Adhesive sheet

Abstract

Provided is an adhesive sheet comprising a base material layer and an adhesive layer that is adhered to an adhesion target and overlaps at least one surface of the base material layer, the adhesive layer containing an epoxy resin and a polyurethane resin that does not have an epoxy group in the molecule thereof.

Description

adhesive sheet CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from Japanese Patent Application No. 2024-027589, which is incorporated herein by reference.

[0002] The present invention relates to an adhesive sheet used, for example, in a drive motor of an automobile.

[0003] Conventionally, a drive motor for an automobile includes a rotor and a stator that generates a force to rotate the rotor. The stator includes multiple coils that generate a magnetic field in the multiple coils to generate a Lorentz force, which rotates the rotor.

[0004] In the above-described drive motor, the coil has, for example, a plurality of interconnected segment conductors. The coil is typically mounted on a component called a stator core or rotor core, which is made up of stacked magnetic steel plates. The magnetic steel plates typically contain highly magnetic iron as a main component. The segment conductors are typically enameled wires, in which copper wires as conductors are coated with an insulating coating (e.g., a polyurethane resin coating).

[0005] In the above-described drive motor, a core such as a stator core or a rotor core has multiple slots formed therein, and a coil is housed in each of the multiple slots. Furthermore, in the above-described drive motor, an insulating sheet is housed in each slot together with the coil to ensure insulation between the coil and the inner wall surface of the slot. More specifically, the insulating sheet is housed in the slot while wrapped around the coil. The coil wrapped with the insulating sheet is fixed in the slot by an insulating resin (e.g., epoxy varnish) in the slot.

[0006] The insulating sheet has a five-layer structure including a base film such as a polyester resin film, two insulating layers such as paper sheets arranged on both sides of the base film, and an adhesive layer arranged between the base film and the two insulating layers. For example, an insulating sheet of this type is known in which the adhesive layer is composed of a resin composition containing a polyurethane resin, an epoxy resin, and an isocyanate-based crosslinking agent, and the resin composition contains at least one isocyanate-based crosslinking agent selected from the group consisting of an aliphatic isocyanate and an aromatic isocyanate (Patent Document 1). The insulating sheet described in Patent Document 1 is used, for example, as a slot liner for a motor. When wrapped around a coil, the insulating sheet can ensure electrical insulation between the coil and the inner wall surface of a slot groove in a stator core.

[0007] Japanese Patent Application Publication No. 2023-013729

[0008] The insulating sheet described in Patent Document 1 prevents the surface portion of the outermost insulating layer from falling off even when an external force is applied, but because the outermost layer is not adhesive, it cannot be adhered to objects (e.g., coils, inner wall surfaces of the slot grooves) on both sides of the sheet. In contrast, in conventional motor manufacturing, an insulating varnish is injected into the slot grooves and allowed to harden, thereby fixing the coils and preventing them from falling off. However, because the varnish has high viscosity, the injection process takes a relatively long time, resulting in poor manufacturing efficiency. Therefore, there is a need for an adhesive sheet that can be adhered to objects without using the above-mentioned varnish and that prevents the surface portion from falling off even when an external force is applied.

[0009] In view of the above-mentioned demands, an object of the present invention is to provide an adhesive sheet that can be adhered to an object to be adhered and that is prevented from falling off of the surface portion even when an external force is applied.

[0010] In order to solve the above problems, the adhesive sheet of the present invention comprises a base layer and an adhesive layer to be adhered to an object to be adhered, the adhesive layer overlapping at least one surface of the base layer, wherein the adhesive layer contains an epoxy resin and a polyurethane resin that does not have an epoxy group in its molecule.

[0011] Fig. 1 is a schematic cross-sectional view of an example of an adhesive sheet according to the present embodiment cut in the thickness direction. Fig. 2 is a schematic cross-sectional view of another example of an adhesive sheet according to the present embodiment cut in the thickness direction. Fig. 3 is a schematic perspective view of a stator of a drive motor for an automobile. Fig. 4 is a schematic plan view of a stator core. Fig. 5 is an enlarged view of part A in Fig. 4.

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An adhesive sheet according to an embodiment of the present invention will now be described with reference to the accompanying drawings. The adhesive sheet according to this embodiment is used as a component of a motor, for example.

[0013] As shown in Fig. 1, a specific example of the adhesive sheet of the present embodiment comprises a multilayer substrate layer 11 and two adhesive layers 12 respectively overlapping both sides of the substrate layer 11. Meanwhile, as shown in Fig. 2, another specific example of the adhesive sheet of the present embodiment comprises a multilayer substrate layer 11 and one adhesive layer 12 overlapping only one side of the substrate layer 11. The specific example of the adhesive sheet shown in Fig. 1 will now be described in detail.

[0014] The adhesive sheet 10 of this embodiment comprises two adhesive layers 12 arranged to face each other, and a base material layer 11 arranged between the two adhesive layers 12. In other words, the adhesive sheet 10 of this embodiment comprises one base material layer 11 and two adhesive layers 12 arranged to sandwich the base material layer 11 in the thickness direction. In the adhesive sheet 10 of this embodiment, the base material layer 11 and one of the adhesive layers 12 are in direct contact, and the base material layer 11 and the other adhesive layer 12 are in direct contact.

[0015] The thickness of the adhesive sheet 10 is, for example, 10 μm or more and 500 μm or less. The thickness of the adhesive sheet 10 may be 50 μm or more, or 70 μm or more. The thickness of the adhesive sheet 10 may also be 400 μm or less, or 300 μm or less. The thickness of the adhesive sheet 10 is preferably 50 μm or more, in order to further improve the workability when inserting the adhesive sheet 10 into the slots of the stator (described in detail later).

[0016] The thickness (total thickness) of the substrate layer 11 is preferably 10 μm or more and 300 μm or less.

[0017] The thickness of the adhesive layer 12 (per layer) may be, for example, 1 μm or more and 150 μm or less. The thickness of the adhesive layer 12 is preferably 5 μm or more and 100 μm or less. Of the two adhesive layers 12, it is preferable that the difference in thickness between one adhesive layer 12 and the other adhesive layer 12 is small. For example, the thickness of one adhesive layer 12 may be 0.8 times or more and 1.2 times or less the thickness of the other adhesive layer 12.

[0018] The thickness of each layer refers to the average thickness. The thickness of each layer is determined by averaging the thicknesses of at least five randomly selected locations. The thickness of each layer can be measured, for example, by observing the side or cross section of the adhesive sheet 10 with a digital microscope.

[0019] The ratio of the thickness of the base layer 11 (total thickness) to the total thickness of the adhesive sheet 10 may be 0.10 or more, or 0.20 or more. A larger ratio has the advantage of further improving the electrical insulation of the adhesive sheet 10. The thickness ratio may be 0.80 or less, or 0.40 or less.

[0020] The ratio of the total thickness of the adhesive layers 12 (thickness of two layers) to the total thickness of the adhesive sheet 10 may be 0.10 or more, or 0.30 or more. Increasing this ratio has the advantage of further improving the adhesiveness of the adhesive sheet 10. Furthermore, this ratio may be 0.90 or less, or 0.80 or less. The ratio of the thickness of each adhesive layer 12 (thickness of one layer) to the total thickness of the adhesive sheet 10 may be 0.05 or more, or 0.15 or more. Furthermore, this ratio may be 0.45 or less, or 0.40 or less.

[0021] It is preferable that the above-mentioned numerical range regarding the ratio of the thickness of each adhesive layer 12 to the thickness of the base layer 11 is satisfied on at least one side or the other side of the base layer 11. It is more preferable that the thickness ratio is within the above-mentioned numerical range on both sides of the base layer 11.

[0022] <Substrate Layer> The substrate layer 11 is sheet-shaped. The substrate layer 11 preferably has insulating properties and heat resistance. The substrate layer 11 may have a single-layer structure or a multi-layer structure in which multiple layers are stacked. The substrate layer 11 has a five-layer structure, as shown in, for example, FIGS. 1 and 2 , and includes a substrate film 11a, two paper-like sheets 11b arranged on both sides of the substrate film 11a, and two fixing layers 11c arranged between the substrate film 11a and the two paper-like sheets 11b. The substrate film 11a and the paper-like sheets 11b may each independently be, for example, a resin film or an insulating paper sheet such as aramid paper. The fixing layer 11c includes, for example, a general adhesive.

[0023] For example, the base layer 11 may have a structure in which heat-resistant resin fiber sheets (paper-like sheets) are bonded to both sides of an insulating resin film (base film) via an adhesive. The insulating resin film is preferably a polyethylene naphthalate resin film or a polyimide resin film having a thickness of 10 μm or more and 250 μm or less. The heat-resistant resin fiber sheet is preferably an aromatic polyamide fiber sheet or a polyethersulfone fiber sheet having a thickness of 10 μm or more and 100 μm or less. Note that instead of the heat-resistant resin fiber sheet (paper-like sheet), a structure in which an insulating resin film different from the base film is bonded via an adhesive may also be used. Furthermore, as described above, the base layer 11 may be a single layer, and the single-layer base layer 11 may be an insulating paper sheet, a resin film, or the like.

[0024] The resin film is preferably an insulating resin film, such as a polyethylene terephthalate (PET) resin film, a polyethylene naphthalate (PEN) resin film, a polyimide (PI) resin film, a polyphenylene sulfide (PPS) resin film, or a polyether ether ketone (PEEK) resin film.

[0025] The insulating paper sheet may be, for example, a resin fiber sheet, such as an aromatic polyamide fiber sheet or a polyethersulfone fiber sheet.

[0026] The base material layer 11 may be subjected to lamination, high-temperature and high-pressure calendaring, or surface treatment, such as roughening or corona treatment, to enhance adhesion to the adhesive layer 12.

[0027] <Adhesive Layer> Next, the adhesive layer 12 will be described in detail. The adhesive layer 12 is adhered (fixed) to an object to be adhered, which will be described in detail later. In other words, the adhesive sheet 10 of this embodiment is used by adhering the adhesive layer 12 to an object to be adhered. The adhesive layer 12 has relatively low tack at room temperature, but can be strongly adhered to an object to be adhered by being heat-treated.

[0028] Each adhesive layer 12 contains a polymer component (adhesive component). Specifically, each adhesive layer 12 contains at least an epoxy resin and a polyurethane resin having no epoxy groups in the molecule as polymer components. The adhesive layer 12 may further contain an epoxy resin curing agent, a foaming agent, a filler, or the like.

[0029] The adhesive layer 12 preferably contains 40% by mass or more, and more preferably 50% by mass or more, of the above-mentioned epoxy resin. The adhesive layer 12 preferably contains 90% by mass or less, and more preferably 70% by mass or less, of the above-mentioned epoxy resin. The adhesive layer 12 preferably contains 3% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, and even more preferably 20% by mass or more of the above-mentioned polyurethane resin. The adhesive layer 12 preferably contains 80% by mass or less, and more preferably 40% by mass or less, of the above-mentioned polyurethane resin. The adhesive layer 12 preferably contains 1% by mass or more and 15% by mass or less of a curing agent for the epoxy resin.

[0030] The adhesive layer 12 may contain 5% by mass or more and 15% by mass or less of a foaming agent.

[0031] The epoxy resin has multiple epoxy groups in its molecule. Examples of the epoxy resin include novolac epoxy resins such as phenol novolac epoxy resins and cresol novolac epoxy resins, and bisphenol epoxy resins such as bisphenol A epoxy resins (including modified bisphenol A epoxy resins) and bisphenol F epoxy resins (including modified bisphenol F epoxy resins). Examples of the epoxy resin include trisphenolmethane (triphenylmethane) epoxy resins, biphenyl epoxy resins, and dicyclopentadiene epoxy resins. These epoxy resins can be used alone or in combination.

[0032] The epoxy equivalent [g / eq] of the epoxy resin may be 100 or more and 3000 or less. The epoxy equivalent is measured in accordance with JIS K7236-2001.

[0033] As the epoxy resin, commercially available products can be used.

[0034] The polyurethane resin is, for example, a urethane reaction product of a polyol component (a) having multiple hydroxy groups in the molecule and a polyisocyanate component (b) having multiple isocyanate groups in the molecule. Preferably, the polyurethane resin is a urethane reaction product of at least a diol having two hydroxy groups and no carboxy group in the molecule as the polyol component (a) and a diol having two hydroxy groups and a carboxy group in the molecule as the polyol component (a), and a diisocyanate having two isocyanate groups in the molecule as the polyisocyanate component (b).

[0035] The acid value of the polyurethane resin is, for example, 0.1 mgKOH / g or more and 25.0 mgKOH / g or less. The acid value of the polyurethane resin is preferably 2.0 mgKOH / g or more, more preferably 5.0 mgKOH / g or more, and even more preferably 7.0 mgKOH / g or more. The acid value of the polyurethane resin is preferably 23.0 mgKOH / g or less. A high acid value of the polyurethane resin increases the crosslink density after reaction between the polyurethane resin and the epoxy resin, and can improve the heat resistance of the adhesive layer 12 after curing. On the other hand, a low acid value further suppresses further chemical reactions originating from functional groups within the adhesive layer 12 during storage of the adhesive sheet 10, improving the stability of the adhesive sheet 10 over time. The acid value of the polyurethane resin is measured by dissolving the polyurethane resin in methyl ethyl ketone (MEK) or similar and measuring the result according to the method of JIS K1557-5:2007.

[0036] The polyurethane resin may have a carboxy group or a hydroxy group in the molecule. For example, the acid value can be increased by synthesizing the polyurethane resin so that the number of carboxy groups in the molecule is increased. On the other hand, the polyurethane resin does not have an epoxy group in the molecule.

[0037] The polyol component (a) may be a general polyol used for synthesizing polyurethane resins, such as polyester polyol, polyether polyol, polycarbonate polyol, or other polyols.

[0038] Examples of polyester polyols include condensation polymers of aliphatic dicarboxylic acids (e.g., succinic acid, adipic acid, sebacic acid, glutaric acid, azelaic acid, etc.) or aromatic dicarboxylic acids (e.g., isophthalic acid, terephthalic acid, etc.) with low-molecular-weight glycols (e.g., ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butylene glycol, 1,6-hexamethylene glycol, neopentyl glycol, 1,4-bishydroxymethylcyclohexane, etc.).

[0039] Specific examples of polyester polyols include polyethylene adipate diol, polybutylene adipate diol, polyhexamethylene adipate diol, polyneopentyl adipate diol, polyethylene / butylene adipate diol, polyneopentyl / hexyl adipate diol, poly-3-methylpentane adipate diol, polybutylene isophthalate diol, polycaprolactone diol, and poly-3-methylvalerolactone diol.

[0040] Specific examples of polyether polyols include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and random / block copolymers thereof.

[0041] Specific examples of polycarbonate polyols include polytetramethylene carbonate diol, polypentamethylene carbonate diol, polyneopentyl carbonate diol, polyhexamethylene carbonate diol, poly(1,4-cyclohexanedimethylene carbonate) diol, and random / block copolymers thereof.

[0042] Specific examples of other polyols include dimer diol or a hydrogenated product thereof, polybutadiene polyol or a hydrogenated product thereof, polyisoprene polyol or a hydrogenated product thereof, acrylic polyol, epoxy polyol, polyether ester polyol, siloxane-modified polyol, α,ω-polymethyl methacrylate diol, α,ω-polybutyl methacrylate diol, and siloxane-modified polyol.

[0043] The number average molecular weight (Mn, determined by the terminal functional group determination method) of the polyol is not particularly limited, but is preferably 500 or more and 6,000 or less.

[0044] In addition to the polyols described above, the polyol component (a) may optionally contain a short-chain diol. Specific examples of short-chain diols include aliphatic glycols such as ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,6-hexamethylene glycol, and neopentyl glycol, or low-molar alkylene oxide adducts thereof. Other examples include alicyclic glycols such as 1,4-bis(hydroxymethyl)cyclohexane and 2-methyl-1,1-cyclohexanedimethanol, or low-molar alkylene oxide adducts thereof. Other examples include aromatic glycols such as xylylene glycol, or low-molar alkylene oxide adducts thereof, or bisphenols such as bisphenol A, thiobisphenol, and sulfonebisphenol, or low-molar alkylene oxide adducts thereof.

[0045] Polyhydric alcohols can also be used as raw materials for polyurethane resins. Specific examples of polyhydric alcohols include glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, tris-(2-hydroxyethyl)isocyanurate, 1,1,1-trimethylolethane, and 1,1,1-trimethylolpropane.

[0046] The above-mentioned polyols can be used alone or in combination of two or more.

[0047] As the polyisocyanate component (b), a general polyisocyanate component used for synthesizing polyurethane resins is adopted. Specific examples of the polyisocyanate component (b) include, for example, toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, 4-methoxy-1,3-phenylene diisocyanate, 4-isopropyl-1,3-phenylene diisocyanate, 4-chloro-1,3-phenylene diisocyanate, 4-butoxy-1,3-phenylene diisocyanate, 2,4-diisocyanate diphenyl ether, 4,4'-methylenebis(phenylene isocyanate) [alias Examples of the diisocyanate include aromatic diisocyanates such as 4,4'-diphenylmethane diisocyanate (MDI), crude MDI or polymeric MDI, durylene diisocyanate, xylylene diisocyanate (XDI), 1,5-naphthalene diisocyanate, benzidine diisocyanate, o-nitrobenzidine diisocyanate, and 4,4'-diisocyanate dibenzyl. Examples of the diisocyanate include aliphatic diisocyanates such as methylene diisocyanate, 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, and 1,10-decamethylene diisocyanate. Other examples include alicyclic diisocyanates such as 1,4-cyclohexylene diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), 1,5-tetrahydronaphthalene diisocyanate, isophorone diisocyanate (IPDI), and hydrogenated XDI.Further examples include polyurethane prepolymers obtained by reacting these diisocyanates with low-molecular-weight polyols so that the terminals are isocyanate groups.

[0048] The polyisocyanate component (b) may be used singly or in combination of two or more.

[0049] The weight average molecular weight (Mw) of the polyurethane resin is preferably 1,000 or more and 500,000 or less. When the weight average molecular weight (Mw) is within this range, the polyurethane resin can have better physical properties such as flexibility, adhesiveness, and heat resistance. The weight average molecular weight is measured by gel permeation chromatography (GPC) under the following measurement conditions. (1) Instrument: For example, instrument name "HLC-8020" (manufactured by Tosoh Corporation) (2) Column: Product name "TSKgel G2000HXL", "G3000HXL", "G4000GXL" (manufactured by Tosoh Corporation) (3) Solvent: THF (4) Flow rate: 1.0 ml / min (5) Sample concentration: 2 g / L (6) Injection volume: 100 μL (7) Temperature: 40°C (8) Detector: Model number "RI-8020" (manufactured by Tosoh Corporation) (9) Standard material: TSK standard polystyrene (manufactured by Tosoh Corporation)

[0050] The polyurethane resin can be produced by a conventionally known synthetic method for polyurethane resins. Specifically, first, a polyol component (a) and a polyisocyanate component (b) are bonded by a urethanization reaction in the presence or absence of an organic solvent that does not contain active hydrogen in the molecule. Generally, the reaction is carried out so that the equivalent ratio of isocyanate groups to hydroxy groups is in the range of 0.8 to 1.25. The urethanization reaction can be carried out using a so-called one-shot method or a multi-stage method, and can be carried out at a temperature of, for example, 20°C to 150°C, preferably 60°C to 110°C.

[0051] In the synthesis of polyurethane resin, a catalyst can be used as needed. Examples of catalysts include salts of metals with organic or inorganic acids, such as dibutyltin laurate, dioctyltin laurate, stannous octoate, zinc octoate, and tetra-n-butyl titanate; organometallic derivatives; organic amines such as triethylamine; and diazabicycloundecene catalysts. The above catalysts promote the reaction in the synthesis of polyurethane resin. However, using an excessive amount of catalyst may induce a decomposition reaction that decomposes substances other than the polyurethane resin, so it is preferable to use an appropriate amount of catalyst.

[0052] In the synthesis of the polyurethane resin, an organic solvent may or may not be used as a reaction solvent, and the organic solvent may be inactive to isocyanate groups.

[0053] The polyurethane resin can be synthesized by the method described above, or a commercially available product can be used as the polyurethane resin.

[0054] Examples of curing agents for the epoxy resin include polymerizable addition curing agents having active hydrogen in the molecule, catalytic curing agents, and other curing agents. Examples of polymerizable addition curing agents include amine compounds, acid compounds such as organic acids and acid anhydrides, mercaptan compounds, and phenolic compounds (e.g., phenolic resins). Examples of amine compounds include aliphatic polyamine compounds and aromatic polyamine compounds. The amine compounds may be tertiary amines or secondary amines. Examples of catalytic curing agents include boron trifluoride-amine complexes. Examples of other curing agents include dicyandiamide (DICY, also known as cyanoguanidine), imidazole compounds, and ketimine compounds. Examples of tertiary amine compounds include 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30), diazabicycloundecene (DBU) and its salts, diazabicyclononene (DBN) and its salts, and tris(dimethylaminomethyl)phenol.

[0055] The curing agent preferably contains a phenolic resin, dicyandiamide, and an imidazole compound.

[0056] Examples of the phenolic resin include novolac-type phenolic resin, aralkyl-type phenolic resin, resol-type phenolic resin, dicyclopentadiene-modified phenolic resin, naphthalene-type phenolic resin, and bisphenol-based phenolic resin. Examples of the novolac-type phenolic resin include phenol novolac resin, cresol novolac resin, bisphenol A novolac resin, and triazine skeleton-containing phenol novolac resin. The novolac-type phenolic resin may be, for example, a xylene novolac resin (phenol-modified) further having a xylene structure. Examples of the aralkyl-type phenolic resin include biphenylaralkyl-type phenolic resin. The curing agent may contain multiple types of phenolic resins.

[0057] The phenolic hydroxy group equivalent of the phenolic resin may be, for example, 100 [g / eq] or more and 300 [g / eq] or less. The "hydroxy group equivalent" of the phenolic resin can be calculated from the hydroxy group value determined in accordance with JIS K0070:1992 (basically by neutralization titration, and if necessary by potentiometric titration) using the following formula: Hydroxy group equivalent = molecular weight of potassium hydroxide / hydroxy group value

[0058] Examples of the imidazole compound include 2-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-phenylimidazole, 2,4-diamino-2-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-phenylimidozolium trimellitate, 2,4-diamino-2-methylimidazole, 1-cyanoethyl-2-phenyl ... imidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2,3-dihydro-1H-pyrrolo[1,2-a]benzimidazole, 1-dodecyl-2-methyl-3-benzylimidazolium chloride, and the like.

[0059] The imidazole compound preferably has a benzene ring structure and a hydroxy group in the molecule, and the molecular weight of the imidazole compound is preferably 100 or more and 250 or less.

[0060] As the curing agent, commercially available products can be used.

[0061] Examples of the foaming agent include a physical foaming agent whose volume increases upon heating, a chemical foaming agent whose components undergo a chemical reaction upon heating to generate gas, and a thermally expandable capsule containing a physical foaming agent.

[0062] Examples of physical foaming agents include hydrocarbons such as n-pentane, isopentane, isobutane, and petroleum ether, and halides thereof.

[0063] Examples of chemical foaming agents include inorganic foaming agents such as sodium bicarbonate, sodium carbonate, ammonium bicarbonate, ammonium carbonate, and ammonium nitrite, and organic foaming agents such as azodicarbonamide (ADCA), N,N'-dinitrosopentamethylenetetramine, benzenesulfonyl hydrazide, and 4,4'-diphenyldisulfonyl azide.

[0064] The thermally expandable capsules include, for example, hollow capsules made of a thermoplastic resin and a physical foaming agent enclosed within the hollow capsules. Thermally expandable capsules are preferred because the foaming initiation temperature can be easily controlled. The particle diameter of each thermally expandable capsule is, for example, 5 μm or more and 50 μm or less. It is preferable that at least half of the thermally expandable capsules have the above particle diameter.

[0065] As the foaming agent, one of the above-mentioned foaming agents may be used alone, or two or more of them may be used in combination.

[0066] The foaming agent preferably has a foaming initiation temperature of 60°C or higher and 170°C or lower, more preferably 80°C or higher and 160°C or lower.

[0067] Examples of the filler include inorganic fillers, such as inorganic nitrides such as boron nitride, aluminum nitride, and silicon nitride, inorganic oxides such as silicon oxide (silica), aluminum oxide (alumina), titanium oxide (titania), magnesium oxide (magnesia), and zirconium oxide (zirconia), clay minerals such as talc, smectite, mica, bentonite, and kaolinite, diamond, silicon carbide, and calcium carbonate.

[0068] The adhesive layer 12 may contain 2% by mass or more and 50% by mass or less of a filler. When the adhesive layer 12 contains an appropriate amount of filler, the processability of the adhesive sheet 10 is improved.

[0069] Since the adhesive layer 12 contains the components described above, the adhesive sheet 10 can adhere well to the object to be adhered on both sides in the thickness direction, and furthermore, the surface portion (adhesive layer) is prevented from falling off due to external force.

[0070] The adhesive layer 12 preferably contains an epoxy resin, a polyurethane resin having no epoxy groups in the molecule, dicyandiamide, and an imidazole compound. When the adhesive layer 12 contains the polyurethane resin, it is possible to prevent a portion of the surface portion (adhesive layer) from peeling off due to an external force.

[0071] The adhesive layer 12 preferably contains 25 to 70 parts by mass of the polyurethane resin per 100 parts by mass of the epoxy resin (assuming the amount of the epoxy resin is 100 parts by mass), more preferably 30 parts by mass or more, and even more preferably 40 parts by mass or more. The adhesive layer 12 preferably contains 95 to 105% of dicyandiamide per 100% epoxy equivalent of the epoxy resin. The adhesive layer 12 preferably contains 0.5 to 2.0 parts by mass of an imidazole compound per 100 parts by mass of the total amount of the epoxy resin and polyurethane resin.

[0072] The adhesive layer 12 preferably contains a foaming agent. In a motor having an adhesive layer 12 containing a foaming agent, when the adhesive sheet 10 is wrapped around a coil or the like and housed in a relatively narrow space (such as a slot groove, described below), better adhesion can be achieved to an object to be adhered on at least one side of the adhesive sheet 10. Such a method of use will be described in detail later.

[0073] Next, a method for manufacturing the adhesive sheet 10 of the above embodiment will be described.

[0074] In the method for producing adhesive sheet 10 of this embodiment, for example, a mixture containing the components that will constitute adhesive layer 12 and (if necessary) an organic solvent is prepared, and this mixture is applied to both sides of substrate layer 11, and the organic solvent contained in the applied mixture is volatilized (if necessary) to produce two adhesive layers 12. Note that a roll coater, for example, can be used as the coating device.

[0075] Examples of the organic solvent that can be used include ethyl acetate, methyl ethyl ketone (MEK), and toluene.

[0076] A general coating method such as a die coating method or a reverse coating method can be used when applying the mixture containing an organic solvent to the base layer 11. The temperature during application is, for example, room temperature (15 to 25° C.).

[0077] The adhesive sheet 10 produced as described above is used, for example, as a component of a motor. The adhesive sheet 10 may be used, for example, as an adhesive sheet for a drive motor of an automobile. Specifically, the adhesive sheet 10 can be used as a slot insulating sheet for a motor stator. The adhesive sheet 10 can be used, for example, in a heated state.

[0078] One side of the adhesive layer 12 is exposed when the adhesive sheet 10 is in use. In other words, the side of the adhesive layer 12 that is not in contact with the base layer 11 is exposed when the adhesive sheet 10 is in use. The adhesive layer 12 of the adhesive sheet 10 can be well bonded to an object to be bonded by being heat-treated, for example, at a temperature of 140°C or higher and 200°C or lower.

[0079] For example, the adhesive sheet 10 (see FIG. 2 ) in which the adhesive layer 12 is superimposed on only one side of the base layer 11 may be used by being disposed so that the adhesive layer 12 faces either the inner surface of the stator core or the coil. On the other hand, the adhesive sheet 10 in which two adhesive layers 12 are superimposed on both sides of the base layer 11 may be used, for example, by being wound around a coil and housed in the slot groove of the stator core, as will be described in detail later, and being bonded to the coil and the inner surface surrounding the slot groove in the stator core.

[0080] The adhesive sheet 10 of this embodiment can be well adhered to an object to be adhered by being heat-treated. Before being heat-treated, the adhesive layer 12 of the adhesive sheet 10 has relatively low tack (pressure-sensitive adhesiveness). Therefore, a coil wrapped with the motor adhesive sheet is less likely to adhere to the inner surface of a slot groove, allowing it to be inserted relatively easily into the slot groove. Furthermore, when the motor adhesive sheet placed in the slot groove is heat-treated while wrapped around a coil, it can be well adhered to the coil and the inner surface of the slot groove (the object to be adhered). Therefore, a coil wrapped with the motor adhesive sheet can be fixed in the slot groove without the need for an insulating resin (e.g., epoxy varnish) placed in the slot groove as in the conventional method. Furthermore, since the adhesive layer 12 further contains the foaming agent, the adhesive layer 12 expands by foaming, allowing the adhesive layer 12 to adhere more fully to the object to be adhered, thereby more reliably fixing the coil in the slot groove.

[0081] Examples of the above-mentioned automobiles include hybrid electric vehicles (HEVs), electric vehicles (EVs), etc. Examples of the drive motors include HV motors, motor generators, alternators, 4WD motors, oil pump motors, EPS motors, compressor motors, in-wheel motors, etc.

[0082] Next, an example of a motor equipped with the adhesive sheet 10 of the above embodiment will be described with reference to the drawings. Such a motor is equipped with the above-mentioned adhesive sheet 10. The adhesive sheet 10 is, for example, an adhesive sheet for a motor.

[0083] For example, the motor is a drive motor mounted on a hybrid vehicle or an electric vehicle.

[0084] An automobile drive motor includes a rotor equipped with a permanent magnet and a stator 20 that generates a force to rotate the rotor. As shown in Fig. 3, the stator 20 has a coil 21 and a stator core 22. The stator 20 rotates the rotor by generating a magnetic field in the coil 21. Fig. 4 is a plan view of the stator 20 as viewed from one side in the direction of the rotation axis of the rotor (not shown). Fig. 5 is a cross-sectional view showing the coil 21 housed in the slot groove P of the stator core 22 (part A in Fig. 4).

[0085] In the above-described drive motor, the coil 21 is formed, for example, by a plurality of interconnected segment conductors 21 a. In the above-described drive motor, a plurality of slot grooves P are formed in a core such as the stator core 22 or the rotor core, and each of the plurality of slot grooves P accommodates one of the coils 21.

[0086] More specifically, in the stator 20, a plurality of slot grooves P are formed on the inner circumferential side of a cylindrical stator core 22. The stator 20 has the stator core 22 and a plurality of coils 21 partially housed in the plurality of slot grooves P formed in the stator core 22. The plurality of slot grooves P are arranged at regular intervals along the circumferential direction of the stator core 22. In the direction of the rotation axis of the stator core 22, the slot grooves P are formed over the length of the stator core 22.

[0087] In the stator core 22, a plurality of slot grooves P are arranged as described above, and plate-shaped protrusions 22a are formed between adjacent slot grooves P. Each plate-shaped protrusion 22a extends radially inward (in the DD direction in FIG. 5 ) from the outer periphery of the stator core 22.

[0088] The coil 21 is made up of a plurality of segment conductors 21a connected to each other. As shown in Fig. 5, for example, four segment conductors 21a forming the coil 21 are housed in each slot groove P of the stator core 22. A total of four segment conductors 21a are housed in each slot groove P, lined up in a row from the inner circumferential surface side to the outer circumferential surface side of the stator core 22.

[0089] In the drive motor described above, a motor adhesive sheet 10 is used to ensure insulation between the coil 21 and the inner wall surface of the slot groove P. In other words, as shown in FIG. 5 , the motor adhesive sheet 10 is interposed between the coil 21 and the wall surface surrounding the slot groove P and is housed within the slot groove P while being wrapped around the coil 21. Specifically, the motor adhesive sheet 10 is placed within the slot groove P while being wrapped around the coil 21 one or more times, with the ends overlapping each other (see FIG. 5 ). The overlapping portions are located outside the radial direction DD of the stator 20. Note that, in the direction of the rotational axis of the stator core 22, both ends of the motor adhesive sheet 10 extend outward from the stator core 22. With the motor adhesive sheet wrapped around the coil 21, the coil 21 is fixed within the slot groove by the adhesive force of the adhesive layer after heat treatment.

[0090] The adhesive sheet of this embodiment is as exemplified above, but the present invention is not limited to the adhesive sheet exemplified above. In other words, various forms used in general adhesive sheets can be adopted as long as they do not impair the effects of the present invention.

[0091] The present specification discloses the following: (1) An adhesive sheet comprising a base layer and an adhesive layer to be adhered to an object to be adhered, the adhesive layer overlapping at least one surface of the base layer, the adhesive layer comprising an epoxy resin and a polyurethane resin having no epoxy groups in its molecule. An adhesive sheet having such a configuration allows the adhesive layer to adhere to an object to be adhered. The adhesive layer is also inhibited from falling off in part due to externally applied force. (2) The adhesive sheet according to (1) above, wherein the adhesive layer comprises 3% by mass or more and 80% by mass or less of the polyurethane resin. (3) The adhesive sheet according to (1) or (2) above, wherein the polyurethane resin has an acid value of 0.1 mgKOH / g or more and 15.0 mgKOH / g or less. (4) The adhesive sheet according to any of (1) to (3) above, wherein the adhesive layer further comprises a foaming agent.

[0092] The present invention will now be described in more detail with reference to experimental examples, but the present invention is not limited to these examples.

[0093] The materials or raw materials for the substrate layer and adhesive layer used to produce the adhesive sheet are shown below.

[0094] <Base layer> Polyethylene naphthalate (PEN) resin film Product name: "Teonex" series (manufactured by Toyobo Co., Ltd.) Thickness: 100 μm <Raw materials for adhesive layer> [Polymer components] Epoxy resin (novolac epoxy resin / O-cresol novolac type) Epoxy equivalent: approximately 208 (g / eq) Product name: "YDCN-704" (manufactured by Nippon Steel Chemical & Material Co., Ltd.) Polyurethane resin Synthesized by the method shown below (represented as PU1 / PU2 / PU3 / PU4 / PU5) [Curing agent] Dicyandiamide DICY (commercially available product) Imidazole compound (2-phenyl-4-methyl-5-hydroxymethylimidazole) Product name: "2P4MHZ-PW" (manufactured by Shikoku Chemicals Corporation) [Foaming agent (expanding agent)] Expandable capsule Product name: "Matsumoto Microsphere FN" series (manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd.)

[0095] <Synthesis of Polyurethane Resin> Five types of polyurethane resin were synthesized as follows.

[0096] (PU1) A reaction vessel equipped with a stirrer, reflux condenser, thermometer, nitrogen inlet, and manhole was prepared. While the inside of the reaction vessel was purged with nitrogen, 200.0 g of polyhexamethylene carbonate diol having hydroxy groups at both ends (Duranol: T6002, manufactured by Asahi Kasei Chemicals, number average molecular weight = 2,000 as determined by terminal functional group determination method), 15.0 g of 1,3-butanediol, and 16.0 g of dimethylolpropionic acid (DMPA) were charged. Next, 99.0 g of methyl ethyl ketone (MEK) was charged as a solvent, and the system was stirred. After stirring, 96.3 g of 4,4'-diphenylmethane diisocyanate (MDI) was charged at 50°C, and the reaction was carried out at 80°C to obtain a reaction solution. The viscosity of the reaction solution was adjusted by diluting it with methyl ethyl ketone (MEK) as a solvent, and the 2,270 cm 3 peak due to free isocyanate groups measured by infrared absorption spectroscopy was measured. －１ The reaction was allowed to proceed until the absorption of 100% by mass disappeared, yielding a resin solution of polyurethane resin PU1. The viscosity of the resulting resin solution was 500 dPa·s / 20°C, the solids content was 30% by mass, and the acid value of polyurethane resin PU1 was 20.5 mgKOH / g. The weight average molecular weight of polyurethane resin PU1 measured by GPC was 86,000.

[0097] (PU2) A reaction vessel equipped with a stirrer, reflux condenser, thermometer, nitrogen inlet, and manhole was prepared. While the inside of the reaction vessel was purged with nitrogen, 200.0 g of polyhexamethylene carbonate diol having hydroxy groups at both ends (Duranol: T6002, manufactured by Asahi Kasei Chemicals Corporation, number average molecular weight = 2,000 as determined by terminal functional group determination method), 25.3 g of neopentyl glycol (NPG), and 8.0 g of dimethylolpropionic acid (DMPA) were charged. Next, 100.0 g of methyl ethyl ketone (MEK) was charged as a solvent, and the system was stirred. After stirring, 100.8 g of 4,4'-diphenylmethane diisocyanate (MDI) was charged at 50°C, and the reaction was carried out at 80°C to obtain a reaction solution. The viscosity of the reaction solution was adjusted by diluting it with methyl ethyl ketone (MEK) as a solvent, and the 2,270 cm 3 peak due to free isocyanate groups measured by infrared absorption spectroscopy was measured. －１ The reaction was allowed to proceed until the absorption of 100% methyl acrylate disappeared, yielding a resin solution of polyurethane resin PU2. The viscosity of the resulting resin solution was 410 dPa·s / 20°C, the solids content was 30% by mass, and the acid value of polyurethane resin PU2 was 10.0 mgKOH / g. The weight average molecular weight of polyurethane resin PU2 measured by GPC was 79,000.

[0098] (PU3) A reaction vessel equipped with a stirrer, reflux condenser, thermometer, nitrogen inlet, and manhole was prepared. While the inside of the reaction vessel was purged with nitrogen, 200.0 g of polyhexamethylene carbonate diol having hydroxy groups at both ends (Duranol: T6002, manufactured by Asahi Kasei Chemicals Corporation, number average molecular weight = 2,000 as determined by terminal functional group determination method), 25.3 g of neopentyl glycol (NPG), and 4.0 g of dimethylolpropionic acid (DMPA) were charged. Next, 98.2 g of methyl ethyl ketone (MEK) was charged as a solvent, and the system was stirred. After stirring, 93.2 g of 4,4'-diphenylmethane diisocyanate (MDI) was charged at 50°C, and the reaction was carried out at 80°C to obtain a reaction solution. The viscosity of the reaction solution was adjusted by diluting it with methyl ethyl ketone (MEK) as a solvent, and the 2,270 cm 3 peak due to free isocyanate groups measured by infrared absorption spectroscopy was measured. －１The reaction was allowed to proceed until the absorption of 100% methyl acrylate disappeared, yielding a resin solution of polyurethane resin PU3. The viscosity of the resulting resin solution was 420 dPa·s / 20°C, the solids content was 30% by mass, and the acid value of polyurethane resin PU3 was 5.2 mgKOH / g. The weight average molecular weight of polyurethane resin PU3 measured by GPC was 83,000.

[0099] (PU4) A reaction vessel equipped with a stirrer, reflux condenser, thermometer, nitrogen inlet, and manhole was prepared. While the inside of the reaction vessel was purged with nitrogen, 200.0 g of polyhexamethylene carbonate diol (Duranol: T6002, manufactured by Asahi Kasei Chemicals Corporation, number average molecular weight = 2,000 measured by terminal functional group quantification method) having hydroxyl groups at both ends, 25.3 g of neopentyl glycol (NPG), and 4.0 g of dimethylolpropionic acid (DMPA) were charged. Next, 133.8 g of methyl ethyl ketone (MEK) was charged as a solvent, and the system was stirred. After stirring, 82.8 g of isophorone diisocyanate (IPDI) was charged at 50 ° C. and reacted at 80 ° C. to obtain a reaction solution. The viscosity of the reaction solution was adjusted by diluting it with a solvent, methyl ethyl ketone (MEK), and the 2,270 cm 3 peak due to free isocyanate groups measured by infrared absorption spectroscopy was measured. －１ The reaction was allowed to proceed until the absorption of 2,000 kJ / cm 2 disappeared, yielding a resin solution of polyurethane resin PU4. The viscosity of the resulting resin solution was 260 dPa·s / 25°C, the solids content was 30% by mass, and the acid value of polyurethane resin PU4 was 5.4 mgKOH / g. The weight average molecular weight of polyurethane resin PU4 measured by GPC was 77,000.

[0100] (PU5) A reaction vessel equipped with a stirrer, reflux condenser, thermometer, nitrogen inlet, and manhole was prepared. While the inside of the reaction vessel was purged with nitrogen, 200.0 g of polyhexamethylene carbonate diol (Duranol: T6002, manufactured by Asahi Kasei Chemicals Corporation, number average molecular weight = 2,000 as determined by terminal functional group determination method) having hydroxyl groups at both ends, 30.0 g of 1,4-bis(hydroxymethyl)-cyclohexane (1,4-CHDM), and 4.0 g of dimethylolpropionic acid (DMPA) were charged. Next, 132.4 g of methyl ethyl ketone (MEK) was charged as a solvent, and the system was stirred. After stirring, 75.0 g of isophorone diisocyanate (IPDI) was charged at 50°C, and the reaction was carried out at 80°C to obtain a reaction solution. The viscosity of the reaction solution was adjusted by diluting it with a solvent, methyl ethyl ketone (MEK), and the 2,270 cm 3 peak due to free isocyanate groups measured by infrared absorption spectroscopy was measured. －１ The reaction was allowed to proceed until the absorption of 100% methyl acrylate disappeared, yielding a resin solution of polyurethane resin PU5. The viscosity of the resulting resin solution was 150 dPa·s / 25°C, the solids content was 30% by mass, and the acid value of polyurethane resin PU5 was 5.4 mgKOH / g. The weight average molecular weight of polyurethane resin PU5 measured by GPC was 77,000.

[0101] <Production of Adhesive Sheet> A mixture containing the above components that would constitute the adhesive layer and an organic solvent (methyl ethyl ketone (MEK)) was prepared. This mixture was applied to one side of the substrate layer using a bar coater so that the thickness of the adhesive layer (for one layer) after drying would be 40 μm. The organic solvent contained in the applied mixture was volatilized (dried) by drying at 110°C for 5 minutes, producing an adhesive layer on one side of the substrate layer. In the same manner, an adhesive layer was produced on the other side of the substrate layer. In this way, each adhesive sheet with a three-layer structure was produced.

[0102] (Examples 1 to 12, Comparative Examples 1 and 2) The formulations of the adhesive layers of the adhesive sheets of each Example and Comparative Example are shown in Table 1 and Table 2. Note that each of the adhesive sheets of the Examples and Comparative Examples has a three-layer laminate structure (one base layer).

[0103]

[0104]

[0105] The adhesive sheets produced in each of the Examples and Comparative Examples were evaluated for abrasion resistance of the adhesive layer as follows.

[0106] <Evaluation of powder shedding due to friction (scrape abrasion test)> This test was conducted in accordance with ISO 6722. Specifically, a scrape abrasion tester was used under the following conditions. The test samples were prepared by cutting the adhesive sheets shown in the above examples and comparative examples into 1.5 cm x 4 cm pieces and wrapping them around a cylindrical rod (diameter 5 mm). The amount of powder that fell due to the friction of the piano wire was then measured. Testing machine (model: 5420-7N, manufactured by TVAB) Travel distance of piano wire (diameter 0.45 mm): 20 mm, 20 reciprocations Travel speed of piano wire: 3 m / min Pressing force of piano wire: approximately 5 MPa Piano wire sliding locations: 5 locations Temperature: 23°C

[0107] The results of the scrape test for each Example and Comparative Example are shown in Tables 1 and 2. As can be seen from these results, the adhesive sheets of the Examples were less susceptible to partial detachment of the adhesive layer due to externally applied force than the adhesive sheets of the Comparative Examples. In the adhesive sheets of the Examples, the outermost adhesive layer is flexible, and detachment of a portion of the adhesive layer is more likely to be suppressed even when external force is applied. Therefore, even when the adhesive sheet is folded in a case where the inner substrate layer is relatively thick, detachment of a portion of the adhesive layer at the folded portion is also suppressed. Furthermore, even when an adhesive layer formed on one side of a release sheet or the like is attached (i.e., transferred) to one side of the substrate layer during production, for example, the adhesive layer of the Examples is flexible and therefore easily conforms to the unevenness of the surface of the substrate layer, resulting in good adhesion of the adhesive layer to the substrate layer.

[0108] The adhesive sheets produced in each of the Examples and Comparative Examples were evaluated for shear adhesive strength as follows.

[0109] <Measurement of Shear Adhesion Strength> (Preparation of Test Specimens for Evaluating Shear Adhesion Strength) Two cold-rolled steel plates SPCC-SD, each 1.0 mm thick, 15 mm wide, and 100 mm long, were prepared. Two spacers were placed at one end of one of the cold-rolled steel plates, spaced a predetermined distance apart along the length of the cold-rolled steel plate. The spacer thickness was 370 μm. Next, the adhesive sheets of each of the above examples and comparative examples were cut into pieces measuring 10 mm x 15 mm and placed between the two spacers. The end of this cold-rolled steel plate was overlapped with one end of another cold-rolled steel plate. A temporary test specimen was prepared by pressurizing and fixing the overlapping portion of the two cold-rolled steel plates using a fixture (e.g., a clamp). The temporary test piece was then heated from room temperature to 170°C in 3 minutes and then heated at 170°C for 15 minutes to cure the adhesive sheet, yielding a test piece (initial before storage) for shear adhesive strength evaluation. Separately, the adhesive sheets of each Example and Comparative Example were stored for 14 days in an environment of 40°C and 90% RH. Using the stored adhesive sheets, test pieces (after storage) for shear adhesive strength evaluation were prepared using the same procedure as above. (Measurement of Shear Adhesion Strength) The test piece for shear adhesive strength evaluation was placed in a thermostatic chamber set to 200°C or higher, and the test piece was chucked into a tensile tester installed in the thermostatic chamber. A tensile test was performed when the test piece reached 200°C. The tensile speed was 5 mm / min.

[0110] The results of the shear adhesive strength measurements for each Example and Comparative Example are shown in Table 1. The results of the scrape abrasion test are also shown in Tables 1 and 2. As can be seen from these results, the adhesive sheets of the Examples had adhesion to the object to be adhered, while being less susceptible to the detachment of part of the adhesive layer due to externally applied force than the adhesive sheets of the Comparative Examples. The adhesive sheets of the Examples in Table 2 also had adhesiveness similar to that of the Examples shown in Table 1.

[0111] The adhesive sheet of the present invention is preferably used, for example, as a component of a motor, for example, as a slot material provided in a motor.

[0112] 11: Base material layer, 12: Adhesive layer, 10: Adhesive sheet.

Claims

1. An adhesive sheet comprising a base layer and an adhesive layer to be adhered to an object to be adhered, the adhesive layer overlapping at least one surface of the base layer, the adhesive layer containing an epoxy resin and a polyurethane resin that does not have an epoxy group in its molecule.

2. The adhesive sheet according to claim 1, wherein the adhesive layer contains 3% by mass or more and 80% by mass or less of the polyurethane resin.

3. The adhesive sheet according to claim 1 or 2, wherein the acid value of the polyurethane resin is 0.1 mgKOH / g or more and 15.0 mgKOH / g or less.

4. The adhesive sheet according to claim 1 or 2, wherein the adhesive layer further contains a foaming agent.

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