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

Abstract

This disclosure provides a stator and rotor for a rotating electric machine that have good heat dissipation properties for heat generated from the coil. [Solution] The present disclosure provides a stator 10 for a rotating electric machine, comprising a stator core 1, coils 3 arranged in slots 2 of the stator core, and an adhesive sheet 4 arranged between the stator core and the coils, wherein the adhesive sheet comprises a foamed layer 11 and a non-foamed layer 12, the ratio of the thickness of the foamed layer to the thickness of the non-foamed layer being 1 or more and 29 or less, and the adhesive sheet is arranged such that the non-foamed layer faces the coil side and the foamed layer faces the stator core side.

Description

[Technical Field]

[0001] This disclosure relates to a stator for a rotating electric machine, a rotor for a rotating electric machine, a foamed 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. [Background technology]

[0002] Generally, vehicles such as hybrid cars and electric cars are equipped with a rotating electric machine that can function as both a motor and a generator. Generally, a rotating electric machine comprises a stator as a stationary element and a rotor as a rotor that rotates with a predetermined gap between itself and the stator.

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

[0004] Furthermore, 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 coil for insulation.

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

[0006] On the other hand, in recent years, it has been proposed to use adhesive sheets containing a foaming agent (foaming adhesive sheets) instead of liquid adhesives. For example, Patent Document 1 discloses a motor in which magnets are fixed to the rotor core using an adhesive tape that expands when heated, although this is not a technique for fixing coils to the stator core or rotor core. For example, Patent Document 2 discloses a stator in which coils are fixed to the stator core using insulating paper having foam layers on both sides. For example, Patent Document 3 discloses an insulating sheet for fixing coils to a stator core, in which the insulating sheet has an insulating base material, a foamed resin layer and a non-foamed resin layer, and the insulating sheet is folded so that the non-foamed resin layer is positioned facing the wall surface of the stator core. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 6274540 [Patent Document 2] Japanese Patent Publication No. 2022-135608 [Patent Document 3] Japanese Patent Publication No. 2021-197888 [Overview of the project] [Problems that the invention aims to solve]

[0008] In rotating electric machines, heat is generated when current flows through a coil. Generally, foamed layers have low thermal conductivity and provide insulation. Therefore, fixing coils to the stator core or rotor core using foamed adhesive sheets may reduce heat dissipation. In particular, heat dissipation is impaired if the foamed layer is in contact with the coil.

[0009] This disclosure has been made in view of the above circumstances, and its main purpose is to provide a stator and rotor for a rotating electric machine that have good heat dissipation properties for heat generated from the coil. [Means for solving the problem]

[0010] One embodiment of the present disclosure provides a stator for a rotating electric machine, comprising a stator core, coils arranged in slots of the stator core, and an adhesive sheet disposed between the stator core and the coils, wherein the adhesive sheet comprises 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 being 1 or more and 29 or less, and the adhesive sheet is arranged such that the non-foamed layer faces the coil side and the foamed layer faces the stator core side.

[0011] Another embodiment of the present disclosure provides a rotor for a rotating electric machine, comprising a rotor core, coils arranged in slots of the rotor core, and an adhesive sheet disposed between the rotor core and the coils, wherein the adhesive sheet comprises 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 being 1 or more and 29 or less, and the adhesive sheet is arranged such that the non-foamed layer faces the coil side and the foamed layer faces the rotor core side.

[0012] Other embodiments of the present disclosure provide a foamed adhesive sheet used for fixing coils to slots in the 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 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 positioned facing the coil side, and the first adhesive layer is positioned facing the stator core side or the rotor core side.

[0013] Other embodiments of the present disclosure are a method for manufacturing a stator for a rotating electrical machine that fixes a coil in a slot of a stator core, including a preparation step of preparing a foaming adhesive sheet having a first adhesive layer containing a curable adhesive and a foaming agent, and a second adhesive layer containing a curable adhesive and not containing a foaming agent; an arrangement step of arranging the foaming adhesive sheet between the stator core and the coil such that the second adhesive layer faces the coil side and the first adhesive layer faces the stator core side; and an adhesion step of foaming and curing the foaming adhesive sheet to adhere the coil to the stator core. In the foaming adhesive sheet, 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. A method for manufacturing a stator for a rotating electrical machine is provided.

[0014] Other embodiments of the present disclosure are a method for manufacturing a rotor for a rotating electrical machine that fixes a coil in a slot of a rotor core, including a preparation step of preparing a foaming adhesive sheet having a first adhesive layer containing a curable adhesive and a foaming agent, and a second adhesive layer containing a curable adhesive and not containing a foaming agent; an arrangement step of arranging the foaming adhesive sheet between the rotor core and the coil such that the second adhesive layer faces the coil side and the first adhesive layer faces the rotor core side; and an adhesion step of foaming and curing the foaming adhesive sheet to adhere the coil to the rotor core. In the foaming adhesive sheet, 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. A method for manufacturing a rotor for a rotating electrical machine is provided.

Advantages of the Invention

[0015] In the present disclosure, there is an effect that the heat dissipation property of the heat generated from the coil can be improved.

Brief Description of the Drawings

[0016] [Figure 1] It is a schematic plan view illustrating a stator for a rotating electrical machine in the present disclosure. [Figure 2] It is a schematic plan view illustrating a stator for a rotating electrical machine in the present disclosure. [Figure 3]This is a schematic plan view illustrating a stator for a rotating electric machine in this disclosure. [Figure 4] This graph illustrates a stress-strain curve. [Figure 5] This is a schematic plan view illustrating a rotor for a rotating electric machine in this disclosure. [Figure 6] This is a schematic cross-sectional view illustrating an example of a foamed adhesive sheet in this disclosure. [Figure 7] This is a schematic cross-sectional view illustrating an example of a foamed adhesive sheet in this disclosure. [Figure 8] This is a schematic cross-sectional view illustrating an example of a foamed adhesive sheet in this disclosure. [Figure 9] This is a schematic cross-sectional view illustrating the tensile shear bond strength test method for the second adhesive layer after curing. [Figure 10] This is a schematic cross-sectional view illustrating the tensile shear bond strength test method for the first adhesive layer after foam curing. [Figure 11] This is a schematic cross-sectional view illustrating the tensile shear bond strength test method for the first adhesive layer after foam curing. [Figure 12] This is a schematic cross-sectional view illustrating the tensile shear adhesive strength test method for foamed adhesive sheets after foaming and curing. [Figure 13] This is a process diagram illustrating a method for manufacturing a stator for a rotating electric machine in this disclosure. [Figure 14] This is a process diagram illustrating the manufacturing method of a rotor for a rotating electric machine in this disclosure. [Modes for carrying out the invention]

[0017] Embodiments of this disclosure will be described below with reference to drawings and other figures. However, this disclosure can be implemented in many different ways and should not be interpreted as being limited to the embodiments described below. In addition, the drawings may be schematically represented in terms of width, thickness, shape, etc. of each part compared to the actual form in order to make the explanation clearer, but these are merely examples and should not limit the interpretation of this disclosure. Furthermore, in this specification and each figure, elements similar to those described above with respect to previously shown figures will be denoted by the same reference numerals, and detailed explanations may be omitted as appropriate.

[0018] In this specification, when describing a configuration in which one member is placed on top of another member, unless otherwise specified, the terms "on top" or "below" include both cases: when the other member is placed directly above or below the other member so as to be in contact with it, and when the other member is placed above or below the other member via yet another member. Similarly, when describing a configuration in this specification in which one member is placed on the surface of another member, unless otherwise specified, the terms "on the surface" or "on the surface" include both cases: when the other member is placed directly above or below the other member so as to be in contact with it, and when the other member is placed above or below the other member via yet another member.

[0019] Furthermore, in this specification, "sheet" also includes a component called "film."

[0020] The following describes in detail the stator for a rotating electric machine, the rotor for a rotating electric machine, the foamed adhesive sheet, the method for manufacturing the stator for a rotating electric machine, and the method for manufacturing the rotor for a rotating electric machine as described in this disclosure.

[0021] A. Stator for rotating electric machine The stator for a rotating electric machine in this disclosure comprises a stator core, coils arranged in slots of the stator core, and an adhesive sheet arranged between the stator core and the coils, wherein the adhesive sheet comprises 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 such that the non-foamed layer faces the coil side and the foamed layer faces the stator core side.

[0022] Figure 1(a) is a schematic plan view illustrating a stator for a rotating electric machine in this disclosure, and Figures 1(b) and (c) are enlarged sections of Figure 1(a). As shown in Figures 1(a) to (c), the stator 10 for a rotating electric machine includes a stator core 1, coils 3 arranged in slots 2 of the stator core 1, and an adhesive sheet 4 arranged between the stator core 1 and the coils 3. The adhesive sheet 4 has a foamed layer 11 and a non-foamed layer 12. In the adhesive sheet 4, the ratio of the thickness of the foamed layer 11 to the thickness of the non-foamed layer 12 is within a predetermined range. The adhesive sheet 4 is arranged such that the non-foamed layer 12 faces the coil 3 side and the foamed layer 11 faces the stator core 1 side.

[0023] Generally, foamed layers have low thermal conductivity and provide insulation. Therefore, fixing coils to a stator core using a foamed adhesive sheet may reduce heat dissipation. In particular, heat dissipation is impaired when the foamed layer is in contact with the coil. On the other hand, non-foamed layers have substantially no bubbles due to the foaming agent and therefore have higher thermal conductivity than foamed layers. In this disclosure, the adhesive sheet is arranged so that the non-foamed layer faces the coil, allowing heat generated from the coil to be conducted through the non-foamed layer. Thus, heat dissipation can be improved.

[0024] Furthermore, as illustrated in Figure 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, these gaps become air layers, and heat generated from the coils is conducted through these air layers. A foamed layer adhesive composition containing a foaming agent is used for the foamed layer, and when the coils are fixed to the stator core, the foamed layer adhesive composition foams and hardens. Therefore, if the adhesive sheet is positioned so that the foamed layer faces the coil side, the gaps between the coils will be filled with the foamed layer, eliminating the air layer and reducing heat dissipation. On the other hand, a non-foamed layer adhesive composition that does not contain a foaming agent is used for the non-foamed layer, and when the coils are fixed to the stator core, the non-foamed layer adhesive composition hardens but does not foam. In this disclosure, by positioning the adhesive sheet so that the non-foamed layer faces the coil side, gaps between the coils can be secured. Therefore, heat generated from the coils is conducted through the air layer, improving heat dissipation.

[0025] Therefore, in this disclosure, the adhesive sheet is arranged such that the non-foamed layer faces the coil, thereby improving the heat dissipation of heat generated from the coil.

[0026] The foam layer uses an adhesive composition for foam layers containing a foaming agent. Therefore, the foam layer before foaming and curing 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 foam layer before foaming and curing, and improve the slipperiness of the foam layer before foaming and curing. Since the adhesive sheet is positioned so that the foam layer faces the stator core, the insertability of the adhesive sheet before foaming and curing can be improved when inserting the adhesive sheet into the slot of the stator core before foaming and curing.

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

[0028] Furthermore, in this disclosure, the adhesive sheet is arranged so that the foamed layer faces the stator core, thereby filling the gap between the stator core and the adhesive sheet with the foamed layer, and thus improving the adhesion between the stator core and the adhesive sheet. In the adhesive sheet, the foamed layer has relatively weaker cohesive force, while the non-foamed layer has relatively stronger cohesive force. Also, as illustrated in Figure 1(b), when multiple coils 3 are arranged in the slots 2 of the stator core 1, there are gaps between the coils, so the adhesive area is smaller on the coil side and larger on the stator core side. Therefore, by arranging the adhesive sheet so that the foamed layer, which has relatively weak cohesive force, is in contact with the stator core where a large adhesive area can be taken, and the non-foamed layer, which has relatively strong cohesive force, is in contact with the coils where the adhesive area is smaller, the coils can be firmly fixed to the stator core.

[0029] Furthermore, when inserting the adhesive sheet into the stator core slot in a folded state before foaming and curing, there is a possibility that a portion of the foamed layer on the stator core side may come into contact with the wall or corner of the stator core slot and be scraped off. In contrast, in this disclosure, the thickness of the foamed layer is greater than or equal to the thickness of the non-foamed layer, and the ratio of the thickness of the foamed layer to the thickness of the non-foamed layer is within a predetermined range, so that even if a portion of the foamed layer before foaming and curing is scraped off, a decrease in foaming properties can be suppressed. Also, when inserting the adhesive sheet into the stator core slot in a folded state before foaming and curing, tensile stress acts on the foamed layer on the stator core side at the bend, causing the thickness of the foamed layer before foaming and curing to decrease. In contrast, in this disclosure, the thickness of the foamed layer is greater than or equal to the thickness of the non-foamed layer, and the ratio of the thickness of the foamed layer to the thickness of the non-foamed layer is within a predetermined range, so that even if the thickness of the foamed layer before foaming and curing decreases due to tensile stress at the bend, a decrease in foaming properties can be suppressed. Therefore, sufficient foaming properties can be ensured.

[0030] The configuration of the stator for a rotating electric machine in this disclosure will be described below.

[0031] 1. Adhesive sheet The adhesive sheet in this disclosure has a foamed layer and a non-foamed layer, and is placed between the stator core and the coil such that the non-foamed layer faces the coil side and the foamed layer faces the stator core side. In this disclosure, the adhesive sheet is placed between the stator core and the coil such that the non-foamed layer is in contact with the coil and the foamed layer is in contact with the stator core.

[0032] (1) Foam layer In this disclosure, the foamed layer is a layer containing air bubbles.

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

[0034] (i) Curing adhesives As the curable adhesive used in the foam layer in this disclosure, a curable adhesive generally used for the adhesive layer of a foam adhesive sheet can be used. Examples of curable adhesives 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] In particular, thermosetting adhesives are preferably epoxy resin-based adhesives. That is, thermosetting adhesives preferably contain epoxy resin and a curing agent. Generally, epoxy resin-based adhesives have excellent mechanical strength, heat resistance, insulation, and chemical resistance, and exhibit low curing shrinkage, making them suitable for a wide range of applications.

[0037] The following explanation will provide an example of a case where the curing adhesive is an epoxy resin-based adhesive.

[0038] (i-1) Epoxy resin The epoxy resins in this disclosure are compounds having at least one epoxy group or glycidyl group, which undergo a crosslinking polymerization reaction and harden when used in combination with a curing agent. The epoxy resins also include monomers having at least one epoxy group or glycidyl group.

[0039] As the epoxy resin, epoxy resins commonly used in epoxy resin adhesives can be used.

[0040] In particular, thermosetting adhesives preferably contain a primary epoxy resin having a softening temperature of 50°C or higher and an epoxy equivalent of 5000 g / eq or less, and a secondary epoxy resin having a softening temperature higher than that of the primary epoxy resin and a weight-average molecular weight of 20,000 or more. By using a combination of the primary and secondary epoxy resins, the tackiness of the adhesive layer formed from the adhesive composition can be reduced, and the slipperiness can be improved. Furthermore, blocking resistance and adhesion after foam curing can be improved.

[0041] For example, if the sole objective is to improve adhesion after foam curing, 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. However, using a low molecular weight (low epoxy equivalent) epoxy resin makes blocking more likely to occur.

[0042] In contrast, when using a primary epoxy resin with a relatively low softening temperature (relatively high crystallinity) and low molecular weight (low epoxy equivalent), the primary epoxy resin rapidly melts and changes into a low-viscosity liquid when the temperature exceeds the softening temperature. Therefore, it is easier to improve adhesion after foaming and curing. On the other hand, because primary epoxy resins have relatively high crystallinity, they can suppress the occurrence of blocking compared to epoxy resins with relatively low crystallinity or epoxy resins that do not have crystallinity. However, if only primary epoxy resin is used, the blocking suppression effect may be insufficient, or the tackiness of the adhesive layer composed of the adhesive composition may become too high. Therefore, by further using a secondary epoxy resin with a relatively high softening temperature (relatively low crystallinity) and high molecular weight, the blocking suppression effect can be improved, and the tackiness of the adhesive layer composed of the adhesive composition can be kept low.

[0043] (i-1-1) Primary epoxy resin The first epoxy resin has a softening temperature of 50°C or higher and an epoxy equivalent of 5000 g / eq or less. Compared to the second epoxy resin described later, the first epoxy resin has a relatively lower softening temperature (relatively higher crystallinity). Because the first epoxy resin has relatively high crystallinity and a low molecular weight, it is easy to improve the adhesion and blocking resistance after foam curing. In addition, because the first epoxy resin has a low molecular weight, a high crosslinking density can be achieved, resulting in an adhesive layer with good mechanical strength, chemical resistance, and curability. Furthermore, it is preferable that the first epoxy resin is a solid epoxy resin at room temperature (23°C).

[0044] The softening temperature of primary epoxy resin is typically 50°C or higher, but may also be 55°C or higher, or even 60°C or higher. On the other hand, the softening temperature of primary 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 primary epoxy resin is, for example, 5000 g / eq or less, but may also 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 primary epoxy resin is, for example, 90 g / eq or more, but may also be 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 bifunctional epoxy resin, a trifunctional epoxy resin, or a tetrafunctional or more functional epoxy resin.

[0047] Furthermore, the weight-average molecular weight (Mw) of the primary epoxy resin is usually smaller than the weight-average molecular weight (Mw) of the secondary epoxy resin, which will be discussed later. The Mw of the primary epoxy resin is, for example, 6,000 or less, may be 4,000 or less, or 3,000 or less. On the other hand, the Mw of the primary epoxy resin is, for example, 400 or more. Mw is the polystyrene equivalent value measured by gel permeation chromatography (GPC).

[0048] The primary epoxy resin has a melt viscosity at 150°C of, for example, 0.005 Pa·s or higher, but may also be 0.015 Pa·s or higher, 0.03 Pa·s or higher, 0.05 Pa·s or higher, or 0.1 Pa·s or higher. If the melt viscosity is too low, good foaming properties may not be obtained. Also, if the melt viscosity of the primary epoxy resin is too low (if the crystallinity of the primary epoxy resin is too high), the tackiness of the adhesive layer formed from the adhesive composition may increase. This is presumed to be because, if the melt viscosity of the primary epoxy resin is too low (if the crystallinity of the primary epoxy resin is too high), its crystallinity decreases significantly when it is compatible with the secondary epoxy resin or acrylic resin, and the Tg of the adhesive layer decreases. On the other hand, the primary epoxy resin has a melt viscosity at 150°C of, for example, 10 Pa·s or less, but may also 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 decrease. 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 primary epoxy resin will be described. Examples of primary epoxy resins include aromatic epoxy resins, aliphatic epoxy resins, alicyclic epoxy resins, and heterocyclic epoxy resins. Specific examples of primary epoxy resins include bisphenol-type epoxy resins such as bisphenol A type epoxy resin and bisphenol F type epoxy resin, novolac-type epoxy resins such as bisphenol A novolac type epoxy resin and cresol novolac type epoxy resin, and modified epoxy resins such as urethane-modified epoxy resin and rubber-modified epoxy resin. Other specific examples include biphenyl-type epoxy resin, stilbene-type epoxy resin, triphenolmethane-type epoxy resin, alkyl-modified triphenolmethane-type epoxy resin, triazine nucleus-containing epoxy resin, dicyclopentadiene-modified phenol-type epoxy resin, naphthalene-type epoxy resin, glycol-type epoxy resin, and pentaerythritol-type epoxy resin. The primary epoxy resin may consist of one type or two or more types.

[0050] Bisphenol A type epoxy resins exist in either a liquid or solid state at room temperature, depending on the number of repeating units in the bisphenol skeleton. Bisphenol A type epoxy resins with, for example, 2 to 10 bisphenol skeletons in the main chain are solid at room temperature. Bisphenol A type epoxy resins are particularly preferred because they can improve heat resistance.

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

[0052] [ka]

[0053] In general formula (1), R 1 C m H 2m It is a group represented by (m is between 1 and 3), and R 2 and R 3 Each of them is independent of Cp 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 where m is 1, that is, R 1 is preferably -CH2-. Similarly, p in R 2 and R 3 is 1, that is, R 2 and R 3 are preferably -CH3. Also, the hydrogen bonded to the benzene ring of general formula (1) may be substituted with other elements or other groups.

[0055] (i-ml-2) Second epoxy resin The second epoxy resin has a higher softening temperature than 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 above-described first epoxy resin. Since the second epoxy resin has relatively low crystallinity and a high molecular weight, it is easy to improve the blocking resistance. Furthermore, since the second epoxy resin has relatively low crystallinity and a high molecular weight, it can suppress an increase in adhesiveness (tackiness) due to the first epoxy resin. Also, the second epoxy resin is preferably an epoxy resin that is solid at normal 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, may be 30,000 or more, and 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. For example, the epoxy equivalent of the second epoxy resin may be 4000 g / eq or more, 5000 g / eq or more, or 6000 g / eq or more. On the other hand, for example, the epoxy equivalent of the second epoxy resin may be 20000 g / eq or less.

[0058] The second epoxy resin may be a monofunctional epoxy resin, a bifunctional epoxy resin, a trifunctional epoxy resin, or a tetrafunctional or more 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 is, for example, 10°C or more, may be 20°C or more, or may be 30°C or more. The softening temperature of the second epoxy resin is, for example, 80°C or more, and may be 90°C or more. On the other hand, the softening temperature of the second epoxy resin is, for example, 180°C or less.

[0060] The composition of the second epoxy resin is the same as that of the first epoxy resin described above, so it will not be described 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 that is compatible with the epoxy resin. The acrylic resin is a resin that is compatible with the epoxy resin. Because the acrylic resin is compatible with the epoxy resin, it is easy to improve its toughness. As a result, the adhesiveness after foam curing can be improved. Furthermore, it is thought that the acrylic resin acts as a compatibilizer for the foaming agent (for example, a foaming agent whose shell is a resin of acrylonitrile copolymer), and by uniformly dispersing and foaming, the adhesiveness after foam curing is improved. In addition, the flexibility of the acrylic resin is exhibited, which can improve adhesion to the substrate after foam curing and crack resistance after foam curing. Also, because the acrylic resin is compatible with the epoxy resin, the hardness of the surface of the adhesive layer composed of the adhesive composition can be kept high. On the other hand, if the acrylic resin is not compatible with the epoxy resin, flexible parts are formed on the surface of the adhesive layer, which can make the interface with the stator core less slippery and reduce workability.

[0062] The acrylic resin in this disclosure is compatible with epoxy resin. Compatibility of the acrylic resin with epoxy resin is confirmed by observing a cross-section of the adhesive layer composed of the adhesive composition using a scanning electron microscope (SEM) or transmission electron microscope (TEM) and noting the absence of micron-sized islands. The average island particle size is preferably 1 μm or less, but may also be 0.5 μm or less, or 0.3 μm or less. A large sample size is preferred, for example, 100 or more. The observation area is a range of 100 μm × 100 μm, or, if the thickness of the adhesive layer is 100 μm or less, a range of thickness × 100 μm.

[0063] The weight-average molecular weight (Mw) of the acrylic resin is, for example, 50,000 or more, but may also be 70,000 or more, or 100,000 or more. Primary epoxy resins have relatively high crystallinity, which can lead to excessively low melt viscosity (or dynamic viscoelasticity) during heating, potentially causing shrinkage during curing after foaming (the period from when the foaming of the foaming agent is finished until the adhesive composition hardens). However, by using an acrylic resin with a certain molecular weight, it is possible to suppress the melt viscosity from becoming too low, making shrinkage during curing after foaming less likely. On the other hand, 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 substance: PS, sample: 20 μL, flow rate: 1 mL / min, column temperature: 40°C).

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

[0065] Acrylic resin has a storage modulus (E') of 1 × 10⁻¹⁰ at the foaming initiation temperature. 6 It may be less than Pa. A low E' at the start of foaming improves fluidity and allows for good foaming. On the other hand, E' at the foaming start temperature is, for example, 1 × 10⁻⁶. 5 The temperature must be above Pa. Note that the foaming initiation temperature varies depending on the type of foaming agent. Furthermore, if two or more foaming agents are used, the foaming initiation temperature shall be the temperature at which the primary foaming reaction begins.

[0066] Acrylic resin has a storage modulus (E') of 1 × 10⁻¹⁰ at the curing start temperature. 5It may be Pa or higher. As mentioned above, shrinkage may occur during curing after foaming (from the time the foaming of the foaming agent is finished until the adhesive composition hardens), but a large E' at the curing start temperature can suppress shrinkage and obtain good shape retention. Note that the curing start temperature is different depending on the type of curing agent. Also, when two or more curing agents are used, the curing start temperature is the temperature at which the main curing reaction starts.

[0067] Furthermore, the average storage modulus (E') of acrylic resin at temperatures between 0°C and 100°C is 1 × 10⁻⁶ 6 It may be Pa or higher. A high average value of E' before foaming allows for good non-stick and blocking resistance. On the other hand, the average value of the storage modulus (E') between 0°C and 100°C is, for example, 1 × 10⁻⁶ 8 It is below Pa.

[0068] Acrylic resins may have polar groups. Examples of polar groups include epoxy groups, hydroxyl groups, carboxyl groups, nitrile groups, and amide groups.

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

[0070] Examples of monomer components constituting the (meth)acrylic acid ester copolymer include the monomer component described in Japanese Patent Publication No. 2014-065889. The above monomer component may have the polar group described above. Examples of the above (meth)acrylic acid ester copolymer include ethyl acrylate-butyl acrylate-acrylonitrile copolymer, ethyl acrylate-acrylonitrile copolymer, and 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] As the above (meth)acrylic acid ester copolymer, block copolymers are preferred, and acrylic block copolymers such as methacrylate-acrylate copolymers are even more preferred. 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. These "acrylic acids" also include "methacrylic acid."

[0072] Specific examples of methacrylate-acrylate copolymers include acrylic copolymers such as methyl methacrylate-butyl acrylate-methyl methacrylate (MMA-BA-MMA) copolymers. MMA-BA-MMA copolymers also include block copolymers of polymethyl methacrylate-polybutyl acrylate-polymethyl methacrylate (PMMA-PBA-PMMA).

[0073] The acrylic copolymer does not necessarily have polar groups, or it may be a modified product in which the aforementioned polar groups are partially introduced. Since the above modified product is easily compatible with epoxy resin, its adhesive properties are further improved.

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

[0075] The manifestation of the above effects can be estimated as follows: By using an acrylic resin that has both soft and hard segments, such as the (meth)acrylic acid ester copolymer described above, the hard segments contribute to heat resistance, and the soft segments contribute to toughness or flexibility, thus improving heat resistance, toughness, and flexibility.

[0076] At least one of the first polymer portion and the second polymer portion contained in the above (meth)acrylic acid ester copolymer is compatible with epoxy resin. When the first polymer portion is compatible with epoxy resin, flexibility can be increased. Furthermore, when the second polymer portion is compatible with epoxy resin, cohesiveness and toughness can be increased.

[0077] If either the first or second polymer portion is incompatible with the epoxy resin, the (meth)acrylic acid ester copolymer will have a compatible portion that is compatible with the epoxy resin and an incompatible 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, while the incompatible portion does not, resulting in 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 primary and secondary polymer portions contained in the (meth)acrylic acid ester copolymer, and whether or not it is modified by the introduction of polar groups. For example, there are sea-island structures in which the compatible parts of the cured epoxy resin and the (meth)acrylic acid ester copolymer are the sea and the incompatible parts of the (meth)acrylic acid ester copolymer are the islands, or in which the incompatible parts of the (meth)acrylic acid ester copolymer are the sea and the compatible parts of the cured epoxy resin and the (meth)acrylic acid ester copolymer are the islands, or in which the (meth)acrylic acid ester copolymer is the sea and the cured epoxy resin is the islands. Having such a sea-island structure makes it easier to distribute stress, thus avoiding interfacial fracture and resulting in excellent adhesion after foam curing.

[0078] The above-mentioned (meth)acrylic acid ester copolymer is preferably a block copolymer, and more preferably an ABA block copolymer in which the compatible parts are polymer block A and the incompatible parts are polymer block B. Furthermore, it is preferable that the first polymer portion is the incompatible part and the second polymer portion is the compatible part, with the first polymer portion being polymer block B and the second polymer portion being polymer block A. By using such an ABA block copolymer as the acrylic resin, in the case of a sea-island structure in which the compatible parts of the cured epoxy resin and the (meth)acrylic acid ester copolymer are the sea and the incompatible parts of the (meth)acrylic acid ester copolymer are the islands, the island portion can be reduced. Also, in the case of a sea-island structure in which the incompatible parts of the (meth)acrylic acid ester copolymer are the sea and the compatible parts of the cured epoxy resin and the (meth)acrylic acid ester copolymer are the islands, or in the case of a sea-island structure in which the (meth)acrylic acid ester copolymer is the sea and the cured epoxy resin is the islands, the sea portion can be reduced.

[0079] Furthermore, 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 portion or the second polymer portion.

[0080] The Tg of the first polymer portion contained in the above (meth)acrylic acid ester copolymer is 10°C or lower, within the range of -150°C or higher and 10°C or lower, particularly within the range of -130°C or higher and 0°C or lower, and especially within 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 listed in "POLYMERHANDBOOK Third Edition" (published by John Wiley & Sons, Inc.). 1 / Tg(K)=W1 / Tg1+W2 / Tg2+····+W n / Tg n W n ; Mass fraction of each monomer Tg n;This refers to the Tg(K) of the homopolymer of each monomer, and you can use publicly available values ​​such as those found in the Polymer Handbook (3rd Ed., J. Brandrup and E. Himmergut, WILEY INTERSCIENCE). The same applies to the Tg of the second polymer portion, which will be discussed later.

[0082] The first polymer portion included in the above (meth)acrylic acid ester copolymer may be a homopolymer or a copolymer, but a homopolymer is preferred. The monomer and polymer components constituting the first polymer portion may be any monomer and polymer components that can obtain a first polymer portion with a predetermined Tg, and examples include acrylic acid ester 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 including the polar group mentioned above, and copolymers such as EVA.

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

[0084] Furthermore, the second polymer portion included in the (meth)acrylic acid ester copolymer may be a homopolymer or a copolymer, but a homopolymer is preferred. The monomer component constituting the second polymer portion may be any monomer component that can obtain a second polymer portion with a predetermined Tg, and examples 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, methacrylonitrile, and polar group-containing monomers including the polar group mentioned above.

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

[0086] (i-3) Hardener In this disclosure, a curing agent commonly used in epoxy resin adhesives can be used. The curing agent is one that undergoes a curing reaction upon heating. Preferably, the curing agent is solid at room temperature (23°C). A curing agent that is solid at room temperature has a longer 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, the curing agent may be used alone or in combination of two or more types.

[0087] The reaction initiation temperature of the curing agent is, for example, 110°C or higher, and may also be 130°C or higher. If the reaction initiation temperature is too low, the reaction may start too early, and curing may occur with low flexibility and fluidity of the resin components, 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 components may deteriorate. In addition to epoxy resin, if a heat-resistant resin such as phenolic resin is used, the deterioration of the resin components is less, so 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 by differential scanning calorimeter (DSC).

[0088] Specific examples of curing agents 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, carboxylate salts of imidazole compounds, and adducts with epoxy compounds. Furthermore, it is preferable that the imidazole-based curing agent has hydroxyl groups. Because crystallization occurs through hydrogen bonding between hydroxyl groups, the reaction initiation temperature tends to be high.

[0090] Examples of phenolic curing agents include phenolic resins. Examples of phenolic resins include resol-type phenolic resins and novolac-type phenolic resins. From the viewpoint of adhesion to the substrate after foam curing and crack resistance after foam curing, phenolic novolac resins with a Tg of 110°C or lower are particularly preferred. Furthermore, a phenolic curing agent and an imidazole-type curing agent may be used in combination. In that 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. In addition, dicyandiamide-based curing agents such as dicyandiamide (DICY), organic acid dihydrazide-based curing agents, amine adduct-based curing agents, and ketimine-based curing agents can be used as amine-based curing agents.

[0092] Examples of acid anhydride-based 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] Examples of isocyanate-based curing agents include blocked isocyanates.

[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 foamed layer in this disclosure can be a foaming agent that is generally used in the adhesive layer of foamed adhesive sheets. The foaming agent is a foaming agent that undergoes a foaming reaction when heated.

[0096] Examples of foaming agents include microencapsulated foaming agents. Microencapsulated foaming agents preferably have a core made of a thermal expander such as a hydrocarbon, and a shell made of a resin such as an acrylonitrile copolymer.

[0097] Furthermore, as a blowing agent, for example, organic blowing agents or inorganic blowing agents may be used. Examples of organic blowing agents include azo blowing agents such as azodicarbonamide (ADCA), azobisformamide, and azobisisobutyronitrile; fluoride alkane blowing agents such as trichloromonofluoromethane; hydrazine blowing agents such as p-toluenesulfonyl hydrazide; semicarbazide blowing agents such as p-toluenesulfonyl semicarbazide; 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 above the softening temperature of the main component of the thermosetting adhesive, such as epoxy resin, and below the activation temperature of the curing reaction of the main component of the thermosetting adhesive, such as epoxy resin. The foaming initiation temperature of the foaming agent is, for example, 70°C or higher, and may also be 100°C or higher. If the foaming initiation temperature is too low, the reaction may start too early, and foaming may occur with low flexibility and fluidity of the resin component, 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 using 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. By having the average particle size of the foaming agent within the above range, the static friction coefficient of the surface of the adhesive layer made of the adhesive composition can be reduced, and the slipperiness can be improved. Furthermore, the average particle size of the foaming agent is preferably less than or equal to the thickness of the adhesive layer made of the adhesive composition, for example, it may be 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 integrated 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 can dissolve components other than the foaming agent in the adhesive composition, and can be appropriately selected depending on the type of thermosetting adhesive, etc. For example, the solvent used in the adhesive composition can be used. Specifically, methyl ethyl ketone, ethyl acetate, and toluene can be used.

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

[0103] (iii) Other ingredients The adhesive composition used in the foam layer in this disclosure may, for example, contain only epoxy resin and acrylic resin as resin components when the curable adhesive is an epoxy resin-based adhesive, or it may further contain other resins. Examples of other resins include urethane resin.

[0104] The adhesive composition may optionally contain additives such as silane coupling agents, fillers, antioxidants, light stabilizers, UV absorbers, lubricants, plasticizers, antistatic agents, crosslinking agents, and colorants. Examples of silane coupling agents include epoxy-based silane coupling agents. Examples of fillers include inorganic fillers such as calcium carbonate, aluminum hydroxide, magnesium hydroxide, antimony trioxide, zinc borate, molybdenum compounds, and titanium dioxide. Examples of antioxidants include phenolic antioxidants and sulfur-based antioxidants.

[0105] (b) Thickness of the foam layer In this disclosure, the ratio of the thickness of the foamed layer to the thickness of the non-foamed layer is 1 or more, may be 3 or more, or may be 5.5 or more. As described above, sufficient foaming can be ensured by having the above thickness ratio within the above range. On the other hand, the ratio of the thickness of the foamed layer to the thickness of the non-foamed layer is 29 or less, may be 20 or less, or may be 13 or less. As long as the above thickness ratio is within the above range, the thickness of the non-foamed layer will not become too thin, and thus a decrease in adhesive strength can be suppressed. Specifically, 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, 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 the above thickness relationship is satisfied, and can be set appropriately according to the application. For example, the thickness of the foam layer may be 30 μm or more, 40 μm or more, or 50 μm or more. Alternatively, the thickness of the foam layer may be 1000 μm or less, 900 μm or less, or 800 μm or less. In other words, the thickness of the foam layer may be 30 μm or more and 1000 μm or less, 40 μm or more and 900 μm or less, or 50 μm or more and 800 μm or less. If the foam layer is too thin, sufficient adhesion may not be obtained. Also, if the foam layer is too thick, the surface quality may deteriorate.

[0107] (c) Other aspects of the foamed 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 foamed layer contains a foamed and cured product of the adhesive composition. Heating is one method for foaming and curing the adhesive composition.

[0109] (2) Non-foamed layer In this disclosure, the non-foaming layer is a layer that substantially does not contain bubbles derived from the foaming agent.

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

[0111] (i) Curing adhesives The curable adhesive used in the non-foamed layer in this disclosure is the same as the curable adhesive used in the foamed layer described above. 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 in this disclosure does not contain a foaming agent. Here, "does not contain a foaming agent" means that the foaming agent content in the adhesive composition is 2.0% by mass or less. Preferably, the foaming agent content in the adhesive composition is 1.0% by mass or less, and more preferably 0% by mass.

[0113] (iii) Other ingredients Other components contained in the adhesive composition used for the non-foamed layer in this disclosure are the same as the other components contained in the adhesive composition used for 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 the above thickness relationship is satisfied, and is set appropriately according to the application. The thickness of the non-foamed layer is, for example, 10 μm or more, may be 15 μm or more, or 20 μm or more. Alternatively, the thickness of the non-foamed layer is, for example, 200 μm or less, may be 150 μm or less, or 100 μm or less. In other words, the thickness of the non-foamed layer is, for example, 10 μm or more and 200 μm or less, may be 15 μm or more and 150 μm or less, or 20 μm or more and 100 μm or less. If the non-foamed layer is too thin, sufficient adhesion may not be obtained. Also, 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 coil with the adhesive sheet, which may reduce adhesion.

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

[0116] The non-foaming layer contains a cured product of the adhesive composition. Heating is one method for curing the adhesive composition.

[0117] (3) Base material The adhesive sheet in this disclosure may have a substrate between the foamed layer and the non-foamed layer. When a substrate is placed between the foamed layer and the non-foamed layer, the insulating properties of the adhesive sheet can be improved. In addition, the handling and workability of the adhesive sheet before foam curing can be improved. On the other hand, when a substrate is not placed between the foamed layer and the non-foamed layer, the overall thickness of the adhesive sheet before foam curing can be reduced, and the adhesive sheet before foam curing can be inserted into narrow gaps.

[0118] For example, in the adhesive sheet 4 shown in Figure 2, the base material 13 is placed between the foamed layer 11 and the non-foamed layer 12. On the other hand, in the adhesive sheet 4 shown in Figure 1(c), for example, the base material 13 is not placed between the foamed layer 11 and the non-foamed layer 12.

[0119] The base material is preferably insulating. Furthermore, the base material is preferably in sheet form. The base material may have a single-layer structure or a multi-layer structure. The base material may or may not have a porous structure internally.

[0120] Examples of substrates include resin substrates and nonwoven fabrics.

[0121] Examples of resins included in the resin substrate include polyester resin, polycarbonate, polyarylate, polyurethane, polyamide resin, polyimide resin, polysulfone resin, polyetherketone 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 polyetheramide. Examples of polyimide resins include polyimide, polyetherimide, and polyamideimide. Examples of polysulfone resins include polysulfone and polyethersulfone. Examples of polyetherketone resins include polyetherketone and polyetheretherketone. Liquid crystal polymer (LCP) may also be used as the resin. The glass transition temperature of the resin is, for example, 80°C or higher, may be 140°C or higher, or may be 200°C or higher.

[0122] Examples of nonwoven fabrics include those 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 improve adhesion with the foamed or non-foamed layer.

[0124] The thickness of the substrate is not particularly limited, but for example it may be 2 μm or more, 5 μm or more, or 9 μm or more. Alternatively, the thickness of the substrate may be 200 μm or less, 100 μm or less, or 50 μm or less.

[0125] (4) First and second mezzanine layers The adhesive sheet in this disclosure may have a first intermediate layer between the substrate and the foamed layer. The adhesive sheet in this disclosure may also have a second intermediate layer between the substrate and the non-foamed layer. The presence of the first or second intermediate layer improves the adhesion of the foamed or non-foamed layer to the substrate. Furthermore, the presence of the first or second intermediate layer relieves stress on the bent portion of the adhesive sheet. As a result, lifting or peeling of the foamed or non-foamed layer from the substrate can be suppressed.

[0126] For example, in the adhesive sheet 4 shown in Figure 3, a first intermediate layer 14 is placed between the base material 13 and the foamed layer 11, and a second intermediate layer 15 is placed between the base material 13 and the non-foamed layer 12. In Figure 3, the adhesive sheet 4 has both the first intermediate layer 14 and the second intermediate layer 15, but 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. For example, it may have only a first intermediate layer placed between the substrate and the foamed layer, or only a second intermediate layer placed between the substrate and the non-foamed layer, or it may have both a first intermediate layer placed between the substrate and the foamed layer and a second intermediate layer placed between the substrate and the non-foamed layer. In particular, it is preferable that the first intermediate layer is placed between the substrate and the foamed layer, and the second intermediate layer is placed between the substrate and the non-foamed layer.

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

[0129] The crosslinked material is a crosslinked material obtained by crosslinking the above-mentioned resin with a curing agent. Examples of curing agents include isocyanate-based curing agents. Furthermore, for example, when the reactive group / NCO equivalent is set to 1, it is preferable to add the isocyanate-based curing agent to the resin in a ratio of 0.5% by mass or more and 20% by mass or less.

[0130] In particular, the first and second intermediate layers preferably contain a cross-linked resin. A cross-linked resin is one that does not melt even at high temperatures. This improves the adhesive strength at high temperatures, i.e., the heat resistance.

[0131] The thickness of the first and second intermediate layers 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 and second intermediate layers are too thin, the effect of suppressing the peeling of the foamed or non-foamed layer from the substrate at the bending portion of the adhesive sheet may not be sufficiently obtained. On the other hand, the thickness of the first and second intermediate layers may be, for example, 4 μm or less, or 3.5 μm or less. Since the first and second intermediate layers themselves do not usually have high heat resistance, if the first and second intermediate layers are too thick, the heat resistance (adhesion strength at high temperatures) may decrease.

[0132] The first and second intermediate layers 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 adhesive sheets (a) Electrical insulation The adhesive sheet in this disclosure preferably has high electrical insulation properties. The dielectric breakdown voltage of the adhesive sheet, based on JIS C2107:2011 corresponding to IEC 60454-2, is preferably, for example, 3kV or higher, and more preferably 5kV or higher. Having the dielectric breakdown voltage within this range makes it possible to apply it to rotating electric machines. Furthermore, the thermal conductivity of the adhesive sheet is preferably, for example, 0.05W / mK or higher, and more preferably 0.10W / mK or higher. Having the thermal conductivity within this range allows for miniaturization of components and promotes the curing reaction during heating.

[0134] (b) Stress-strain curve (i) Stress-strain curve of the non-foamed layer In the adhesive sheet of this disclosure, when the tensile shear adhesive strength test method is performed on the non-foamed layer, the slope of the approximate straight line in the section from strain 3% to strain 5% in the stress-strain curve 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 the foamed and non-foamed layers, the non-foamed layer is prone to peeling from the substrate, raising concerns about the generation of foreign matter. Furthermore, when shear stress is applied to the adhesive sheet, excessive load is placed on layers other than the non-foamed layer, raising concerns about failure. Here, for the non-foamed layer, a steeper slope of the above approximation line tends to make the non-foamed layer harder, while a shallower slope tends to make the non-foamed layer softer. When the slope of the above approximation line for the non-foamed layer is below a predetermined value, the non-foamed layer becomes appropriately hard. Therefore, the difference in hardness between the non-foamed layer and the foamed layer can be reduced. Thus, the adhesion of the non-foamed layer to the substrate in the adhesive sheet can be improved, thereby suppressing the generation of foreign matter. In addition, when shear stress is applied to the adhesive sheet, excessive load on layers other than the non-foamed layer can be suppressed, improving the durability of the adhesive sheet.

[0136] On the other hand, the slope of the above 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. With respect to the non-foamed layer, if the slope of the above approximation line is below a predetermined value, there is a concern that the non-foamed layer will become too soft, and the adhesion of the non-foamed layer will decrease. If the slope of the above approximation curve is within the above range, the non-foamed layer will have an appropriate hardness, and the adhesion of the non-foamed layer can be ensured.

[0137] Specifically, the slope of the above approximation curve is between 0.05 MPa and 0.20 MPa, and may also be between 0.07 MPa and 0.15 MPa.

[0138] (ii) Stress-strain curves of foamed and non-foamed layers In the adhesive sheet according to this disclosure, the difference between the slope of the approximate straight line in the stress-strain curve obtained when the tensile shear adhesive strength test method is performed on the foamed layer, in the section from strain 3% to strain 5%, and the difference between the slope of the approximate straight line in the stress-strain curve obtained when the tensile shear adhesive strength test method is performed on the non-foamed layer, in the section from strain 3% to strain 5%, 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 the slope of the above approximate curves is within the above range, the difference between the hardness of the non-foamed layer and the hardness of the foamed layer becomes small. Therefore, when the adhesive sheet has a substrate between the foamed layer and the non-foamed layer, it is possible to suppress the peeling of the non-foamed layer from the substrate, thereby suppressing the generation of foreign matter. In addition, it is possible to suppress excessive load on layers other than the non-foamed layer in the adhesive sheet, and the durability of the adhesive sheet can be improved. On the other hand, the difference in the slope of the above approximation curve may be, for example, 0.05 MPa or more, but may also be 0.07 MPa or more, or 0.10 MPa or more. If the difference in slope is within the above range, the non-foamed layer will have an appropriate hardness, and thus the adhesion of the non-foamed layer can be ensured. Specifically, the difference in the slope of the above approximation curve may be 0.05 MPa or more and 0.20 MPa or less, and may also be 0.07 MPa or more and 0.15 MPa or less.

[0139] (iii) Method for measuring stress-strain curves When performing the tensile shear adhesive strength test on a non-foamed layer, the 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 for the non-foamed layer is known, the non-foamed layer is formed using that adhesive composition, or by preparing an adhesive composition of that composition. Performing the tensile shear adhesive strength test on the non-foamed layer is the same as when performing the tensile shear adhesive strength test on the second adhesive layer after curing in a foamed adhesive sheet, as described later. In this case, the thickness of the non-foamed layer before curing is the same as 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 foamed layer, the foamed layer is prepared before foaming and curing. For example, if the adhesive sheet before foaming and curing is known, and the adhesive composition used in the foamed layer or its composition is known, the foamed layer before foaming and curing is formed using that adhesive composition or by preparing an adhesive composition of that composition. Performing the tensile shear adhesive strength test on the foamed layer is the same as when performing the tensile shear adhesive strength test on the first adhesive layer after foaming and curing in the foamed adhesive sheet described later. In this case, the thickness of the foamed layer before foaming and curing is the same as the thickness of the foamed layer before foaming and curing in the adhesive sheet before foaming and curing. The thickness of the spacer is the distance between the inner walls facing each other in the circumferential direction within the slot of the stator core. If there are manufacturing tolerances, the thickness of the spacer is the maximum allowable value.

[0141] The stress-strain curve, obtained in the tensile-shear adhesive strength test method described above, plots the relationship between shear stress and strain, with strain (%) on the horizontal axis and shear stress (MPa) on the vertical axis, as shown in Figures 4(a) and 4(b). The strain is the value obtained by dividing the increase in the distance between the grips by the length of the foamed or non-foamed layer, i.e., 12.5 mm. Figure 4(b) is a magnified view of a portion of Figure 4(a).

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

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

[0144] Regarding the non-foaming layer, methods for controlling the slope of the above-mentioned approximate straight line include, for example, adjusting the composition of the adhesive composition used in the non-foaming layer, and adjusting the drying conditions during the formation of the non-foaming layer.

[0145] In a method for adjusting the composition of an adhesive composition used in a non-foaming layer, as described later, by including flexible particles in the adhesive composition, the hardness of the non-foaming layer tends to decrease, and the slope of the above-mentioned approximate line tends to decrease. Furthermore, in an adhesive composition containing 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-foaming layer tends to decrease, and the slope of the above-mentioned approximate line tends to decrease. Also, in an adhesive composition containing epoxy resin and a curing agent, by reducing the content of polyfunctional epoxy resin, the crosslinking density after curing decreases, so the hardness of the non-foaming layer tends to decrease, and the slope of the above-mentioned approximate line tends to decrease.

[0146] 2. Stator core The stator core has slots into which the coils are inserted. Since the stator core is similar to a typical stator core, a detailed explanation is omitted here.

[0147] 3. Coil The coil is the same as a typical coil, so we will omit its explanation here.

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

[0149] B. Rotors for rotating electric machines The rotor for a rotating electric machine in this disclosure comprises a rotor core, coils arranged in slots of the rotor core, and an adhesive sheet arranged between the rotor core and the coils, wherein the adhesive sheet comprises 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 such that the non-foamed layer faces the coil side and the foamed layer faces the rotor core side.

[0150] Figure 5(a) is a schematic plan view illustrating a rotor for a rotating electric machine in this disclosure, and Figures 5(b) and (c) are enlarged views of Figure 5(a). As shown in Figures 5(a) to (c), the rotor 20 for a rotating electric machine includes a rotor core 21, coils 23 arranged in slots 22 of the rotor core 21, and an adhesive sheet 4 arranged between the rotor core 21 and the coils 23. The adhesive sheet 4 has a foamed layer 11 and a non-foamed layer 12. In the adhesive sheet 4, the ratio of the thickness of the foamed layer 11 to the thickness of the non-foamed layer 12 is within a predetermined range. The adhesive sheet 4 is arranged such that the non-foamed layer 12 faces the coils 23 side and the foamed layer 11 faces the rotor core 21 side.

[0151] In this disclosure, the adhesive sheet is positioned so that the non-foamed layer faces the coil, allowing heat generated from the coil to be conducted through the non-foamed layer. Furthermore, positioning the adhesive sheet so that the non-foamed layer faces the coil ensures that gaps are maintained between the coils. Therefore, heat generated from the coil is conducted through the air layer. Consequently, in this disclosure, positioning the adhesive sheet so that the non-foamed layer faces the coil improves the heat dissipation of heat generated from the coil.

[0152] Furthermore, as described in "A. Stator for Rotating Electric Machines" above, the unevenness caused by the foaming agent tends to lower the coefficient of friction of the foamed layer before hardening, resulting in improved slipperiness of the foamed layer before hardening. Since the adhesive sheet is positioned so that the foamed layer faces the rotor core, it is possible to improve the insertability of the adhesive sheet before hardening when inserting it into the slots of the rotor core.

[0153] Furthermore, as described in "A. Stator for Rotating Electric Machines" above, the un-foamed layer before curing does not have irregularities caused by the foaming agent. Since the adhesive sheet is positioned so that the un-foamed layer faces the coil side, when inserting the coil into the slot of the rotor core into which the un-foamed adhesive sheet is inserted, it is possible to prevent the coil from getting caught on the surface of the un-foamed layer before curing. Therefore, it is possible to prevent the foaming agent from falling off or the un-foamed layer from being scraped off when inserting the coil. Thus, the wear resistance of the un-foamed adhesive sheet before curing can be improved.

[0154] Furthermore, in this disclosure, the adhesive sheet is arranged so that the foamed layer faces the rotor core, thereby filling the gap between the rotor core and the adhesive sheet, and improving the adhesion between the rotor core and the adhesive sheet. In addition, the adhesive sheet is arranged so that the foamed layer, which has relatively weak cohesive force, is in contact with the rotor core where a large bonding area can be provided, and the non-foamed layer, which has relatively strong cohesive force, is in contact with the coil, where the bonding area is smaller, thereby firmly fixing the coil to the rotor core.

[0155] Furthermore, when inserting the adhesive sheet into the rotor core slot in a folded state before foaming and curing, there is a possibility that a portion of the foamed layer located on the rotor core side may come into contact with the wall or corner of the rotor core slot and be scraped off. In contrast, in this disclosure, since the thickness of the foamed layer is greater than or equal to the thickness of the non-foamed layer, and the ratio of the thickness of the foamed layer to the thickness of the non-foamed layer is within a predetermined range, even if a portion of the foamed layer before foaming and curing is scraped off, a decrease in foaming properties can be suppressed. Also, when inserting the adhesive sheet into the rotor core slot in a folded state before foaming and curing, tensile stress acts on the foamed layer located on the rotor core side at the bend, causing the thickness of the foamed layer before foaming and curing to decrease. In contrast, in this disclosure, since the thickness of the foamed layer is greater than or equal to the thickness of the non-foamed layer, and the ratio of the thickness of the foamed layer to the thickness of the non-foamed layer is within a predetermined range, even if the thickness of the foamed layer before foaming and curing decreases due to tensile stress at the bend, a decrease in foaming properties can be suppressed. Therefore, sufficient foaming properties can be ensured.

[0156] The configuration of the rotor for the rotating electric machine in this disclosure will be described below.

[0157] 1. Adhesive sheet The adhesive sheet in this disclosure has a foamed layer and a non-foamed layer, and is positioned between the rotor core and the coil such that the non-foamed layer faces the coil side and the foamed layer faces the rotor core side. In this disclosure, the adhesive sheet is positioned between the rotor core and the coil such that the non-foamed layer is in contact with the coil and the foamed layer is in contact with the rotor core.

[0158] The adhesive sheet in this disclosure is the same as the adhesive sheet in the stator for the rotating electric machine described above, so a further explanation is omitted here.

[0159] 2. Rotor core The rotor core has slots into which the coils are inserted. The rotor is similar to the rotor core generally used in wound-field motors, so its explanation is omitted here.

[0160] 3. Coil The coil is the same as a typical coil, so we will omit its explanation here.

[0161] 4. Other aspects of rotors for rotating electric machines The rotor for a rotating electric machine in this disclosure is, for example, a rotor used in a wound-field motor.

[0162] The method for manufacturing rotors for rotating electric machines will be described later.

[0163] C. Foamed adhesive sheet The foamed adhesive sheet in this disclosure is a foamed adhesive sheet used to fix coils to slots in the stator core or rotor core of a rotating electric machine, and comprises 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 positioned facing the coil side, and the first adhesive layer is positioned facing the stator core side or the rotor core side.

[0164] Figure 6 is a schematic cross-sectional view illustrating a foamed adhesive sheet in this disclosure. As shown in Figure 6, the foamed 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 the first adhesive layer 31 to the thickness T2 of the second adhesive layer 32 is within a predetermined range. The foamed adhesive sheet 30 is arranged such that the second adhesive layer faces the coil side and the first adhesive layer faces the stator core side or rotor core side.

[0165] The first adhesive layer contains a foaming agent, and after foaming and curing, it becomes a foamed layer. Generally, foamed layers have low thermal conductivity and insulating properties. Therefore, if a coil is fixed to a stator core using a foamed adhesive sheet, heat dissipation may decrease. In particular, if the foamed layer is in contact with the coil, heat dissipation is impaired. On the other hand, the second adhesive layer does not contain a foaming agent, and after curing, it becomes a non-foamed layer. Since the non-foamed layer does not have bubbles caused by the foaming agent, it has higher thermal conductivity than the foamed layer. In this 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. Thus, heat dissipation can be improved.

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

[0167] Therefore, in this disclosure, the foamed adhesive sheet is arranged such that the second adhesive layer faces the coil, thereby improving the heat 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 caused by the foaming agent tend to lower the coefficient of friction of the first adhesive layer, improving its slipperiness. Since the foamed adhesive sheet is positioned so that the first adhesive layer faces either the stator core side or the rotor core side, the insertability of the foamed adhesive sheet can be improved when inserting it 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 any irregularities caused by the foaming agent. Since the foamed adhesive sheet is positioned so that the second adhesive layer faces the coil side, it is possible to prevent the coil from catching on the surface of the second adhesive layer when inserting the coil into the slot of the stator core or rotor core in which the foamed adhesive sheet is inserted. Therefore, it is possible to prevent the foaming agent from falling off or the second adhesive layer from being worn down when inserting the coil. Thus, the wear resistance of the foamed adhesive sheet can be improved.

[0170] Furthermore, in this disclosure, by arranging the foamed adhesive sheet so that the first adhesive layer faces the stator core side or the rotor core side, the gap between the stator core or rotor core and the foamed 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 foamed adhesive sheet after foaming and curing. In addition, by arranging the foamed adhesive sheet so that the first adhesive layer, which has relatively weaker cohesive force, is in contact with the stator core or rotor core where a large bonding area can be obtained, and the second adhesive layer, which has relatively stronger cohesive force, is in contact with the coil where the bonding area is smaller, the coil can be firmly fixed to the stator core or rotor core.

[0171] Furthermore, when inserting a foamed adhesive sheet into a slot of a stator core or rotor core in a folded state, a portion of the first adhesive layer located on the stator core side or rotor core side may come into contact with the wall or corner of the slot of the stator core or rotor core and be scraped off. In contrast, in this disclosure, the thickness of the first adhesive layer is greater than or equal to 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, so that even if a portion of the first adhesive layer is scraped off, a decrease in foaming properties can be suppressed. Also, when inserting a foamed adhesive sheet into a slot of a stator core or rotor core in a folded state, tensile stress acts on the first adhesive layer located on the stator core side or rotor core side at the bend, causing the thickness of the first adhesive layer to decrease. In contrast, in this disclosure, the thickness of the first adhesive layer is greater than or equal to 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, so that even if the thickness of the first adhesive layer decreases due to tensile stress at the bend, a decrease in foaming properties can be suppressed. Therefore, sufficient foaming properties can be ensured.

[0172] The following describes the various components of the foamed adhesive sheet in this disclosure.

[0173] 1.First adhesive layer (1) Material of the first adhesive layer The first adhesive layer in this disclosure contains a curable adhesive and a foaming agent.

[0174] The material for the first adhesive layer is the same as the material used for the foam layer in the stator for the rotating electric machine described above, so its explanation is omitted here.

[0175] When the thermosetting adhesive is an epoxy resin-based adhesive, and the thermosetting adhesive contains a primary epoxy resin and a secondary epoxy resin as described above, the content of the primary epoxy resin may be, 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, per 100 parts by mass of the resin component contained in the first adhesive layer. If the content of the primary epoxy resin is too low, the adhesiveness and blocking resistance after foam curing may decrease. On the other hand, the content of the primary epoxy resin may be, 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, per 100 parts by mass of the resin component contained in the first adhesive layer. If the primary epoxy resin content is too high, the secondary epoxy resin and acrylic resin content will be relatively low, which may make it difficult to balance non-stick properties, blocking resistance, adhesion to the substrate after foam curing, crack resistance after foam curing, and adhesive properties after foam curing.

[0176] Furthermore, 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, based on 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 tackiness may increase and the blocking resistance may decrease. 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, based on 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 content of the first epoxy resin and acrylic resin will be relatively low, and it may not be possible to balance non-tackiness, blocking resistance, adhesion to the substrate after foam curing, crack resistance after foam curing, and adhesion after foam curing.

[0177] The proportion of the first epoxy resin to the total of the first and second epoxy resins is, for example, 5% by mass or more, may be 10% by mass or more, may be 15% by mass or more, or may be 20% by mass or more. On the other hand, the above proportion of the first epoxy resin is, for example, 80% by mass or less, may be 75% by mass or less, or may be 60% by mass or less.

[0178] Furthermore, the total ratio 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, may be 70% by mass or more, may be 90% by mass or more, or may be 100% by mass.

[0179] When the first and second adhesive layers are substantially non-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.

[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 tacky and the second adhesive layer is substantially non-tacky, 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 acrylic resin content is, 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, per 100 parts by mass of the resin component contained in the first adhesive layer. If the acrylic resin content is too low, the adhesion to the substrate after foam curing, crack resistance after foam curing, and adhesiveness after foam curing may decrease. On the other hand, the acrylic resin content is, 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, per 100 parts by mass of the resin component contained in the first adhesive layer. If the acrylic resin content is too high, the content of the first epoxy resin and the second epoxy resin will be relatively low, and it may not be possible to balance non-stick properties, blocking resistance, adhesion to the substrate after foam curing, crack resistance after foam curing, and adhesiveness after foam curing. Furthermore, if the acrylic resin content is too high, the film strength may decrease.

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

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

[0185] The curing agent content is, for example, 1 part by mass or more and 40 parts by mass or less per 100 parts by mass of resin components contained in the first adhesive layer. Furthermore, when an imidazole-based curing agent is used as the main component of the curing agent, the curing agent content is preferably, for example, 1 part by mass or more and 15 parts by mass or less per 100 parts by mass of resin components 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 curing agent content is preferably, for example, 5 parts by mass or more and 40 parts by mass or less per 100 parts by mass of resin components contained in the first adhesive layer. Note that 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 largest in the curing agent.

[0186] The foaming agent content is, for example, 0.5 parts by mass or more, but may be 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, based on 100 parts by mass of the resin component contained in the first adhesive layer. On the other hand, the foaming agent content is, for example, 25 parts by mass or less, but may be 20 parts by mass or less, or 15 parts by mass or less, based on 100 parts by mass of the resin component contained in the adhesive layer. If the foaming agent content is too high, the content of the curable adhesive will be relatively low, which may reduce the adhesiveness after foaming and curing.

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

[0188] The ratio of the thickness of the first adhesive layer to the thickness of the second adhesive layer is 1 or more, may be 1.2 or more, or may be 1.4 or more. As described above, sufficient foaming can be ensured by having the above thickness ratio within the above range. 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, may be 6.6 or less, or may be 4.8 or less. If the above thickness ratio is within the above range, the thickness of the second adhesive layer will not become too thin, and thus a decrease in adhesive strength can be suppressed. 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, may be 1.2 or more and 6.6 or less, or may be 1.4 or more and 4.8 or less.

[0189] The thickness of the first adhesive layer satisfies the above-mentioned thickness relationship and is preferably greater than or equal to the average particle size of the foaming agent. The thickness of the first adhesive layer is, for example, 10 μm or more, may be 15 μm or more, or 20 μm or more. If the first adhesive layer is too thin, sufficient adhesion to the substrate and adhesion after foaming and curing may not be obtained. On the other hand, the thickness of the first adhesive layer is, for example, 200 μm or less, may be 150 μm or less, or 100 μm or less. If the first adhesive layer is too thick, the surface quality may deteriorate. Specifically, the thickness of the first adhesive layer is 10 μm or more and 200 μm or less, may be 15 μm or more and 150 μm or less, or 20 μm or more and 100 μm or less.

[0190] (3) Other aspects of the first adhesive layer The first adhesive layer can be foamed at a foaming ratio of, for example, 1.5 times or more and 15 times or less. The foaming ratio may also be, for example, 3.5 times or more, 4 times or more, or 4.5 times or more. Alternatively, the foaming ratio may also be, for example, 15 times or less, 14 times or less, or 13 times or less. If the foaming ratio is too low or too high, the adhesive strength after foaming and curing may decrease.

[0191] Here, the expansion ratio is calculated using the following formula. Foaming ratio (times) = Thickness of the first adhesive layer after foaming and curing / Thickness of the 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 patterns such as stripes and dots. The surface of the first adhesive layer may also have an uneven shape such as an embossed surface.

[0193] The first adhesive layer can be formed, for example, by applying an adhesive composition containing the above-mentioned curable adhesive and foaming agent, 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, "solvent" has a broad meaning, including not only a strict solvent (a solvent that dissolves the solute) but also a dispersion medium. Furthermore, any solvent contained in the adhesive composition is removed by volatilization when the adhesive composition is applied and dried to form an adhesive layer.

[0195] Adhesive compositions can be obtained by mixing the above-mentioned components and kneading and dispersing them as necessary. Suitable mixing and dispersion methods include general kneading and dispersing machines such as two-roll mills, three-roll mills, pebble mills, thron mills, Szegvari attritors, high-speed impeller dispersers, high-speed stone mills, high-speed impact mills, despersers, high-speed mixers, ribbon blenders, conespers, intensive mixers, tumblers, blenders, despersers, homogenizers, and ultrasonic dispersers.

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

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

[0198] The material for the second adhesive layer is the same as the material used for the non-foamed layer in the stator for the rotating electric machine described above, so its explanation is omitted here.

[0199] When the first and second adhesive layers are substantially non-adhesive 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 tacky and the second adhesive layer is 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.

[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 is preferably such that it 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 foamed adhesive sheet after foaming and curing, which may reduce the adhesive strength.

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

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

[0205] 3.Base material The foamed adhesive sheet in this disclosure may have a substrate between the first adhesive layer and the second adhesive layer. For example, in the foamed adhesive sheet 30 shown in Figure 7, a substrate 33 is placed between the first adhesive layer 31 and the second adhesive layer 32. On the other hand, in the foamed adhesive sheet 30 shown in Figure 6, for example, a substrate 33 is not placed between the first adhesive layer 31 and the second adhesive layer 32.

[0206] The base material is the same as that of the adhesive sheet used in the stator for the rotating electric machine described above.

[0207] 4. First and second meso-intermediate layers The foamed adhesive sheet in this disclosure may have a first intermediate layer between the substrate and the first adhesive layer. The foamed adhesive sheet in this disclosure may also have a second intermediate layer between the substrate and the second adhesive layer. The presence of the first and second intermediate layers improves the adhesion of the first and second adhesive layers to the substrate. Furthermore, the presence of the first and second intermediate layers can, for example, alleviate stress on the bent portion when the foamed adhesive sheet is folded, or alleviate stress on the cut portion when the foamed adhesive sheet is cut. As a result, lifting or peeling of the first and second adhesive layers from the substrate can be suppressed when the foamed adhesive sheet is bent or cut.

[0208] For example, in the foamed adhesive sheet 30 shown in Figure 8, a first intermediate layer 34 is placed between the base material 33 and the first adhesive layer 31, and a second intermediate layer 35 is placed between the base material 33 and the second adhesive layer 32. In Figure 8, the foamed adhesive sheet 30 has both the first intermediate layer 34 and the second intermediate layer 35, but it may have only one of them.

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

[0210] 5. First separator and second separator The foamed adhesive sheet in this disclosure may have a first separator on the side of the first adhesive layer opposite to the second adhesive layer. Furthermore, the foamed adhesive sheet in this disclosure may have a second separator on the side of the second adhesive layer opposite to the first adhesive layer.

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

[0212] Examples of single-layer separators include fluororesin-based films.

[0213] Furthermore, examples of multilayer separators include laminates having release layers on one or both sides of a base layer. Examples of base layers include resin films such as polypropylene, polyethylene, and polyethylene terephthalate, and papers such as fine paper, coated paper, and impregnated paper. The material of the release layer is not particularly limited as long as it has release properties, and examples include silicone compounds, organic compound-modified silicone compounds, fluorine compounds, amino alkyd compounds, melamine compounds, acrylic compounds, polyester compounds, and long-chain alkyl compounds. These compounds can be used in emulsion, solvent, or solvent-free forms.

[0214] 6. Characteristics of foamed adhesive sheets (1) Tack of the first and second adhesive layers In this disclosure, both the first adhesive layer and the second adhesive layer may be substantially non-tack-free, or one of the first adhesive layer and the second adhesive layer may be substantially non-tack-free and the other tack-free.

[0215] When both the first and second adhesive layers are substantially non-adhesive, good slipperiness and blocking resistance can be achieved. This improves the handling and workability of the foamed adhesive sheet. Specifically, the foamed adhesive sheet can be smoothly inserted into the slots of the stator core or rotor core, or the coil and foamed adhesive sheet can be smoothly inserted into the slots of the stator core or rotor core after the foamed adhesive sheet has been placed around the coil.

[0216] Here, non-adhesiveness is generally used to mean having low adhesive strength, and in this specification, "non-adhesive" means having a tack of less than 0.1 N.

[0217] On the other hand, if one of the first adhesive layer and the second adhesive layer is substantially non-adhesive and the other is adhesive, for example, if the first adhesive layer is substantially non-adhesive and the second adhesive layer is adhesive, good adhesion to the coil can be achieved. Specifically, when the surface of the second adhesive layer of a foam adhesive sheet is attached to a coil and the coil with the foam adhesive sheet attached is inserted into a slot of a stator core or rotor core, the adhesiveness of the second adhesive layer allows the surface of the second adhesive layer of the foam adhesive sheet to be attached to the coil by utilizing the adhesiveness of the second adhesive layer, thereby improving the adhesion of the second adhesive layer to the coil. This makes it possible to suppress peeling and displacement of the foam adhesive sheet when inserting the coil with the foam adhesive sheet attached into a slot of a stator core or rotor core.

[0218] Furthermore, in the above case, the tackiness of the second adhesive layer improves reworkability. For example, when attaching the surface of the second adhesive layer of the foam adhesive sheet to the coil using the tackiness of the second adhesive layer as described above, the misalignment of the foam adhesive sheet can be corrected.

[0219] Furthermore, in the above case, the non-adhesive nature of the first adhesive layer improves lubricity. Therefore, when inserting a coil with a foamed adhesive sheet attached into a slot in the stator core or rotor core, the coil can be inserted smoothly, improving insertability. This suppresses peeling and misalignment of the foamed adhesive sheet. In addition, 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 moved smoothly relative to the stator core or rotor core with the coil inserted into the slot, making alignment easier.

[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 can suppress peeling and displacement of the foamed adhesive sheet. Therefore, it is possible to suppress the decrease in adhesiveness of the foamed adhesive sheet after foaming and curing due to peeling and displacement of the foamed adhesive sheet, and to reduce the variation in adhesive strength of the foamed adhesive sheet after foaming and curing due to peeling and displacement of the foamed adhesive sheet.

[0221] Furthermore, in the above case, the adhesive properties of the second adhesive layer can suppress lifting of the second adhesive layer, for example, when the second adhesive layer is formed by a transfer method. Moreover, as will be described later, if the second separator is placed on the side of the second adhesive layer opposite to the first adhesive layer, the adhesive properties of the second adhesive layer allow the second separator to be easily peeled off, improving workability.

[0222] When both the first and second adhesive layers are substantially non-tacky, specifically, the tack of the first and second adhesive layers is preferably less than 0.1 N, may be 0.05 N or less, or 0.02 N or less. By having the tack of the first and second adhesive layers within the above range, the first and second adhesive layers can be made substantially non-tacky, and good slipperiness and blocking resistance can be achieved. In this case, the lower limit of the tack of the first and second adhesive layers 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 preferably less than 0.1N, and the tack of the second adhesive layer is preferably 0.1N or more and 5N or less.

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

[0225] Furthermore, in the above case, the tack of the second adhesive layer is preferably 0.1N or higher, may be 0.3N or higher, or 0.5N or higher. If the tack of the second adhesive layer is too low, for example, when using the tack of the second adhesive layer to attach the surface of the second adhesive layer of the foamed adhesive sheet to the coil, the adhesion between the second adhesive layer and the coil may decrease. Also, when inserting the coil with the foamed adhesive sheet attached into the slot of the stator core or rotor core, poor adhesion between the second adhesive layer and the coil may cause the foamed adhesive sheet to peel off or shift position, potentially reducing the adhesion between the first and second adhesive layers after foam curing, or causing variations in adhesive strength. Furthermore, the tack of the second adhesive layer is 5N or lower, may be 4N or lower, or 3N or lower. If the tack of the second adhesive layer is too high, reworkability decreases, and for example, when using the tack of the second adhesive layer to attach the surface of the second adhesive layer of the foamed adhesive sheet to the coil, it may become difficult to correct the positional shift of the foamed adhesive sheet.

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

[0227] The tack of the first and second adhesive layers can be brought within a predetermined range, for example, by adjusting the composition of the first and second adhesive layers.

[0228] Specifically, in an adhesive layer containing epoxy resin and a curing agent, the tackiness of the adhesive layer can be reduced by using an epoxy resin that is solid at room temperature or a curing agent that is solid at room temperature. On the other hand, in an adhesive layer containing epoxy resin and a curing agent, the tackiness of the adhesive layer tends to increase when an epoxy resin that is liquid at room temperature or a curing agent that is liquid at room temperature is used.

[0229] Furthermore, in an adhesive layer containing epoxy resin and a curing agent, the tackiness of the adhesive layer can be reduced by including an epoxy resin with a high softening temperature or an epoxy resin with a large weight-average molecular weight. On the other hand, in an adhesive layer containing epoxy resin and a curing agent, the tackiness of the adhesive layer tends to increase when an epoxy resin with a low softening temperature or an epoxy resin with a small weight-average molecular weight is included. For example, the tackiness of the adhesive layer can be reduced by including multiple types of epoxy resins with different softening temperatures in the adhesive layer, that is, by including one epoxy resin and another epoxy resin whose softening temperature is 25°C or higher and at least 10°C higher than the softening temperature of the first epoxy resin. Also, for example, the tackiness of the adhesive layer can be reduced by including multiple types of epoxy resins with different weight-average molecular weights in the adhesive layer, that is, by including one epoxy resin and another epoxy resin whose weight-average molecular weight is 370 or higher and at least 300 higher than the weight-average molecular weight of the first epoxy resin. More specifically, in an adhesive layer containing epoxy resin and a curing agent, the tackiness of the adhesive layer can be reduced by including a primary epoxy resin with a low softening temperature and low molecular weight, and a secondary epoxy resin with a high softening temperature and high molecular weight, as the epoxy resin.

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

[0231] Furthermore, adding a tackifier to the adhesive layer tends to increase its tackiness.

[0232] While using a liquid curing agent at room temperature tends to increase tackiness, it may reduce storage stability. Therefore, it is preferable to adjust the tack of the adhesive layer by adjusting the properties and type of components other than the curing agent, such as epoxy resin.

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

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

[0235] (2) Bending moment The foamed adhesive sheet in this disclosure preferably has good shape retention. The bending moment according to JIS P8125-2:2017 corresponding 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 above bending moment may be, for example, less than 4 mN·N, and may be less than 3 mN·N. Conventionally, in foamed adhesive sheets, it is common to increase the bending moment to improve shape retention and insertion into narrow gaps. In contrast, the inventors of this disclosure have found that shape retention can be ensured by designing the shape, and that a high bending moment has other drawbacks, and that, considering other characteristics, it is preferable for the bending moment to be within the above range. If the bending moment is smaller than the above range, it may be difficult to maintain the shape even with techniques such as folding. Also, if the bending moment is larger than the above range, the shape will return to its original state after bending, so it is necessary to heat the sheet or make creases at the folds during bending. Heating can reduce the sheet life, and creating streaks may decrease the insulation properties in those areas.

[0236] (3) Electrical insulation The foamed adhesive sheet in this disclosure preferably has high electrical insulation properties after foaming and curing. After foaming and curing of the foamed adhesive sheet, the dielectric breakdown voltage according to JIS C2107:2011 corresponding to IEC 60454-2 is preferably, for example, 3kV or higher, and more preferably 5kV or higher. Having the dielectric breakdown voltage within the above range makes it possible to apply it to rotating electric machines. Furthermore, after foaming and curing of the foamed adhesive sheet, the thermal conductivity is preferably, for example, 0.05W / mK or higher, and more preferably 0.10W / mK or higher. Having the thermal conductivity within the above range makes it possible to miniaturize the parts and promote the curing reaction during heating.

[0237] (4) Tensile shear bond strength The foamed adhesive sheet in this disclosure preferably has high adhesiveness after foaming and curing. After foaming and curing of the foamed adhesive sheet, the tensile shear adhesive strength according to JIS K6850:1999 corresponding 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 above 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, in the case of high-strength acrylic foam adhesive tape that does not require heating, the tensile shear adhesive strength is about 1 MPa to 2 MPa at room temperature and has no heat resistance at 200°C. Therefore, if the above tensile shear adhesive strength is within the above range at 23°C, there is an advantage in terms of strength. Furthermore, if the above tensile shear adhesive strength is within the above range at 130°C, it becomes possible to apply it to rotating electric machines where heat resistance is required.

[0238] (5) Stress-strain curve In this disclosure, when the tensile shear adhesive strength test method is performed on the second adhesive layer after curing, the slope of the approximate straight line in the section from 3% strain to 5% strain in the stress-strain curve is preferably 0.20 MPa or less, may be 0.15 MPa or less, or may be 0.10 MPa or less. By having the slope of the approximate curve within the above range, the second adhesive layer after curing becomes appropriately hard. Therefore, the difference between the hardness of the second adhesive layer after curing and the hardness of the first adhesive layer after foam curing can be reduced. Thus, after foam curing of the foamed adhesive sheet, peeling of the second adhesive layer after curing can be suppressed, thereby suppressing the generation of foreign matter. Furthermore, after foam curing of the foamed adhesive sheet, excessive load on layers other than the second adhesive layer can be suppressed, and the durability of the foamed adhesive sheet after foam curing can be improved. In addition, the slope of the approximate 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 above approximation curve is within the above range, the second adhesive layer after curing will have an appropriate hardness, thus improving the adhesion of the second adhesive layer after curing. Specifically, the slope of the above approximation curve is between 0.05 MPa and 0.20 MPa, and may also be between 0.07 MPa and 0.15 MPa.

[0239] Furthermore, in this disclosure, the difference between the slope of the approximate straight line in the stress-strain curve obtained when the tensile shear adhesive strength test method is performed on the first adhesive layer after foam curing, in the section from strain 3% to strain 5%, and the difference between the slope of the approximate straight line in the stress-strain curve obtained when the tensile shear adhesive strength test method is performed on the second adhesive layer after curing, in the section from strain 3% to strain 5%, 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 between the hardness of the second adhesive layer after curing and the hardness of the first adhesive layer after foam curing becomes small. Therefore, after foam curing of the foamed adhesive sheet, it is possible to suppress the peeling of the cured second adhesive layer from the substrate, thereby suppressing the generation of foreign matter. In addition, after foam curing of the foamed adhesive sheet, it is possible to suppress excessive load on layers other than the second adhesive layer, and the durability of the foamed adhesive sheet after foam curing can be improved. Furthermore, the difference in the slope of the above approximation curve may be, for example, 0.05 MPa or more, but may also be 0.07 MPa or more, or 0.10 MPa or more. If the difference in the slope of the above approximation curve is within the above range, the second adhesive layer after curing will have an appropriate hardness, and the adhesion of the second adhesive layer after curing will be high. Specifically, the difference in the slope of the above approximation curve may be 0.05 MPa or more and 0.20 MPa or less, and may also be 0.07 MPa or more and 0.15 MPa or less.

[0240] The tensile shear adhesive strength test method for the cured second adhesive layer shall be carried out in accordance with JIS K6850:1999, which corresponds to ISO 4587, and shall be performed by the following method. First, a second adhesive layer measuring 12.5 mm × 25 mm shall be prepared. For example, if the adhesive composition used for the second adhesive layer of the foamed adhesive sheet or its composition is known, the second adhesive layer shall be formed using that adhesive composition or by preparing an adhesive composition of the same composition. Alternatively, the composition of the second adhesive layer of the foamed adhesive sheet may be analyzed, and an adhesive composition of the same composition may be prepared to form the second adhesive layer. A known method may be applied for the analysis of the composition of the second adhesive layer. The thickness of the second adhesive layer shall be the same as the thickness of the second adhesive layer of the foamed adhesive sheet. In addition, as shown in Figure 9, two metal plates 41a and 41b with a thickness of 1.6 mm, a width of 25 mm, and a length of 100 mm shall be prepared. For example, cold-rolled steel sheet SPCC-SD shall be used as the metal plate. A spacer 42 shall be placed at a predetermined interval at one end of one of the metal plates 41a. The thickness of the spacer 42 shall be at least the thickness of the second adhesive layer minus 15 μm and less than or equal to the thickness of the second adhesive layer. The thickness of the spacer 42 is adjusted by stacking multiple sheets of Kapton adhesive tape manufactured by Teraoka Seisakusho Co., Ltd., for example. 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, and it is fixed with a clip 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 as appropriate according to the curable adhesive contained in the second adhesive layer. Next, the tensile shear adhesive strength test method is performed on the cured test specimen in accordance with JIS K6850:1999. The measurement conditions are: tensile speed: 10 mm / min, distance between grips: 100 mm, temperature: room temperature (23°C), humidity: 50% RH. As a tensile testing machine, for example, a 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 foam curing shall be carried out in accordance with JIS K6850:1999, which corresponds to ISO 4587, and shall be performed by the following method. First, a first adhesive layer measuring 12.5 mm × 25 mm shall be prepared. For example, if the adhesive composition used for the first adhesive layer of the foam adhesive sheet or its composition is known, the first adhesive layer shall be formed using that adhesive composition or by preparing an adhesive composition of that composition. Alternatively, the composition of the first adhesive layer of the foam adhesive sheet may be analyzed, and an adhesive composition of that composition may be prepared and used to form the first adhesive layer. A known method may be applied for the analysis of the composition of the first adhesive layer. The thickness of the first adhesive layer shall be the same as the thickness of the first adhesive layer of the foam adhesive sheet. Also, as shown in Figure 10, two metal plates 41a and 41b with a thickness of 1.6 mm, a width of 25 mm, and a length of 100 mm shall be prepared. For example, cold-rolled steel sheet SPCC-SD shall be used as the metal plate. A spacer 42 shall be placed at a predetermined interval on one end of one of the metal plates 41a. The thickness of the spacer 42 is set appropriately according to the foaming ratio of the first adhesive layer. For example, as shown in Figure 11, when a foaming adhesive sheet 30 is placed between the stator core 1 or rotor core 21 and the coils 3 and 23, and then, although not shown, the foaming adhesive sheet 30 is foamed and cured to bond the stator core 1 or rotor core 21 and the coils 3 and 23, if the distance d1 between the stator core 1 or rotor core 21 and the coils 3 and 23 is known, first, the gap d2 after placing the foaming adhesive sheet 30 between the stator core 1 or rotor core 21 and the coils 3 and 23 is determined. The gap d2 is obtained by subtracting the thickness t1 of the foaming adhesive sheet 30 from the distance d1. Next, the thickness of the spacer 42 is set based on the thickness of the first adhesive layer and the gap d2. The thickness of the spacer 42 is obtained by adding the thickness of the first adhesive layer and the gap d2. The thickness of the spacer 42 should 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 and 23 is unknown, first determine the foaming ratio of the first adhesive layer. Here, the foaming ratio refers to the foaming ratio when the first adhesive layer is foamed and cured without being sandwiched between any members.The foaming ratio of the first adhesive layer can be determined by foaming and curing the foaming adhesive sheet without sandwiching it between any materials. In this case, the thickness of the spacer 42 is set to be (thickness of the first adhesive layer) × (foaming ratio of the first adhesive layer) × 0.3 or more, and (thickness of the first adhesive layer) × (foaming ratio of the first adhesive layer) × 0.8 or less. However, the thickness of the spacer 42 must be greater than or equal to the thickness of the first adhesive layer. The thickness of the spacer 42 is adjusted by stacking multiple sheets of Kapton adhesive tape manufactured by Teraoka Seisakusho Co., Ltd., for example. 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, and fixed with a clip or adhesive tape such as Kapton tape to obtain a test piece. Next, the first adhesive layer of the test piece is foamed and cured. The foaming and curing conditions are adjusted as appropriate according to the curable adhesive and foaming agent contained in the first adhesive layer. Next, the tensile shear adhesive strength test method is performed on the test piece after foaming and curing in accordance with JIS K6850:1999. The measurement conditions are as follows: tensile speed: 10 mm / min, grip distance: 100 mm, temperature: room temperature (23°C), humidity: 50% RH. For the tensile testing machine, for example, a Tensilon RTF1350 manufactured by A&D Corporation will be used.

[0242] The stress-strain curve, obtained in the tensile-shear bond strength test method described above, plots the relationship between shear stress and strain, with strain (%) on the horizontal axis and shear stress (MPa) on the vertical axis, as shown in Figures 4(a) and 4(b), for example. The strain is the value obtained by dividing the increase in the distance between the grips by the length of the first or second adhesive layer, i.e., 12.5 mm. Figure 4(b) is a magnified view of a portion of Figure 4(a).

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

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

[0245] Regarding the second adhesive layer after curing, methods for controlling the slope of the approximate straight line mentioned above include, for example, adjusting the composition of the second adhesive layer and adjusting the drying conditions during the formation of the second adhesive layer.

[0246] In the method for adjusting the composition of the second adhesive layer, as described later, by including flexible particles in the second adhesive layer, the hardness of the second adhesive layer after curing tends to decrease, and the slope of the above approximate straight line tends to decrease. Furthermore, in a second adhesive layer containing epoxy resin and a curing agent, if the number of functional groups of the epoxy resin is the same, reducing the molecular weight of the epoxy resin tends to decrease the hardness of the second adhesive layer after curing, and the slope of the above approximate straight line tends to decrease. Also, in a second adhesive layer containing epoxy resin and a curing agent, reducing the content of polyfunctional epoxy resin lowers the crosslinking density after curing, so the hardness of the second adhesive layer after curing tends to decrease, and the slope of the above approximate straight line tends to decrease.

[0247] (6) Mode of destruction In this disclosure, when a tensile shear adhesive strength test method is performed on a foamed adhesive sheet after foaming and curing, 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 higher strength than the first adhesive layer after foaming and curing.

[0248] The tensile shear adhesive strength of the foamed adhesive sheet after foaming and curing is measured according to JIS K6850:1999, which corresponds to ISO 4587, using the method described below. First, a foamed adhesive sheet measuring 12.5 mm x 25 mm is prepared. Also, as shown in Figure 12, two metal plates 41a and 41b with a thickness of 1.6 mm, a width of 25 mm, and a length of 100 mm are prepared. For the metal plates, for example, cold-rolled steel sheet SPCC-SD is used. A spacer 42 is placed at one end of one of the metal plates 41a at a predetermined interval. The thickness of the spacer 42 is set appropriately according to the foaming ratio of the first adhesive layer. For example, as shown in Figure 4, when a foam adhesive sheet 30 is placed between a first member 20a and a second member 20b, and then, although not shown, the foam adhesive sheet 30 is 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 above distance d1. The thickness of the spacer 42 should be within ±5% of the above distance d1. On the other hand, if the distance d1 between the first member 20a and the second member 20b is unknown, first, the foaming ratio of the first adhesive layer is determined. The foaming ratio here refers to the foaming ratio when the first adhesive layer is foamed and cured without being sandwiched between any members. The foaming ratio of the first adhesive layer can be determined by foaming and curing the foam adhesive sheet without being sandwiched between any members. In this case, the thickness of the spacer 42 shall be at least {(thickness of the foamed adhesive sheet)-(thickness of the first adhesive layer)}+(thickness of the first adhesive layer)×(foaming ratio of the first adhesive layer)×0.3 and at least {(thickness of the foamed adhesive sheet)-(thickness of the first adhesive layer)}+(thickness of the first adhesive layer)×(foaming ratio of the first adhesive layer)×0.8. However, the thickness of the spacer 42 shall be at least the thickness of the foamed 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, the foamed adhesive sheet 30 is placed between the spacers 42, and the other metal plate 41b is placed so that one end overlaps, and fixed with a clip or adhesive tape such as Kapton tape to obtain a test piece. Next, the first adhesive layer of the test piece is foamed and hardened, and the second adhesive layer is hardened.The foaming and curing conditions are appropriately adjusted according to the curable adhesive and foaming agent contained in the first adhesive layer and the curable adhesive contained in the second adhesive layer. Next, for the test piece after foaming and curing, in accordance with JIS K6850:1999, a tensile shear adhesive strength test method is performed. The measurement conditions are: tensile speed: 10 mm / min, temperature: normal temperature (23 °C), humidity: 50% RH. As the tensile testing machine, for example, Tensilon RTF1350 manufactured by A&D Company Limited is used. Next, the fracture surface of the test piece is visually observed.

[0249] Note that the fracture mode being cohesive failure of the first adhesive layer after foaming and curing means that the cohesive failure rate inside 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 part inside the first adhesive layer to the entire adhesive area. The above tensile shear adhesive strength test method is performed three times, and the above cohesive failure rate adopts the average value of the three times.

[0250] (7) Thickness of the foaming adhesive sheet The thickness of the foaming 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 foaming adhesive sheet is, for example, 1000 μm or less, and may be 200 μm or less. That is, the thickness of the foaming adhesive sheet is, 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 points of the foaming adhesive sheet The foaming adhesive sheet in the present disclosure is used to fix a coil in a slot of a stator core or rotor core of a rotating electrical machine. Also, the foaming adhesive sheet in the present disclosure is arranged such that the second adhesive layer faces the coil side and the first adhesive layer faces the stator core side or rotor core side. Since the stator for a rotating electrical machine and the rotor for a rotating electrical machine have been described above, the description here is omitted.

[0252] The manufacturing method of the foaming adhesive sheet in the present disclosure is not particularly limited and is appropriately selected according to the layer configuration of the foaming adhesive sheet.

[0253] D. Manufacturing Method of Rotor for Rotating Electric Machine The manufacturing method of the stator for a rotating electric machine in the present disclosure is a manufacturing method of a stator for a rotating electric machine that fixes a coil in a slot of a stator core, and includes 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 and not containing 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 side and the first adhesive layer faces the stator core side; and an adhesion step of foaming and curing the foamable adhesive sheet to adhere the coil to the stator core. In the foamable adhesive sheet, 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.

[0254] Figs. 13(a) to (b) are process diagrams illustrating the manufacturing method of the stator for a rotating electric machine in the present disclosure. First, although not shown, 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 and not containing a foaming agent is prepared. In the foamable adhesive sheet, 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), the coil 3 and the foamable adhesive sheet 30 are inserted into the slot 2 of the stator core 1, and the foamable adhesive sheet 30 is arranged between the stator core 1 and the coil 3 so that the second adhesive layer faces the coil 3 side and the first adhesive layer faces the stator core 1 side. Next, as shown in Fig. 13(b), the first adhesive layer of the foamable adhesive sheet 30 is foamed and cured by heating, and the second adhesive layer is cured. The coil 3 is adhered to the stator core 1 by the adhesive sheet 4. Thereby, the stator 10 for a rotating electric machine is obtained.

[0255] Hereinafter, each step of the manufacturing method of the stator for a rotating electric machine in 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 and not containing a foaming agent.

[0257] If the foamed adhesive sheet has a first separator and a second separator, when placing the foamed adhesive sheet between the stator core and the coil, the first separator and the second separator should be peeled off from the foamed adhesive sheet before use.

[0258] Further details regarding the foamed adhesive sheet are described in section "C. Foamed Adhesive Sheet" above, so an explanation will be omitted here.

[0259] 2.Placement process In the arrangement process described herein, a foamed adhesive sheet is placed between the stator core and the coil such that the second adhesive layer faces the coil side and the first adhesive layer faces the stator core side.

[0260] The method for placing the foam adhesive sheet between the stator core and the coil can be 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 foam adhesive sheet tends to lose its rigidity, so it is preferable to place the foam adhesive sheet around the coil and then insert the coil and foam adhesive sheet into the slots of the stator core. On the other hand, if the foam adhesive sheet has a base material, the methods include placing 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 then inserting the foam adhesive sheet into the slots of the stator core.

[0261] 3.Gluing process In the bonding process described herein, heating is one method for foaming and curing the foamed adhesive sheet.

[0262] The heating conditions are set appropriately depending on the type 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 substrate, 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 more and 3 hours or less.

[0263] E. Manufacturing method of rotor for rotating electric machines The present disclosure relates to a method for manufacturing a rotor for a rotating electric machine, which involves fixing coils to slots in a rotor core, and comprises: a preparation step of preparing a foamed adhesive sheet having a first adhesive layer containing a curable adhesive and a foaming agent, and a second adhesive layer containing a curable adhesive and not containing a foaming agent; a placement step of arranging the foamed adhesive sheet between the rotor core and the coils such that the second adhesive layer faces the coil side and the first adhesive layer faces the rotor core side; and an bonding step of foaming and curing the foamed adhesive sheet to bond the coils 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.

[0264] Figures 14(a) and 14(b) are process diagrams illustrating a method for manufacturing a rotor for a rotating electric machine according to this disclosure. First, a foamed adhesive sheet is prepared, which has a first adhesive layer containing a curable adhesive and a foaming agent (not shown), and a second adhesive layer containing a curable adhesive but not a foaming agent. In the foamed adhesive sheet, the ratio of the thickness of the first adhesive layer to the thickness of the second adhesive layer is set to a predetermined range. Next, as shown in Figure 14(a), the coil 33 and the foamed adhesive sheet 30 are inserted into the slot 22 of the rotor core 21, and the foamed adhesive sheet 30 is positioned between the rotor core 21 and the coil 23 such that the second adhesive layer faces the coil 23 and the first adhesive layer faces the rotor core 21. Next, as shown in Figure 14(b), the first adhesive layer of the foamed adhesive sheet 30 is foamed and cured by heating, and the second adhesive layer is cured. The coil 23 is bonded to the rotor core 21 by the adhesive sheet 4. This gives rise to a rotor for a rotating electric machine 20.

[0265] The foam adhesive sheet preparation process, placement process, and bonding process are the same as those described above in the manufacturing method for a stator for a rotating electric machine.

[0266] This disclosure is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of this disclosure and achieves similar effects is included within the technical scope of this disclosure. [Examples]

[0267] [Examples 1-16 and Comparative Examples 1-4] (1) Material The components used in the adhesive composition are shown below. • Epoxy resin A: Bisphenol A phenoxy type, solid at room temperature, epoxy equivalent 7500-8500 g / eq, Mw 50,000, bifunctional. • Epoxy resin B: Bisphenol A novolac type, solid at room temperature, epoxy equivalent 200-220 g / eq, softening temperature 70°C, polyfunctional. • Acrylic resin: PMMA-PBuA-PMMA (partially containing acrylamide groups), Tg -20℃, 120℃, Mw 150,000 • Hardener A: α-(hydroxy(or dihydroxy)phenylmethyl)-ω-hydropoly[biphenyl-4,4'-diylmethylene(hydroxy(or dihydroxy)phenylenemethylene)] • Hardener 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 initiation temperature 145°C~155°C, active range 155°C~173°C • Foaming agent: Thermally expandable microcapsules, average particle size 10μm~16μm, expansion start temperature 123℃~133℃, maximum expansion temperature 168℃~178℃, core: hydrocarbon, shell: thermoplastic polymer • Solvent: Methyl ethyl ketone

[0268] (2) Preparation of the first adhesive composition The first adhesive composition with the following composition was prepared. <Composition of the 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 · Blowing agent: 13.5 parts by mass · Solvent: 86 parts by mass

[0269] (3) Preparation of the second adhesive composition The first adhesive composition with the following composition was prepared. <Composition of the 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 the foaming adhesive sheet As a base material, a polyethylene naphthalate film (PEN film) with a thickness of 100 μm was prepared. Next, a polyester polymer and a curing agent (polyisocyanate) were diluted with methyl ethyl ketone (MEK) so that the solid content became 15% by mass to prepare a resin composition. The resin composition was applied to one surface of the base material with a bar coater and dried in an oven at 100 °C for 1 minute to form a first intermediate layer. Further, a second intermediate layer was formed on the other surface of the base material in the same manner as the first intermediate layer.

[0271] Next, the first adhesive composition was applied to the side of the first intermediate layer opposite to the substrate using an applicator. Then, it was dried in an oven at 100°C for 3 minutes to form the first adhesive layer. Furthermore, using the second adhesive composition, a second adhesive layer was formed on the side of the second intermediate layer opposite to the substrate, in the same manner as the first adhesive layer. This resulted in a foamed 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] [Rating 1] (1) Shear bond strength test method The shear bond strength test method was performed on the foamed adhesive sheet after foam curing, as described in section C. Foamed Adhesive Sheet 6. Characteristics of Foamed Adhesive Sheet above. After that, the fracture surface of the test specimen was visually observed. In the shear bond strength test method, the thickness of the spacer was set to 300 μm. The foam curing conditions were 165°C for 8.5 minutes (3.5 minutes heating, 5 minutes holding) using a hot press machine.

[0273] [Table 1]

[0274] [Table 2]

[0275] [Table 3]

[0276] In foamed adhesive sheets, it was confirmed that 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 becomes cohesive failure of the first adhesive layer, resulting in higher adhesive strength. In other words, it was confirmed that when the ratio of the thickness of the first adhesive layer after foam curing to the thickness of the second adhesive layer after curing is within a predetermined range, the failure mode becomes cohesive failure of the first adhesive layer, resulting in higher adhesive strength.

[0277] [Examples 17-23] (1) Material The components used in the adhesive composition are shown below. • Epoxy resin A: Bisphenol A phenoxy type, solid at room temperature, epoxy equivalent 7500-8500 g / eq, Mw 50,000, bifunctional. • Epoxy resin B: Bisphenol A novolac type, solid at room temperature, epoxy equivalent 200-220 g / eq, softening temperature 70°C, polyfunctional. • Epoxy resin C: Bisphenol A type, solid at room temperature, epoxy equivalent 2400-3300 g / eq, softening temperature 144°C, Mw 3,800, bifunctional. • Acrylic resin: PMMA-PBuA-PMMA (partially containing acrylamide groups), Tg -20℃, 120℃, Mw 150,000 • Hardener 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 initiation temperature 145°C~155°C, active range 155°C~173°C • Foaming agent: Thermally expandable microcapsules, average particle size 10μm~16μm, expansion start temperature 123℃~133℃, maximum expansion temperature 168℃~178℃, core: hydrocarbon, shell: thermoplastic polymer • Hollow particles: Microballoons formed by inflating thermally expandable microcapsules, with an average particle size of 15 μm to 25 μm. • Solvent: Methyl ethyl ketone

[0278] (2) Preparation of foamed adhesive sheet A polyethylene naphthalate (PEN) film with a thickness of 100 μm was used as the substrate. A resin composition was prepared by diluting a polyester polymer and a curing agent (polyisocyanate) with methyl ethyl ketone (MEK) to a solid content of 15% by mass. 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.

[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 to a thickness of 58 μm after coating. Then, it was dried in an oven at 100°C for 3 minutes to form the 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 to a thickness of 48 μm after coating. Then, it was dried in an oven at 100°C for 3 minutes to form the second adhesive layer. This resulted in a foamed adhesive sheet with the first adhesive layer, first intermediate layer, substrate, second intermediate layer, and second adhesive layer arranged in this order.

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

[0281] For the first adhesive layer after foam curing, the shear adhesive strength was measured by performing a shear adhesive strength test as described in section "C. Foamed Adhesive Sheet 6. Characteristics of Foamed Adhesive Sheet" above. In addition, the slope of the approximate straight line in the stress-strain curve for the section from strain 3% to strain 5% was determined. In the shear adhesive strength test, the thickness of the spacer was set to 180 μm. The foam curing conditions were 160°C for 8.5 minutes (heating for 3.5 minutes, holding for 5 minutes) using a hot press machine.

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

[0283] For the second adhesive layer after curing, the shear adhesive strength was measured by performing a shear adhesive strength test as described in section "C. Foamed Adhesive Sheet 6. Characteristics of Foamed Adhesive Sheet" above. In addition, the slope of the approximate straight line in the stress-strain curve for the section from strain 3% to strain 5% was determined. In the shear adhesive strength test, the thickness of the spacer was set to 35 μm. The curing conditions were 160°C for 8.5 minutes (heating for 3.5 minutes, holding for 5 minutes) using a hot press.

[0284] (1-3) Foamed adhesive sheet after foaming and curing For the foamed adhesive sheets after foam curing, the shear adhesive strength was measured by performing a shear adhesive strength test as described in section "C. Foamed Adhesive Sheets 6. Characteristics of Foamed Adhesive Sheets" above. The fracture surface of the test specimen was also visually observed. In the shear adhesive strength test, the thickness of the spacer was set to 338 μm. The foam curing conditions were 160°C for 8.5 minutes (3.5 minutes heating, 5 minutes holding) using a hot press machine.

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

[0286] [Table 4]

[0287] [Table 5]

[0288] When the slope of the approximate 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] This disclosure provides, for example, the following inventions. [1] Stator core and, The coils are arranged in the slots of the stator core described above, An adhesive sheet is placed between the stator core and the coil, A stator for a rotating electric machine having, The above 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. The above adhesive sheet is arranged such that the non-foamed layer faces the coil side and the foamed layer faces the stator core side, in a stator for a rotating electric machine. [2] The stator for a rotating electric machine according to [1], wherein the adhesive sheet has a base material between the foamed layer and the non-foamed layer. [3] The stator for a rotating electric machine as described in [1] or [2], wherein, 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 approximate straight line in the section from strain 3% to strain 5% is 0.20 MPa or less. [4] A stator for a rotating electric machine according to any one of [1] to [3], wherein the difference between the slope of the approximate straight line in the section from strain 3% to strain 5% in the stress-strain curve obtained when the tensile shear adhesive strength test method is performed on the foamed layer and the slope of the approximate straight line in the section from strain 3% to strain 5% in the 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] Rotor core and The coils arranged in the slots of the rotor core, An adhesive sheet is placed between the rotor core and the coil, A rotor for a rotating electric machine having, The above 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. The above adhesive sheet is arranged such that the non-foamed layer faces the coil side and the foamed layer faces the rotor core side, in a rotor for a rotating electric machine. [6] The rotor for a rotating electric machine according to [5], wherein the adhesive sheet has a base material between the foamed layer and the non-foamed layer. [7] The rotor for a rotating electric machine as described in [5] or [6], wherein, in the stress-strain curve obtained when the tensile shear bonding strength test method is performed on the non-foamed layer, the slope of the approximate straight line in the section from strain 3% to strain 5% is 0.20 MPa or less. [8] A rotor for a rotating electric machine as described in any of [5] to [7], wherein the difference between the slope of the approximate straight line in the section from strain 3% to strain 5% in the stress-strain curve obtained when the tensile shear adhesive strength test method is performed on the foamed layer and the slope of the approximate straight line in the section from strain 3% to strain 5% in the 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. [9] A foam adhesive sheet used for fixing coils to slots in the stator core or rotor core of a rotating electric machine, It comprises 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. 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. A foamed adhesive sheet in which the second adhesive layer is positioned facing the coil side and the first adhesive layer is positioned facing the stator core side or the rotor core side.

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

[11] A method for manufacturing a stator for a rotating electric machine, comprising fixing coils in slots of the stator core, A preparation step for preparing a foamed 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, The arrangement step involves placing a foamed adhesive sheet between the stator core and the coil such that the second adhesive layer faces the coil side and the first adhesive layer faces the stator core side. The bonding process involves foaming and curing the above-mentioned foamed adhesive sheet and bonding the above-mentioned coil to the above-mentioned stator core, A method for manufacturing a stator for a rotating electric machine, 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.

[12] A method for manufacturing a rotor for a rotating electric machine, in which a coil is fixed in a slot of the rotor core, A preparation step for preparing a foamed 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, The arrangement step involves placing a foamed adhesive sheet between the rotor core and the coil such that the second adhesive layer faces the coil side and the first adhesive layer faces the rotor core side. The bonding process involves foaming and curing the above-mentioned foamed adhesive sheet and bonding the above-mentioned coil to the above-mentioned rotor core, A method for manufacturing a rotor for a rotating electric machine, 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. [Explanation of Symbols]

[0290] 1… Stator core 2… Slots 3… coil 4… Adhesive sheet 10… Stator for rotating electric machine 11… Foam layer 12… Non-foamed layer 13 … Base material 14 … First intermediate layer 15 … second middle layer 20… Rotor for rotating electric machine 21… Rotor core 22… Slot 23… Coil 30… Foamed adhesive sheet 31 … First adhesive layer 32 … Second layer 33 … Substrate 34 … First Intermediate Layer 35 … Second Intermediate Layer

Claims

[Claim 1] Stator core and A coil arranged in the slot of the stator core, An adhesive sheet is placed between the stator core and the coil, A stator for a rotating electric machine having, 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. The adhesive sheet is arranged such that the non-foamed layer faces the coil side and the foamed layer faces the stator core side, in a stator for a rotating electric machine.

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