Polyimide coating

Abstract

The present invention provides a polyimide coating that has low dielectric properties and prevents dielectric breakdown and partial discharge, while improving adhesion between the conductor and the coating and flexibility of the coating, and a coating and a coated electric wire.

Description

Technical Field

[0001] The present invention relates to a polyimide coating.

Background Art

[0002] For an insulating layer (coating) that coats a conductor, excellent insulation properties, adhesion to the conductor, heat resistance, mechanical strength, etc. are required.

[0003] In addition, in electrical equipment with a high applied voltage, such as a motor used at a high voltage, a high voltage is applied to the insulated wire that constitutes the electrical equipment, and partial discharge (corona discharge) is likely to occur on the surface of the coating.

[0004] The occurrence of corona discharge causes local temperature rise and generation of ozone or ions. As a result, deterioration occurs in the coating of the insulated wire, which may cause insulation breakdown at an early stage and shorten the life of the electrical equipment.

[0005] For insulated wires used at high voltages, improvement of the corona discharge inception voltage is required for the above reasons, and it is known that reducing the dielectric constant of the insulating layer is effective for this purpose.

[0006] Examples of the resin for forming the insulating layer include polyimide resin, polyamideimide resin, and polyesterimide resin.

[0007] Generally, a polyimide resin refers to a high heat-resistant resin produced by solution polymerization of an aromatic dianhydride and an aromatic diamine or aromatic diisocyanate to produce a polyamic acid derivative, followed by ring-closing dehydration at a high temperature to cause imidization.

[0008] The polyimide resin has excellent heat resistance and relatively low dielectric constant, and has excellent properties for use as a material for coating a conductor.

[0009] However, on the other hand, since the polyimide resin has a rigid structure, it has low tensile elongation at break and flexibility, and it is also a fact that it has properties disadvantageous for use as a conductor coating.

[0010] For example, in a coil used in a motor, in order to increase the space factor, after winding an insulated wire to form a coil and then inserting the coil into a slot, there may be a process of greatly deforming the insulated wire.

[0011] At this time, if the flexibility of the insulating layer is low, the coating may be damaged during processing, or cracks may occur in the coating.

[0012] When producing a polyimide resin by reacting diamines and dianhydrides having a flexible structure to improve flexibility, there is a problem that the heat resistance is lower than that of a polyimide resin not containing diamines or dianhydrides having a flexible structure.

[0013] Therefore, while improving the corona resistance, it is necessary to develop a technology that maintains the adhesion between the conductor and the coating and the flexibility of the coating.

Summary of the Invention

Problems to be Solved by the Invention

[0014] The purpose of the present invention is to solve the problems and technical issues of the prior art as described above. This application provides a polyimide coating that has low dielectric constant characteristics and can simultaneously improve the adhesion between the conductor and the coating and the flexibility of the coating while preventing dielectric breakdown and partial discharge.

Means for Solving the Problems

[0015] This application relates to polyimide. The polyimide may be applied for conductor coating. This application provides a polyimide coating. The polyimide coating may include a polyimide having a dianhydride monomer component and a diamine monomer component as polymerization units.

[0016] The polyimide coating according to the present application may have a relative dielectric constant (Dk) of less than 3.6 in the frequency band of 10 GHz. The lower limit of the dielectric constant after curing is not particularly limited, and may be, for example, 1.0 or more, and the upper limit may be 3.58 or less, 3.55 or less, 3.53 or less, 3.5 or less, 3.48 or less, 3.45 or less, or 3.42 or less. Since the polyimide resin obtained by curing the polyamic acid composition of the present application has a particularly low dielectric constant in the high frequency band, it can have excellent dielectric properties.

[0017] Further, the polyimide coating may have a breakdown voltage (BDV) measured according to the ASTM D149 standard of 230 kV / mm or more. The lower limit of the breakdown voltage may be 233 kV / mm or more, 235 kV / mm or more, 238 kV / mm or more, 240 kV / mm or more, 243 kV / mm or more, 244 kV / mm or more, 245 kV / mm or more, 246 kV / mm or more, 247 kV / mm or more, 248 kV / mm or more, or 249 kV / mm or more, and the upper limit may be, for example, 300 kV / mm or less, 290 kV / mm or less, 280 kV / mm or less, 270 kV / mm or less, 265 kV / mm or less, or 260 kV / mm or less. The polyimide coating of the present application can provide a polyimide that simultaneously satisfies low dielectric constant, heat resistance, insulation, adhesion, and mechanical properties at high temperatures. Thus, when used for wire coating, it can prevent partial discharge, local deterioration, and breakdown, and provide a highly reliable coating.

[0018] The breakdown voltage (BDV) may be measured by a method known in the art. In one example, the breakdown voltage may be measured according to the ASTM D149 standard. A wire coated with the polyamic acid composition may be used as a specimen, and the measuring equipment PHENIX CO., LTD. TEXNOLOGIES 6CCE50-5 may be used. After the manufactured specimen is pretreated in an oven at 100 °C to remove moisture, the specimen may be fixed to the measuring equipment set in a normal temperature atmosphere, and a voltage of 10 KVAc may be applied from the lower and upper electrodes to increase the AC voltage from 0 at a constant speed to measure the BDV.

[0019] In addition, for the polyimide coating according to the present application, after manufacturing an electric wire specimen coated with the polyimide on a conductor wire having a length of 250 mm, when both ends of the specimen are pulled and stretched by 15% in a state where only the coating is cut at the central portion of the specimen excluding the conductor wire, the length of the gap generated by the spread of the cut portion of the coating may be less than 5 mm. The length of the gap may be less than 4.8 mm, less than 4.5 mm, less than 4.3 mm, less than 4.0 mm, less than 3.8 mm, less than 3.5 mm, less than 3.3 mm, less than 3.0 mm, less than 2.8 mm, less than 2.5 mm, less than 2.3 mm, or less than 2.0 mm, and the lower limit is not particularly limited, but may be 0.01 mm or more or 0.1 mm or more. The conductor wire may be a copper wire. The polyimide coating of the present application can effectively ensure the adhesion and flexibility of the polyimide coating to the conductor wire through the tensile test.

[0020] The present application can provide a polyimide that can simultaneously satisfy low dielectric characteristics, heat resistance, insulation, adhesion, and mechanical characteristics at high temperatures by simultaneously realizing the breakdown voltage value, relative permittivity value, and physical property values in the tensile test. Thus, when used for wire coating, it can prevent partial discharge, local deterioration, and breakdown, and can provide a highly reliable coating.

[0021] In addition, the diamine monomer component may contain the compound of Chemical Formula 1 below. By including a diamine monomer with a specific structure, the present application can simultaneously realize adhesion and flexibility to the object to be coated while preventing breakdown and partial discharge.

[0022]

Chemical Formula

[0023] In Chemical Formula 1, A 1 and A 2 may each independently be an ether group, an ester group, or an amide group. The A 1 and A2 Any of the hydrogens of the aromatic ring may be eliminated and linked to the aromatic ring. The above A 1 or A 2 may be linked to the meta or para position based on the amine group considering the steric structure. The above X may represent a single bond, an alkylene group, an alkylidene group, an aryl group, or Chemical Formula 2 below.

[0024]

Chemical Formula

[0025] In Chemical Formula 2, Q may be oxygen, a carbonyl group, an alkylcarbonyl group, a single bond, an alkylene group, an alkylidene group, or a sulfone group. The "*" linked to the aromatic ring in Chemical Formula 2 、 Any of the hydrogens of the aromatic ring is eliminated, and the structure of Chemical Formula 2 is linked to A of Chemical Formula 1 1 or A 2 to indicate a linker. Considering the steric structure, the linker may be linked to the meta or para position based on Q. Q may have an alkyl group, an alkenyl group, or an alkynyl group as a substituent. Or Q may have a fluorine-substituted alkyl group, an alkenyl group, or an alkynyl group as a substituent. In one example, when Q is an alkylene group, it may have one or two alkyl groups, or two or more and five or fewer alkyl groups.

[0026] In this specification, the term "single bond" means a bond that connects both atoms without any arbitrary atoms. For example, in Chemical Formula 1, when X is a single bond, A 1 and A 2 may be directly linked to each other.

[0027] As used herein, the term "alkyl group" means an alkyl group having 1 to 30 carbon atoms, 1 to 25 carbon atoms, 1 to 20 carbon atoms, 1 to 16 carbon atoms, 1 to 12 carbon atoms, 1 to 8 carbon atoms or 1 to 4 carbon atoms, unless otherwise specified. The alkyl group may have a linear, branched or cyclic structure and may optionally be substituted with one or more substituents. Examples of the substituents include polar functional groups and the like.

[0028] As used herein, the term "alkenyl group" means an alkenyl group having 1 to 30 carbon atoms, 1 to 25 carbon atoms, 1 to 20 carbon atoms, 1 to 16 carbon atoms, 1 to 12 carbon atoms, 1 to 8 carbon atoms or 1 to 4 carbon atoms, unless otherwise specified. The alkenyl group may have a linear, branched or cyclic structure and may optionally be substituted with one or more substituents. Examples of the substituents include polar functional groups and the like.

[0029] As used herein, the term "alkynyl group" means an alkynyl group having 1 to 30 carbon atoms, 1 to 25 carbon atoms, 1 to 20 carbon atoms, 1 to 16 carbon atoms, 1 to 12 carbon atoms, 1 to 8 carbon atoms or 1 to 4 carbon atoms, unless otherwise specified. The alkynyl group may have a linear, branched or cyclic structure and may optionally be substituted with one or more substituents. Examples of the substituents include polar functional groups and the like.

[0030] As used herein, the term "alkylene group" means an alkylene group having 2 to 30 carbon atoms, 2 to 25 carbon atoms, 2 to 20 carbon atoms, 2 to 16 carbon atoms, 2 to 12 carbon atoms, 2 to 10 carbon atoms or 2 to 8 carbon atoms, unless otherwise specified. The alkylene group may have a linear, branched or cyclic structure and may optionally be substituted with one or more substituents. Examples of the substituents include polar functional groups and the like.

[0031] As used herein, the term "alkylidene group" means an alkylidene group having 2 to 30 carbon atoms, 2 to 25 carbon atoms, 2 to 20 carbon atoms, 2 to 16 carbon atoms, 2 to 12 carbon atoms, 2 to 10 carbon atoms or 2 to 8 carbon atoms, unless otherwise specified. The alkylidene group may have a linear, branched or cyclic structure and may be optionally substituted with one or more substituents. Examples of the substituent include polar functional groups and the like.

[0032] In one example, the compound of Chemical Formula 1 may be included in a proportion of 99 mol% or less of the diamine monomer component. In a specific example, the compound of Chemical Formula 1 may be 95 mol% or less, 90 mol% or less, 85 mol% or less, 80 mol% or less, 75 mol% or less, 70 mol% or less, 65 mol% or less, 60 mol% or less, 55 mol% or less, 50 mol% or less, 45 mol% or less, 40 mol% or less, 38 mol% or less, 35 mol% or less, 33 mol% or less, 31 mol% or less, 25 mol% or less, 20 mol% or less or 14 mol% or less of all the diamine monomer components in the composition, and the lower limit may be, for example, 5 mol% or more, 8 mol% or more, 9 mol% or more, 10 mol% or more, 12 mol% or more, 15 mol% or more, 18 mol% or more, 20 mol% or more, 23 mol% or more, 25 mol% or more, 28 mol% or more, 33 mol% or more, 38 mol% or more, 43 mol% or more, 48 mol% or more, 53 mol% or more, 58 mol% or more, 63 mol% or more or 68 mol% or more. By adjusting the content range of the compound having the structure of Chemical Formula 1 in the present application, the heat resistance, electrical properties, flexibility and adhesion to an adhesive of the polyimide resin after polymerization are excellently embodied.

[0033] In a specific example of the present application, the diamine monomer component may further include the compound of Chemical Formula 3 below.

[0034]

Chemical Formula

[0035] In Chemical Formula 3, R represents a single bond, an ether group, an ester group, an amide group, a carbonyl group, an alkylcarbonyl group, an alkylene group, an alkylidene group, or an aryl group. The structure of Chemical Formula 3 has a structure excluding the compound of the structure of Chemical Formula 1 described above.

[0036] The compound of Chemical Formula 3 may be contained at a ratio of 5 mol% or more of the diamine monomer component. In a specific example, the compound of Chemical Formula 3 is 10 mol% or more, 15 mol% or more, 20 mol% or more, 25 mol% or more, 30 mol% or more, 35 mol% or more, 40 mol% or more, 45 mol% or more, 50 mol% or more, 55 mol% or more, 60 mol% or more, 63 mol% or more, 65 mol% or more, 68 mol% or more, 70 mol% or more, 80 mol% or more, 85 mol% or more, or 88 mol% or more of all the diamine monomer components in the composition, and the upper limit may be, for example, 95 mol% or less, 93 mol% or less, 91 mol% or less, 85 mol% or less, 80 mol% or less, 78 mol% or less, 75 mol% or less, 73 mol% or less, 71 mol% or less, 68 mol% or less, 63 mol% or less, 58 mol% or less, 53 mol% or less, 48 mol% or less, 43 mol% or less, 38 mol% or less, 33 mol% or less, or 28 mol% or less. Further, when based on 100 parts by weight of the compound of Chemical Formula 3, the compound of Chemical Formula 1 may be in the range of 5 to 150 parts by weight with respect to 100 parts by weight of the compound of Chemical Formula 3. In this range, the lower limit may be 7 parts by weight or more, 9 parts by weight or more, 10 parts by weight or more, 11 parts by weight or more, 15 parts by weight or more, 20 parts by weight or more, 25 parts by weight or more, 30 parts by weight or more, 33 parts by weight or more, 35 parts by weight or more, 38 parts by weight or more, 40 parts by weight or more, 42 parts by weight or more, 45 parts by weight or more, 50 parts by weight or more, 55 parts by weight or more, 60 parts by weight or more, 65 parts by weight or more, 70 parts by weight or more, 75 parts by weight or more, 80 parts by weight or more, 85 parts by weight or more, 90 parts by weight or more, 95 parts by weight or more, 100 parts by weight or more, or 105 parts by weight or more, and the upper limit may be, for example, 145 parts by weight or less, 140 parts by weight or less, 135 parts by weight or less, 130 parts by weight or less, 125 parts by weight or less, 120 parts by weight or less, 115 parts by weight or less, 110 parts by weight or less, 108 parts by weight or less, 103 parts by weight or less, 98 parts by weight or less, 93 parts by weight or less, 88 parts by weight or less, 83 parts by weight or less, 78 parts by weight or less, 73 parts by weight or less, 68 parts by weight or less, 63 parts by weight or less, 58 parts by weight or less, 53 parts by weight or less, 50 parts by weight or less, 48 parts by weight or less, 45 parts by weight or less, 43 parts by weight or less, 40 parts by weight or less, 37 parts by weight or less, 34 parts by weight or less, 31 parts by weight or less, 28 parts by weight or less, 23 parts by weight or less, 18 parts by weight or less, or 13 parts by weight or less.The polyimide resin according to the present application uses two or more types of diamines. By adjusting the content ratio of each diamine, corona resistance can be imparted, and the adhesion between the conductor and the coating and the flexibility of the coating can be improved.

[0037] The diamine monomer according to the present application can be classified and exemplified as follows, for example, as an aromatic diamine.

[0038] 1) Diamines having one benzene nucleus in structure, such as 1,4-diaminobenzene (or paraphenylenediamine, PDA), 1,3-diaminobenzene, 2,4-diaminotoluene, 2,6-diaminotoluene, or 3,5-diaminobenzoic acid, which are diamines with a relatively rigid structure.

[0039] 2) Diamines having two benzene nuclei in structure, such as 4,4'-diaminodiphenylmethane (methylenediamine), 3,3'-dimethyl-4,4'-diaminobiphenyl, 2,2'-dimethyl-4,4'-diaminobiphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 3,3'-dicarboxy-4,4'-diaminodiphenylmethane, 3,3',5,5'-tetramethyl-4,4'-diaminodiphenylmethane, bis(4-aminophenyl)sulfide, 4,4'-diaminobenzanilide, 3,3'-dichlorobenzidine, 3,3'-dimethylbenzidine (or o-tolidine), 2,2'-dimethylbenzidine (or m-tolidine), 3,3'-dimethoxybenzidine, 2,2'-dimethoxybenzidine, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether (or oxydianiline, ODA), 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, 3,3'-diamino-4,4'-dichlorobenzophenone, 3,3'-diamino-4,4'-dimethoxybenzophenone, 3,3'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 2,2-bis(3-aminophenyl)propane, 2,2-bis(4-aminophenyl)propane, 2,2-bis(3-aminophenyl)-1,1,1,3,3,3-hexafluoropropene, 2,2-bis(4-aminophenyl)-1,1,1,3,3,3-hexafluoropropene, 3,3'-diaminodiphenyl sulfoxide, 3,4'-diaminodiphenyl sulfoxide, 4,4'-diaminodiphenyl sulfoxide, or 4,4'-(1,3-propanediyl)dioxydianiline (PDDA),

[0040] 3) Diamines having three benzene nuclei in structure, such as 1,3-bis(3-aminophenyl)benzene, 1,3-bis(4-aminophenyl)benzene, 1,4-bis(3-aminophenyl)benzene, 1,4-bis(4-aminophenyl)benzene, 1,3-bis(4-aminophenoxy)benzene (TPE-R), 1,4-bis(3-aminophenoxy)benzene (or TPE-Q), 1,4-bis(4-aminophenoxy)benzene (or TPE-Q), 1,3-bis(3-aminophenoxy)-4-trifluoromethylbenzene, 3,3'-diamino-4-(4-phenyl)phenoxybenzophenone, 3,3'-diamino-4,4'-di(4-phenylphenoxy)benzophenone, 1,3-bis(3-aminophenylsulfide)benzene, 1,3-bis(4-aminophenylsulfide)benzene, 1,4-bis(4-aminophenylsulfide)benzene, 1,3-bis(3-aminophenylsulfone)benzene, 1,3-bis(4-aminophenylsulfone)benzene, 1,4-bis(4-aminophenylsulfone)benzene, 1,3-bis[2-(4-aminophenyl)isopropyl]benzene, 1,4-bis[2-(3-aminophenyl)isopropyl]benzene, 1,4-bis[2-(4-aminophenyl)isopropyl]benzene, or [3-(4-aminobenzoyl)oxyphenyl] 4-aminobenzoate (p-BABB),

[0041] Diamines having four benzene nuclei in structure, such as 3,3'-bis(3-aminophenoxy)biphenyl, 3,3'-bis(4-aminophenoxy)biphenyl, 4,4'-bis(3-aminophenoxy)biphenyl, 4,4'-bis(4-aminophenoxy)biphenyl, bis[3-(3-aminophenoxy)phenyl]ether, bis[3-(4-aminophenoxy)phenyl]ether, bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(4-aminophenoxy)phenyl]ether, bis[3-(3-aminophenoxy)phenyl]ketone, bis[3-(4-aminophenoxy)phenyl]ketone, bis[4-(3-aminophenoxy)phenyl]ketone, bis[4-(4-aminophenoxy)phenyl]ketone, bis[3-(3-aminophenoxy)phenyl]sulfide, bis[3-(4-aminophenoxy)phenyl]sulfide, bis[4-(3-aminophenoxy)phenyl]sulfide, bis[4-(4-aminophenoxy)phenyl]sulfide, bis[3-(3-aminophenoxy)phenyl]sulfone, bis[3-(4-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(4-aminophenoxy)phenyl]sulfone, bis[3-(3-aminophenoxy)phenyl]methane, bis[3-(4-aminophenoxy)phenyl]methane, bis[4-(3-aminophenoxy)phenyl]methane, bis[4-(4-aminophenoxy)phenyl]methane, 2,2-bis[3-(3-aminophenoxy)phenyl]propane, 2,2-bis[3-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(3-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), 2,2-bis[3-(3-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, 2,2-bis[3-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropene, 2,2-bis[4-(3-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropene, or 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane.

[0042] Preferably, the compound of Chemical Formula 1 may be 4,4'-(1,3-propanediyl)dioxy dianiline (PDDA), or [3-(4-aminobenzoyl)oxy phenyl] 4-aminobenzoate (p-BABB), and the compound of Chemical Formula 3 may be 4,4'-diaminodiphenyl ether (or oxydianiline, ODA).

[0043] On the other hand, the dianhydride monomer contained in the polyimide resin according to the present application may be an aromatic tetracarboxylic acid dianhydride. The dianhydride monomer component may have one or more aromatic rings. The upper limit of the number of aromatic rings may be, for example, five.

[0044] The aromatic tetracarboxylic dianhydride may be pyromellitic dianhydride (or PMDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (or BPDA), 2,3,3',4'-biphenyltetracarboxylic dianhydride (a-BPDA), oxydiphthalic dianhydride (or ODPA), diphenylsulfone-3,4,3',4'-tetracarboxylic dianhydride (or DSDA), bis(3,4-dicarboxyphenyl)sulfide dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, 2,3,3',4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride (or BTDA), bis(3,4-dicarboxyphenyl)methane dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, p-phenylene bis(trimellitic monoester anhydride), p-biphenylene bis(trimellitic monoester anhydride), m-terphenyl-3,4,3',4'-tetracarboxylic dianhydride, p-terphenyl-3,4,3',4'-tetracarboxylic dianhydride, 1,3-bis(3,4-dicarboxyphenoxy)benzene dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)biphenyl dianhydride, 2,2-bis[(3,4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA), 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, or 4,4'-(2,2-hexafluoroisopropylidene)diphthalic dianhydride, etc.

[0045] Preferably, the aromatic tetracarboxylic dianhydride may be pyromellitic dianhydride (or PMDA).

[0046] In a specific example of the present application, the polyimide coating may further contain a silane compound. The silane compound may be, for example, one or more selected from the group consisting of epoxy-based, amino-based, and thiol-based compounds, or a mixture of two or more thereof. Specifically, the epoxy-based compound may contain glycidoxypropyl trimethoxysilane (GPTMS), the amino-based compound may contain (3-Aminopropyl)trimethoxy-silane (APTMS), and the thiol-based compound may contain mercapto-propyl-trimethoxysilane (MPTMS), but is not limited thereto. Further, the silane compound may contain an alkoxysilane compound exemplified by dimethyldimethoxysilane (DMDMS), methyltrimethoxysilane (MTMS), methyltriethoxysilane (MTES), or tetraethoxysilane (TEOS).

[0047] Preferably, the silane compound may be an amino-based silane compound.

[0048] The silane compound may be contained in the range of 0.01 to 1 part by weight based on 100 parts by weight of the polyimide. In a specific example, the content ratio of the silane compound may be 0.03 part by weight or more, 0.05 part by weight or more, 0.08 part by weight or more, 0.1 part by weight or more, 0.15 part by weight or more, or 0.18 part by weight or more based on 100 parts by weight of the polyamic acid. The upper limit may be, for example, 0.8 part by weight or less, 0.5 part by weight or less, 0.3 part by weight or less, 0.23 part by weight or less, or 0.15 part by weight or less. By including the silane compound, the present application improves the adhesion to the adhesive while maintaining the electrical properties together with the polyimide resin having the specific structure described above.

[0049] In one specific example, the polyimide resin may have a molecular weight in the range of 10,000 to 50,000 g / mol or 15,000 to 30,000 g / mol. The weight average molecular weight means the conversion value with respect to standard polystyrene or polymethyl methacrylate (PMMA) measured by GPC (Gel permeation Chromatograph).

[0050] In one example, this application can evaluate elongation to indirectly measure the properties of the coating. The elongation of the polyimide may be 70% or more. In a specific example, it may be 72% or more, 73% or more, 75% or more, 78% or more, 80% or more, 83% or more, 85% or more, 87% or more, 90% or more, 93% or more, 100% or more, 110% or more, 120% or more, 130% or more, or 140% or more. The upper limit may be, for example, 150% or less, 148% or less, 145% or less, 140% or less, 130% or less, 120% or less, 110% or less, 100% or less, 98% or less, 95% or less, 90% or less, 85% or less, or 80% or less. Such mechanical properties can similarly appear in the coating coated on the wire as described above.

[0051] In one example, the polyimide coating may have an adhesive strength to copper of 0.65 N / cm or more. The measurement of the adhesive strength may be performed after producing the polyamic acid composition in a film shape (10 mm in width × 50 mm in length × 20 μm in thickness). The adhesive strength may be measured at a temperature of 23°C, a peel angle of 180°, and a peel rate of 20 mm / min.

[0052] In a specific example of this application, the partial discharge inception voltage (PDIV) of the polyimide coating measured according to the ASTM2275-01 standard specification may be 800 Vp or more. In a specific example, the lower limit of the partial discharge inception voltage may be 800 Vp or more, 820 Vp or more, 830 Vp or more, or 850 Vp or more, and the upper limit may be 1000 Vp or 950 Vp or less.

[0053] Also, the partial discharge inception voltage (PDIV) may be measured by a method known in the art. The partial discharge inception voltage, for example, produces a sample twisted in two rows by applying load and torsion to a pair of ends of a specimen of the manufactured insulated wire according to ASTM2275-01 standard. Then, a voltage with a frequency of 50 to 60 Hz is applied to the bare conductors at both ends of the sample at a constant speed, and the voltage at which partial discharge (100 pC or more) occurs is recorded.

[0054] This application further relates to a polyimide precursor composition. The polyimide precursor composition may be a precursor composition of the polyimide coating described above or may be a polyamic acid composition.

[0055] The polyamic acid composition according to this application may have a solid content in the range of 10 to 50% by weight. The solid content may be 13% by weight or more, 15% by weight or more, 18% by weight or more, 20% by weight or more, 25% by weight or more, or 28% by weight or more, and the upper limit may be, for example, 48% by weight or less, 45% by weight or less, 43% by weight or less, 40% by weight or less, 38% by weight or less, 35% by weight or less, 33% by weight or less, or 30% by weight or less. This application can embody desired physical properties and viscosity within the above range.

[0056] This application may include a first solvent, which is an organic solvent, in the polyamic acid composition.

[0057] The organic solvent is not particularly limited as long as it is an organic solvent in which polyamic acid can be dissolved, and as an example, it may be an aprotic polar solvent.

[0058] The aprotic polar solvent includes, for example, amide solvents such as N,N'-dimethylformamide (DMF), N,N'-diethylformamide (DEF), N,N'-dimethylacetamide (DMAc), dimethylpropionamide (DMPA), phenolic solvents such as p-chlorophenol and o-chlorophenol, N-methyl-pyrrolidone (NMP), γ-butyrolactone (GBL), and diglyme (Diglyme). These may be used alone or in combination of two or more.

[0059] In one example, the polyamic acid composition of the present application may further include a second solvent having at least one or more polar functional groups selected from the group consisting of a hydroxy group, a carboxyl group, an alkoxy group, an ester group, and an ether group. The second solvent may also be an organic solvent, but the first solvent and the second solvent may be different components from each other.

[0060] In one specific example, the dianhydride monomer may include a monomer having an unpolymerized and ring-opened structure in addition to the monomers included in the polymerization unit. That is, a part of the dianhydride monomer may be included in the polymerization unit, and a part may not be included in the polymerization unit. The dianhydride monomer not included in the polymerization unit may have a structure ring-opened by the organic solvent according to the present application. The polyamic acid composition according to the present application may exist in the form of an aromatic carboxylic acid having two or more carboxylic acids in a state where the dianhydride monomer is not polymerized. The aromatic carboxylic acid exists as a monomer before curing to lower the viscosity of the entire polyamic acid composition and improve processability. The aromatic carboxylic acid having two or more carboxylic acids is polymerized with the dianhydride monomer in the main chain after curing to increase the length of the entire polymer chain. Such a polymer can be applied to a coating to exhibit excellent heat resistance, dimensional stability, and mechanical properties.

[0061] Specifically, during the heat treatment for imidizing the polyamic acid composition into polyimide, the aromatic carboxylic acid having two or more carboxylic acids becomes a dianhydride monomer through a ring-closing dehydration reaction, reacts with the terminal amine groups of the polyamic acid chain or the polyimide chain, increasing the length of the polymer chain. As a result, the dimensional stability and thermal stability at high temperatures of the produced polyimide film can be improved, and the mechanical properties at room temperature can be enhanced.

[0062] In one example, as described above, the polyamic acid composition of the present application may contain a second solvent, and the second solvent may be contained within a range of 0.01 to 10% by weight in the total polyamic acid composition. The lower limit of the content of the second solvent may be, for example, 0.015% by weight, 0.03% by weight, 0.05% by weight, 0.08% by weight, 0.1% by weight, 0.3% by weight, 0.5% by weight, 0.8% by weight, 1% by weight or 2% by weight or more, and the upper limit may be, for example, 10% by weight, 9% by weight, 8% by weight, 7% by weight, 6% by weight, 5.5% by weight, 5.3% by weight, 5% by weight, 4.8% by weight, 4.5% by weight, 4% by weight, 3% by weight, 2.5% by weight, 1.5% by weight, 1.2% by weight, 0.95% by weight or 0.4% by weight or less. Further, the first solvent may be contained within a range of 60 to 95% by weight in the total polyamic acid composition. The lower limit of the content of the first solvent may be, for example, 65% by weight, 68% by weight, 70% by weight, 73% by weight, 75% by weight, 78% by weight or 80% by weight or more, and the upper limit may be, for example, 93% by weight, 90% by weight, 88% by weight, 85% by weight, 83% by weight, 81% by weight or 79% by weight or less. The polyamic acid composition according to the present application contains a dianhydride monomer component and a diamine monomer component, and the two monomers constitute polymerization units with each other. However, a part of the dianhydride monomer cannot participate in the polymerization reaction by ring-opening with the organic solvent. The dianhydride monomer that is ring-opened without polymerization acts as a diluent monomer and can relatively lower the viscosity of the total polyamic acid composition. The dianhydride monomer having the ring-opened structure can participate in the reaction during the imidization reaction to embody a polyimide having heat resistance, flexibility, low dielectric properties and adhesion as a desired coating material.

[0063] In one example, the second solvent may have a solubility of less than 1.5 g / 100 g with respect to the dianhydride monomer. That is, the second solvent may have a solubility of less than 1.5 g / 100 g with respect to the dianhydride monomer. The upper limit of the solubility range may be, for example, 1.3 g / 100 g, 1.2 g / 100 g, 1.1 g / 100 g, 1.0 g / 100 g, 0.9 g / 100 g, 0.8 g / 100 g, 0.7 g / 100 g, 0.6 g / 100 g, 0.5 g / 100 g, 0.4 g / 100 g, 0.3 g / 100 g, 0.25 g / 100 g, 0.23 g / 100 g, 0.21 g / 100 g, 0.2 g / 100 g, or 0.15 g / 100 g or less, and the lower limit may be, for example, 0 g / 100 g, 0.01 g / 100 g, 0.05 g / 100 g, 0.08 g / 100 g, 0.09 g / 100 g, or 0.15 g / 100 g or more. The present application can provide a polyamic acid composition having desired physical properties by including a second solvent having a low solubility with respect to the dianhydride monomer contained in the polymerization unit or the unpolymerized dianhydride monomer. When the physical properties measured in the present application are physical properties affected by temperature, unless otherwise specified, they may be measured at room temperature of 23°C.

[0064] In a specific example of the present application, the first solvent may have a solubility of 1.5 g / 100 g or more with respect to the dianhydride monomer, for example. The lower limit of the solubility may be, for example, 1.6 g / 100 g, 1.65 g / 100 g, 1.7 g / 100 g, 2 g / 100 g, 2.5 g / 100 g, 5 g / 100 g, 10 g / 100 g, 30 g / 100 g, 45 g / 100 g, 50 g / 100 g, or 51 g / 100 g or more, and the upper limit may be, for example, 80 g / 100 g, 70 g / 100 g, 60 g / 100 g, 55 g / 100 g, 53 g / 100 g, 48 g / 100 g, 25 g / 100 g, 10 g / 100 g, 5 g / 100 g, or 3 g / 100 g or less. The first solvent may have a higher solubility than the second solvent.

[0065] In one example, the first solvent may have a boiling point of 150°C or higher, and the second solvent may have a boiling point lower than that of the first solvent. That is, the first solvent may have a higher boiling point than the second solvent. The second solvent may have a boiling point within the range of 30°C or higher and less than 150°C. The lower limit of the boiling point of the first solvent may be, for example, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C, 185°C, 190°C, 195°C, 200°C, or 201°C or higher, and the upper limit may be, for example, 500°C, 450°C, 300°C, 280°C, 270°C, 250°C, 240°C, 230°C, 220°C, 210°C, or 205°C or lower. Also, the lower limit of the boiling point of the second solvent may be, for example, 35°C, 40°C, 45°C, 50°C, 53°C, 58°C, 60°C, or 63°C or higher, and the upper limit may be, for example, 148°C, 145°C, 130°C, 120°C, 110°C, 105°C, 95°C, 93°C, 88°C, 85°C, 80°C, 75°C, 73°C, 70°C, or 68°C or lower. This application can produce polyimide with desired physical properties by using two solvents with different boiling points.

[0066] The first solvent according to this application is not particularly limited as long as it can dissolve polyamic acid. The first solvent may also be a polar solvent in this case. For example, examples of the first solvent include amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone. For example, the first solvent may have an amide group or a ketone group in its molecular structure. The first solvent may have a lower polarity than the second solvent.

[0067] The first solvent may be, for example, an aprotic polar solvent. The second solvent may be an aprotic polar solvent or a protic polar solvent. For example, the second solvent may include alcohol solvents such as methanol, ethanol, 1-propanol, butyl alcohol, isobutyl alcohol, or 2-propanol; ester solvents such as methyl acetate, ethyl acetate, or isopropyl acetate; carboxylic acid solvents such as formic acid, acetic acid, propionic acid, butyric acid, or lactic acid; ether solvents such as dimethyl ether, diethyl ether, diisopropyl ether, dimethoxyethane, or methyl t-butyl ether; dimethyl carbonate, methyl methacrylate, or propylene glycol monomethyl ether acetate.

[0068] As described above, this application may include the first solvent and the second solvent together. In this case, the first solvent may contain a higher content than the second solvent. Also, the second solvent may be contained in a proportion of 0.01 to 10 parts by weight with respect to 100 parts by weight of the first solvent. The lower limit of the content ratio may be, for example, 0.02 parts by weight, 0.03 parts by weight, 0.04 parts by weight, 0.1 parts by weight, 0.3 parts by weight, 0.5 parts by weight, 0.8 parts by weight, 1 part by weight, or 2 parts by weight or more, and the upper limit may be, for example, 8 parts by weight, 6 parts by weight, 5 parts by weight, 4.5 parts by weight, 4 parts by weight, 3 parts by weight, 2.5 parts by weight, 1.5 parts by weight, 1.2 parts by weight, 0.95 parts by weight, 0.4 parts by weight, 0.15 parts by weight, or 0.09 parts by weight or less.

[0069] The polyamic acid composition of this application may be a composition having low viscosity characteristics. The polyamic acid composition of this application has a temperature of 23°C and 1 s -1The viscosity measured under the condition of shear rate may be 10,000 cP or less, or may be 9,000 cP or less. The lower limit is not particularly limited, but may be 500 cP or more, or 1000 cP or more. The viscosity may be measured using, for example, Rheostress 600 of Haake, and may be measured under the conditions of a shear rate of 1 / s, a temperature of 23 ° C, and a plate gap of 1 mm. By adjusting the viscosity range, the present application provides a precursor composition having excellent processability and can form a coating having desired physical properties when coating a conductor wire.

[0070] The present application further relates to a method for producing a polyamic acid composition. The production method may be a method for producing the polyamic acid composition described above.

[0071] The method for producing the polyamic acid composition may include a step of dividing and charging at least one of a dianhydride monomer and a diamine monomer two or more times.

[0072] The polyamic acid composition may be produced by polymerizing a dianhydride monomer and a diamine monomer in an organic solvent.

[0073] Further, the dianhydride monomer and the diamine monomer may be charged in the form of powder, lump, or solution. It is preferable to charge them in powder form at the initial stage of the reaction to carry out the reaction, and then charge them in solution form for adjusting the polymerization viscosity.

[0074] For example, after charging the dianhydride monomer and the diamine monomer in powder form to carry out the reaction, the dianhydride can be charged in solution form and reacted until the viscosity of the polyamic acid composition reaches a predetermined range.

[0075] On the one hand, the present invention provides a method for producing the polyamic acid composition, which comprises introducing at least one of the dianhydride monomer and the diamine monomers into the organic solvent and dissolving them, and polymerizing and stirring the polyamic acid by introducing at least one of the dianhydride monomer and the diamine monomers into the organic solvent in two or more divided portions.

[0076] During the process of introducing the dianhydride monomer and the diamine monomer in divided portions, the equivalent ratio of the diamine monomer to the dianhydride monomer may be adjusted.

[0077] Specifically, at least one of the dianhydride monomer and the diamine monomers may be introduced in divided portions at least two times to five times.

[0078] The polyimide coating according to the present application may be coated and cured, for example, on the surface of a conductor. In one example, the method for manufacturing the coating may include coating the polyamic acid composition on the conductor surface and imidizing the polyamic acid composition coated on the conductor surface. The conductor may be a copper wire made of copper or a copper alloy, but conductors made of other metal materials such as silver wires, and various metal-coated wires such as aluminum and tin-coated wires may also be included as conductors. The thickness of the conductor and the coating conforms to the KSC 3107 standard. The diameter of the conductor may be in the range of 0.3 to 3.2 mm, and the standard coating thickness (average value of the maximum coating thickness and the minimum coating thickness) of the coating may be 21 to 194 μm for type 0, 14 to 169 μm for type 1, and 10 to 31 μm for type 2. The cross-sectional shape of the conductor may be a loop wire, a flat wire, a hexagonal wire, etc., but is not limited thereto.

[0079] The present application can further provide a coated electric wire including a polyimide coating produced by coating and imidizing the polyamic acid composition on the surface of an electric wire. In one specific example, the coated electric wire may include an electric wire and a coating in which the aforementioned polyimide is coated and imidized on the surface of the electric wire.

[0080] In addition, this application can provide an electronic device including the coated electric wire. Examples of the electronic device include an electric motor.

Advantages of the Invention

[0081] As described above, this application can provide a polyimide coating having low dielectric constant characteristics, which can improve the adhesion between the conductor and the coating and the flexibility of the coating while preventing dielectric breakdown and partial discharge.

Embodiments for Carrying Out the Invention

[0082] Hereinafter, the present invention will be described in more detail through examples according to the present invention and comparative examples not according to the present invention, but the scope of the present invention is not limited by the following examples.

[0083] <Example 1> Dimethylacetamide was charged as a solvent into a 1 L reactor under a nitrogen atmosphere.

[0084] After setting the temperature to 23 to 50°C, 95 parts by weight of pyromellitic dianhydride (PMDA) as a dianhydride monomer was charged, and 90 parts by weight of 4,4'-diaminodiphenyl ether (4,4'-ODA) and 10 parts by weight of 4,4'-(1,3-propanediyl)dioxydianiline (PDDA) as diamine monomers were charged and dissolved, and 5 parts by weight of the pyromellitic dianhydride (PMDA) was charged in three portions at 30-minute intervals to polymerize polyamic acid.

[0085] 0.2 part by weight of an amino-based silane compound PAPTES (Z-6883 silane of DOW) as a silane compound was mixed with the produced polyamic acid composition to produce a polyamic acid composition.

[0086] Manufacture of polyimide coating The manufactured polyamic acid composition was coated on a copper wire with a conductor diameter of 1 mm in a coating curing furnace, and the coating thickness was adjusted to be between 5 and 15 μm each time. The minimum temperature and the maximum temperature of the coating curing furnace were adjusted to 350 to 550 °C, and an electric wire (coated electric wire) containing a polyimide coating with a coating thickness of 33 to 35 μm was manufactured under the condition that the coating speed of the copper wire was adjusted to 12 to 32 m / min.

[0087] <Example 2> A polyamic acid composition, a polyimide coating, and a coated electric wire were manufactured in the same manner as in Example 1, except that 70 parts by weight of 4,4'-ODA and 30 parts by weight of 4,4'-(1,3-propanediyl)dioxydianiline (PDDA) were introduced as diamine monomers.

[0088] <Example 3> A polyamic acid composition, a polyimide coating, and a coated electric wire were manufactured in the same manner as in Example 2, except that no silane compound was blended.

[0089] <Example 4> A polyamic acid composition, a polyimide coating, and a coated electric wire were manufactured in the same manner as in Example 3, except that 30 parts by weight of [3-(4-Aminobenzoyl)oxyphenyl]4-aminobenzoate (p-BABB) was blended instead of 4,4'-(1,3-propanediyl)dioxydianiline (PDDA) as the diamine monomer.

[0090] <Comparative Example 1> A polyamic acid composition, a polyimide coating, and a coated electric wire were manufactured in the same manner as in Example 1, except that only 100 parts by weight of 4,4'-ODA was introduced and dissolved as the diamine monomer, and 100 parts by weight of PMDA was introduced as the dianhydride monomer.

[0091] <Comparative Example 2> A polyamic acid composition, a polyimide coating, and a coated electric wire were manufactured in the same manner as in Comparative Example 1, except that no silane compound was blended.

[0092] <Comparative Example 3> A polyamic acid composition, a polyimide coating, and a coated electric wire were produced in the same manner as in Example 2, except that 30 parts by weight of 4,4'-Diaminobenzanilide (DABA) was blended instead of 4,4'-(1,3-propanediyl)dioxydianiline (PDDA) as the diamine monomer.

[0093] <Comparative Example 4> A polyamic acid composition, a polyimide coating, and a coated electric wire were produced in the same manner as in Comparative Example 2, except that 70 parts by weight of PMDA and 30 parts by weight of 3,3',4,4'-Biphenyltetracarboxylic dianhydride (BPDA) were charged instead of 100 parts by weight of PMDA as the dianhydride monomer.

[0094] <Comparative Example 5> A polyamic acid composition, a polyimide coating, and a coated electric wire were produced in the same manner as in Comparative Example 2, except that 70 parts by weight of PMDA and 30 parts by weight of 3,3',4,4'-Benzophenone tetracarboxylic dianhydride (BTDA) were charged instead of 100 parts by weight of PMDA as the dianhydride monomer.

[0095] <Experimental Example 1: Adhesion> After cutting a copper foil (Cu foil) into a certain size, it is fixed on a glass substrate with an adhesive tape. The polyamic acid composition produced in the examples and comparative examples is applied onto the Cu foil, and a thin film with a certain thickness (10 mm in width × 50 mm in length × 20 μm in thickness) is formed through spin coating. The applied polyamic acid composition is cured, and a polyimide cured product is coated on the Cu foil.

[0096] The copper foil (Cu foil) layer and the cured polyimide layer are peeled off, and the UTM (Peel strength) strength is measured. After fixing the cured polyimide layer to the upper grip and the copper foil (Cu foil) layer to the lower grip, a force is applied at a peeling angle of 180° and a peeling speed of 20 mm / min at a normal temperature of 23 °C to measure the strength of the adhesive force.

[0097] <Experimental Example 2: Tensile Test> For the polyimide coatings of the electric wires manufactured in the examples and comparative examples, a tensile test was conducted to confirm the adhesion between the conductor and the coating, and the results are shown in Table 1 below.

[0098] Specifically, for a straight wire specimen having a free measurement length of 200 to 250 mm, only the coating is cut with a knife at the center (only the coating part is cut except for the copper wire). Both ends of the specimen are pulled to cause a 15% elongation.

[0099] Measure the length of the gap generated by the spreading of the cut portion of the coating.

[0100] <Experimental Example 3: Elongation> The polyamic acid compositions produced in the examples and comparative examples are formed into films and cured.

[0101] After cutting the polyimide film into a width of 10 mm and a length of 50 mm, the elongation was measured by the ASTM D-882 method using an Instron 5564 UTM equipment of Instron.

[0102] <Experimental Example 4: Dielectric Constant Measurement> The relative dielectric constant at 10 GHz of the polyimide coatings produced according to the above examples and comparative examples was measured under the conditions of 23 °C and 50% RH using a Network analyzer EVA Vector Network Analyzer (E5063A, Keysight).

[0103] <Experimental Example 5: Breakdown Voltage (BDV) Evaluation> The BDV values of the polyimide coatings produced in the above Examples and Comparative Examples were measured according to the ASTM D149 standard.

[0104] Measuring equipment: TECHNOLOGIES 6CCE50-5 from PHENIX

[0105] After the produced specimens were pretreated in an oven at 100 °C to remove moisture, the specimens were fixed to the above-mentioned measuring equipment set in a normal-temperature atmosphere, and a voltage of 10 KVAc was applied with the lower and upper electrodes and increased at a constant speed from 0 to measure the BDV.

[0106] <Experimental Example 6: Evaluation of Partial Discharge Initiation Voltage (PDIV)> For the polyimide coatings according to each of the Examples and Comparative Examples, a voltage having a 60 Hz sine wave was applied at room temperature to measure the voltage at which partial discharge was initiated. Here, the voltage at which a charge amount of 100 pC or more was detected when the applied voltage was increased was measured.

[0107] <Experimental Example 7: Evaluation of Coating Damage> The coating damage evaluation was performed on the polyimide coatings according to each of the Examples and Comparative Examples in accordance with Standard JIS C3003, Section 7.1.2. Specifically, among three specimens bent with a mandrel having a diameter (3W) three times the conductor width (W) and three specimens bent with a mandrel having a diameter (3T) three times the conductor height (T), if cracks occur, it is a failure to meet the standard (fail).

[0108]

Table 1

Claims

1. Pyromellitic dianhydride as the dianhydride monomer component, and a combination of 4,4'-diaminodiphenyl ether and 4,4'-(1,3-propanediyl)dioxydianiline, or a combination of 4,4'-diaminodiphenyl ether and [3-(4-aminobenzoyl)oxyphenyl]4-aminobenzoate as the diamine monomer component, having a polyimide as a polymerization unit, the relative dielectric constant (Dk) in the frequency band of 10 GHz after curing is less than 3.6, and the breakdown voltage (BDV) measured according to ASTM D149 standard specification is 230 kV / mm or more, After manufacturing an electric wire specimen coated with the polyimide on a conductor wire having a length of 250 mm and coated with a coating, with the central part of the specimen cut only the coating excluding the conductor wire, when both ends of the specimen are pulled and stretched by 15%, the length of the gap generated by the spread of the cut part of the coating is less than 5 mm, a polyimide coating.

2. 4,4'-(1,3-propanediyl)dioxydianiline, or [3-(4-aminobenzoyl)oxyphenyl]4-aminobenzoate is contained in a proportion of 99 mol% or less among the diamine monomer components, the polyimide coating according to Claim 1.

3. 4,4'-Diaminodiphenyl ether is contained in a proportion of 5 mol% or more among the diamine monomer components, the polyimide coating according to Claim 1.

4. 4,4'-(1,3-propanediyl)dioxydianiline, or [3-(4-aminobenzoyl)oxyphenyl]4-aminobenzoate is in the range of 5 to 150 parts by weight with respect to 100 parts by weight of 4,4'-diaminodiphenyl ether, the polyimide coating according to Claim 1.

5. The polyimide coating according to Claim 1, further comprising a silane compound.

6. The silane compound is contained in the range of 0.01 to 1 part by weight with respect to 100 parts by weight of the polyamic acid, the polyimide coating according to Claim 5.

7. The polyimide coating according to Claim 1, having an elongation of 70% or more.

8. The polyimide coating according to Claim 1, having an adhesive strength to copper of 0.65 N / cm or more.

9. The polyimide coating according to claim 1, wherein the partial discharge inception voltage (PDIV) measured according to ASTM 2275-01 standard specification is 800 Vp or more.

10. An electric wire comprising the polyimide coating according to claim 1.

11. An electronic device comprising the electric wire according to claim 10.

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