Electrically insulating laminates for electrical machinery applications

Abstract

In a first aspect, an electrically insulating laminate comprises a flexible polymer layer with a first thermoplastic polyimide having a glass transition temperature (Tg) in the range of 140 to 280 °C and a first flexible mat layer with a first organic material. The first organic material includes a fabric, nonwoven, or fiber. The flexible polymer layer is thermally bonded and in direct contact with the first organic material. In a second aspect, an electrical machine encloses the electrically insulating laminate of the first aspect.

Description

AREA OF REVELATION

[0001] The scope of this disclosure relates to electrically insulating laminates for electrical machine applications. BACKGROUND OF THE REVELATION

[0002] Gap linings are used in the stators and / or rotors of electrical machines, such as generators and / or motors, to provide insulation between the stator core and / or rotor core and the stator windings and / or rotor windings. The gap lining also separates the rotor windings from the rotor core.

[0003] Stator design constraints include stator laminations, magnet wire, gap insulation, and thermal management.

[0004] Common gap lining materials consist of multi-layered structures bonded together by an adhesive or glue. Typically, a core layer is surrounded by two outer layers of a different material and bonded to them using additional layers of adhesive applied between the core and outer layers. Adhesives include polyurethane, acrylic, epoxy resin, and silicone chemicals.

[0005] In the case of an electrically insulating laminate structure where the outer layer is removed from the core layer solely by physical force, e.g., by a peeling process, the typical type of material failure observed is adhesive failure at the adhesive-bonded material interface. This is not a desirable failure mode. A more preferred failure mode is cohesive failure, which occurs in the bulk layers of either the adhesive or, sometimes, in the bulk of one of the components being bonded (i.e., the materials being bonded).

[0006] Good adhesion is particularly crucial when using high-temperature electric motors, where the temperature stress is combined with exposure of the laminate material to chemicals (such as automatic transmission fluid) that may contain impurities which typical adhesive formulations cannot withstand due to their low glass transition temperature (Tg). g) or incompatibility with other chemicals can degrade. If the gap lining material delaminates during the lifespan of the electric machine, fast-switching inverters build up charges and reduce the effective partial discharge peak voltage of the electrical insulation system. Furthermore, there is a risk of unintentionally introducing voids into the adhesive layer during application due to air entrapment during the coating process. These voids could trigger corona discharge or adhesive breakdown when exposed to high electric fields. Therefore, using a chemically, electrically, and thermally stable insulation design is in the OEMs' interest to ensure machine reliability.One option is to use a gap lining that does not contain adhesive layers between the bonded parts. An additional advantage of eliminating adhesive layers is an overall thinner gap lining material construction without compromising the desired performance properties of the gap lining material, since the presence of adhesive layers typically thickens the entire gap lining material laminate by approximately 1 µm.

[0007] Previous efforts to avoid the use of adhesives in gap lining laminate materials while simultaneously using a polyimide material as a core are described in US patents 10,173,403 B2 and 10,836,112 B2, as well as in US patent application 2012 / 0128988 A1. These patents describe plasma treatment of the surfaces of the materials to be bonded and their subsequent joining by applying temperature and pressure. However, this approach requires additional material processing steps, increasing complexity and cost. Furthermore, US patent 10,836,112 B2 describes the lamination of polyimide film and aramid paper in the absence of adhesives by applying high temperature and high pressure.However, the bond strength between the individual layers in the resulting laminate is only described qualitatively, and it therefore remains unclear whether the laminates would withstand subsequent processing steps such as folding. DETAILED DESCRIPTION

[0008] In a first aspect, an electrically insulating laminate encloses a flexible polymer layer with a first thermoplastic polyimide having a glass transition temperature (Tg). g ) in a temperature range of 140 to 280 °C and a first flexible mat layer containing a first organic material. The first organic material comprises a fabric, nonwoven, or fiber. The flexible polymer layer is thermally bonded and in direct contact with the first organic material.

[0009] In a second aspect, an electrical machine encloses the electrically insulating laminate of the first aspect.

[0010] Many aspects and embodiments have been described above and are merely exemplary and not limiting. After reading this description, those skilled in the art will recognize that other aspects and embodiments are possible without deviating from the scope of the invention. Further features and advantages of the invention will become apparent from the following detailed description and from the claims.

[0011] Within the scope of the present invention, an “aromatic diamine” is understood to be a diamine with at least one aromatic ring, either alone (i.e., a substituted or unsubstituted, functionalized or unfunctionalized benzene ring or similar aromatic ring) or linked to another (aromatic or aliphatic) ring, and such an amine is considered aromatic irrespective of any non-aromatic units that might also be a component of the diamine. Thus, an aromatic diamine main chain segment is understood to be at least one aromatic unit between two adjacent imide bonds. Within the scope of the present invention, an “aliphatic amine” is understood to be any organic diamine that does not meet the definition of an aromatic diamine.

[0012] Depending on the context, “diamine,” as used herein, shall mean: (i) the unreacted form (i.e., a diamine monomer); (ii) a partially reacted form (i.e., the part or parts of an oligomer or other polymer precursor derived from or otherwise attributable to the diamine monomer); or (iii) a fully reacted form (the part or parts of the polymer derived from or otherwise attributable to the diamine monomer). The diamine may be functionalized with one or more units, depending on the specific embodiment selected in carrying out the present invention.

[0013] The term “diamine” is not intended to impose any restriction (or literal interpretation) regarding the number of amine units in the diamine component. For example, (ii) and (iii) above include polymeric materials that may contain two, one, or no amine units. Alternatively, the diamine may be functionalized with additional amine units (besides the amine units at the ends of the monomer that react with dianhydride to continue a polymer chain). Such additional amine units could be used to crosslink the polymer or to provide further functionality to the polymer.

[0014] Similarly, the term "dianhydride," as used here, is intended to refer to the component that reacts with the diamine (is complementary to the diamine) and, in combination, is capable of reacting to form a polyamic acid intermediate (which can then be cured to a polyimide). Depending on the context, the term "anhydride," as used here, can mean not only an anhydride unit per se, but also a precursor to an anhydride unit, such as: (i) a pair of carboxylic acid groups (which can be converted to anhydride by dehydration or a similar reaction); or (ii) an acid halide (e.g., chloride) ester functionality (or any other functionality currently known or developed in the future) that can be converted into an anhydride functionality.

[0015] Depending on the context, “dianhydride” can mean: (i) the unreacted form (that is, a dianhydride monomer, regardless of whether the anhydride functionality is in a true anhydride form or in a precursor anhydride form, as discussed in the preceding paragraph); (ii) a partially reacted form (that is, the part or parts of an oligomer or other partially reacted or precursor polymer composition that has been reacted from or is otherwise attributable to a dianhydride monomer); or (iii) a fully reacted form (the part or parts of the polymer that are derived from or are otherwise attributable to the dianhydride monomer).

[0016] The dianhydride can be functionalized with one or more units, depending on the specific embodiment chosen in the practice of the present invention. The term "dianhydride" is not intended to be restrictive (or literal) with regard to the number of anhydride units in the dianhydride component. For example, (i), (ii), and (iii) (in the preceding paragraph) include organic substances that may have two, one, or no anhydride units, depending on whether the anhydride is in a precursor state or a reaction state. Alternatively, the dianhydride component can be functionalized with additional anhydride units (besides those that react with diamine to form a polyimide). Such additional anhydride units could be used to crosslink the polymer or to provide further functional properties to the polymer.

[0017] Any of a number of polymer manufacturing processes can be used to produce polymer films. It would be impossible to discuss or describe all possible polymer manufacturing processes suitable for the present invention. It should be noted that the monomer systems of the present invention are capable of providing the advantageous properties described above in a multitude of manufacturing processes. The compositions of the present invention can be prepared as described herein and can be readily prepared by those skilled in the art using any conventional or unconventional polymer manufacturing technology in one of many (possibly countless) ways.

[0018] Although methods and materials similar or equivalent to those described herein may also be used in carrying out or testing the present invention, suitable methods and materials are described here.

[0019] When a quantity, concentration, or other value or parameter is specified as a range, preferred range, or list of upper preferred values ​​and lower preferred values, this is to be understood as including all ranges formed by any pair of an upper range limit or preferred value and a lower range limit or preferred value, regardless of whether ranges are disclosed separately. Where a range of numerical values ​​is specified herein, unless otherwise stated, this range shall include the endpoints and all integers and fractions within the range. The scope of the invention shall not be limited to the specific values ​​specified in the definition of a range.

[0020] When describing certain polymers, it should be noted that applicants sometimes refer to the polymers based on the monomers used in their manufacture or the quantity of monomers used in their manufacture. While such a description may not include the specific nomenclature for describing the final polymer or contain product-specific terminology, any reference to monomers and quantities should be interpreted as indicating that the polymer was manufactured from those monomers or that quantity of monomers, and that the corresponding polymers and combinations thereof are meant.

[0021] The materials, procedures and examples presented here are for illustrative purposes only and are not intended to be restrictive unless explicitly stated otherwise.

[0022] As used herein, the terms “comprises,” “comprehensive,” “includes,” “including,” “exhibit,” “exhibiting,” or any variation thereof are intended to cover non-exclusive inclusion. For example, a method, process, item, or device that includes a list of elements is not necessarily limited to only those elements but may also include other elements not expressly listed or inherent in such method, process, item, or device. Furthermore, unless expressly stated otherwise, “or” refers to an inclusive “or” and not an exclusive “or.” For example, a condition “A or B” is satisfied by each of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

[0023] Furthermore, the articles "a" or "an" are used to describe elements and components of the invention. This is done solely for the sake of clarity and to generalize the invention. This description should be understood to include one or at least one, and the singular also includes the plural unless it is obvious that something else is meant. Organic solvents

[0024] Organic solvents suitable for the synthesis of the polymers of the present invention are preferably capable of dissolving the polymer precursor materials. Such a solvent should furthermore have a relatively low boiling point, such as below 225 °C, so that the polymer can be dried at moderate (i.e., more convenient and cost-effective) temperatures. A boiling point of less than 210, 205, 200, 195, 190, or 180 °C is preferred.

[0025] Suitable organic solvents include: N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAc), methyl ethyl ketone (MEK), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), tetramethylurea (TMU), glycol ethyl ether, diethylene glycol diethyl ether, 1,2-dimethoxyethane (Monoglyme), diethylene glycol dimethyl ether (Diglyme), 1,2-bis(2-methoxyethoxy)ethane (Triglyme), gamma-butyrolactone and bis(2-methoxyethyl) ether, tetrahydrofuran (THF), ethyl acetate, hydroxyethyl acetate glycol monoacetate, acetone, and mixtures thereof. In one embodiment, preferred solvents include N-methylpyrrolidone (NMP) and N,N-dimethylacetamide (DMAc). Diamine

[0026] In one embodiment, a suitable diamine for forming the polymer film can include an aliphatic diamine such as 1,2-diaminoethane, 1,6-diaminohexane (FIMD), 1,4-diaminobutane, 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane, 1,10-diaminodecane (DMD), 1,11-diaminoundecane, 1,12-diaminododecane (DDD), 1,16-hexadecamethylenediamine, 1,3-bis(3-aminopropyl)tetramethyldisiloxane, isophoronediamine, bicyclo[2.2.2]octane-1,4-diamine and combinations thereof. Other aliphatic diamines suitable for carrying out the invention include those with six to twelve carbon atoms or a combination of longer-chain and shorter-chain diamines, provided that both scalability and flexibility are maintained. Long-chain aliphatic diamines increase flexibility.

[0027] In one embodiment, a suitable diamine for forming the polymer film can further include a fluorinated aromatic diamine, such as 2,2'-bis(trifluoromethyl)benzidine (TFMB), trifluoromethyl-2,4-diaminobenzene, trifluoromethyl-3,5-diaminobenzene, 2,2'-bis-(4-aminophenyl)hexafluoropropane, 4,4'-diamino-2,2'-trifluoromethyldiphenyl oxide, 3,3'-diamino-5,5'-trifluoromethyldiphenyl oxide, 9,9'-bis(4-aminophenyl)fluorene, 4,4'-trifluoromethyl-2,2'-diaminobiphenyl, 4,4'-oxy-bis-[2-trifluoromethyl)benzenamine] (1,2,4-OBABTF), 4,4'-oxy-bis-[3-trifluoromethyl)benzenamine], 4,4'-Thio-bis-[(2-trifluoromethyl)benzene], 4,4'-Thiobis[(3-trifluoromethyl)benzene], 4,4'-Sulfoxyl-bis-[(2-trifluoromethyl)benzene], 4,4'-Sulfoxyl-bis-[(3-trifluoromethyl)benzene], 4,4'-Keto-bis-[(2-trifluoromethyl)benzene], 1,1-Bis[4'-(4“-amino-2"-trifluoromethylphenoxy)phenyl]cyclopentane, 1,1-Bis[4'-(4“-amino-2"-trifluoromethylphenoxy)phenyl]cyclohexane, 2-Trifluoromethyl-4,4'-diaminodiphenyl ether;1,4-(2'-Trifluoromethyl-4',4''-diaminodiphenoxy)benzene, 1,4-Bis(4'-aminophenoxy)-2-[(3',5'-ditrifluoromethyl)phenyl]benzene, 1,4-Bis[2'-cyano-3'(4-aminophenoxy)phenoxy]-2-[(3',5'-ditrifluoromethyl)phenyl]benzene (6FC-diamine), 3,5-Diamino-4-methyl-2',3',5',6'-tetrafluoro-4'-trifluoromethyldiphenyloxide, 2,2-Bis[4'(4''-aminophenoxy)phenyl]phthalein-3',5'-bis(trifluoromethyl)anilide (6FADAP), and 3,3',5,5'-Tetrafluoro-4,4'-diamino-diphenylmethane (TFDAM). In a specific embodiment, the fluorinated diamine 2,2'-Bis(trifluoromethyl)benzidine (TFMB). In one embodiment, a fluorinated aromatic diamine can be present in a range of 40 to 95 mol percent, based on the total diamine content of the polyimide. In a more specific embodiment, the fluorinated aromatic diamine can be present in a range of 50 to 75 mol percent, based on the total diamine content of the polyimide.

[0028] In one embodiment, any number of additional diamines can be used to form the polymer film, including p-phenylenediamine (PPD), m-phenylenediamine (MPD), 2,5-dimethyl-1,4-diaminobenzene, 2,5-dimethyl-1,4-phenylenediamine (DPX), 2,2-bis-(4-aminophenyl)propane, 1,4-naphthalenediamine, 1,5-naphthalenediamine, 4,4'-diaminobiphenyl, 4,4''-diamino-terphenyl, 4,4'-diaminobenzanilide, 4,4'-diaminophenylbenzoate, 4,4'-diaminobenzophenone, 4,4'-diaminodiphenylmethane (MDA), 4,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, and bis-(4-(4-aminophenoxy)phenylsulfone). (BAPS), 4,4'-bis-(aminophenoxy)biphenyl (BAPB), 4,4'-diaminodiphenyl ether (ODA), 3,4'-diaminodiphenyl ether, 4,4'-diaminobenzophenone, 4,4'-isopropylidenedianiline, 2,2'-bis-(3-aminophenyl)propane, N,N-Bis-(4-aminophenyl)-n-butylamine, N,N-Bis-(4-aminophenyl)methylamine, 1,5-diaminonaphthalene, 3,3'-dimethyl-4,4'-diaminobiphenyl, m-aminobenzoyl-p-aminoanilide, 4-aminophenyl-3-aminobenzoate, N,N-Bis-(4-aminophenyl)aniline, 2,4-Diaminotoluene, 2,5-Diaminotoluene, 2,6-Diaminotoluene, 2,4-Diamine-5-chlorotoluene, 2,4-Diamine-6-chlorotoluene, 2,4-Bis-(beta-amino-t-butyl)toluene, Bis-(p-beta-amino-t-butylphenyl) ether, p-Bis-2-(2-methyl-4-aminopentyl)benzene, m-Xylylenediamine and p-Xylylenediamine.

[0029] Other suitable diamines include 1,2-bis-(4-aminophenoxy)benzene, 1,3-bis-(4-aminophenoxy)benzene (RODA), 1,2-bis-(3-aminophenoxy)benzene, 1,3-bis-(3-aminophenoxy)benzene, 1-(4-aminophenoxy)-3-(3-aminophenoxy)benzene, 1,4-bis-(4-aminophenoxy)benzene, 1,4-bis-(3-aminophenoxy)benzene, 1-(4-aminophenoxy)-4-(3-aminophenoxy)benzene, 2,2-bis-(4-[4-aminophenoxy]phenyl)propane (BAPP), 2,2'-bis-(4-phenoxyaniline)isopropylidene, 2,4,6-trimethyl-1,3-diaminobenzene, and 2,4,6-trimethyl-1,3-diaminobenzene a.

[0030] Diamines that can be used in the polymer film include the following: meta-phenylenediamine; para-phenylenediamine; 2,2-bis(4-aminophenyl)propane; 4,4'-diaminodiphenylmethane; 4,4'-diaminodiphenyl sulfide; 4,4'-diaminodiphenyl sulfone; 3,3'-diaminodiphenyl sulfone; 4,4'-diaminodiphenyl ether; 2,6-diaminopyridine; bis(3-aminophenyl)diethylsilane; benzidine; 3,3'-dichlorobenzidine; 3,3'-dimethoxybenzidine; 4,4'-diaminobenzophenone; N,N-bis(4-aminophenyl)-n-butylamine; N,N-bis(4-aminophenyl)methylamine; 1,5-diaminonaphthalene; 3,3'-dimethyl-4,4'-diaminobiphenyl; m-Aminobenzoyl-p-aminoanilide; 4-Aminophenyl-3-aminobenzoate, N,N-Bis(4-aminophenyl)aniline; 2,4-Bis(beta-amino-t-butyl)toluene; Bis(p-beta-amino-t-butylphenyl)ether; p-Bis-2-(2-methyl-4-aminopentyl)benzene; p-Bis(1,1-dimethyl-5-aminopentyl)benzene; m-Xylylenediamine; p-Xylylenediamine; Positional isomers of the above-mentioned compounds and mixtures thereof. Dianhydrides

[0031] In one embodiment, any number of suitable dianhydrides can be used to form the polymer film. The dianhydrides can be used in their tetraacid form (or as mono-, di-, tri-, or tetraesters of the tetraacid) or as their diester acid halides (chlorides). In some embodiments, however, the dianhydride form may be preferred because it is generally more reactive than the acid or the ester.

[0032] Examples of suitable dianhydrides include 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 2-(3',4'-dicarboxyphenyl)-5,6-dicarboxybenzimidazole dianhydride, 2-(3',4'-dicarboxyphenyl)-5,6-dicarboxybenzoxazole dianhydride, 2-(3',4'-dicarboxyphenyl)-5,6-dicarboxybenzothiazole dianhydride, 2,2',3,3'-benzophenonetetracarboxylic dianhydride, 2,3,3',4'-benzophenonetetracarboxylic dianhydride, and 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA). 2,2',3,3'-biphenyltetracarboxylic acid dianhydride, 2,3,3',4'-biphenyltetracarboxylic acid dianhydride, bicyclo-[2,2,2]-octene-(7)-2,3,5,6-tetracarboxylic acid 2,3,5,6-dianhydride, 4,4'-thio-diphthalic anhydride, Bis(3,4-dicarboxyphenyl)sulfone dianhydride, Bis(3,4-dicarboxyphenyl) sulfoxide dianhydride (DSDA), Bis(3,4-dicarboxyphenyl-oxadiazole-1,3,4) p-phenylenedianhydride, Bis(3,4-dicarboxyphenyl) 2,5-oxadiazole-1,3,4-dianhydride,Bis-2,5-(3',4'-dicarboxydiphenyl ether)-1,3,4-oxadiazole dianhydride, 4,4'-oxydiphthalic anhydride (ODPA), Bis(3,4-dicarboxyphenyl)thioether dianhydride, Bisphenol A dianhydride (BPADA), Bisphenol S dianhydride, Bis-1,3-isobenzofuranedione, 1,4-Bis(4,4'-oxyphthalic anhydride)benzene, Bis(3,4-dicarboxyphenyl)methane dianhydride, Cyclopentadienyl tetracarboxylic dianhydride, Cyclopentane tetracarboxylic dianhydride, Ethylene tetracarboxylic dianhydride, Perylene 3,4,9,10-tetracarboxylic dianhydride, Pyromellitic dianhydride (PMDA), Tetrahydrofuran tetracarboxylic dianhydride, 1,3-Bis-(4,4'-oxydiphthalic anhydride)benzene 2,2-Bis(3,4-dicarboxyphenyl)propane dihydride, 2,6-Dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,7-Dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,3,6,7-Tetrachloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, Phenanthrene-1,8,9,10-tetracarboxylic dianhydride, Pyrazine-2,3,5,6-tetracarboxylic dianhydride, Benzene-1,2,3,4-tetracarboxylic dianhydride and Thiophene-2,3,4,5-tetracarboxylic acid dianhydride.

[0033] In one embodiment, a suitable dianhydride may include an alicyclic dianhydride, such as cyclobutane dianhydride (CBDA), cyclohexane dianhydride, 1,2,3,4-cyclopentanetetracarboxylic acid dianhydride (CPDA), hexahydro-4,8-ethano-1H,3H-benzo[1,2-c:4,5-c']difuran-1,3,5,7-tetrone (BODA), 3-(carboxymethyl)-1,2,4-cyclopentanetricarboxylic acid 1,4:2,3-dianhydride (TCA) and meso-butane-1,2,3,4-tetracarboxylic acid dianhydride.

[0034] In one embodiment, a suitable dianhydride for forming the polymer film can include a fluorinated dianhydride, such as 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 9,9-bis(trifluoromethyl)-2,3,6,7-xanthene tetracarboxylic dianhydride. In a specific embodiment, the fluorinated dianhydride is 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA).

[0035] Dianhydrides that can be used in the polymer film include the following: pyromellitic dianhydride; 3,4,9,10-perylene tetracarboxylic dianhydride; naphthalene 2,3,6,7-tetracarboxylic dianhydride; naphthalene 1,4,5,8-tetracarboxylic dianhydride; bis(3,4-dicarboxyphenyl)ether dianhydride; bis(3,4-dicarboxyphenyl)sulfone dianhydride; 2,3,2',3'-benzophenone tetracarboxylic dianhydride; bis(3,4-dicarboxyphenyl)sulfide dianhydride; bis(3,4-dicarboxyphenyl)methane dianhydride; 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride; 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane; 3,4,3',4'-biphenyl tetracarboxylic dianhydride; 2,6-Dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride; 2,7-Dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride; 2,3,6,7-Tetrachloronaphthalene-1,4,5,8-tetracarboxylic dianhydride; Phenanthrene-1,8,9,10-tetracarboxylic dianhydride; Pyrazine-2,3,5,6-tetracarboxylic dianhydride; Benzene-1,2,3,4-tetracarboxylic dianhydride; and Thiophene-2,3,4,5-tetracarboxylic dianhydride. Polymer film

[0036] In one embodiment, a polymer film or polymer layer may have a dielectric constant in the range of 3.0 to 4.5 when measured at 1 MHz according to the method described in IPC-TM-650 2.5.5.3. In another embodiment, a polymer film may have a coefficient of thermal expansion (CTE) along the XY axis in the range of 10 to 75 ppm / °C when measured over a temperature range of 50 to 250 °C according to the method described in IPC-TM-650 2.4.41. In another embodiment, a polymer film may have a dielectric strength in the range of 3000 to 7000 V / µm when measured according to the method described in ASTM D149. In another embodiment, a polymer film has a thermal class rating of H. In yet another embodiment, the polymer film has one or more of the aforementioned properties but includes two, three, or more polymer layers.

[0037] Polymer films can be plasma-treated by passing them through a low-temperature plasma treatment device of the type with an internal electrode, as described in Japanese patent application No. 4607826 B2. The ratio of the number of oxygen atoms (O) to the number of carbon atoms (C) in the plasma-treated surface of the material exceeds 150% relative to the theoretical value of the ratio before treatment. Methods for determining the ratio of the number of oxygen atoms (O) to the number of carbon atoms (C) in the surface of the material include X-ray photoelectron spectroscopy (XPS). Flexible polymer layers

[0038] In one embodiment, a flexible polymer layer encloses a thermoplastic polymer with a glass transition temperature (Tg) in the range of 140 to 280 °C. Methods suitable for determining the Tg include the use of dynamic mechanical analysis (DMA), as described, for example, in ASTM E1640 or IPC-TM-650. In one embodiment, a thermoplastic polymer with a Tg in the range of 140 to 280 °C can include a polyimide, a polyamide, a polycarbonate, a polyester, a polysulfone, a poly(amide-imide), a poly(ether-imide), a poly(ether-sulfone), a poly(ether-ether-sulfone), a poly(phenylsulfone), a bisphenol A polysulfone, a poly(etherketone), a poly(etheretherketone), a poly((1,4-phenylenoxy-1,4-phenylenecarbonyl-1,4-phenylenecarbonyl), a poly-para-phenylene copolymer, a self-reinforced polyphenylene, a perfluorosulfonic acid ionomer, or a cyclic olefin copolymer.

[0039] In one embodiment, a flexible polymer layer encloses a polyimide film layer. In a more specific embodiment, the flexible polymer layer encloses a thermoplastic polyimide film layer. Polyimide film layers according to the present invention can be produced by combining the diamine and the dianhydride (monomer or other polyimide precursor form) together with a solvent to form a polyamic acid solution. The dianhydride and the diamine can be combined in a molar ratio of about 0.90 to 1.10. The molecular weight of the polyamic acid formed therefrom can be adjusted by modifying the molar ratio of dianhydride and diamine.

[0040] In one embodiment, a polyamic acid casting solution is derived from the polyamic acid solution. The polyamic acid casting solution preferably comprises the polyamic acid solution and may optionally be combined with conversion chemicals such as: i.) one or more dehydrating agents, such as aliphatic anhydrides (acetic anhydride, etc.) and / or aromatic anhydrides; and ii.) one or more catalysts, such as aliphatic tertiary amines (triethylamine, etc.), aromatic tertiary amines (dimethylaniline, etc.), and heterocyclic tertiary amines (pyridine, picoline, isoquinoline, etc.). The anhydride dehydrating material is often used in a molar excess compared to the amount of amide groups in the polyamic acid. The amount of acetic anhydride used is typically about 2.0 to 4.0 moles per equivalent (repeating unit) of polyamic acid. Generally, a comparable amount of tertiary amine catalyst is used.

[0041] In one embodiment, the polyamic acid solution and / or the polyamic acid casting solution are dissolved in an organic solvent at a concentration of about 5.0 or 10 to about 15, 20, 25, 30, 35 or 40 wt.%.

[0042] The polyamic acid (and casting solution) may further comprise any of a number of additives, such as processing aids (e.g., oligomers), antioxidants, light stabilizers, flame retardants, antistatic agents, heat stabilizers, UV absorbers, (organic or inorganic) fillers, or various reinforcing agents. Fillers may include inorganic fillers such as thermally conductive fillers, a corona-resistant composite filler, and electrically conductive fillers such as metals, graphitic carbon and carbon fibers, and electrically conductive polymers. Common inorganic fillers are aluminum oxide, silicon dioxide, silicon carbide, diamond, clay, boron nitride, aluminum nitride, aluminum oxide, titanium dioxide, dicalcium phosphate, and pyrogenic metal oxides.Common organic fillers include polyaniline, polythiophene, polypyrrole, polyphenylenevinylene, polydialkylfluorene, carbon black, graphite, multi-walled and single-walled carbon nanotubes and carbon nanofibers.

[0043] Suitable thermally conductive fillers that are also electrically insulating include BN, AlN, Al₂O₃, Si₃N₄, ZnO, MgCO₃, MgO, BeO, diamond, SiC, many other oxide, nitride, and carbide compounds, and mixtures thereof. These thermally conductive fillers can be of any desired shape and size and have an average primary particle size (D50) in the range of about 0.001 to about 8 µm. In one embodiment, a flexible polymer layer containing thermally conductive fillers has a thermal conductivity of 0.4 W / mK or greater, or 0.6 W / mK or greater, when the thermal conductivity is measured according to the method described in ASTM D5470.

[0044] In one embodiment, a corona-resistant composite filler may comprise an organic component and an inorganic ceramic oxide component, wherein the weight ratio of the organic component to the inorganic ceramic oxide component is from 0.01:1 to 1:1. In some embodiments, the weight ratio of the organic component to the inorganic ceramic oxide component may be in a range between (and optionally including) any two of the following: 0.01:1, 0.05:1, 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, and 1:1. In one embodiment, at least a portion of the organic component may include an organosiloxane unit or an organometalloxane unit (e.g., organozirconate, organotitanate, organoaluminate). In one embodiment, the inorganic ceramic oxide component may include silicon dioxide, aluminum oxide, titanium dioxide, zirconium dioxide or mixtures thereof.In one embodiment, the inorganic ceramic oxide component includes silicon dioxide, aluminum oxide, or a mixture thereof. In another embodiment, the inorganic ceramic oxide component is pyrogenic aluminum oxide. In one embodiment, the organic component of the corona-resistant composite filler material is selected primarily to provide or improve the dispersibility of the corona-resistant composite filler material in a particular solvated polymer matrix or solvated polymer matrix precursor. In some embodiments, the organic component of the corona-resistant composite filler is selected to reduce the moisture absorption of the inorganic ceramic oxide component. Optimizing the organic component for a particular solvent system may require common technical expertise and experimentation.In some embodiments, the organosiloxane unit is n-octylsilane or one of its structural isomers. In some embodiments, the corona-resistant composite filler is an inorganic ceramic oxide without an organic component. In another embodiment, the organic component is a coating on the inorganic ceramic oxide component. The organic component may or may not cover the entire surface of the inorganic ceramic oxide component. In one embodiment, the electrically insulating, corona-resistant composite filler is present in an amount between and including any two of the following: 5, 10, 15, 20, 25, and 30 percent by weight, based on the total weight of the polymer film. In another embodiment, the corona-resistant composite filler is present in an amount in the range of 5 to 30, 5 to 25, or 5 to 20 percent by weight, based on the total weight of the polymer film.In one embodiment, the corona-resistant composite filler can have a mean particle size of 0.1 to 5 µm, wherein at least 80, 85, 90, 92, 94, 95, 96, 98, 99, or 100 percent of the dispersed corona-resistant composite filler lies within the size range defined above. The median particle size can be measured using a Horiba LA-930 particle size analyzer (Horiba Instruments, Inc., Irvine, CA). DMAc can be used as the carrier fluid. In some embodiments, the corona-resistant composite filler is a nanofiller. The term "nanofiller" is intended to refer to a filler in which at least one dimension is smaller than 1000 nm, i.e., smaller than 1 µm.

[0045] In one embodiment, a filler is dispersed or suspended in a polar, aprotic solvent such as DMAc or another solvent or solvent mixture compatible with polyamic acid. In another embodiment, the filler may be dispersed in an organic solvent at a concentration of approximately 5, 10, or 15 wt% to approximately 20, 30, 40, 50, and 75 wt%. In another embodiment, the solvent used to disperse or suspend the filler is the same as, or different from, the solvent used for the polyamic acid solution. The dispersion or suspension of the filler may then be added to the polyamic acid casting solution to achieve the desired filler loading of the finished film. The filler may be added using any commonly employed technique, such as batch mixing using solvent(s), dry mixing, or continuous mixing using solvent(s).Parameters such as the order of raw material addition, the mixing speed, the shear rate, the type of mixing paddle (e.g., shear paddle), the mixing time, the temperature, and the pressure are known to influence the final degree of mixing between the filler and the matrix material. In one embodiment, the filler slurry is mixed with a polyamic acid solution to form the filler-polyamic acid casting solution, using high-shear mixing. In one embodiment, the first outer layer of a multilayer film can contain filler in an amount of more than 0 to approximately 50 wt.% of the dry film. In another embodiment, the core layer of a multilayer film can contain filler in an amount of more than 0 to approximately 60 wt.% of the dry film. In another embodiment, the second outer layer of a multilayer film can contain filler in an amount of more than 0 to approximately 50 wt.% of the dry film.-% of the dry film. In one embodiment, the first outer layer, the core layer, and the second outer layer can each contain the same or a different amount of filler, based on the weight percentage of the dry film, as the other layers in the multilayer film. In one embodiment, the weight percentage of filler in the core layer can be higher than that of the first outer layer, the second outer layer, or both. In another embodiment, the weight percentage of filler in the core layer can be lower than that of the first outer layer, the second outer layer, or both. In yet another embodiment, in the case of a multilayer film, only the core layer contains a filler, or conversely, only the outer layers contain a filler.In one embodiment, the presence of a filler in the flexible polymer layer leads to an improvement in the failure time in a stress-resistance test compared to a flexible polymer layer of comparable thickness that does not contain a substantial amount of filler, when the stress resistance is tested according to the procedure described in ASTM D2275. The amount of filler present in a given layer can be determined, for example, by ash testing or thermogravimetric analysis (TGA). The chemical identity of a filler can be determined, for example, by mechanical preparation of cross-sections in conjunction with microscopy-assisted optical evaluation, such as by scanning electron microscopy using energy-dispersive X-ray analysis (EDX).

[0046] The solvated mixture (the polyamic acid casting solution, which may also contain a filler) can then be cast or applied to a support, such as an endless belt or a rotating drum, to obtain a film. Subsequently, the solvent-containing film can be converted into a self-supporting film by heating it to a suitable temperature (thermal curing) together with the chemical conversion reactants (chemical curing). The film can then be separated from the support and oriented, for example, by tensioning, with the thermal and chemical curing continuing to produce a polyimide film.

[0047] Suitable methods for producing polyimide film according to the present invention can be found in US patents Nos. 5,166,308 A and 5,298,331 A, which are hereby incorporated in their entirety by reference into this description. Numerous variations are also possible, such as… (a) a process wherein the diamine components and the dianhydride components are pre-mixed together and then the mixture is added in portions to a solvent while stirring. (b) A process wherein a solvent is added to a stirring mixture of diamine and dianhydride components. (in contrast to (a) above) (c) A process wherein diamines are dissolved exclusively in a solvent and then dianhydrides are added in such a ratio that the reaction rate can be controlled. (d) A process wherein the dianhydride components are dissolved exclusively in a solvent and then amine components are added in such a ratio that the reaction rate can be controlled. (e) A process wherein the diamine components and the dianhydride components are dissolved separately in solvents and these solutions are then mixed in a reactor. (f) A process wherein the polyamic acid with an excess of amine component and another polyamic acid with an excess of dianhydride component are preformed and then reacted together in a reactor, in particular in such a way as to produce a non-random or block copolymer. (g) A process wherein a specific proportion of the amine components and the dianhydride components is reacted first and then the remaining diamine components are reacted, or vice versa. (h) A process wherein the conversion chemicals are mixed with the polyamic acid to form a polyamic acid casting solution and then cast to form a gel film. (i) A process wherein the components are added partially or completely in any order to part or all of the solvent, even if part or all of a component may be added as a solution in part or all of the solvent. (j) A process wherein first one of the dianhydride components is reacted with one of the diamine components to form a first polyamic acid. Then the other dianhydride component is reacted with the other amine component to obtain a second polyamic acid. Subsequently, the amino acids are combined with one another in various ways before film formation.

[0048] The polymer film layer can comprise more than one layer, with one or more polymer layers arranged on a first layer. The composition and thickness of each layer are chosen independently and can be the same or different. Consequently, the mechanical, thermal, and optical properties of a single layer in a multilayer polymer film can be the same or different from those of the other surrounding layers. In one embodiment, the multilayer film has at least two polymer layers. In another embodiment, the multilayer film has fewer than ten layers. In one embodiment, the multilayer polymer film comprises at least one core layer and two thermoplastic polymer layers. In a particular embodiment, the outermost layers in a multilayer polymer film with at least two layers are thermoplastic polymer layers.In one embodiment, the polymer in each layer is a polyimide. In a more specific embodiment, the outermost layers in a multilayer polyimide film with at least three layers are thermoplastic polyimide layers, in addition to a core polyimide layer as the inner layer. In the case of multilayer polyimide films, the thermal conductivity (Tg) of the core layer is higher than the Tg of the thermoplastic polyimide layer.

[0049] The thickness of each polymer layer can be adjusted depending on the intended use of the film or final application specifications. In one embodiment, the multilayer film has a total thickness of approximately 5 to approximately 150 µm. In another embodiment, the multilayer film has a total thickness of approximately 5 to approximately 75 µm. In one embodiment, the thickness of the core layer is in the range of approximately 35 to approximately 73% of the total thickness of the multilayer film. For example, a multilayer film may have a total thickness of 30 µm, with a core layer that is 22 µm thick and a first and second outer layer on either side of the core layer that are each 4 µm thick. In another example of a thicker film, a multilayer film could have a total thickness of 50 µm, with a 34 µm thick core layer and a 7 µm thick first and second outer layer on either side of the core layer.In another example, for a very thin film, a multilayer film could have a total thickness of 5 µm, with a 2 µm thick core layer and a 1.5 µm thick first and second outer layer on either side of the core layer. In one embodiment, the thickness of the core layer is in the range of approximately 55 to approximately 73% of the total thickness of the multilayer film. Those skilled in the art know that a minimum thickness of the outer layers with thermoplastic polyimide is required to provide sufficient adhesion during lamination to other layers. Furthermore, a minimum thickness of the core layer is necessary to maintain the mechanical integrity of the multilayer film. Methods for determining the thickness of each layer involve the mechanical preparation of cross-sections together with microscopically assisted optical evaluation, for example, using a scanning electron microscope.

[0050] In one embodiment, the first thermoplastic polyimide and the second thermoplastic polyimide of the multilayer film both have a T g in the range of approximately 140 to approximately 320 °C. In a specific embodiment, the first thermoplastic polyimide and the second thermoplastic polyimide of the multilayer film both have a T g in the range of approximately 160 to approximately 300 °C. In a more specific embodiment, the first thermoplastic polyimide and the second thermoplastic polyimide of the multilayer film both have a T g in the range of approximately 180 to approximately 280 °C. This is achieved through thermoplastic polyimides in the outer layers with a higher temperature rating. gThe thermal resistance of the multilayer film is improved. Laminates can be subjected to processes such as hot-bar machining or spot welding after lamination at temperatures sometimes exceeding 300 °C. Under these conditions, a thermoplastic polyimide layer with low thermal resistance (Tw) is suitable. g prone to loss of adhesion and delamination, deformation and blistering.

[0051] In one embodiment, the first thermoplastic polyimide and the second thermoplastic polyimide of the multilayer film are each individually derived from an aromatic dianhydride selected from the group consisting of 4,4'-oxydiphthalic dianhydride, pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride and mixtures thereof, and an aromatic diamine selected from the group consisting of 1,3-bis(4-aminophenoxy)benzene, hexamethylenediamine, 2,2-bis-(4-[4-aminophenoxy]phenyl)propane and mixtures thereof. In one embodiment, the first thermoplastic polyimide and the second thermoplastic polyimide of the multilayer film are each individually derived from an aromatic dianhydride comprising 4,4'-oxydiphthalic dianhydride and pyromellitic dianhydride, and an aromatic diamine comprising 1,3-bis(4-aminophenoxy)benzene.

[0052] In one embodiment, the core layer has a Tg of more than 320 °C. In a more specific embodiment, the core layer has a T g of more than 340 °C. In another special embodiment, the core layer has no detectable temperature. g below 375 °C.

[0053] In one embodiment, the core layer and the outer layers can be solution-cast simultaneously by co-extrusion. At the time of casting, the polyimides can be present in the form of a polyamic acid solution. The cast solutions form an uncured polyamic acid film, which is subsequently cured to a polyimide. The adhesive strength of such laminates can be improved by applying various techniques to increase adhesion.

[0054] In some embodiments, a finished polyamic acid solution is filtered and pumped to a slot die, where the stream is split to form the first outer layer and the second outer layer of a three-layer coextruded film. In some embodiments, a second stream of polyimide is filtered and then pumped to a casting die to form the middle polyimide core layer of a three-layer coextruded film. The flow rates of the solutions can be adjusted to achieve the desired layer thickness.

[0055] In some embodiments, the multilayer film is produced by simultaneously extruding the first outer layer, the core layer, and the second outer layer. In some embodiments, the layers are extruded through an extrusion die with a single or multiple cavities. In another embodiment, the multilayer film is produced using a die with a single cavity. When using a die with a single cavity, the laminar flow of the streams should have a sufficiently high viscosity to prevent mixing of the streams and to provide uniform layering. In some embodiments, the multilayer film is produced by casting from the slot die onto a moving stainless steel belt.In one embodiment, the tape is then passed through a convection oven to evaporate solvents and partially imidize the polymer to produce a "green" film. The green film can be peeled off the casting tape and wound up. The green film can then be passed through a tensioning oven to obtain a fully cured polyimide film. In some embodiments, shrinkage during tensioning can be minimized by securing the film along its edges (i.e., using clamps or pins).

[0056] In one embodiment, the outer layers of the present invention can also be applied to the core layer during an intermediate manufacturing stage of the production of a polyimide film, such as a gel film or a green film.

[0057] The term "gel film" refers to a polyamic acid film so heavily saturated with volatile substances, primarily solvents, that the polyamic acid transitions into a gel-like or rubbery state and can be shaped through a chemical transformation process. The volatile content is typically in the range of 70 to 90 wt%, and the polymer content is typically in the range of 10 to 30 wt% of the gel film. The final film becomes self-supporting in the gel film stage. It can be peeled from the substrate onto which it was poured and heated to a final curing temperature. The gel film generally has an amidic acid to imide ratio between 10:90 and 50:50, very often 30:70.

[0058] The gel film structure can be produced by the process described in U.S. Patent No. 3,410,826 A. This patent discloses the mixing of a chemical conversion agent and a catalyst, such as a lower fatty acid anhydride and a tertiary amine, into the polyamic acid solution at low temperature. Subsequently, the polyamic acid solution is poured in film form onto a casting drum. After pouring, the film is gently heated, for example to 100 °C, to activate the conversion agent and the catalyst and to convert the poured film into a polyamic acid / polyimide gel film.

[0059] Another type of polyimide film is a "green film," which consists partly of polyamic acid and partly of polyimide and can be formed in a thermal conversion process. Green film generally contains about 50 to 75 wt% polymer and 25 to 50 wt% solvent. It should generally be stable enough to be essentially self-supporting. Green film can be produced by pouring the polyamic acid solution in film form onto a suitable support such as a casting drum or belt and removing the solvent by heating to up to 150 °C. A small proportion of amidic acid units in the polymer, e.g., up to 25%, can be converted into imide units.

[0060] The application of the polymer films of the present invention can be achieved in a variety of ways. Such methods include the use of a slot die, dip coating, or kiss-roll coating of a film, followed by metered application with a doctor blade, doctor rollers, squeeze rollers, or an air knife. The coating can also be applied by brushing or spraying. Both single-sided and double-sided coated laminates can be produced using such techniques. In the production of double-sided coated structures, the coating can be applied to both sides of a polyimide either simultaneously or sequentially before the curing and drying stage of the polyimide is initiated.

[0061] In one embodiment, a single polymer layer or the entire multilayer polymer film has a coefficient of thermal expansion (CTE) of less than 70 ppm / °C (average of machine and transverse values), less than 40 ppm / °C, or less than 30 ppm / °C over a temperature range of 50 to 250 °C. Thermoplastic polymer layers and the core layer in a multilayer film can have different CTE values ​​(when evaluated separately as individual films). In one embodiment, the CTE value of a core layer in a multilayer film is lower than that of the thermoplastic polymer layers (when evaluated separately as individual films). In another embodiment, the core layer has a coefficient of thermal expansion of less than 70 ppm / °C (average of machine and transverse values), less than 40 ppm / °C, or less than 30 ppm / °C over a temperature range of 50 to 250 °C.By maintaining a low CTE over a wide temperature range, the multilayer film can maintain good adhesion even during curing at higher temperatures. This can be used to stabilize materials that undergo post-processing at higher temperatures after lamination. Laminates may be subjected to hot-bar machining or spot welding at temperatures sometimes exceeding 300 °C. Under these conditions, a multilayer film with a high CTE is susceptible to loss of adhesion and delamination, distortion, and blistering. Suitable methods for determining the CTE include measurements using a thermomechanical analyzer (TMA), as described, for example, in ASTM D3386. In one embodiment, the multilayer film has a CTE close to that of a flexible mat layer (described below).Appropriate CTE values ​​between a multilayer film and a flexible mat layer minimize the risk of deformation, wrinkling, and bulging when such layers are combined to form a laminate structure. Flexible mat layers

[0062] In one embodiment, a first flexible mat layer encloses a first organic material that is thermally bonded to the flexible polymer layer, wherein the first organic material comprises a woven fabric, nonwoven, or fiber. The first organic material may comprise 35 to 75 wt.% of a first binder and 25 to 65 wt.% of a first aramid flake, based on the total amount of the first binder and the first flake in the first flexible mat layer. In some embodiments, the first organic material comprises 40 to 60 wt.% of a first binder and 40 to 60 wt.% of a first aramid flake, based on the total amount of the first binder and the first flake in the first flexible mat layer. In some embodiments, the first flexible mat layer contains more binder than flake.

[0063] The use of this first flexible mat layer provides higher mechanical strength for the electrically insulating laminate structure, which is desirable for use in electrical machine applications. On a weight basis, a multilayer structure comprising the first flexible mat layer has better mechanical strength than a structure comprising only the flexible polymer layer. Preferably, the first flexible mat layer is free or substantially free of any inorganic filler. The term "substantially free" as used here means that the first flexible mat layer functions thermally and mechanically as if no inorganic filler were present in the layer, even if trace amounts of inorganic filler impurities are present in this layer.In one embodiment, a binder can be any chemical, treatment, or additive known in the art to bind flake or fibrous material to form paper, wherein in one embodiment the binder is a binder particle, such as a particle with a film-like structure. In another embodiment, the binder particle can be a fibrid, such as an aramid fibrid.

[0064] The term "flock" here refers to fibers cut to a short length, typically used for the production of wet-laid webs and / or papers. Typically, the flock has a length of approximately 3 to 20 mm. In one embodiment, the flock has a length of approximately 3 to 7 mm. The flock is normally produced by cutting continuous fibers to the required lengths using well-known techniques.

[0065] The term "aramid," as used here, means aromatic polyamide in which at least 85% of the amide (-CONH-) bonds are directly linked to two aromatic rings. Additives can optionally be used with the aramid and dispersed within the polymer structure. It has been found that up to approximately 10 wt% of other polymeric materials can be mixed with the aramid. It has also been found that copolymers with up to approximately 10 mol% of other diamines can be used as a replacement for the diamine in the aramid, or up to approximately 10 mol% of other diacid chlorides can be used as a replacement for the diacid chloride in the aramid.

[0066] In one embodiment, an aramid is a meta-aramid. An aramid polymer is considered a meta-aramid if the two rings or residues along the molecular chain are meta-oriented to each other. In one embodiment, a meta-aramid is poly(metaphenyleneisophthalamide) (MPD-I). US Patents Nos. 3,063,966 A, 3,227,793 A, 3,287,324 A, 3,414,645 A, and 5,667,743 A illustrate suitable methods for producing aramid fibers that could be used to produce aramid flakes.

[0067] Alternatively, the aramid flake could be a para-aramid or an aramid copolymer. The aramid polymer is considered a para-aramid if the two rings or radicals are para-oriented with respect to each other along the molecular chain. Methods for producing para-aramid fibers are generally disclosed, for example, in U.S. Patents Nos. 3,869,430 A, 3,869,429 A, and 3,767,756 A. In one embodiment, a para-aramid is poly(paraphenylene terephthalamide). In another embodiment, a para-aramid copolymer is a copoly(p-phenylene / 3,4'-diphenyl ester terephthalamide).

[0068] In one embodiment, an aramid flake is a meta-aramid flake, such as a flake made from the meta-aramid poly(meta-phenyleneisophthalamide) (MPD-I).

[0069] The term "fibrids" here refers to very small, non-granular, fibrous, or film-like particles in which at least one of their three dimensions is small relative to the largest dimension. These particles are produced by precipitation of a solution of polymeric material using a non-solvent under high shear. Aramid fibrids are non-granular, film-like particles of aromatic polyamide with a melting point or decomposition point above 320 °C. The preferred aramid fibrid is a meta-aramid fibrid; fibrids of the meta-aramid poly(metaphenyleneisophthalamide) (MPD-I) are particularly preferred. Aramid fibers can be produced as generally described in U.S. Patent No. 3,756,908 A.

[0070] Fibrides generally have a maximum longitudinal dimension in the range of approximately 0.1 mm to 1 mm, with a length-to-width ratio of approximately 5:1 to 10:1. The thickness is on the order of a fraction of a micrometer, for example, approximately 0.1 µm to 1.0 µm. Although not required, aramid fibrides can be incorporated into the layers while the fibrides are still wet.

[0071] The term "flexible mat layer," as used here, refers to a thin, sheet-like material of a special composition, sometimes called "paper." Paper can be manufactured as generally described in U.S. Patents Nos. 9,844,928 B2, 10,173,403 B2, and 10,836,112 B2.

[0072] In one embodiment, a flexible mat layer has a thickness of 0.5 mm or less, 0.25 mm or less, 0.13 mm or less, or 0.1 mm or less. It is assumed that a single flexible mat layer should have a thickness of at least 0.025 mm to provide sufficient tensile strength for the electrically insulating laminate. Examples of flexible mat layer products include DuPont™ Nomex® papers (available from DuPont de Nemours Inc., Wilmington, DE).

[0073] In one embodiment, a flexible mat layer exhibits a dielectric strength in the range of 400 to 800 V / µm when measured according to the method described in ASTM D149. In another embodiment, a flexible mat layer has a dielectric constant in the range of 1.5 to 4.0, measured at 60 Hz according to the method described in ASTM D150. In another embodiment, a flexible mat layer exhibits desirable mechanical properties, including high tensile strength in the range of 40 to 200 N / cm in the machine direction (MD) and 5 to 20 N / cm in the transverse direction (TD), and elongation at break in the range of 10 to 25% in MD and 5 to 20% in TD, measured according to the method described in ASTM D828. In another embodiment, a flexible mat layer has a thermal class rating of H.

[0074] In one embodiment, a flexible mat layer has a T gof more than 320 °C. In a more specific embodiment, the flexible mat layer has a T g of more than 340 °C. In another embodiment, the flexible mat layer has a T g of more than 360 °C.

[0075] In one embodiment, a flexible mat layer can be plasma-treated by passing it through a low-temperature, internal-electrode-type plasma treatment device described in Japanese patent application No. 4607826 B2. The ratio of the number of oxygen atoms (O) to the number of carbon atoms (C) in the plasma-treated surface of the material exceeds 150% relative to the theoretical value of the ratio of the number of atoms before treatment. Production of electrically insulating laminates

[0076] In one embodiment, the flexible mat layer is arranged on one or both sides of the electrically insulating laminate, and the polymer film is arranged as the core layer of the laminate. The flexible mat layer provides satisfactory electrical insulation, chemical stability (chemical resistance), mechanical stability, and heat resistance, while the polymer film not only provides satisfactory chemical stability and heat resistance but also offers additional electrical insulation and gas-liquid impermeability. The individual layers can be laminated by any method commonly used in this field, in which temperature and pressure can be applied to the materials to be laminated during the process. In one embodiment, methods for forming the electrically insulating laminate include heating, pressing, heating under pressure, and the like.Examples of these processes include, but are not limited to, a hot-pressing process, a process involving passing between a pair of heated rollers or belts, a process using hot air, bonding by ultrasound. Here, it is desirable to control the temperature for forming the laminate via the T. gThe temperature of the polymer layer (or a single thermoplastic polyimide layer in the case of a multilayer polyimide film) is increased, but the temperature for forming the laminate is not raised to a temperature close to the melting point or decomposition temperature of any of the layers, but rather set lower than these temperatures. In one embodiment, the temperature used to form the laminate does not exceed the glass transition temperature of the polymer layer (or a single thermoplastic polyimide layer in the case of a multilayer polyimide film) by more than 150 °C.

[0077] The dimensions of the flexible mat layer and the polymer film are not limited to specific sizes. The sizes to be used can be determined taking into account various factors such as the application of the electrically insulating laminate, production costs, and existing equipment limitations. From a productivity standpoint, one roll of flexible mat layer and one roll of polymer film are prepared, and the laminate is produced using a continuous heating and pressing process. When producing a prototype or a special order, manufacturing can be simplified by using smaller sizes of flexible mat layer and polymer film.

[0078] The heating and pressure process refers to a method in which both heat and pressure are applied to the laminate. Although a device that performs the heating and pressure process is not limited to a specific type of equipment, one embodiment uses a calender machine. Calender machines are widely used in industry and consist of several calender rolls that exert a compressive force on a sheet being processed by passing it between the rolls. Passing the target material between the calender rolls can increase its density and improve its smoothness. Depending on the pressure and temperature conditions to be applied to the target material, rolls of suitable size and material, such as steel or elastic, are selected.The configuration of the calender rollers is not limited to a specific configuration. A laminate in which different materials are bonded together can be produced by passing multiple target webs between the calender rollers. A suitable calendering machine is selected depending on the dimensions of the webs to be laminated. For example, if the flexible mat layer and the polymer film to be layered are long and in rolled form, a calendering machine with a paper feed function for two or more rollers can be used.

[0079] In one embodiment, the flexible mat layer and the polymer film are laminated directly onto each other without an additional adhesive layer in between. This mode makes it possible to reduce manufacturing costs and increase productivity. According to the present invention, an electrically insulating laminate with sufficient adhesion can be produced without the presence of an adhesive layer. Methods for detecting the absence of additional adhesive layers include the mechanical preparation of cross-sections together with a microscopically assisted optical evaluation, for example, using a scanning electron microscope, or a mechanically based evaluation, for example, by nanoindentation.

[0080] In one embodiment, the adhesive surfaces of the flexible mat layer and the polymer film are not plasma-treated before the heating and pressure application process. Although the adhesion can be improved by plasma treatment of the adhesive surfaces, the present invention allows for the production of an electrically insulating laminate with sufficient adhesion without plasma treatment. Using a method for producing the laminate without plasma treatment can reduce manufacturing costs and increase productivity.

[0081] The temperature during the heating and pressure process is set to at least the glass transition temperature of the polyimide material forming the laminate. If the heating and pressure process is carried out using calender rolls, the temperature of the calender rolls is set to at least the glass transition temperature of the polyimide forming the laminate.

[0082] In one embodiment, a temperature in the range of 200 to 360 °C can be used in the heating and pressurization process. In a specific embodiment, a temperature in the range of 240 to 340 °C or 260 to 320 °C can be used. The temperature in the heating and pressurization process can generally be set by a control mechanism of the device used. For example, the temperature of a heating and pressurization device, such as the calender rolls, can be controlled as the target temperature of the calender rolls.

[0083] In one embodiment, in addition to the aforementioned specific temperature, a pressure in the range of 400 to 800 psi (2758 to 5516 kPa) can be used in the heating and pressurizing process. In a particular embodiment, a pressure in the range of 450 to 750 psi (3103 to 5171 kPa), 500 to 700 psi (3447 to 4826 kPa), or 525 to 675 psi (3620 to 4654 kPa) can be used. The pressure in the heating and pressurizing process can generally be adjusted via the control mechanism of the equipment used. For example, the pressure of the heating and pressurizing device, such as the calender rolls, can generally be controlled using the device's control mechanism.

[0084] In one embodiment of an electrically insulating laminate, the composition ratio of the number of oxygen atoms (O) to the number of carbon atoms (C) on the surface of the first thermoplastic polyimide layer differs by less than 1% when compared to the same ratio found within the volume of the first thermoplastic polyimide layer. In another embodiment, the composition ratio of the number of oxygen atoms (O) to the number of carbon atoms (C) on the surface of the first organic material differs by less than 1% when compared to the same ratio found within the volume of the first organic material.

[0085] In one embodiment of an electrically insulating laminate, both the flexible polymer layer and the first flexible mat layer have a thermal class rating of at least H. In one embodiment of an electrically insulating laminate, the flexible polymer layer has a dielectric strength of at least 5000 V / µm and the first flexible mat layer has a dielectric strength of at least 400 V / µm. In one embodiment of an electrically insulating laminate, the peel strength between the flexible polymer layer and the first flexible mat layer is at least 0.100 N / mm.

[0086] Electrically insulating laminates of the present invention are suitable for use in electrical machines, for example as gap linings for stators and rotors, such as generators and motors, providing electrical insulation between the stator core and / or rotor core and the stator windings and / or rotor windings. Gap linings also separate the rotor windings from the rotor core. In one embodiment, the electrically insulating laminates are used as gap linings in the form of folded sheets. In another embodiment, the electrically insulating laminates are used as gap linings in the form of tubes, preferably as multilayer spiral tubes manufactured without layer overlap, i.e., the thickness of the tube is uniform around its circumference. EXAMPLES Test methods Peel resistance

[0087] Peel strength results were obtained using an Instron 180° T-peel test. Laminate samples were 1 inch (2.54 cm) wide, had an initial gripping distance of 2 inches (5.08 cm), and were evaluated at a crosshead speed of 12 inches / min (30.48 cm / min). The maximum load observed after a 3-inch (7.62 cm) elongation was reported. The numerical average of 5 independent samples was reported. Glass transition temperature

[0088] The glass transition temperature (T g The tan ΔT of each material was measured according to the IPC-TM-650 test procedure using dynamic mechanical analysis (Q800 DMA, TA Instrument, New Castle, DE). The test specimens were conditioned for at least 24 hours at 23 °C and 50% relative humidity prior to testing. Heating was carried out at a rate of 5 °C / min in dry air, and the value of the first tan ΔT peak was reported unless otherwise stated.

[0089] The glass transition temperature (Tg) was determined for selected samples. g ) individual materials were measured using differential scanning calorimetry according to the method described in US Patent No. 10,836,112 B2. Thermal conductivity

[0090] Thermal conductivity was measured according to the method described in ASTM D5470 at 50 °C and 150 psi (1034 kPa) without the use of oil. One, two, and four layers of material were used. Pull test

[0091] Tensile tests, which allow the determination of mechanical properties such as elongation at break, tensile strength, modulus of elasticity, etc., were performed according to ASTM D882. Coefficient of thermal expansion

[0092] The tests were performed according to ASTM D3386. The results shown are the average of the CTE observed in the transverse direction (TD) and in the machine direction (MD). Example 1

[0093] For Example 1 (E1), to prepare a polyamic acid solution with a monomer composition of BPDA 0.9 / BTDA 0.1 / RODA 0.25 / HMD 0.75, 0.05 mol of the diamines were dissolved in DMAc and stirred under nitrogen with a mechanical stirrer. Stirring was continued, and 0.05 mol of the dianhydrides were added as solids over a short period. The polyamic acid solution with a solids content of about 20 wt% was decanted and then completed by the stepwise addition of a 6 wt% solution of pyromellith dianhydride (PMDA) in DMAc to obtain a maximum viscosity of 2500–3000 poise (250–300 Pa s). Using a stainless steel pouring rod, the polymer mixture was manually poured onto a glass plate and placed on a hot plate set to 80 °C. The film was heated until it could be removed from the glass plate and transferred to a pen frame.The film was then imidied by heating it in an oven, with the temperature being increased from 100 °C to approximately 20 °C above the glass transition temperature of the final polyimide film. The film was then removed from the oven, allowed to cool to room temperature, and subsequently removed from the pin frame. A polyimide film with a thickness of approximately 25 µm and a glass transition temperature of 199 °C was obtained. Example 2

[0094] For Example 2 (E2), a first polyamic acid solution “A” with a monomer composition of ODPA 0.8 / PMDA 0.2 / RODA 0.7 / HMD 0.3 was prepared according to the procedure described above for E1. A second polyamic acid solution “B” with a monomer composition of BPDA 0.9 / PMDA 0.1 / PPD 0.9 / ODA 0.1 was prepared according to the procedure described above for E1. Both polyamic acid solutions were poured together onto a stainless steel strip and subsequently imidized by heating in an oven. A three-layer polyimide film ABA with a total thickness of approximately 25 µm was obtained. The glass transition temperature of layer A in the three-layer polyimide film ABA was determined to be 210 °C, and that of layer B to be over 345 °C. The thickness of layers A in the three-layer film was on the order of 3 µm. The three-layer film had a CTE value of less than 30 ppm / °C. Example 3

[0095] For Example 3 (E3), a first polyamic acid solution “A” with a monomer composition of ODPA 0.8 / PMDA 0.2 / RODA 1.0 was prepared according to the procedure described above for E1. A second polyamic acid solution “B” with a monomer composition of BPDA 0.35 / PMDA 0.65 / PPD 0.13 / ODA 0.87 was prepared according to the procedure described above for E1. Both polyamic acid solutions were poured together onto a stainless steel strip and subsequently imidized by heating in an oven. A three-layer polyimide film ABA with a total thickness of approximately 25 µm was obtained. The glass transition temperature of layer A in the three-layer polyimide film ABA was determined to be 235 °C, and that of layer B to be over 345 °C. The thickness of layers A in the three-layer film was on the order of 3 µm. The three-layer film had a CTE value of less than 30 ppm / °C. Example 4

[0096] For Example 4 (E4), the procedure described above for E1 was followed to prepare a polyamic acid solution and to make a polyimide film with a monomer composition of ODPA 0.8 / PMDA 0.2 / RODA 1.0. A polyimide film with a thickness of approximately 25 µm and a glass transition temperature of 233°C was obtained. The film had a CTE value of less than 70 ppm / °C. Example 5

[0097] For Example 5 (E5), the procedure described above for E1 was followed to prepare a polyamic acid solution and to make a polyimide film with a monomer composition of ODPA 0.8 / PMDA 0.2 / RODA 1.0. A polyimide film with a thickness of approximately 75 µm and a glass transition temperature of 240°C was obtained. The film had a CTE value of less than 70 ppm / °C. Example 6

[0098] For Example 6 (E6), a first polyamic acid solution “A” with a monomer composition of ODPA 0.8 / PMDA 0.2 / RODA 1.0 was prepared according to the procedure described above for E1, and 25 wt% boron nitride was additionally incorporated as a filler (filler content based on the polyimide content in the final film). A second polyamic acid solution “B” with a monomer composition of PMDA / ODA was prepared according to the procedure described above for E1, with the addition of 50 wt% boron nitride as a filler (filler content based on the polyimide content in the final film). Both polyamic acid solutions were poured together onto a stainless steel strip and subsequently imidied by heating in an oven. A three-layer polyimide film ABA with a total thickness of approximately 38 µm was obtained. The glass transition temperature of layer A in the three-layer polyimide film ABA was determined to be 232 °C, and that of layer B to be over 375 °C.The thickness of layers A in the three-layer film was on the order of 5 µm. The thermal conductivity of the finished film was approximately 0.60 W / mK. Example 7

[0099] For Example 7 (E7), a first polyamic acid solution “A” with a monomer composition of ODPA 0.8 / PMDA 0.2 / / RODA 1.0 was prepared according to the procedure described above for E1. A second polyamic acid solution “B” with a monomer composition of PMDA / / ODA was prepared according to the procedure described above for E1. Both polyamic acid solutions were poured together onto a stainless steel strip and subsequently imidized by heating in an oven. A three-layer polyimide film ABA with a total thickness of approximately 25 µm was obtained. The glass transition temperature of layer A in the three-layer polyimide film ABA was determined to be 228°C, and that of layer B to be over 345°C. The thickness of layers A in the three-layer film was on the order of 3 µm. The three-layer film had a CTE value of less than 70 ppm / °C. Example 8

[0100] For Example 8 (E8), a first polyamic acid solution “A” with a monomer composition of ODPA 0.8 / PMDA 0.2 / / RODA 1.0 was prepared according to the procedure described above for E1. A second polyamic acid solution “B” with a monomer composition of PMDA / / ODA was prepared according to the procedure described above for E1. Both polyamic acid solutions were co-cast on a hot rotating drum under chemical curing conditions, and the resulting self-supporting film was removed from the drum and subsequently further dried and imidized by heating in an oven. A three-layer polyimide film ABA with a total thickness of about 25 µm was obtained. The glass transition temperature of layer A in the three-layer polyimide film ABA was determined to be 228°C, and that of layer B to be over 345°C. The thickness of layers A in the three-layer film was on the order of 3 µm.The three-layer film had a CTE value of less than 40 ppm / °C. Comparison examples 1 and 2

[0101] In comparative examples 1 and 2 (CE1 and CE2), a polyimide film Kapton® HA (DuPont) with the composition PMDA / / ODA, a thickness of 25 µm and a glass transition temperature of more than 375 °C was used. Comparative examples 3 and 4

[0102] In comparative examples 3 and 4 (CE3 and CE4), a polyimide film Kapton® HN (DuPont) with the composition PMDA / / ODA, a thickness of 25 µm and a glass transition temperature of more than 375 °C was used. Comparative examples 5 and 6

[0103] In comparative examples 5 and 6 (CE5 and CE6), a polyimide film Kapton® HN with the composition PMDA / / ODA, a thickness of 12.5 µm and a glass transition temperature of more than 375 °C was used. Comparative examples 7 and 8

[0104] For comparative examples 7 and 8 (CE7 and CE8), the procedure described above for E1 was used to prepare a polyamic acid solution and a polyimide film with a monomer composition of BPDA 0.88 / PMDA 0.12 / / ODA 0.5 / PPD 0.95. This resulted in a polyimide film with a thickness of approximately 25 µm and a glass transition temperature of more than 345 °C but less than 375 °C. Comparative example 9

[0105] In comparative example 9 (CE9), a Kapton® HN polyimide film with the composition PMDA / / ODA, a thickness of 25 µm, and a glass transition temperature greater than 375 °C was used. The film was plasma-treated on both sides (treatment duration 30 seconds, power setting 100 W, gas type argon, chamber pressure 100 mTorr) and used within 24 hours of treatment. Similarly, sheets of Nomex® type 464 LAM were plasma-treated and used within 24 hours of treatment. Comparative example 10 (CE10)

[0106] In comparative example 10 (CE10), the polyimide film obtained in CE7CE8 was used. The film was plasma-treated on both sides (treatment time 30 seconds, power setting 100 W, gas type argon, chamber pressure 100 mTorr) and used within 24 hours of treatment. Similarly, sheets of Nomex® Type 464 LAM were plasma-treated and used within 24 hours of treatment. Comparative example 11

[0107] In comparative example 11 (CE11), a polyimide film Kapton® H (DuPont-Toray Co., Japan) with the composition PMDA / / ODA, a thickness of 50 µm, and a glass transition temperature above 375 °C was used. Using DSC, no endothermic change in the film, traditionally associated with a glass transition temperature, could be detected below 375 °C. Comparative example 12

[0108] In comparative example 12 (CE12), a polyimide film Kapton® HA with the composition PMDA / / ODA, a thickness of 25 µm and a glass transition temperature above 375 °C was used. Comparative example 13

[0109] In comparative example 13, a polyimide film Kapton® HN with the composition PMDA / / ODA, a thickness of 25 µm and a glass transition temperature of over 375 °C was used. Comparative example 14

[0110] In comparative example 14 (CE14), a polyimide film Kapton® HN with the composition PMDA / / ODA, a thickness of 12.5 µm and a glass transition temperature of over 375 °C was used. Electrically insulating laminates

[0111] Electrically insulating three-layer laminate structures were fabricated using the polyimide films produced in Examples E1-E6 and Comparative Examples CE1-CE14. These films consist of a polyimide core bonded to two outer layers of flexible mat. The thermoplastic polyimides, with glass transition temperatures between approximately 199 °C and 240 °C, were laminated onto 50 µm aramid paper. In Examples E1-E5 and Comparative Examples CE1-CE11, Nomex® Type 464 LAM (DuPont) was used. Nomex® 464 LAM exhibited a glass transition temperature of approximately 275 °C by DSC. In Example E6 and Comparative Examples CE12-CE14, Nomex® Type 410 (DuPont) was used. In Examples E7 and E8, Nomex® Type 410 (DuPont) was used.

[0112] The individual films of the three-layer laminate structures were dried prior to lamination to reduce the moisture content to below 3%. Subsequently, the three-layer structures were laminated using highly polished steel plates with two buffer layers of 1.0 µm Kapton® HN (DuPont) using a hydraulic hot press at temperatures of 280 °C, 300 °C, and 320 °C, respectively, and 625 psi (4309 kPa) to form the electrically insulating laminate. The Nomex® sheets were prepared with a 2-inch (5.08 cm) extension in the machine direction relative to the polyimide layer to facilitate peel initiation in the subsequent peel strength test. The peel strength and T gValues ​​are listed in Table 1. “*” means that the interlaminar bond strength exceeded the tensile strength of the peeled material, which was assigned a peel strength value of more than 0.400 N / mm² based on experimental determination. Table 1 Example Peel strength (N / mm) T g vonPolyimid(°C) Polyimide thickness (µm) 280°C 300°C 320°C E1 0,122 0,192 * 199 25 E2 0,380 * * 210 25 E3 0,319 0,280 * 235 25 E4 0,321 * * 233 25 E5 0,359 0,373 * 240 75 E6 * - * 232 38 E7 228 25 E8 228 25 CE1 0,023 - - >375 25 CE2 - - 0,025 >375 25 CE3 0,025 - - >375 25 CE4 - - 0,030 >375 25 CE5 0,023 - - >375 12,5 CE6 - - 0,037 >375 12,5 CE7 0,030 - - >345 25 CE8 - - 0,032 >345 25 CE9 - - 0,081 >375 25 CE10 - - 0,026 >345 25 CE11 - - 0,077 >345 50 CE12 - - 0,032 >375 25 CE13 - - 0,032 >375 25 CE14 - - 0,033 >375 25 QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 10,173,403 B2

[0007] US 10,836,112 B2 [0007, 0089] US 2012 / 0128988 A1

[0007] JP 4607826 B2 [0037, 0075] US 3,410,826 A

[0058] US 3,756,908 A

[0069]

Claims

[1] Electrically insulating laminate, comprising: a flexible polymer layer comprising a first thermoplastic polyimide with a glass transition temperature (T g ) in the range of 140 to 280 °C; and a first flexible mat layer comprising a first organic material, wherein the first organic material comprises a fabric, a fleece, or a fiber; and The flexible polymer layer is thermally bonded and in direct contact with the first organic material. [2] Electrically insulating laminate according to claim 1, wherein the first organic material is selected from the group consisting of aramid paper, aramid fiber and mixtures thereof. [3] Electrically insulating laminate according to claim 1 or 2, further comprising a second flexible mat layer comprising a second organic material adhering to the flexible polymer layer on one side opposite the first flexible mat layer, wherein the second organic material comprises a fabric, a nonwoven or a fiber. [4] Electrically insulating laminate according to claim 3, wherein the second organic material is selected from the group consisting of aramid paper, aramid fiber and mixtures thereof. [5] Electrically insulating laminate according to any one of claims 1 to 4, wherein the first comprises thermoplastic polyimide: an aromatic dianhydride selected from the group consisting of 4,4'-oxydiphthalic dianhydride, pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride and mixtures thereof; and an aromatic diamine selected from the group consisting of 1,3-bis(4-aminophenoxy)benzene, hexamethylenediamine, 2,2-bis-(4-[4-aminophenoxy]phenyl)propane and mixtures thereof. [6] Electrically insulating laminate according to any one of claims 1 to 5, wherein the flexible polymer layer further comprises: a core layer comprising a polyimide adhered to the first thermoplastic polyimide; and a second thermoplastic polyimide that adheres to the core layer on a side opposite the first thermoplastic polyimide. [7] Electrically insulating laminate according to claim 6, wherein the second comprises thermoplastic polyimide: an aromatic dianhydride selected from the group consisting of 4,4'-oxydiphthalic dianhydride, pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride and mixtures thereof; and an aromatic diamine selected from the group consisting of 1,3-bis(4-aminophenoxy)benzene, hexamethylenediamine and mixtures thereof. [8] Electrically insulating laminate according to claim 6 or 7, wherein the first thermoplastic polyimide and the second thermoplastic polyimide are the same or different. [9] Electrically insulating laminate according to any one of claims 6 to 8, wherein the core layer comprises: an aromatic dianhydride selected from the group consisting of 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxydiphthalic dianhydride, pyromellitic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, bisphenol A dianhydride, 1,2,5,6-naphthalene tetracarboxylic dianhydride, 1,4,5,8-naphthalene tetracarboxylic dianhydride and 2,3,6,7-naphthalene tetracarboxylic dianhydride and mixtures thereof. [10] Electrically insulating laminate according to any one of claims 6 to 9, wherein the core layer comprises: an aromatic diamine selected from the group consisting of p-phenylenediamine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 2,2'-bis(trifluoromethyl)benzidine, m-phenylenediamine and 4,4'-diaminodiphenylmethane. [11] Electrically insulating laminate according to any one of claims 1 to 10, wherein the flexible polymer layer contains an inorganic or organic filler or a mixture thereof. [12] Electrically insulating laminate according to any one of claims 6 to 10, wherein the core layer and both thermoplastic polyimide layers contain an inorganic or organic filler or a mixture thereof. [13] Electric machine comprising the electrically insulating laminate according to any one of claims 1 to 12.