Electrically insulated conductors and methods for electrically insulating conductors

Abstract

To provide electrically insulated conductors that are resistant to partial discharge (PD), and methods for electrically insulating conductors.SOLUTION: Disclosed herein are exemplary embodiments and methods for electrically insulated conductors. The electrically insulated conductors are resistant to partial discharge (PD), and suitable for PD resistant design schemes (e.g., 800 V or above electric motors, etc.). An exemplary method includes applying an enamel coating along an electrical conductor, wrapping an electrically insulative tape around the enameled electrical conductor, and heat-sealing the tape-wrapped, enameled electrical conductor to ensure good adhesion of the electrically insulative tape to the enamel coating. The electrically insulative tape comprises polyimide and a sufficient amount of an electrically insulative, corona-resistant filler for PD resistance. The tape-wrapped, enameled electrical conductor is resistant to partial discharge (PD), e.g., suitable for use in a stator winding of an 800 volt or above electric motor, etc.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to electrically insulated conductors that are resistant to partial discharge (PD) and suitable for use, for example, in the stator windings of electric motors of 800 volts or greater, and methods for electrically insulating conductors. [Background technology]

[0002] This section provides background information related to the present disclosure that is not necessarily prior art. Electric vehicles are in common use today, and their use is expected to increase significantly over time. The electric motors used in electric vehicles may be driven by pulse width modulated (PWM) inverters. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0003] Example embodiments will now be described more fully with reference to the accompanying drawings. Hairpin winding technology is becoming more common in the design of electric motors (e-motors) for electric vehicles, especially for traction motor applications that require high power density. Another common design shift in e-motors is the increase in system voltage from the current 400V standard to 800V. The increase to 800V places more stress on the wire insulation material around the copper hairpin conductors in e-motors. Also, a failure in the wire insulation material used to insulate the copper conductors to prevent short circuits to ground in e-motors would render the entire e-motor useless and unrepairable.

[0004] A particular stress that the wire insulation material in an 800V motor is potentially subjected to is so-called "partial discharge" ("PD"). Partial discharge is a phenomenon whereby, under certain conditions, the wire insulation material continuously degrades under the influence of an applied electric field until the insulation eventually fails and the e-motor shorts out. Partial discharge is not an issue with insulation materials commonly used in 400Ve motors and can be avoided in 800Ve motors as part of a so-called "PD-free" motor design scheme. In a PD-free design approach, the thickness of the wire insulation material is increased beyond a certain thickness threshold that is derived from empirical formulas known in the industry and avoids the PD phenomenon from occurring. The drawback of increasing the thickness of the wire insulation is that the amount of copper that can be placed in the e-motor (commonly referred to as the copper fill factor) is reduced, which increases the electrical resistance of the copper wire in the e-motor and thus reduces the performance of the e-motor. Thus, the safer PD-free design of the e-motor directly results in reduced motor performance.

[0005] A competing design approach for wire insulation in 800Ve motors is the so-called "PD-resistant" design. In the PD-resistant design approach, the wire insulation material is kept thinner than necessary to avoid partial discharge events occurring inside e-motors, which allows for a higher copper fill factor. To address the partial discharge events currently occurring in e-motors, the insulation material is made resistant to partial discharge, which is why this design approach is commonly referred to as a "PD-resistant" design. The resistance of the wire insulation material to PD is generally achieved by filling a portion of the wire insulation material (typically composed of organic polymers) with inorganic fillers.

[0006] As further recognized herein, the industry standard for wire insulation in 400V e-motors is currently a varnish / enamel organic polymer, which is coated onto rectangular shaped copper wires (round copper wires or aluminum as conductor materials are less common) before the rectangular shaped copper wires are inserted into the e-motors. Increasing the system voltage of electric vehicles from 400V to 800V requires the application of thicker insulation materials around each wire in the e-motor to accommodate the increased electrical insulation requirements and stay in the PD-free design regime. However, the use of thicker enamel coatings (i.e., "Grade 3", enamel thickness of 100 μm or more) has limitations in its manufacture. First, thickness uniformity of the enamel coating around the wire is difficult to achieve with enameled rectangular copper wires as the thickness increases (especially around the corners or edges of the wire when the wire exhibits a small corner radius). Second, residual solvent content is a common issue with thick grades of enamel. Solvents used during the enamel manufacturing process (e.g., N,N-dimethylacetamide (DMAc) or N-methylpyrrolidone (NMP)) have come under increasing scrutiny in parts of the world, such as Europe, and there have been strong calls from regulatory agencies to eliminate these solvents in the European Union (EU). In addition, the mechanical stresses applied to the enamel coating during the formation of the enameled wire (to produce the hairpins that are later inserted into the e-motor) can result in pinhole or crack issues in the enamel, leading to electrical failure. Furthermore, the temperatures during the hairpin welding process (connecting the individual hairpins in the motor to a continuous electrical circuit) can affect the wire insulation material locally, creating weak spots in the enamel. For example, heat exposure during welding can make the enamel more brittle and more susceptible to electrical failure.

[0007] An alternative to achieve a larger insulation thickness around the copper wire is to use an extrusion process (instead of a coating process using enamel). In this process, a polymer (typically polyaryletherketone (PAEK) with a glass transition temperature of about 140°C to 160°C) is extruded onto the wire, which allows the formation of a continuous insulation layer per side with a thickness of 200 μm or more, sufficient to stay in the PD-free design regime. To achieve better adhesion of the PAEK to the copper wire, a thin primer layer such as an enamel layer can be first coated onto the wire and then the PAEK polymer can be extruded onto it (see, for example, U.S. Pat. Nos. 9,224,523 and 9,536,636, which are incorporated herein by reference). Common enamel types such as polyimide, polyamideimide, or polyamideimide / polyesterimide can be used as primers. A drawback of using PAEK-based insulation is that their thermal transition points (more specifically, their glass transition points) are typically below the operating temperatures of e-motors (generally 180°C to 200°C), which can raise potential issues regarding the long-term reliability of this type of wire insulation material.

[0008] A third approach is to wrap the copper wire with tape. This results in an insulation that has edges on the surface instead of a smooth surface. The tape can be made from a variety of materials, but typically polyimide-based tapes are used for applications in harsh environments such as e-motors. The polyimide tape can contain inorganic fillers to make it PD-resistant and can have one or more fluoropolymer-based layers on the surface that act as adhesives to provide adhesion to the copper wire. The disadvantage of using tape insulation is that when the wire is bent to create a hairpin, delamination, abrasion, and fraying of the tape insulation can occur, thus completely penetrating the tape insulation and creating an electrical failure.

[0009] Having recognized the above, exemplary embodiments have been developed and / or disclosed herein in which wires (broadly speaking, electrical conductors) are insulated based on a partial discharge (PD) resistant design approach such that the insulated wire can be used in 800V and higher e-motors. The exemplary embodiments disclosed herein use a dual layer approach for wire insulation by combining an enamel coating under a polyimide-containing tape wrap, whereby the electrically insulated wire is PD resistant and can be used in 800V and higher applications.

[0010] In an exemplary embodiment, an enamel coating (e.g., an average thickness of 90 μm or less per side, but more preferably an average thickness range of 50 μm to 70 μm per side) is applied to a copper wire (broadly, a conductor) and cured. A polyimide-containing tape is then wrapped around the enameled copper wire with some overlap value of the tape (e.g., in the range of 15% to 70%) and heat sealed to ensure good adhesion of the tape to the enamel. The polyimide-containing tape includes a sufficient amount (e.g., 17 weight percent (wt%)) of an electrically insulating corona resistant composite filler (e.g., aluminum oxide) in the polyimide polymer to make the tape PD resistant.

[0011] The advantage of this dual layer approach is that the resulting wire insulation material has an overall average thickness of less than 170 μm per side, which theoretically results in a higher copper filling factor compared to PAEK-based extrusion materials when the same copper conductor dimensions are used. In addition, the resulting wire insulation material can withstand partial discharge (PD) phenomena, making it suitable for PD-resistant design schemes (e.g., for e-motors 800V and above). Compared to using only enamel on the copper wire, this dual layer approach can achieve a uniform insulation thickness around the copper wire and requires less processing solvents during the manufacturing process of the insulated copper wire. Compared to tape-only insulation systems, this dual layer approach includes enamel that is still present under the tape wrap and still provides electrical insulation in the event of delamination or fraying of the applied tape.

[0012] Enamel Coating Process A description of the enamel coating process used in the exemplary embodiment is now provided. In the exemplary embodiment, the conductors that can be used in conjunction with the enamel coating process are primarily composed of either copper (preferably copper classified as CDA 10100, 10200, and 110000) or aluminum. Other conductors include alloys of copper with other metals, stainless steel, and graphite. The conductors preferably have a rectangular shape with dimensions of about 1-6 mm by 1.5-20 mm, with a defined corner radius of 1 millimeter (mm) or less, and properties as described in ASTM B250, ASTM B48, ANSI / NEMA MW 1000, and / or IEC 60317. However, conductors with other shapes (e.g., round, square, stranded, Litz, hollow, etc.) can also be used in the exemplary embodiment. Further dimensions of a rectangular conductor used in busbar applications of 800V or more are 1 to 20mm x 20 to 200mm, with a corner radius of 0.1 to 0.3mm.

[0013] In an exemplary embodiment, the enamel is applied to a bare rectangular copper wire via a process such as those disclosed in, for example, U.S. Pat. Nos. 2,345,390, 9,543,058, and / or 10,020,092. It is known in the art that careful selection of process parameters such as line speed, cure temperature, line tension, absolute humidity and temperature of the ambient atmosphere, thickness of the applied wet coating, configuration and shape of the coating die, residual solvent content, and viscosity of the applied coating solution can affect the properties of the cured enamel. For example, the degree of cure, adhesion, uniformity and concentricity of the coating thickness, abrasion and scuff resistance, resistance to organic solvents and moisture, hardness of the cured enamel, etc. are all directly affected by careful selection of these process parameters. In one exemplary embodiment, the average thickness of the enamel per side is less than 90 micrometers. In other exemplary embodiments, the preferred average thickness of the enamel per side is 30 to 80 micrometers.

[0014] In exemplary embodiments, the chemical composition of the enamel is generally described as either a polyamideimide (e.g., as described in DOI 10.1002 / mame.200700365, or Applied Plastics Engineering Handbook (2011), Part 1, Chapter 2, or Plastics in Medical Devices (2010), Chapter 8), a polyimide (formally derived from monomers as disclosed in the section entitled "Polyimide Film Manufacturing" below), a polyesterimide (e.g., as described in DOI 10.1002 / mame.200700363), or a combination thereof. For example, the enamel coating may be of a single chemical composition. Or, for example, the enamel coating may comprise multiple layers of different compositions coated on top of each other. The thickness of each layer in such cases is not limited by the presence of the other layers. The preferred enamel composition is a polyamideimide, more specifically a polymer formally derived from a diamine such as 4,4'-methylenedianiline and an anhydride such as trimellitic anhydride. Other diamines formally derived from monomers disclosed in the section entitled "Polyimide Film Production" below may also be suitable for use in the polyamideimide enamel composition, either by themselves or as part of a mixture of two or more diamines. Additional layers may be present that improve adhesion or improve abrasion resistance or other properties relevant to this application. The surface of the wire with the enamel coating is preferably free of lubricants or other layers that attempt to reduce the surface energy of the enamel coating.

[0015] In an exemplary embodiment, the surface of the enamel coating may be treated to improve adhesion to a layer that is subsequently placed over the enamel surface, such as a tape material. Suitable methods for improving adhesion include those disclosed below in the following sections and may include, but are not limited to, plasma or corona treatment.

[0016] A conductor that is fully coated with enamel may have certain desirable properties, including (a) an appearance of the enamel that is free of defects such as blisters or bubbles, (b) a thermal class rating of 200°C or greater when the enamel is applied to copper, (c) a residual solvent content of 5% by weight or less, (d) a breakdown voltage value of at least 2 kV that is retained to at least 50% of its initial value after at least 5% elongation, bending, chemical exposure, or thermal exposure of the conductor, (e) no visible cracks when bent edgewise or flatwise through a 180° rotation around a mandrel having a diameter twice the width of the conductor, and (f) a thermal resistance of at least 200°C. (g) no visible cracks when exposed for at least 30 minutes or when first bent flatwise or edgewise or when first stretched to at least 10%, (h) an elongation at break of at least 30%, (i) a specified static coefficient of friction, (j) a specified partial discharge inception voltage of 700V or greater at ambient conditions at a threshold of 20 picocoulombs, and (k) a specified abrasion / scuff resistance. Testing of these properties can be performed according to standard procedures known in the industry, such as IEC 60851, ASTM, or ANSI / NEMA MW 1000.

[0017] Polyimide film manufacturing In an exemplary embodiment, the tape is comprised of a polyimide layer of nominal thickness (e.g., 0.75 mils, etc.) and a fluoropolymer layer of nominal thickness (e.g., 0.5 mils, etc.). The chemical composition of the polyimide layer is preferably a copolymer of 4,4'-oxydianiline and pyromellitic dianhydride, containing a uniformly dispersed inorganic filler (e.g., aluminum oxide, etc.) at a predetermined weight percent (e.g., 17 weight percent). The inorganic filler is surface treated with a silane, and a dispersant is used as a processing aid to uniformly disperse the filler during the film-forming manufacturing step. In an exemplary embodiment, the aluminum oxide filler has a particle size distribution of d99 of 0.5 μm or less, as determined by an LA-960 Horiba Particle Analyzer. The chemical composition of the fluoropolymer layer is preferably fluorinated ethylene propylene (FEP).

[0018] A more detailed description of the polyimide composition, fluoropolymer composition, and film production according to exemplary embodiments is provided below. Diamine Monomers Suitable for Producing Polyimide Layers In an exemplary embodiment, any number of suitable diamines may be used as monomers to form the polymer backbone. Aromatic diamines include fluorinated aromatic diamines such as 2,2'-bis(trifluoromethyl)benzidine (TFMB), 2,2'-bis-(4-aminophenyl)hexafluoropropane, 4,4'-diamino-2,2'-trifluoromethyldiphenyloxide, 3,3'-diamino-5,5'-trifluoromethyldiphenyloxide, 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'-thiobis[(2-trifluoromethyl)benzenamine], 4,4'-thiobis[(3-trifluoromethyl)benzenamine], 4,4'-sulfoxyl-bis[(2-trifluoromethyl)benzenamine], 4,4'-sulfoxyl-bis[(3-trifluoromethyl)benzenamine], 4,4'-keto-bis[(2-trifluoromethyl)benzenamine], 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 (6F-amine), 1,4-bis[2'-cyano-3' ("4-aminophenoxy)phenoxy]-2-[(3',5'-ditrifluoro-methyl)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) may be mentioned.

[0019] Other useful aromatic diamines include 4,4'-diaminobiphenyl, 4,4"-diaminoterphenyl, 4,4'-diaminobenzanilide (DABA), 4,4'-diaminophenyl benzoate, 4,4'-diaminobenzophenone, 4,4'-diaminodiphenylmethane (MDA), 4,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, bis[4-(4-aminophenoxy)phenyl]sulfone (BAPS), 4,4'-bis(4-aminophenoxy)biphenyl (BAPB), 4,4'-diaminodiphenyl ether (ODA), 3,4'-diamino Examples of suitable diamines include diphenyl ether, 4,4'-isopropylidenedianiline, 2,2'-bis(3-aminophenyl)propane, 2,2-bis(4-aminophenyl)propane, 3,3'-dimethyl-4,4'-diaminobiphenyl, 4-aminophenyl-3-aminobenzoate, bis(p-β-amino-t-butylphenyl)ether, p-bis-2-(2-methyl-4-aminopentyl)benzene. In an exemplary embodiment, the diamine is a triamine, such as N,N-bis(4-aminophenyl)-n-butylamine, N,N-bis(4-aminophenyl)methylamine, or N,N-bis(4-aminophenyl)aniline.

[0020] Other useful aromatic diamines may 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.

[0021] Other useful aromatic diamines can include p-phenylenediamine (PPD), m-phenylenediamine (MPD), 2,5-dimethyl-1,4-diaminobenzene, 2,5-dimethyl-1,4-phenylenediamine (DPX), 1,4-naphthalenediamine, 1,5-naphthalenediamine, 1,5-diaminonaphthalene, m-xylylenediamine, and p-xylylenediamine.

[0022] In an exemplary embodiment, additional useful diamines for forming polyimides may include aliphatic diamines such as 1,2-diaminoethane, 1,6-diaminohexane (HMD), 1,4-diaminobutane, 1,5 diaminopentane, 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, trans-1,4-diaminocyclohexane (CHDA), isophoronediamine (IPDA), bicyclo[2.2.2]octane-1,4-diamine, and combinations thereof. Other aliphatic diamines suitable for practicing the invention include those having 6 to 12 carbon atoms, or combinations of longer and shorter chain diamines, so long as both the malleability and flexibility of the polymer are maintained. Long chain aliphatic diamines may improve flexibility.

[0023] Other useful diamines for forming polyimides may include alicyclic diamines (which may be fully or partially saturated), such as cyclobutane diamines (e.g., cis- and trans-1,3-diaminocyclobutane, 6-amino-3-azaspiro[3.3]heptane, and 3,6-diaminospiro[3.3]heptane), bicyclo[2.2.1]heptane-1,4-diamine, isophorone diamine, and bicyclo[2.2.2]octane-1,4-diamine. Other alicyclic diamines may include cis-1,4-cyclohexanediamine, trans-1,4-cyclohexanediamine, 1,4-bis(aminomethyl)cyclohexane, 4,4'-methylenebis(cyclohexylamine), 4,4'-methylenebis(2-methyl-cyclohexylamine), bis(aminomethyl)norbornane.

[0024] Dianhydride Monomers Suitable for Producing Polyimide Layers In exemplary embodiments, any number of suitable dianhydrides can be used as monomers to form the polymer backbone. The dianhydrides can be used in their tetraacid form (or as mono-, di-, tri-, or tetraesters of the tetraacids) or as their diester acid halides (chlorides). However, in some exemplary embodiments, the dianhydride forms may be preferred, as they are generally more reactive than the acids or esters.

[0025] Examples of suitable aromatic dianhydrides include 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 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, 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 2,2',3,3'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 4,4'-thio-diphthalic anhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride, bis(3,4-dicarboxyphenyl)sulfoxide dianhydride (DSDA), bis(3,4-dicarboxyphenyloxadiazole-1, 3,4)-p-phenylene dianhydride, bis(3,4-dicarboxyphenyl)-2,5-oxadiazole-1,3,4-dianhydride, bis(3',4'-dicarboxydiphenylether)-2,5-oxadiazole-1,3,4-dianhydride, 4,4'-oxydiphthalic anhydride (ODPA), bis(3,4-dicarboxyphenyl)thioether dianhydride, bisphenol A dianhydride (BPADA), bisphenol S dianhydride, bis-1,3-isobenzofurandione, 1,4-bis(4 ,4'-oxyphthalic anhydride)benzene, bis(3,4-dicarboxyphenyl)methane dianhydride, perylene-3,4,9,10-tetracarboxylic dianhydride, 1,3-bis-(4,4'-oxydiphthalic anhydride)benzene, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), and 9,9-bis(trifluoromethyl)-2,3,6,7-xanthenetetracarboxylic dianhydride.

[0026] In an exemplary embodiment, additional dianhydrides for forming polyimides include 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, bicyclo-[2,2,2]-octene-(7)-2,3,5,6-tetracarboxylic-2,3,5,6-dianhydride, cyclopentadienyltetracarboxylic dianhydride, ethylenetetracarboxylic dianhydride, pyromellitic dianhydride (PMDA), tetrahydrofurantetracarboxamide, tetramethylsilyl tetracarboxylic acid ... Examples of suitable dianhydrides include 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.

[0027] In an exemplary embodiment, additional dianhydrides for forming polyimides may include alicyclic dianhydrides such as cyclobutane-1,2,3,4-tetracarboxylic dianhydride (CBDA), 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 1,2,3,4-cyclohexanetetracarboxylic dianhydride, 1,2,3,4-tetramethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic 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 1,4:2,3-dianhydride (TCA), and meso-butane-1,2,3,4-tetracarboxylic dianhydride.

[0028] In an exemplary embodiment, the polyimide is derived from 50 mole percent pyromellitic dianhydride (PMDA) and 50 mole percent 4,4'-diaminodiphenyl ether (ODA). In an exemplary embodiment, the polyimide can have a weight average molecular weight (Mw) of 100,000 Daltons or greater, 150,000 Daltons or greater, 200,000 Daltons or greater, or 250,000 Daltons or greater.

[0029] Imidization Catalyst In an exemplary embodiment, an imidization catalyst (sometimes referred to as an "imidization accelerator") can be used as a conversion chemical that can lower the imidization temperature and shorten the imidization time to form a polyimide. The polyamic acid casting solution of the present invention comprises any polyamic acid solution combined with an amount of a conversion chemical. Conversion chemicals found to be useful in the present invention include, but are not limited to, (i) one or more dehydrating agents and / or cocatalysts, such as aliphatic acid anhydrides (such as acetic anhydride, trifluoroacetic anhydride, propionic anhydride, monochloroacetic anhydride, bromoadipic anhydride, etc.) and aromatic acid anhydrides; and (ii) one or more imidization catalysts, such as aliphatic tertiary amines (such as triethylamine), aromatic tertiary amines (such as dimethylaniline, N,N-dimethylbenzylamine, etc.), and heterocyclic tertiary amines (such as pyridine, α-, β-, γ-picoline, 3,5-lutidine, 3,4-lutidine, isoquinoline, etc.), and guanidines (e.g., tetramethylguanidine). In an exemplary embodiment, the imidization catalyst does not include a diazole. Other useful dehydrating agents may include diacetyl oxide, butyryl oxide, benzoyl oxide, 1,3-dicyclohexylcarbodiimide, N,N-dicyclohexylcarbodiimide, benzenesulfonyl chloride, thionyl chloride, and phosphorus pentachloride. In some embodiments, the dehydrating agent can also act as a catalyst to enhance the reaction rate of imidization. Anhydride dehydrating materials are typically used in slight molar excess over the amount of amic acid groups present in the polyamic acid solution. In an exemplary embodiment, the amount of dehydrating agent used is typically about 2.0 to 4.0 moles per equivalent of polyamic acid formula units. Generally, comparable amounts of tertiary amine catalysts are used. The ratio of these catalysts and their concentrations in the polyamic acid solution affect the imidization rate and film properties. A polyimide film having a substantially chemically converted polyimide can have the imidization catalyst present in the polyimide film in an amount ranging from 1 part per billion (ppb) to 1 weight percent, from 10 ppb to 0.1 weight percent, or from 100 ppb to 0.01 weight percent.

[0030] Corona-resistant composite filler In an exemplary embodiment, the polyimide film includes an electrically insulating, corona resistant composite filler.

[0031] In exemplary embodiments, the corona-resistant composite filler can have an organic component and an inorganic ceramic oxide component, and the weight ratio of the organic component to the inorganic ceramic oxide component is 0.01:1 to 1:1. In some exemplary embodiments, the weight ratio of the organic component to the inorganic ceramic oxide component can be within a range between (and optionally including) any two of the following numbers: 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 exemplary embodiments, at least a portion of the organic component can include an organosiloxane moiety or an organometalloxane moiety (e.g., organozirconate, organotitanate, organoaluminate).

[0032] In an exemplary embodiment, the filler has an inorganic ceramic oxide component, such as a ceramic oxide of Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ge, Zr, Nb, Mo, Sn, Sb, Ta, W, Pb, or Ce. In an exemplary embodiment, the inorganic ceramic oxide component can include silica, alumina, titania, zirconia, iron, calcium, or mixtures thereof. In an exemplary embodiment, the inorganic ceramic oxide component includes silica, alumina, or mixtures thereof. In an exemplary embodiment, the inorganic ceramic oxide component is alumina.

[0033] In exemplary embodiments, 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 solvating polymer matrix or polymer matrix precursor. In some embodiments, the organic component of the corona-resistant composite filler material is selected to reduce moisture absorption in the inorganic ceramic oxide component. Optimizing the organic component for any particular solvent system selected may require routine practice and experimentation. In some exemplary embodiments, the organosiloxane moiety is either n-octylsilane, or a structural isomer thereof. In some embodiments, the corona-resistant composite filler is an inorganic ceramic oxide that does not include an organic component. In other exemplary embodiments, 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.

[0034] In exemplary embodiments, the electrically insulating, corona-resistant composite filler is present in an amount between any two of the following numbers (inclusive): 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, and 30 wt%, based on the total weight of the polyimide film. In exemplary embodiments, the corona-resistant composite filler is present in an amount within the range of 5-30 wt%, 5-25 wt%, or 5-20 wt%, based on the total weight of the polyimide film.

[0035] In exemplary embodiments, the corona-resistant composite filler may have a median particle size of 0.1-5 μm, with at least 80%, 85%, 90%, 92%, 94%, 95%, 96%, 98%, 99%, or 100% of the dispersed corona-resistant composite filler being within the size range defined above. The median particle size may be measured using a Horiba LA-930 particle size analyzer (Horiba Instruments, Inc., Irvine, CA). DMAc may be used as the carrier fluid. In some embodiments, the corona-resistant composite filler is a nanofiller. The term "nanofiller" is intended to mean a filler having at least one dimension less than 1000 nanometers (nm), i.e., less than 1 μm.

[0036] In an exemplary embodiment, the polyimide film further comprises a dispersing aid. In some embodiments, the polyimide film further comprises a dispersing aid in an amount in the range of 1 to 100 weight percent based on the weight of the inorganic ceramic oxide component. In some exemplary embodiments, the dispersing aid is selected from the group consisting of phosphorylated polyethers, phosphorylated polyesters, and mixtures thereof. In another exemplary embodiment, the dispersing aid is an alkylol ammonium salt of a polyglycol ester. In another embodiment, the dispersing aid is selected from the group consisting of Disperbyk 180, an alkylol ammonium salt of a polyglycol ester, Disperbyk 111, a phosphorylated polyester, Byk W-9010, a phosphorylated polyester, or mixtures thereof, all available from Byk-Chemie GmbH, Wesel, Germany. In another exemplary embodiment, the dispersing aid is Solplus D540, a phosphorylated ethylene oxide / propylene oxide copolymer available from Lubrizol, Inc., Cleveland, Ohio. In yet another exemplary embodiment, the dispersing aid is a mixture of any of the above dispersing aids. In some exemplary embodiments, the dispersing aid is an aromatic polyamic acid or an aromatic polyimide. In another embodiment, the dispersing aid is a polyalkylene ether, such as polytetramethylene glycol and polyethylene glycol. Typically, aromatic polyamic acid or aromatic polyimide has high temperature stability and therefore remains mostly in the polyimide. On the other hand, dispersing aids such as polyalkylene ether have low temperature stability and are mostly decomposed or burned off at the temperatures used in the imidization process.

[0037] Polyimide film manufacturing In an exemplary embodiment, polyimide films can be made by combining a diamine and a dianhydride (either monomer or other polyimide precursor form) together with a solvent to form a polyamic acid (also called polyamic acid) solution. The dianhydride and 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 adjusting the molar ratio of the dianhydride to the diamine.

[0038] In an exemplary embodiment, the polyamic acid casting solution is derived from a polyamic acid solution. The polyamic acid casting solution and / or the polyamic acid solution are combined with (i) one or more dehydrating agents, such as aliphatic acid anhydrides (such as acetic anhydride) and / or aromatic acid anhydrides, and (ii) one or more catalysts, such as aliphatic tertiary amines (such as triethylamine), aromatic tertiary amines (such as dimethylaniline), and heterocyclic tertiary amines (such as pyridine, picoline, isoquinoline). The anhydride dehydrating agents are often used in molar excess compared to the amount of amide acid 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. The filler, dispersed or suspended in a solvent as described above, is then added to the polyamic acid solution.

[0039] In an exemplary embodiment, the polyamic acid solution is dissolved in an organic solvent at a concentration of about 5.0% by weight or 10% to 15% by weight, 20% by weight, 25% by weight, 30% by weight, 35% by weight, or 40% by weight. In an exemplary embodiment, a slurry is prepared with the filler, the slurry having a solids content in the range of 0.1 to 70% by weight, 0.5 to 60% by weight, 1 to 55% by weight, 5 to 50% by weight, or 10 to 45% by weight. The slurry may or may not be milled using a ball mill to reach a desired particle size. The slurry may or may not be filtered to remove residual large particles. The polyamic acid solution may be made by methods known in the art. The polyamic acid solution may or may not be filtered. In some embodiments, the solution is mixed with the filler slurry in a high shear mixer. If the polyamic acid solution is made with a slight excess of diamine, additional dianhydride solution may or may not be added to raise the viscosity of the mixture to the desired level for film casting. The amount of polyamic acid solution and filler slurry can be adjusted to achieve the desired loading level in the cured film. In some embodiments, the mixture is cooled to below 10°C and mixed with the conversion chemical prior to casting.

[0040] The solvated mixture (polyamic acid casting solution) can then be cast or applied onto a support such as an endless belt or rotating drum to obtain a partially imidized gel film. Alternatively, it can be cast onto a polymeric carrier such as PET, other forms of Kapton® polyimide film (e.g., Kapton® HN or Kapton® E film) or other polymeric carriers. The gel film can be peeled off the drum or belt, placed on a tenter frame, and cured in an oven using convection and radiant heat to remove the solvent and complete the imidization to a solids level of over 98%. The film can then be separated from the support, oriented such as by tentering, and continued heating (drying and curing) to obtain a substantially chemically converted polyimide film.

[0041] Useful methods for making polyimide films can be found in U.S. Patent Nos. 5,166,308 and 5,298,331, which are incorporated herein by reference. A number of variations are also possible, such as the following:

[0042] (a) The diamine and dianhydride components are premixed together and then this mixture is added in portions to the solvent with stirring. (b) Adding a solvent to a stirred mixture of the diamine and dianhydride components (opposite to (a) above).

[0043] (c) A method in which only the diamine is dissolved in a solvent and then the dianhydride is added thereto at a ratio that allows the reaction rate to be controlled. (d) A method in which only the dianhydride component is dissolved in a solvent, and then the amine component is added thereto at a ratio that allows the reaction rate to be controlled.

[0044] (e) A method in which the diamine component and the dianhydride component are dissolved in a solvent separately, and then these solutions are mixed in a reactor. (f) A process in which a polyamic acid having an excess of an amine component and another polyamic acid having an excess of a dianhydride component are preformed and then reacted with one another in a reactor in such a way as to produce, inter alia, non-random or block copolymers.

[0045] (g) A specific portion of the amine component is reacted first with the dianhydride component and then with the remaining diamine component, or vice versa. (h) A method in which a conversion chemical (catalyst) is mixed with a polyamic acid to form a polyamic acid casting solution which is then cast to form a gel film.

[0046] (i) A process in which the components are added in any order to some or all of the solvent, with any or all of the components also being added as solutions in any or all of the solvent. (j) First react one of the dianhydride components with one of the diamine components to obtain a first polyamic acid, then react another dianhydride component with another amine component to obtain a second polyamic acid, and then combine the amine acids in any one of a number of ways prior to film formation.

[0047] In an exemplary embodiment, the filler is first dispersed in a solvent to form a slurry. The slurry is then dispersed in a polyamic acid solution. In an exemplary embodiment, the concentration of the filler relative to the polyimide (in the final film) is in the range of 10-50%, 15-45%, 15-40%, 20-35%, or 25-30% by volume. In an exemplary embodiment, the concentration of the filler relative to the polyimide (in the final film) is at least 10%, at least 15%, at least 20%, or at least 25% by volume. The composition of the cured film can be calculated from the composition of the components in the mixture, excluding the DMAc solvent (which is removed during curing) and taking into account the removal of water during the conversion of the polyamic acid to polyimide.

[0048] In an exemplary embodiment, the filled polyamic acid casting solution is a blend of polyamic acid solution and filler. In this casting solution, the filler is present in a concentration range of 0.1-70%, 1-60%, 2-50%, 5-45%, or 5-40% by volume. In an exemplary embodiment, the filler is first dispersed in the same polar aprotic solvent (e.g., DMAc) used to make the polyamic acid solution. Optionally, a small amount of polyamic acid solution may be added to the filler slurry to increase the viscosity of the slurry. Optionally, a dispersant or dispersion aid may be added to disperse or modify the rheology of the slurry.

[0049] The filler can be blended into a particular solvated polymer matrix or polymer matrix precursor by using any commonly used technique such as batch mixing with a solvent, dry mixing, or continuous mixing with a solvent. Parameters such as the order of ingredient addition, mixing speed, shear rate, type of mixing blade (e.g., shear blade), mixing time, temperature, and pressure are known to affect the final degree of mixing between the filler and the matrix material.

[0050] In an exemplary embodiment, blending the filler slurry with the polyamic acid solution to form a filled polyamic acid casting solution is performed using high shear mixing. In such an exemplary embodiment, if the filler is present in the final film at more than 50% by volume, the film may be too brittle and may not be flexible enough to form a free-standing, mechanically strong, flexible sheet.

[0051] In an exemplary embodiment, the casting solution can further include any one of a number of additives, such as processing aids (e.g., oligomers), antioxidants, light stabilizers, flame retardant additives, antistatic agents, heat stabilizers, UV absorbers, or various toughening agents.

[0052] In some exemplary embodiments, a coextrusion process can be used to form a multi-layer polyimide film in which an inner core layer is sandwiched between two outer layers. In this method, the completed polyamic acid solution is filtered and pumped into a slot die, and the flow is split to form the first and second outer layers of a three-layer coextruded film. In some embodiments, the second stream of polyimide is filtered and then pumped into a casting die to form the middle polyimide core layer of the three-layer coextruded film. The flow rate of the solution can be adjusted to achieve the desired layer thickness.

[0053] In some exemplary embodiments, the multilayer film is prepared by simultaneously extruding a first outer layer, a core layer, and a second outer layer. In some exemplary embodiments, the layers are extruded through a single or multiple cavity extrusion die. In other exemplary embodiments, the multilayer film is produced using a single cavity die. If a single cavity die is used, the laminar flow of the streams should be of high enough viscosity to prevent intermingling of the streams and provide uniform stratification. In some exemplary embodiments, the multilayer film is prepared by casting from a slot die onto a moving stainless steel belt. In exemplary embodiments, the belt is then passed through a convection oven to evaporate the solvent and partially imidize the polymer to produce a "green" film. The green film can be peeled from the casting belt and wound up. The green film can then be passed through a tenter oven to produce a fully cured polyimide film. In some exemplary embodiments, shrinkage can be minimized by restraining the film along the edges (i.e., by using clips or pins) during tentering.

[0054] In an exemplary embodiment, the outer layer of the present invention may also be applied to the core layer during an intermediate manufacturing stage of making a polyimide film, such as a gel film or green film. When forming a polyimide film, the term "gel film" refers to a polyamic acid sheet that may be formed in a chemical conversion process that contains volatiles, primarily solvents, to the extent that the polyamic acid is in a gel swollen or rubbery state. The volatiles are typically in the range of 70-90% by weight of the gel film, and the polymer content is typically in the range of 10-30% by weight of the gel film. The final film becomes "self-supporting" at the gel film stage. It may be peeled from the support on which it was cast and heated to a final cure temperature. Gel films generally have an amic acid to imide ratio of 10:90 to 50:50, most often 30:70.

[0055] The gel film structure can be prepared by the method described in U.S. Pat. No. 3,410,826. This patent discloses mixing chemical conversion agents and catalysts, such as lower fatty acid anhydrides and tertiary amines, at low temperatures to form a polyamic acid solution. The polyamic acid solution is then cast in film form onto a casting drum. To convert the cast film into a polyamic acid / polyimide gel film, the film is gently heated after casting, such as at 100° C., to activate the conversion agents and catalysts.

[0056] Another type of polymer film is the "green film", which in the case of polyimide film is part polyamic acid and part polyimide, and can be formed by a thermal conversion process. The green film generally contains about 50-75% by weight polymer and 25-50% by weight solvent. Generally, it should be strong enough to be substantially self-supporting. The green film can be prepared by casting a polyamic acid solution into a film form on a suitable support such as a casting drum or belt, and removing the solvent by gentle heating at or below 150°C. A small percentage of the amic acid units in the polymer, for example 25% or less, can be converted to imide units.

[0057] Application of the polyimide film in the exemplary embodiments disclosed herein can be accomplished in any number of ways. Such methods include using a slot die, dip coating, or kiss roll coating of the film followed by metering with a doctor knife, doctor roll, squeeze roll, or air knife. The coating may also be applied by brushing or spraying. Using such techniques, it is possible to prepare both single-sided and double-sided coated laminates. In preparing a double-sided coated structure, coatings can be applied to both sides of the polymer either simultaneously or sequentially before proceeding to the polymer curing and drying steps.

[0058] The electrically insulating corona resistant composite filler (its dispersion or colloid) can be added at several points during the polyimide film preparation. In an exemplary embodiment, the colloid or dispersion is incorporated into a prepolymer having a Brookfield solution viscosity in the range of about 50-100 poise at 25°C. "Prepolymer" is intended to mean a lower molecular weight polymer, typically made with a small stoichiometric excess (about 2-4%) of diamine monomer (or excess dianhydride monomer). In another embodiment, the colloid or dispersion can be combined directly with the monomer, in which case polymerization occurs with the filler present during the reaction. In another embodiment, the colloid or dispersion can be combined with the "finished" high viscosity polyimide. The monomer can have an excess of either monomer (diamine or dianhydride) during this "in situ" polymerization. The monomer may also be added in a 1:1 ratio. When monomer is added with an excess of either amine (case i) or dianhydride (case ii), an increase in molecular weight (and an increase in solution viscosity) can be achieved, if necessary, by adding incremental amounts of additional dianhydride (case i) or diamine (case ii) to approach a 1:1 stoichiometric ratio of dianhydride to amine.

[0059] The thickness of the polyimide film can be adjusted depending on the intended purpose or end use specifications of the film. In an exemplary embodiment, the polyimide film is of a total thickness in the range of 2 to 300 μm, 5 to 200 μm, 7 to 150 μm, 10 to 100 μm, or 15 to 80 μm.

[0060] In one embodiment, one or more imidization catalysts are used to produce a single layer polyimide film that is 19 μm and contains about 17% by weight of well-dispersed aluminum oxide. The polyimide film may have certain desirable properties, including (a) an elongation at break of 40% or more in both the machine and transverse directions of the film, (b) a tensile strength of 20 kpsi or more, (c) a tensile modulus of 2 GPa or more, (d) a coefficient of thermal expansion of less than 60 ppm / °C in both the machine and transverse directions of the film, (e) a dielectric strength of 3 kV / mil or more, (f) a thermal glass transition temperature of 250°C or more, (g) a thermal rating of 200°C or more, and (h) less than 1% by weight of residual volatiles (excluding water). Testing for these properties may be performed according to standard procedures known in the industry, such as those published by IEC 60851, ASTM, or UL.

[0061] Fluoropolymer Layer In an exemplary embodiment, a polyimide film with an electrically insulating corona resistant composite filler has a first fluoropolymer layer adhered to a first surface of the polyimide. The fluoropolymer layer is used to bond the polyimide film to a metal layer, an enamel layer, or a wire, such as a rectangular conductor (e.g., a rectangular copper wire, etc.). Additional fluoropolymer layers may be present either on the same surface as the first fluoropolymer layer or on the opposite surface of the polyimide film. In other embodiments, polymers based on silicone, acrylate, epoxy, urethane, urethane-acrylate, or mixtures thereof may be adhered to the polyimide film to perform a similar function as the fluoropolymer layer.

[0062] In an exemplary embodiment, the base film tape comprises a polyimide film having a first fluoropolymer layer. In an exemplary embodiment, the base film tape can be used as a wrap for an electrically insulated wire or cable that includes rectangular conductors (e.g., rectangular copper wires, etc.). In an exemplary embodiment, the base film tape has a thickness, measured in an unwrapped state, in the range of 25 μm to 40 μm.

[0063] In an exemplary embodiment, the fluoropolymer layer comprises a fluoropolymer selected from the group consisting of tetrafluoroethylene-hexafluoropropylene copolymer (FEP), perfluoroalkoxy resin (PFA), polytetrafluoroethylene (PTFE), or mixtures thereof. In an exemplary embodiment, the fluoropolymer layer comprises FEP in an amount in the range of 65-100% by weight, based on the total weight of the fluoropolymer layer. In an exemplary embodiment, the fluoropolymer layer comprises FEP in an amount between (and optionally including) any two of the following values, based on the total weight of the fluoropolymer layer: 65%, 70%, 75%, 80%, 85%, 90%, 95%, and 100% by weight. In an exemplary embodiment, the first fluoropolymer layer, the second fluoropolymer layer, or both the first and second fluoropolymer layers are in direct contact with the polyimide film, such that there is no intervening layer between the fluoropolymer layer and the polyimide film. In an exemplary embodiment, the fluoropolymer layer comprises 100% by weight of FEP. In an exemplary embodiment, the fluoropolymer in the fluoropolymer layer is not crosslinked. In an exemplary embodiment, the first fluoropolymer layer and the second fluoropolymer layer are the same or different.

[0064] The fluoropolymer layer generally has a thickness within the range of any two of the following numbers: 0.25 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.25 μm, 1.5 μm, 1.75 μm, 2 μm, 3 μm, 4 μm, 5 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, and 25 μm (optionally including both ends). Useful thickness ranges are often within the range of about 5 μm to 15 μm. In practice, the desired thickness may vary depending on the specifications, particularly for motor vehicles or heavy load traction applications. The thickness of the fluoropolymer layer can affect the adhesive strength of the polyimide film to a conductor (bare or coated with an insulating material) when the fluoropolymer layer is located between the polyimide film and the conductor.

[0065] In some exemplary embodiments, the fluoropolymer layer may be applied to the polyimide film by, but not limited to, solution coating, colloidal dispersion coating, extrusion, or lamination. In one embodiment, the fluoropolymer is coated or laminated to a polyimide film that has previously been surface modified to improve adhesion.

[0066] The polyimide film may be surface modified to improve adhesion to other layers, such as fluoropolymer layers. Examples of useful surface modifications include, but are not limited to, corona treatment, plasma treatment at atmospheric pressure, plasma treatment at reduced pressure, treatment with coupling agents such as silanes and titanates, sandblasting, alkali treatment, and acid treatment.

[0067] The fluoropolymer layers of the present disclosure may include flame retardant and thermally conductive fillers, as well as fillers to adjust the opacity, color, and rheology of the fluoropolymer layer. In some exemplary embodiments, the fluoropolymer layer may contain inorganic fillers such as silica, alumina, titania, and / or zirconia. The fillers may be the same or different as those present in the polyimide film. The fillers may be present in the range of 1-10 wt. %, based on the dry weight of the coating. When more than one fluoropolymer layer is present on the polyimide film, each fluoropolymer layer may independently be filled or unfilled.

[0068] Wire Wrap Process In an exemplary embodiment, the electrical insulating film with electrically insulating corona resistant composite filler is useful as a wire wrap. Suitable materials for wrapping include bare conductors, conductors coated with enamel, conductors coated with extruded resin, or conductors coated with film tape. In some exemplary embodiments, the wire wrap may include additional layers such as adhesive layers or abrasion resistant layers. The wire wrap film or sheet can be cut into narrow widths to provide the tape. The particular width of the tape is selected depending on the dimensions of the conductor to be wrapped. These tapes can be wrapped around the conductor in a spiral or overlapping manner. The amount of tape overlap can vary depending on the angle of the wrap. In an exemplary embodiment, the overlap is 70% or less. The tension used during the wrapping operation can also vary widely, ranging from just enough tension to prevent wrinkles to tension high enough to stretch the tape and neck down. Even with low tension, a tight wrap is possible since the tape often shrinks under the influence of heat during any subsequent heat sealing operation. Heat sealing of the tape can be accomplished by treating the tape wrapped conductor at a temperature and time sufficient to fuse the bonding layer to the other layers in the composite. The required heat sealing temperature generally ranges from 240°C, 250°C, 275°C, 300°C, 325°C, or 350°C to 375°C, 400°C, 425°C, 450°C, 475°C, or 500°C, depending on the insulation thickness, gauge of the metal conductor, production line speed, and length of the seal. If there is only one fluoropolymer layer on the polyimide film, the fluoropolymer layer in the tape preferentially faces the conductor. Parameters such as the absolute humidity level and temperature of the surrounding atmosphere, line tension, wrap angle, heating and cooling rates, and the means of applying heat (e.g., convection, radiation, or induction) and pressure may affect the performance of the final wire insulation material.

[0069] The wrapped conductor may have certain desirable properties, including (a) an appearance free of defects such as blisters or bubbles or wrinkles or lifted tape edges, (b) a thermal class rating of 200°C or greater when applied to copper, (c) a residual solvent content of 1% by weight or less, (d) a breakdown voltage value of at least 2 kV or greater that is retained to at least 50% of its initial value after at least 5% elongation, bending, chemical exposure, or thermal exposure of the wrapped conductor, (e) no visible damage when bent edgewise or flatwise through a 180° rotation around a mandrel having a diameter twice the width of the conductor, and (f) a dielectric strength of at least 2 kV. (g) no visible damage when exposed to 00° C. for at least 30 minutes or when initially bent flatwise or edgewise or when initially stretched to at least 10%, (h) an insulation adhesion loss of less than 1× the width of the conductor after at least 20% elongation or when initially heat aged at at least 150° C. for at least 30 minutes, (i) a coefficient of friction at a specified state, (j) a specified partial discharge inception voltage of 700 V or greater at ambient conditions at a threshold of 20 picocoulombs, and (k) a specified abrasion / scuff resistance. Testing of these properties can be performed according to standard procedures known in the industry, such as IEC 60851, ASTM, or ANSI / NEMA MW 1000.

[0070] Wire Performance Data Table 1 below includes a comparison of partial discharge inception voltages (PDIV) (the voltage above which partial discharge events begin to occur inside the wire insulation) between PAI (polyamide-imide) enamel, PAEK (having a glass transition temperature of about 140°C to 150°C) with an underlayer of primer (e.g., PAI enamel), and three samples prepared by the dual layer approach disclosed herein. Table 1 also includes a comparison of their temperature dependences. In Table 1 below, Vrms is the root mean square voltage, OL is the overlap ratio, and RT indicates the ambient temperature in the range of 19°C to 25°C.

[0071] [Table 1]

[0072] In general, the results shown in Table 1 above indicate that the dual layer approach produces similar average PDIV values ​​as existing wire insulation solutions. Furthermore, the degradation of PDIV values ​​at higher temperatures is similar to or less severe than other existing wire insulation solutions for the dual layer insulation approach.

[0073] Each of the samples in Table 1 comprised a rectangular copper wire having dimensions of approximately 2 mm by 4 mm with a corner radius of approximately 0.5 mm. The first sample (PAI enamel) comprised a rectangular copper wire coated with a polyamideimide (PAI) enamel coating having an average thickness of 80 μm per side. The insulation thickness was determined according to IEC 60851-2.

[0074] The second sample (PAEK with primer) comprises a rectangular copper wire first coated with a PAI enamel coating having an average thickness of 40-50 μm per side, followed by an extruded layer of PAEK (having a glass transition temperature of about 140° C.-150° C.) having an average thickness of 160 μm per side. The third, fourth, and fifth samples (dual layer examples) comprise a rectangular copper wire first coated with a PAI enamel coating having an average thickness of 60-65 μm per side, then tape wrapped and heat sealed to achieve a total average thickness of 93 μm (20% overlap, OL) or 125 μm (53% or 66% OL) per side. Insulation thickness was determined according to IEC 60851-2. The tape used in all dual layer examples was a 20-22 μm thick single layer polyimide film (containing monomers ODA and PMDA and about 16-17 wt % well dispersed aluminum oxide) that was surface treated and then laminated to a single FEP polymer film about 11-13 μm thick. The FEP layer faced the conductor during the wrapping process.

[0075] Test conditions included the determination of PDIV values ​​according to ASTM D1868 using an AC power source, with the samples arranged in a "bar-to-bar" wire test configuration, and using 20 picocoulombs as the selected threshold for PD activity.

[0076] Table 2 below contains the average PDIV and dielectric breakdown values ​​(at RT) at RT and elevated temperature (180° C.) for the dual layer construction as a function of enamel composition.

[0077] [Table 2]

[0078] Each of the specimens comprised a rectangular copper wire having dimensions of approximately 2 mm x 4 mm with a corner radius of approximately 0.5 mm. The average thickness of the polyimide (PI) enamel was 40-45 μm per side, the average thickness of the PAI enamel was 60-65 μm per side, and the average thickness of the polyesterimide / polyamideimide (PEI / PAI) enamel was 60-65 μm per side. Each rectangular copper wire coated with enamel on top was then tape wrapped with the indicated percent overlap (%OL) and heat sealed. Insulation thickness was determined in accordance with IEC 60851-2.

[0079] Test conditions included the determination of average PDIV values ​​according to ASTM D1868 using an AC source, with samples arranged in a "bar-to-bar" wire test configuration, and using 20 picocoulombs as the threshold for PD activity. Dielectric breakdown values ​​were determined according to IEC 60851-5, using a steel ball bath.

[0080] Table 3 below contains a comparison of average durability life between enamel, PAEK with primer, and the dual layer approach of the present application.

[0081] [Table 3]

[0082] Each of the samples comprised a rectangular copper wire having dimensions of approximately 2 mm x 4 mm with a corner radius of approximately 0.5 mm. The average thickness of the PAI enamel was 80 μm per side in the first sample. For the second sample (PAEK with primer), the first PAI enamel primer layer was an average of 40-50 μm thick per side, and the top extruded layer of PAEK (having a glass transition temperature of approximately 140°C to 150°C) was 160 μm thick per side. The third and fourth samples (double layer) included polyamideimide enamel with an average thickness of 60-65 μm per side, which were then tape wrapped to achieve a total average thickness of 123 μm (53% OL) or 91 μm (20% OL) per side after heat sealing. Insulation thickness was determined according to IEC 60851-2.

[0083] Test conditions include a bipolar square wave pulse endurance tester with an applied voltage of 1.5 kV peak-to-peak at 180° C., a frequency of 20 kHz, a voltage rise time of 14 ns, and a time to peak voltage of 50 ns.

[0084] Table 4 below contains the average durability life of the bilayer construction as a function of enamel composition.

[0085] [Table 4]

[0086] Each of the specimens included a rectangular copper wire having dimensions of approximately 2 mm x 4 mm with a corner radius of approximately 0.5 mm. The average thickness of the PI enamel was 40-45 μm per side for the first and second specimens. The average thickness of the PAI enamel was 60-65 μm per side for the third and fourth specimens. The average thickness of the PEI / PAI enamel was 60-65 μm per side for the fifth specimen. Each wire was tape wrapped to achieve an overall average total thickness and percent overlap (%OL) and heat sealed. Insulation thickness was determined according to IEC 60851-2.

[0087] Test conditions include a bipolar square wave pulse endurance tester with an applied voltage of 1.5 kV peak-to-peak at 180° C., a frequency of 20 kHz, a voltage rise time of 14 ns, and a time to peak voltage of 50 ns.

[0088] Adhesion and elongation at break tests The wire samples were subjected to adhesion and elongation tests according to IEC 60851-3. Elongation at break tests: Elongation at break of more than 30% was observed for wire specimens having bare copper wire with dimensions of approximately 2 mm x 4 mm, corner radius of approximately 0.5 mm, a PAI enamel layer with an average thickness of 60 μm per side, and tape overlap in the range of 20-66%. Insulation thickness was determined according to IEC 60851-2.

[0089] Adhesion testing: For identical wire samples with tape overlap ranging from 20-66%, the length along the wire where adhesion loss occurred after stretching individual wire samples to 20% was <1 mm for <50% OL and <2 mm for 66% OL.

[0090] Adhesion test after heat aging The wire samples were subjected to 180° C. continuously for 168 hours in a convection oven and then the adhesion behavior was evaluated according to IEC 60851-3.

[0091] For wire samples having bare copper wire with dimensions of approximately 2 mm x 4 mm, corner radius of approximately 0.5 mm, a PAI enamel layer with an average thickness of 60 μm per side, and a tape overlap of 53%, the length along the wire where adhesion loss occurred after stretching the sample by 20% was <2 mm. Insulation thickness was determined according to IEC 60851-2.

[0092] Bending test Wire specimens with a PAI enamel layer of average thickness of 60 μm and tape overlap in the range of 20-53% were subjected to a 180° turn bending (according to IEC 60851-3.5) around a mandrel with a diameter twice the width of the conductor. The bending was performed either edgewise or flatwise on separate occasions. No exposed conductor material was visually observed on the wire specimens in the areas subjected to the bending process. The insulation thickness was determined according to IEC 60851-2.

[0093] The exemplary embodiments disclosed herein are not limited to use only in electric motors in electric vehicles, but may be used in a wide range of electronic devices, including power electronic devices for aircraft, marine, industrial, automotive, etc., electric motors driven by pulse width modulated inverters, high switching frequency converters providing signals with high levels of dv / dt, traction motors for e-mobility applications, other windings driven by converter devices, etc.

[0094] Exemplary embodiments of and exemplary methods for electrically insulated conductors are disclosed herein, resulting in electrically insulated conductors that are resistant to partial discharge (PD) and are therefore suitable for PD resistant design schemes (e.g., 800V and above electric motors, etc.). The exemplary method includes applying an enamel coating along an electrical conductor, wrapping an electrically insulating tape around the fully enameled electrical conductor, and heat sealing the tape-wrapped enameled electrical conductor to ensure good adhesion of the electrically insulating tape to the enamel coating. The electrically insulating tape includes a polyimide, an additional polymer bonded to the polyimide, and an electrically insulating corona resistant filler in a sufficient amount for PD resistance. The tape-wrapped enameled electrical conductor is resistant to partial discharge (PD) and is suitable for use in, for example, stator windings of 800V and above electric motors.

[0095] In an exemplary embodiment, the electrically insulating tape comprises about 17% by weight of an electrically insulating, corona resistant composite filler in polyimide. For example, the electrically insulating, corona resistant composite filler may comprise aluminum oxide.

[0096] In an exemplary embodiment, the enamel coating has an average thickness of about 90 micrometers or less per side. For example, the enamel coating may have an average thickness of about 30 micrometers to about 80 micrometers per side.

[0097] In an exemplary embodiment, the electrically insulating tape is wrapped around the enameled conductor with a tape overlap in the range of about 15% to about 70%. In an exemplary embodiment, the tape wrapped enameled conductor has an overall average thickness, defined by the conductor, the enamel coating, and the electrically insulating tape, of less than about 170 micrometers per side.

[0098] In an exemplary embodiment, the electrical conductor has a uniform insulation thickness defined by the enamel coating and the electrically insulating tape, and does not require processing solvents during the tape wrapping step.

[0099] In an exemplary embodiment, the enamel coating under the electrically insulating tape is configured to provide sufficient electrical insulation to the conductor if the electrically insulating tape is peeled and / or scraped off the enameled conductor wrapped by the tape.

[0100] In an exemplary embodiment, the enamel coating comprises a polyamideimide (PAI) enamel coating; or a polyimide (PI) enamel coating; or a polyesterimide / polyamideimide (PEI / PAI) enamel. In such an exemplary embodiment, the exemplary method comprises applying a polyamideimide (PAI) enamel coating along the conductor; or applying a polyimide (PI) enamel coating along the conductor; or applying a polyesterimide / polyamideimide (PEI / PAI) enamel coating along the conductor.

[0101] In an exemplary embodiment, the conductors comprise copper, aluminum, or stainless steel wire having a generally rectangular cross-sectional shape with rounded corners. In such exemplary embodiment, the exemplary method includes applying a polyamideimide (PAI) enamel coating along a copper, aluminum, or stainless steel wire such that the PAI enamel coating has an average thickness within a range of about 60 micrometers to about 65 micrometers per side, and wrapping an electrically insulating tape around the enameled conductor includes wrapping an electrically insulating tape around the PAI enameled copper, aluminum, or stainless steel wire, whereby the tape overlap is about 66% and the average insulation thickness defined by the PAI enamel coating and the electrically insulating tape is about 125 micrometers per side, or the tape overlap is about 53% and the average insulation thickness defined by the PAI enamel coating and the electrically insulating tape is about 123 micrometers per side, or the tape overlap is about 20% and the average insulation thickness defined by the PAI enamel coating and the electrically insulating tape is about 91 micrometers per side.

[0102] In an exemplary embodiment, the electrical conductor comprises a copper, aluminum, or stainless steel wire having a generally rectangular cross-sectional shape with rounded corners. In such an exemplary embodiment, the exemplary method includes applying an enamel coating along the electrical conductor includes applying a polyimide (PI) enamel coating along the copper, aluminum, or stainless steel wire such that the PI enamel coating has an average thickness within a range of about 40 micrometers to about 45 micrometers per side, and wrapping an electrically insulating tape around the enameled electrical conductor includes wrapping an electrically insulating tape around the PI enameled copper, aluminum, or stainless steel wire, whereby the tape overlap is about 53% and the average insulation thickness defined by the PI enamel coating and the electrically insulating tape is about 108 micrometers per side, or the tape overlap is about 15% and the average insulation thickness defined by the PI enamel coating and the electrically insulating tape is about 75 micrometers per side.

[0103] In an exemplary embodiment, the electrical conductor comprises a copper, aluminum, or stainless steel wire having a generally rectangular cross-sectional shape with rounded corners. In such an exemplary embodiment, the exemplary method includes applying an enamel coating along the electrical conductor includes applying a polyesterimide / polyamideimide (PEI / PAI) enamel coating along the copper, aluminum, or stainless steel wire such that the PEI / PAI enamel coating has an average thickness within a range of about 60 micrometers to about 65 micrometers per side, and wrapping an electrically insulating tape around the enameled electrical conductor includes wrapping the electrically insulating tape around the PEI / PAI enameled copper, aluminum, or stainless steel wire, whereby the tape overlap is about 53% and the average insulation thickness defined by the PEI / PAI enamel coating and the electrically insulating tape is about 125 micrometers per side.

[0104] In an exemplary embodiment, the exemplary method includes applying an enamel coating along the conductor includes applying a polyamideimide (PAI) enamel coating along the conductor such that the PAI enamel coating has an average thickness in the range of about 60 micrometers to about 65 micrometers per side, and wrapping an electrically insulating tape around the enameled conductor includes wrapping the electrically insulating tape around the PAI enameled conductor whereby the tape overlap is in the range of about 20% to about 66%, and the average insulation thickness defined by the PAI enamel coating and the electrically insulating tape is in the range of about 91 micrometers to about 125 micrometers per side.

[0105] In an exemplary embodiment, the exemplary method includes applying an enamel coating along the conductor includes applying a polyimide (PI) enamel coating along the conductor such that the PI enamel coating has an average thickness in the range of about 40 micrometers to about 45 micrometers per side, and wrapping an electrically insulating tape around the enameled conductor includes wrapping the electrically insulating tape around the PI enameled conductor whereby the tape overlap is in the range of about 15% to about 53%, and the average insulation thickness defined by the PI enamel coating and the electrically insulating tape is in the range of about 75 micrometers to about 108 micrometers per side.

[0106] In an exemplary embodiment, the exemplary method includes applying an enamel coating along the conductor includes applying a polyesterimide / polyamideimide (PEI / PAI) enamel coating along the conductor such that the PEI / PAI enamel coating has an average thickness in the range of about 50 micrometers to about 70 micrometers per side, and wrapping an electrically insulating tape around the enameled conductor includes wrapping the electrically insulating tape around the PEI / PAI enameled conductor, whereby the tape overlap is in the range of about 15% to about 70%, and the tape wrapped PEI / PAI enameled conductor has an overall thickness of less than about 170 micrometers per side.

[0107] In an exemplary embodiment, the exemplary method includes applying an enamel coating along the conductor includes applying a polyamideimide (PAI) enamel coating along the conductor such that the PAI enamel coating has an average thickness in the range of about 50 micrometers to about 70 micrometers per side, and wrapping an electrically insulating tape around the enameled conductor includes wrapping an electrically insulating tape around the PAI enameled conductor, whereby the tape overlap is in the range of about 15% to about 70%, and the tape wrapped PAI enameled conductor has an overall thickness of less than about 170 micrometers per side.

[0108] In an exemplary embodiment, the exemplary method includes applying an enamel coating along the conductor includes applying a polyimide (PI) enamel coating along the conductor such that the PI enamel coating has an average thickness in the range of about 50 micrometers to about 70 micrometers per side, and wrapping an electrically insulating tape around the enameled conductor includes wrapping an electrically insulating tape around the PI enameled conductor such that the tape overlap is in the range of about 15% to about 70% and the tape wrapped PI enameled conductor has an overall thickness of less than about 170 micrometers per side.

[0109] In an exemplary embodiment, the enamel coating along the conductor comprises a polyamideimide (PAI) enamel coating that includes 4,4'-methylenedianiline and trimellitic anhydride.

[0110] In an exemplary embodiment, the electrically insulating tape comprises a polyimide film that includes pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA). In an exemplary embodiment, the electrically insulating tape comprises about 10-25% by weight of an electrically insulating, corona resistant composite filler in a polyimide. The electrically insulating tape has a thickness less than 30 micrometers and does not include an additional polymer adhered to the polyimide. In such an exemplary embodiment, the exemplary method comprises: applying an enamel coating along the conductor comprises applying a polyamideimide (PAI) enamel coating along the conductor such that the PAI enamel coating has an average thickness in the range of about 30 micrometers to about 80 micrometers per side; and wrapping an electrically insulating tape around the enameled conductor comprises wrapping the electrically insulating tape around the PAI enameled conductor, whereby the tape overlap is in the range of about 15% to about 70%, and the tape wrapped PAI enameled conductor has an overall thickness less than about 170 micrometers per side. The PAI enamel coating may comprise 4,4'-methylenedianiline and trimellitic anhydride. The electrically insulating tape may also comprise a polyimide film that includes pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA).

[0111] In an exemplary embodiment, the tape wrapped enameled conductor is configured such that the tape wrapped enameled conductor has one or more of the following: (a) an appearance free of defects such as blisters or bubbles or wrinkled or lifted tape edges; (b) a thermal class rating of 200° C. or greater when applied to copper; (c) a residual solvent content of 1% or less by weight; (d) a breakdown voltage value of at least 2 kV or greater that is retained to at least 50% of its initial value after at least 5% elongation, bending, chemical exposure, or thermal exposure of the wrapped conductor; (e) a dielectric breakdown voltage value that is capable of being edge wrapped by rotating 180° around a mandrel having a diameter twice the width of the conductor; (f) no visible damage when exposed to at least 200° C. for at least 30 minutes or when initially bent flatwise or edgewise or when initially stretched to at least 10%; (g) an elongation at break of at least 30%; (h) an adhesion loss of insulating material of less than 1× the width of the conductor after an elongation of at least 20% or when initially heat aged at at least 150° C. for at least 30 minutes; (i) a coefficient of friction at a specified state; (j) a specified partial discharge inception voltage of 700 V or greater at ambient conditions at a threshold of 20 picocoulombs; and / or (k) a specified abrasion / scuff resistance.

[0112] In an exemplary embodiment, the enameled conductor prior to being wrapped with tape is configured such that the enameled conductor has one or more of the following: (a) an appearance of the enamel free of defects such as blisters or bubbles; (b) a thermal class rating of 200° C. or greater when the enamel is applied to copper; (c) a residual solvent content of 5% or less by weight; (d) a breakdown voltage value of at least 2 kV or greater that is retained to at least 50% of its initial value after at least 5% elongation, bending, chemical exposure, or thermal exposure of the conductor; (e) the conductor can be wound edgewise or flat-wired by rotating 180° around a mandrel having a diameter twice the width of the conductor. (f) no visible cracks when exposed to at least 200°C for at least 30 minutes or when initially bent flatwise or edgewise or when initially stretched to at least 10%; (g) an elongation at break of at least 30%; (h) an enamel adhesion loss of less than one conductor width after an elongation of at least 20% or when initially heat aged at at least 150°C for at least 30 minutes; (i) a specified static coefficient of friction; (j) a specified partial discharge inception voltage of 700V or greater at ambient conditions at a threshold of 20 picocoulombs; and (k) a specified abrasion / scuff resistance.

[0113] In an exemplary embodiment, the electrically insulating tape comprises a polyimide film configured such that the polyimide film has one or more of the following: (a) an elongation at break of 40% or greater in both the machine and transverse directions of the film, (b) a tensile strength of 20 kpsi or greater, (c) a tensile modulus of 2 GPa or greater, (d) a coefficient of thermal expansion of less than 60 ppm / °C in both the machine and transverse directions of the film, (e) a dielectric strength of 3 kV / mil or greater, (f) a thermal glass transition temperature of 250°C or greater, (g) a thermal rating of 200°C or greater, and (h) less than 1% by weight residual volatiles (excluding water).

[0114] In an exemplary embodiment, the electrical conductors comprise magnet wire and / or copper, aluminum, or stainless steel wire having a generally rectangular, circular, oval, rhomboid, hollow, or rounded rectangular cross-sectional shape.

[0115] In exemplary embodiments, the conductors comprise copper, aluminum, or stainless steel wire having a generally rectangular cross-sectional shape with rounded corners, and / or the conductors have dimensions of approximately 1-6 millimeters by 1.5-20 millimeters with a corner radius of 1 millimeter or less, or dimensions of approximately 1-20 millimeters by 20-200 millimeters with a corner radius of 0.1-3 millimeters.

[0116] In an exemplary embodiment, the exemplary method includes wrapping an electrically insulating tape around the enameled conductor after the enamel coating is cured. In an exemplary embodiment, the tape wrapped enameled conductor is suitable for use in stator windings for electric motors of 800 volts or greater.

[0117] In an exemplary embodiment, a stator winding for an 800 volt or greater electric motor includes tape wrapped enameled conductors as disclosed herein. The exemplary embodiments are provided so that the disclosure is thorough and fully conveys the scope to those skilled in the art. Numerous specific details, such as examples of specific components, devices, and methods, are described to provide a thorough understanding of the embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be used, that the exemplary embodiments can be embodied in many different forms, and that none of these should be construed to limit the scope of the present disclosure. In some exemplary embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. In addition, advantages and improvements that may be achieved by one or more exemplary embodiments of the present disclosure are provided for illustrative purposes only and are not intended to limit the scope of the present disclosure, and the exemplary embodiments disclosed herein may provide all or none of the above advantages and improvements and still be within the scope of the present disclosure.

[0118] The specific numerical dimensions and values, specific materials, and / or specific shapes disclosed herein are exemplary in nature and do not limit the scope of the present disclosure. The disclosure herein of a specific value and a specific range of values ​​for a given parameter does not exclude other values ​​and ranges of values ​​that may be useful in one or more of the examples disclosed herein. Furthermore, it is contemplated that any two specific values ​​for a particular parameter described herein may identify the endpoints of a range of values ​​that may be suitable for the given parameter (disclosure of a first value and a second value for a given parameter may be construed as disclosing that any value between the first and second values ​​may also be employed for the given parameter). For example, if a parameter X is exemplified herein as having a value A and is also exemplified as having a value Z, it is contemplated that the parameter X may have a range of values ​​from about A to about Z. Similarly, the disclosure of two or more ranges of values ​​for a parameter (whether such ranges are nested, overlapping, or separate) is contemplated to encompass all possible combinations of ranges for values ​​that may be claimed using the endpoints of the disclosed ranges. For example, if a parameter X is exemplified herein as having a value in the range of 1 to 10, or 2 to 9, or 3 to 8, it is contemplated that the parameter X may have other ranges of values, including 1 to 9, 1 to 8, 1 to 3, 1 to 2, 2 to 10, 2 to 8, 2 to 3, 3 to 10, and 3 to 9.

[0119] The terms used herein are for the purpose of describing particular exemplary embodiments only and are not intended to be limiting. As used herein, the singular forms "a", "an" and "the" may be intended to include the plural unless the context clearly indicates otherwise. The terms "comprises", "comprising", "includes", "including", "has", "have" and "having" are inclusive and thus specify the presence of stated features, integers, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof. The method steps, processes and operations described herein should not be construed as necessarily requiring their execution in the particular order described or illustrated, unless specifically identified as an order of execution. It should also be understood that additional or alternative steps may be used.

[0120] When an element or layer is referred to as being "on," "engaged to," "connected to," or "coupled to" another element or layer, it may be directly on, engaged, connected, or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being "directly on," "directly engaged to," "directly connected to," or "directly coupled to" another element or layer, there may not be intervening elements or layers. Other words used to describe relationships between elements should be interpreted similarly (e.g., "between" vs. "directly between," "adjacent" vs. "directly adjacent," etc.). As used herein, the term "and / or" includes any and all combinations of one or more of the listed items associated with the term.

[0121] The term "about", when applied to a value, indicates that the calculation or measurement allows for some slight imprecision in the value (somewhat close to the accuracy of the value; approximately or reasonably close to the value; approximately). If for some reason the imprecision provided by "about" is not otherwise understood in the art in this ordinary sense, then "about" as used herein at least indicates the variation that may result from ordinary methods of measuring or using such parameters. For example, the terms "generally", "about" and "substantially" may be used herein to mean within manufacturing tolerances. Alternatively, for example, the term "about" as used herein when modifying the amounts of components or reactants of the present invention or used refers to the variation in numerical values ​​that may occur when making concentrates or solutions in the real world through typical measuring and handling procedures used, for example, through inadvertent errors in these procedures; through differences in the manufacture, source, or purity of components used to make the composition or to carry out the method, etc. The term "about" also encompasses amounts that vary due to different equilibrium conditions for a composition obtained from a particular initial mixture. Whether or not modified by the term "about," the claims include equivalents of the quantities.

[0122] Terms such as first, second, third, etc. may be used herein to describe various elements, components, regions, layers, and / or sections, but these elements, components, regions, layers, and / or sections should not be limited by these terms. These terms may only be used to distinguish one element, component, region, layer, or section from another region, layer, or section. Terms such as "first," "second," and other numerical terms, when used herein, do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer, or section can be referred to as a second element, component, region, layer, or section without departing from the teachings of the exemplary embodiments.

[0123] Spatially relative terms such as "inner," "outer," "beneath," "below," "lower," "above," "upper," and the like may be used herein for ease of description to describe the relationship of one element or feature to another element or feature as shown in the figures. Spatially relative terms may be intended to encompass different orientations of the device during use or operation in addition to the orientation shown in the figures. For example, if a device in the figures were turned over, elements described as "below" or "beneath" other elements or features would be oriented "above" the other elements or features. Thus, the exemplary term "below" may encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein would be interpreted accordingly.

[0124] The foregoing detailed description of the embodiments is provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the present disclosure. Individual elements, intended or described uses, or features of a particular embodiment are generally not limited to that particular embodiment, but may be interchangeable, where applicable, and may be used in selected embodiments even if not specifically shown or described. The same may also be modified in many ways. Such variations should not be considered as departures from the present disclosure, and all such modifications are intended to be included within the scope of the present disclosure.

Claims

1. 1. A method for electrically insulating a conductor to obtain an electrically insulated conductor that is resistant to partial discharge (PD), comprising the steps of: applying an enamel coating along the conductor; wrapping an electrically insulating tape around the enameled conductor, the electrically insulating tape including a polyimide, an additional polymer adhered to the polyimide, and an electrically insulating corona resistant filler in an amount sufficient for PD resistance; and heat sealing the tape wrapped enameled conductor to ensure good adhesion of the electrical insulating tape to the enamel coating; The method whereby the tape wrapped enameled conductor is resistant to partial discharge (PD).

2. 10. The method of claim 1 , The electrically insulating tape comprises about 17% by weight of an electrically insulating, corona resistant composite filler in a polyimide; The method of claim 1, wherein the electrically insulating, corona resistant composite filler comprises aluminum oxide.

3. 10. The method of claim 1 , The method includes wrapping an electrically insulating tape around an enameled conductor with a tape overlap in the range of about 15% to about 70%; the tape-wrapped enameled conductor has an overall average thickness defined by the conductor, the enamel coating, and the electrically insulating tape of less than about 170 micrometers per side; The method wherein the enamel coating has an average thickness of about 90 micrometers or less per side.

4. 10. The method of claim 1 , The method provides a uniform insulation thickness on the electrical conductor defined by the enamel coating and the electrical insulating tape, and does not require processing solvents during the tape wrapping step; The method includes wrapping an electrically insulating tape around the enameled conductor after the enamel coating has cured; The method, wherein the enamel coating under the electrically insulating tape is configured to provide sufficient electrical insulation to the conductor when the electrically insulating tape is peeled and / or scraped off the enameled conductor wrapped by the tape.

5. 10. The method of claim 1 , The enamel coating along the conductor comprises 4,4'-methylenedianiline and trimellitic anhydride; The method, wherein the electrically insulating tape comprises pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA).

6. The method according to any one of claims 1 to 5, Applying an enamel coating along a conductor Applying a polyamideimide (PAI) enamel coating along the conductor; or Applying a polyimide (PI) enamel coating along the conductor; or Applying a polyesterimide / polyamideimide (PEI / PAI) enamel coating along the conductor A method comprising:

7. The method according to any one of claims 1 to 5, the conductor comprises copper, aluminum, or stainless steel wire having a generally rectangular cross-sectional shape with rounded corners; applying an enamel coating along the conductor includes applying a polyamideimide (PAI) enamel coating along a copper, aluminum, or stainless steel wire such that the PAI enamel coating has an average thickness within a range of about 60 micrometers to about 65 micrometers per side; Wrapping the electrical insulating tape around the enameled conductor includes wrapping the electrical insulating tape around the PAI enameled copper, aluminum, or stainless steel wire, thereby the tape overlap is about 66% and the average insulation thickness defined by the PAI enamel coating and the electrically insulating tape is about 125 micrometers per side; or the tape overlap is about 53% and the average insulation thickness defined by the PAI enamel coating and the electrically insulating tape is about 123 micrometers per side; or The method wherein the tape overlap is about 20% and the average insulation thickness defined by the PAI enamel coating and the electrically insulating tape is about 91 micrometers per side.

8. The method according to any one of claims 1 to 5, the conductor comprises copper, aluminum, or stainless steel wire having a generally rectangular cross-sectional shape with rounded corners; applying an enamel coating along the conductor includes applying a polyimide (PI) enamel coating along a copper, aluminum, or stainless steel wire such that the PI enamel coating has an average thickness within a range of about 40 micrometers to about 45 micrometers per side; Wrapping the electrical insulating tape around the enameled conductor includes wrapping the electrical insulating tape around a PI enameled copper, aluminum, or stainless steel wire, thereby the tape overlap is about 53% and the average insulation thickness defined by the PI enamel coating and the electrically insulating tape is about 108 micrometers per side; or The method wherein the tape overlap is about 15% and the average insulation thickness defined by the PI enamel coating and the electrically insulating tape is about 75 micrometers per side.

9. The method according to any one of claims 1 to 5, the conductor comprises copper, aluminum, or stainless steel wire having a generally rectangular cross-sectional shape with rounded corners; applying an enamel coating along the conductor includes applying a polyesterimide / polyamideimide (PEI / PAI) enamel coating along a copper, aluminum, or stainless steel wire such that the PEI / PAI enamel coating has an average thickness within a range of about 60 micrometers to about 65 micrometers per side; The method wherein wrapping an electrically insulating tape around the enameled conductor includes wrapping an electrically insulating tape around a PEI / PAI enameled copper, aluminum, or stainless steel wire, whereby the tape overlap is about 53% and the average insulation thickness defined by the PEI / PAI enamel coating and the electrically insulating tape is about 125 micrometers per side.

10. The method according to any one of claims 1 to 5, The method includes applying a polyamideimide (PAI) enamel coating along a conductor and wrapping an electrically insulating tape around the PAI enameled conductor, thereby: a polyamideimide (PAI) enamel coating having an average thickness within the range of about 60 micrometers to about 65 micrometers per side, with a tape overlap within the range of about 20% to about 66%, and an average insulation thickness defined by the PAI enamel coating and the electrically insulating tape within the range of about 91 micrometers to about 125 micrometers per side; or A method in which the polyamideimide (PAI) enamel coating has an average thickness in the range of about 50 micrometers to about 70 micrometers per side, the tape overlap is in the range of about 15% to about 70%, and the tape wrapped PAI enameled conductor has an overall thickness of less than about 170 micrometers per side.

11. The method according to any one of claims 1 to 5, applying an enamel coating along the conductor includes applying a polyimide (PI) enamel coating along the conductor such that the PI enamel coating has an average thickness within a range of about 40 micrometers to about 45 micrometers per side; The method, wherein wrapping the electrically insulating tape around the enameled conductor includes wrapping the electrically insulating tape around the PI enameled conductor, whereby the tape overlap is in the range of about 15% to about 53% and the average insulation thickness defined by the PI enamel coating and the electrically insulating tape is in the range of about 75 micrometers to about 108 micrometers per side.

12. The method according to any one of claims 1 to 5, applying an enamel coating along the conductor includes applying a polyesterimide / polyamideimide (PEI / PAI) enamel coating along the conductor such that the PEI / PAI enamel coating has an average thickness within a range of about 50 micrometers to about 70 micrometers per side; The method, wherein wrapping an electrically insulating tape around the enameled conductor includes wrapping an electrically insulating tape around the PEI / PAI enameled conductor, whereby the tape overlap is in the range of about 15% to about 70% and the tape wrapped PEI / PAI enameled conductor has an overall thickness of less than about 170 micrometers per side.

13. The method according to any one of claims 1 to 5, The electrically insulating tape comprises about 10-25 weight percent of an electrically insulating, corona resistant composite filler in a polyimide; The electrically insulating tape has a thickness of less than 30 micrometers; applying an enamel coating along the conductor includes applying a polyamideimide (PAI) enamel coating along the conductor such that the PAI enamel coating has an average thickness within a range of about 30 micrometers to about 80 micrometers per side; The method, wherein wrapping an electrically insulating tape around the enameled conductor includes wrapping an electrically insulating tape around the PAI enameled conductor, whereby the tape overlap is in the range of about 15% to about 70% and the tape wrapped PAI enameled conductor has an overall thickness of less than about 170 micrometers per side.

14. An electrically insulated conductor comprising: an electrically conductive core; an enamel coating along an electrically conductive core; an electrically insulating tape wrapped around an enameled conductor, the electrically insulating tape comprising a polyimide, an additional polymer adhered to the polyimide, and an electrically insulating, corona resistant filler in an amount sufficient for PD resistance; Tape wrapped enameled conductors are electrically insulated conductors that are resistant to partial discharge (PD).

15. 15. The electrically insulated conductor of claim 14, The electrically insulating tape comprises about 17% by weight of an electrically insulating, corona resistant composite filler in a polyimide; and / or The electrically insulating, corona resistant composite filler comprises aluminum oxide, an electrically insulating conductor.

16. 15. The electrically insulated conductor of claim 14, an electrically insulating tape is wrapped around the enameled electrically conductive core with a tape overlap in the range of about 15% to about 70%; the electrically insulated conductor has an overall average thickness defined by the electrically conductive core, the enamel coating, and the electrically insulating tape of less than about 170 micrometers per side; The enamel coating is an electrically insulating conductor having an average thickness of about 90 micrometers or less per side.

17. 15. The electrically insulated conductor of claim 14, the enamel coating along the electrically conductive core comprises a polyamideimide (PAI) enamel coating comprising 4,4'-methylenedianiline and trimellitic anhydride; The electrically insulating tape is an electrically insulating conductor comprising a polyimide film containing pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA).

18. 15. The electrically insulated conductor of claim 14, The enamel coating is cured and an electrically insulating tape is wrapped and heat sealed around the cured enameled electrically conductive core to ensure good adhesion of the electrically insulating tape to the cured enamel coating; An electrically insulated conductor, wherein the enamel coating under the electrically insulating tape is configured to provide sufficient electrical insulation to the electrically conductive core when the electrically insulating tape is peeled and / or scraped off the tape wrapped enameled electrically conductive core.

19. 15. The electrically insulated conductor of claim 14, Polyamide-imide (PAI) enamel coating, or Polyimide (PI) enamel coating, or Polyesterimide / Polyamideimide (PEI / PAI) enamel an electrically insulated conductor comprising:

20. An electrically insulated conductor according to any one of claims 14 to 19, the electrically conductive core comprises copper, aluminum, or stainless steel wire having a generally rectangular cross-sectional shape with rounded corners; the enamel coating comprises a polyamideimide (PAI) enamel coating along the copper, aluminum, or stainless steel wire such that the PAI enamel coating has an average thickness within a range of about 60 micrometers to about 65 micrometers per side; The electrically insulating tape is wrapped around the PAI enameled copper, aluminum, or stainless steel wire, thereby the tape overlap is about 66% and the average insulation thickness defined by the PAI enamel coating and the electrically insulating tape is about 125 micrometers per side; or the tape overlap is about 53% and the average insulation thickness defined by the PAI enamel coating and the electrically insulating tape is about 123 micrometers per side; or An electrically insulated conductor having a tape overlap of about 20% and an average insulation thickness defined by the PAI enamel coating and the electrically insulating tape of about 91 micrometers per side.

21. An electrically insulated conductor according to any one of claims 14 to 19, the electrically conductive core comprises copper, aluminum, or stainless steel wire having a generally rectangular cross-sectional shape with rounded corners; the enamel coating comprises a polyimide (PI) enamel coating along the copper, aluminum, or stainless steel wire such that the PI enamel coating has an average thickness within a range of about 40 micrometers to about 45 micrometers per side; The electrical insulating tape is wrapped around a PI enameled copper, aluminum, or stainless steel wire, thereby the tape overlap is about 53% and the average insulation thickness defined by the PI enamel coating and the electrically insulating tape is about 108 micrometers per side; or An electrically insulated conductor having a tape overlap of about 15% and an average insulation thickness defined by the PI enamel coating and the electrically insulating tape of about 75 micrometers per side.

22. An electrically insulated conductor according to any one of claims 14 to 19, the electrically conductive core comprises copper, aluminum, or stainless steel wire having a generally rectangular cross-sectional shape with rounded corners; the enamel coating comprises a polyesterimide / polyamideimide (PEI / PAI) enamel coating along a copper, aluminum, or stainless steel wire such that the PEI / PAI enamel coating has an average thickness within the range of about 60 micrometers to about 65 micrometers per side; An electrically insulated conductor in which the electrically insulating tape is wrapped around a PEI / PAI enameled copper, aluminum, or stainless steel wire, whereby the tape overlap is about 53% and the average insulation thickness defined by the PEI / PAI enamel coating and the electrically insulating tape is about 125 micrometers per side.

23. An electrically insulated conductor according to any one of claims 14 to 19, The enamel coating comprises a polyamideimide (PAI) enamel coating along an electrically conductive core, and an electrically insulating tape is wrapped around the PAI enameled electrically conductive core, thereby the PAI enamel coating has an average thickness within the range of about 60 micrometers to about 65 micrometers per side, the tape overlap is within the range of about 20% to about 66%, and the average insulation thickness defined by the PAI enamel coating and the electrically insulating tape is within the range of about 91 micrometers to about 125 micrometers per side; or 1. An electrically insulated conductor, wherein the PAI enamel coating has an average thickness within the range of about 50 micrometers to about 70 micrometers per side, the tape overlap is within the range of about 15% to about 70%, and the tape wrapped PAI enameled electrically conductive core has an overall thickness of less than about 170 micrometers per side.

24. An electrically insulated conductor according to any one of claims 14 to 19, the enamel coating comprises a polyimide (PI) enamel coating along the electrically conductive core such that the PI enamel coating has an average thickness within a range of about 40 micrometers to about 45 micrometers per side; 1. An electrically insulated conductor, wherein an electrically insulating tape is wrapped around a PI enameled, electrically conductive core, whereby the tape overlap is in the range of about 15% to about 53%, and the average insulation thickness defined by the PI enamel coating and the electrically insulating tape is in the range of about 75 micrometers to about 108 micrometers per side.

25. An electrically insulated conductor according to any one of claims 14 to 19, the enamel coating comprises a polyesterimide / polyamideimide (PEI / PAI) enamel coating or a polyimide (PI) enamel coating along the electrically conductive core, such that the PEI / PAI enamel coating has an average thickness within the range of about 50 micrometers to about 70 micrometers per side; 1. An electrically insulated conductor, wherein an electrically insulating tape is wrapped around an enameled electrically conductive core, whereby a tape overlap is within the range of about 15% to about 70%, and whereby the tape wrapped enameled electrically conductive core has an overall thickness of less than about 170 micrometers per side.

26. An electrically insulated conductor according to any one of claims 14 to 19, The electrically insulating tape comprises about 10-25 weight percent of an electrically insulating, corona resistant composite filler in a polyimide; The electrically insulating tape has a thickness of less than 30 micrometers and does not include an additional polymer adhered to the polyimide; the enamel coating comprises a polyamideimide (PAI) enamel coating along the electrically conductive core such that the PAI enamel coating has an average thickness within a range of about 30 micrometers to about 80 micrometers per side; An electrically insulated conductor, wherein an electrically insulating tape is wrapped around a PAI enameled electrically conductive core, whereby the tape overlap is in the range of about 15% to about 70%, and the tape wrapped PAI enameled electrically conductive core has an overall thickness of less than about 170 micrometers per side.

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