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

Abstract

To provide a polyimide varnish with excellent voltage endurance characteristics, and a polyimide coating material prepared therefrom.SOLUTION: Provided is a polyimide varnish comprising polyamic acid and nanosilica, where the content of the nanosilica is 5-23 wt.% based on the solid content of the polyamic acid, and where the nanosilica has a moisture content of less than 0.5 wt.%.SELECTED DRAWING: None

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] Generally, polyimide (PI) resin is a highly heat-resistant resin 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, infusible, and ultra-high heat-resistant resins with excellent properties, including thermal oxidation resistance, heat resistance, radiation resistance, low-temperature resistance, and chemical resistance. They are used in a wide range of applications, including advanced heat-resistant materials for automobiles, aviation, and space radiation, as well as in electronic materials such as insulating coatings, insulating films, semiconductors, and TFT-LCD electrode protective 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, in electrical equipment requiring high voltages, such as high-voltage motors, some insulating layers or coatings are used. 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, leading to early dielectric breakdown and shortening 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 that is excellent in physical properties such as voltage endurance characteristics and haze by including nanosilica having a moisture content within a predetermined range.

[0007] The present invention also provides a cured polyimide product obtained by curing the polyimide varnish.

[0008] The present invention also provides a polyimide coated article comprising 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 not to preclude the presence or additional possibility of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0011] Whenever an amount, concentration, or other value or parameter is given herein by a list of ranges, preferred ranges, or upper preferred values ​​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] Where a range of numerical values ​​is recited herein, unless otherwise stated, it is intended that the endpoints of the range and the scope of the invention within that range are 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 in turn can 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 in turn can 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 realizing 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.

[0017] In one aspect of the present invention, there is provided a polyimide varnish comprising polyamic acid and nanosilica, wherein the nanosilica comprises 5 to 23% by weight based on the solid content of the polyamic acid, and the nanosilica has a water content of less than 0.5% by weight.

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

[0019] The nanosilica may be present in an amount of 5 to 23 wt % based on the solid content of the polyamic acid. For example, the lower limit of the nanosilica content may be 5.5 wt %, 6.0 wt %, 6.5 wt %, 7.0 wt %, 8.0 wt %, 9.0 wt %, 10.0 wt %, or 11.0 wt % or more. The upper limit of the nanosilica content may be 22.0 wt %, 21.5 wt %, 21.0 wt %, 20.5 wt %, 20.0 wt %, 19.0 wt %, 18.5 wt %, 18.0 wt %, 17.0 wt %, 16.0 wt %, 15.0 wt %, 14.0 wt %, 13.5 wt %, or 13.0 wt % or less. A nanosilica content of less than 5 wt % is not effective in improving voltage endurance characteristics, while a nanosilica content of more than 23 wt % is undesirable because it may cause deterioration in physical properties. Here, the solid content of the polyamic acid is the total amount of the dianhydride monomer and the diamine monomer used in the polymerization reaction.

[0020] The nanosilica may have a water content of less than 0.5 wt%. For example, the upper limit of the water content of the nanosilica may be 0.49 wt%, 0.48 wt%, 0.47 wt%, 0.46 wt%, 0.45 wt%, 0.44 wt%, 0.43 wt%, or 0.42 wt%. The lower limit of the water content of the nanosilica is not particularly limited, but may be greater than 0 wt%, 0.01 wt%, 0.05 wt%, 0.10 wt%, or 0.15 wt%. A water content of 0.5 wt% or greater is undesirable because it may affect the molecular weight formation of the polymer and result in a deterioration in physical properties. The nanosilica may be a dispersion in an organic solvent, and the water content refers to the water content of the dispersion in which the nanosilica is dispersed.

[0021] The water content of the nanosilica can be measured by the Karl Fischer method, which quantitatively measures the water content in a KS M 0034 sample by reacting it with iodine and sulfur dioxide.

[0022] 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, and zeta potential.

[0023] The nanosilica may be nanosilica whose surface has been modified with an organic silane.

[0024] 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, vinyltriisopropenoxysilane, 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

[0025] 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)).

[0026] The nanosilica surface-modified with an organosilane can be produced by subjecting nanosilica to a surface treatment with an organosilane. For example, nanosilica can be obtained by heating the organosilane under acidic or basic conditions and subjecting the surface to a surface treatment for approximately 1 to 24 hours. Alternatively, surface modification can be achieved by other known methods, such as 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 obtain surface-modified nanosilica. To bond two or more compounds to the surface of nanosilica, the above methods can be used, respectively.

[0027] 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), improving dispersibility and miscibility.

[0028] Polyamic Acid In the present invention, the polyamic acid may contain a dianhydride monomer and a diamine monomer as polymerization units.

[0029] The dianhydride monomers include 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-biphenyl The compound may include one or more selected from the group consisting of nylene 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.

[0030] 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).

[0031] 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), 3,3'-dimethyl-4,4'-diaminobiphenyl, 2,2'-dimethyl-4,4'-diaminobiphenyl (m-tolidine), 2,2'-bis(trifluoromethyl)-2,2 ... (trimethyl)-4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 3,3'-dicarboxy-4,4'-diaminodiphenylmethane, 3,3',5,5'-tetramethyl-4,4'-diaminodiphenylmethane, 4,4'-diaminobenzanilide, 3,3'-dimethoxybenzidine, 2,2'-dimethoxybenzidine, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-di Aminodiphenyl 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-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-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, 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.

[0032] 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).

[0033] The polyamic acid can contain pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) as polymerized units.

[0034] 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.

[0035] 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.

[0036] In the polyamic acid of the present invention, the dianhydride monomer may be present in an amount of 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. In one embodiment, the diamine monomer and the dianhydride monomer may be reacted in substantially equimolar amounts.

[0037] 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.

[0038] The solid content of the polyamic acid may be 10 to 50 wt%. The lower limit of the solid content may be, for example, 13 wt% or more, 15 wt% or more, 18 wt% or more, 20 wt% or more, 23 wt% or more, or 24 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, 30 wt% or less, or 27 wt% or less. Adjusting the solid content of the polyamic acid can control the increase in viscosity and shorten the process time during the curing process.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] Polyimide Varnish The polyimide varnish is heated at 30°C for 1 s -1 The viscosity measured under the conditions of a shear rate of 1 / s may be in the range of 500 to 20,000 cP. For example, the upper limit may be 20,000 cP, 15,000 cP, or 10,000 cP. 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 the 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.

[0043] 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 using equipment manufactured by HunterLab in accordance with ASTM E308.

[0044] Cured polyimide varnish and coatings 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 include a film-shaped cured polyimide product or a polyimide coating material.

[0045] The cured polyimide 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%, while 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, Inc., and the thickness of the cured polyimide is 20±1.0 μm.

[0046] 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, and the lower limit of the voltage endurance characteristic may be, for example, 400 minutes or more, 500 minutes or more, 550 minutes or more, 600 minutes or more, 650 minutes or more, 700 minutes or more, 750 minutes or more, 800 minutes or more, 850 minutes or more, 900 minutes or more, 950 minutes or more, 970 minutes or more, 980 minutes or more, 1000 minutes or more, 1100 minutes or more, 1200 minutes or more, 1300 minutes or more, 1400 minutes or more, 1500 minutes or more, or 2000 minutes or more. The upper limit is not particularly limited, but may be 4,000 minutes or less. The voltage durability was measured by connecting the polyimide-coated material 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. Here, the thickness of the cured polyimide material may be 26±1.0 μm.

[0047] Furthermore, the present invention can improve voltage endurance characteristics by including nanosilica having a moisture content within a predetermined range at a high content within a predetermined range.

[0048] In another aspect of the present invention, there is provided a polyimide coated article comprising the above-described cured polyimide.

[0049] 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.

[0050] The conductor may be a copper wire made of copper or a copper alloy, but may also be a conductor made of other metal materials such as silver tin, or various metal-plated wires such as aluminum or tin-plated wire. The thickness of the conductor and coating may conform to KS C 3107. The diameter of the conductor may 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) 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, but is not limited to, a circular wire, a rectangular wire, a hexagonal wire, or the like.

[0051] In another aspect of the present invention, there is provided an electric wire comprising the polyimide coating.

[0052] 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.

[0053] The present invention also provides an electronic device including the coated electric wire, such as an electric motor.

[0054] In another aspect of the present invention, a part is provided that includes a molded body formed from a polyimide varnish.

[0055] 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]

[0056] The polyimide varnish of the present invention contains nanosilica having a moisture content within a predetermined range, and thus has the effect of exhibiting excellent voltage endurance characteristics and excellent physical properties such as haze.

[0057] Furthermore, the present invention has an effect of being highly applicable to conductor coatings used in windings for electric vehicles (EVs). DETAILED DESCRIPTION OF THE INVENTION

[0058] 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.

[0059] <Example> Manufacturing Example 1. Nanosilica surface-treated with organic silane Nanosilica 1 (dimethylacetamide-dispersed silica sol, silica solids concentration 30 wt%, average silica particle size 10-30 nm, water content 0.4 wt%) was prepared and surface-treated with organosilane. The water content is measured by the Karl Fischer method, which quantitatively measures the water content in a KS M 0034 sample by reacting with iodine and sulfur dioxide.

[0060] Comparative Example 1: Nanosilica Nanosilica (silica sol dispersed in N-methylpyrrolidone, silica solids concentration 30 wt%, average silica particle size 10-20 nm, water content 0.8 wt%) was prepared. The water content is expressed as a weight percent relative to the total mass of the nanosilica dispersion. The water content of the nanosilica was measured by the Karl Fischer method. Specifically, the water content was measured by quantitatively reacting the water in the KS M 0034 sample with iodine and sulfur dioxide.

[0061] Example 1. Polyimide varnish Example 1-1 An organic solvent containing dimethylacetamide (DMAc) and a modifier (0-2 mol%) was added to a reaction vessel purged with nitrogen gas. The organosilane-surface-treated nanosilica (6 wt% based on the polyimide solids content) from Preparation Example 1 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%) were added as diamine monomers, and the mixture was stirred and polymerized at 40°C for approximately 1 hour to produce a polyimide varnish (polyimide solids content 25 wt%).

[0062] Examples 1-2 to 1-7 As shown in Table 1 below, polyimide varnishes were prepared in the same manner as in Example 1-1, except that different amounts of nanosilica surface-treated with organosilane according to Preparation Example 1 were used.

[0063] Comparative Examples 1-1 to 1-2 Polyimide varnishes were prepared in the same manner as in Example 1-1, except that instead of using the nanosilica surface-treated with organosilane according to Preparation Example 1, the nanosilica according to Preparation Comparative Example 1 was used at different contents as shown in Table 1 below.

[0064] Comparative Examples 1-3 to 1-4 As shown in Table 1 below, polyimide varnishes were prepared in the same manner as in Example 1-1, except that different amounts of nanosilica surface-treated with organosilane according to Preparation Example 1 were used.

[0065] Table 1 below shows the composition, solid content, and type and content of nanosilica of the polyamic acids of Examples 1-1 to 1-7 and Comparative Examples 1-1 to 1-4.

[0066] [Table 1]

[0067] 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.

[0068] 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).

[0069] Examples 2-2 to 2-7 Cured polyimide materials were prepared in the same manner as in Example 2-1, except that the polyimide varnishes of Examples 1-2 to 1-7 were used instead of the polyimide varnish of Example 1-1.

[0070] Comparative Examples 2-1 to 2-4 Cured polyimide materials were prepared in the same manner as in Example 2-1, except that the polyimide varnishes of Comparative Examples 1-1 to 1-4 were used instead of the polyimide varnish of Example 1-1.

[0071] Example 3. Polyimide coating Example 3-1 In a coating and curing oven, the polyimide varnish according to Example 1-1 was applied to a rectangular copper wire 20 to 28 times, followed by drying and curing, to produce an electric wire having a polyimide coating with a coating thickness of 110±10 μm.

[0072] Examples 3-2 to 3-7 Electric wires including polyimide coatings were manufactured in the same manner as in Example 3-1, except that the polyimide varnishes of Examples 1-2 to 1-7 were used instead of the polyimide varnish of Example 1-1.

[0073] <Experimental Example> Experimental Example 1: Evaluation of polyimide properties (1) Voltage endurance characteristics The polyimide film-form cured products (thickness: 26±1.0 μm) of the Examples and Comparative Examples 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.

[0074] (2) Haze The haze of the polyimide varnishes or film-type polyimide cured products (thickness: 20±1.0 μm) of the Examples and Comparative Examples was measured in accordance with ASTM E308 using equipment manufactured by HunterLab, and the results are shown in Table 2 or Table 3 below.

[0075] [Table 2]

[0076] [Table 3]

[0077] Table 3 shows that the polyimide films of the present invention, which use nanosilica with a water content of less than 0.5 wt%, have significantly better voltage endurance characteristics than those of Comparative Examples 2-1 and 2-2. Furthermore, Examples 2-1 to 2-7, which contain 6 to 20 wt% nanosilica relative to the polyimide solid content, exhibit significantly improved voltage endurance characteristics. However, Comparative Example 2-3, which falls outside the above content range, exhibits a very low voltage endurance characteristic of less than 300 minutes, and Comparative Example 2-4 was not formed into a film and therefore could not be measured.

[0078] Furthermore, as shown in Tables 3 and 4, the polyimide varnish of the present invention and its cured film form both achieved low levels of haze. Specifically, the haze was confirmed to be 0.7% or less for the varnishes of Examples 1-1 to 1-7, and 0.8% or less for the films of Examples 2-1 to 2-7. This means that the nanosilica was not aggregated and was uniformly dispersed.

[0079] Therefore, the present invention provides a polyimide varnish having excellent physical properties such as haze by containing nanosilica having a moisture content within a predetermined range at a high content within a predetermined range, and by using the polyimide varnish, it is possible to provide a polyimide cured product that achieves excellent voltage endurance characteristics and also has excellent physical properties such as haze.

[0080] This specification omits detailed descriptions of content that can be fully recognized 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 herein 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 polyimide varnish comprising a polyamic acid and a nanosilica dispersion, wherein the nanosilica dispersion contains nanosilica and an organic solvent, the nanosilica is contained in an amount of 5 to 23% by weight based on the solid content of the polyamic acid; The nanosilica dispersion has a water content of less than 0.45% by weight, The polyimide varnish has a haze of 1.5% or less, The haze is measured according to the ASTM E308 standard; The polyamic acid contains a dianhydride monomer and a diamine monomer as polymerization units, The dianhydride monomer includes at least one selected from the group consisting of pyromellitic dianhydride (PMDA), biphenyltetracarboxylic dianhydride (BPDA), and benzophenonetetracarboxylic dianhydride (BTDA), The diamine monomer comprises 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).

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

3. 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 Phenyldimethylethoxysilane, styrylethyltrimethoxysilane, phenyltriethoxysilane, p-tolyltriethoxysilane, vinylmethyldiacetoxysilane, vinyldimethylethoxysilane, vinylmethyldiethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriacetoxysilane, vinyltriisopropoxysilane, vinyltriphenoxysilane, vinyltri-t-butoxysilane, vinyltris(isobutoxy)silane, vinyltriisopropenoxysilane, vinyltris(2-methoxyethoxy)silane, diisopropylethylamine, phenyltrimethoxysilane (N,N-Diisopropylethylamine 3. The polyimide varnish according to claim 2, 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).

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

5. 2. The polyimide varnish according to claim 1, wherein the solid content of the polyamic acid is 10 to 50% by weight.

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

7. 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, p-chlorophenol, o-chlorophenol, γ-butyrolactone (GBL), diglyme, and naphthalene.

8. A cured polyimide product obtained by curing the polyimide varnish according to any one of claims 1 and 5 to 7.

9. The polyimide cured product has a haze of 1.5% or less, 9. The cured polyimide according to claim 8, wherein the haze is measured in accordance with ASTM E308 standard using the cured polyimide having a thickness of 20±1.0 μm.

10. The polyimide cured material has a voltage endurance characteristic of 300 minutes or more, which is the time an insulating material can withstand a predetermined voltage in accordance with IEC-60851-5, 9. The cured polyimide material according to claim 8, wherein the voltage endurance characteristic is measured by connecting the polyimide-coated material to a jig, applying an AC voltage of 1.5 kV (at a frequency of 60 Hz), and measuring the time until a leakage current of 5 mA or more is detected.

11. A polyimide coating comprising the polyimide varnish according to any one of claims 1 and 5 to 7.

12. An electric wire comprising the polyimide coating of claim 11.

Images