Insulating sheet

Abstract

To provide an insulation sheet having a comparatively sufficient heat resistance even without an aging at comparatively high temperature, and furthermore, comparatively superior in adhesion to an adherend after a cross-linking reaction.SOLUTION: An insulation sheet includes a substrate film and an insulation layer laminated interposing an adhesive layer at least on one side of the substrate film. The adhesive layer is composed of a resin composition including a polyurethane resin, an epoxy resin and an isocyanate-based cross-linking agent. The resin composition contains, as the isocyanate-based cross-linking agent, at least one kind selected from a group including an aliphatic isocyanate and an aromatic isocyanate.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an insulating sheet. More specifically, the present invention relates to an insulating sheet used as an insulating sheet for a motor for an eco-car such as an electric vehicle (EV) or a hybrid electric vehicle (HEV).

Background Art

[0002] Conventionally, in eco-cars such as EVs and HEVs, it is known to use an oil-cooled drive motor as a drive motor. Such an oil-cooled drive motor includes a rotor and a stator that generates a force for rotating the rotor. The stator includes a plurality of coils, and a Lorentz force is obtained by generating a magnetic field in the plurality of coils, and the rotor is rotated by the Lorentz force.

[0003] In the oil-cooled drive motor as described above, the coil is constituted by, for example, a plurality of segment conductors connected to each other, and is usually used by being mounted on a member in which magnetic steel sheets called a stator core or a rotor coil are laminated.

[0004] In the oil-cooled drive motor as described above, cores such as a stator core and a rotor core have a plurality of slot grooves, and the coil is accommodated in each of the plurality of slot grooves. Further, in the oil-cooled drive motor as described above, an insulating sheet for ensuring insulation between the coil and the inner wall surface of the slot groove is accommodated in each of the slot grooves together with the coil. More specifically, the insulating sheet is accommodated in the slot groove in a state of being wound around the coil. And the coil wound around the insulating sheet is fixed in the slot groove by an insulating resin (for example, epoxy varnish) impregnated in the slot groove.

[0005] Further, as described in Patent Document 1 below, for example, the insulating sheet has a five-layer structure including a base film (a polyethylene terephthalate resin film) and surface films (a polyethylene naphthalate resin film) laminated via adhesive layers containing a resin such as an acrylic resin formed on both surfaces of the base film. And the insulating sheet is usually aged at a relatively high temperature (for example, 130°C) for a predetermined time (for example, 24 hours) while being accommodated in the slot groove in order to thermally crosslink a resin such as an acrylic resin to improve the heat resistance of the adhesive layer.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, when the insulating sheet is used for an oil-cooled drive motor, as described above, aging at a relatively high temperature to thermally crosslink a resin such as an acrylic resin increases the man-hours of work before assembling the oil-cooled drive motor to the vehicle body, and also requires equipment for aging, so it cannot be said to be preferable. On the other hand, if aging is not performed at a relatively high temperature, as described above, a resin such as an acrylic resin cannot be sufficiently thermally crosslinked, so the insulating sheet will be inferior in heat resistance. As described above, although there is a trade-off relationship between imparting heat resistance to the insulating sheet and increasing the man-hours of work before assembling the oil-cooled drive motor to the vehicle body or the like, the study to solve this problem has not yet been sufficiently carried out.

[0008] In addition, in the insulating sheet, it is also required that the adhesiveness of the adhesive layer to the adherend (in the insulating sheet of Patent Document 1, the base film and the surface layer film) be excellent after the crosslinking reaction.

[0009] Therefore, an object of the present invention is to provide an insulating sheet that has relatively sufficient heat resistance without performing aging at a relatively high temperature and also has relatively excellent adhesiveness to an adherend after a crosslinking reaction.

Means for Solving the Problems

[0010] As a result of intensive studies by the present inventors, it is provided with a base film and an insulating layer laminated on at least one surface of the base film via an adhesive layer, and the adhesive layer is composed of a resin composition containing a polyurethane resin, an epoxy resin, and an isocyanate-based crosslinking agent. In the insulating sheet, by making the resin composition contain at least one selected from the group consisting of an aliphatic isocyanate and an aromatic isocyanate as the isocyanate-based crosslinking agent, the insulating sheet has relatively sufficient heat resistance without performing aging at a relatively high temperature, and moreover, it has been found that the adhesiveness to the adherend is also relatively excellent after the crosslinking reaction. And the present invention was conceived.

[0011] That is, the insulating sheet according to the present invention has a base film and an insulating layer laminated on at least one surface of the base film via an adhesive layer, 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 selected from the group consisting of an aliphatic isocyanate and an aromatic isocyanate as the isocyanate-based crosslinking agent.

[0012] According to such a configuration, even if aging is performed at a relatively low temperature (a temperature of 60°C or lower. For example, 40°C), the insulating sheet has relatively sufficient heat resistance, and moreover, after the crosslinking reaction, the adhesiveness to the adherend is also relatively excellent.

[0013] In the above insulating sheet, it is preferable that the polyurethane resin has a carboxyl group.

[0014] According to such a configuration, even if aging is performed at a relatively low temperature, in addition to the insulating sheet having even more sufficient heat resistance, after the crosslinking reaction, the adhesiveness to the adherend is also even more excellent.

[0015] In the above insulating sheet, the polyurethane resin contains a hydroxyl group-containing polyurethane resin having a hydroxyl group at the terminal, it is preferable that the epoxy resin contains a hydroxyl group-containing epoxy resin having a hydroxyl group.

[0016] According to such a configuration, even if aging is performed at a relatively low temperature, the insulating sheet has even more sufficient heat resistance, and moreover, after the crosslinking reaction, the adhesiveness to the adherend is also even more excellent.

[0017] In the above insulating sheet, the aliphatic isocyanate is at least one of hexamethylene diisocyanate and isophorone diisocyanate, it is preferable that the aromatic isocyanate is at least one of diphenylmethane diisocyanate and tolylene diisocyanate.

[0018] According to such a configuration, even if aging is performed at a relatively low temperature, the insulating sheet has even more sufficient heat resistance, and moreover, after the crosslinking reaction, the adhesiveness to the adherend is also even more excellent.

[0019] In the above-mentioned insulating sheet, it is preferable that the isocyanate-based crosslinking agent is contained in an amount of 3 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the total amount of the polyurethane resin and the epoxy resin.

[0020] According to such a configuration, even if aging is performed at a relatively low temperature, the insulating sheet has relatively sufficient heat resistance, and in addition, after the crosslinking reaction, it has relatively excellent adhesiveness to the adherend, and also exhibits relatively sufficient hydrolysis resistance (moisture and heat resistance).

Advantages of the Invention

[0021] According to the present invention, it is possible to provide an insulating sheet that has relatively sufficient heat resistance without performing aging at a relatively high temperature, and in addition, has relatively excellent adhesiveness to the adherend after the crosslinking reaction.

Brief Description of the Drawings

[0022]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0023] Hereinafter, an embodiment of the present invention will be described. Note that, hereinafter, an example in which the insulating sheet is configured by laminating insulating layers on both surfaces of a base film via adhesive layers will be described. That is, an example in which the insulating sheet has a five-layer structure will be described.

[0024] As shown in FIG. 1, the insulating sheet 10 according to the present embodiment includes a base film 10a and insulating layers 10c1 and 10c2 laminated on both surfaces of the base film 10a via adhesive layers 10b1 and 10b2.

[0025] The insulating sheet 10 according to the present embodiment is used, for example, as an insulating sheet for an oil-cooled drive motor of an automobile. That is, the insulating sheet 10 according to the present embodiment is used, for example, as an insulating sheet for a drive motor cooled by cooling oil (such as ATF). Examples of the automobile include an electric vehicle (EV) and a hybrid vehicle (HEV).

[0026] In the insulating sheet 10 according to the present embodiment, the base film 10a is preferably a polyester film made of a polyester resin. Examples of the polyester resin include polybutylene terephthalate (PBT) resin, polyethylene terephthalate (PET) resin, polybutylene naphthalate (PBN) resin, polyethylene naphthalate (PEN) resin, and poly-1,4-cyclohexanedimethylene terephthalate resin. Among these, the polyester resin constituting the polyester film is preferably either PET resin or PEN resin. That is, the polyester film is preferably either a PET film or a PEN film. Further, the base film 10a may be a polyimide film made of a polyimide (PI) resin.

[0027] The thickness of the base film 10a is preferably 10 μm or more and 250 μm or less, more preferably 15 μm or more and 100 μm or less, and even more preferably 25 μm or more and 75 μm or less. The thickness of the base film 10a can be obtained by measuring the thicknesses of any 10 randomly selected locations using a digital micrometer and calculating the arithmetic mean of these measured values.

[0028] As the base film 10a, either a stretched and formed one or a non-stretched one (unstretched one) can be used, but a stretched and formed one is preferred, and a biaxially stretched and formed one is more preferred.

[0029] Also, when the base film 10a is a PET film or a PEN film, it is preferable that the film is composed of a low-oligomer product with an oligomer content of 1% by mass or less. By configuring the film with a low-oligomer product, the base film 10a becomes excellent in hydrolysis resistance. When the base film 10a is a PEN film and is a low-oligomer product, the base film 10a is particularly excellent in hydrolysis resistance. The oligomer content can be determined, for example, by washing a film sample in a substantially square shape with a side length of about 5 cm with methanol, then drying the film sample in a hot air oven at 160 °C for 1 hour to obtain the initial mass (M1 (g)), and then using a Soxhlet extractor or the like to perform an extraction treatment on the film sample with boiling xylene (about 400 mL) for 48 hours, measuring the mass (M2 (g)) of the film sample after the extraction treatment, and calculating the ratio of the mass reduction (M1 - M2) to the initial mass (M1) ((M1 - M2) / M1 × 100). Here, if the mass (M2 (g)) of the film sample after the extraction treatment is not measured after sufficiently removing the xylene used in the extraction treatment from the film sample, the mass reduction cannot be accurately obtained. Therefore, after the xylene extraction, the film sample is washed with water, and the xylene adhering to the surface is gently wiped off, and then dried in a hot air oven at 160 °C for 8 hours and cooled in a desiccator before measurement.

[0030] In the insulating sheet 10 according to the present embodiment, the insulating layers 10c1 and 10c2 are each composed of a paper-like sheet formed using fibers.

[0031] Examples of fibers used for forming the paper sheet include organic fibers such as aromatic polyamide fibers, polyether sulfide fibers, polyphenylene sulfide fibers, polypropylene fibers, polyether ether ketone fibers, polyethylene terephthalate fibers, acrylate fibers, polyethylene naphthalate fibers, and inorganic fibers such as glass fibers, rock wool, asbestos, boron fibers, alumina fibers, and carbon fibers. Natural fibers such as silk and cotton, and semi-synthetic fibers such as cellulose are also included. Note that the paper sheet may be formed using only one of these fibers, or may be formed by mixing multiple types of these fibers. Among these, a paper sheet called "aramid paper" mainly made of wholly aromatic polyamide fibers is excellent in slidability and is suitable.

[0032] As such aramid paper, a sheet-like material formed mainly from fibers (wholly aromatic polyamide fibers) made of a resin material in which portions other than amide groups are composed of benzene rings, such as a condensation polymer of phenylenediamine and phthalic acid, can be used.

[0033] The thicknesses of the insulating layers 10c1 and 10c2 are preferably 20 μm or more and 250 μm or less, more preferably 25 μm or more and 100 μm or less, and even more preferably 30 μm or more and 70 μm or less. In particular, when the paper sheet is aramid paper, by setting the thickness within the above numerical range, high mechanical properties can be imparted to the insulating sheet 10, and the insulating sheet 10 can have excellent shape retention when bent. The insulating layers 10c1 and 10c2 may have the same thickness or may have different thicknesses from each other, but it is preferable that they have the same thickness.

[0034] A coating containing a polyamide resin may be applied to at least one surface of the insulating layers 10c1 and 10c2 to form a film. In such a case, the film serves as the surface portion of the insulating sheet 10. As the polyamide contained in the coating, a methoxymethylated polyamide resin in which at least a part of the amide group moiety is methoxymethylated is preferably used.

[0035] In the insulating sheet 10 according to the present embodiment, the adhesive layers 10b1 and 10b2 are composed of a resin composition containing a polyurethane resin, an epoxy resin, and an isocyanate-based crosslinking agent. In the insulating sheet 10 according to the present embodiment, the resin composition contains at least one selected from the group consisting of an aliphatic isocyanate and an aromatic isocyanate as the isocyanate-based crosslinking agent. The insulating sheet 10 according to the present embodiment is configured as described above, and thus has relatively sufficient heat resistance even when aged at a relatively low temperature (a temperature of 60°C or lower, for example, 40°C), and moreover, has relatively excellent adhesiveness to the adherend after the crosslinking reaction. In the insulating sheet 10 according to the present embodiment, the adherends are the base film 10a and the insulating layers 10c1 and 10c2.

[0036] The polyurethane resin is obtained by urethane-bonding reaction components including a polyol component having two or more hydroxyl groups in one molecule and a polyisocyanate component having two or more isocyanate groups in one molecule.

[0037] In the insulating sheet 10 according to the present embodiment, the polyurethane resin preferably has a carboxyl group. That is, the polyurethane resin is preferably a polyurethane resin having a carboxyl group. When the polyurethane resin is a polyurethane resin having a carboxyl group, usually, a plurality of epoxy resins are grafted to the polyurethane resin. That is, when the polyurethane resin is a polyurethane resin having a carboxyl group, in the adhesive layers 10b1 and 10b2, usually, a structure in which a plurality of epoxy resins are bonded to the carboxyl group bonded to the main chain having a polyurethane structure via an epoxy group is included.

[0038] As described above, when the polyurethane resin is a polyurethane resin having a carboxyl group, the adhesive layers 10b1 and 10b2 usually include a structure (urethane-epoxy graft body) in which a plurality of epoxy resins are bonded to the carboxyl group bonded to the main chain having a polyurethane structure via an epoxy group. In a situation where such a urethane-epoxy graft body and an isocyanate-based crosslinking agent (at least one selected from the group consisting of an aliphatic isocyanate and an aromatic isocyanate) coexist, at a relatively low temperature (a temperature of 60°C or lower. For example, 40°C), at the terminal of the main chain having a urethane structure, it is considered that the crosslinking reaction proceeds sufficiently due to the sufficient reaction between the isocyanate group and the hydroxyl group of the above-mentioned isocyanate-based crosslinking agent. In particular, when the isocyanate-based crosslinking agent is at least one selected from the group consisting of an aliphatic polyisocyanate and an aromatic polyisocyanate, it is considered that the crosslinking reaction at the above-mentioned relatively low temperature proceeds more remarkably. Also, as will be described later, the epoxy resin is usually bifunctional or polyfunctional and has two or more epoxy groups in one molecule. Therefore, in the urethane-epoxy graft body as described above, at least one epoxy group that has not polymerized with the carboxyl group of the urethane resin having a carboxyl group remains in one molecule of the epoxy resin. Thus, in the urethane-epoxy graft body, since the epoxy group that has not polymerized with the carboxyl group of the urethane resin having a carboxyl group remains, in the adhesive layers 10b1 and 10b2, this epoxy group also contributes to the crosslinking reaction. For the reasons described above, when the polyurethane resin is a polyurethane resin having a carboxyl group, the crosslinking reaction proceeds sufficiently at a relatively low temperature (a temperature of 60°C or lower, for example, 40°C). Therefore, in addition to having even more sufficient heat resistance, the insulating sheet 10 according to the present embodiment is considered to be even more excellent in adhesiveness to the adherend (the insulating layers 10c1, 10c2, and the base film 10a) after the crosslinking reaction.

[0039] When the polyurethane resin is a polyurethane resin having a carboxyl group, the polyurethane resin having a carboxyl group preferably has an acid value of 5 mgKOH / g or more and 30 mgKOH / g or less, and more preferably 9 mgKOH / g or more and 25 mgKOH / g or less. When the acid value of the polyurethane resin having a carboxyl group is within the above numerical range, the reaction with the isocyanate-based crosslinking agent can proceed favorably. In addition, when the acid value of the polyurethane resin having a carboxyl group is within the above range, the crosslinking density with the epoxy resin can be made relatively high. Therefore, when the resin composition is crosslinked to form a cured product, the cured product is excellent in heat resistance for a long time. In addition, since the generation of strain can be relatively suppressed, the cured product is excellent in flexibility. The acid value of the polyurethane resin can be measured according to the method of JIS K1557-5:2007 by dissolving the polyurethane resin in methyl ethyl ketone (MEK) or the like to form a solution.

[0040] The polyurethane resin preferably contains a hydroxyl group-containing polyurethane resin having a hydroxyl group at the terminal. By containing the hydroxyl group-containing polyurethane resin, the reaction with the isocyanate-based crosslinking agent can proceed favorably. The hydroxyl value of the hydroxyl group-containing polyurethane resin is preferably 0.1 mgKOH / g or more and 20 mgKOH / g or less, and more preferably 1 mgKOH / g or more and 15 mgKOH / g or less. The hydroxyl value of the hydroxyl group-containing polyurethane resin can be measured in accordance with JIS K1557-1:2007. In the insulating sheet of the present embodiment, it is preferable that the polyurethane resin is crosslinked with the epoxy resin by the isocyanate-based crosslinking agent. Specifically, in the insulating sheet according to the present embodiment, it is preferable that the polyurethane resin and the epoxy resin are crosslinked by the isocyanate-based crosslinking agent at a relatively low temperature (a temperature of 60°C or lower. For example, 40°C).

[0041] As described above, when the polyurethane resin has a carboxyl group, the carboxyl group can be provided in the polyurethane resin by including it in the polyol component or the polyisocyanate component.

[0042] The carboxyl group can be provided in the polyurethane resin by including a hydroxyl group-containing compound having a carboxyl group in the polyol component. In this case, it is preferable that the polyol component contains a general polyol together with the hydroxyl group-containing compound having a carboxyl group.

[0043] The hydroxyl group-containing compound having a carboxyl group has two or more hydroxyl groups in one molecule. Therefore, it reacts with a polyisocyanate component having two or more isocyanate groups in one molecule to obtain a polyurethane resin.

[0044] Examples of the hydroxyl group-containing compound having a carboxyl group include dimethylolpropanoic acid, dimethylolbutanoic acid, their alkylene oxide low-molar adducts (number average molecular weight Mn less than 500), γ-caprolactam low-molar adducts (number average molecular weight Mn less than 500), half-esters derived from acid anhydrides and glycerin, compounds derived by free radical reaction of a monomer containing a hydroxyl group and an unsaturated group, a monomer containing a carboxyl group and an unsaturated group, and the like. These compounds may be used alone or in combination of two or more. In addition, the number average molecular weight Mn in this specification means the value measured by the terminal functional group quantification method. Among these, the hydroxyl group-containing compound having a carboxyl group is preferably dimethylolpropanoic acid or dimethylolbutanoic acid, and particularly preferably dimethylolpropanoic acid.

[0045] As the above-mentioned general polyol, a conventionally known polyol used in the synthesis of polyurethane resins can be used. Specific examples of such polyols include polyester polyols, polyether polyols, polycarbonate polyols, and other polyols.

[0046] Examples of the polyester polyol include those obtained by polycondensing an aliphatic dicarboxylic acid (for example, succinic acid, adipic acid, sebacic acid, glutaric acid, azelaic acid, etc.) and an aromatic dicarboxylic acid (for example, isophthalic acid, terephthalic acid, etc.) with a low molecular weight glycol (for example, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butylene glycol, 1,6-hexamethylene glycol, neopentyl glycol, 1,4-bishydroxymethylcyclohexane, etc.).

[0047] Specific examples of such 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, poly-3-methylvalerolactone diol, and the like. Since the polyester polyol is superior in heat resistance to the polyether polyol, by including the polyester polyol in the polyol component, the adhesive layers 10b1 and 10b2 can be made to have more excellent heat resistance.

[0048] Specific examples of the polyether polyol include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and random / block copolymers thereof. Since the polyether polyol is superior in hydrolysis resistance to the polyester polyol, by including the polyether polyol in the polyol component, the adhesive layers 10b1 and 10b2 can be made more excellent in hydrolysis resistance.

[0049] Specific examples of the polycarbonate polyol include polytetramethylene carbonate diol, polypentamethylene carbonate diol, polyneopentyl carbonate diol, polyhexamethylene carbonate diol, poly(1,4-cyclohexanedimethylene carbonate) diol, and random / block copolymers thereof. By using various polycarbonate diols as described above as the polycarbonate polyol, the polyurethane resin can be provided with a structural unit of the carbonate diol. Since the polycarbonate polyol is excellent in both heat resistance and hydrolysis resistance, by including the polycarbonate polyol in the polyol component, the adhesive layers 10b1 and 10b2 can be made more excellent in both heat resistance and hydrolysis resistance. Among the polycarbonate polyols, it is preferable to use polyhexamethylene carbonate from the viewpoints of cost and availability.

[0050] Specific examples of other polyols include dimer diol and its hydrogenated product, polybutadiene polyol and its hydrogenated product, polyisoprene polyol and its hydrogenated product, acrylic polyol, epoxy polyol, polyether ester polyol, siloxane-modified polyol, α,ω-polymethyl methacrylate diol, α,ω-polybutyl methacrylate diol, siloxane-modified polyol, and the like. Among other polyols, the hydrogenated product of dimer diol and the hydrogenated product of polybutadiene polyol are excellent in both heat resistance and hydrolysis resistance. Therefore, by including these polyols in the polyol component, the adhesive layers 10b1 and 10b2 can be made to have excellent heat resistance and hydrolysis resistance.

[0051] The number average molecular weight Mn (value measured by the terminal functional group quantification method) of the polyol is not particularly limited, but is preferably 500 or more and 6,000 or less. When the number average molecular weight Mn of the polyol is within the above numerical range, the cohesive force of the urethane bond is likely to be exhibited, so the mechanical properties can be improved. In addition, when the polyol is a crystalline polyol, if the number average molecular weight Mn is too large, a whitening phenomenon may occur in the adhesive layers 10b1 and 10b2. Therefore, when using a crystalline polyol alone, it is preferable to use one having a number average molecular weight Mn of 3,000 or less. The above-described polyol may be used alone or in combination of two or more.

[0052] As the polyol component, in addition to the above-described polyol, a short-chain diol can be used as necessary. Specific examples of the short-chain diol 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, neopentyl glycol, and alkylene oxide low-molar adducts thereof (number average molecular weight Mn less than 500 by end-group quantitative method); alicyclic glycols such as 1,4-bishydroxymethylcyclohexane, 2-methyl-1,1-cyclohexanedimethanol, and alkylene oxide low-molar adducts thereof (number average molecular weight Mn less than 500 by end-group quantitative method); aromatic glycols such as xylylene glycol, and alkylene oxide low-molar adducts thereof (number average molecular weight Mn less than 500 by end-group quantitative method); bisphenols such as bisphenol A, thiobisphenol, sulfone bisphenol, and alkylene oxide low-molar adducts thereof (number average molecular weight Mn less than 500 by end-group quantitative method). Among the short-chain diols as described above, it is preferable to use ethylene glycol, 1,3-propylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,6-hexamethylene glycol, neopentyl glycol, etc., and it is particularly preferable to use ethylene glycol, 1,3-butylene glycol, 1,4-butylene glycol. These short-chain diols can be used alone or in combination of two or more.

[0053] In addition, when producing the polyurethane resin, a polyhydric alcohol-based compound can also be used as a material for the polyurethane resin in the same manner as the short-chain diol component. Specific examples of the polyhydric alcohol-based compound include glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, tris-(2-hydroxyethyl) isocyanurate, 1,1,1-trimethylolethane, 1,1,1-trimethylolpropane, etc.

[0054] As the polyisocyanate component, a conventionally known polyisocyanate component used in the production of the polyurethane resin can be used. Specific examples of the polyisocyanate component include toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, mixtures thereof, 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) (MDI), and crude or polymeric MDI, durylene diisocyanate, xylylene diisocyanate (XDI), 1,5-naphthalene diisocyanate, benzidine diisocyanate, o-nitrobenzidine diisocyanate, 4,4'-diisocyanate dibenzyl and other aromatic diisocyanates; aliphatic diisocyanates such as methylene diisocyanate, 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 1,10-decamethylene diisocyanate; alicyclic diisocyanates such as 1,4-cyclohexylene diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), hydrogenated XDI; and polyurethane prepolymers obtained by reacting the above-mentioned diisocyanates with a low molecular weight polyol so that the terminals are isocyanates.

[0055] Among the above-mentioned polyisocyanate components, from the viewpoint of stably obtaining adhesives layers 10b1 and 10b2 that are industrially inexpensive and have excellent heat resistance, it is preferable to use aromatic isocyanates. Among aromatic isocyanates, it is particularly preferable to use toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, mixtures thereof, 4,4'-methylenebis(phenylene isocyanate) (MDI), and crude or polymeric MDI. By using an aromatic isocyanate as the polyisocyanate component, the polyurethane resin can be provided with a structural unit of the aromatic isocyanate. The above-mentioned polyisocyanate components may be used alone or in combination of two or more.

[0056] The polyurethane resin can be produced by a conventionally known method for producing polyurethane. Specifically, first, in the presence or absence of an organic solvent that does not contain active hydrogen in the molecule, as reaction components, a hydroxyl group-containing compound having a carboxyl group, a polyol, a polyisocyanate component, and a short-chain polyol that is used as a chain extender as needed are reacted to obtain a polyurethane resin. Generally, the reaction composition may have a mixing composition in which the equivalent ratio of the isocyanate group to the hydroxyl group is 0.8 to 1.25. The reaction may be carried out by a one-shot method or a multi-step method, usually at 20 to 150 °C, preferably 60 to 110 °C.

[0057] The mass average molecular weight Mw of the polyurethane resin obtained as described above is preferably 1,000 or more and 100,000 or less. When the mass average molecular weight Mw of the polyurethane resin is within the above numerical range, the polyurethane resin exhibits more effectively properties such as flexibility, adhesiveness, and heat resistance. The mass average molecular weight Mw of the polyurethane resin means a value measured by gel permeation chromatography (GPC). For example, it can be measured under the following apparatus and conditions. (1) Instrument device: Trade name "HLC-8020" (manufactured by Tosoh Corporation) (2) Column: Trade 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 substance: TSK standard polystyrene (manufactured by Tosoh Corporation)

[0058] In this embodiment, a catalyst can be used as needed in the synthesis of the polyurethane resin. Examples of the catalyst include salts of metals and organic acids 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-based catalysts. The catalyst promotes the reaction of the synthesis of the polyurethane resin. On the other hand, if the catalyst is used in excess, there is a risk of inducing a decomposition reaction that decomposes substances other than the polyurethane resin. As a result, the resulting adhesive may be inferior in heat resistance in the high-temperature range (e.g., 255°C) and long-term heat resistance. Therefore, when using the catalyst, it is preferable to use an appropriate amount of the catalyst.

[0059] The polyurethane resin may be synthesized without using an organic solvent or may be synthesized using an organic solvent. As the organic solvent, an organic solvent that is inert to the isocyanate group or an organic solvent that is less active than the reaction component with respect to the isocyanate group can be used. Specific examples of the organic solvent include ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; aromatic hydrocarbon solvents such as toluene, xylene, Swazol (trade name, manufactured by Cosmo Oil Co., Ltd.), and Solvesso (trade name, manufactured by Exxon Chemical Co., Ltd.); aliphatic hydrocarbon solvents such as n - hexane; alcohol solvents such as methanol, ethanol, and isopropyl alcohol; ether solvents such as dioxane and tetrahydrofuran; ester solvents such as ethyl acetate, butyl acetate, and isobutyl acetate; carbonate ester solvents such as dimethyl carbonate, diethyl carbonate, and ethylene carbonate; glycol ether ester solvents such as ethylene glycol ethyl ether acetate, propylene glycol methyl ether acetate, 3 - methyl - 3 - methoxybutyl acetate, and ethyl - 3 - ethoxypropionate; amide solvents such as dimethylformamide and dimethylacetamide; lactam solvents such as N - methyl - 2 - pyrrolidone, etc. Particularly, toluene and methyl ethyl ketone are preferable from the viewpoints of enhancing the solubility of the polyurethane resin and enhancing the drying property of the adhesive.

[0060] Epoxy resins usually have two or more epoxy groups in one molecule. That is, epoxy resins are usually bifunctional or polyfunctional (for example, trifunctional or tetrafunctional). Examples of the bifunctional epoxy resin include bisphenol A type epoxy resin, hydrogenated bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, bisphenol AD type epoxy resin, bixylenol type epoxy resin, biphenol type epoxy resin, etc. Examples of the polyfunctional epoxy resin include phenol novolac type epoxy resin, bisphenol A type novolac epoxy resin, trifunctional phenol type epoxy resin, and tetrafunctional phenol type epoxy resin, etc. Examples of commercially available phenol novolac type epoxy resins include jER152 and jER154 (both manufactured by Mitsubishi Chemical Corporation), etc. Examples of commercially available bisphenol A type novolac epoxy resins include jER157S65 and jER157S70 (both manufactured by Mitsubishi Chemical Corporation), etc. Examples of commercially available trifunctional phenol type epoxy resins include jER1032S50 and jER1032H60 (both manufactured by Mitsubishi Chemical Corporation), etc. Examples of commercially available tetrafunctional phenol type epoxy resins include jER1031S (manufactured by Mitsubishi Chemical Corporation), etc. The above epoxy resins may be used alone or in combination of two or more.

[0061] In the insulating sheet 10 according to the present embodiment, it is preferable that the epoxy resin is contained in an amount of 10 parts by mass or more and 100 parts by mass or less, and more preferably 20 parts by mass or more and 80 parts by mass or less, based on 100 parts by mass of the polyurethane resin. When the content of the epoxy resin is 10 parts by mass or more, the adhesive layers 10b1 and 10b2 can have sufficient heat resistance. Also, when the content of the epoxy resin is 100 parts by mass or less, the flexibility derived from the urethane resin can be sufficiently exhibited in the adhesive layers 10b1 and 10b2. Thereby, it is possible to prevent the adhesive layers 10b1 and 10b2 from becoming excessively hard and brittle after curing (after the crosslinking reaction).

[0062] The epoxy resin preferably contains a hydroxyl group-containing epoxy resin having a hydroxyl group. Also, the epoxy resin preferably has an epoxy equivalent of 450 g / eq or more and 3000 g / eq or less. When the epoxy equivalent is within the above numerical range, the adhesive layers 10b1 and 10b2 become even more excellent in adhesiveness to the adherend at a relatively low temperature (a temperature of 60°C or lower. For example, 40°C). The epoxy equivalent can be determined in accordance with JIS K 7236.

[0063] The hydroxyl value of the hydroxyl group-containing epoxy resin is preferably 50 mgKOH / g or more and 250 mgKOH / g or less, and more preferably 100 mgKOH / g or more and 220 mgKOH / g or less. When the hydroxyl value of the hydroxyl group-containing epoxy resin is 50 mgKOH / g or more, after the crosslinking reaction of the hydroxyl group-containing epoxy resin with the isocyanate-based crosslinking agent, the crosslinking density can be further increased. Thereby, the cured product obtained after the crosslinking reaction can be made to have more excellent long-term heat resistance. Moreover, when the hydroxyl value of the hydroxyl group-containing epoxy resin is 250 mgKOH / g or less, it is possible to suppress the crosslinking density from becoming excessively high. Thereby, it is possible to suppress the cured product obtained after the crosslinking reaction from becoming excessively inferior in flexibility and the occurrence of distortion in the cured product. Furthermore, when the hydroxyl value of the hydroxyl group-containing epoxy resin is 250 mgKOH / g or less, the unreacted hydroxyl groups can be made relatively few. Thereby, it is possible to suppress a decrease in the long-term durability of the adhesive layers 10b1 and 10b2 caused by the reaction of the relatively large amount of remaining unreacted hydroxyl groups with moisture in the air or the like.

[0064] The epoxy resin is preferably mixed with the polyurethane resin in a state dissolved in an organic solvent.

[0065] Specific examples of the organic solvent include ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; aromatic hydrocarbon solvents such as toluene, xylene, Swasol (trade name, manufactured by Cosmo Oil Co., Ltd.), and Solvesso (trade name, manufactured by Exxon Chemical Co., Ltd.); aliphatic hydrocarbon solvents such as n-hexane; alcohol solvents such as methanol, ethanol, and isopropyl alcohol; ether solvents such as dioxane and tetrahydrofuran; ester solvents such as ethyl acetate, butyl acetate, and isobutyl acetate; carbonate ester solvents such as dimethyl carbonate, diethyl carbonate, and ethylene carbonate; glycol ether ester solvents such as ethylene glycol ethyl ether acetate, propylene glycol methyl ether acetate, 3-methyl-3-methoxybutyl acetate, and ethyl 3-ethoxypropionate; amide solvents such as dimethylformamide and dimethylacetamide; lactam solvents such as N-methyl-2-pyrrolidone, and the like. Particularly, toluene and methyl ethyl ketone are preferable from the viewpoints of solubility in epoxy resin, drying property of the adhesive, and the like. Also, toluene and methyl ethyl ketone are preferable from the viewpoint that they are less likely to deactivate isocyanate groups compared to alcohol solvents.

[0066] The aliphatic isocyanate is preferably an aliphatic polyisocyanate, and more preferably an aliphatic diisocyanate. The aromatic isocyanate is preferably an aromatic polyisocyanate, and more preferably an aromatic diisocyanate.

[0067] As the aliphatic isocyanate, hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), and the like are preferably used. Examples of the aliphatic isocyanate include a biuret form of HDI, an isocyanurate form of HDI, a TMP adduct form of HDI, and the like. Note that TMP is an abbreviation of trimethylolpropane.

[0068] As the aromatic isocyanate, diphenylmethane diisocyanate (MDI), tolylene diisocyanate (TDI), etc. are preferably used. Examples of the aromatic isocyanate include an isocyanurate form of TDI, a TMP adduct form of TDI, etc.

[0069] In addition, the isocyanate-based crosslinking agent may contain an alicyclic isocyanate. The alicyclic isocyanate is preferably an alicyclic polyisocyanate, and more preferably an alicyclic diisocyanate. Examples of the alicyclic diisocyanate include an isocyanurate form of IPDI, an isocyanurate form of hydrogenated XDI, a TMP adduct form of hydrogenated XDI, etc. Note that the XDI is an abbreviation of xylylene diisocyanate.

[0070] The insulating sheet 10 according to the present embodiment preferably contains 3 to 20 parts by mass of the isocyanate-based crosslinking agent with respect to 100 parts by mass of the total amount of the polyurethane resin and the epoxy resin. According to such a configuration, even if the insulating sheet 10 is aged at a relatively low temperature, it has relatively sufficient heat resistance. Moreover, after the crosslinking reaction, in addition to having relatively excellent adhesiveness to the adherend, it also exhibits relatively sufficient hydrolysis resistance (moisture and heat resistance).

[0071] The resin composition may contain various known additives. Examples of the additive include a crosslinking accelerator that promotes the crosslinking reaction. In addition, examples of the additive also include a dispersant, a tackifier, an anti-aging agent, an antioxidant, a processing aid, a stabilizer, an antifoaming agent, a flame retardant, a thickener, a pigment, etc.

[0072] The thicknesses of the adhesive layers 10b1 and 10b2 are preferably 3 μm or more and 20 μm or less, more preferably 4 μm or more and 15 μm or less, and even more preferably 5 μm or more and 10 μm or less.

[0073] The insulating sheet 10 according to the present embodiment is used, for example, for an oil-cooled drive motor of an automobile as described above. Hereinafter, with reference to FIGS. 2 to 4, specific examples of the use of the insulating sheet 10 according to the present embodiment will be described. In the following, the case where the oil-cooled drive motor is used as an oil-cooled drive motor of an electric vehicle or a hybrid vehicle will be described as an example.

[0074] The oil-cooled drive motor includes a rotor having a permanent magnet, a stator having a coil, and a coil formed by a segment conductor. And the insulating sheet 10 according to the present embodiment is used for insulation between the coil and the core in the stator.

[0075] FIG. 2 is a perspective view of the stator 1 of the oil-cooled drive motor. As also shown in the figure, the stator 1 has a stator core 20 and a coil 30. FIG. 3 is a plan view of the stator 1 viewed from the rotational axis direction (arrow AD) of a rotor (not shown), and FIG. 4 is a cross-sectional view showing a state in which a plurality of coils 30 are accommodated in part A of the stator core 20 shown in FIG. 3.

[0076] As also shown in these figures, in the stator 1, a plurality of slot grooves 21 are formed on the inner peripheral surface side of the cylindrical stator core 20. The stator 1 has a stator core 20 and a plurality of coils 30 accommodated in a plurality of slot grooves 21 formed in the stator core 20. The plurality of slot grooves 21 are arranged in the stator core 20 such that each slot groove 21 extends along the rotation axis direction (AD in FIG. 2) of the stator core 20 and maintains a constant interval from each other in the circumferential direction (RD in FIG. 2) of the stator core 20. The slot groove 21 is formed over the entire length in the rotation axis direction AD of the stator core 20, and openings 21b having the same shape as the cross-sectional shape of the slot groove 21 are formed in one end face 20a (the upper side in FIG. 2, hereinafter also referred to as the "upper end face 20a") and the other end face 20b (hereinafter also referred to as the "lower end face 20b") of the stator core 20.

[0077] In the stator core 20, since the plurality of slot grooves 21 are parallel as described above, the space between adjacent slot grooves 21 forms plate-like protrusions 22. A plurality of these plate-like protrusions 22 (hereinafter also referred to as "teeth 22") are formed in a state of protruding toward the inner side in the radial direction (DD direction in FIG. 2) of the stator core 20. As shown in FIGS. 3 and 4, the teeth 22 have wide portions 22a that extend in the circumferential direction RD of the stator core 20 at the tip ends in the protruding direction, and the cross-sectional shape is T-shaped. Therefore, on the inner peripheral surface side of the stator core 20, the width of the slot groove 21 becomes narrow, and only a linear opening 21a is slightly formed.

[0078] The coil 30 is composed of a plurality of segment conductors 31 connected to each other. Before forming the coil, the segment conductor 31 is a flat enameled wire bent into a U shape as shown in FIG. 2, and includes two leg portions 31b and a head portion 31a connecting the two leg portions 31b.

[0079] The segment conductor 31 has a copper wire exposed portion where the insulating coating is peeled off at the tip end 31bx of the leg portion 31b on the side opposite to the head portion 31a. The coil 30 is manufactured by inserting the leg portion 31b of the segment conductor 31 from the opening 21b of the slot groove 21 on the upper end surface 20a of the stator core 20, and exposing the tip portion 31bx from the lower end surface 20b of the stator core 20. Then, the leg portion 31b of one segment conductor 31 and the leg portion 31b of another segment conductor 31 are electrically connected at the copper wire exposed portion to form the connection portion 31x. Further, an insulation process is performed on this connection portion 31x to produce the coil 30. Note that the two leg portions 31b of one segment conductor 31 are respectively inserted into different slot grooves 21.

[0080] Since the coil 30 is manufactured as described above, the stator 1 has an upper coil end portion formed by the head portion 31a of the segment conductor 31 on the upper end surface 20a side of the stator core 20, and a lower coil end portion formed by the connection portion 31x formed by connecting the leg portions 31b on the lower end surface 20b side.

[0081] As shown in FIG. 4, four leg portions 31b of the segment conductors 31 forming the coil 30 are respectively accommodated in the slot grooves 21 of the stator core 20 (one leg portion 31b of each of the four segment conductors 31 is accommodated), and a total of four leg portions 31b are accommodated in each slot groove 21 in a state of being arranged in a row from the inner peripheral surface side to the outer peripheral surface side.

[0082] As shown in FIG. 4, the insulating sheet 10 according to the present embodiment is interposed between the four leg portions 31b and the inner peripheral surface of the slot groove 21. The insulating sheet 10 is vertically attached along the longitudinal direction of the leg portion 31b of the segment conductor 31, is arranged in the slot groove 21 in a form that goes around the four leg portions 31b more than once, and both end portions in the rotation axis direction AD protrude outward from the upper end surface 20a and the lower end surface 20b of the stator core 20 and are arranged in the slot groove 21. Since the insulating sheet 10 is arranged in the slot groove 21 so as to go around the four leg portions 31b more than once as described above, both end portions in the circumferential direction are overlapped and arranged in the slot groove 21. That is, in the stator 1, an overlapping portion 10a1 where the insulating sheets 10 overlap each other is formed in the slot groove 21 (FIG. 4). And, as shown in FIG. 4, in the stator 1, the overlapping portion 10a1 is located outside in the radial direction DD. Note that the portions protruding from the upper end surface 20a and the lower end surface 20b of the stator core 20 in the rotational axis direction AD may be bent outward of the slot groove 21 so as to be hooked (locked) on at least one of the upper end side and the lower end side of the slot groove 21.

[0083] The coil 30 wound around the insulating sheet 10 is fixed in the slot groove 21 by the insulating resin by impregnating the slot groove 21 with an insulating resin (for example, epoxy varnish).

[0084] Note that the insulating sheet according to the present invention is not limited to the above-described embodiment. Further, the insulating sheet according to the present invention is not limited by the above-described operation and effect. The insulating sheet according to the present invention can be variously modified without departing from the gist of the present invention.

[0085] For example, in the above-described embodiment, an example in which the insulating layers 10c1 and 10c2 of the insulating sheet 10 are each formed of a paper-like sheet formed using fibers has been described, but the insulating layers 10c1 and 10c2 are not limited thereto. Films made of insulating resins such as polyethylene naphthalate (PEN), polyimide (PI), polyphenylene sulfide (PPS), and polyether ether ketone (PEEK) may be used for the insulating layers 10c1 and 10c2. Also, films both made of insulating resins may be used for the insulating layers 10c1 and 10c2. Furthermore, for the insulating layers 10c1 and 10c2, films made of the same type of insulating resin may be used (for example, both may be films made of PEN), or films made of different insulating resins may be used for one and the other (for example, a film made of PEN may be used for one, and a film made of PI may be used for the other). In addition, for the insulating layers 10c1 and 10c2, a paper-like sheet formed by using fibers may be used for one, or a film made of an insulating resin may be used for the other.

[0086] Also, when workability of assembly operations is required for insulating materials such as slots and wedges provided in the stator or rotor of an automotive motor, it is preferable to use a paper-like sheet for the insulating layers 10c1 and 10c2. By using a paper-like sheet, the slipperiness of the surfaces of the insulating layers 10c1 and 10c2 (that is, the surface of the insulating sheet 10) can be enhanced. On the other hand, when high tear strength is required for the insulating sheet, it is preferable to use a film made of an insulating resin for the insulating layers 10c1 and 10c2.

Examples

[0087] Next, the present invention will be described more specifically with reference to examples, comparative examples, and test examples.

[0088] <Synthesis of polyurethane resin> A reaction vessel equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen inlet tube, and a manhole was prepared. While purging the inside of the reaction vessel with nitrogen, 200.0 g of polyhexamethylene carbonate diol having hydroxyl groups at both ends (Duranol: T6002, manufactured by Asahi Kasei Chemicals Corporation, number average molecular weight = 2,000 by terminal functional group quantification method), 10.0 g of 1,3-butylene glycol, and 14.4 g of dimethylolpropanoic acid were charged. Next, 100.6 g of methyl ethyl ketone (MEK) was charged as a solvent, and the system was stirred. After the system became uniform, 77.3 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 the reaction solution with methyl ethyl ketone (MEK) as a solvent, and the reaction was allowed to proceed until the absorption at 2,270 cm -1 due to free isocyanate groups measured by infrared absorption spectrum analysis disappeared, and a resin solution AA containing polyurethane resin A was obtained. The obtained resin solution AA had a solid content of 30%, and polyurethane resin A had a hydroxyl value of 3.6 mg KOH / g and an acid value of 20.0 mg KOH / g. The weight average molecular weight of polyurethane resin A measured by GPC was 92,000.

[0089] <Dissolution of epoxy resin> A reaction vessel equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen inlet tube, and a manhole was prepared. While purging the inside of the reaction vessel with nitrogen, 400.0 g of bisphenol A type epoxy resin (epoxy equivalent: 450 g / eq, jER1001: manufactured by Mitsubishi Chemical Corporation. Hereinafter referred to as epoxy resin B) was charged, and while stirring, 600.0 g of methyl ethyl ketone (MEK) was charged as a solvent, and the temperature of the system was raised to 60 °C to completely dissolve epoxy resin B, and a dissolved product BB of epoxy resin B (hereinafter referred to as epoxy resin solution BB) was obtained. The solid content of the obtained epoxy resin solution BB was 40%.

[0090] (Example 1) An insulating layer, an adhesive layer, and a base film were laminated in the following order into 5 layers to obtain an insulating sheet according to Example 1 (thickness of the insulating sheet: 139 μm). Nomex paper (insulating layer. Thickness: 50 μm) Resin layer (adhesive layer. Thickness: 7 μm) Polyethylene terephthalate film (base film. Thickness: 25 μm) Resin layer (adhesive layer. Thickness: 7 μm) Nomex paper (insulating layer. Thickness 50 μm) In the insulating sheet according to Example 1, the adhesive layer was composed of an adhesive containing polyurethane resin A (a polyurethane resin having a carboxyl group), epoxy resin B, and isocyanate-based crosslinking agent A (an aliphatic isocyanate. Isocyanurate of hexamethylene diisocyanate (HDI)). In the insulating sheet according to Example 1, the adhesive was prepared by mixing resin solution AA containing polyurethane resin A, epoxy resin solution BB containing epoxy resin B, and isocyanate-based crosslinking agent A. Further, resin solution AA and epoxy resin solution BB were blended so that the epoxy resin (solid content) was 45 parts by mass with respect to 100 parts by mass of the polyurethane resin (solid content). Furthermore, isocyanate-based crosslinking agent A was blended in an amount of 10 parts by mass with respect to a total of 100 parts by mass of the polyurethane resin (solid content) and the epoxy resin (solid content). Note that the insulating sheet according to Example 1 was subjected to an aging treatment (crosslinking treatment) at 40 °C for 5 days (120 hours) to advance the curing reaction (crosslinking reaction) in the adhesive layer.

[0091] (Example 2) An insulating sheet according to Example 2 (5-layer structure. Thickness: 139 μm) was produced in the same manner as in Example 1, except that isocyanate-based crosslinking agent C (an aromatic isocyanate. Isocyanurate of tolylene diisocyanate (TDI)) was used instead of isocyanate-based crosslinking agent A. Also in Example 2, isocyanate-based crosslinking agent C was blended in an amount of 10 parts by mass with respect to a total of 100 parts by mass of the polyurethane resin (solid content) and the epoxy resin (solid content). Note that the insulating sheet according to Example 2 was also subjected to an aging treatment at 40°C for 5 days (120 hours) to advance the curing reaction (crosslinking reaction) in the adhesive layer.

[0092] (Example 3) An insulating sheet according to Example 3 (5-layer structure; thickness: 139 μm) was produced in the same manner as in Example 1, except that an isocyanate-based crosslinking agent D (a mixture of an isocyanurate of HDI and an isocyanurate of TDI; that is, a mixture of an aliphatic isocyanate and an aromatic isocyanate) was used instead of the isocyanate-based crosslinking agent A. Also, in Example 3, 10 parts by mass of the isocyanate-based crosslinking agent D was blended with respect to 100 parts by mass in total of the polyurethane resin (solid content) and the epoxy resin (solid content). Note that the insulating sheet according to Example 3 was also subjected to an aging treatment at 40°C for 5 days (120 hours) to advance the curing reaction (crosslinking reaction) in the adhesive layer.

[0093] (Comparative Example 1) An insulating sheet according to Comparative Example 1 (5-layer structure; thickness: 139 μm) was produced in the same manner as in Example 1, except that an aliphatic amine crosslinking agent (dicyandiamide (DICY)) was used instead of the isocyanate-based crosslinking agent A. Also, in Comparative Example 1, 10 parts by mass of the aliphatic amine crosslinking agent was blended with respect to 100 parts by mass in total of the polyurethane resin (solid content) and the epoxy resin (solid content). Note that the insulating sheet according to Comparative Example 1 was also subjected to an aging treatment at 40°C for 5 days (120 hours) to advance the curing reaction (crosslinking reaction) in the adhesive layer.

[0094] (Comparative Example 2) An insulating sheet according to Comparative Example 2 (5-layer structure; thickness: 139 μm) was produced in the same manner as in Example 1, except that an aromatic amine crosslinking agent (4,4'-diaminodiphenyl sulfone (DDS)) was used instead of the isocyanate-based crosslinking agent A. Also, in Comparative Example 2, the aromatic amine crosslinking agent was blended in an amount of 10 parts by mass with respect to 100 parts by mass in total of the polyurethane resin (solid content) and the epoxy resin (solid content). Note that the insulating sheet according to Comparative Example 2 was also subjected to an aging treatment at 40°C for 5 days (120 hours) to advance the curing reaction (crosslinking reaction) in the adhesive layer.

[0095] (Comparative Example 3) An insulating sheet according to Comparative Example 3 (five-layer structure; thickness: 139 μm) was produced in the same manner as in Example 1, except that a polyfunctional epoxy crosslinking agent (triphenylmethane type epoxy resin; trade name "EPPN501HY", manufactured by Nippon Kayaku Co., Ltd.) was used instead of the isocyanate-based crosslinking agent A. Also, in Comparative Example 3, the polyfunctional epoxy crosslinking agent was blended in an amount of 10 parts by mass with respect to 100 parts by mass in total of the polyurethane resin (solid content) and the epoxy resin (solid content). Note that the insulating sheet according to Comparative Example 3 was also subjected to an aging treatment at 40°C for 5 days (120 hours) to advance the curing reaction (crosslinking reaction) in the adhesive layer.

[0096] (Comparative Example 4) An insulating layer, an adhesive layer, and a base film were laminated in five layers in the following order to obtain an insulating sheet according to Comparative Example 4 (thickness of the insulating sheet: 184 μm). Nomex paper (insulating layer; thickness: 37 μm) Acrylic resin layer (adhesive layer; thickness: 30 μm) Polyethylene terephthalate film (base film; thickness: 50 μm) Acrylic resin layer (adhesive layer; thickness: 30 μm) Nomex paper (insulating layer; thickness: 37 μm) In the insulating sheet according to Comparative Example 4, the acrylic resin layer was composed of a resin composition containing acrylic resin A (a composition obtained by adding terpene phenol to polybutyl acrylate (PAB)) as a resin component and an isocyanate-based crosslinking agent E (aromatic isocyanate; trimethylolpropane (TMP) adduct of TDI). Also, in the insulating sheet according to Comparative Example 4, 7 parts by mass of an isocyanate-based crosslinking agent E was added to 100 parts by mass of acrylic resin A. Note that the insulating sheet according to Comparative Example 4 was subjected to an aging treatment (crosslinking treatment) at 130°C for 1 day.

[0097] (Comparative Example 5) An insulating sheet having the same configuration as that of Comparative Example 4 was obtained, and an aging treatment (crosslinking treatment) was performed at 40°C for 5 days to advance the curing reaction (crosslinking reaction) in the adhesive layer.

[0098] [Evaluation of Initial Adhesion] After aging the insulating sheets according to each example, the initial adhesion was evaluated by evaluating whether or not the insulating layer lifted from the adhesive layer. Specifically, visually, those in which the insulating layer lifted from the adhesive layer were evaluated as "non-conforming", and those in which no lifting was observed were evaluated as "excellent". The results are shown in Table 1 below. From Table 1, it can be seen that the insulating sheet according to Comparative Example 5 has an evaluation of "non-conforming" for the initial adhesion, and the insulating sheets according to the other examples (Examples 1 to 3 and Comparative Examples 1 to 4) all have an evaluation of "excellent" for the initial adhesion.

[0099] [Evaluation of Hydrolysis Resistance (Moist Heat Resistance)] Next, the hydrolysis resistance of the insulating sheets according to Examples 1 to 3 and Comparative Examples 1 to 4, which had an evaluation of "excellent" for the initial adhesion, was evaluated. The hydrolysis resistance was evaluated by performing a pressure cooker test (PCT) on the insulating sheets according to Examples 1 to 3 and Comparative Examples 1 to 4 in the form of loop-shaped test specimens under the conditions of 120°C, a relative humidity of 100%, and an atmospheric pressure of 0.2 MPa, and then visually observing the loop-shaped test specimens to evaluate whether or not the insulating layer lifted from the adhesive layer. The loop-shaped test piece was made by using two pieces of insulating paper, which are insulating layers with a planar dimension of width 25 mm × length 160 mm. For each piece of insulating paper, one end side and the other end side in the length direction were overlapped (hereinafter, also referred to as the overlapping part) to form a loop body respectively (in a top view, a loop shaped like a substantially ellipse was formed). In a state where the overlapping parts of these two loop bodies were overlapped, the one end side and the other end side in the width direction were fastened with a stapler. Regarding whether or not there was any lifting of the insulating layer from the adhesive layer, specifically, visually, those with the insulating layer lifted from the adhesive layer were evaluated as "non-conforming", and those without any lifting were evaluated as "excellent". The pressure cooker test was carried out by exposing the test piece to the conditions of 120 °C, relative humidity 100%, and atmospheric pressure 0.2 MPa for 48 hours, 96 hours, and 144 hours. The results were shown in Table 1 below. From Table 1, in the loop-shaped test pieces according to Examples 1 to 3 and the loop-shaped test piece according to Comparative Example 4, even after 144 hours, visually, no lifting of the insulating layer from the adhesive layer was observed. On the contrary, in the loop-shaped test pieces according to Comparative Examples 1 to 3, after 48 hours, visually, lifting of the insulating layer from the adhesive layer was observed. For the loop-shaped test pieces according to Comparative Examples 1 to 3, since lifting of the insulating layer from the adhesive layer was observed visually after 48 hours, visual observation was not carried out for 96 hours and 144 hours.

[0100] From the above results, it was found that the adhesive layer is composed of an adhesive layer (resin composition) containing a polyurethane resin (specifically, a polyurethane resin having a carboxyl group), an epoxy resin, and an isocyanate-based crosslinking agent, and the adhesive (resin composition) contains 10 parts by mass of the isocyanate-based crosslinking agent with respect to a total of 100 parts by mass of the polyurethane resin and the epoxy resin, thereby being excellent in hydrolysis resistance.

[0101]

Table 1

[0102] [Heat resistance evaluation] The heat resistance of the insulating sheets according to Examples 1 to 3 after the aging treatment and the insulating sheets according to Comparative Examples 2, 4, and 5 after the aging treatment was evaluated. The heat resistance was evaluated using TG-DTA (manufactured by Rigaku Corporation, model TG8120). Specifically, the evaluation of heat resistance was carried out by heating from room temperature (23 ± 2°C) at a rate of 5°C / min in an atmosphere of 100 mL / min of air to obtain a TG-DTA curve, and paying attention to the temperature at which the mass decreased by 10% (10 mass% reduction temperature) and the temperature at which the mass decreased by 50% (50 mass% reduction temperature). Note that the 10 mass% reduction temperature indicates short-term heat resistance, and the 50 mass% reduction temperature indicates long-term heat resistance. The heat resistance was judged based on the following evaluation criteria. Excellent: The 10 mass% reduction temperature is 330°C or higher, and the 50 mass% reduction temperature is 360°C or higher Not acceptable: Others than the above The results of evaluating the heat resistance of Examples 1 to 3 and Comparative Examples 2, 4, and 5 are shown in Table 2 below.

[0103]

Table 2

[0104] From Table 2, it can be seen that the insulating sheets according to Examples 1 to 3 and the insulating sheet according to Comparative Example 4 are all evaluated as "excellent" in terms of heat resistance. On the other hand, it can be seen that the insulating sheets according to Comparative Examples 2 and 5 are both evaluated as "not acceptable" in terms of heat resistance. From these results, it can be seen that the adhesive layer is composed of an adhesive layer (resin composition) containing a polyurethane resin (specifically, a polyurethane resin having a carboxyl group), an epoxy resin, and an isocyanate-based crosslinking agent, and the adhesive (resin composition) contains 10 parts by mass of the isocyanate-based crosslinking agent with respect to a total of 100 parts by mass of the polyurethane resin and the epoxy resin. Even when aged at a relatively low temperature of 40 °C (Examples 1 to 3), it exhibits heat resistance comparable to that of the one aged at a relatively high temperature of 130 °C (Comparative Example 4), that is, it can be seen that it exhibits relatively high heat resistance. Also, when the adhesive layer is not composed of an adhesive (resin composition) containing a polyurethane resin (specifically, a polyurethane resin having a carboxyl group), an epoxy resin, and an isocyanate-based crosslinking agent (in the cases of Comparative Examples 2 and 5), it can be seen that the heat resistance is inferior when aged at a relatively low temperature of 40 °C.

[0105] [Peel Test] Strip-shaped samples with a width of 10 mm were cut out from the insulating sheets according to Examples 1 to 3 after aging treatment and the insulating sheet according to Comparative Example 4 after aging treatment. Then, using a tensile testing machine, in an environment at room temperature (23 °C ± 2 °C) and at a test speed of 300 mm / min, the insulating layer was pulled from the adhesive layer on one side to conduct a 180-degree peel test, and the peel strength (N / 10 mm) at room temperature was determined. The measurement results of the peel strength of the insulating sheets according to Examples 1 to 3 and the insulating sheet according to Comparative Example 4 measured as described above are shown in Table 3 below. In addition, when the peel strength was 3 N / 10 mm or more, the adhesiveness was evaluated as "excellent".

[0106]

Table 3

[0107] From Table 3, it can be seen that the peel strength values of the insulating sheets according to Examples 1 to 3 are higher than those of the insulating sheet according to Comparative Example 4, and since the peel strength is 3 N / 10 mm or more, it can be understood that the evaluation of adhesiveness is also "excellent". From this result, it can be seen that the adhesive layer is composed of an adhesive layer (resin composition) containing a polyurethane resin (specifically, a polyurethane resin having a carboxyl group), an epoxy resin, and an isocyanate-based crosslinking agent, and the adhesive (resin composition) contains 10 parts by mass of the isocyanate-based crosslinking agent with respect to a total of 100 parts by mass of the polyurethane resin and the epoxy resin. Thus, even when aged at a relatively low temperature of 40 °C, it exhibits adhesiveness comparable to or higher than that of the product aged at a relatively high temperature of 130 °C, that is, it exhibits relatively high adhesiveness.

[0108] [Influence of the addition amount of the crosslinking agent] (Test Example 1A) An insulating sheet according to Test Example 1A (thickness of the insulating sheet: 139 μm) was obtained by laminating an insulating layer, an adhesive layer, and a base film into five layers in the same manner as in Example 1, except that the formulation of the adhesive (resin composition) constituting the resin layer was changed. In the insulating sheet according to Test Example 1A, the resin layer was composed of an adhesive (resin composition) containing polyurethane resin A and epoxy resin B and not containing a crosslinking agent. That is, in the adhesive (resin composition) according to Test Example 1A, the addition amount of the crosslinking agent was 0 parts by mass with respect to a total of 100 parts by mass of polyurethane resin A and epoxy resin B. The insulating sheet according to Test Example 1A was aged (crosslinked) at 40 °C for 5 days.

[0109] (Test Example 2A) An insulating sheet according to Test Example 2A (thickness of the insulating sheet: 139 μm) was obtained by laminating an insulating layer, an adhesive layer, and a base film into five layers in the same manner as in Example 1, except that the formulation of the adhesive (resin composition) constituting the resin layer was changed. In the insulating sheet according to Test Example 2A, the resin layer was composed of an adhesive (resin composition) containing polyurethane resin A, epoxy resin B, and isocyanate-based crosslinking agent D (a mixture of the isocyanurate form of HDI and the isocyanurate form of TDI; that is, a mixture of an aliphatic isocyanate and an aromatic isocyanate). Also, in the adhesive (resin composition) according to Test Example 2A, 1 part by mass of isocyanate-based crosslinking agent D was added to a total of 100 parts by mass of polyurethane resin A and epoxy resin B. Note that the insulating sheet according to Test Example 2A was subjected to an aging treatment (crosslinking treatment) at 40°C for 5 days.

[0110] (Test Example 3A) An insulating sheet according to Test Example 3A (thickness of the insulating sheet: 139 μm) was obtained by laminating an insulating layer, an adhesive layer, and a base material film in five layers in the same manner as in Example 1, except that the formulation of the adhesive (resin composition) constituting the resin layer was changed. In the insulating sheet according to Test Example 3A, the resin layer was composed of an adhesive (resin composition) containing polyurethane resin A, epoxy resin B, and isocyanate-based crosslinking agent D. Also, in the adhesive (resin composition) according to Test Example 3A, 2 parts by mass of isocyanate-based crosslinking agent D was added to a total of 100 parts by mass of polyurethane resin A and epoxy resin B. Note that the insulating sheet according to Test Example 3A was subjected to an aging treatment (crosslinking treatment) at 40°C for 5 days.

[0111] (Test Example 4A) An insulating sheet according to Test Example 4A (thickness of the insulating sheet: 139 μm) was obtained by laminating an insulating layer, an adhesive layer, and a base material film in five layers in the same manner as in Example 1, except that the formulation of the adhesive (resin composition) constituting the resin layer was changed. In the insulating sheet according to Test Example 4A, the resin layer was composed of an adhesive (resin composition) containing polyurethane resin A, epoxy resin B, and isocyanate-based crosslinking agent D. In addition, in the adhesive (resin composition) according to Test Example 4A, 3 parts by mass of an isocyanate-based crosslinking agent D was added to a total of 100 parts by mass of polyurethane resin A and epoxy resin B. Note that the insulating sheet according to Test Example 4A was subjected to an aging treatment (crosslinking treatment) at 40°C for 5 days.

[0112] (Test Example 5A) An insulating sheet according to Test Example 5A (thickness of the insulating sheet: 139 μm) was obtained by laminating an insulating layer, an adhesive layer, and a base material film in 5 layers in the same manner as in Example 1, except that the formulation of the adhesive (resin composition) constituting the resin layer was changed. In the insulating sheet according to Test Example 5A, the resin layer was composed of an adhesive (resin composition) containing polyurethane resin A, epoxy resin B, and isocyanate-based crosslinking agent D. In addition, in the adhesive (resin composition) according to Test Example 5A, 10 parts by mass of an isocyanate-based crosslinking agent D was added to a total of 100 parts by mass of polyurethane resin A and epoxy resin B. Note that the insulating sheet according to Test Example 5A was subjected to an aging treatment (crosslinking treatment) at 40°C for 5 days.

[0113] (Test Example 6A) An insulating sheet according to Test Example 6A (thickness of the insulating sheet: 139 μm) was obtained by laminating an insulating layer, an adhesive layer, and a base material film in 5 layers in the same manner as in Example 1, except that the formulation of the adhesive (resin composition) constituting the resin layer was changed. In the insulating sheet according to Test Example 6A, the resin layer was composed of an adhesive (resin composition) containing polyurethane resin A, epoxy resin B, and isocyanate-based crosslinking agent D. In addition, in the adhesive (resin composition) according to Test Example 6A, 20 parts by mass of an isocyanate-based crosslinking agent D was added to a total of 100 parts by mass of polyurethane resin A and epoxy resin B. Note that the insulating sheet according to Test Example 6A was subjected to an aging treatment (crosslinking treatment) at 40°C for 5 days.

[0114] (Test Example 7A) An insulating sheet (thickness of the insulating sheet: 139 μm) according to Test Example 7A was obtained by laminating an insulating layer, an adhesive layer, and a base film in five layers in the same manner as in Example 1, except that the formulation of the adhesive (resin composition) constituting the resin layer was changed. In the insulating sheet according to Test Example 7A, the resin layer was composed of an adhesive (resin composition) containing polyurethane resin A, epoxy resin B, and isocyanate-based crosslinking agent D. In the adhesive (resin composition) according to Test Example 7A, 30 parts by mass of the isocyanate-based crosslinking agent D was added to a total of 100 parts by mass of polyurethane resin A and epoxy resin B. The insulating sheet according to Test Example 7A was subjected to an aging treatment (crosslinking treatment) at 40°C for 5 days.

[0115] (Test Example 8A) An insulating sheet (thickness of the insulating sheet: 139 μm) according to Test Example 8A was obtained by laminating an insulating layer, an adhesive layer, and a base film in five layers in the same manner as in Example 1, except that the formulation of the adhesive (resin composition) constituting the resin layer was changed. In the insulating sheet according to Test Example 8A, the resin layer was composed of an adhesive (resin composition) containing polyurethane resin A, epoxy resin B, and isocyanate-based crosslinking agent D. In the adhesive (resin composition) according to Test Example 8A, 40 parts by mass of the isocyanate-based crosslinking agent D was added to a total of 100 parts by mass of polyurethane resin A and epoxy resin B. The insulating sheet according to Test Example 8A was subjected to an aging treatment (crosslinking treatment) at 40°C for 5 days.

[0116] The insulating sheets according to Test Examples 1A to 8A obtained as described above were evaluated for initial adhesive strength and hydrolysis resistance (moisture and heat resistance). The initial adhesive strength was evaluated by visually observing whether or not the insulating layer lifted from the adhesive layer in the insulating sheets according to Test Examples 1A to 8A after the aging treatment, in the same manner as described above. The hydrolysis resistance was evaluated in the same manner as above. For the insulating sheets according to Test Examples 1A to 8A, which were made into loop-shaped test specimens, after performing a pressure cooker test (PCT) under the conditions of 120°C, 100% relative humidity, and 0.2 MPa of atmospheric pressure, it was determined by observing whether or not the insulation layer lifted from the adhesive layer when visually observing the loop-shaped test specimen. In addition, the pressure cooker test was conducted by exposing the test specimen to the conditions of 120°C, 100% relative humidity, and 0.2 MPa of atmospheric pressure for 48 hours, 96 hours, and 144 hours. The results are shown in Table 4 below.

[0117]

Table 4

[0118] From Table 4, although the evaluation of the initial adhesive strength of the insulating sheets with the addition amount of the curing agent being 0 parts by mass or more and 2 parts by mass or less (the insulating sheets according to Test Examples 1A to 3A) was "excellent", after 48 hours, visually, the insulation layer was observed to lift from the adhesive layer. For the insulating sheets according to Test Examples 1A to 3A, since the insulation layer was visually observed to lift from the adhesive layer after 48 hours, visual observation was not performed after 96 hours and 144 hours. Also, the insulating sheets with the addition amount of the curing agent being 30 parts by mass and 40 parts by mass (the insulating sheets according to Test Examples 7A and 8A) were "inferior" at the time of evaluating the initial adhesive strength. Therefore, for the insulating sheets according to Test Examples 7A and 8A, evaluation by the pressure cooker test was not performed. On the other hand, the insulating sheets with the addition amount of the curing agent being 3 parts by mass or more and 20 parts by mass or less (the insulating sheets according to Test Examples 4A to 6A) had an "excellent" evaluation of the initial adhesive strength, and the evaluations after 48 hours, 96 hours, and 144 hours were also "excellent". That is, even after 144 hours, visually, the insulation layer was not observed to lift from the adhesive layer. From this result, it can be seen that by setting the addition amount of the curing agent to 3 parts by mass or more and 20 parts by mass or less, the insulating sheet becomes excellent in hydrolysis resistance (moisture and heat resistance).

[0119] Also, the heat resistance of the insulating sheets according to Test Examples 1A and 4A to 6A obtained as described above was evaluated. The heat resistance was evaluated in the same manner as described above. Also, the heat resistance was judged based on the following evaluation criteria. Excellent: The 10 mass% reduction temperature is 330 °C or higher, and the 50 mass% reduction temperature is 360 °C or higher. Poor: Other than the above. The results are shown in Table 5 below.

[0120]

Table 5

[0121] From Table 5, it can be seen that the insulating sheets according to Test Examples 4A to 6A, in which the addition amount of the curing agent is 3 parts by mass or more and 20 parts by mass or less, exhibit excellent heat resistance, while the insulating sheet according to Test Example 1A, in which the addition amount of the curing agent is 0 parts by mass, is inferior in heat resistance. In addition, when the peel strength of the insulating sheets according to Test Examples 4A to 6A was measured in the same manner as described above, a value exceeding 3 N / 10 mm was obtained. From this, it can be seen that by setting the addition amount of the curing agent to 3 parts by mass or more and 20 parts by mass or less, the insulating sheet has sufficient adhesiveness.

[0122] [Influence of epoxy equivalent and hydroxyl value of epoxy resin, and hydroxyl value and acid value of polyurethane resin] In order to examine the influence of the epoxy equivalent and hydroxyl value of the epoxy resin, and the hydroxyl value and acid value of the polyurethane resin on the heat resistance of the insulating sheet and the adhesiveness to the adherend, adhesives according to Test Examples 1B to 18B were obtained by using the materials shown in Table 6 below at the compounding ratios shown in Table 6 below.

[0123] As the resin solution containing a polyurethane resin, the resin solutions AA1 to AA3 shown in Synthesis Examples A1 to A3 described below were used.

[0124] As the epoxy resin solution containing an epoxy resin, the epoxy resin solutions BB1 to BB5 shown in Dissolution Examples B1 to B5 of the epoxy resin described below were used.

[0125] As the isocyanate-based crosslinking agent, the isocyanurate form of HDI (C1) (D-170N: manufactured by Mitsui Chemicals, Inc.), the TMP adduct form of TDI (C2) (D-101E: manufactured by Mitsui Chemicals, Inc.), and the isocyanurate form of TDI (C3) (D-204: manufactured by Mitsui Chemicals, Inc.) were used.

[0126]

Table 6

[0127] [Synthesis Example of Polyurethane Resin: A1] A reaction vessel equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen inlet tube, and a manhole was prepared. While replacing the inside of the reaction vessel with nitrogen, 200.0 g of polyhexamethylene carbonate diol having hydroxyl groups at both ends (Duranol: T6002, manufactured by Asahi Kasei Chemicals Corporation, number average molecular weight = 2,000 by terminal functional group quantification method) and 10.0 g of 1,3-butylene glycol were charged. Next, 87.1 g of methyl ethyl ketone (MEK) was charged as a solvent, and the system was stirred. After the system became homogeneous, 51.2 g of 4,4'-diphenylmethane diisocyanate (MDI) 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 the reaction solution with methyl ethyl ketone (MEK) as a solvent, and the absorption at 2,270 cm by the free isocyanate groups measured by infrared absorption spectrum analysis -1The reaction was allowed to proceed until the absorption of disappeared, and a resin solution AA1 containing polyurethane resin A1 was obtained. The obtained resin solution AA1 had a solid content of 30%, and the polyurethane resin A1 had a hydroxyl value of 2.7 mg KOH / g. Also, the weight-average molecular weight of the polyurethane resin A1 measured by GPC was 69,000.

[0128] [Synthesis Example of Polyurethane Resin: A2] The same procedure as described in the above "Synthesis Example of Polyurethane Resin" was carried out.

[0129] [Synthesis Example of Polyurethane Resin: A3] A reaction vessel equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen inlet tube, and a manhole was prepared. While replacing the inside of the reaction vessel with nitrogen, 200.0 g of polyhexamethylene carbonate diol with hydroxyl groups at both ends (Duranol: T6002, manufactured by Asahi Kasei Chemicals Corporation, number-average molecular weight = 2,000 by terminal functional group quantification method) and 10.0 g of 1,3-butylene glycol were charged. Next, 85.8 g of methyl ethyl ketone (MEK) was charged as a solvent, and the system was stirred. After the system became uniform, 47.5 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 the reaction solution with methyl ethyl ketone (MEK) as a solvent, and the absorption at 2,270 cm -1 due to free isocyanate groups measured by infrared absorption spectrum analysis disappeared, and a resin solution AA3 containing polyurethane resin A3 was obtained. The obtained resin solution AA3 had a solid content of 30%, and the polyurethane resin A3 had a hydroxyl value of 9.2 mg KOH / g. Also, the weight-average molecular weight of the polyurethane resin A3 measured by GPC was 24,000.

[0130] [Dissolution Example of Epoxy Resin: B1] The same procedure as described in the above "Dissolution Example of Epoxy Resin" was carried out.

[0131] [Dissolution Example of Epoxy Resin: B2] A reaction vessel equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen inlet tube, and a manhole was prepared. While purging the inside of the reaction vessel with nitrogen, 400.0 g of bisphenol A type epoxy resin (epoxy equivalent: 925 g / eq, jER1004: manufactured by Mitsubishi Chemical Corporation; hereinafter referred to as epoxy resin B2) was charged, and while stirring, 600.0 g of methyl ethyl ketone (MEK) was charged as a solvent. The temperature of the system was raised to 60 °C to completely dissolve epoxy resin B2, and a solution BB2 of epoxy resin B2 (hereinafter referred to as epoxy resin solution BB2) was obtained. The solid content of the obtained epoxy resin solution BB2 was 40%.

[0132] [Example of dissolution of epoxy resin: B3] A reaction vessel equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen inlet tube, and a manhole was prepared. While purging the inside of the reaction vessel with nitrogen, 400.0 g of bisphenol A type epoxy resin (epoxy equivalent: 1975 g / eq, jER1007: manufactured by Mitsubishi Chemical Corporation; hereinafter referred to as epoxy resin B3) was charged, and while stirring, 600.0 g of methyl ethyl ketone (MEK) was charged as a solvent. The temperature of the system was raised to 60 °C to completely dissolve epoxy resin B3, and a solution BB3 of epoxy resin B3 (hereinafter referred to as epoxy resin solution BB3) was obtained. The solid content of the obtained epoxy resin solution BB3 was 40%.

[0133] [Example of dissolution of epoxy resin: B4] A reaction vessel equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen inlet tube, and a manhole was prepared. While purging the inside of the reaction vessel with nitrogen, 400.0 g of bisphenol A type phenoxy resin (epoxy equivalent: 8500 g / eq, jER1256: manufactured by Mitsubishi Chemical Corporation; hereinafter referred to as epoxy resin B4) was charged, and while stirring, 600.0 g of methyl ethyl ketone (MEK) was charged as a solvent. The temperature of the system was raised to 60 °C to completely dissolve epoxy resin B4, and a solution BB4 of epoxy resin B4 (hereinafter referred to as epoxy resin solution BB4) was obtained. The solid content of the obtained epoxy resin solution BB4 was 40%.

[0134] [Example of dissolution of epoxy resin: B5] A reaction vessel equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen inlet tube, and a manhole was prepared. While purging the inside of the reaction vessel with nitrogen, 800.0 g of a bisphenol A novolak type epoxy resin (trifunctional or higher) (epoxy equivalent: 200 g / eq, jER157S70: manufactured by Mitsubishi Chemical Corporation. Hereinafter referred to as epoxy resin B5) was charged, and while stirring, 200.0 g of methyl ethyl ketone (MEK) was charged as a solvent. The temperature of the system was raised to 60 °C to completely dissolve epoxy resin B5, and a dissolved product BB5 of epoxy resin B5 (epoxy resin solution BB5) was obtained. The solid content of the obtained epoxy resin solution BB5 was 80%.

[0135] [Coating on the adhesive film] Using methyl ethyl ketone (MEK), the adhesives of each example were diluted so that the solid content became 25%. In Test Example 1B, the diluted adhesive was applied to the entire one-sided surface of a PET film (length: 210 mm, width: 150 mm, thickness: 100 μm, Lumirror: manufactured by Panac Co., Ltd.), and then dried at 100 °C for 1 minute to produce a PET film with an adhesive layer. Note that the coating was performed so that the thickness of the adhesive layer after drying would be 12 μm. In Test Example 2B, coating was performed in the same manner as in Test Example 1B, except that the PET film was changed to a PEN film (length: 210 mm, width: 150 mm, thickness: 100 μm, Teonex: manufactured by Toyobo Film Solutions Co., Ltd.). Furthermore, in Test Example 3B, coating was performed in the same manner as in Test Example 1B, except that the PET film was changed to a PBT film (length: 210 mm, width: 150 mm, thickness: 25 μm, Bobret: manufactured by Kojin Film & Chemicals Co., Ltd.). In Test Examples 4B - 18B, coating was performed in the same manner as in Test Example 1B, except that the PET film was changed to a PEN film in the same manner as in Test Example 2B.

[0136] [Initial adhesion] The initial adhesion of the films with an adhesive layer of each example was evaluated. Specifically, the evaluation was carried out according to the following procedure. (1) The film with the adhesive layer of each example is superimposed on the aramid paper so that the exposed surface of the adhesive layer of the film with the adhesive layer of each example is in contact with one surface of the aramid paper (having the same shape as the film with the adhesive layer). (2) Using a laminator adjusted to 80° C., the film with the adhesive layer of each example and aramid paper are laminated together to prepare an insulating sheet according to each example. (3) At room temperature (23±2°C), the aramid paper is peeled off from the film with the adhesive layer of each example by pulling it with your hand, and the initial adhesion is evaluated according to the following criteria. Excellent: Material failure occurs in the aramid paper. In other words, a part of one side of the aramid paper remains bonded to the entire area of ​​the contact surface with the adhesive layer, and the remaining aramid paper is peeled off. Good: Part of one side of the aramid paper remains adhered to part of the contact surface with the adhesive layer, and the remaining aramid paper is peeled off. Poor: The aramid paper is easily peeled off and no trace of the aramid paper is found on the surface in contact with the adhesive layer.

[0137] [Peelability] The peelability of the film with the adhesive layer of each example was evaluated using an Autograb (Shimadzu Corporation, Autograph AGS-J500N). Specifically, the evaluation was performed according to the following procedure. (1) The film with the adhesive layer of each example is superimposed on the aramid paper so that the exposed surface of the adhesive layer of the film with the adhesive layer of each example is in contact with one surface of the aramid paper (having the same shape as the film with the adhesive layer). (2) Using a laminator adjusted to 80° C., the film with the adhesive layer of each example and aramid paper are laminated together to prepare an insulating sheet according to each example. (3) Leave the insulating sheets of each example in an oven at a predetermined temperature for a predetermined time to allow the curing reaction to proceed. For the insulating sheets of Test Examples 1B to 17B, leave them in an oven at 50 °C for 72 hours to allow the curing reaction to proceed. On the other hand, for the insulating sheet of Test Example 18B, leave it in an oven at 100 °C for 12 hours to allow the curing reaction to proceed. (4) Cut out a test piece with a size of 25 mm in width and 80 mm in length from the insulating sheet, and perform a peel test on the test piece using an autograph, and evaluate the peelability according to the following criteria. The peel test is performed by a T-peel test, and the tensile speed is 100 mm / min. · Excellent: Material failure occurs in the aramid paper. · Good: No material failure occurs in the aramid paper, and the measured value of the peel strength is 1 N or more. · Poor: The measured value of the peel strength is less than 1 N.

[0138] [Heat resistance evaluation at 255 °C] The heat resistance at 255 °C of the film with an adhesive layer of each example was evaluated. Specifically, the evaluation was carried out according to the following procedure. (1) Overlap the film with an adhesive layer of each example and the aramid paper so that the exposed surface of the adhesive layer of the film with an adhesive layer of each example and one surface of the aramid paper (having the same shape as the film with an adhesive layer) are in contact. (2) Using a laminator adjusted to 80 °C, bond the film with an adhesive layer of each example and the aramid paper to produce an insulating sheet having a three-layer structure according to each example. (3) Apply the adhesive of each example diluted to a solid content of 25% using methyl ethyl ketone (MEK) to the entire surface on the side opposite to the adhesive layer (the first adhesive layer) of the insulating sheet having a three-layer structure of each example, and then dry it at 100 °C for 1 minute to form a second adhesive layer on the insulating sheet having a three-layer structure of each example, and obtain an insulating sheet having a four-layer structure. Note that the coating is performed so that the thickness of the adhesive layer after drying is 12 μm. (4)Superpose the insulating sheet with a four-layer structure in each example and the aramid paper such that the exposed surface of the second adhesive layer in the insulating sheet with a four-layer structure in each example contacts one surface of the aramid paper (having the same shape as the film with the adhesive layer). (5)Using a laminator adjusted to 80°C, bond the insulating sheet with a four-layer structure in each example and the aramid paper to produce an insulating sheet with a five-layer structure according to each example. That is, produce an insulating sheet in which aramid paper / second adhesive layer / film / first adhesive layer / aramid paper are arranged in this order. (6)Leave the insulating sheet with a five-layer structure in each example in an oven at a predetermined temperature for a predetermined time to allow the curing reaction to proceed in the second adhesive layer. For the insulating sheets of Test Examples 1B to 17B, leave them in an oven at 50°C for 72 hours to allow the curing reaction to proceed. On the other hand, for the insulating sheet of Test Example 18B, leave it in an oven at 100°C for 12 hours to allow the curing reaction to proceed. (7)Cut out specimens with a planar size of 5 cm × 5 cm from the insulating sheet with a five-layer structure in each example, and leave each specimen in an oven at 255°C for 24 hours. Then, evaluate the heat resistance of each specimen according to the following criteria. · Excellent: After treatment at 255°C, no deformation is observed in the insulating sheet, and no peeling is observed. · Good: After treatment at 255°C, deformation is observed in the insulating sheet, but no peeling or excessive swelling is observed. · Poor: After treatment at 255°C, peeling is observed in the insulating sheet, and excessive swelling is observed.

[0139] [Evaluation of heat resistance by thermogravimetric differential thermal analysis (TG-DTA)] Evaluate the heat resistance of the adhesives in each example by thermogravimetric differential thermal analysis (TG-DTA). Specifically, the evaluation was carried out according to the following procedure. (1)Using methyl ethyl ketone (MEK), coat the entire one surface of the release paper with the adhesive in each example diluted to a solid content of 30%, and then dry it at 100°C for 1 minute to produce a release paper with an adhesive layer in each example. In addition, the coating is performed such that the thickness of the adhesive layer after drying becomes 12 μm. (2) The release paper with the adhesive layer in each example is left in an oven at a predetermined temperature for a predetermined time to allow the curing reaction to proceed in the adhesive layer. For the release papers with the adhesive layers in Test Examples 1B to 17B, they are left in an oven at 50 °C for 72 hours to allow the curing reaction to proceed. On the other hand, for the release paper with the adhesive layer in Test Example 18B, it is placed in an oven at 100 °C for 12 hours to allow the curing reaction to proceed. After allowing the curing reaction to proceed, the release paper is peeled off from the release papers with the adhesive layers in each test example. (3) Using a thermogravimetric differential thermal analyzer (TG8120, manufactured by Rigaku Corporation), under an atmosphere of 100 mL / min of air, the temperature is raised from room temperature (23 ± 2 °C) at a rate of 5 °C / min to obtain the TG-DTA curve for the adhesive layer of each test example peeled off from the release paper. Then, paying attention to the temperature at which 5% of the mass is reduced (5% weight loss temperature) and the temperature at which 50% of the mass is reduced (50% weight loss temperature), the heat resistance is judged. Incidentally, the 5% weight loss temperature in the TG-DTA curve indicates short-term heat resistance, and the 50% weight loss temperature in the TG-DTA curve indicates long-term heat resistance. The heat resistance in thermogravimetric differential thermal analysis (TG-DTA) is evaluated according to the following criteria. · Excellent: The 5% weight loss temperature is 280 °C or higher, and the 50% weight loss temperature is 350 °C or higher. · Good: The 5% weight loss temperature is 200 °C or higher and less than 280 °C, and the 50% weight loss temperature is 300 °C or higher and less than 350 °C. · Poor: The 5% weight loss temperature is less than 200 °C, and the 50% weight loss temperature is less than 300 °C.

[0140]

Table 7

[0141] From the results shown in Table 7, it can be seen that Test Examples 1B to 13B, despite allowing the curing reaction to proceed at a relatively low temperature of 50°C, are evaluated as excellent in terms of initial adhesion, peelability, heat resistance evaluation at 255°C, and heat resistance evaluation by thermogravimetric differential analysis (TG-DTA), similar to Test Example 18B where the curing reaction proceeded at a relatively high temperature of 100°C. On the other hand, it can be seen that Test Examples 14B to 17B are evaluated as having a failure in any of the items in terms of initial adhesion, peelability, heat resistance evaluation at 255°C, and heat resistance evaluation by thermogravimetric differential analysis (TG-DTA). From this, it is understood that by using a polyurethane resin with a hydroxyl value of 0.1 mgKOH / g or more and 20 mgKOH / g or less, an epoxy resin with an epoxy equivalent of 450 g / eq or more and 3000 g / eq or less and a hydroxyl value of 50 mgKOH / g or more and 250 mgKOH / g or less, and at least one selected from the group consisting of aliphatic isocyanates and aromatic isocyanates as an isocyanate-based crosslinking agent, the insulating sheet can have relatively sufficient heat resistance without aging at a relatively high temperature, and moreover, can have relatively excellent adhesiveness to the adherend after the crosslinking reaction.

Explanation of Symbols

[0142] 1 Stator, 10 Insulating sheet, 20 Stator core, 30 Coil, 21 Slot groove, 22 Plate-like protrusion (teeth), 31 Segment conductor, 10a Base film, 10a1 Overlapping part, 10b1 Adhesive layer, 10b2 Adhesive layer, 10c1 Insulating layer, 10c2 Insulating layer, 20a End face (upper end face), 20b End face (lower end face), 21a Linear opening, 21b Opening, 22a Wide part, 31a Head, 31b Leg, 31bx Tip, 31x Connection part, AD Axial direction of rotation, RD Circumferential direction, DD Radial direction.

Claims

1. A base film, and an insulating layer laminated on at least one surface of the base film via an adhesive layer, wherein the adhesive layer is composed of a resin composition containing a polyurethane resin, an epoxy resin, and an isocyanate-based crosslinking agent, the resin composition contains at least one selected from the group consisting of an aliphatic isocyanate and an aromatic isocyanate as the isocyanate-based crosslinking agent, the polyurethane resin is a hydroxyl group-containing polyurethane resin having a hydroxyl group at its terminal, and the hydroxyl value of the hydroxyl group-containing polyurethane resin is 0.1 mgKOH / g or more and 20 mgKOH / g or less. An insulating sheet.

2. The polyurethane resin has a carboxyl group. The insulating sheet according to Claim 1.

3. The epoxy resin contains a hydroxyl group-containing epoxy resin having a hydroxyl group. The insulating sheet according to Claim 1 or 2.

4. The aliphatic isocyanate is at least one of hexamethylene diisocyanate and isophorone diisocyanate, and the aromatic isocyanate is at least one of diphenylmethane diisocyanate and tolylene diisocyanate. The insulating sheet according to any one of Claims 1 to 3.

5. Based on 100 parts by mass of the total amount of the polyurethane resin and the epoxy resin, the isocyanate-based crosslinking agent is contained in an amount of 3 parts by mass or more and 20 parts by mass or less. The insulating sheet according to any one of Claims 1 to 4.

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