Polyimide varnish with excellent voltage endurance characteristics and polyimide coating produced therefrom

Abstract

To provide polyimide varnish with an excellent voltage endurance property.SOLUTION: Provided is polyimide varnish comprising: polyamic acid comprising a dianhydride monomer and a diamine monomer as polymerized units; and nanosilica; where the nanosilica has an absolute value of zeta potential of 10.0 mV to 40.0 mV.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a polyimide varnish and a polyimide coating produced therefrom, and more particularly to a polyimide varnish having excellent voltage endurance properties and a polyimide coating produced therefrom. [Background technology]

[0002] Polyimide (PI) resin is a highly heat-resistant resin typically produced by solution polymerization of aromatic dianhydrides and aromatic diamines or aromatic diisocyanates to produce polyamic acid derivatives, followed by cyclodehydration and imidization at high temperatures. Polyimide resins are insoluble and infusible, possessing excellent thermal oxidation resistance, heat resistance, radiation resistance, low-temperature resistance, and chemical resistance. They are widely used in a wide range of applications, including advanced heat-resistant materials for automobiles, aircraft, and spacecraft, as well as in electronic materials such as insulating coatings, insulating films, semiconductors, and TFT-LCD electrode protection films. Recently, they have also been used in display materials such as optical fibers and liquid crystal alignment films, and in transparent electrode films, either containing conductive fillers within the film or coated on the surface.

[0003] In particular, insulated wires used as coil windings for motors and other devices require the insulating layer (insulating coating) that covers the conductor to have excellent insulation properties, adhesion to the conductor, heat resistance, mechanical strength, and other characteristics, and polyimide is used as the resin that forms the insulating layer.

[0004] However, among insulating layers or coatings, in electrical equipment requiring high voltage applications, such as motors operated at high voltages, high voltages are applied to the insulated wires that make up the electrical equipment, and there is still a need to develop polyimides with excellent voltage durability that can withstand such high voltages.

[0005] Specifically, partial discharge (corona discharge) is likely to occur on the surface of the coating to which high voltage is applied, and if corona discharge occurs, local temperature rise and generation of ozone or ions occur, causing deterioration of the coating of the insulated wire, which can lead to early dielectric breakdown and shorten the life of the electrical equipment. Therefore, in order to use polyimide as a coating material for conductors, especially as a coating to which high voltage is applied, improvements in voltage endurance properties such as dielectric breakdown voltage performance and corona discharge inception voltage are required. Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention provides a polyimide varnish having excellent voltage endurance characteristics.

[0007] The present invention also provides a polyimide produced by imidizing the polyimide varnish.

[0008] The present invention also provides a polyimide coated article comprising a cured product of the polyimide varnish. [Means for solving the problem]

[0009] Since the present invention can be modified in various ways and can have various embodiments, specific embodiments will be illustrated and described in detail, but it should be understood that this does not limit the present invention to the specific embodiments, and that the present invention includes all modifications, equivalents, and alternatives that fall within the spirit and technical scope of the present invention.

[0010] The terms used in this application are merely used to describe specific embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless the context clearly indicates otherwise. In this application, the terms "comprise" or "have" and the like specify the presence of a feature, number, step, operation, component, part, or combination thereof described in the specification, and should be understood as not precluding the presence or additional possibility of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0011] When an amount, concentration, or other value or parameter is given herein as a range, a preferred range, or a list of upper and lower preferred values, that should be understood to specifically disclose all ranges formed by any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are otherwise disclosed.

[0012] When a range of numerical values ​​is recited herein, unless otherwise stated, it is intended that the range include its endpoints and any values ​​within the range. The scope of the invention is not limited to the specific values ​​recited when defining the range.

[0013] As used herein, "dianhydride" is intended to include precursors or derivatives thereof, but may also be referred to as "dianhydride acids," "dianhydrides," or "acid dianhydrides," which may not technically be dianhydrides but nevertheless react with diamines to form polyamic acids, which can also be converted to polyimides.

[0014] As used herein, "diamine" is intended to include precursors or derivatives thereof, which may not technically be diamines, but which nevertheless react with dianhydride acids to form polyamic acids, which can also be converted to polyimides.

[0015] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person of ordinary skill in the art to which this invention pertains. Terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning consistent with the meaning they have in the context of the relevant art, and should not be interpreted in an ideal or overly formal sense unless expressly defined in this application. Specific details for implementing the above invention are described below.

[0016] Polyimide Varnish The present invention relates to a polyimide varnish that has improved voltage endurance characteristics and can be used for conductor coating applications.

[0017] In one aspect of the present invention, there is provided a polyimide varnish comprising: a polyamic acid containing polymerized units of a dianhydride monomer and a diamine monomer; and nanosilica, wherein the nanosilica has an absolute value of a zeta potential of 10.0 mV to 40.0 mV.

[0018] Nano Silica The polyimide varnish of the present invention may contain inorganic particles to improve physical properties such as voltage endurance characteristics. The inorganic particles are nanosilica, which are nano-sized silicon dioxide (SiO2) fine particles having an average particle diameter of 1000 nm or less, and the form and shape of the inorganic particles are not particularly limited.

[0019] The lower limit of the absolute value of the zeta potential can be 10.5 mV or more, 11.0 mV or more, 11.5 mV or more, 12.0 mV or more, 12.5 mV or more, 13.0 mV or more, 13.5 mV or more, 14.0 mV or more, 14.5 mV or more, or 15.0 mV or more, and the upper limit can be 38.0 mV or less, 35.0 mV or less, 32.0 mV or less, 30.0 mV or less, 28.0 mV or less, 27.0 mV or less, 26.0 mV or less, 25.0 mV or less, 24.0 mV or less, 23.5 mV or less, 23.0 mV or less, 22.5 mV or less, 22.0 mV or less, 21.0 mV or less, 20.5 mV or less, or 20.0 mV or less. By controlling the range of the absolute value of the zeta potential, it is possible to maintain high dispersibility without causing entanglement between nanosilica particles in the polyimide varnish, thereby improving voltage durability (corona resistance). Here, the zeta potential is the zeta potential of nanosilica (silica sol) dispersed in an organic solvent, and the pH of the silica sol can be 2 to 12.

[0020] In one embodiment, the zeta potential of nanosilica dispersed in an organic solvent was measured using a Benano 180 Zeta Pro instrument manufactured by Bettersize, with the refractive index, viscosity, and dielectric constant of the organic solvent (dispersant) input into the instrument. The organic solvent may be any one selected from the group consisting of N-methylpyrrolidone (NMP), N-ethylpyrrolidone (NEP), dimethylacetamide (DMAc), dimethylformamide (DMF), and diethylformamide (DEF).

[0021] The organic solvent may have, for example, a refractive index of 1.2 to 1.6, a viscosity of 0.5 cP to 2.0 cP, and a dielectric constant of 30 to 40 at 25°C. Preferably, the organic solvent may have a refractive index of 1.3 to 1.5, a viscosity of 0.7 cP to 1.7 cP, and a dielectric constant of 32 to 39 at 25°C, more preferably a refractive index of 1.35 to 1.47, a viscosity of 0.8 cP to 1.0 cP, and a dielectric constant of 35 to 38.5 at 25°C, and even more preferably a refractive index of 1.4 to 1.45, a viscosity of 0.85 cP to 0.95 cP, and a dielectric constant of 37 to 38 at 25°C.

[0022] In one embodiment, nanosilica dispersed in dimethylacetamide (wherein the silica solids concentration is 30 wt %) can be used.

[0023] The zeta potential is the potential difference between colloidal particles suspended in a liquid. Particles dispersed in a solution carry a negative (-) or positive (+) electrical charge on their surfaces. The concentration of (+) ions increases around the (-)-charged colloidal particles, forming a stern layer. Outside the stern layer, there is a diffuse layer where the concentration of (+) ions decreases, balancing the (-) and (+) ions. The potential difference between the start of the diffuse layer and the point where the (-) and (+) ions balance is the zeta potential. This zeta potential indicates the strength of the repulsive force between charged particles in a dispersion, and is therefore used as a measure to evaluate the stability of a dispersed sol. The higher the (-) or (+) zeta potential, the greater the electrical repulsive force between particles, resulting in greater distance between the particles and a stable state without aggregation. The zeta potential can be used to gauge dispersion stability. In other words, the greater the absolute value of the zeta potential, the better the dispersibility. Furthermore, the zeta potential values ​​may differ depending on the solvent, concentration, pH, functional group, and surface properties of the particles, and it is preferable to compare them as a measure of stability.

[0024] The nanosilica may have an average particle size of 1 to 200 nm, specifically, for example, 5 to 150 nm, 5 to 100 nm, 5 to 70 nm, 10 to 50 nm, or 10 to 30 nm. The average particle size can be measured using equipment such as BET, SEM, or zeta potential.

[0025] The nanosilica may be nanosilica whose surface has been modified with an organic silane.

[0026] In addition, the organic silane of the nanosilica surface-modified with the organic silane may be methyltrimethoxysilane, hexamethyldisiloxane, n-octyltrimethoxysilane, n-octyltriethoxysilane, isooctyltrimethoxysilane, dodecyltrimethoxysilane, octadecyltrimethoxysilane, propyltrimethoxysilane, hexyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-(methacryloxy)propyltriethoxysilane, 3-(methacryloxy)propylmethyldimethoxysilane, 3-(acryloxypropyl)methyldimethoxysilane, 3-(methacryloxy)propyl ... Propyldimethylethoxysilane, styrylethyltrimethoxysilane, phenyltriethoxysilane, p-tolyltriethoxysilane, vinylmethyldiacetoxysilane, vinyldimethylethoxysilane, vinylmethyldiethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriacetoxysilane, vinyltriisopropoxysilane, vinyltriphenoxysilane, vinyltri-t-butoxysilane, vinyltris(isobutoxy)silane, vinyltriisoprofenoxysilane, vinyltris(2-methoxyethoxy)silane, diisopropylethylamine phenyltrimethoxysilane (N,N-Diisopropylethylamine The silane may include one or more selected from the group consisting of N-phenyl-3-aminopropyltrimethoxysilane (PAPTES), N-phenyl-3-aminopropyltrimethoxysilane (PAPTES), N-phenyl-3-aminopropyltrimethoxysilane (PAPTES), N-phenyl-3-aminopropyltrimethoxysilane (PAPTES), N-phenyl-3-aminopropyltrimethoxysilane (PAPTES), N-phenyl-3-aminopropyltrimethoxysilane (PAPTES), N-phenyl-3-aminopropyltrimethoxysilane (PAPTES), N-phenyl-3-aminopropyltrimethoxysilane (PAPTES), N-phenyl-3-aminopropyltrimethoxysilane (PAPTES), N-phenyl-3-aminopropyltrimethoxysilane (PAPTES), N-phenyl-3-aminopropyltrimethoxysilane (PAPTES), N-phenyl-3-aminopropyltrimethoxysilane (PAPTMS ...MS), N-phenyl-3-aminopropyltrimethoxysilane (PAPTES), N-phenyl-3-aminopropyltrimethoxysilane (PAPTMS), N-phenyl-3-aminopropyltrimethoxysilane (PAPTES), N-phenyl-3-aminopropyltrimethoxysilane (PAPTMS), N-phenyl-3-aminopropyltrimethoxysilane (PAPTMS), N-phenyl-3-aminopropyltrimethoxysilane (PAPTES), N-phenyl-3-aminopropyltrimethoxysilane (PAPTMS), N-phenyl-3-aminopropyltrimethoxysilane (PAPTMS), N-phenyl

[0027] The nanosilica surface-modified with the organosilane may have a compound containing at least one phenyl group at the terminal of the nanosilica surface and a compound containing at least one amine group, hydroxy group, thiol group, or epoxide group at the terminal. Specifically, the compound containing at least one phenyl group at the terminal may be phenyltrimethoxysilane (PTMS) or phenylaminopropyltrimethoxysilane (N-Phenyl-3-aminopropyltrimethoxysilane (PAPTES)). The compound containing at least one amine group, hydroxy group, thiol group, or epoxide group at the terminal may be glycidoxypropyltrimethoxysilane (GPTMS) or aminopropyltrimethoxysilane ((3-Aminopropyl)trimethoxysilane (APTMS)).

[0028] The nanosilica surface-modified with an organosilane can be produced by surface-treating nanosilica with an organosilane. For example, nanosilica can be obtained by heating the organosilane under acidic or basic conditions and surface-treating for approximately 1 to 24 hours. Alternatively, surface modification can be achieved by other known methods. For example, the surface-modified nanosilica can be obtained by mixing the organosilane with a solvent and then reacting at a temperature of 10 to 100°C or 20 to 60°C for 1 to 10 hours or 1 to 5 hours. To bond two or more compounds to the surface of nanosilica, each of the above methods can be used.

[0029] The nanosilica surface-modified with the organic silane of the present invention prevents aggregation of inorganic particles in the polyimide varnish, and the functional groups of the compound enhance interaction with the solid content (polyamic acid), thereby improving dispersibility and miscibility.

[0030] The nanosilica may be included in an amount of 4 to 30 parts by weight based on 100 parts by weight of the polyimide solids content of the total polyimide varnish. For example, the lower limit of the nanosilica content may be 4.3 parts by weight or more, 4.5 parts by weight or more, 4.8 parts by weight or more, 5.0 parts by weight or more, 5.3 parts by weight or more, 5.5 parts by weight or more, 5.7 parts by weight or more, 5.8 parts by weight or more, or 5.9 parts by weight or more. The upper limit of the nanosilica content may be 25 parts by weight or less, 20 parts by weight or less, 19 parts by weight or less, 18 parts by weight or less, 17 parts by weight or less, 16 parts by weight or less, 15 parts by weight or less, 14.5 parts by weight or less, 14 parts by weight or less, 13.5 parts by weight or less, 13.3 parts by weight or less, or 13 parts by weight or less. A nanosilica content of less than 4 parts by weight is not effective in improving voltage endurance characteristics, and a content of more than 30 parts by weight is undesirable because it may cause deterioration in physical properties.

[0031] Polyamic Acid In the present invention, the dianhydride monomer may be pyromellitic dianhydride (PMDA), biphenyltetracarboxylic dianhydride (BPDA), benzophenonetetracarboxylic dianhydride (BTDA), oxydiphthalic dianhydride (ODPA), diphenylsulfone-3,4,3',4'-tetracarboxylic dianhydride (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'-benzophenonetetracarboxylic dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, p-phenylenebis(trimeric monoester acid anhydride), The compound may include one or more selected from the group consisting of p-biphenylene bis(trimeric monoester acid 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, and 4,4'-(2,2-hexafluoroisopropylidene)diphthalic dianhydride.

[0032] Specifically, the dianhydride monomer may include one or more selected from the group consisting of pyromellitic dianhydride (PMDA), biphenyltetracarboxylic dianhydride (BPDA), and benzophenonetetracarboxylic dianhydride (BTDA), and preferably includes pyromellitic dianhydride (PMDA).

[0033] In addition, the diamine monomer may be 1,4-diaminobenzene (PPD), 4,4'-diaminodiphenyl ether (ODA), 2,2-bisaminophenoxyphenylpropane (BAPP), metaphenylenediamine, 3,3'-dimethylbenzidine, 2,2'-dimethylbenzidine, 2,4-diaminotoluene, 2,6-diaminotoluene, 3,5-diaminobenzoic acid (DABA), 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane (MDA), 3,3'-dimethyl-4,4'-diaminobiphenyl, 2,2'-dimethyl 4,4'-diaminobiphenyl (m-tolidine), 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'-dimethoxybenzidine, 2,2'-dimethoxybenzidine, 3,3'-diaminodiphenyl ether, 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, 2,2-bis(3-aminodiphenyl) 2,2-bis(4-aminophenyl)propane, 2,2-bis(3-aminophenyl)-1,1,1,3,3,3-hexafluoropropane, 2,2-bis(4-aminophenyl)-1,1,1,3,3,3-hexafluoropropane, 3,3'-diaminodiphenyl sulfoxide, 3,4'-diaminodiphenyl sulfoxide, 4,4'-diaminodiphenyl sulfoxide, 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 (TPE-Q), 1,3-bis(3-aminophenoxy)-4-trifluoromethylbenzene, 3,3'-diamino-4-(4-phenylphenoxy)benzophenone, 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) bis(4-aminophenylsulfone)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, 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-amino phenoxy)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-aminophen 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[3-( The fluorocarbon polymer may include one or more selected from the group consisting of 2,2-bis[3-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, 2,2-bis[3-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, 2,2-bis[4-(3-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, and 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane.

[0034] Specifically, the diamine monomer may include at least one selected from the group consisting of 1,4-diaminobenzene (PPD), 4,4'-diaminodiphenyl ether (ODA), 2,2-bisaminophenoxyphenylpropane (BAPP), and 1,3-bis(4-aminophenoxy)benzene (TPE-R), and preferably includes 4,4'-diaminodiphenyl ether (ODA).

[0035] The polyamic acid can contain polymerized units of pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA).

[0036] In the present invention, pyromellitic dianhydride (PMDA) may be contained in a ratio of 50 mol% or more of the total dianhydride monomers, specifically, 60 mol% or more, 70 mol% or more, 75 mol% or more, 80 mol% or more, 85 mol% or more, 90 mol% or more, 95 mol% or more, 99 mol% or more, or 100 mol% or more.

[0037] In addition, 4,4'-diaminodiphenyl ether (ODA) may be contained in a ratio of 50 mol% or more of the total diamine monomers, specifically, 60 mol% or more, 70 mol% or more, 75 mol% or more, 80 mol% or more, 85 mol% or more, 90 mol% or more, 95 mol% or more, 99 mol% or more, or 100 mol% or more.

[0038] In the polyamic acid of the present invention, the dianhydride monomer may be 95 to 105 mol% relative to 100 mol% of the diamine monomer. For example, the lower limit may be 96 mol% or more, 97 mol% or more, 98 mol% or more, 99 mol% or more, or 99.5 mol% or more, and the upper limit may be 104 mol% or less, 103 mol% or less, 102 mol% or less, 101 mol% or less, or 100.5 mol% or less.

[0039] The molar ratio of the dianhydride monomer to the diamine monomer may be 6:4 to 4:6, preferably 5.5:4.5 to 4.5:6.5, and more preferably 5:5.

[0040] The polyimide varnish may have a polyimide solids content of 10 to 50 wt%. The lower limit of the polyimide solids content may be, for example, 13 wt% or more, 15 wt% or more, 18 wt% or more, 20 wt% or more, or 25 wt% or more, and the upper limit may be, for example, 48 wt% or less, 45 wt% or less, 43 wt% or less, 40 wt% or less, 38 wt% or less, 35 wt% or less, 33 wt% or less, or 30 wt% or less. By adjusting the polyimide solids content of the polyimide varnish, it is possible to control the increase in viscosity and shorten the process time during the curing process.

[0041] organic solvents In the present invention, the polyimide varnish further includes an organic solvent. The organic solvent is not particularly limited as long as it is an organic solvent in which polyamic acid can be dissolved. For example, the organic solvent may be an aprotic polar solvent.

[0042] Specifically, the organic solvent may include one or more selected from the group consisting of N-methylpyrrolidone (NMP), N,N'-dimethylformamide (DMF), N,N'-diethylformamide (DEF), N,N'-dimethylacetamide (DMAc), dimethylpropanamide (DMPA), N,N-diethylacetamide (DEAc), dimethyl sulfoxide (DMSO), 3-methoxy-N,N-dimethylpropanamide (KJCMPA), p-chlorophenol, o-chlorophenol, γ-butyrolactone (GBL), diglyme, and naphthalene. Preferably, N-methylpyrrolidone (NMP), N,N'-dimethylformamide (DMF), N,N'-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), or the like can be used.

[0043] The organic solvent may further include a modifier containing a hydroxyl group (OH) or an amine group (NH). Examples of modifiers containing a hydroxyl group (OH) or an amine group (NH) include ethylamine, triethanolamine, dimethylamine, trimethylamine, diethylenetriamine, ethylenediamine, tributylamine, pyridine, pyrrolidine, methanol, ethanol, propanol, isopropanol, sec-butanol, tert-butanol, n-amyl alcohol, isoamyl alcohol, hexanol, octanol, capryl alcohol, nonyl alcohol, decyl alcohol, undecyl alcohol, lauryl alcohol, myristyl alcohol, cetyl alcohol, stearyl alcohol, allyl alcohol, crotyl alcohol, propargyl alcohol, ethylene glycol, propylene glycol, benzyl alcohol, and phenol. The modifier may react with the dianhydride monomer to control the reactivity.

[0044] Polyimide varnish and its cured product The polyimide varnish is heated at 30°C for 1 s -1 The viscosity measured under conditions of a shear rate of 1 / s may be in the range of 500 cP to 20,000 cP. For example, the upper limit may be 20,000 cP, 15,000 cP, or 10,000 cP or less. The lower limit is not particularly limited, but may be 1,000 cP, 1,200 cP, 1,500 cP, or 1,800 cP or more. In one embodiment, the viscosity may be measured using a Rheostress 600 manufactured by Haake, under conditions of a shear rate of 1 / s, a temperature of 30°C, and a plate gap of 1 mm. By adjusting the viscosity range, the present invention can provide a polyimide varnish with excellent processability.

[0045] The polyimide varnish may have a haze of 1.5% or less. For example, the upper limit of the haze may be 1.4% or less, 1.3% or less, 1.2% or less, 1.1% or less, 1% or less, 0.9% or less, or 0.8% or less, and the lower limit may be, but is not limited to, greater than 0%, 0.05% or more, or 0.1% or more. In one embodiment, the haze was measured in accordance with ASTM E308 using equipment manufactured by HunterLab.

[0046] The polyimide obtained by curing the polyimide varnish may have a haze of 1.5% or less. For example, the upper limit of the haze may be 1.4%, 1.3%, 1.2%, 1.1%, 1%, 0.9%, 0.8%, 0.7%, 0.6%, or 0.5%, and the lower limit may be, but is not limited to, greater than 0%, 0.05%, or 0.1%. In one embodiment, the haze is measured in accordance with ASTM E308 using equipment manufactured by HunterLab, and the thickness of the polyimide is 20±1.0 μm.

[0047] Furthermore, the polyimide varnish and its cured product of the present invention use nanosilica having a predetermined absolute value range of zeta, which prevents aggregation of the nanosilica in the polyimide varnish and provides excellent dispersibility, thereby achieving a low level of haze.

[0048] The polyimide obtained by curing the polyimide varnish may have an elongation of 25% or more, and the lower limit of the elongation may be, for example, 30%, 33%, 35%, 36%, 37%, 38%, or 39% or more. The upper limit is not particularly limited, but may be 80% or less. In one embodiment, the elongation can be measured in accordance with ASTM D-882 using an Instron 5564 UTM instrument manufactured by Instron Corporation after curing the polyimide varnish into a polyimide film and cutting it into a 10 mm wide x 40 mm long piece.

[0049] The polyimide obtained by curing the polyimide varnish may have a tensile strength of 100 MPa or more, and the lower limit of the tensile strength may be, for example, 105 MPa, 110 MPa, 115 MPa, 120 MPa, 124 MPa, or 128 MPa or more. The upper limit is not particularly limited, but may be 400 MPa or less. The tensile strength was measured using an Instron 5564 UTM instrument manufactured by Instron Corporation on samples measuring 500 mm in length and 10 mm in width at a speed of 50 mm / min, and the average of 10 samples was calculated.

[0050] In another aspect of the present invention, there is provided a cured polyimide product obtained by curing the polyimide varnish, and the cured polyimide product may be a polyimide film.

[0051] The polyimide cured product may have a voltage endurance characteristic, which is the time an insulating material can withstand a predetermined voltage according to IEC-60851-5, of 300 minutes or more. The lower limit of the voltage endurance characteristic may be, for example, 330 minutes or more, 370 minutes or more, 400 minutes or more, 450 minutes or more, 500 minutes or more, 550 minutes or more, 600 minutes or more, 650 minutes or more, 700 minutes or more, 720 minutes or more, 750 minutes or more, 770 minutes or more, 800 minutes or more, 820 minutes or more, or 830 minutes or more. The upper limit is not particularly limited, but may be 3,000 minutes or less. The voltage endurance characteristic was measured by connecting a polyimide-coated product to a jig, applying an AC voltage of 1.5 kV (frequency 60 Hz), and measuring the time until a leakage current of 5 mA or more was detected. The polyimide may have a thickness of 26±1.0 μm.

[0052] Furthermore, the polyimide varnish of the present invention and its cured product were able to improve voltage endurance characteristics by using nanosilica having a predetermined absolute value range of zeta.

[0053] The polyimide cured product may have a breakdown voltage (BDV) of 200 kV / mm or more, as measured in accordance with the ASTM D149 standard. The lower limit of the breakdown voltage may be, for example, 205 kV / mm or more, 210 kV / mm or more, 215 kV / mm or more, 220 kV / mm or more, 225 kV / mm or more, 230 kV / mm or more, 233 kV / mm or more, 235 kV / mm or more, 238 kV / mm or more, 240 kV / mm or more, 241 kV / mm or more, or 242 kV / mm or more. The upper limit is not particularly limited, but may be 500 kV / mm or less.

[0054] In another aspect of the present invention, there is provided a polyimide prepared by imidizing the polyimide varnish, and the polyimide may be in the form of a film.

[0055] In another aspect of the present invention, there is provided a polyimide coated article comprising the above-described cured polyimide.

[0056] In one embodiment, the method for producing the polyimide coating may include the steps of coating a surface of a conductor with a polyimide varnish and imidizing the polyimide varnish coated on the surface of the conductor.

[0057] The conductor can be a copper wire made of copper or a copper alloy, but can also be a conductor made of other metal materials such as silver wire, or various metal-plated wires such as aluminum or tin-plated wire. The thickness of the conductor and coating can conform to the KS C3107 standard. The diameter of the conductor can be within the range of 0.3 to 3.2 mm, and the standard coating thickness of the coating (average value of the maximum and minimum coating thicknesses) can 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 can include, but is not limited to, a circular wire, a rectangular wire, a hexagonal wire, etc.

[0058] In another aspect of the present invention, there is provided an electric wire comprising the polyimide coating.

[0059] Specifically, the coated electric wire may include a polyimide coating produced by coating the surface of an electric wire with the polyimide varnish and imidizing the polyimide varnish. In one specific example, the coated electric wire may include an electric wire and a coating formed by coating the surface of the electric wire with the polyimide and imidizing the polyimide.

[0060] The present application also provides an electronic device including the coated electric wire, such as an electric motor.

[0061] In another aspect of the present invention, a part is provided that includes a molded body formed from a polyimide varnish.

[0062] Specifically, the parts can be electronic circuit board parts, semiconductor devices, lithium ion battery parts, solar cell parts, fuel cell parts, motor windings, engine peripheral parts, paints, optical parts, heat dissipation materials, electromagnetic wave shielding materials, surge parts, dental materials, slide coatings, and electrostatic chucks. [Effects of the Invention]

[0063] The polyimide varnish of the present invention has excellent voltage durability characteristics and also has the effect of improving physical properties such as polyimide haze.

[0064] Furthermore, the present invention has an effect of being highly applicable to conductor coatings used in windings for electric vehicles (EVs). [Brief explanation of the drawings]

[0065] [Figure 1] 2 shows SEM images of film-type cured polyimide materials according to Example 2-1 and Comparative Example 2-1. DETAILED DESCRIPTION OF THE INVENTION

[0066] Examples are presented below to aid in understanding the present invention. The following examples are provided to facilitate understanding of the present invention, and are not intended to limit the scope of the present invention. [Example]

[0067] <Example> Production Example 1. Nanosilica 1 surface-treated with organic silane Nanosilica 1 (dimethylacetamide-dispersed silica sol, silica solids concentration 30 wt%, average silica particle size 10-30 nm, average zeta potential (absolute value) 17.86 mV) was prepared using an organosilane surface treatment. The zeta potential was measured twice using a Bettersize Benano 180 Zeta Pro instrument, with the refractive index, viscosity, and dielectric constant of dimethylacetamide entered into the instrument, and the arithmetic average was calculated.

[0068] Comparative Example 1: Nanosilica Nanosilica (silica sol dispersed in N-methylpyrrolidone, silica solids concentration 30 wt%, average silica particle size 10-20 nm, average zeta potential (absolute value) 8.42 mV) was prepared. The zeta potential was measured twice using a Benano 180 Zeta Pro instrument manufactured by Bettersize, with the refractive index, viscosity, and dielectric constant of N-methylpyrrolidone entered into the instrument, and the arithmetic average was calculated.

[0069] Comparative Example 2: Nanosilica 2 surface-treated with organic silane Nanosilica 2 (dimethylacetamide-dispersed silica sol, silica solids concentration 30 wt%, average silica particle size 10-20 nm, average zeta potential (absolute value) 4.59 mV) was prepared using an organosilane surface treatment. The zeta potential was measured twice using a Bettersize Benano 180 Zeta Pro instrument, with the refractive index, viscosity, and dielectric constant of dimethylacetamide entered into the instrument, and the arithmetic average was calculated.

[0070] Comparative Example 3: Nanosilica 3 surface-treated with organic silane Nanosilica 3 (dimethylacetamide-dispersed silica sol, silica solids concentration 30 wt%, average silica particle size 10-20 nm, average zeta potential (absolute value) 1.51 mV) was prepared using an organosilane surface treatment. The zeta potential was measured twice using a Bettersize Benano 180 Zeta Pro instrument, with the refractive index, viscosity, and dielectric constant of dimethylacetamide entered into the instrument, and the arithmetic average was calculated.

[0071] Example 1. Polyimide varnish Example 1-1 An organic solvent containing dimethylacetamide (DMAc) and a modifier (0-2 mol%) was placed in a reaction vessel purged with nitrogen gas, and nanosilica surface-treated with the organosilane from Preparation Example 1 (6 wt% based on the polyimide solids content) and pyromellitic dianhydride (PMDA) (92 mol%) as a dianhydride monomer were mixed and stirred at 40°C for 30 minutes. Next, 4,4'-diaminodiphenyl ether (ODA) (100 mol%) and pyromellitic dianhydride (PMDA) (8 mol%) as diamine monomers were added, and the mixture was stirred and polymerized at 40°C for about 1 hour to produce a polyimide varnish (polyimide solids content 25 wt%).

[0072] Example 1-2 A polyimide varnish was produced in the same manner as in Example 1, except that instead of using the nanosilica surface-treated with organosilane (6 wt % based on the polyimide solid content) in Example 1, nanosilica surface-treated with organosilane (12 wt % based on the polyimide solid content) was used.

[0073] Comparative Examples 1-1 to 1-3 Polyimide varnishes were prepared in the same manner as in Example 1-1, except that the components and content ratios of the dianhydride monomer, diamine monomer, and nanosilica surface-treated with organosilane were adjusted as shown in Table 1 below.

[0074] [Table 1]

[0075] Example 2. Cured polyimide (polyimide film) Example 2-1 The polyimide varnish prepared in Example 1-1 was rotated at a high speed of 2,000 rpm to remove air bubbles, and then the degassed polyimide varnish was applied to a glass substrate (230 mm × 230 mm, thickness: 0.55 mm) using a spin coater.

[0076] The mixture was then cured under a nitrogen atmosphere at 110°C (20 minutes), 150°C (20 minutes), 200°C (20 minutes), and 300°C (20 minutes) to obtain a polyimide film (thickness: 20±1.0 μm or 26±1.0 μm).

[0077] Example 2-2 A cured polyimide material was prepared in the same manner as in Example 2-1, except that the polyimide varnish of Example 1-2 was used instead of the polyimide varnish of Example 1-1.

[0078] Comparative Example 2-1 A cured polyimide material was prepared in the same manner as in Example 2-1, except that the polyimide varnish of Comparative Example 1-1 was used instead of the polyimide varnish of Example 1-1.

[0079] Comparative Example 2-2 A cured polyimide material was prepared in the same manner as in Example 2-1, except that the polyimide varnish of Comparative Example 1-2 was used instead of the polyimide varnish of Example 1-1.

[0080] Comparative Example 2-3 A cured polyimide material was prepared in the same manner as in Example 2-1, except that the polyimide varnish of Comparative Example 1-3 was used instead of the polyimide varnish of Example 1-1.

[0081] Example 3. Polyimide coating Example 3-1 The polyimide varnish according to Example 1-1 was applied to a rectangular copper wire 20 to 28 times in a coating and curing oven, followed by drying and curing, to prepare an electric wire having a polyimide coating with a coating thickness of 110±10 μm.

[0082] Example 3-2 A polyimide coating was produced in the same manner as in Example 3-1, except that the polyimide varnish of Example 1-2 was used instead of the polyimide varnish of Example 1-1.

[0083] <Experimental Example> Experimental Example 1. SEM analysis The polyimide film-type cured products obtained in Example 2-1 and Comparative Example 2-1 were analyzed using a scanning electron microscope, VEGA3 manufactured by Tescan, and the SEM images are shown in FIG.

[0084] As shown in Figure 1, in Comparative Example 2-1, particles of 200 nm were observed, which were particles of aggregated nanosilica. On the other hand, in Example 2-1, it was observed that the nanosilica was uniformly dispersed without aggregation. Therefore, it was found that the degree of dispersion and aggregation of nanosilica differs depending on the absolute value of the zeta potential.

[0085] Experimental example 2: Physical property evaluation The polyimide varnishes prepared in Examples 1-1 and 1-2 and Comparative Examples 1-1 and 1-2 were cured to obtain cured products of Examples 2-1 and 2-2 and Comparative Examples 2-1 and 2-2, and the physical properties thereof were determined by the following methods. The results are shown in Tables 2 and 3 below.

[0086] (1) Voltage endurance characteristics The polyimide films (thickness 26±1.0 μm) of Examples 2-1 and 2-2 and Comparative Example 2-1 were connected to a jig, and a voltage of 1.5 kV AC (frequency 60 Hz) was applied to measure the time until a leak current of 5 mA or more was detected, thereby measuring the voltage endurance characteristics in accordance with IEC-60851-5. The results are shown in Table 2 below.

[0087] (2) Haze The haze of the polyimide varnishes (Examples 1-1 and 1-2, Comparative Examples 1-1 to 1-3) was measured in accordance with ASTM E308 using equipment manufactured by HunterLab, and the results are shown in Table 3 below.

[0088] [Table 2]

[0089] [Table 3]

[0090] As shown in Table 2, by using nanosilica having a zeta potential within a predetermined range, it was confirmed that the voltage endurance characteristics of the polyimide varnish of the present invention and its cured film form were significantly improved by about three times or more compared to Comparative Example 2-1.

[0091] Furthermore, Table 3 shows that both the polyimide varnish of the present invention and its film-form cured product achieved low levels of haze. Specifically, in the case of varnish, Examples 1-1 and 1-2 had a haze of 0.6%, which is about 4 to 10 times lower than Comparative Examples 1-1 to 1-3, indicating that the nanosilica was uniformly dispersed without agglomeration. Comparative Examples 1-1 to 1-3 showed increased haze due to aggregation of substances in the varnish, which could result in deterioration of mechanical properties and quality.

[0092] This specification omits detailed descriptions of content that can be fully understood and inferred by a person having ordinary skill in the art of the present invention, and various modifications are possible within the scope of the specific examples described in this specification without changing the technical idea or essential configuration of the present invention. Therefore, the present invention may be implemented in ways different from those specifically explained and exemplified in this specification, and this is something that can be understood by a person having ordinary skill in the art of the present invention.

Claims

1. a polyamic acid containing a dianhydride monomer and a diamine monomer as polymerization units; nanosilica dispersed in dimethylacetamide (DMAc), The pH of the nanosilica dispersed in DMAc is 2 to 12; The nanosilica dispersed in DMAc has an absolute value of zeta potential of 10.0 mV to 40.0 mV, The zeta potential of the nanosilica dispersed in DMAc was measured using a Bettersize Benano 180 zeta pro instrument by inputting the refractive index, viscosity and dielectric constant of dimethylacetamide into the instrument; The polyimide varnish has a haze of 1.5% or less. Polyimide varnish.

2. 2. The polyimide varnish according to claim 1, wherein the nanosilica has an average particle size of 1 to 200 nm.

3. The polyimide varnish according to claim 1 , wherein the nanosilica is nanosilica surface-modified with an organosilane.

4. The organic silane of the nanosilica surface-modified with organic silane may be methyltrimethoxysilane, hexamethyldisiloxane, n-octyltrimethoxysilane, n-octyltriethoxysilane, isooctyltrimethoxysilane, dodecyltrimethoxysilane, octadecyltrimethoxysilane, propyltrimethoxysilane, hexyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-(methacryloxy)propyltriethoxysilane, 3-(methacryloxy)propylmethyldimethoxysilane, 3-(acryloxypropyl)methyldimethoxysilane, 3-(methacryloxy)propyl Pyldimethylethoxysilane, styrylethyltrimethoxysilane, phenyltriethoxysilane, p-tolyltriethoxysilane, vinylmethyldiacetoxysilane, vinyldimethylethoxysilane, vinylmethyldiethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriacetoxysilane, vinyltriisopropoxysilane, vinyltriphenoxysilane, vinyltri-t-butoxysilane, vinyltris(isobutoxy)silane, vinyltriisoprofenoxysilane, vinyltris(2-methoxyethoxy)silane, diisopropylethylamine, phenyltrimethoxysilane (N,N-Diisopropylethylamine 4. The polyimide varnish according to claim 3, comprising one or more selected from the group consisting of phenyltrimethoxysilane (N-phenyl-3-aminopropyltrimethoxysilane), glycidoxypropyltrimethoxysilane (GPTMS), aminopropyltrimethoxysilane ((3-aminopropyl)trimethoxysilane: APTMS), phenyltrimethoxysilane (Phenyltrimethoxysilane: PTMS), and phenylaminopropyltrimethoxysilane (N-Phenyl-3-aminopropyltrimethoxysilane: PAPTES).

5. The dianhydride monomer is selected from the group consisting of pyromellitic dianhydride (PMDA), biphenyltetracarboxylic dianhydride (BPDA), benzophenonetetracarboxylic dianhydride (BTDA), oxydiphthalic dianhydride (ODPA), diphenylsulfone-3,4,3',4'-tetracarboxylic dianhydride (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'-benzophenonetetracarboxylic dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, p-phenylenebis(trimeric monoester acid anhydride), p-bi ... (trimeric monoester acid 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 2. The polyimide varnish according to claim 1, comprising one or more selected from the group consisting of 2,3,6,7-naphthalenetetracarboxylic acid dianhydride, 1,4,5,8-naphthalenetetracarboxylic acid dianhydride, 4,4'-(2,2-hexafluoroisopropylidene)diphthalic acid dianhydride, 2,2-bis[(3,4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA), 2,3,6,7-naphthalenetetracarboxylic acid dianhydride, 1,4,5,8-naphthalenetetracarboxylic acid dianhydride, and 4,4'-(2,2-hexafluoroisopropylidene)diphthalic acid dianhydride.

6. The diamine monomer is 1,4-diaminobenzene (PPD), 4,4'-diaminodiphenyl ether (ODA), 2,2-bisaminophenoxyphenylpropane (BAPP), metaphenylenediamine, 3,3'-dimethylbenzidine, 2,2'-dimethylbenzidine, 2,4-diaminotoluene, 2,6-diaminotoluene, 3,5-diaminobenzoic acid (DABA), 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane (MDA), 3,3'-dimethyl-4,4'-diaminobiphenyl, 2,2'-dimethyl-4 ,4'-diaminobiphenyl (m-tolidine), 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'-dimethoxybenzidine, 2,2'-dimethoxybenzidine, 3,3'-diaminodiphenyl ether, 3,3'-diamin aminodiphenyl 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, 2,2-bis(3-amino phenyl)propane, 2,2-bis(4-aminophenyl)propane, 2,2-bis(3-aminophenyl)-1,1,1,3,3,3-hexafluoropropane, 2,2-bis(4-aminophenyl)-1,1,1,3,3,3-hexafluoropropane, 3,3'-diaminodiphenyl sulfoxide, 3,4'-diaminodiphenyl sulfoxide, 4,4'-diaminodiphenyl sulfoxide, 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 (TPE-Q), 1,3-bis(3-aminophenoxy)-4-trifluoromethylbenzene, 3,3'-diamino-4-(4-phenylphenoxy)benzophenone, 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) bis(4-aminophenylsulfone)benzene, 1,3-bis(3-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, 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-aminophen hydroxy)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] 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[3-(3-aminophenoxy)phenyl] The polyimide varnish according to claim 1, comprising one or more members selected from the group consisting of 2,2-bis[3-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, 2,2-bis[4-(3-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, 2,2-bis[4-(3-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, and 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane.

7. 2. The polyimide varnish according to claim 1, wherein the polyamic acid contains polymerized units of pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA).

8. The polyimide varnish further contains an organic solvent, 2. The polyimide varnish according to claim 1, wherein the organic solvent comprises one or more selected from the group consisting of N-methyl-pyrrolidone (NMP), N,N'-dimethylformamide (DMF), N,N'-diethylformamide (DEF), N,N'-dimethylacetamide (DMAc), dimethylpropanamide (DMPA), N,N-diethylacetamide (DEAc), dimethyl sulfoxide (DMSO), 3-methoxy-N,N-dimethylpropanamide (KJCMPA), p-chlorophenol, o-chlorophenol, γ-butyrolactone (GBL), diglyme, and naphthalene.

9. 2. The polyimide varnish according to claim 1, wherein the polyimide varnish has a polyimide solids content of 10 to 50% by weight.

10. 10. The polyimide varnish according to claim 9, wherein the nanosilica is contained in an amount of 4 to 30 parts by weight based on 100 parts by weight of the polyimide solid content contained in the entire polyimide varnish.

11. The polyimide varnish is heated at 30°C and 1s －１ 2. The polyimide varnish according to claim 1, wherein the viscosity measured under a shear rate condition is 500 cP to 20,000 cP.

12. A cured polyimide product obtained by curing the polyimide varnish according to any one of claims 1 to 11.

13. 13. The polyimide cured material according to claim 12, wherein the voltage endurance characteristic of the polyimide cured material, which is the time that an insulating material can withstand a predetermined voltage in accordance with IEC-60851-5, is 300 minutes or more.

14. A polyimide coating comprising the polyimide cured product according to claim 12.

15. An electric wire comprising the polyimide coating of claim 14.

Images