insulating sheet

Abstract

The insulating sheet of the present application comprises: a base material film, and an insulating layer laminated to at least one side of the base material film by means of an adhesive layer, the aforementioned adhesive layer being composed of a resin composition comprising a polyurethane resin, an epoxy resin, and an isocyanate-based crosslinking agent, the aforementioned resin composition comprising at least one selected from the group consisting of aliphatic isocyanate and aromatic isocyanate as the aforementioned isocyanate-based crosslinking agent.

Description

Technical Field

[0001] This invention relates to insulating sheets. More specifically, it relates to insulating sheets used as insulating sheets for electric motors in eco-friendly vehicles such as electric vehicles (EVs) and hybrid electric vehicles (HEVs). Background Technology

[0002] Previously, oil-cooled drive motors were known to be used as drive motors in eco-friendly vehicles such as EVs and HEVs. These oil-cooled drive motors consist of a rotor and a stator, the stator generating the force required to rotate the rotor.

[0003] The aforementioned stator has multiple coils, and Lorentz force is obtained by generating a magnetic field in these multiple coils.

[0004] Then, the aforementioned stator rotates the aforementioned rotor through the Lorentz force.

[0005] In the oil-cooled drive motor described above, the aforementioned coil is composed of multiple segment conductors connected to each other, and is typically mounted on a component called the stator core or rotor core, which is made of stacked magnetic steel plates.

[0006] In the oil-cooled drive motor described above, the stator core, rotor core, and other cores have multiple grooves, and the aforementioned coils are accommodated in each of the aforementioned multiple grooves.

[0007] Furthermore, in the oil-cooled drive motor described above, an insulating sheet for ensuring insulation between the coil and the inner wall of the groove is housed together with the coil within each of the grooves. More specifically, the insulating sheet is housed within the grooves in a manner that surrounds the coil.

[0008] Furthermore, the coil surrounded by the aforementioned insulating sheet is fixed in the aforementioned groove by an insulating resin (e.g., epoxy varnish) impregnated in the aforementioned groove.

[0009] In addition, the aforementioned insulating sheet, for example as described in Patent Document 1 below, employs a five-layer structure comprising a substrate film (polyethylene terephthalate resin film) and a surface film (polyethylene naphthalate resin film) laminated on both surfaces of the substrate film by means of an adhesive layer, wherein the adhesive layer is formed of an adhesive comprising an acrylic resin or the like.

[0010] Furthermore, for the aforementioned insulating sheet, in order to thermally crosslink the resin such as acrylic resin to improve the heat resistance of the aforementioned adhesive layer, it is usually cured at a higher temperature (e.g., 130°C) for a specified time (e.g., 24 hours) while contained in the aforementioned trench.

[0011] Existing technical documents

[0012] Patent documents

[0013] Patent Document 1: Japanese Patent Application Publication No. 2016-165806 Summary of the Invention

[0014] The problem the invention aims to solve

[0015] However, when the aforementioned insulating sheet is used for an oil-cooled drive motor, as described above, the process of curing the resin at a higher temperature to thermally crosslink the acrylic resin or the like increases the number of operations required before assembling the aforementioned oil-cooled drive motor onto the vehicle body, and therefore cannot be considered preferred.

[0016] Furthermore, from the perspective of the equipment required for aging, it cannot be considered the preferred option.

[0017] On the other hand, if the curing is not carried out at a higher temperature, as mentioned above, the resins such as acrylic resins cannot be fully thermally cross-linked, and therefore the heat resistance of the aforementioned insulating sheet deteriorates.

[0018] Thus, there is a trade-off between imparting heat resistance to the insulating sheet and increasing the number of workers required to assemble the aforementioned oil-cooled drive motor into the vehicle body, and research to solve this problem is not yet sufficient.

[0019] In addition, for the aforementioned insulating sheet, it is also required that the adhesive layer has excellent adhesion to the adherend (the substrate film and the surface film in the insulating sheet of Patent Document 1) after the cross-linking reaction.

[0020] Therefore, the objective of this invention is to provide an insulating sheet that has sufficient heat resistance even without curing at high temperatures, and also exhibits excellent adhesion to the adherend after the crosslinking reaction.

[0021] Solution for solving the problem

[0022] The insulating sheet of the present invention comprises:

[0023] Substrate film, and

[0024] An insulating layer is laminated onto at least one side of the substrate film using an adhesive layer.

[0025] The aforementioned adhesive layer is composed of a resin composition comprising polyurethane resin, epoxy resin, and isocyanate-based crosslinking agent.

[0026] The aforementioned resin composition comprises at least one selected from the group consisting of aliphatic isocyanates and aromatic isocyanates as the aforementioned isocyanate-based crosslinking agent. Attached Figure Description

[0027] Figure 1A cross-sectional view showing the structure of an insulating sheet according to one embodiment of the present invention.

[0028] Figure 2 A three-dimensional schematic diagram of the stator of an oil-cooled drive motor for electric vehicles (EVs) and hybrid electric vehicles (HEVs).

[0029] Figure 3 This is a top view of the stator core.

[0030] Figure 4 for Figure 3 Enlarged view of part A.

[0031] Explanation of reference numerals in the attached figures

[0032] 1 stator, 10 insulating sheets, 20 stator core, 30 coils, 21 grooves, 22 plate-shaped protrusions (teeth), 31 segmented conductors,

[0033] 10a Substrate film, 10a1 Repeating portion, 10b1 Adhesive layer, 10b2 Adhesive layer, 10c1 Insulating layer, 10c2 Insulating layer, 20a End face (top end face), 20b End face (bottom end face), 21a Linear opening, 21b Opening, 22a Wide portion, 31a Head, 31b Foot, 31bx Front end portion, 31x Connecting portion.

[0034] AD is the direction of rotation axis, RD is the circumferential direction, and DD is the radial direction. Detailed Implementation

[0035] The following describes one embodiment of the present invention.

[0036] It should be noted that the following example illustrates an insulating sheet formed by laminating an insulating layer onto both surfaces of a substrate film using an adhesive layer.

[0037] That is, an example of an insulating sheet consisting of a 5-layer structure will be given for illustration.

[0038] like Figure 1 As shown, the insulating sheet 10 of this embodiment includes: a substrate film 10a, and insulating layers 10c1 and 10c2 that are laminated on both surfaces of the substrate film 10a by means of adhesive layers 10b1 and 10b2.

[0039] The insulating sheet 10 of this embodiment is used, for example, as an insulating sheet for an oil-cooled drive motor in an automobile. That is, the insulating sheet 10 of this embodiment is used, for example, as an insulating sheet for a drive motor cooled by cooling oil (ATF, etc.). Examples of such automobiles include electric vehicles (EVs) and hybrid electric vehicles (HEVs).

[0040] In the insulating sheet 10 of this embodiment, the substrate film 10a is preferably a polyester film made of polyester resin. Examples of polyester resins include polybutylene terephthalate (PBT) resin, polyethylene terephthalate (PET) resin, polybutylene naphthalate (PBN) resin, polyethylene naphthalate (PEN) resin, and polyethylene terephthalate 1,4-cyclohexanediol resin.

[0041] Of these, the polyester resin constituting the polyester film is preferably either PET resin or PEN resin. That is, the polyester film is preferably either PET film or PEN film.

[0042] Alternatively, the substrate film 10a may also be a polyimide film made of polyimide (PI) resin.

[0043] The thickness of the substrate 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.

[0044] The thickness of the substrate film 10a can be obtained by measuring the thickness at 10 randomly selected locations using a digital micrometer and then arithmetically averaging these measurements.

[0045] As the substrate film 10a, either a stretched film or an unstretched film (unstretched film) can be used, but a stretched film is preferred, and a biaxially stretched film is more preferred.

[0046] Furthermore, when the substrate film 10a is a PET film or a PEN film, the film is preferably composed of low-molecular-weight oligomers with an oligomer content of 1% by mass or less. By composing the aforementioned film from low-molecular-weight oligomers, the substrate film 10a exhibits excellent hydrolysis resistance.

[0047] When the substrate film 10a is a PEN film and is a low-volume oligomer, the substrate film 10a exhibits particularly excellent hydrolysis resistance.

[0048] The oligomer content can be determined, for example, as described below.

[0049] (1) After cleaning the roughly square film sample with one side of about 5 cm with methanol, the film sample was dried in a hot air oven at 160℃ for 1 hour and the initial mass (M1(g)) was calculated.

[0050] (2) The aforementioned film sample was extracted for 48 hours using a Soxhlet extractor or similar device and boiling xylene (approximately 400 mL).

[0051] (3) Determine the mass (M2(g)) of the extracted film sample and calculate the proportion of mass reduction (M1-M2) relative to the initial mass (M1) ((M1-M2) / M1).

[0052] Here, regarding the mass (M2(g)) of the extracted film sample, if the measurement is not performed after the xylene used in the extraction process has been sufficiently removed from the film sample, the mass reduction cannot be accurately determined.

[0053] Therefore, it is preferable to wash the film sample with water after xylene extraction, gently wipe off the xylene adhering to the surface, and then dry it in a hot air oven at 160°C for 8 hours, and then perform the measurement after cooling in a desiccator.

[0054] In the insulating sheet 10 of this embodiment, the insulating layers 10c1 and 10c2 are respectively composed of paper-like sheets formed using fibers.

[0055] Fibers used to form paper-like sheets include organic fibers such as aromatic polyamide fibers, polysulfide fibers, polyphenylene sulfide fibers, polypropylene fibers, polyetheretherketone fibers, polyethylene terephthalate fibers, acrylate fibers, and polyethylene naphthalate fibers, as well as inorganic fibers such as glass fibers, rock wool, asbestos, boron fibers, alumina fibers, and carbon fibers. Additionally, natural fibers such as silk and cotton, and semi-synthetic fibers such as cellulose can also be included.

[0056] It should be noted that the paper-like sheet can be formed using only one type of fiber, or it can be obtained by mixing multiple types of fibers.

[0057] Among these, paper-like sheets made primarily of aromatic polyamide fibers, known as "aramid paper," also exhibit excellent sliding properties and are suitable.

[0058] As such aramid paper, a sheet-like material can be formed using fibers (fully aromatic polyamide fibers) made primarily of resin materials composed of benzene rings other than amide groups, such as condensation polymers of phenylenediamine and phthalic acid.

[0059] The thickness of the insulating layers 10c1 and 10c2 is 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 aforementioned paper-like sheet is aramid paper, by making the thickness within the numerical range described above, high mechanical properties can be imparted to the insulating sheet 10, and excellent shape retention can be achieved during bending processing.

[0060] The aforementioned insulating layers 10c1 and 10c2 may have the same thickness or different thicknesses, but preferably have the same thickness.

[0061] A coating containing polyamide resin can be applied to the surface of at least one of the insulating layers 10c1 and 10c2 to form a film. In this case, the aforementioned film becomes part of the surface of the insulating sheet 10.

[0062] It should be noted that, as the polyamide contained in the aforementioned coating, a methoxymethylated polyamide resin in which at least a portion of the amide group is methoxymethylated may be used.

[0063] In the insulating sheet 10 of this embodiment, the adhesive layers 10b1 and 10b2 are composed of a resin composition comprising polyurethane resin, epoxy resin and isocyanate-based crosslinking agent.

[0064] In the insulating sheet 10 of this embodiment, the aforementioned resin composition includes at least one selected from the group consisting of aliphatic isocyanates and aromatic isocyanates as the aforementioned isocyanate-based crosslinking agent.

[0065] The insulating sheet 10 of this embodiment, being constructed as described above, exhibits sufficient heat resistance even when cured at relatively low temperatures (temperatures below 60°C, for example, 40°C), and also demonstrates superior adhesion to the adhered material after the crosslinking reaction.

[0066] It should be noted that in the insulating sheet 10 of this embodiment, the aforementioned adhered material is the substrate film 10a and the insulating layers 10c1 and 10c2.

[0067] Polyurethane resin is obtained by reacting a polyol component containing two or more hydroxyl groups in one molecule with a polyisocyanate component containing two or more isocyanate groups in one molecule with urethane bonding.

[0068] In the insulating sheet 10 of this embodiment, the aforementioned polyurethane resin preferably has carboxyl groups.

[0069] That is, the aforementioned polyurethane resin is preferably a polyurethane resin having carboxyl groups.

[0070] When the aforementioned polyurethane resin is a polyurethane resin with carboxyl groups, the polyurethane resin is usually grafted with multiple epoxy resins.

[0071] That is, when the aforementioned polyurethane resin is a polyurethane resin with carboxyl groups, the adhesive layers 10b1 and 10b2 typically contain the following structure: multiple epoxy resins are bonded to the carboxyl groups of the main chain having a polyurethane structure by means of epoxy groups.

[0072] As described above, when the polyurethane resin is a polyurethane resin with carboxyl groups, the adhesive layers 10b1 and 10b2 typically contain the following structure (urethane-epoxy graft): multiple epoxy resins are bonded to the carboxyl groups of the main chain having a polyurethane structure by means of epoxy groups.

[0073] It is believed that when this urethane-epoxy graft coexists with an isocyanate-based crosslinking agent (selected from at least one of the group consisting of aliphatic isocyanates and aromatic isocyanates), at a relatively low temperature (below 60°C, for example, 40°C), the crosslinking reaction proceeds sufficiently at the ends of the main chain having the urethane structure, as described above, through the sufficient reaction between the isocyanate groups and hydroxyl groups of the isocyanate-based crosslinking agent. In particular, when the aforementioned isocyanate-based crosslinking agent is at least one of the group consisting of aliphatic polyisocyanates and aromatic polyisocyanates, the crosslinking reaction at the aforementioned lower temperature is believed to be significantly advanced.

[0074] In addition, as described later, epoxy resins are typically difunctional or multifunctional. Since they have more than two epoxy groups in one molecule, in the urethane-epoxy graft as described above, at least one epoxy group remains in one molecule of epoxy resin that has not been polymerized with the aforementioned carboxyl group of the urethane resin having a carboxyl group.

[0075] Thus, in the aforementioned urethane-epoxy graft, since there are residual epoxy groups that have not polymerized with the aforementioned carboxyl groups of the urethane resin having carboxyl groups, these epoxy groups also contribute to the crosslinking reaction in the adhesive layers 10b1 and 10b2.

[0076] For the reasons stated above, when the polyurethane resin is a polyurethane resin containing carboxyl groups, the crosslinking reaction can proceed sufficiently at lower temperatures (temperatures below 60°C, for example, 40°C). Therefore, it is believed that the insulating sheet 10 of this embodiment has not only more sufficient heat resistance, but also better adhesion to the adherends (insulating layers 10c1, 10c2 and substrate film 10a) after the crosslinking reaction.

[0077] When the aforementioned polyurethane resin is a polyurethane resin containing carboxyl groups, the acid value of the polyurethane resin containing carboxyl groups is preferably 5 mg KOH / g or more and 30 mg KOH / g or less, more preferably 9 mg KOH / g or more and 25 mg KOH / g or less.

[0078] By setting the acid value of the aforementioned polyurethane resin containing carboxyl groups within the above-mentioned range, the reaction with the aforementioned isocyanate-based crosslinking agent can be carried out appropriately.

[0079] Furthermore, by ensuring the acid value of the aforementioned carboxyl-containing polyurethane resin is within the above-mentioned range, a higher crosslinking density with the epoxy resin can be achieved. Therefore, when the aforementioned resin composition undergoes crosslinking to form a cured product, the cured product exhibits excellent long-term heat resistance. Additionally, deformation can be more effectively suppressed, resulting in excellent flexibility of the cured product.

[0080] It should be noted that the acid value of the aforementioned polyurethane resin can be determined by solvating the aforementioned polyurethane resin with methyl ethyl ketone (MEK) or the like, and then measuring it according to the method of JIS K1557-5:2007.

[0081] The aforementioned polyurethane resin is preferably a hydroxyl-containing polyurethane resin having hydroxyl groups at the ends.

[0082] By using the aforementioned hydroxyl-containing polyurethane resin, the reaction with the aforementioned isocyanate-based crosslinking agent can be carried out appropriately.

[0083] The hydroxyl value of the aforementioned hydroxyl-containing polyurethane resin is preferably 0.1 mg KOH / g or more and 20 mg KOH / g or less, more preferably 1 mg KOH / g or more and 15 mg KOH / g or less.

[0084] The hydroxyl value of the aforementioned hydroxyl-containing polyurethane resin can be determined according to JIS K1557-1:2007.

[0085] In the insulating sheet of this embodiment, the aforementioned polyurethane resin is preferably cross-linked together with the aforementioned epoxy resin using the aforementioned isocyanate-based cross-linking agent.

[0086] Specifically, in the insulating sheet of this embodiment, the aforementioned polyurethane resin and epoxy resin are preferably cross-linked at a relatively low temperature (below 60°C, for example, 40°C) using the aforementioned isocyanate-based cross-linking agent.

[0087] As described above, when the aforementioned polyurethane resin has a carboxyl group, the aforementioned carboxyl group can be imparted to the aforementioned polyurethane resin by being contained in the aforementioned polyol component and the aforementioned polyisocyanate component.

[0088] The aforementioned carboxyl group can be imparted to the aforementioned polyurethane resin by including a hydroxyl-containing compound having a carboxyl group in the aforementioned polyol component. In this case, the polyol component preferably includes a hydroxyl-containing compound having a carboxyl group and a conventional polyol.

[0089] The aforementioned hydroxyl-containing compounds with carboxyl groups have two or more hydroxyl groups per molecule. Therefore, reacting them with polyisocyanate components that have two or more isocyanate groups per molecule yields polyurethane resins.

[0090] Examples of hydroxyl-containing compounds with carboxyl groups include dimethylolpropionic acid, dimethylolbutyric acid, their low-molar adducts of alkyl epoxides (number-average molecular weight Mn less than 500), low-molar adducts of γ-caprolactam (number-average molecular weight Mn less than 500), hemiesters derived from acid anhydrides and glycerol, and compounds derived from monomers containing hydroxyl and unsaturated groups via free radical reactions with monomers containing carboxyl and unsaturated groups. These compounds can be used alone or in combination of two or more.

[0091] It should be noted that the number-average molecular weight Mn in this specification refers to the value measured using the terminal functional group quantitative method.

[0092] Among these, hydroxyl compounds with carboxyl groups are preferably dimethylolpropionic acid and dimethylolbutyric acid, with dimethylolpropionic acid being particularly preferred.

[0093] As the aforementioned common polyol, conventionally known polyols used in the synthesis of polyurethane resins can be used.

[0094] Specific examples of such polyols include polyester polyols, polyether polyols, polycarbonate polyols, and other polyols.

[0095] Examples of polyester polyols include substances obtained by polycondensation of aliphatic dicarboxylic acids (such as succinic acid, adipic acid, sebacic acid, glutaric acid, azelaic acid, etc.) and aromatic dicarboxylic acids (such as isophthalic acid, terephthalic acid, etc.) with low molecular weight diols (such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,6-hexamethylenediol, neopentyl glycol, 1,4-dihydroxymethylcyclohexane, etc.).

[0096] Specific examples of such polyester polyols include polyethylene adipate diol, polybutylene adipate diol, polyhexamethylene adipate diol, polypentylene adipate diol, polyethylene / butylene adipate diol, polypentyl / hexane adipate diol, poly-3-methylpentanediol adipate diol, polybutylene isophthalate diol, polycaprolactone diol, and poly-3-methylpentanediol.

[0097] Polyester polyols have superior heat resistance compared to polyether polyols. Therefore, by including polyester polyols in the aforementioned polyol components, the heat resistance of adhesive layers 10b1 and 10b2 can be further improved.

[0098] Specific examples of polyether polyols include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and their random / block copolymers.

[0099] Polyether polyols exhibit superior hydrolysis resistance compared to polyester polyols. Therefore, by including polyether polyols in the aforementioned polyol components, the hydrolysis resistance of adhesive layers 10b1 and 10b2 can be further improved.

[0100] Specific examples of polycarbonate polyols include polytetramethylene carbonate diol, polypentamethylene carbonate diol, polyneoplastic carbonate diol, polyhexamethylene carbonate diol, poly(1,4-cyclohexanedimethylene carbonate) diol, and their random / block copolymers.

[0101] As a polycarbonate polyol, by using various polycarbonate diols as described above, it is possible to incorporate carbonate diol structural units into the aforementioned polyurethane resin.

[0102] Polycarbonate polyols have excellent heat resistance and hydrolysis resistance. Therefore, by including polycarbonate polyols in the aforementioned polyol components, the heat resistance and hydrolysis resistance of adhesive layers 10b1 and 10b2 can be further improved.

[0103] Among polycarbonate polyols, polyhexamethylene carbonate is preferred from the perspectives of cost and ease of acquisition.

[0104] Other specific examples of polyols include dimer diols, their hydrogenation, polybutadiene polyols, their hydrides, polyisoprene polyols, their hydrides, acrylic polyols, epoxy polyols, polyether ester polyols, siloxane-modified polyols, α,ω-polymethyl methacrylate diol, α,ω-polybutyl methacrylate diol, and siloxane-modified polyols.

[0105] Among other polyols, the hydrides of dimer diols and polybutadiene polyols have excellent heat resistance and hydrolysis resistance. Therefore, by including these polyols in the aforementioned polyol components, the heat resistance and hydrolysis resistance of adhesive layers 10b1 and 10b2 can be made even better.

[0106] The number-average molecular weight Mn of the polyol (the value measured by the terminal functional group quantitative method) is not particularly limited, but is preferably 500 or more and 6000 or less.

[0107] By ensuring that the number-average molecular weight Mn of the polyol is within the range mentioned above, the cohesive force of the urethane bond is more readily apparent, thus improving mechanical properties.

[0108] It should be noted that when the polyol is crystalline, if the number-average molecular weight Mn is too high, it may sometimes cause whitening in the adhesive layers 10b1 and 10b2. Therefore, when using crystalline polyols alone, it is preferable to use polyols with a number-average molecular weight Mn of 3000 or less.

[0109] It should be noted that the above polyols can be used alone or in combination of two or more.

[0110] In addition to the polyols mentioned above, short-chain diols may also be used as polyol components as needed.

[0111] Specific examples of short-chain diols include aliphatic diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,6-hexamethylenediol, and neopentyl glycol, and their low-molar additions of epoxides (with a number-average molecular weight Mn below 500 based on the terminal functional group quantification method); alicyclic diols such as 1,4-dihydroxymethylcyclohexane and 2-methyl-1,1-cyclohexanediethanol, and their low-molar additions of epoxides (with a number-average molecular weight Mn below 500 based on the terminal functional group quantification method); aromatic diols such as diphenyl diol, and their low-molar additions of epoxides (with a number-average molecular weight Mn below 500 based on the terminal functional group quantification method); bisphenol A, thiobisphenol, and sulfone bisphenol (Sulfone). Bisphenols such as bisphenol, and their low molar adducts of epoxides (with a number-average molecular weight Mn of less than 500 based on the quantitative method of terminal functional groups).

[0112] Among the short-chain diols mentioned above, ethylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,6-hexamethylenediol, neopentyl glycol, etc. are preferred, with ethylene glycol, 1,3-butanediol, and 1,4-butanediol being particularly preferred.

[0113] These short-chain diols can be used alone or in combination of two or more.

[0114] It should be noted that, in the production of polyurethane resin, polyol compounds can also be used as materials for the polyurethane resin, similar to short-chain diol components. Specific examples of polyol compounds include glycerol, trimethylolethane, trimethylolpropane, pentaerythritol, tris(2-hydroxyethyl)isocyanurate, 1,1,1-trimethylolethane, and 1,1,1-trimethylolpropane.

[0115] As a polyisocyanate component, conventionally known polyisocyanate components used in the manufacture of polyurethane resins can be used.

[0116] Specific examples of polyisocyanate components include toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, mixtures thereof, 4-methoxy-1,3-phenyl diisocyanate, 4-isopropyl-1,3-phenyl diisocyanate, 4-chloro-1,3-phenyl diisocyanate, 4-butoxy-1,3-phenyl diisocyanate, 2,4-diisocyanate diphenyl ether, 4,4'-methylene bis(phenyl isocyanate) (MDI) and crude MDI or polymeric MDI, Durylene diisocyanate, phenyl dimethyl diisocyanate (XDI), 1,5-naphthalene diisocyanate, benzidine diisocyanate, o-nitrobenzidine diisocyanate, and 4,4'-diisocyanate dibenzyl (4,4'-Diisocyanate). Aromatic diisocyanates such as dibenzyl; aliphatic diisocyanates such as methylene diisocyanate, 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, and 1,10-dedecimethylene diisocyanate; alicyclic diisocyanates such as 1,4-cyclohexane diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), and hydrogenated XDI; and polyurethane prepolymers obtained by reacting the diisocyanates mentioned above with low molecular weight polyols in a manner where the ends are isocyanates.

[0117] From the viewpoint of obtaining industrially stable, inexpensive, and heat-resistant adhesive layers 10b1 and 10b2, aromatic isocyanates are preferred among the above-mentioned polyisocyanate components. Among aromatic isocyanates, toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, mixtures thereof, 4,4'-methylenebis(phenyl isocyanate) (MDI), crude MDI, or polymeric MDI are particularly preferred.

[0118] As the aforementioned polyisocyanate component, by using aromatic isocyanates, the aforementioned polyurethane resin can possess the structural units of aromatic isocyanates.

[0119] The above-mentioned polyisocyanate components can be used alone or in combination of two or more.

[0120] The aforementioned polyurethane resin can be manufactured using conventionally known methods for manufacturing polyurethane.

[0121] Specifically, firstly, a polyurethane resin is obtained by reacting a reaction composition containing a hydroxyl-containing compound with a carboxyl group, a polyol, a polyisocyanate component, and a short-chain polyol used as a chain extender as needed, in the presence or absence of an organic solvent that does not contain active hydrogen in the molecule.

[0122] The aforementioned reaction composition is typically set with an isocyanate group to hydroxyl group equivalent ratio of 0.8 to 1.25.

[0123] In addition, the reaction can be carried out in one step or in multiple stages at a temperature of typically 20–150°C, preferably 60–110°C.

[0124] 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.

[0125] By ensuring that the mass-average molecular weight Mw of the aforementioned polyurethane resin is within the range described above, the polyurethane resin can more effectively exhibit properties such as flexibility, adhesion, and heat resistance.

[0126] It should be noted that the weight-average molecular weight (Mw) of the aforementioned polyurethane resin refers to the value measured using gel permeation chromatography (GPC). For example, the following apparatus and conditions can be used for determination.

[0127] (1) Equipment: Trade name "HLC-8020" (manufactured by Tosoh Corporation)

[0128] (2) Column: Trade names "TSKgel G2000HXL", "G3000HXL", "G4000GXL" (manufactured by Tosoh Corporation)

[0129] (3) Solvent: THF

[0130] (4) Flow rate: 1.0 ml / min

[0131] (5) Sample concentration: 2 g / L

[0132] (6) Injection volume: 100 μL

[0133] (7) Temperature: 40℃

[0134] (8) Detector: Model "RI-8020" (manufactured by Tosoh Corporation)

[0135] (9) Standard material: TSK standard polystyrene (manufactured by Tosoh Corporation)

[0136] In this embodiment, a catalyst may be used as needed in the synthesis of polyurethane resin.

[0137] Examples of catalysts mentioned above include dibutyltin dilaurate, dioctyltin dilaurate, stannous octoate, zinc octoate, tetra-n-butyl titanate, salts of metals and organic or inorganic acids, organometallic derivatives, organic amines such as triethylamine, and diazabicycloundecene catalysts.

[0138] The aforementioned catalysts promote the synthesis reaction of polyurethane resins.

[0139] On the other hand, if the aforementioned catalyst is used in excess, there is a concern that it may induce a decomposition reaction that causes substances other than polyurethane resin to decompose. As a result, there is a concern that the heat resistance of the obtained adhesive in high-temperature areas (e.g., 255°C) and its long-term heat resistance may deteriorate.

[0140] Therefore, when using the aforementioned catalyst, it is preferable to use an appropriate amount of the aforementioned catalyst.

[0141] The aforementioned polyurethane resin can be synthesized without the use of organic solvents or with the use of organic solvents.

[0142] As the aforementioned organic solvent, an organic solvent that is inactive to the isocyanate group or an organic solvent with low activity to the isocyanate group compared to the reactant can be used.

[0143] Specific examples of the aforementioned organic solvents include: ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; aromatic hydrocarbon solvents such as toluene, xylene, Swazole (trade name, manufactured by Cosmo Oil Co., Ltd.), and Solvesso (trade name, manufactured by ExxonMobil Corporation); aliphatic hydrocarbon solvents such as n-hexane; alcohol solvents such as methanol, ethanol, and isopropanol; ether solvents such as dioxane and tetrahydrofuran; ester solvents such as ethyl acetate, butyl acetate, and isobutyl acetate; carbonate 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; and lactam solvents such as N-methyl-2-pyrrolidone.

[0144] From the viewpoints of improving the solubility of polyurethane resin and improving the drying properties of adhesive, toluene and methyl ethyl ketone are particularly preferred.

[0145] Epoxy resins typically have two or more epoxy groups in one molecule. That is, epoxy resins are usually difunctional or multifunctional (e.g., trifunctional or tetrafunctional).

[0146] Examples of bifunctional epoxy resins 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, and biphenol type epoxy resin.

[0147] Examples of multifunctional epoxy resins include phenolic varnish epoxy resin, bisphenol A phenolic varnish epoxy resin, trifunctional phenolic epoxy resin, and tetrafunctional phenolic epoxy resin.

[0148] Commercially available phenolic varnish epoxy resins include jER152 and jER154 (both manufactured by Mitsubishi Chemical Corporation); commercially available bisphenol A type phenolic varnish epoxy resins include jER157S65 and jER157S70 (both manufactured by Mitsubishi Chemical Corporation); commercially available trifunctional phenolic epoxy resins include jER1032S50 and jER1032H60 (both manufactured by Mitsubishi Chemical Corporation); and commercially available tetrafunctional phenolic epoxy resins include jER1031S (manufactured by Mitsubishi Chemical Corporation).

[0149] The epoxy resins mentioned above can be used alone or in combination of two or more.

[0150] In the insulating sheet 10 of this embodiment, it is preferable to contain 10 or more but less than 100 parts by mass of the aforementioned epoxy resin relative to the aforementioned 100 parts by mass of polyurethane resin, and more preferably 20 or more but less than 80 parts by mass.

[0151] By making the content of the aforementioned epoxy resin 10 parts by mass or more, the adhesive layers 10b1 and 10b2 can have sufficient heat resistance.

[0152] In addition, by keeping the content of the aforementioned epoxy resin at 100 parts by mass or less, the flexibility derived from the urethane resin can be fully utilized in the adhesive layers 10b1 and 10b2.

[0153] Therefore, it is possible to prevent the adhesive layers 10b1 and 10b2 from becoming excessively hard and brittle after curing (after the cross-linking reaction).

[0154] The aforementioned epoxy resin is preferably a hydroxyl-containing epoxy resin containing hydroxyl groups.

[0155] In addition, the epoxy resin mentioned above preferably has an epoxy equivalent of 450 g / eq or more and 3000 g / eq or less.

[0156] By keeping the epoxy equivalent within the above-mentioned range, adhesive layers 10b1 and 10b2 exhibit superior adhesion to the adherend at lower temperatures (below 60°C, for example, 40°C).

[0157] The aforementioned epoxy equivalent can be calculated according to JIS K 7236.

[0158] The hydroxyl value of the aforementioned hydroxyl-containing epoxy resin is preferably 50 mg KOH / g or more and 250 mg KOH / g or less, more preferably 100 mg KOH / g or more and 220 mg KOH / g or less.

[0159] By making the hydroxyl value of the aforementioned hydroxyl-containing epoxy resin 50 mg KOH / g or higher, the crosslinking density can be further increased after the aforementioned hydroxyl-containing epoxy resin undergoes a crosslinking reaction with the aforementioned isocyanate-based crosslinking agent.

[0160] This results in better long-term heat resistance of the cured product obtained after the cross-linking reaction.

[0161] In addition, by keeping the hydroxyl value of the aforementioned hydroxyl-containing epoxy resin below 250 mg KOH / g, it is possible to suppress excessively high crosslinking density.

[0162] Therefore, it is possible to suppress the deformation of the cured product due to poor flexibility after the cross-linking reaction.

[0163] Furthermore, by making the hydroxyl value of the aforementioned hydroxyl-containing epoxy resin below 250 mg KOH / g, the number of unreacted hydroxyl groups can be reduced.

[0164] Therefore, it is possible to suppress the long-term durability reduction of adhesive layers 10b1 and 10b2 caused by the reaction of a large number of residual unreacted hydroxyl groups with moisture in the atmosphere.

[0165] The aforementioned epoxy resin is preferably mixed with the aforementioned polyurethane resin in a state of being dissolved in an organic solvent.

[0166] Specific examples of the aforementioned organic solvents include: ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; aromatic hydrocarbon solvents such as toluene, xylene, Swazole (trade name, manufactured by Cosmo Oil Co., Ltd.), and Solvesso (trade name, manufactured by ExxonMobil Corporation); aliphatic hydrocarbon solvents such as n-hexane; alcohol solvents such as methanol, ethanol, and isopropanol; ether solvents such as dioxane and tetrahydrofuran; ester solvents such as ethyl acetate, butyl acetate, and isobutyl acetate; carbonate 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; and lactam solvents such as N-methyl-2-pyrrolidone.

[0167] Based on the solubility of epoxy resin and the drying properties of adhesive, toluene and methyl ethyl ketone are particularly preferred.

[0168] Furthermore, toluene and methyl ethyl ketone are preferred from the viewpoint that they are less likely to deactivate isocyanate groups compared to alcohol-based solvents.

[0169] The aforementioned aliphatic isocyanate is preferably an aliphatic polyisocyanate, and more preferably an aliphatic diisocyanate.

[0170] The aforementioned aromatic isocyanate is preferably an aromatic polyisocyanate, and more preferably an aromatic diisocyanate.

[0171] As the aforementioned aliphatic isocyanates, hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI) may be used appropriately.

[0172] Examples of the aforementioned aliphatic isocyanates include the biuret form of HDI, the isocyanurate form of HDI, and the TMP adduct of HDI.

[0173] It should be noted that TMP is an abbreviation for trimethylolpropane.

[0174] As the aforementioned aromatic isocyanates, diphenylmethane diisocyanate (MDI) and toluene diisocyanate (TDI) may be suitably used.

[0175] Examples of the aforementioned aromatic isocyanates include the isocyanurate form of TDI and the TMP adduct of TDI.

[0176] Furthermore, the aforementioned isocyanate-based crosslinking agent may include alicyclic isocyanates. The aforementioned alicyclic isocyanates are preferably alicyclic polyisocyanates, and more preferably alicyclic diisocyanates.

[0177] Examples of the aforementioned alicyclic diisocyanates include the isocyanurate form of IPDI, the isocyanurate form of hydrogenated XDI, and the TMP adduct of hydrogenated XDI.

[0178] It should be noted that XDI is an abbreviation for phenyl dimethyl diisocyanate.

[0179] In this embodiment, the insulating sheet 10 preferably contains 3 or more but less than 20 parts by mass of the aforementioned isocyanate-based crosslinking agent relative to 100 parts by mass of the total amount of the aforementioned polyurethane resin and the aforementioned epoxy resin.

[0180] According to this configuration, the insulating sheet 10 has sufficient heat resistance even when cured at a lower temperature, and in addition to having excellent adhesion to the adhered material after the crosslinking reaction, it also exhibits sufficient hydrolysis resistance (damp heat resistance).

[0181] The aforementioned resin composition may contain various known additives.

[0182] Examples of the aforementioned additives include cross-linking promoters that facilitate cross-linking reactions.

[0183] In addition, other additives mentioned above include dispersants, tackifiers, anti-aging agents, antioxidants, processing aids, stabilizers, defoamers, flame retardants, thickeners, and pigments.

[0184] The thickness of the adhesive layers 10b1 and 10b2 is preferably 3 μm or more and 20 μm or less, more preferably 4 μm or more and 15 μm or more, and even more preferably 5 μm or more and 10 μm or less.

[0185] The insulating sheet 10 of this embodiment is used, for example, in an oil-cooled drive motor of an automobile, as described above. Hereinafter, with reference to... Figures 2-4 A specific example of the use of the insulating sheet 10 in this embodiment will be explained.

[0186] It should be noted that the following examples illustrate the use of oil-cooled drive motors in electric vehicles and hybrid vehicles.

[0187] An oil-cooled drive motor has a rotor with permanent magnets and a stator with coils, and the coils are formed by segment conductors.

[0188] Furthermore, the insulating sheet 10 of this embodiment is used for insulation between the coil and the core in the aforementioned stator.

[0189] Figure 2 The figure shows a perspective view of the stator 1 of an oil-cooled drive motor. The stator 1 has a stator core 20 and a coil 30.

[0190] Figure 3 A top view of the stator 1 viewed from the direction of the rotor's (not shown) rotation axis (arrow AD). Figure 4 To show in Figure 3 The diagram shows a cross-sectional view of the stator core 20, where part A houses multiple coils 30.

[0191] As shown in these figures, in stator 1, multiple grooves 21 are formed on the inner circumferential surface of the cylindrical stator core 20.

[0192] The stator 1 has a stator core 20 and a plurality of coils 30 housed in a plurality of grooves 21 formed in the stator core 20.

[0193] Multiple grooves 21 are arranged on the stator core 20 in the following manner: each groove 21 is along the rotation axis direction of the stator core 20. Figure 2 The AD extends in the circumferential direction of the stator core 20. Figure 2 The RDs maintain a certain interval between each other.

[0194] Groove 21 is formed along the entire length of the stator core 20 in the rotational axis direction AD, at one end face 20a of the stator core 20. Figure 2The upper side (hereinafter also referred to as "upper end face 20a") and the other end face 20b (hereinafter also referred to as "lower end face 20b") are formed with openings 21b of the same shape as the cross-sectional shape of the groove 21.

[0195] In the stator core 20, since multiple grooves 21 are parallel as described above, plate-like protrusions 22 are formed between adjacent grooves 21.

[0196] The plate-shaped protrusion 22 (hereinafter also referred to as "tooth 22") is radially toward the stator core 20. Figure 2 Multiple structures are formed by the inner protrusion of the DD direction.

[0197] It should be noted that, as Figure 3 and Figure 4 As shown, the tooth 22 has a wide portion 22a at its front end in the protruding direction, which is widened in the circumferential direction RD along the stator core 20, and has a T-shaped cross-section.

[0198] Therefore, on the inner circumferential surface side of the stator core 20, the width of the groove 21 narrows, forming only a slightly linear opening 21a.

[0199] The coil 30 is composed of a plurality of segmented conductors 31 connected to each other.

[0200] It should be noted that the segmented conductor 31 before coil formation is as follows: Figure 2 As shown, the flat enameled wire is bent into a U-shape and has two legs 31b and a head 31a that connects the two legs 31b to each other.

[0201] The split conductor 31 has a copper wire exposed at the front end 31bx of the foot 31b on the opposite side of the head 31a, with the insulating coating removed.

[0202] The coil 30 is manufactured as follows: the foot 31b of the dividing conductor 31 is inserted into the opening 21b of the groove 21 of the upper end face 20a of the stator core 20, and its front end 31bx is exposed from the lower end face 20b of the stator core 20. Then, the foot 31b of one dividing conductor 31 is electrically connected to the foot 31b of other dividing conductors 31 at the exposed copper wire to form a connection part 31x. Then, the connection part 31x is insulated.

[0203] It should be noted that the two legs 31b of a split conductor 31 are inserted into different grooves 21 respectively.

[0204] The coil 30 is manufactured as described above. Therefore, the stator 1 has an upper coil end on the upper end face 20a side of the stator core 20, which is composed of the head 31a of the dividing conductor 31, and a lower coil end on the lower end face 20b side, which is composed of the connecting portion 31x formed by connecting the legs 31b to each other.

[0205] like Figure 4 As shown, in the groove 21 of the stator core 20, each groove 21 contains a foot 31b of a segmented conductor 31 forming a coil 30 (each groove 21 contains one foot 31b of the four segmented conductors 31). Each groove 21 contains a total of four feet 31b arranged in a row from the inner peripheral surface to the outer peripheral surface.

[0206] like Figure 4 As shown, in this embodiment, the insulating sheet 10 is sandwiched between the four legs 31b and the inner circumferential surface of the groove 21.

[0207] The insulating sheet 10 is arranged longitudinally along the length direction of the feet 31b of the split conductor 31, and is arranged in the groove 21 in such a way that it surrounds the four feet 31b more than once, and the two ends of the rotation axis AD are arranged in the groove 21 protruding from the upper end face 20a and the lower end face 20b of the stator core 20 toward the outside of the rotation axis AD.

[0208] As described above, the insulating sheet 10 is arranged in the groove 21 in such a way that it surrounds the four legs 31b more than once, so that the two ends of the surrounding direction coincide and are arranged in the groove 21.

[0209] That is, in the stator 1, a repeating portion 10a1 is formed in the groove 21 by overlapping insulating sheets 10. Figure 4 ).

[0210] And, as Figure 4 As shown, in stator 1, the repeating part 10a1 is located outside the radial direction DD.

[0211] It should be noted that the portion protruding from the upper end face 20a and the lower end face 20b of the stator core 20 in the direction AD of rotation can be bent outward of the groove 21 in such a way that it is hooked (locked) to at least one of the upper end side and the lower end side of the groove 21.

[0212] The coil 30, which is surrounded by the insulating sheet 10, is fixed in the groove 21 by impregnating the groove 21 with insulating resin (e.g., epoxy varnish).

[0213] The matters disclosed in this specification include the following. (1)

[0215] An insulating sheet comprising:

[0216] Substrate film, and

[0217] An insulating layer is laminated onto at least one side of the substrate film using an adhesive layer.

[0218] The aforementioned adhesive layer is composed of a resin composition comprising polyurethane resin, epoxy resin, and isocyanate-based crosslinking agent.

[0219] The aforementioned resin composition comprises at least one selected from the group consisting of aliphatic isocyanates and aromatic isocyanates as the aforementioned isocyanate-based crosslinking agent.

[0220] According to this configuration, even when cured at lower temperatures (below 60°C, for example, 40°C), the aforementioned insulating sheet exhibits sufficient heat resistance and excellent adhesion to the adhered material after the cross-linking reaction. (2)

[0222] According to the insulating sheet described in (1) above, the aforementioned polyurethane resin has carboxyl groups.

[0223] According to this configuration, the aforementioned insulating sheet has more adequate heat resistance even when cured at lower temperatures, and on this basis, its adhesion to the adhered objects is also better after the cross-linking reaction. (3)

[0225] According to the insulating sheet described in (1) or (2) above, wherein the aforementioned polyurethane resin comprises a hydroxyl-containing polyurethane resin having hydroxyl groups at the ends,

[0226] The aforementioned epoxy resins include hydroxyl-containing epoxy resins having hydroxyl groups.

[0227] According to this configuration, even when cured at lower temperatures, the aforementioned insulating sheet exhibits more adequate heat resistance and superior adhesion to the adhered material after the cross-linking reaction. (4)

[0229] The insulating sheet according to any one of (1) to (3) above, wherein the aforementioned aliphatic isocyanate is at least one of hexamethylene diisocyanate and isophorone diisocyanate.

[0230] The aforementioned aromatic isocyanate is at least one of diphenylmethane diisocyanate and toluene diisocyanate.

[0231] According to this configuration, even when cured at lower temperatures, the aforementioned insulating sheet exhibits more adequate heat resistance and superior adhesion to the adhered material after the cross-linking reaction. (5)

[0233] The insulating sheet according to any one of (1) to (4) above, wherein, relative to 100 parts by mass of the total amount of the aforementioned polyurethane resin and the aforementioned epoxy resin, comprises 3 or more and 20 or less of the aforementioned isocyanate-based crosslinking agent.

[0234] According to this structure, even when cured at lower temperatures, the aforementioned insulating sheet exhibits sufficient heat resistance and excellent adhesion to the adhered material after the cross-linking reaction. Furthermore, it also demonstrates sufficient resistance to hydrolysis (damp heat resistance).

[0235] It should be noted that the insulating sheet of the present invention is not limited to the embodiments described above. Furthermore, the insulating sheet of the present invention is not limited to the effects described above. Various modifications can be made to the insulating sheet of the present invention without departing from the spirit of the invention.

[0236] For example, in the above embodiment, an example was described in which the insulating layers 10c1 and 10c2 in the insulating sheet 10 are respectively made of paper-like sheets formed using fibers, but the insulating layers 10c1 and 10c2 are not limited to this.

[0237] The insulating layers 10c1 and 10c2 can also use films made of insulating resins such as polyethylene naphthalate (PEN), polyimide (PI), polyphenylene sulfide (PPS), and polyether ether ketone (PEEK).

[0238] Alternatively, insulating layers 10c1 and 10c2 can both be thin films made of insulating resin.

[0239] Furthermore, insulating layers 10c1 and 10c2 can both be made of the same type of insulating resin (e.g., both are made of PEN), or one can be made of a different type of insulating resin (e.g., one is made of PEN and the other is made of PI).

[0240] In addition, the insulating layers 10c1 and 10c2 can be either paper sheets made of fibers or films made of insulating resin.

[0241] Furthermore, when the insulating sheets are required to be easy to assemble as insulating materials for slots, wedges, etc., installed in the stator and rotor of an automotive electric motor, paper-like sheets are preferably used for insulating layers 10c1 and 10c2.

[0242] By using paper-like sheets, the slip properties of the surfaces of insulating layers 10c1 and 10c2 (i.e., the surface of insulating sheet 10) can be improved.

[0243] On the other hand, when high tear strength is required for the insulating sheet, the insulating layers 10c1 and 10c2 are preferably thin films made of insulating resin.

[0244] Example

[0245] Next, embodiments, comparative examples, and test examples will be listed to further illustrate the present invention.

[0246] Synthesis of Polyurethane Resins

[0247] A reaction vessel equipped with a stirrer, reflux condenser, thermometer, nitrogen inlet pipe, and manhole was prepared. While purging the interior of the reaction vessel with nitrogen, 200.0 g of polyhexamethylene carbonate diol (DURANOL: T6002, manufactured by Asahi Kasei Chemicals Co., Ltd., number-average molecular weight = 2000 based on terminal functional group quantification method), 10.0 g of 1,3-butanediol, and 14.4 g of dimethylolpropionic acid were added. Next, 100.6 g of methyl ethyl ketone (MEK) was added as a solvent, and the system was stirred. After the system became homogeneous, 77.3 g of 4,4'-diphenylmethane diisocyanate (MDI) was added at 50°C, and the reaction was carried out at 80°C to obtain a reaction solution. The viscosity of the reaction solution was adjusted by diluting it with methyl ethyl ketone (MEK) as a solvent, and the reaction was continued until the viscosity based on the free isocyanate groups reached 2270 cm⁻¹, as measured by infrared absorption spectroscopy. -1 The absorption continued until the polyurethane resin A was completely absorbed, resulting in a resin solution AA containing polyurethane resin A. The solid content of the obtained resin solution AA was 30%, the hydroxyl value of polyurethane resin A was 3.6 mg KOH / g, and the acid value was 20.0 mg KOH / g. Furthermore, the weight-average molecular weight of polyurethane resin A, measured by GPC, was 92,000.

[0248] <Dissolution of epoxy resin>

[0249] Prepare a reaction vessel equipped with a stirrer, reflux condenser, thermometer, nitrogen inlet pipe, and manhole. While purging the interior of the reaction vessel with nitrogen, add 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). Simultaneously, add 600.0 g of methyl ethyl ketone (MEK) as a solvent. Heat the system to 60°C to completely dissolve epoxy resin B, obtaining a dissolved epoxy resin B, BB (hereinafter referred to as epoxy resin solution BB). The solid content of the obtained epoxy resin solution BB is 40%.

[0250] (Example 1)

[0251] The insulating layer, adhesive layer and substrate film are stacked in the following order to form 5 layers, resulting in the insulating sheet of Example 1 (insulating sheet thickness: 139 μm).

[0252] NOMEX paper (insulation layer. Thickness: 50μm)

[0253] Resin layer (adhesive layer. Thickness: 7μm)

[0254] Polyethylene terephthalate film (substrate film. Thickness: 25μm)

[0255] Resin layer (adhesive layer. Thickness: 7μm)

[0256] NOMEX paper (insulating layer, 50μm thick)

[0257] In the insulating sheet of Example 1, the adhesive layer is composed of an adhesive comprising polyurethane resin A (a polyurethane resin with carboxyl groups), epoxy resin B, and isocyanate-based crosslinking agent A (an isocyanurate body of aliphatic isocyanate and hexamethylene diisocyanate (HDI)).

[0258] In the insulating sheet of Example 1, the aforementioned adhesive is prepared by mixing a resin solution AA containing polyurethane resin A, an epoxy resin solution BB containing epoxy resin B, and an isocyanate-based crosslinking agent A.

[0259] In addition, resin solution AA and epoxy resin solution BB are mixed in such a way that 45 parts by mass of epoxy resin (solid component) are in a ratio of 100 parts by mass to polyurethane resin (solid component).

[0260] Furthermore, isocyanate-based crosslinking agent A is mixed with 10 parts by mass relative to 100 parts by mass of the aforementioned polyurethane resin (solid component) and the aforementioned epoxy resin (solid component).

[0261] It should be noted that the insulating sheet of Example 1 was cured at 40°C for 5 days (120 hours) (crosslinking treatment) to carry out the curing reaction (crosslinking reaction) in the adhesive layer.

[0262] (Example 2)

[0263] The insulating sheet of Example 2 (5-layer structure, thickness: 139 μm) was prepared in the same manner as in Example 1, except that an isocyanate-based crosslinking agent C (an isocyanurate of aromatic isocyanate, toluene diisocyanate (TDI)) was used instead of isocyanate-based crosslinking agent A.

[0264] In addition, in Example 2, 10 parts by mass of the isocyanate-based crosslinking agent C were also mixed relative to the total amount of the aforementioned polyurethane resin (solid component) and the aforementioned epoxy resin (solid component) of 100 parts by mass.

[0265] It should be noted that the insulating sheet of Example 2 also underwent a curing reaction (crosslinking reaction) in the adhesive layer by curing at 40°C for 5 days (120 hours).

[0266] (Example 3)

[0267] The insulating sheet (5-layer structure, thickness: 139 μm) of Example 3 was prepared in the same manner as in Example 1, except that an isocyanate-based crosslinking agent D (a mixture of isocyanurate products of HDI and TDI, i.e., a mixture of aliphatic and aromatic isocyanates) was used instead of isocyanate-based crosslinking agent A.

[0268] In addition, in Example 3, 10 parts by mass of the isocyanate-based crosslinking agent D were also mixed relative to the total amount of the aforementioned polyurethane resin (solid component) and the aforementioned epoxy resin (solid component) of 100 parts by mass.

[0269] It should be noted that the insulating sheet of Example 3 also underwent a curing reaction (crosslinking reaction) in the adhesive layer by curing at 40°C for 5 days (120 hours).

[0270] (Comparative Example 1)

[0271] The insulating sheet of Comparative Example 1 (5-layer structure, thickness: 139 μm) was prepared in the same manner as in Example 1, except that an aliphatic amine crosslinking agent (dicyandiamide (DICY)) was used instead of isocyanate-based crosslinking agent A.

[0272] In addition, in Comparative Example 1, 10 parts by mass of aliphatic amine crosslinking agent were also prepared relative to 100 parts by mass of the total amount of the aforementioned polyurethane resin (solid component) and the aforementioned epoxy resin (solid component).

[0273] It should be noted that the insulating sheet of Comparative Example 1 also underwent a curing reaction (crosslinking reaction) in the adhesive layer by curing at 40°C for 5 days (120 hours).

[0274] (Comparative Example 2)

[0275] The insulating sheet of Comparative Example 2 (5-layer structure, thickness: 139 μm) was prepared in the same manner as in Example 1, except that an aromatic amine crosslinking agent (4,4'-diaminodiphenyl sulfone (DDS)) was used instead of isocyanate crosslinking agent A.

[0276] In addition, in Comparative Example 2, 10 parts by mass of the aromatic amine crosslinking agent were also prepared relative to 100 parts by mass of the total amount of the aforementioned polyurethane resin (solid component) and the aforementioned epoxy resin (solid component).

[0277] It should be noted that the insulating sheet of Comparative Example 2 also underwent a curing reaction (crosslinking reaction) in the adhesive layer by curing at 40°C for 5 days (120 hours).

[0278] (Comparative Example 3)

[0279] A multifunctional epoxy crosslinking agent (triphenylmethane type epoxy resin, trade name "EPPN501HY", manufactured by Nippon Kayaku Co., Ltd.) was used instead of isocyanate-based crosslinking agent A. Otherwise, the insulating sheet (5-layer structure, thickness: 139 μm) of Comparative Example 3 was prepared in the same manner as in Example 1.

[0280] In addition, in Comparative Example 3, 10 parts by mass of the multifunctional epoxy crosslinking agent were also mixed relative to 100 parts by mass of the total amount of the aforementioned polyurethane resin (solid component) and the aforementioned epoxy resin (solid component).

[0281] It should be noted that the insulating sheet of Comparative Example 3 also underwent a curing reaction (crosslinking reaction) in the adhesive layer by curing at 40°C for 5 days (120 hours).

[0282] (Comparative Example 4)

[0283] The insulating layer, adhesive layer and substrate film were stacked in the following order to form 5 layers, resulting in the insulating sheet of Comparative Example 4 (insulating sheet thickness: 184 μm).

[0284] NOMEX paper (insulation layer. Thickness: 37μm)

[0285] Acrylic resin layer (adhesive layer. Thickness: 30μm)

[0286] Polyethylene terephthalate film (substrate film. Thickness: 50μm)

[0287] Acrylic resin layer (adhesive layer. Thickness: 30μm)

[0288] NOMEX paper (insulation layer. Thickness: 37μm)

[0289] In the insulating sheet of Comparative Example 4, the acrylic resin layer is composed of a resin composition comprising acrylic resin A (a substance obtained by adding terpene phenols to polybutyl acrylate (PAB)) and isocyanate crosslinking agent E (an aromatic isocyanate, trimethylolpropane (TMP) adduct of TDI).

[0290] In addition, in the insulating sheet of Comparative Example 4, 7 parts by weight of isocyanate-based crosslinking agent E were added relative to 100 parts by weight of acrylic resin A.

[0291] It should be noted that the insulating sheet of Comparative Example 4 was subjected to a curing treatment (crosslinking treatment) at 130°C for 1 day.

[0292] (Comparative Example 5)

[0293] An insulating sheet with the same structure as Comparative Example 4 was obtained, and the adhesive layer was cured by a curing treatment (crosslinking reaction) at 40°C for 5 days.

[0294] [Evaluation of initial adhesion]

[0295] After curing the insulating sheets in each case, the initial adhesive strength was evaluated to determine whether the insulation layer could be confirmed to lift off from the adhesive layer.

[0296] Specifically, cases where the self-adhesive layer of the insulation layer is visually confirmed to be floating are rated as "unacceptable," while cases where no floating is confirmed are rated as "excellent."

[0297] The results are shown in Table 1 below.

[0298] According to Table 1, the initial adhesive strength of the insulating sheet in Comparative Example 5 was rated as "unacceptable", while the initial adhesive strength of the insulating sheets in the other examples (Examples 1-3 and Comparative Examples 1-4) was rated as "excellent".

[0299] [Evaluation of hydrolysis resistance (damp heat resistance)]

[0300] Next, the hydrolysis resistance of the insulating sheets of Examples 1-3 and Comparative Examples 1-4, which were rated as "excellent" in initial adhesion, was evaluated.

[0301] Regarding hydrolysis resistance, the test subjects were made into ring-shaped test subjects of the insulating sheets of Examples 1-3 and Comparative Examples 1-4. After the test subjects were subjected to a pressure cooker test (PCT) at 120°C, 100% relative humidity and 0.2 MPa, the evaluation was conducted by visually observing the aforementioned ring-shaped test subjects to determine whether the self-adhesive layer of the insulating layer was lifted.

[0302] The aforementioned ring-shaped test body is made as follows: using two sheets of insulating paper with a width of 25mm and a length of 160mm as the insulating layer, one end of each insulating paper is overlapped with the other end in the length direction (hereinafter also referred to as the overlapping part) to form a ring (forming a ring that is approximately elliptical in top view). With the overlapping parts of the two rings overlapping each other, one end of the width direction is fixed to the other end with a stapler, thus making the test body.

[0303] Regarding whether the lifting of the self-adhesive layer of the insulation layer is confirmed, specifically, the situation where the lifting of the self-adhesive layer of the insulation layer is visually confirmed is evaluated as "unacceptable", and the situation where the lifting is not confirmed is evaluated as "excellent".

[0304] The pressure cooker test was conducted by exposing the test specimens to 120°C, 100% relative humidity, and 0.2 MPa pressure for 48 hours, 96 hours, and 144 hours.

[0305] The results are shown in Table 1 below.

[0306] According to Table 1, in the annular test specimens of Examples 1-3 and the annular test specimen of Comparative Example 4, no floating of the self-adhesive layer of the insulating layer was visually confirmed after 144 hours.

[0307] In contrast, in the annular test specimens of Comparative Examples 1-3, the lifting of the self-adhesive layer of the insulating layer was visually confirmed after 48 hours. It should be noted that, for the annular test specimens of Comparative Examples 1-3, the lifting of the self-adhesive layer of the insulating layer was visually confirmed after 48 hours, therefore, no visual observation was conducted after 96 hours and 144 hours.

[0308] Based on the above results, it can be seen that by making the adhesive layer consist of an adhesive layer (resin composition) containing polyurethane resin (more specifically, polyurethane resin having carboxyl groups), epoxy resin and isocyanate-based crosslinking agent, and the aforementioned adhesive (resin composition) contains 10 parts by mass of isocyanate-based crosslinking agent relative to 100 parts by mass of the total amount of polyurethane resin and epoxy resin, excellent hydrolysis resistance is achieved.

[0309] [Table 1]

[0310]

[0311] [Heat Resistance Evaluation]

[0312] The heat resistance of the insulating sheets of Examples 1-3 after curing treatment and the insulating sheets of Comparative Examples 2, 4 and 5 after curing treatment was evaluated. The heat resistance was evaluated using TG-DTA (Rigiku Co., Ltd., model TG8120).

[0313] Specifically, the evaluation of heat resistance was conducted by increasing the temperature at 5°C / min from room temperature (23±2°C) in an atmosphere of 100 mL / min, focusing on the temperatures at which the mass decreased by 10% (10% mass reduction temperature) and the temperatures at which the mass decreased by 50% (50% mass reduction temperature).

[0314] It should be noted that a 10% decrease in temperature by mass indicates short-term heat resistance, while a 50% decrease in temperature by mass indicates long-term heat resistance.

[0315] Heat resistance is judged based on the following evaluation criteria.

[0316] Advantages: 10% mass reduction at temperatures above 330°C and 50% mass reduction at temperatures above 360°C. Not applicable to: any of the above.

[0317] The results of evaluating the heat resistance of Examples 1-3 and Comparative Examples 2, 4 and 5 are shown in Table 2 below.

[0318] [Table 2]

[0319]

[0320] As shown in Table 2, the heat resistance of the insulating sheets in Examples 1-3 and the insulating sheet in Comparative Example 4 was rated as "excellent".

[0321] In contrast, it can be seen that the heat resistance of the insulating sheets in Comparative Examples 2 and 5 is rated as "not good".

[0322] According to the results, by making the adhesive layer consist of an adhesive layer (resin composition) containing polyurethane resin (specifically, polyurethane resin having carboxyl groups), epoxy resin and isocyanate-based crosslinking agent, and the aforementioned adhesive (resin composition) contains 10 parts by mass of isocyanate-based crosslinking agent per 100 parts by mass of the total amount of polyurethane resin and epoxy resin, even when cured at a relatively low temperature of 40°C (Examples 1-3), it shows the same degree of heat resistance as the sample cured at a relatively high temperature of 130°C (Comparative Example 4), that is, it shows higher heat resistance.

[0323] It is also known that when the adhesive layer is not composed of an adhesive (resin composition) containing polyurethane resin (more specifically, polyurethane resin with carboxyl groups), epoxy resin and isocyanate-based crosslinking agent (in the cases of Comparative Examples 2 and 5), the heat resistance is poor when it is cured at a relatively low temperature of 40°C.

[0324] [Peeling Test]

[0325] Strip samples with a width of 10 mm were cut from the insulating sheets of Examples 1-3 after curing treatment and the insulating sheet of Comparative Example 4 after curing treatment.

[0326] Then, using a tensile testing machine, the insulation layer was pulled from the adhesive layer on one side at a test speed of 300 mm / min at room temperature (23℃±2℃) to perform a 180-degree peel test, and the peel strength (N / 10mm) at room temperature was determined.

[0327] The results of the peel strength measurements of the insulating sheets of Examples 1-3 and Comparative Example 4, as measured as described above, are shown in Table 3 below.

[0328] It should be noted that a peel strength of 3 N / 10 mm or higher is considered as "excellent" adhesion.

[0329] [Table 3]

[0330] Example 1 40℃ x 5 days 3.84 excellent Example 2 40℃ x 5 days 3.66 excellent Example 3 40℃ x 5 days 3.92 excellent Comparative Example 4 130℃ x 1 day 3.14 excellent

[0331] As shown in Table 3, the insulating sheets of Examples 1 to 3 have higher peel strength values ​​than the insulating sheet of Comparative Example 4, with a peel strength of 3 N / 10 mm or more. Therefore, the evaluation of their adhesion is also "excellent".

[0332] The results show that by making the adhesive layer consist of an adhesive layer (resin composition) containing polyurethane resin (specifically, polyurethane resin having carboxyl groups), epoxy resin and isocyanate-based crosslinking agent, and the aforementioned adhesive (resin composition) contains 10 parts by mass of isocyanate-based crosslinking agent per 100 parts by mass of the total amount of polyurethane resin and epoxy resin, even when cured at a relatively low temperature of 40°C, it exhibits the same or higher degree of adhesion as the sample cured at a relatively high temperature of 130°C, that is, it exhibits higher adhesion.

[0333] [The effect of the amount of crosslinking agent added]

[0334] (Experimental Example 1A)

[0335] By changing the formulation of the adhesive (resin composition) constituting the resin layer, and otherwise stacking the insulating layer, adhesive layer and substrate film into 5 layers in the same manner as in Example 1, the insulating sheet of Test Example 1A (insulating sheet thickness: 139 μm) was obtained.

[0336] In the insulating sheet of Test Example 1A, the resin layer is composed of an adhesive (resin composition) containing polyurethane resin A and epoxy resin B and without a crosslinking agent.

[0337] That is, in the adhesive (resin composition) of Test Example 1A, the amount of crosslinking agent added is 0 parts by mass relative to the total amount of polyurethane resin A and epoxy resin B, which is 100 parts by mass.

[0338] It should be noted that the insulating sheet of Test Example 1A underwent a curing treatment (crosslinking treatment) at 40°C for 5 days.

[0339] (Experimental Example 2A)

[0340] By changing the formulation of the adhesive (resin composition) constituting the resin layer, and otherwise stacking the insulating layer, adhesive layer and substrate film into 5 layers in the same manner as in Example 1, the insulating sheet of Test Example 2A (insulating sheet thickness: 139 μm) was obtained.

[0341] In the insulating sheet of Test Example 2A, the resin layer is composed of an adhesive (resin composition) comprising polyurethane resin A, epoxy resin B, and isocyanate-based crosslinking agent D (a mixture of isocyanurate body of HDI and isocyanurate body of TDI. That is, a mixture of aliphatic isocyanate and aromatic isocyanate).

[0342] In addition, in the adhesive (resin composition) of Test Example 2A, 1 part by mass of isocyanate-based crosslinking agent D was added relative to 100 parts by mass of the total amount of polyurethane resin A and epoxy resin B.

[0343] It should be noted that the insulating sheet of Test Example 2A underwent a curing treatment (crosslinking treatment) at 40°C for 5 days.

[0344] (Experimental Example 3A)

[0345] By changing the formulation of the adhesive (resin composition) constituting the resin layer, and otherwise stacking the insulating layer, adhesive layer and substrate film into 5 layers in the same manner as in Example 1, the insulating sheet of Test Example 3A (insulating sheet thickness: 139 μm) was obtained.

[0346] In the insulating sheet of Test Example 3A, the resin layer is composed of an adhesive (resin composition) comprising polyurethane resin A, epoxy resin B and isocyanate-based crosslinking agent D.

[0347] In addition, in the adhesive (resin composition) of Test Example 3A, 2 parts by mass of isocyanate-based crosslinking agent D were added relative to 100 parts by mass of the total amount of polyurethane resin A and epoxy resin B.

[0348] It should be noted that the insulating sheet of Test Example 3A underwent a 5-day curing treatment (cross-linking treatment) at 40°C.

[0349] (Experimental Example 4A)

[0350] By changing the formulation of the adhesive (resin composition) constituting the resin layer, and otherwise stacking the insulating layer, adhesive layer and substrate film into 5 layers in the same manner as in Example 1, the insulating sheet of Test Example 4A (insulating sheet thickness: 139 μm) was obtained.

[0351] In the insulating sheet of Test Example 4A, the resin layer is composed of an adhesive (resin composition) comprising polyurethane resin A, epoxy resin B and isocyanate-based crosslinking agent D.

[0352] In addition, in the adhesive (resin composition) of Test Example 4A, 3 parts by mass of isocyanate-based crosslinking agent D were added relative to 100 parts by mass of the total amount of polyurethane resin A and epoxy resin B.

[0353] It should be noted that the insulating sheet of Test Example 4A underwent a curing treatment (crosslinking treatment) at 40°C for 5 days.

[0354] (Experimental Example 5A)

[0355] By changing the formulation of the adhesive (resin composition) constituting the resin layer, and otherwise stacking the insulating layer, adhesive layer and substrate film into 5 layers in the same manner as in Example 1, the insulating sheet of Test Example 5A (insulating sheet thickness: 139 μm) was obtained.

[0356] In the insulating sheet of Test Example 5A, the resin layer is composed of an adhesive (resin composition) comprising polyurethane resin A, epoxy resin B and isocyanate-based crosslinking agent D.

[0357] In addition, in the adhesive (resin composition) of Test Example 5A, 10 parts by mass of isocyanate-based crosslinking agent D were added relative to 100 parts by mass of the total amount of polyurethane resin A and epoxy resin B.

[0358] It should be noted that the insulating sheet of Test Example 5A underwent a curing treatment (crosslinking treatment) at 40°C for 5 days.

[0359] (Experimental Example 6A)

[0360] By changing the formulation of the adhesive (resin composition) constituting the resin layer, and otherwise stacking the insulating layer, adhesive layer and substrate film into 5 layers in the same manner as in Example 1, the insulating sheet of Test Example 6A (insulating sheet thickness: 139 μm) was obtained.

[0361] In the insulating sheet of Test Example 6A, the resin layer is composed of an adhesive (resin composition) comprising polyurethane resin A, epoxy resin B and isocyanate-based crosslinking agent D.

[0362] In addition, in the adhesive (resin composition) of Test Example 6A, 20 parts by mass of isocyanate-based crosslinking agent D were added relative to 100 parts by mass of the total amount of polyurethane resin A and epoxy resin B.

[0363] It should be noted that the insulating sheet of Test Example 6A underwent a curing treatment (crosslinking treatment) at 40°C for 5 days.

[0364] (Experimental Example 7A)

[0365] By changing the formulation of the adhesive (resin composition) constituting the resin layer, and otherwise stacking the insulating layer, adhesive layer and substrate film into 5 layers in the same manner as in Example 1, the insulating sheet of Test Example 7A (insulating sheet thickness: 139 μm) was obtained.

[0366] In the insulating sheet of Test Example 7A, the resin layer is composed of an adhesive (resin composition) comprising polyurethane resin A, epoxy resin B and isocyanate-based crosslinking agent D.

[0367] In addition, in the adhesive (resin composition) of Test Example 7A, 30 parts by mass of isocyanate-based crosslinking agent D were added relative to 100 parts by mass of the total amount of polyurethane resin A and epoxy resin B.

[0368] It should be noted that the insulating sheet of Test Example 7A underwent a curing treatment (crosslinking treatment) at 40°C for 5 days.

[0369] (Experimental Example 8A)

[0370] By changing the formulation of the adhesive (resin composition) constituting the resin layer, and otherwise stacking the insulating layer, adhesive layer and substrate film into 5 layers in the same manner as in Example 1, the insulating sheet of Test Example 8A (insulating sheet thickness: 139 μm) was obtained.

[0371] In the insulating sheet of Test Example 8A, the resin layer is composed of an adhesive (resin composition) comprising polyurethane resin A, epoxy resin B and isocyanate-based crosslinking agent D.

[0372] In addition, in the adhesive (resin composition) of Test Example 8A, 40 parts by mass of isocyanate-based crosslinking agent D were added relative to 100 parts by mass of the total amount of polyurethane resin A and epoxy resin B.

[0373] It should be noted that the insulating sheet of Test Example 8A underwent a curing treatment (crosslinking treatment) at 40°C for 5 days.

[0374] The initial adhesion and hydrolysis resistance (damp heat resistance) of the insulating sheets of Test Examples 1A to 8A obtained as described above were evaluated.

[0375] Regarding the initial adhesive strength, similarly as above, in the insulating sheets of Test Examples 1A to 8A after curing treatment, visual evaluation was conducted to confirm whether the insulation layer lifted off the adhesive layer.

[0376] Regarding hydrolysis resistance, similarly to the above, for the insulating sheets of Test Examples 1A to 8A, a ring-shaped test body was made, and a pressure cooker test (PCT) was conducted under the conditions of 120°C, 100% relative humidity, and 0.2 MPa. When the aforementioned ring-shaped test body was visually observed, it was evaluated whether the lifting of the insulating layer from the adhesive layer was confirmed.

[0377] It should be noted that the pressure cooker test was conducted by exposing the test subject to 120°C, 100% relative humidity, and 0.2MPa pressure for 48 hours, 96 hours, and 144 hours.

[0378] The results are shown in Table 4 below.

[0379] [Table 4]

[0380]

[0381] According to Table 4, although the initial adhesion of the insulating sheets (insulating sheets of Test Examples 1A to 3A) with a curing agent content of 0 to 2 parts by mass was rated as "excellent," visual observation of the self-adhesive layer of the insulation layer was observed after 48 hours. It should be noted that for the insulating sheets of Test Examples 1A to 3A, since the self-adhesive layer of the insulation layer was visually observed after 48 hours, visual observation was not conducted after 96 hours and 144 hours.

[0382] Furthermore, the insulating sheets with 30 and 40 parts by weight of curing agent (insulating sheets of Test Examples 7A and 8A) were rated as "unacceptable" at the time of initial adhesion evaluation. Therefore, the insulating sheets of Test Examples 7A and 8A were not evaluated based on the pressure cooker test.

[0383] In contrast, the initial adhesive strength of insulating sheets with a curing agent content of 3 to 20 parts by weight (insulating sheets in Test Examples 4A to 6A) was rated as "excellent," and the evaluations after 48 hours, 96 hours, and 144 hours were also rated as "excellent." That is, even after 144 hours, no visual observation was made of the insulation layer lifting off the adhesive layer.

[0384] The results show that by adding 3 or more parts by mass and less than 20 parts by mass of curing agent, the insulation sheet exhibits excellent hydrolysis resistance (damp heat resistance).

[0385] In addition, the heat resistance of the insulating sheets of Test Examples 1A and 4A to 6A obtained as described above was evaluated.

[0386] The evaluation of heat resistance is carried out in the same manner as described above.

[0387] In addition, heat resistance is judged based on the following evaluation criteria.

[0388] Advantages: 10% mass reduction at temperatures above 330°C and 50% mass reduction at temperatures above 360°C. Not applicable to: any of the above.

[0389] The results are shown in Table 5 below.

[0390] [Table 5]

[0391]

[0392] As shown in Table 5, the insulating sheets of Test Examples 4A to 6A, which have an addition of 3 to 20 parts by mass of curing agent, exhibit excellent heat resistance, while the insulating sheet of Test Example 1A, which has an addition of 0 parts by mass of curing agent, has poor heat resistance.

[0393] It should be noted that the peel strength of the insulating sheets in test examples 4A to 6A was measured in the same manner as above, and the results showed a value higher than 3N / 10mm.

[0394] Therefore, it can be seen that by adding 3 or more but less than 20 parts by mass of curing agent, the insulating sheet has sufficient adhesion.

[0395] [The influence of epoxy equivalent and hydroxyl value of epoxy resins, and hydroxyl value and acid value of polyurethane resins]

[0396] In order to study the effects of epoxy equivalent and hydroxyl value of epoxy resin, and hydroxyl value and acid value of polyurethane resin on the heat resistance of insulating sheets and their adhesion to the adhered objects, the materials shown in Table 6 were used in the mixing ratios shown in Table 6 below to obtain adhesives for Test Examples 1B to 18B.

[0397] As a resin solution containing polyurethane resin, resin solutions AA1 to AA3 as described in the following synthesis examples A1 to A3 are used.

[0398] As an epoxy resin solution containing epoxy resin, epoxy resin solutions BB1 to BB5 as described in the following epoxy resin dissolution examples B1 to B5 are used.

[0399] As isocyanate-based crosslinking agents, the isocyanurate ester of HDI (C1) (D-170N: manufactured by Mitsui Chemicals Co., Ltd.), the TMP adduct of TDI (C2) (D-101E: manufactured by Mitsui Chemicals Co., Ltd.), and the isocyanurate ester of TDI (C3) (D-204: manufactured by Mitsui Chemicals Co., Ltd.) are used.

[0400] [Table 6]

[0401]

[0402] [Example of polyurethane resin synthesis: A1]

[0403] A reaction vessel equipped with a stirrer, reflux condenser, thermometer, nitrogen inlet pipe, and manhole was prepared. While purging the interior of the reaction vessel with nitrogen, 200.0 g of polyhexamethylene carbonate diol (DURANOL: T6002, manufactured by Asahi Kasei Chemicals Co., Ltd., number-average molecular weight = 2000 based on terminal functional group quantification method) and 10.0 g of 1,3-butanediol were added. Next, 87.1 g of methyl ethyl ketone (MEK) was added as a solvent, and the system was stirred. After the system became homogeneous, 51.2 g of 4,4'-diphenylmethane diisocyanate (MDI) was added at 50°C, and the reaction was carried out at 80°C to obtain a reaction solution. The viscosity of the reaction solution was adjusted by diluting it with methyl ethyl ketone (MEK) as a solvent, and the reaction was continued until the viscosity based on the free isocyanate groups reached 2270 cm⁻¹, as measured by infrared absorption spectroscopy. -1 The absorption continued until the polyurethane resin A1 disappeared, resulting in a resin solution AA1 containing polyurethane resin A1. The solid content of the obtained resin solution AA1 was 30%, and the hydroxyl value of polyurethane resin A1 was 2.7 mg KOH / g. Furthermore, the weight-average molecular weight of polyurethane resin A1, measured by GPC, was 69,000.

[0404] [Example of polyurethane resin synthesis: A2]

[0405] The same procedure as described in the above "Synthesis Example of Polyurethane Resin" shall be followed.

[0406] [Example of polyurethane resin synthesis: A3]

[0407] A reaction vessel equipped with a stirrer, reflux condenser, thermometer, nitrogen inlet pipe, and manhole was prepared. While purging the interior of the reaction vessel with nitrogen, 200.0 g of polyhexamethylene carbonate diol (DURANOL: T6002, manufactured by Asahi Kasei Chemicals Co., Ltd., number-average molecular weight = 2000 based on terminal functional group quantification method) and 10.0 g of 1,3-butanediol were added. Next, 85.8 g of methyl ethyl ketone (MEK) was added as a solvent, and the system was stirred. After the system became homogeneous, 47.5 g of 4,4'-diphenylmethane diisocyanate (MDI) was added at 50°C, and the reaction was carried out at 80°C to obtain a reaction solution. The viscosity of the reaction solution was adjusted by diluting it with methyl ethyl ketone (MEK) as a solvent, and the reaction was continued until the viscosity based on the free isocyanate groups reached 2270 cm⁻¹, as measured by infrared absorption spectroscopy. -1 The absorption continued until the polyurethane resin A3 was completely absorbed, resulting in a resin solution AA3 containing polyurethane resin A3. The solid content of the obtained resin solution AA3 was 30%, and the hydroxyl value of polyurethane resin A3 was 9.2 mg KOH / g. Furthermore, the weight-average molecular weight of polyurethane resin A3, measured by GPC, was 24000.

[0408] [Example of epoxy resin solubility: B1]

[0409] The procedure is carried out in the same manner as described in the above "Example of Epoxy Resin Dissolution".

[0410] [Example of epoxy resin solubility: B2]

[0411] Prepare a reaction vessel equipped with a stirrer, reflux condenser, thermometer, nitrogen inlet pipe, and manhole. While purging the interior of the reaction vessel with nitrogen, add 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). Simultaneously, add 600.0 g of methyl ethyl ketone (MEK) as a solvent. Heat the system to 60°C to completely dissolve the epoxy resin B2, obtaining a dissolved epoxy resin B2, BB2 (hereinafter referred to as epoxy resin solution BB2). The solid content of the obtained epoxy resin solution BB2 is 40%.

[0412] [Example of epoxy resin solubility: B3]

[0413] Prepare a reaction vessel equipped with a stirrer, reflux condenser, thermometer, nitrogen inlet pipe, and manhole. While purging the interior of the reaction vessel with nitrogen, add 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). Simultaneously, add 600.0 g of methyl ethyl ketone (MEK) as a solvent. Heat the system to 60°C to completely dissolve the epoxy resin B3, obtaining a dissolved epoxy resin B3, BB3 (hereinafter referred to as epoxy resin solution BB3). The solid content of the obtained epoxy resin solution BB3 is 40%.

[0414] [Example of epoxy resin solubility: B4]

[0415] Prepare a reaction vessel equipped with a stirrer, reflux condenser, thermometer, nitrogen inlet pipe, and manhole. While purging the interior of the reaction vessel with nitrogen, add 400.0 g of bisphenol A phenoxy resin (epoxy equivalent: 8500 g / eq, JER1256: manufactured by Mitsubishi Chemical Corporation; hereinafter referred to as epoxy resin B4) while stirring. Simultaneously add 600.0 g of methyl ethyl ketone (MEK) as a solvent. Heat the system to 60°C to completely dissolve the epoxy resin B4, obtaining a dissolved epoxy resin B4, BB4 (hereinafter referred to as epoxy resin solution BB4). The solid content of the obtained epoxy resin solution BB4 is 40%.

[0416] [Example of epoxy resin solubility: B5]

[0417] Prepare a reaction vessel equipped with a stirrer, reflux condenser, thermometer, nitrogen inlet pipe, and manhole. While purging the interior of the reaction vessel with nitrogen, add 800.0 g of bisphenol A phenolic varnish-type epoxy resin (trifunctional or higher) (epoxy equivalent: 200 g / eq, JER157S70: manufactured by Mitsubishi Chemical Corporation; hereinafter referred to as epoxy resin B5). Simultaneously, add 200.0 g of methyl ethyl ketone (MEK) as a solvent. Heat the system to 60°C to completely dissolve the epoxy resin B5, obtaining a dissolved epoxy resin B5, BB5 (epoxy resin solution BB5). The solid content of the obtained epoxy resin solution BB5 is 80%.

[0418] [Adhesive coating on film]

[0419] The adhesive in each case was diluted to a solid content of 25% using methyl ethyl ketone (MEK).

[0420] In Experiment 1B, diluted adhesive was applied to one side of a PET film (length: 210 mm, width: 150 mm, thickness: 100 μm, Lumirror: PANAC CO.,LTD) and then dried at 100°C for 1 minute to produce a PET film with an adhesive layer.

[0421] It should be noted that the coating is applied in such a way that the thickness of the dried adhesive layer is 12μm.

[0422] In addition, in Test Example 2B, the PET film was changed to a PEN film (length: 210 mm, width: 150 mm, thickness: 100 μm, made by Theonex: TOYOBO FILM SOLUTIONS LIMITED), and the coating was performed in the same manner as in Test Example 1B.

[0423] Furthermore, in Experiment 3B, the PET film was changed to a PBT film (length: 210 mm, width: 150 mm, thickness: 25 μm, BOBLET: KOHJIN Film & Chemicals Co., Ltd.), and otherwise coated in the same manner as in Experiment 1B.

[0424] In addition, in Test Examples 4B-18B, the PET film was changed to a PEN film in the same manner as in Test Example 2B, and the coating was performed in the same manner as in Test Example 1B.

[0425] [Initial fit]

[0426] For each example of a film with an adhesive layer, the initial adhesion was evaluated.

[0427] Specifically, the evaluation should be conducted according to the following steps.

[0428] (1) The adhesive layer of the film with adhesive layer in each example is overlapped with the aramid paper (which has the same shape as the film with adhesive layer) by abutting the exposed surface of the adhesive layer of the film with adhesive layer in each example.

[0429] (2) Using a laminator set to 80°C, the film with adhesive layer in each example is laminated with aramid paper to make the insulating sheet in each example.

[0430] (3) At room temperature (23±2℃), the aramid paper was peeled off from the film with adhesive layer in each example by pulling by hand, and the initial adhesion was evaluated according to the following criteria.

[0431] Advantages: Aramid paper causes material damage. That is, the remaining aramid paper is peeled off while a portion of the side of the adhesive layer is still adhered to the entire area of ​​the surface in contact with the adhesive layer.

[0432] • Good: Peel off the remaining aramid paper while a portion of the side of the adhesive layer that is bonded to the adhesive layer is still attached.

[0433] • Not acceptable: The aramid paper was simply peeled off, and no residue of the aramid paper was found on the surface where it met the adhesive layer.

[0434] [Peelability]

[0435] For each example of a film with an adhesive layer, peelability was evaluated using Autograph (Shimadzu Corporation, Autograph AGS-J500N).

[0436] Specifically, the evaluation should be conducted according to the following steps.

[0437] (1) The adhesive layer of the film with adhesive layer in each example is overlapped with the aramid paper (which has the same shape as the film with adhesive layer) by abutting the exposed surface of the adhesive layer of the film with adhesive layer in each example.

[0438] (2) Using a laminator set to 80°C, the film with adhesive layer in each example is laminated with aramid paper to make the insulating sheet in each example.

[0439] (3) The insulating sheets of each example were placed in an oven at a specified temperature for a specified time to allow the curing reaction to proceed. For the insulating sheets of Test Examples 1B to 17B, the curing reaction was carried out by placing them in an oven at 50°C for 72 hours. On the other hand, for the insulating sheet of Test Example 18B, the curing reaction was carried out by placing it in an oven at 100°C for 12 hours.

[0440] (4) Cut a test piece with a width of 25 mm and a length of 80 mm from the insulating sheet. Perform a peel test on the test piece using Autograph and evaluate the peelability according to the following criteria. The peel test is performed by a T-shaped peel test with a tensile speed of 100 mm / min.

[0441] • Advantage: Aramid paper causes material damage.

[0442] • Good: The aramid paper did not suffer material damage, and the measured peel strength was above 1N.

[0443] • Not allowed: The measured peel strength is less than 1N.

[0444] [Heat resistance evaluation at 255℃]

[0445] For each example of a film with an adhesive layer, the heat resistance at 255°C was evaluated.

[0446] Specifically, the evaluation should be conducted according to the following steps.

[0447] (1) The adhesive layer of the film with adhesive layer in each example is overlapped with the aramid paper (which has the same shape as the film with adhesive layer) by abutting the exposed surface of the adhesive layer of the film with adhesive layer in each example.

[0448] (2) Using a laminator set to 80°C, the film with adhesive layer in each example is laminated with aramid paper to make a 3-layer insulating sheet in each example.

[0449] (3) The adhesive of each example, diluted with methyl ethyl ketone (MEK) to a solid content of 25%, is applied to the entire side of the 3-layer insulating sheet opposite to the adhesive layer (first adhesive layer) side, and then dried at 100°C for 1 minute to form a second adhesive layer on the 3-layer insulating sheet of each example, thus obtaining a 4-layer insulating sheet.

[0450] It should be noted that the coating is applied in such a way that the thickness of the dried adhesive layer is 12μm.

[0451] (4) The insulating sheet and the aramid paper of each example are overlapped in such a way that the exposed surface of the second adhesive layer in the 4-layer insulating sheet of each example abuts against one side of the aramid paper (which has the same shape as the film with the adhesive layer).

[0452] (5) Using a laminator set to 80°C, the 4-layer insulating sheet of each example is laminated with aramid paper to produce a 5-layer insulating sheet of each example. That is, an insulating sheet is produced by sequentially configuring aramid paper / second adhesive layer / film / first adhesive layer / aramid paper.

[0453] (6) The 5-layer insulating sheets of each example were placed in an oven at a specified temperature for a specified time to allow the curing reaction to proceed in the second adhesive layer. For the insulating sheets of Test Examples 1B to 17B, the curing reaction was carried out by placing them in an oven at 50°C for 72 hours. On the other hand, for the insulating sheet of Test Example 18B, the curing reaction was carried out by placing it in an oven at 100°C for 12 hours.

[0454] (7) Cut out test specimens from the 5-layer insulating sheet of each example with a planar size of 5cm × 5cm, and place each test specimen in an oven at 255°C for 24 hours. Then, evaluate the heat resistance of each test specimen according to the following criteria.

[0455] • Excellent: No deformation or peeling was detected in the insulating sheet after treatment at 255℃.

[0456] • Good: After treatment at 255℃, deformation was confirmed in the insulating sheet, but peeling and excessive expansion were not confirmed.

[0457] • Not acceptable: After treatment at 255°C, peeling and excessive expansion were observed in the insulation sheet.

[0458] [Heat Resistance Evaluation under Thermogravimetric Differential Thermal Analysis (TG-DTA)]

[0459] For each adhesive example, the heat resistance under thermogravimetric differential calorimetry (TG-DTA) was evaluated.

[0460] Specifically, the evaluation should be conducted according to the following steps.

[0461] (1) Apply the adhesive of each example, which is diluted with methyl ethyl ketone (MEK) to a solid content of 30%, to one side of the release paper and dry it at 100°C for 1 minute to make the release paper with the adhesive layer of each example.

[0462] It should be noted that the coating is applied in such a way that the thickness of the dried adhesive layer is 12μm.

[0463] (2) The release paper with the adhesive layer in each example was placed in an oven at a specified temperature for a specified time to allow the curing reaction to occur in the aforementioned adhesive layer. For the release paper with the adhesive layer in Test Examples 1B to 17B, the curing reaction was carried out by placing it in an oven at 50°C for 72 hours. On the other hand, for the release paper with the adhesive layer in Test Example 18B, the curing reaction was carried out by placing it in an oven at 100°C for 12 hours. After the curing reaction was carried out, the release paper was peeled off from the release paper with the adhesive layer in each test example.

[0464] (3) Using a thermogravimetric differential calorimeter (Rigaku Corporation, TG8120), under an air atmosphere of 100 ml / min, the temperature was increased from room temperature (23±2℃) at a rate of 5℃ / min to obtain the TG-DTA curves of the adhesive layer of each test example peeled from the release paper. Then, the temperature at which the mass decreased by 5% (5% reduction temperature) and the temperature at which the mass decreased by 50% (50% reduction temperature) were observed to determine the heat resistance. It should be noted that the 5% reduction temperature in the TG-DTA curve represents short-term heat resistance, and the 50% reduction temperature in the TG-DTA curve represents long-term heat resistance.

[0465] Heat resistance under thermogravimetric differential thermal analysis (TG-DTA) is evaluated according to the following criteria.

[0466] • Excellent: 5% reduction in temperature above 280℃ and 50% reduction in temperature above 350℃.

[0467] • Good: 5% reduction in temperature above 200℃ and below 280℃, and 50% reduction in temperature above 300℃ and below 350℃.

[0468] • Not allowed: 5% reduction in temperature below 200℃ and 50% reduction in temperature below 300℃.

[0469] [Table 7]

[0470]

[0471] As shown in Table 7, although Test Examples 1B to 13B were cured at a relatively low temperature of 50°C, they, like Test Example 18B which was cured at a relatively high temperature of 100°C, received excellent ratings in initial adhesion, peelability, heat resistance at 255°C, and heat resistance under thermogravimetric differential analysis (TG-DTA).

[0472] In contrast, it can be seen that in the evaluation of initial adhesion, peelability, heat resistance at 255°C, and heat resistance under thermogravimetric differential analysis (TG-DTA), all items of test examples 14B to 17B are unacceptable.

[0473] Therefore, it can be understood that by using polyurethane resin with a hydroxyl value of 0.1 mgKOH / g or higher and 20 mgKOH / g or lower as polyurethane resin, and epoxy resin with an epoxy equivalent of 450 g / eq or higher and 3000 g / eq or lower and a hydroxyl value of 50 mgKOH / g or higher and 250 mgKOH / g or lower as epoxy resin, and using at least one of the groups selected from aliphatic isocyanates and aromatic isocyanates as isocyanate-based crosslinking agents, the insulating sheet can have sufficient heat resistance even without high-temperature curing, and the adhesion to the adhered object is also excellent after the crosslinking reaction.

Claims

1. An insulating sheet comprising: Substrate film, and An insulating layer is laminated onto at least one side of the substrate film using an adhesive layer. The adhesive layer is composed of a resin composition comprising polyurethane resin, epoxy resin, and isocyanate-based crosslinking agent. The resin composition comprises at least one selected from the group consisting of aliphatic isocyanates and aromatic isocyanates as the isocyanate-based crosslinking agent. The polyurethane resin contains carbonate diol as a structural unit, has a carboxyl group, and is a hydroxyl-containing polyurethane resin with hydroxyl groups at the ends. The adhesive layer further comprises urethane-epoxy grafts onto the polyurethane resin, wherein a plurality of the epoxy resins are grafted. The hydroxyl value of this polyurethane resin is above 0.1 mgKOH / g and below 20 mgKOH / g.

2. The insulating sheet according to claim 1, wherein, The epoxy resin includes hydroxyl-containing epoxy resins having hydroxyl groups.

3. The insulating sheet according to claim 1 or 2, wherein, The aliphatic isocyanate is at least one of hexamethylene diisocyanate and isophorone diisocyanate. The aromatic isocyanate is at least one of diphenylmethane diisocyanate and toluene diisocyanate.

4. The insulating sheet according to claim 1 or 2, wherein, The isocyanate-based crosslinking agent comprises 3 to 20 parts by weight of the total amount of the polyurethane resin and the epoxy resin, relative to 100 parts by weight of the total amount of the polyurethane resin and the epoxy resin.

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