Polyimide varnish for high-performance conductor coating and polyimide coating produced therefrom

Abstract

To provide polyimide varnish for a high-functional conductor coating, and a polyimide coating prepared therefrom.SOLUTION: Provided is polyimide varnish comprising: a polyamic acid solution comprising a diamine monomer and a dianhydride monomer as polymerized units; a first additive containing boron nitride; a second additive containing nanosilica; and a dispersant.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 and a polyimide coating produced therefrom that have improved voltage durability, adhesive strength, thermal conductivity, and a coefficient of friction after curing. [Background technology]

[0002] The insulating layer (insulating coating) that covers the conductor is required to have excellent insulation properties, adhesion to the conductor, heat resistance, mechanical strength, etc. Examples of resins that can be used for the insulating layer include polyimide resin, polyamide-imide resin, and polyester-imide resin. Of these, polyimide resin in particular is a material with excellent heat resistance and insulation properties, and has excellent properties that make it suitable for use as a coating material for conductors.

[0003] Polyimide resin is a highly heat-resistant resin produced by solution polymerization of an aromatic dianhydride with an aromatic diamine or aromatic diisocyanate to produce a polyamic acid derivative, followed by ring-closing dehydration at high temperature to imidize the polyimide resin. For example, an insulating coating can be formed using such a polyimide resin by coating a conductor wire with a polyimide varnish, which is a precursor of the polyimide resin, and then imidizing the polyimide varnish in a curing oven capable of heat treatment at a predetermined temperature.

[0004] The method of forming such an insulating coating can vary in the physical properties, productivity, and manufacturing costs of the resulting insulating coating depending on conditions such as the temperature of the curing oven, the number of coats of polyimide varnish, the coating speed, etc. That is, forming the insulating coating at a high temperature can be advantageous for producing an insulating coating with excellent physical properties, and the fewer the number of coats or the faster the coating speed, the more improved the productivity.

[0005] However, if the curing oven temperature is too high, defects may occur on the surface of the insulating coating or the polyimide resin may be carbonized, and if the number of coatings is too small or the coating speed is too fast, the physical properties of the polyimide coating may be reduced. Furthermore, despite their excellent physical properties, typical polyimide resins lack good adhesion to conductors, which may result in poor appearance when the insulating coating is formed.

[0006] As described above, there are various drawbacks to improving the properties required for polyimide varnishes and polyimide resins produced therefrom. In particular, improving one property generally results in a decrease in other properties. Therefore, simultaneously satisfying various properties is a challenge that continues to be researched in the related technical fields.

[0007] Therefore, there is a great need for a polyimide varnish for conductor coating that has excellent productivity and process efficiency as described above, simultaneously satisfies the heat resistance, insulating properties, and mechanical properties of polyimide, and has excellent adhesive strength to the conductor. Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a polyimide varnish which, after curing, has improved voltage durability, adhesive strength, thermal conductivity, and a coefficient of friction, and a polyimide coating produced therefrom.

[0009] Another object of the present invention is to provide a polyimide varnish for a highly functional conductor coating to be used for windings of electric vehicles (EVs), and a polyimide-coated article produced using the same. [Means for solving the problem]

[0010] 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.

[0011] 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.

[0012] 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.

[0013] When a range of numerical values ​​is recited herein, unless otherwise stated, the range includes its endpoints and any values ​​within the range. The scope of the invention is not intended to be limited to the specific values ​​recited when defining the range.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] The present invention relates to a polyimide varnish for high-performance conductor coating and a polyimide coating produced therefrom.

[0018] Polyimide Varnish The present invention provides a polyimide varnish comprising a polyamic acid solution containing a diamine monomer and a dianhydride monomer as polymerized units, a first additive containing boron nitride, a second additive containing nanosilica, and a dispersant.

[0019] Polyamic Acid Solution The diamine monomer is selected from the group consisting of 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) (ethyl)-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'-diamino diphenyl 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 phenyl)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-aminophenoxy)phenyl]ketone, bis[3-(3-aminophenoxy)phenyl]ketone 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- 2,2-bis[3-(3-aminophenoxy)phenyl]methane, bis[4-(4-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]-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, and preferably, one or more selected from the group consisting of 1,4-diaminobenzene (PPD) and 4,4'-diaminodiphenyl ether (ODA), more preferably, 1,4-diaminobenzene (PPD) and 4,It may contain 4'-diaminodiphenyl ether (ODA).

[0020] 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- ... (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-biphenylenebis(trimeric monoester acid anhydride) Terphenyl 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[( The dianhydride may include one or more selected from the group consisting of 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, and preferably includes pyromellitic dianhydride (PMDA).

[0021] 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.

[0022] In addition, 4,4'-diaminodiphenyl ether (ODA) may be contained in a ratio of 0 to 100 mol% of the total diamine monomers, specifically, 50 to 95 mol%, 60 to 90 mol%, 65 to 85 mol%, 70 to 80 mol%, or 73 to 77 mol%. When 4,4'-diaminodiphenyl ether (ODA) is contained in a ratio of 0 mol%, 1,4-diaminobenzene (PPD) may be contained in a ratio of 100 mol%.

[0023] In addition, 1,4-diaminobenzene (PPD) may be contained in a ratio of 0 to 100 mol% of the total diamine monomers, specifically, 5 to 45 mol%, 10 to 40 mol%, 15 to 35 mol%, 20 to 30 mol%, or 23 to 27 mol%. When 1,4-diaminobenzene (PPD) is contained in a ratio of 0 mol%, 4,4'-diaminodiphenyl ether (ODA) may be contained in a ratio of 100 mol%.

[0024] The polyamic acid solution may contain the diamine monomer in an amount of 90 to 110 mol %, preferably 95 to 105 mol %, more preferably 98 to 102 mol %, and even more preferably 99 to 101 mol %.

[0025] The polyamic acid solution may contain the dianhydride monomer in an amount of 90 to 110 mol %, preferably 95 to 105 mol %, more preferably 98 to 102 mol %, and even more preferably 100 mol %.

[0026] The polyamic acid solution may contain 95 to 105 mol% of the dianhydride monomer relative to 100 mol% of the diamine monomer. For example, the lower limit may be 95.5 mol% or more, 96 mol% or more, 96.5 mol% or more, 97 mol% or more, 97.5 mol% or more, 98 mol% or more, 98.5 mol% or more, 99 mol% or more, or 99.5 mol% or more, and the upper limit may be 105 mol% or less, 104 mol% or less, 103 mol% or less, 102 mol% or less, 101 mol% or less, or 100 mol% or less.

[0027] The polyamic acid solution may contain the dianhydride monomer and the diamine monomer in a molar ratio of 6:4 to 4:6.

[0028] The polyamic acid solution may further include an organic solvent.

[0029] The organic solvent may include one or more selected from the group consisting of N,N'-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), N,N'-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), diethylacetamide (DEAc), N-ethyl-2-pyrrolidone (NEP), N,N'-diethylformamide (DEF), dimethylpropanamide (DMPA), and γ-butyrolactone (GBL), and preferably, N,N'-dimethylacetamide (DMAc) can be used.

[0030] First Additive The polyimide varnish of the present invention may contain a first additive comprising boron nitride.

[0031] The first additive may be contained in an amount of 1 to 40% by weight, preferably 2.5 to 20% by weight, more preferably 3 to 15% by weight, and even more preferably 4 to 12% by weight, based on the solid content weight of the polyimide varnish.

[0032] If the content of the first additive exceeds 40 wt%, the mechanical properties of the resulting polyimide coating may be reduced and the amount of additive is too large to make it difficult to uniformly disperse, which is undesirable.On the other hand, if the content of the first additive is less than 1 wt%, the effect of improving heat dissipation properties is not exhibited, which is undesirable.

[0033] The particle size (D90) of the first additive may be 1 to 20 μm. For example, the lower limit may be 1.5 μm, 1.7 μm, 1.9 μm, 2.0 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, 3.0 μm, 3.1 μm, 3.2 μm, 3.3 μm, 3.4 μm, or 3.5 μm or more, and the upper limit may be 9.5 μm, 9.0 μm, 8.5 μm, 8.0 μm, 7.5 μm, 7.0 μm, 6.5 μm, 6.0 μm, 5.8 μm, 5.7 μm, or 5.5 μm or less.

[0034] The boron nitride may be one or more selected from the group consisting of cubic boron nitride (cBN), amorphous boron nitride (aBN), and hexagonal boron nitride (hBN), and is preferably hexagonal boron nitride (hBN).

[0035] Second Additive The polyimide varnish of the present invention may include a second additive comprising nanosilica.

[0036] The second additive may be included in an amount of 0.01 to 60 wt % based on the solid content of the polyimide varnish. For example, the lower limit of the content of the second additive may be 0.03 wt % or more, 0.05 wt % or more, 0.07 wt % or more, 0.1 wt % or more, 0.3 wt % or more, 0.4 wt % or more, or 0.5 wt % or more, and the upper limit may be 50 wt % or less, 30 wt % or less, 10 wt % or less, 7 wt % or less, 3 wt % or less, 1.5 wt % or less, 1.2 wt % or less, or 1 wt % or less.

[0037] If the content of the second additive exceeds 60 wt %, the mechanical properties of the resulting polyimide coating may be reduced, which is undesirable. If the content is less than 0.01 wt %, the voltage durability is not improved, which is undesirable.

[0038] The average particle size of the second additive may be 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.

[0039] Dispersants The polyimide varnish of the present invention may contain a dispersant to improve the dispersibility of the first additive.

[0040] The dispersant may comprise one or more selected from the group consisting of polyethylene dispersants, polyester dispersants, polycarboxylic acid ester dispersants, unsaturated polyamide dispersants, polycarboxylic acid dispersants, polycarboxylic acid alkyl salt dispersants, polyacrylic dispersants, polyethyleneimine dispersants, and polyurethane dispersants. The strong polarity of the polyurethane dispersant can improve the dispersing power of boron nitride.

[0041] The polyurethane-based dispersant may be a polyurethane polymer as a dispersant having an amine value and / or an acid value, or preferably a polymer containing a urethane bond in its structure as a high-dispersity dispersant having only an amine value.

[0042] The dispersant may have an acid value in the range of 10 to 200 mgKOH / g or an amine value in the range of 5 to 200 mgKOH / g, but is not limited thereto.

[0043] In one embodiment, the acid value of the dispersant may be about 20 mgKOH / g or more, 30 mgKOH / g or more, 40 mgKOH / g or more, 50 mgKOH / g or more, 60 mgKOH / g or more, 70 mgKOH / g or more, 80 mgKOH / g or more, or 90 mgKOH / g or more, or about 190 mgKOH / g or less, 180 mgKOH / g or less, 170 mgKOH / g or less, 160 mgKOH / g or less, 150 mgKOH / g or less, 140 mgKOH / g or less, 130 mgKOH / g or less, 120 mgKOH / g or less, 110 mgKOH / g or less, or 100 mgKOH / g or less. Here, the acid value refers to the value obtained by titrating the acid groups (—COOH) of the dispersant with KOH and dividing the result by the amount of KOH consumed (the value expressed in mg per gram of dispersant).

[0044] In one embodiment, the amine number of the dispersant may be about 10 mgKOH / g or more, about 15 mgKOH / g or more, about 20 mgKOH / g or more, 30 mgKOH / g or more, 40 mgKOH / g or more, 50 mgKOH / g or more, 60 mgKOH / g or more, 70 mgKOH / g or more, 80 mgKOH / g or more, or 90 mgKOH / g or more, or about 190 mgKOH / g or less, 180 mgKOH / g or less, 170 mgKOH / g or less, 160 mgKOH / g or less, 150 mgKOH / g or less, 140 mgKOH / g or less, 130 mgKOH / g or less, 120 mgKOH / g or less, 110 mgKOH / g or less, or 100 mgKOH / g or less. Here, the amine value refers to the value obtained by titrating the amino groups (-NH2, -NHR, or -NR2) contained in the dispersant with KOH and dividing the result by the amount of KOH consumed (the value expressed in mg of the amount of KOH titrated per 1 g of dispersant).

[0045] The dispersant may have a specific gravity of 0.5 to 1.5 g / ml at 20°C, and for example, the lower limit may be 0.6 g / ml, 0.7 g / ml, 0.8 g / ml, 0.9 g / ml, or 1.00 g / ml or more, and the upper limit may be 1.4 g / ml, 1.3 g / ml, 1.2 g / ml, 1.1 g / ml, 1.07 g / ml, or 1.05 g / ml or less.

[0046] The dispersant may be contained in an amount of 1 to 25% by weight, preferably 2.5 to 20% by weight, more preferably 3 to 15% by weight, even more preferably 3.3 to 10% by weight, and even more preferably 3.5 to 6.5% by weight, relative to the weight of the first additive.

[0047] If the content of the dispersant is less than 1% by weight, it is not preferable because it does not improve the dispersibility of the first additive, and if the content of the dispersant is more than 25% by weight, it is not preferable because it reduces the thermal stability.

[0048] Polyimide varnish and its cured product The polyimide varnish may further contain a silane coupling agent. The silane coupling agent may modify the surface of one or more of the first additive and the second additive. The surface modification by the silane coupling agent prevents aggregation of the additives in the polyimide varnish, and the functional groups of the silane coupling agent enhance interaction with the solid content (polyamic acid), thereby improving dispersibility and miscibility.

[0049] The silane coupling agent may include at least one selected from the group consisting of epoxy silanes, alkyloxy silanes, amino silanes, methacryloxy silanes, isocyanate silanes, and fluorine silanes, and preferably includes an epoxy silane.

[0050] The epoxy silane system may include one or more selected from the group consisting of (3-glycidoxypropyl)trimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, (3-glycidoxypropyl)methyldimethoxysilane, (3-glycidoxypropyl)methyldiethoxysilane, and (3-glycidoxypropyl)triethoxysilane. Preferably, the epoxy silane system may include (3-glycidoxypropyl)trimethoxysilane. More preferably, OFS-6040, a (3-glycidoxypropyl)trimethoxysilane product, may be used.

[0051] The content of the silane coupling agent in the polyimide varnish may be 0.01 to 1% by weight, preferably 0.1 to 0.9% by weight, more preferably 0.3 to 0.7% by weight, and even more preferably 0.4 to 0.6% by weight.

[0052] The solid content of the polyimide varnish may be 5 to 40 wt %, preferably 10 to 38 wt %, and more preferably 12 to 35 wt %. If the solid content of the polyimide varnish exceeds this range, the viscosity increases, which is undesirable as it is difficult to use it as a coating material thereafter. If the solid content is below this range, a large amount of solvent needs to be removed during the curing process, which can increase the manufacturing cost and process time, which is undesirable.

[0053] The polyimide varnish according to the present invention may be cured into a film, and the thickness of the cured product may be appropriately selected in consideration of the intended use, the environment in which it is used, its physical properties, and the like.

[0054] In one embodiment, the polyimide varnish according to the present invention may have a thickness after curing of 20 to 40 μm. For example, the lower limit may be 21 μm or more, 22 μm or more, 23 μm or more, or 24 μm or more, and the upper limit may be 35 μm or less, 30 μm or less, 29 μm or less, 28 μm or less, or 27 μm or less.

[0055] In one embodiment, the polyimide varnish according to the present invention may have a coefficient of thermal expansion (CTE) after curing of 20 to 30 ppm / ° C., preferably 23 to 27 ppm / ° C., and more preferably 24 to 26 ppm / ° C. The CTE was measured using a TMA device (Q400) manufactured by TA Corporation, as a gradient in the range of 100 to 250° C. when the temperature was increased from room temperature to 350° C. at a rate of 10° C. / min.

[0056] In one embodiment, the polyimide varnish according to the present invention may have a thermal conductivity after curing of 0.2 to 0.8 W / mK, preferably 0.23 to 0.5 W / mK, and more preferably 0.25 to 0.45 W / mK. The thermal conductivity was calculated by measuring the thermal diffusivity in the thickness direction (through-plane) of a cured product obtained by curing the polyimide varnish under N2 nitrogen gas conditions using a thermal conductivity meter (LFA, manufactured by NETZSCH, LFA467), and multiplying the measured thermal diffusivity by the density (weight / volume) and the specific heat (measured using DSC).

[0057] In one embodiment, the polyimide varnish according to the present invention has a voltage durability of 400 minutes or more after curing, which is the time an insulating material can withstand a predetermined voltage according to IEC-60851-5. The voltage durability may be measured for the polyimide (thickness: 26±0.5 μm) under conditions of AC 1.5 kV, a frequency of 60 Hz, and a maximum leakage current of 5 mA. Specifically, the voltage durability may be 410 minutes or more, 415 minutes or more, 420 minutes or more, 425 minutes or more, or 430 minutes or more. The voltage durability was measured using a voltage resistance tester (TSURUGA, 8526) to fix a film-form cured polyimide varnish to a jig, apply a predetermined voltage, and measure the time until a leakage current of 5 mA or more flows.

[0058] In one embodiment, the polyimide varnish according to the present invention may have a coefficient of friction (PI-PI) between cured polyimide varnishes after curing of 0.38 or less, preferably 0.35 or less. The coefficient of friction was measured using a friction coefficient tester (QMESYS, QM110CF) by fixing one of the cured polyimide films to a weight and pulling it at a constant speed over another cured polyimide film under conditions of a load of 200 gf and a speed of 2.5 mm / s.

[0059] In one embodiment, the polyimide varnish according to the present invention has a coefficient of friction (PI-SUS) between the cured polyimide varnish and a stainless steel substrate after curing of 0.35 or less, preferably 0.32 or less. The coefficient of friction was measured using a friction coefficient tester (QMESYS, QM110CF) by attaching a film of the cured polyimide varnish to a weight and pulling it at a constant speed over a stainless steel substrate under conditions of a load of 200 gf and a speed of 2.5 mm / s.

[0060] In one embodiment, the polyimide varnish according to the present invention may have a peel strength of 6 N / cm or more after curing, preferably 6.5 N / cm or more, and more preferably 7 N / cm or more. The peel strength was measured at 90° peeling speed of 50 mm / sec at room temperature using a UTM (Instron, model 5564) device, using a sample prepared by curing a 25 μm thick film of polyimide and placing it on a 36 μm thick copper foil.

[0061] In another aspect of the present invention, there is provided a polyimide coated article comprising a cured product of the polyimide varnish.

[0062] 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.

[0063] 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.

[0064] In another aspect of the present invention, there is provided an electric wire comprising the polyimide coating.

[0065] 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.

[0066] The present invention also provides an electronic device including the coated electric wire, such as an electric motor. [Effects of the Invention]

[0067] The polyimide varnish according to the present invention and the polyimide coating containing the same contain a first additive (boron nitride), a second additive (nanosilica), and a dispersant, and therefore have the effects of improving voltage durability, adhesive strength, and thermal conductivity, improving the coefficient of friction, and having excellent dispersibility for the first additive and the second additive.

[0068] In addition, the present invention can improve motor durability and lifespan against partial discharge by improving voltage durability, and improves yield and processability by improving friction coefficient to reduce buckling during hairpin processing and reduce friction during stator insertion to improve defects.

[0069] Furthermore, the present invention can help improve motor performance by suppressing the temperature rise of the motor and enabling an increase in the rated current due to the improved thermal conductivity.

[0070] Furthermore, the present invention provides improved adhesive strength and can achieve structural and functional reliability even in harsh environments. [Brief explanation of the drawings]

[0071] [Figure 1] 1 shows SEM images of the surfaces of film-shaped cured polyimide materials prepared by curing the polyimide varnishes of Example 1-1, Comparative Example 1-1, and Comparative Example 1-2. DETAILED DESCRIPTION OF THE INVENTION

[0072] 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]

[0073] <Example> Example 1. Polyimide varnish Example 1-1 A polyamic acid solution was prepared by dispersing 99.5-100 mol% of the dianhydride compound pyromellitic dianhydride (PMDA) and 75 mol% of the diamine compounds 4,4'-diaminodiphenyl ether (ODA) and 25 mol% of the p-phenylenediamine (PPD) in 100 mol% of N,N'-dimethylacetamide (DMAc), with a target polyimide solids content of 13-25 wt%.

[0074] To the polyamic acid solution, 5 wt% of boron nitride (BN) additive (particle diameter (D90): 5.4 μm), 0.6 wt% of nanosilica additive (average silica particle diameter 10-20 nm), 0.25 wt% of polyurethane-based dispersant (amine value 48 mg KOH / g, specific gravity (20°C) 1.05 g / ml), and 0.5 wt% of epoxy-based silane (OFS-6040) were added to produce a polyimide varnish.

[0075] Example 1-2 A polyimide varnish was prepared in the same manner as in Example 1-1, except that 10 wt% of boron nitride additive and 0.5 wt% of polyurethane dispersant were added instead of 5 wt% of boron nitride additive and 0.25 wt% of polyurethane dispersant in Example 1-1.

[0076] Examples 1-3 A polyimide varnish was prepared in the same manner as in Example 1-1, except that instead of adding 5 wt% of boron nitride additive and 0.25 wt% of polyurethane dispersant in Example 1-1, 20 wt% of boron nitride additive and 1 wt% of polyurethane dispersant were added.

[0077] Comparative Example 1-1 A polyimide varnish was prepared in the same manner as in Example 1-1, except that instead of adding the boron nitride additive, nanosilica additive, epoxy-based silane, and polyurethane-based dispersant in Example 1-1, the boron nitride additive, nanosilica additive, epoxy-based silane, and polyurethane-based dispersant were not added.

[0078] Comparative Example 1-2 A polyimide varnish was produced in the same manner as in Example 1-1, except that instead of adding 5 wt% boron nitride additive, 0.6 wt% nanosilica additive, and 0.25 wt% polyurethane dispersant in Example 1-1, 5 wt% boron nitride additive and 0.25 wt% polyurethane dispersant were not added, and only 3 wt% nanosilica additive was added.

[0079] The compositions and contents of the polyimide varnishes of Examples 1-1 to 1-3 and Comparative Examples 1-1 and 1-2 are shown in Table 1. In Table 1, the weight percentages (wt%) of the boron nitride additive, nanosilica additive, and epoxy-based silane indicate the respective contents of the boron nitride additive, nanosilica additive, and epoxy-based silane relative to the solid weight of the polyamic acid varnish, and the weight percentage (wt%) of the dispersant indicates the total content of the dispersant relative to the total weight of the boron nitride additive.

[0080] [Table 1]

[0081] Example 2. Polyimide coating Example 2-1 The polyimide varnish according to Example 1-1 was applied to a copper wire having a diameter of 1 mm in a coating and curing oven, and the process of coating, drying, and curing was repeated 20 times or more to produce an electric wire having a polyimide coating with a coating thickness of 100 μm or more.

[0082] Example 2-2 An electric wire including a polyimide coating having a coating thickness of 100 μm or more was produced 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.

[0083] Example 2-3 An electric wire including a polyimide coating having a coating thickness of 100 μm or more was produced in the same manner as in Example 2-1, except that the polyimide varnish of Example 1-3 was used instead of the polyimide varnish of Example 1-1.

[0084] <Experimental Example> Experimental example 1. Physical property evaluation Preparation of cured polyimide varnish in film form for property measurements The polyimide varnishes prepared in Examples 1-1 to 1-3 and Comparative Examples 1-1 and 1-2 were spun at 2,000 rpm to remove air bubbles. The degassed polyimide varnishes were then applied to glass substrates (230 mm × 230 mm, 0.55 mm thick) using a spin coater. The varnishes were 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 film-form cured polyimide products. The film-form cured polyimide products used to measure voltage durability were prepared to a thickness of 26±1 μm, while the film-form cured polyimide products used to measure other physical properties (coefficient of thermal expansion, thermal conductivity, coefficient of friction, and peel strength) were prepared to a thickness of 20±1 μm.

[0085] FIG. 1 shows SEM images of the surfaces of the polyimide film-shaped cured products prepared by curing the polyimide varnishes of Example 1-1, Comparative Example 1-1, and Comparative Example 1-2 by the above-mentioned method.

[0086] As shown in FIG. 1, Comparative Example 1-1 has a clean surface without using any additives, whereas Example 1-1 and Comparative Example 1-2 have additives visible on the surface, confirming that the dispersant is well dispersed.

[0087] Furthermore, since Comparative Example 1-2 contains an excess amount of nanosilica, which has a relatively small particle size, it can be confirmed that smaller particles are dispersed in it compared to Example 1-1, which contains both boron nitride and nanosilica.

[0088] (1) Coefficient of thermal expansion (CTE) The cured polyimide films prepared from the polyimide varnishes of Examples 1-1 to 1-3 and Comparative Examples 1-1 and 1-2 were heated from room temperature to 350°C at a rate of 10°C / min using a TMA (Testerson Instruments) Q400 manufactured by TA Corporation, and the gradient in the 100-250°C range was measured. The results are shown in Table 2 below.

[0089] (2) Thermal conductivity For the polyimide film-form cured products prepared from the polyimide varnishes of Examples 1-1 to 1-3 and Comparative Examples 1-1 and 1-2, the thermal diffusivity in the through-plane direction of the cured polyimide varnish was measured under N2 nitrogen gas conditions using a thermal conductivity meter (LFA, manufactured by NETZSCH, LFA467).The thermal conductivity was calculated by multiplying the thermal diffusivity measurement value by the density (weight / volume) and specific heat (specific heat measurement value using DSC).The results are shown in Table 2 below.

[0090] (3) Voltage durability The voltage durability of the film-shaped polyimide cured products (thickness: 26±1 μm) produced from the polyimide varnishes of Examples 1-1 to 1-3 and Comparative Examples 1-1 and 1-2 was measured using a voltage resistance tester (TSURUGA, 8526) under conditions of AC 1.5 kV, frequency 60 Hz, and maximum leakage current of 5 mA. Specifically, the voltage durability was measured by fixing the polyimide to a jig, applying a predetermined voltage, and measuring the time until a leakage current of 5 mA or more flowed. The results are shown in Table 2 below.

[0091] (4) Friction coefficient The coefficients of friction of the film-form cured polyimides prepared from the polyimide varnishes of Examples 1-1 to 1-3 and Comparative Examples 1-1 and 1-2 were measured using a friction coefficient tester (QM110CF, manufactured by QMESYS). Specifically, the coefficients of friction were measured by fixing one of the film-form cured polyimides to a weight and pulling it at a constant speed over another film-form cured polyimide at a load of 200 gf and a speed of 2.5 mm / s, measuring the PI-PI kinetic friction coefficient, and by fixing the polyimide to a weight and pulling it at a constant speed over a stainless steel substrate, measuring the PI-SUS kinetic friction coefficient. The results are shown in Table 2 below.

[0092] (5) Peel strength The 90° peel strength of the cured polyimide films prepared from the polyimide varnishes of Examples 1-1 to 1-3 and Comparative Examples 1-1 and 1-2 was measured at room temperature at 50 mm / sec using a UTM (Instron, model 5564) and the results are shown in Table 2. The peel strength was measured using a sample prepared by curing a 25 μm thick polyimide film and placing it on a 36 μm thick copper foil.

[0093] Table 2 below shows the measurement results of the coefficient of thermal expansion (CTE), thermal conductivity, voltage durability, coefficient of friction, and peel strength of the cured polyimide films prepared from the polyimide varnishes of Examples 1-1 to 1-3 and Comparative Examples 1-1 and 1-2.

[0094] [Table 2]

[0095] From Table 2, it can be seen that the coefficient of thermal expansion (CTE) values ​​of Examples 1-1 to 1-3, which contain the first additive (boron nitride), the second additive (nanosilica), and the dispersant, are smaller than those of Comparative Examples 1-1 and 1-2, and the thermal conductivity is significantly improved compared to Comparative Examples 1-1 and 1-2.

[0096] It can also be seen that the voltage durability and peel strength (adhesion strength) of Examples 1-1 to 1-3 were significantly improved, and the friction coefficient values ​​were relatively small, confirming that the friction coefficient was improved.

[0097] These results indicate that by appropriately combining dispersants and additives, it is possible to obtain polyimide varnishes with excellent thermal properties, voltage durability, and adhesive strength, as well as an improved coefficient of friction.

[0098] 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 present invention, other than 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 solution containing a diamine monomer and a dianhydride monomer as polymerized units; a first additive comprising boron nitride; a second additive comprising nanosilica; a dispersant comprising a polyurethane-based dispersant; Including, The particle size (D90) of the first additive is 1 to 20 μm, The average particle size of the second additive is 1 to 200 nm. Polyimide varnish.

2. 2. The polyimide varnish according to claim 1, wherein the first additive is contained in an amount of 1 to 40% by weight based on the weight of the solid content of the polyimide varnish.

3. 2. The polyimide varnish according to claim 1, wherein the second additive is contained in an amount of 0.01 to 60% by weight based on the weight of the solid content of the polyimide varnish.

4. A polyimide varnish as described in claim 1, wherein the dispersant is contained in an amount of 1 to 25 weight % relative to the weight of the first additive.

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 selected from the group consisting of 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) methyl)-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'-diamino 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-amino phenyl)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-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. The polyimide varnish according to claim 1 , wherein the polyamic acid solution further comprises an organic solvent.

8. 8. The polyimide varnish according to claim 7, wherein the organic solvent comprises one or more selected from the group consisting of N,N'-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), N,N'-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), diethylacetamide (DEAc), N-ethyl-2-pyrrolidone (NEP), N,N'-diethylformamide (DEF), dimethylpropanamide (DMPA), and γ-butyrolactone (GBL).

9. The polyimide varnish according to claim 1 , further comprising a silane coupling agent.

10. 2. The polyimide varnish according to claim 1, wherein the polyimide varnish has a solids content of 5 to 40% by weight.

11. 2. The polyimide varnish according to claim 1, wherein the coefficient of thermal expansion (CTE) of the polyimide varnish after curing is 20 to 30 ppm / °C.

12. 2. The polyimide varnish according to claim 1, wherein the thermal conductivity of the polyimide varnish after curing is 0.2 to 0.8 W / mK.

13. 2. The polyimide varnish according to claim 1, wherein after curing, the polyimide varnish has a voltage durability of 400 minutes or more, which is the time that an insulating material can withstand a predetermined voltage in accordance with IEC-60851-5.

14. After curing of the polyimide varnish, the coefficient of friction (PI-PI) between cured polyimide varnishes is 0.38 or less; 2. The polyimide varnish according to claim 1, wherein after curing, the coefficient of friction (PI-SUS) between the cured polyimide varnish and a stainless steel substrate is 0.35 or less.

15. 2. The polyimide varnish according to claim 1, wherein the polyimide varnish has a peel strength of 6 N / cm or more after curing.

16. A polyimide coated article comprising a cured product of the polyimide varnish according to any one of claims 1 to 15.

17. An electrical wire comprising the polyimide coating of claim 16.

Images