adhesive and the second adhesive layer is substantially non-adhesive, and the curable adhesive is an epoxy resin-based adhesive, it is preferable that the second adhesive layer contains a first epoxy resin and a second epoxy resin as described above.

[0201] On the other hand, when the first adhesive layer is substantially non-adhesive and the second adhesive layer is adhesive, and the curable adhesive is an epoxy resin-based adhesive, it is preferable that the second adhesive layer contains an epoxy resin that is liquid at room temperature, such as bisphenol A type epoxy resin or bisphenol F type epoxy resin, or an epoxy resin with a low softening point.

[0202] (2) Thickness of the Second Adhesive Layer The thickness of the second adhesive layer preferably satisfies the above-mentioned thickness relationship. The thickness of the second adhesive layer is the same as the thickness of the first adhesive layer. Furthermore, if the second adhesive layer is too thick, the thickness of the first adhesive layer becomes relatively thin, making it difficult to fill the gap between the stator core or rotor core and the coil with the foamable adhesive sheet after foaming and curing, which may result in reduced adhesion.

[0203] (3) Other Features of the Second Adhesive Layer The second adhesive layer may be a continuous layer or a discontinuous layer. The surface of the second adhesive layer may have an uneven shape such as an embossed shape.

[0204] The method for forming the second adhesive layer is the same as the method for forming the first adhesive layer.

[0205] 3. Substrate The foamable adhesive sheet of the present disclosure may have a substrate between the first adhesive layer and the second adhesive layer. For example, in the foamable adhesive sheet 30 shown in Figure 7, a substrate 33 is disposed between the first adhesive layer 31 and the second adhesive layer 32. On the other hand, in the foamable adhesive sheet 30 shown in Figure 6, for example, a substrate 33 is not disposed between the first adhesive layer 31 and the second adhesive layer 32.

[0206] The substrate is the same as the substrate of the adhesive sheet in the stator for a rotating electric machine described above.

[0207] 4. First Intermediate Layer and Second Intermediate Layer The foamable adhesive sheet of the present disclosure may have a first intermediate layer between the substrate and the first adhesive layer. The foamable adhesive sheet of the present disclosure may also have a second intermediate layer between the substrate and the second adhesive layer. The presence of the first intermediate layer or second intermediate layer can improve the adhesion of the first adhesive layer or second adhesive layer to the substrate. Furthermore, the presence of the first intermediate layer or second intermediate 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 second adhesive layer from the substrate can be suppressed when the foamable adhesive sheet is bent or cut.

[0208] For example, in the foamable adhesive sheet 30 shown in Fig. 8, a first intermediate layer 34 is disposed between the substrate 33 and the first adhesive layer 31, and a second intermediate layer 35 is disposed between the substrate 33 and the second adhesive layer 32. Although the foamable adhesive sheet 30 in Fig. 8 has both the first intermediate layer 34 and the second intermediate layer 35, it may have only one of them.

[0209] The first and second intermediate layers are similar to the first and second intermediate layers of the adhesive sheet in the stator for a rotating electric machine described above.

[0210] 5. First Separator and Second Separator The foamable adhesive sheet according to the present disclosure may have a first separator on the side of the first adhesive layer opposite the second adhesive layer. Also, the foamable adhesive sheet according to the present disclosure may have a second separator on the side of the second adhesive layer opposite the first adhesive layer.

[0211] The first separator and the second separator are not particularly limited as long as they can be peeled from the first adhesive layer and the second adhesive layer, and can have a strength sufficient to protect the first adhesive layer and the second adhesive layer. Examples of such first separators and second separators include release films and release papers. The first separator and the second separator may have a single-layer structure or a multi-layer structure.

[0212] An example of a separator having a single layer structure is a fluororesin film.

[0213] Further, examples of multilayer separators include laminates having a release layer on one or both sides of a substrate layer. Examples of substrate layers include resin films such as polypropylene, polyethylene, and polyethylene terephthalate, as well as paper such as fine paper, coated paper, and impregnated paper. The material for the release layer is not particularly limited as long as it has releasability, and examples include silicone compounds, organic compound-modified silicone compounds, fluorine compounds, aminoalkyd compounds, melamine compounds, acrylic compounds, polyester compounds, and long-chain alkyl compounds. These compounds can be emulsion-type, solvent-type, or solventless.

[0214] 6. Properties of the Foamable Adhesive Sheet (1) Tack of the First Adhesive Layer and the Second Adhesive Layer In the present disclosure, both the first adhesive layer and the second adhesive layer may be substantially non-tacky (tack-free), or one of the first adhesive layer and the second adhesive layer may be substantially non-tacky and the other may be tacky.

[0215] When both the first adhesive layer and the second adhesive layer are substantially non-tacky, the slipperiness and blocking resistance can be improved. This improves the handleability and workability of the foamable adhesive sheet. Specifically, the foamable adhesive sheet can be smoothly inserted into the slots of a stator core or rotor core, or after the foamable adhesive sheet is placed around a coil, the coil and the foamable adhesive sheet can be smoothly inserted into the slots of the stator core or rotor core.

[0216] Here, the term "non-tacky" is generally used to mean that the adhesive strength is low, and in this specification, "non-tacky" means that the tack is less than 0.1 N.

[0217] On the other hand, when one of the first adhesive layer and the second adhesive layer is substantially non-adhesive and the other is adhesive, for example, when the first adhesive layer is substantially non-adhesive and the second adhesive layer is adhesive, adhesion to the coil can be improved. Specifically, when the second adhesive layer surface of the foamable adhesive sheet is attached to the coil and the coil with the foamable adhesive sheet attached is inserted into a slot in a stator core or rotor core, the adhesiveness of the second adhesive layer allows the adhesiveness of the second adhesive layer to be used to attach the second adhesive layer surface of the foamable adhesive sheet to the coil, thereby improving adhesion of the second adhesive layer to the coil. This prevents peeling or misalignment of the foamable adhesive sheet when inserting the coil with the foamable adhesive sheet attached into a slot in a stator core or rotor core.

[0218] In the above case, the adhesiveness of the second adhesive layer can improve reworkability, so that, for example, when the adhesiveness of the second adhesive layer is used to attach the surface of the foamable adhesive sheet to the coil as described above, misalignment of the foamable adhesive sheet can be corrected.

[0219] In the above case, the non-adhesive first adhesive layer can provide good sliding properties. Therefore, when inserting a coil with a foamable adhesive sheet attached thereto into a slot in a stator core or rotor core, the coil can be smoothly inserted, improving insertion ease. This can prevent the foamable adhesive sheet from peeling off or shifting out of position. Furthermore, when moving the coil relative to the stator core or rotor core to align the coil with the stator core or rotor core, the coil can be smoothly moved relative to the stator core or rotor core while inserted into the slot in the stator core or rotor core, facilitating alignment.

[0220] Furthermore, in the above case, as described above, the second adhesive layer has excellent adhesion to the coil, and the first adhesive layer has excellent slipperiness, which prevents peeling or misalignment of the foamable adhesive sheet, thereby preventing a decrease in the adhesive strength of the foamable adhesive sheet after foaming and curing due to peeling or misalignment of the foamable adhesive sheet, and reducing variations in the adhesive strength of the foamable adhesive sheet after foaming and curing due to peeling or misalignment of the foamable adhesive sheet.

[0221] In the above case, the adhesiveness of the second adhesive layer can prevent the second adhesive layer from lifting, for example, when the second adhesive layer is formed by a transfer method. Furthermore, as will be described later, when a second separator is disposed on the side of the second adhesive layer opposite the first adhesive layer, the adhesiveness of the second adhesive layer can easily peel off the second separator, improving workability.

[0222] When both the first adhesive layer and the second adhesive layer are substantially non-tacky, specifically, the tackiness of each of the first adhesive layer and the second adhesive layer is preferably less than 0.1 N, and may be 0.05 N or less, or may be 0.02 N or less. By having the tackiness of the first adhesive layer and the second adhesive layer within the above range, the first adhesive layer and the second adhesive layer can be made substantially non-tacky, and good sliding properties and blocking resistance can be achieved. In this case, the lower limit of the tackiness of the first adhesive layer and the second adhesive layer is not particularly limited and may be 0 N.

[0223] Furthermore, when the first adhesive layer is substantially non-adhesive and the second adhesive layer is adhesive, specifically, the tack of the first adhesive layer is less than 0.1 N, and the tack of the second adhesive layer is preferably 0.1 N or more and 5 N or less.

[0224] In the above case, the tackiness of the first adhesive layer is preferably less than 0.1 N, and may be 0.05 N or less, or may be 0.02 N or less. When the tackiness of the first adhesive layer is within the above range, the first adhesive layer can be made substantially non-sticky, and the slipperiness and blocking resistance can be improved. In this case, the lower limit of the tackiness of the first adhesive layer is not particularly limited, and may be 0 N.

[0225] In the above case, the tackiness of the second adhesive layer is preferably 0.1 N or more, and may be 0.3 N or more, or even 0.5 N or more. If the tackiness of the second adhesive layer is too low, for example, when using the tackiness of the second adhesive layer to attach the second adhesive layer surface of the foamable adhesive sheet to the coil, the adhesion between the second adhesive layer and the coil may be reduced. Furthermore, when inserting a coil to which the foamable adhesive sheet is attached into a slot in a stator core or rotor core, poor adhesion between the second adhesive layer and the coil may cause the foamable adhesive sheet to peel off or become misaligned, resulting in reduced adhesion between the first adhesive layer and the second adhesive layer after foaming and curing, or in variations in adhesive strength. Furthermore, the tackiness of the second adhesive layer is 5 N or less, or may be 4 N or less, or may be 3 N or less. If the tackiness of the second adhesive layer is too high, reworkability may be reduced. For example, when using the tackiness of the second adhesive layer to attach the second adhesive layer surface of the foamable adhesive sheet to the coil, it may be difficult to correct misalignment of the foamable adhesive sheet.

[0226] Here, the tackiness of the first adhesive layer and the second adhesive layer is measured by a probe tack test. Specifically, a cylindrical stainless steel probe with a diameter of 5 mm is pressed against the surface of the first adhesive layer or the second adhesive layer of the foamable adhesive sheet at a temperature of 25°C with a load of 10.0 gf and a speed of 30 mm / min, and after holding for 1.0 second, it is peeled off at a speed of 30 mm / min, and the load at the time of peeling is measured. This measurement is performed five times, and the average value is taken as the tackiness. As a probe tack tester, for example, a tackiness tester "TAC-II" manufactured by RHESCA is used.

[0227] The tackiness of the first adhesive layer and the second adhesive layer can be adjusted to fall within a predetermined range, for example, by adjusting the composition of the first adhesive layer and the second adhesive layer.

[0228] Specifically, the adhesive layer containing an epoxy resin and a curing agent can have a lower adhesive strength by using an epoxy resin that is solid at room temperature or a curing agent that is solid at room temperature, whereas the adhesive layer tends to have a higher adhesive strength by using an epoxy resin that is liquid at room temperature or a curing agent that is liquid at room temperature.

[0229] Furthermore, the adhesive layer containing an epoxy resin and a curing agent can have a reduced adhesive strength by incorporating an epoxy resin with a high softening temperature or an epoxy resin with a high weight-average molecular weight. On the other hand, the adhesive layer containing an epoxy resin and a curing agent tends to have a higher adhesive strength by incorporating an epoxy resin with a low softening temperature or an epoxy resin with a low weight-average molecular weight. For example, the adhesive layer can have a reduced adhesive strength by incorporating multiple epoxy resins with different softening temperatures, i.e., by incorporating one epoxy resin and another epoxy resin with a softening temperature of 25°C or higher and 10°C or higher than the softening temperature of the first epoxy resin. The adhesive layer can also have a reduced adhesive strength by incorporating multiple epoxy resins with different weight-average molecular weights, i.e., by incorporating one epoxy resin and another epoxy resin with a weight-average molecular weight of 370 or higher and 300 or higher than the weight-average molecular weight of the first epoxy resin. More specifically, in an adhesive layer containing an epoxy resin and a curing agent, the adhesive layer can be made to have a reduced adhesiveness by including a first epoxy resin having a low softening temperature and a low molecular weight and a second epoxy resin having a high softening temperature and a high molecular weight.

[0230] Furthermore, by adding an acrylic resin that is compatible with the epoxy resin to an adhesive layer containing an epoxy resin and a curing agent, the adhesiveness of the adhesive layer can be reduced.

[0231] Furthermore, by adding a tackifier to the adhesive layer, the adhesive layer tends to have increased adhesiveness.

[0232] In addition, when a curing agent that is liquid at room temperature is used, the adhesiveness tends to increase, but storage stability may decrease. Therefore, it is preferable to adjust the tackiness of the adhesive layer by adjusting the properties and type of components other than the curing agent, such as the epoxy resin.

[0233] Here, "adhesion" is a concept included in "bonding." The two are sometimes distinguished in that "adhesion" is used to mean a temporary adhesive phenomenon, while "bonding" is used to mean a substantially permanent adhesive phenomenon (Iwanami Shoten, Physics and Chemistry Dictionary, 5th Edition). "Adhesion" and "adhesive strength" refer to the property of adhesion through pressure and the adhesive strength at that time.

[0234] In this specification, unless otherwise specified, the terms "adhesion of the adhesive layer" and "adhesion strength of the adhesive layer" refer to the adhesion and adhesive strength of the adhesive layer before curing. In addition, in this specification, unless otherwise specified, the terms "adhesion of the adhesive layer" and "adhesion strength of the adhesive layer" refer to the adhesion and adhesive strength of the adhesive layer after curing.

[0235] (2) Bending Moment The foamable adhesive sheet of the present disclosure preferably has good shape retention. The bending moment based on JIS P8125-2:2017, which corresponds to ISO 2493, is, for example, 0.01 mN·N or more, and may be 0.1 mN·N or more. On the other hand, the bending moment may be, for example, less than 4 mN·N, and may be less than 3 mN·N. Conventionally, foamable adhesive sheets typically have a high bending moment to improve shape retention and ease of insertion into narrow gaps. In contrast, the inventors of the present disclosure have found that shape retention can be ensured by devising the shape, and that a high bending moment has other drawbacks. Therefore, taking other characteristics into consideration, it is preferable that the bending moment be within the above range. If the bending moment is smaller than the above range, shape retention may be difficult even with measures such as folding. Furthermore, if the bending moment is greater than the above range, the sheet will return to its original shape after bending, so it is necessary to heat the sheet or to score the folds. Heating reduces the sheet life, and scoring can reduce the insulation properties of the scored areas.

[0236] (3) Electrical Insulation The foamable adhesive sheet according to the present disclosure preferably has high electrical insulation properties after foaming and curing. After foaming and curing, the foamable adhesive sheet preferably has a breakdown voltage of 3 kV or more, more preferably 5 kV or more, based on JIS C2107:2011, which corresponds to IEC 60454-2. Having the breakdown voltage within the above range enables application to rotating electrical machines. Furthermore, after foaming and curing, the foamable adhesive sheet preferably has a thermal conductivity of 0.05 W / mK or more, more preferably 0.10 W / mK or more. Having the thermal conductivity within the above range allows for miniaturization of components and promotes the curing reaction during heating.

[0237] (4) Tensile Shear Adhesive Strength: The foamable adhesive sheet of the present disclosure preferably has high adhesiveness after foaming and curing. After foaming and curing, the tensile shear adhesive strength based on JIS K6850:1999, which corresponds to ISO 4587:1995, may be, for example, 1.5 MPa or more, 1.8 MPa or more, or 2.1 MPa or more at 23°C. Furthermore, the tensile shear adhesive strength may be, for example, 0.5 MPa or more, 0.75 MPa or more, or 1.0 MPa or more at 130°C. For example, a high-strength acrylic foam adhesive tape that does not require heating has a tensile shear adhesive strength of approximately 1 MPa or more and 2 MPa or less at room temperature and is not heat resistant at 200°C. Therefore, if the tensile shear adhesive strength is within the above range at 23°C, it has advantages in terms of strength. Furthermore, if the tensile shear adhesive strength is within the above range at 130° C., the adhesive can be applied to rotating electrical machines that require heat resistance.

[0238] (5) Stress-Strain Curve In the present disclosure, in the stress-strain curve obtained when the tensile shear adhesive strength test method is performed on the cured second adhesive layer, the slope of the approximation line in the section from 3% strain to 5% strain is preferably 0.20 MPa or less, and may be 0.15 MPa or less, or even 0.10 MPa or less. When the slope of the approximation curve is within the above range, the cured second adhesive layer has an appropriate hardness. Therefore, the difference between the hardness of the cured second adhesive layer and the hardness of the first adhesive layer after foaming and curing can be reduced. Therefore, after the foamable adhesive sheet has foamed and cured, the cured second adhesive layer is prevented from peeling from the substrate, thereby preventing the generation of foreign matter. Furthermore, after the foamable adhesive sheet has foamed and cured, excessive load on layers other than the second adhesive layer can be prevented, improving the durability of the foamable adhesive sheet after foaming and curing. Furthermore, the slope of the approximation curve is, for example, 0.05 MPa or more, may be 0.07 MPa or more, or may be 0.10 MPa or more. If the slope of the approximation curve is within the above range, the second adhesive layer after curing will have an appropriate hardness, and the adhesiveness of the second adhesive layer after curing will be high. Specifically, the slope of the approximation curve may be 0.05 MPa or more and 0.20 MPa or less, or may be 0.07 MPa or more and 0.15 MPa or less.

[0239] In the present disclosure, the difference between the slope of the approximate straight line in the section from 3% to 5% strain in the stress-strain curve obtained when the first adhesive layer after foaming and curing is subjected to a tensile shear bond strength test method and the slope of the approximate straight line in the section from 3% to 5% strain in the stress-strain curve obtained when the second adhesive layer after curing is subjected to a tensile shear bond strength test method is preferably 0.20 MPa or less, but may also be 0.15 MPa or less, or 0.10 MPa or less. When the difference in slope is within the above range, the difference in hardness between the second adhesive layer after curing and the first adhesive layer after foaming and curing is small. Therefore, after the foamable adhesive sheet is foamed and cured, the second adhesive layer after curing is prevented from peeling from the substrate, thereby preventing the generation of foreign matter. Furthermore, after the foamable adhesive sheet is foamed and cured, excessive load on layers other than the second adhesive layer is prevented, improving the durability of the foamable adhesive sheet after foaming and curing. Furthermore, the difference in the slopes of the approximation curves is, for example, 0.05 MPa or more, may be 0.07 MPa or more, or may be 0.10 MPa or more. If the difference in the slopes of the approximation curves is within the above range, the second adhesive layer after curing will have an appropriate hardness, and the adhesiveness of the second adhesive layer after curing will be high. Specifically, the difference in the slopes of the approximation curves may be 0.05 MPa or more and 0.20 MPa or less, or 0.07 MPa or more and 0.15 MPa or less.

[0240] The tensile shear bond strength test for the cured second adhesive layer is performed according to JIS K6850:1999, which corresponds to ISO 4587, using the following method. First, a second adhesive layer measuring 12.5 mm x 25 mm is prepared. For example, if the adhesive composition used in the second adhesive layer of the foamable adhesive sheet or its composition is known, the second adhesive layer can be formed using that adhesive composition or by preparing an adhesive composition with that composition. Alternatively, the composition of the second adhesive layer of the foamable adhesive sheet can be analyzed, and an adhesive composition with that composition can be prepared to form the second adhesive layer. Known methods can be used to analyze the composition of the second adhesive layer. The thickness of the second adhesive layer is the same as that of the second adhesive layer of the foamable adhesive sheet. Furthermore, as shown in FIG. 9, two metal plates 41a and 41b, each 1.6 mm thick, 25 mm wide, and 100 mm long, are prepared. For example, cold-rolled steel plate SPCC-SD can be used as the metal plate. A spacer 42 is placed at one end of one metal plate 41a at a predetermined distance. The thickness of the spacer 42 is at least 15 μm less than the thickness of the second adhesive layer and at most the thickness of the second adhesive layer. The thickness of the spacer 42 is adjusted, for example, by stacking multiple sheets of Kapton adhesive tape (manufactured by Teraoka Seisakusho Co., Ltd.). Next, the second adhesive layer 32 is placed between the spacers 42, and the other metal plate 41b is placed so that one end overlaps the other and secured with clips or adhesive tape such as Kapton tape to obtain a test specimen. Next, the second adhesive layer of the test specimen is cured. The curing conditions are adjusted appropriately depending on the curable adhesive contained in the second adhesive layer. Next, the tensile shear bond strength test method is performed on the cured test specimen in accordance with JIS K6850:1999. The measurement conditions are a tensile speed of 10 mm / min, a grip distance of 100 mm, room temperature (23°C), and humidity of 50% RH. As the tensile tester, for example, Tensilon RTF1350 manufactured by A&D Co., Ltd. is used.

[0241] Furthermore, the tensile shear adhesive strength test method for the first adhesive layer after foaming and curing is performed in accordance with JIS K6850:1999, which corresponds to ISO 4587, using the following method. First, a first adhesive layer measuring 12.5 mm x 25 mm is prepared. For example, if the adhesive composition used in the first adhesive layer of the foamable adhesive sheet or its composition is known, the first adhesive layer can be formed using that adhesive composition or by preparing an adhesive composition with that composition. Alternatively, the composition of the first adhesive layer of the foamable adhesive sheet can be analyzed, and an adhesive composition with that composition can be prepared to form the first adhesive layer. Known methods can be used to analyze the composition of the first adhesive layer. The thickness of the first adhesive layer is the same as that of the first adhesive layer of the foamable adhesive sheet. Furthermore, as shown in FIG. 10, two metal plates 41a and 41b, each 1.6 mm thick, 25 mm wide, and 100 mm long, are prepared. For example, cold-rolled steel plate SPCC-SD can be used as the metal plate. A spacer 42 is disposed at one end of one of the metal plates 41a with a predetermined gap therebetween. The thickness of the spacer 42 is appropriately set depending on the foaming ratio of the first adhesive layer. For example, as shown in FIG. 11 , a foamable adhesive sheet 30 is disposed between the stator core 1 or rotor core 21 and the coils 3, 23, and then, although not shown, the foamable adhesive sheet 30 is foamed and cured to bond the stator core 1 or rotor core 21 and the coils 3, 23. If the distance d1 between the stator core 1 or rotor core 21 and the coils 3, 23 is known, the gap d2 after the foamable adhesive sheet 30 is disposed between the stator core 1 or rotor core 21 and the coils 3, 23 is first calculated. The gap d2 is calculated by subtracting the thickness t1 of the foamable adhesive sheet 30 from the distance d1. Next, the thickness of the spacer 42 is determined based on the thickness of the first adhesive layer and the gap d2. The thickness of the spacer 42 is calculated by adding the thickness of the first adhesive layer to the gap d2. The thickness of the spacer 42 may be within ±5% of the sum of the thickness of the first adhesive layer and the gap d2. On the other hand, if the distance d1 between the stator core 1 or rotor core 21 and the coils 3, 23 is unknown, the foaming ratio of the first adhesive layer is first determined. The foaming ratio here refers to the foaming ratio when the first adhesive layer is foamed and cured without being sandwiched between any other components.The expansion ratio of the first adhesive layer can be determined by foaming and curing the foamable adhesive sheet without sandwiching it between any other components. In this case, the thickness of the spacer 42 is at least (thickness of the first adhesive layer) × (expansion ratio of the first adhesive layer) × 0.3 and at most (thickness of the first adhesive layer) × (expansion ratio of the first adhesive layer) × 0.8. However, the thickness of the spacer 42 must be at least the thickness of the first adhesive layer. The thickness of the spacer 42 is adjusted, for example, by stacking multiple sheets of Kapton adhesive tape (manufactured by Teraoka Seisakusho Co., Ltd.). Next, the first adhesive layer 1 is placed between the spacers 42, and the other metal plate 41b is placed so that one end overlaps the other and secured with clips or adhesive tape such as Kapton tape to obtain a test specimen. Next, the first adhesive layer of the test specimen is foamed and cured. The foaming and curing conditions are adjusted appropriately depending on the curable adhesive and foaming agent contained in the first adhesive layer. Next, the tensile shear bond strength test method is performed on the foamed and cured test specimen in accordance with JIS K6850:1999. The measurement conditions are a tensile speed of 10 mm / min, a grip distance of 100 mm, a room temperature (23° C.), and a humidity of 50% RH. As a tensile tester, for example, a Tensilon RTF1350 manufactured by A&D Co., Ltd. is used.

[0242] The stress-strain curve is a plot of the relationship between shear stress and strain obtained in the above-mentioned tensile shear bond strength test method, with strain (%) on the horizontal axis and shear stress (MPa) on the vertical axis, as shown in Figures 4(a) and (b). The strain is the increase in the distance between the grippers divided by the length of the first adhesive layer or the second adhesive layer, i.e., 12.5 mm. Figure 4(b) is a partially enlarged view of Figure 4(a).

[0243] In the stress-strain curve obtained by the above-mentioned tensile shear bond strength test method, the approximate straight line in the section from 3% strain to 5% strain is obtained by linearly approximating the curve in the section from 3% strain to 5% strain using the least squares method. The slope of the approximate straight line is then calculated. The above-mentioned tensile shear bond strength test method is performed three times, and the average value of the three measurements is used as the slope of the approximate straight line.

[0244] In the stress-strain curve obtained by the above-mentioned tensile shear bond strength test method, the initial slope is the slope in the elastic region. Therefore, in the present disclosure, the initial slope is adopted. Furthermore, in the stress-strain curve, shear stress tends to be unstable in the section below 3% strain. Therefore, in the present disclosure, the slope in the section from 3% strain to 5% strain is adopted as the initial slope.

[0245] Methods for controlling the slope of the above approximate straight line for the second adhesive layer after curing include, for example, adjusting the composition of the second adhesive layer and adjusting the drying conditions when forming the second adhesive layer.

[0246] In the method of adjusting the composition of the second adhesive layer, as described below, by incorporating flexible particles into the second adhesive layer, the hardness of the second adhesive layer after curing tends to be reduced, and the slope of the above-mentioned approximate straight line tends to be smaller. Furthermore, in a second adhesive layer containing an epoxy resin and a curing agent, if the number of functional groups of the epoxy resin is the same, by reducing the molecular weight of the epoxy resin, the hardness of the second adhesive layer after curing tends to be reduced, and the slope of the above-mentioned approximate straight line tends to be smaller. Furthermore, in a second adhesive layer containing an epoxy resin and a curing agent, by reducing the content of a multifunctional epoxy resin, the crosslink density after curing decreases, and therefore the hardness of the second adhesive layer after curing tends to be reduced, and the slope of the above-mentioned approximate straight line tends to be smaller.

[0247] (6) Failure Mode In the present disclosure, when a tensile shear adhesive strength test is performed on a foamed and cured foamable adhesive sheet, the failure mode is preferably cohesive failure of the first adhesive layer after foaming and curing. If the failure mode is cohesive failure of the first adhesive layer after foaming and curing, it can be said that the second adhesive layer after curing has a higher strength than the first adhesive layer after foaming and curing.

[0248] The tensile shear adhesive strength of the foamable adhesive sheet after foaming and curing is measured according to the following method in accordance with JIS K6850:1999, which corresponds to ISO 4587. First, a foamable adhesive sheet measuring 12.5 mm x 25 mm is prepared. Also, as shown in FIG. 12, two metal plates 41a and 41b, each 1.6 mm thick, 25 mm wide, and 100 mm long, are prepared. For example, cold-rolled steel plate SPCC-SD is used as the metal plate. A spacer 42 is placed at one end of one of the metal plates 41a, with a predetermined distance between them. The thickness of the spacer 42 is appropriately set depending on the foaming ratio of the first adhesive layer. For example, as shown in FIG. 4 , a foamable adhesive sheet 30 is placed between a first member 20a and a second member 20b, and then, although not shown, foamed and cured to bond the first member 20a and the second member 20b. If the distance d1 between the first member 20a and the second member 20b is known, the thickness of the spacer 42 is set to the distance d1. The thickness of the spacer 42 may be within ±5% of the distance d1. On the other hand, if the distance d1 between the first member 20a and the second member 20b is unknown, the foaming ratio of the first adhesive layer is first determined. The foaming ratio here refers to the foaming ratio when the first adhesive layer is foamed and cured without being sandwiched between any other members. The foaming ratio of the first adhesive layer can be determined by foaming and curing the foamable adhesive sheet without being sandwiched between any other members. In this case, the thickness of the spacer 42 must be equal to or greater than {(thickness of the foamable adhesive sheet) - (thickness of the first adhesive layer)} + ​​(thickness of the first adhesive layer) x (expansion ratio of the first adhesive layer) x 0.3, and equal to or less than {(thickness of the foamable adhesive sheet) - (thickness of the first adhesive layer)} + ​​(thickness of the first adhesive layer) x (expansion ratio of the first adhesive layer) x 0.8. However, the thickness of the spacer 42 must be equal to or greater than the thickness of the foamable adhesive sheet. The thickness of the spacer 42 is adjusted by stacking multiple sheets of Kapton adhesive tape manufactured by Teraoka Seisakusho Co., Ltd. Next, a foamable adhesive sheet 30 is placed between the spacers 42, and the other metal plate 41b is placed so that one tip overlaps the other and secured in place with a clip or adhesive tape such as Kapton tape to obtain a test specimen. Next, the first adhesive layer of the test specimen is foamed and cured, and the second adhesive layer is cured.The foaming and curing conditions are adjusted appropriately depending on the curable adhesive and foaming agent contained in the first adhesive layer and the curable adhesive contained in the second adhesive layer. Next, the test piece after foaming and curing is subjected to a tensile shear bond strength test method in accordance with JIS K6850:1999. The measurement conditions are a tensile speed of 10 mm / min, room temperature (23°C), and humidity of 50% RH. For example, a Tensilon RTF1350 manufactured by A&D Co., Ltd. is used as a tensile tester. Next, the fracture surface of the test piece is visually observed.

[0249] The failure mode being cohesive failure of the first adhesive layer after foaming and curing means that the cohesive failure rate within the first adhesive layer after foaming and curing is 90% or more. The cohesive failure rate is the ratio of the area of ​​the cohesive failure portion within the first adhesive layer to the total adhesive area. The above tensile shear bond strength test method is performed three times, and the cohesive failure rate is the average value of the three measurements.

[0250] (7) Thickness of the Foamable Adhesive Sheet The thickness of the foamable adhesive sheet in the present disclosure is, for example, 10 μm or more, and may be 20 μm or more. On the other hand, the thickness of the foamable adhesive sheet is, for example, 1000 μm or less, and may be 200 μm or less. That is, the thickness of the foamable adhesive sheet may be, for example, 10 μm or more and 1000 μm or less, and may be 20 μm or more and 200 μm or less.

[0251] 7. Other Features of the Foamable Adhesive Sheet The foamable adhesive sheet of the present disclosure is used to secure coils to slots in the stator core or rotor core of a rotating electric machine. The foamable adhesive sheet of the present disclosure is also arranged so that the second adhesive layer faces the coil side and the first adhesive layer faces the stator core side or rotor core side. Stators for rotating electric machines and rotors for rotating electric machines have been described above, so further description here is omitted.

[0252] The method for producing the foamable adhesive sheet of the present disclosure is not particularly limited, and may be appropriately selected depending on the layer structure of the foamable adhesive sheet.

[0253] D. Manufacturing Method of a Stator for a Rotating Electric Machine A manufacturing method of a stator for a rotating electric machine according to the present disclosure is a manufacturing method of a stator for a rotating electric machine for fixing coils in slots of a stator core, the manufacturing method including the following steps: preparing a foamable adhesive sheet having a first adhesive layer containing a curable adhesive and a foaming agent and a second adhesive layer containing a curable adhesive but not a foaming agent; arranging the foamable adhesive sheet between the stator core and the coil so that the second adhesive layer faces the coil and the first adhesive layer faces the stator core; and foaming and curing the foamable adhesive sheet to adhere the coil to the stator core, wherein the ratio of the thickness of the first adhesive layer to the thickness of the second adhesive layer in the foamable adhesive sheet is 1 or more and 8 or less.

[0254] FIGS. 13( a ) and 13 ( b ) are process diagrams illustrating a method for manufacturing a stator for a rotating electric machine according to the present disclosure. First, a foamable adhesive sheet (not shown) is prepared. The foamable adhesive sheet has a first adhesive layer containing a curable adhesive and a foaming agent, and a second adhesive layer containing a curable adhesive but no foaming agent. The ratio of the thickness of the first adhesive layer to the thickness of the second adhesive layer is set within a predetermined range. Next, as shown in FIG. 13( a ), a coil 3 and a foamable adhesive sheet 30 are inserted into slots 2 of a stator core 1. The foamable adhesive sheet 30 is then positioned between the stator core 1 and the coil 3, with the second adhesive layer facing the coil 3 and the first adhesive layer facing the stator core 1. Next, as shown in FIG. 13( b ), the first adhesive layer of the foamable adhesive sheet 30 is foamed and cured by heating, thereby curing the second adhesive layer. The coil 3 is then bonded to the stator core 1 by the adhesive sheet 4. This completes the stator 10 for a rotating electric machine.

[0255] Hereinafter, each step of the method for manufacturing a stator for a rotating electric machine according to the present disclosure will be described.

[0256] 1. Foamable Adhesive Sheet Preparation Step In the present disclosure, the foamable adhesive sheet has a first adhesive layer containing a curable adhesive and a foaming agent, and a second adhesive layer containing a curable adhesive but no foaming agent.

[0257] When the foamable adhesive sheet has a first separator and a second separator, the first separator and the second separator are peeled off from the foamable adhesive sheet when the foamable adhesive sheet is disposed between the stator core and the coil.

[0258] Details of the foamable adhesive sheet are described above in the section "C. Foamable adhesive sheet," and therefore will not be described here.

[0259] 2. Arranging Step In the arranging step of the present disclosure, a foam adhesive sheet is arranged between the stator core and the coil so that the second adhesive layer faces the coil side and the first adhesive layer faces the stator core side.

[0260] The method for disposing the foam adhesive sheet between the stator core and the coil is appropriately selected depending on whether or not the foam adhesive sheet has a base material. If the foam adhesive sheet does not have a base material, the stiffness of the foam adhesive sheet tends to be weak, so a method of disposing the foam adhesive sheet around the coil and then inserting the coil and foam adhesive sheet into the slots of the stator core is preferred. On the other hand, if the foam adhesive sheet has a base material, methods include disposing the foam adhesive sheet around the coil and then inserting the coil and foam adhesive sheet into the slots of the stator core, inserting the foam adhesive sheet into the slots of the stator core and then inserting the coil into the slots of the stator core, and inserting the coil into the slots of the stator core and then inserting the foam adhesive sheet into the slots of the stator core.

[0261] 3. Bonding Step In the bonding step of the present disclosure, heating can be used as a method for foaming and curing the foamable adhesive sheet.

[0262] The heating conditions are appropriately set depending on the types of curable adhesive and foaming agent contained in the first adhesive layer, the type of curable adhesive contained in the second adhesive layer, the type of base material, etc. The heating temperature is, for example, 130° C. or higher and 200° C. or lower. The heating time is, for example, 3 minutes or higher and 3 hours or lower.

[0263] E. Manufacturing Method of Rotor for Rotating Electric Machine A manufacturing method of a rotor for a rotating electric machine according to the present disclosure is a manufacturing method of a rotor for a rotating electric machine for fixing coils in slots of a rotor core, the manufacturing method including: a preparation step of preparing a foamable adhesive sheet having a first adhesive layer containing a curable adhesive and a foaming agent, and a second adhesive layer containing a curable adhesive but not a foaming agent; an arrangement step of arranging the foamable adhesive sheet between the rotor core and the coil so that the second adhesive layer faces the coil and the first adhesive layer faces the rotor core; and an adhesion step of foaming and curing the foamable adhesive sheet to adhere the coil to the rotor core, wherein the ratio of the thickness of the first adhesive layer to the thickness of the second adhesive layer in the foamable adhesive sheet is 1 or more and 8 or less.

[0264] FIGS. 14( a ) and 14 ( b ) are process diagrams illustrating a method for manufacturing a rotor for a rotating electric machine according to the present disclosure. First, a foamable adhesive sheet (not shown) is prepared. The foamable adhesive sheet has a first adhesive layer containing a curable adhesive and a foaming agent, and a second adhesive layer containing a curable adhesive but no foaming agent. The ratio of the thickness of the first adhesive layer to the thickness of the second adhesive layer is set within a predetermined range. Next, as shown in FIG. 14( a ), a coil 33 and a foamable adhesive sheet 30 are inserted into the slot 22 of the rotor core 21. The foamable adhesive sheet 30 is then positioned between the rotor core 21 and the coil 23, with the second adhesive layer facing the coil 23 and the first adhesive layer facing the rotor core 21. Next, as shown in FIG. 14( b ), the first adhesive layer of the foamable adhesive sheet 30 is foamed and cured by heating, thereby curing the second adhesive layer. The coil 23 is then bonded to the rotor core 21 by the adhesive sheet 4. This completes the rotor for a rotating electric machine 20.

[0265] The foam adhesive sheet preparation step, arrangement step, and adhesion step are the same as the respective steps in the above-described method for manufacturing a stator for a rotating electric machine.

[0266] 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.

[0267] [Examples 1 to 16 and Comparative Examples 1 to 4] (1) Materials The components used in the adhesive compositions are as follows: Epoxy resin A: bisphenol A phenoxy type, solid at room temperature, epoxy equivalent 7500 to 8500 g / eq, Mw 50,000, bifunctional Epoxy resin B: bisphenol A novolac type, solid at room temperature, epoxy equivalent 200 to 220 g / eq, softening temperature 70°C, multifunctional Acrylic resin: PMMA-PBuA-PMMA (partially containing acrylamide groups), Tg -20°C, 120°C, Mw 150,000 Curing agent A: α-(hydroxy(or dihydroxy)phenylmethyl)-ω-hydropoly[biphenyl-4,4'-diylmethylene(hydroxy(or dihydroxy)phenylenemethylene)] Curing agent B: dicyandiamide, particle size: 10 μm or less, melting point 209°C・Curing catalyst: 2-phenyl-4,5-dihydroxymethylimidazole, average particle size 3 μm, melting point 230°C, reaction start temperature 145°C to 155°C, active region 155°C to 173°C ・Foaming agent: thermally expandable microcapsules, average particle size 10 μm to 16 μm, expansion start temperature 123°C to 133°C, maximum expansion temperature 168°C to 178°C, core: hydrocarbon, shell: thermoplastic polymer ・Solvent: methyl ethyl ketone

[0268] (2) Preparation of First Adhesive Composition A first adhesive composition was prepared having the following composition: <Composition of First Adhesive Composition> Epoxy resin A: 43 parts by mass Epoxy resin B: 40 parts by mass Acrylic resin: 13 parts by mass Curing agent A: 6 parts by mass Curing catalyst: 8 parts by mass Foaming agent: 13.5 parts by mass Solvent: 86 parts by mass

[0269] (3) Preparation of second adhesive composition A first adhesive composition was prepared having the following composition: <Composition of second adhesive composition> Epoxy resin A: 43 parts by mass Epoxy resin B: 40 parts by mass Acrylic resin: 13 parts by mass Curing agent A: 6 parts by mass Curing agent B: 5 parts by mass Curing catalyst: 8 parts by mass Solvent: 120 parts by mass

[0270] (4) Preparation of Foamable Adhesive Sheet A 100 μm thick polyethylene naphthalate film (PEN film) was prepared as a substrate. Next, a polyester polymer and a curing agent (polyisocyanate) were diluted with methyl ethyl ketone (MEK) to a solids content of 15% by mass to prepare a resin composition. The resin composition was applied to one side of the substrate using a bar coater and dried in an oven at 100°C for 1 minute to form a first intermediate layer. Furthermore, a second intermediate layer was formed on the other side of the substrate in the same manner as the first intermediate layer.

[0271] Next, a first adhesive composition was applied using an applicator to the surface of the first intermediate layer opposite the substrate. This was then dried in an oven at 100°C for 3 minutes to form a first adhesive layer. Furthermore, a second adhesive layer was formed on the surface of the second intermediate layer opposite the substrate in the same manner as the first adhesive layer using the second adhesive composition. This resulted in a foamable adhesive sheet in which the first adhesive layer, first intermediate layer, substrate, second intermediate layer, and second adhesive layer were arranged in this order.

[0272] [Evaluation 1] (1) Shear Adhesion Strength Test Method The foamed and cured foamable adhesive sheet was subjected to the shear adhesion strength test method as described in the above section "C. Foamable Adhesive Sheet 6. Properties of Foamable Adhesive Sheet." The fracture surface of the test piece was then visually inspected. In the shear adhesion strength test method, the spacer thickness was 300 μm. The foaming and curing conditions were 165°C and 8.5 minutes (3.5 minutes for temperature increase, 5 minutes for holding) using a heat press.

[0273]

[0274]

[0275]

[0276] It has been confirmed that in a foamable adhesive sheet, when the ratio of the thickness of the first adhesive layer to the thickness of the second adhesive layer is within a predetermined range, the failure mode is cohesive failure of the first adhesive layer, and adhesive strength is increased. That is, when the ratio of the thickness of the first adhesive layer after foaming and curing to the thickness of the second adhesive layer after curing is within a predetermined range, the failure mode is cohesive failure of the first adhesive layer, and adhesive strength is increased.

[0277] [Examples 17 to 23] (1) Materials The components used in the adhesive compositions are shown below.・Epoxy resin A: bisphenol A phenoxy type, solid at room temperature, epoxy equivalent 7500 to 8500 g / eq, Mw 50,000, bifunctional ・Epoxy resin B: bisphenol A novolac type, solid at room temperature, epoxy equivalent 200 to 220 g / eq, softening temperature 70°C, multifunctional ・Epoxy resin C: bisphenol A type, solid at room temperature, epoxy equivalent 2400 to 3300 g / eq, softening temperature 144°C, Mw 3,800, bifunctional ・Acrylic resin: PMMA-PBuA-PMMA (partially containing acrylamide groups), Tg -20°C, 120°C, Mw 150,000 ・Hardening agent A: α-(hydroxy (or dihydroxy) phenylmethyl)-ω-hydropoly[biphenyl-4,4'-diylmethylene (hydroxy (or dihydroxy) phenylenemethylene)]・Curing catalyst: 2-phenyl-4,5-dihydroxymethylimidazole, average particle size 3 μm, melting point 230°C, reaction start temperature 145°C to 155°C, active region 155°C to 173°C ・Blowing agent: thermally expandable microcapsules, average particle size 10 μm to 16 μm, expansion start temperature 123°C to 133°C, maximum expansion temperature 168°C to 178°C, core: hydrocarbon, shell: thermoplastic polymer ・Hollow particles: microballoons formed by expanding thermally expandable microcapsules, average particle size 15 μm to 25 μm ・Solvent: methyl ethyl ketone

[0278] (2) Preparation of Foamable Adhesive Sheet A 100 μm thick polyethylene naphthalate (PEN) film was used as the substrate. A polyester polymer and a curing agent (polyisocyanate) were diluted with methyl ethyl ketone (MEK) to a solids content of 15% by mass to prepare a resin composition. The resin composition was applied to one side of the substrate using a bar coater and dried in an oven at 100°C for 1 minute to form a first intermediate layer. A second intermediate layer was then formed on the other side of the substrate in the same manner as the first intermediate layer.

[0279] Next, the adhesive composition shown in Table 4 below was applied to the surface of the first intermediate layer opposite the substrate using an applicator so that the thickness after application was 58 μm. This was then dried in an oven at 100°C for 3 minutes to form a first adhesive layer. Furthermore, the adhesive composition shown in Table 4 below was applied to the surface of the second intermediate layer opposite the substrate using an applicator so that the thickness after application was 48 μm. This was then dried in an oven at 100°C for 3 minutes to form a second adhesive layer. This resulted in a foamable adhesive sheet in which the first adhesive layer, first intermediate layer, substrate, second intermediate layer, and second adhesive layer were arranged in this order.

[0280] [Evaluation 2] (1) Shear adhesive strength test method (1-1) First adhesive layer after foaming and curing An adhesive composition shown in Table 3 below was applied to a 38 μm thick silicone-treated polyethylene terephthalate (PET) separator using an applicator so that the thickness after application was 58 μm. The composition was then dried in an oven at 100° C. for 3 minutes to form a single first adhesive layer.

[0281] The first adhesive layer after foaming and curing was subjected to the shear bond strength test method described in the above section "C. Foamable Adhesive Sheet 6. Properties of the Foamable Adhesive Sheet" to measure the shear bond strength. The slope of the approximate line in the stress-strain curve from 3% strain to 5% strain was also determined. In the shear bond strength test method, the spacer thickness was 180 μm. The foaming and curing conditions were 160°C and 8.5 minutes (3.5 minutes for temperature increase and 5 minutes for hold) using a heat press.

[0282] (1-2) Second adhesive layer after curing An adhesive composition shown in Table 3 below was applied to a 38 μm thick silicone-treated polyethylene terephthalate (PET) separator using an applicator so that the thickness after application was 48 μm. The composition was then dried in an oven at 100° C. for 3 minutes to form a single second adhesive layer.

[0283] The shear adhesive strength of the cured second adhesive layer was measured using the shear adhesive strength test method described in the above section "C. Foamable Adhesive Sheet 6. Properties of the Foamable Adhesive Sheet." The slope of the approximate line in the stress-strain curve from 3% strain to 5% strain was also determined. In the shear adhesive strength test method, the spacer thickness was 35 μm. The curing conditions were 160°C and 8.5 minutes (3.5 minutes for temperature increase and 5 minutes for hold) using a heat press.

[0284] (1-3) Foamable adhesive sheet after foaming and curing The foamable adhesive sheet after foaming and curing was subjected to the shear bond strength test method as described above in the section "C. Foamable adhesive sheet 6. Properties of foamable adhesive sheet" to measure the shear bond strength. The fracture surface of the test piece was also visually observed. In the shear bond strength test method, the spacer thickness was 338 μm. The foaming and curing conditions were 160°C and 8.5 minutes (3.5 minutes for temperature increase, 5 minutes for holding) using a heat press.

[0285] (2) Adhesion A cross-cut test in accordance with JIS K5600-5-6:1999 was performed three times on the surface of the second adhesive layer of the foamable adhesive sheet after foaming and curing, and the number of peeled squares was counted. The cut interval was 1 mm. The tape used was Nitto Denko Corporation's adhesive tape No. 31B. The tape peeling conditions were a peeling speed of 3 m / s or more and 5 m / s or less, and a peeling angle of approximately 60°.

[0286]

[0287]

[0288] When the slope of the approximated straight line in the stress-strain curve for the cured second adhesive layer was within a predetermined range, the adhesion of the cured second adhesive layer to the substrate was good.

[0289] The present disclosure provides, for example, the following inventions. [1] A stator for a rotating electric machine having a stator core, coils arranged in slots of the stator core, and an adhesive sheet arranged between the stator core and the coil, wherein the adhesive sheet has a foam layer and a non-foam layer, and the ratio of the thickness of the foam layer to the thickness of the non-foam layer is 1 or more and 29 or less, and the adhesive sheet is arranged so that the non-foam layer faces the coil and the foam layer faces the stator core. [2] The stator for a rotating electric machine according to [1], wherein the adhesive sheet has a substrate between the foam layer and the non-foam layer. [3] The stator for a rotating electric machine according to [1] or [2], wherein a stress-strain curve obtained when the non-foam layer is subjected to a tensile shear adhesive strength test method has a slope of an approximation line in the section from 3% strain to 5% strain of 0.20 MPa or less. [4] The stator for a rotating electric machine according to any one of [1] to [3], wherein a difference between a slope of an approximation line in a section from 3% strain to 5% strain in a stress-strain curve obtained when the foam layer is subjected to a tensile shear adhesive strength test method and a slope of an approximation line in a section from 3% strain to 5% strain in a stress-strain curve obtained when the non-foamed layer is subjected to a tensile shear adhesive strength test method is 0.20 MPa or less. [5] A rotor for a rotating electric machine, comprising: a rotor core; coils arranged in slots of the rotor core; and an adhesive sheet arranged between the rotor core and the coil, wherein the adhesive sheet has a foam layer and a non-foam layer, and the ratio of the thickness of the foam layer to the thickness of the non-foam layer is 1 or more and 29 or less, and the adhesive sheet is arranged so that the non-foam layer faces the coil and the foam layer faces the rotor core. [6] The rotor for a rotating electric machine according to [5], wherein the adhesive sheet has a substrate between the foam layer and the non-foam layer. [7] The rotor for a rotating electric machine according to [5] or [6], wherein a gradient of an approximation line in a section from 3% strain to 5% strain in a stress-strain curve obtained by subjecting the non-foam layer to a tensile shear adhesive strength test method is 0.20 MPa or less.[8] The rotor for a rotating electric machine according to any one of [5] to [7], wherein the difference between the slope of the approximated straight line in the section from 3% strain to 5% strain in a stress-strain curve obtained when the foamed layer is subjected to a tensile shear bond strength test method and the slope of the approximated straight line in the section from 3% strain to 5% strain in a stress-strain curve obtained when the non-foamed layer is subjected to a tensile shear bond strength test method is 0.20 MPa or less. [9] A foamable adhesive sheet used to fix a coil in a slot of a stator core or rotor core of a rotating electric machine, comprising: a first adhesive layer containing a curable adhesive and a foaming agent; and a second adhesive layer containing the curable adhesive but not a foaming agent, wherein the ratio of the thickness of the first adhesive layer to the thickness of the second adhesive layer is 1 or more and 8 or less, and wherein the second adhesive layer is arranged so that it faces the coil, and the first adhesive layer faces the stator core or the rotor core.

[10] The foamable adhesive sheet according to [9], wherein the foamable adhesive sheet has a base material between the first adhesive layer and the second adhesive layer.

[11] A method for manufacturing a stator for a rotating electric machine for fixing a coil in a slot of a stator core, comprising: a preparation step of preparing a foamable adhesive sheet having a first adhesive layer containing a curable adhesive and a foaming agent, and a second adhesive layer containing the curable adhesive but not a foaming agent, a placement step of placing the foamable adhesive sheet between the stator core and the coil so that the second adhesive layer faces the coil and the first adhesive layer faces the stator core, and a bonding step of foaming and curing the foamable adhesive sheet to bond the coil to the stator core, wherein a ratio of a thickness of the first adhesive layer to a thickness of the second adhesive layer is 1 or more and 8 or less.

[12] A manufacturing method of a rotor for a rotating electric machine that fixes a coil in a slot of a rotor core, comprising: a preparation step of preparing a foamable adhesive sheet having a first adhesive layer containing a curable adhesive and a foaming agent, and a second adhesive layer containing a curable adhesive but not a foaming agent; an arrangement step of arranging the foamable adhesive sheet between the rotor core and the coil so that the second adhesive layer faces the coil and the first adhesive layer faces the rotor core; and an adhesion step of foaming and hardening the foamable adhesive sheet and adhering the coil to the rotor core, wherein the ratio of the thickness of the first adhesive layer to the thickness of the second adhesive layer is 1 or more and 8 or less.

[0290] REFERENCE SIGNS LIST 1 stator core 2 slot 3 coil 4 adhesive sheet 10 stator for rotating electric machine 11 foam layer 12 non-foam layer 13 substrate 14 first intermediate layer 15 second intermediate layer 20 rotor for rotating electric machine 21 rotor core 22 slot 23 coil 30 foam adhesive sheet 31 first adhesive layer 32 second adhesive layer 33 substrate 34 first intermediate layer 35 second intermediate layer

Claims

1. A stator for a rotating electric machine comprising: a stator core; coils arranged in slots of the stator core; and an adhesive sheet arranged between the stator core and the coil, wherein the adhesive sheet has a foamed layer and a non-foamed layer, the ratio of the thickness of the foamed layer to the thickness of the non-foamed layer is 1 or more and 29 or less, and the adhesive sheet is arranged so that the non-foamed layer faces the coil side and the foamed layer faces the stator core side.

2. The stator for a rotating electric machine according to claim 1, wherein said adhesive sheet has a substrate between said foamed layer and said non-foamed layer.

3. A stator for a rotating electric machine as described in claim 1 or 2, wherein in a stress-strain curve obtained when the non-foamed layer is subjected to a tensile shear adhesive strength test method, the gradient of an approximation line in the section from 3% strain to 5% strain is 0.20 MPa or less.

4. A stator for a rotating electric machine as described in claim 1 or claim 2, wherein the difference between the slope of the approximation line in the section from 3% strain to 5% strain in a stress-strain curve obtained when the tensile shear adhesive strength test method is performed on the foamed layer and the slope of the approximation line in the section from 3% strain to 5% strain in a stress-strain curve obtained when the tensile shear adhesive strength test method is performed on the non-foamed layer is 0.20 MPa or less.

5. A rotor for a rotating electric machine comprising: a rotor core; a coil arranged in a slot of the rotor core; and an adhesive sheet arranged between the rotor core and the coil, wherein the adhesive sheet has a foamed layer and a non-foamed layer, the ratio of the thickness of the foamed layer to the thickness of the non-foamed layer is 1 or more and 29 or less, and the adhesive sheet is arranged so that the non-foamed layer faces the coil side and the foamed layer faces the rotor core side.

6. The rotor for a rotating electric machine according to claim 5, wherein said adhesive sheet has a substrate between said foamed layer and said non-foamed layer.

7. A rotor for a rotating electric machine as described in claim 5 or 6, wherein in a stress-strain curve obtained when the non-foamed layer is subjected to a tensile shear adhesive strength test method, the gradient of an approximation straight line in the section from 3% strain to 5% strain is 0.20 MPa or less.

8. A rotor for a rotating electric machine as described in claim 5 or claim 6, wherein the difference between the slope of an approximation line in a section from 3% strain to 5% strain in a stress-strain curve obtained when the foamed layer is subjected to a tensile shear adhesive strength test method and the slope of an approximation line in a section from 3% strain to 5% strain in a stress-strain curve obtained when the non-foamed layer is subjected to a tensile shear adhesive strength test method is 0.20 MPa or less.

9. A foamable adhesive sheet used to fix a coil in a slot of a stator core or rotor core of a rotating electric machine, comprising: a first adhesive layer containing a curable adhesive and a foaming agent; and a second adhesive layer containing a curable adhesive and no foaming agent, wherein the ratio of the thickness of the first adhesive layer to the thickness of the second adhesive layer is 1 or more and 8 or less, and the second adhesive layer is arranged so as to face the coil side, and the first adhesive layer is arranged so as to face the stator core side or the rotor core side.

10. The foamable adhesive sheet according to claim 9, wherein the foamable adhesive sheet has a substrate between the first adhesive layer and the second adhesive layer.

11. A manufacturing method for a stator for a rotating electric machine, which fixes a coil in a slot of a stator core, comprising: a preparation step of preparing a foamable adhesive sheet having a first adhesive layer containing a curable adhesive and a foaming agent, and a second adhesive layer containing a curable adhesive but not a foaming agent; a placement step of placing the foamable adhesive sheet between the stator core and the coil, with the second adhesive layer facing the coil side and the first adhesive layer facing the stator core side; and a bonding step of foaming and hardening the foamable adhesive sheet, and bonding the coil to the stator core, wherein the ratio of the thickness of the first adhesive layer to the thickness of the second adhesive layer in the foamable adhesive sheet is 1 or more and 8 or less.

12. A manufacturing method for a rotor for a rotating electric machine in which a coil is fixed in a slot of a rotor core, comprising: a preparation step of preparing a foamable adhesive sheet having a first adhesive layer containing a curable adhesive and a foaming agent, and a second adhesive layer containing a curable adhesive but not a foaming agent; a placement step of placing the foamable adhesive sheet between the rotor core and the coil so that the second adhesive layer faces the coil side and the first adhesive layer faces the rotor core side; and a bonding step of foaming and hardening the foamable adhesive sheet, and bonding the coil to the rotor core, wherein the ratio of the thickness of the first adhesive layer to the thickness of the second adhesive layer in the foamable adhesive sheet is 1 or more and 8 or less.

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