Polyimide paint for coated conductor having improved heat dissipation of coated conductor and polyimide coating material comprising same

Abstract

Provided is a polyimide paint comprising: a polyamic acid solution containing a diamine monomer and a dianhydride monomer as polymerization units; an additive containing boron nitride; and a dispersant.

Description

Technical Field

[0001] The present invention relates to a polyimide varnish and a polyimide coating material containing the same. Specifically, the present invention relates to a polyimide varnish for coating a conductor having improved heat dissipation characteristics and a polyimide coating material containing the same. Background Art

[0002] An insulating layer (insulating coating) that covers a conductor is required to have excellent insulating properties, adhesion to the conductor, heat resistance, mechanical strength, etc. In addition, in an electrical device having a high applied voltage (for example, a motor used at a high voltage), a high voltage is applied to the insulating wire that forms the electrical device, and there is a high possibility of partial discharge (corona discharge) occurring on the surface of the insulating coating. The occurrence of corona discharge may cause a local temperature increase or generate ozone or ions, which may cause deterioration of the insulating coating of the insulating wire, resulting in premature insulation breakdown and shortening the service life of the electrical device. For the above reasons, an insulating wire used at a high voltage is required to increase the corona discharge inception voltage, and in order to achieve such an increase, it is known that reducing the dielectric constant of the insulating layer is effective.

[0003] Examples of resins that can be used in the insulating layer may include polyimide resins, polyamide-imide resins, and polyester-imide resins, etc. In particular, the polyimide resin among these resins is a material having excellent heat resistance and insulating properties, and has excellent properties as a coating material for a conductor.

[0004] A polyimide resin refers to a highly heat-resistant resin that is obtained by solution polymerization of an aromatic dianhydride and an aromatic diamine or an aromatic diisocyanate to produce a polyamic acid derivative, and then performing ring-closure dehydration and imidization at a high temperature. For example, a method of forming an insulating coating using a polyimide resin may include a method of applying or coating a polyimide varnish (a precursor of a polyimide resin) around a wire, and then imidizing the polyimide varnish in a curing furnace capable of performing heat treatment at a predetermined temperature.

[0005] Depending on conditions such as the temperature of the curing furnace, the number of polyimide varnish coatings, and the coating speed, the method of forming an insulating coating may result in differences in the physical properties, productivity, and manufacturing cost of the resulting insulating coating. In other words, forming an insulating coating at a high temperature may be beneficial for producing an insulating coating having excellent physical properties, and when the number of coatings is small or the coating speed is fast, the productivity can be increased.

[0006] However, when the temperature of the curing furnace is very high, problems such as defects on the surface of the produced insulating coating or carbonization of the polyimide resin may occur. When the number of coatings is very small or the coating speed is very fast, the physical properties of the polyimide coating material to be produced may be deteriorated. In addition, although the physical properties of general polyimide resins are excellent, they do not have excellent adhesion to conductors. Therefore, when forming an insulating coating, problems with appearance defects may occur.

[0007] As described above, there are many difficulties in improving the required properties of polyimide varnishes and polyimide resins produced therefrom. In particular, since it is common for improving one property to cause a decline in other properties, simultaneously satisfying multiple properties is an ongoing research task in the relevant technical field.

[0008] Therefore, there is a great need for such a polyimide varnish for coating conductors, which has excellent productivity and process efficiency, and simultaneously satisfies the heat resistance, insulation, and mechanical properties of polyimide, while having excellent adhesion to conductors as described above. Summary of the Invention

[0009] Technical Problem

[0010] An object of the present invention is to provide a polyimide varnish containing an additive and a dispersant, which can maintain excellent heat dissipation characteristics over time and improve the dispersibility of the additive.

[0011] Another object of the present invention is to provide a polyimide varnish for coating conductors used in windings for electric vehicles (EVs) and a polyimide coating material containing the same.

[0012] Yet another object of the present invention is to provide a polyimide in which the polyimide varnish is imidized.

[0013] Technical Solution

[0014] In the present invention, various modifications can be made and multiple embodiments can be implemented, and specific exemplary embodiments are shown and described in detail in the drawings. However, these exemplary embodiments are not intended to limit the present invention, and should be understood to include all modification schemes, equivalent schemes, and alternative schemes included in the spirit and scope of the present invention.

[0015] The terms used in this application are only for describing specific embodiments and are not intended to limit the present invention. Unless the context clearly indicates otherwise, singular expressions include plural expressions. In this specification, terms such as "including" or "having" are intended to specify the presence of the features, quantities, steps, operations, components, parts, or combinations thereof described in the specification, and it should be understood that the possibility of the presence or addition of one or more other features, quantities, steps, operations, components, parts, or combinations thereof is not excluded.

[0016] When quantities, concentrations, or other values or parameters herein are given as a range, a preferred range, or a list of upper and lower expected values, it is to be understood that all ranges formed by any pair of any upper range or preferred value and any lower range or preferred value are specifically disclosed, whether or not the ranges are separately disclosed.

[0017] Unless otherwise specified, when stating a range of numerical values herein, it is intended that the endpoints of the range and the scope of the present invention within the range are not limited to the specific values recited when defining the range.

[0018] As used herein, "dianhydride" is intended to include its precursors or derivatives, which are also referred to as "diacid anhydride" or "acid dianhydride". These products may not technically be dianhydrides, but will still react with diamines to form polyamic acids, and the polyamic acids can be converted back to polyimides.

[0019] As used herein, "diamine" is intended to include its precursors or derivatives, which may not technically be diamines, but will still react with dianhydric acids to form polyamic acids, and the polyamic acids can be converted back to polyimides.

[0020] Furthermore, unless otherwise defined, all terms (including technical or scientific terms) used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the relevant art, and are not to be interpreted in an idealized or overly formal sense unless explicitly defined in this application. Specific details for implementing the present invention will be described below.

[0021] In one general aspect, the present invention relates to a polyimide varnish and a polyimide coating material containing the same, the polyimide varnish containing an additive and a dispersant, which can maintain excellent heat dissipation characteristics even over time and improve the dispersibility of the additive.

[0022] Polyimide varnish

[0023] The present invention provides a polyimide varnish, which comprises: a polyamic acid solution containing diamine monomers and dianhydride monomers as polymerization units; an additive containing boron nitride; and a dispersant.

[0024] Polyamic acid solution

[0025] The diamine monomer may include at least one selected from the following: 1,4-diaminobenzene (PPD), 4,4'-diaminodiphenyl ether (ODA), 2,2-bis(aminophenoxy)benzene propane (BAPP), m-phenylenediamine, 3,3'-dimethylbenzidine, 2,2'-dimethylbenzidine, 2,4-diaminotoluene, 2,6-diaminotoluene, 3,5-diaminobenzoic acid (DABA), 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane (4,4'-methylenedianiline), 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-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-phenylphenoxy)benzophenone, 3,3'-diamino-4,4'-bis(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]sulfide, bis[3-(4-aminophenoxy)phenyl]sulfide, bis[4-(3-aminophenoxy)phenyl]sulfide, bis[4-(4-aminophenoxy)phenyl]sulfide, bis[3-(3-aminophenoxy)phenyl]sulfone, bis[3-(4-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(4-aminophenoxy)phenyl]sulfone, bis[3-(3-aminophenoxy)phenyl]methane, bis[3-(4-aminophenoxy)phenyl]methane, bis[4-(3-aminophenoxy)phenyl]methane, bis[4-(4-aminophenoxy)phenyl]methane, 2,2-bis[3-(3-aminophenoxy)phenyl]propane, 2,2-bis[3-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(3-aminophenoxy)phenyl]propane, 2,2-bis[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 may preferably be 4,4'-diaminodiphenyl ether (ODA).

[0026] The dianhydride monomer may include at least one selected from the following: pyromellitic dianhydride (PMDA), biphenyltetracarboxylic dianhydride (BPDA), benzophenone tetracarboxylic dianhydride (BTDA), oxydiphthalic dianhydride (ODPA), diphenyl sulfone-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'-benzophenone tetracarboxylic dianhydride, bis(3,4-dicarboxyphenyl) methane dianhydride, 2,2-bis(3,4-dicarboxyphenyl) propane dianhydride, p-phenylene bis(trimellitic monoester anhydride), p-phenylenebis(trimellitic monoester anhydride), m-terphenyl-3,4,3',4'-tetracarboxylic dianhydride, p-terphenyl-3,4,3',4'-tetracarboxylic dianhydride, 1,3-bis(3,4-dicarboxyphenoxy)benzene dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)biphenyl dianhydride, 2,2-bis[(3,4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA), 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, and 4,4'-(2,2-hexafluoroisopropylidene)diphthalic dianhydride, and may preferably be pyromellitic dianhydride (PMDA).

[0027] In the present invention, among all the dianhydride monomers, pyromellitic dianhydride (PMDA) may be included in a ratio of 50 mol% or more, 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.

[0028] In addition, among all the diamine monomers, 4,4'-diaminodiphenyl ether (ODA) may be included in a ratio of 50 mol% or more, 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.

[0029] The polyamic acid solution may contain the diamine monomer in an amount of 90 mol% to 110 mol%, preferably 95 mol% to 105 mol%, more preferably 98 mol% to 102 mol%, and even more preferably 99 mol% to 101 mol%.

[0030] The polyamic acid solution may contain the dianhydride monomer in an amount of 90 mol% to 110 mol%, preferably 95 mol% to 105 mol%, more preferably 98 mol% to 102 mol%, and even more preferably 100 mol%.

[0031] Based on 100 mol% of the diamine monomer, the polyamic acid solution may contain 95 mol% to 105 mol% of the dianhydride monomer. For example, the lower limit of the dianhydride monomer 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 thereof 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.

[0032] The polyamic acid solution may contain the dianhydride monomer and the diamine monomer in a molar ratio of 6:4 to 4:6.

[0033] The polyamic acid solution may further contain an organic solvent.

[0034] The organic solvent may include at least one selected from the following: N-methylpyrrolidone (NMP), N,N'-dimethylformamide (DMF), N,N'-diethylformamide (DEF), N,N'-dimethylacetamide (DMAc), dimethylpropionamide (DMPA), naphtha, diethylpropionamide (DEPA), N-ethylpyrrolidone (NEP), xylene, γ-butyrolactone, γ-valerolactone, and N,N-diethylacetamide (DEAc), and preferably, it may be a mixed solvent containing N,N'-dimethylacetamide (DMAc) and naphtha.

[0035] The mixed solvent may be a mixture of N,N'-dimethylacetamide (DMAc) and naphtha having a mass ratio (weight / weight) of 70:30 to 100:0, preferably 80:20 to 90:10, and more preferably 85:15.

[0036] Additive

[0037] The polyimide varnish of the present invention may contain an additive to improve heat dissipation characteristics, and may particularly contain boron nitride. Boron nitride has high thermal conductivity characteristics and is preferably used as an additive for producing materials with high electrical insulation, high temperature stability, and excellent acid corrosion resistance.

[0038] The amount of the additive can be from 0.1% by weight to 20% by weight relative to the weight of the polyamic acid solution. For example, the lower limit of the amount of the additive can be 0.5% by weight or more, 1.0% by weight or more, 1.5% by weight or more, 2.0% by weight or more, 2.5% by weight or more, 3.0% by weight or more, 3.5% by weight or more, 4.0% by weight or more, 4.5% by weight or more, or 5.0% by weight or more, and the upper limit thereof can be 18% by weight or less, 16% by weight or less, 15% by weight or less, 10% by weight or less, 9.5% by weight or less, 9.0% by weight or less, 8.5% by weight or less, 8.0% by weight or less, 7.5% by weight or less, 7.0% by weight or less, 6.5% by weight or less, 6.0% by weight or less, 5.5% by weight or less, or 5.0% by weight or less.

[0039] When the amount of the additive exceeds 20% by weight, this is not desirable because the mechanical properties of the produced polyimide coating material may be reduced, and the amount of the additive is too large, making it difficult to achieve uniform dispersion. At the same time, when the amount of the additive is less than 0.1% by weight, this is not preferred because there is no effect of improving the heat dissipation characteristics.

[0040] The particle size (D90) of the additive can be from 1 μm to 10 μm. For example, the lower limit can 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 can 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, 5.5 μm, 5.0 μm, 4.5 μm, 4.0 μm, 3.8 μm, 3.7 μm, or 3.6 μm or less.

[0041] The boron nitride can be at least one type selected from cubic boron nitride (cBN), amorphous boron nitride (aBN), and hexagonal boron nitride (hBN), and is preferably hexagonal boron nitride (hBN).

[0042] Dispersant

[0043] At the same time, boron nitride (BN) may have a problem of being easily aggregated into polyimide due to its different polarity from polyimide (PI). Therefore, the polyimide varnish of the present invention can contain a dispersant to improve the dispersibility of the additive.

[0044] The dispersant may include at least one selected from the following: polyvinyl-based dispersants, polyethylene-based dispersants, polyester-based dispersants, polycarboxylate-based dispersants, unsaturated polyamide-based dispersants, polycarboxylic acid-based dispersants, polycarboxylic acid alkyl salt dispersants, polyacrylic acid-based dispersants, polyethyleneimine-based dispersants, and polyurethane-based dispersants, and preferably, a polyurethane-based dispersant may be used. Due to the strong polarity of the polyurethane-based dispersant, the dispersing ability of boron nitride can be improved.

[0045] The dispersant may have an acid value in the range of 10 mgKOH / g to 200 mgKOH / g or an amine value in the range of 5 mgKOH / g to 200 mgKOH / g, but is not limited thereto.

[0046] In one embodiment, the acid value of the dispersant may have a lower limit of about 20 mgKOH / g or greater, 30 mgKOH / g or greater, 40 mgKOH / g or greater, 50 mgKOH / g or greater, 60 mgKOH / g or greater, 70 mgKOH / g or greater, 80 mgKOH / g or greater, or 90 mgKOH / g or greater, and may have an upper limit of 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 dividing the acid groups (-COOH) of the dispersant by the amount of potassium hydroxide (KOH) required for titration with KOH (the value expressed in milligrams (mg) of the amount of titrant KOH required per 1 g of the dispersant).

[0047] In one embodiment, the amine value of the dispersant can have a lower limit of about 10 mg KOH / g or greater, about 15 mg KOH / g or greater, about 20 mg KOH / g or greater, 30 mg KOH / g or greater, 40 mg KOH / g or greater, 50 mg KOH / g or greater, 60 mg KOH / g or greater, 70 mg KOH / g or greater, 80 mg KOH / g or greater, or 90 mg KOH / g or greater, or can have an upper limit of about 190 mg KOH / g or less, 180 mg KOH / g or less, 170 mg KOH / g or less, 160 mg KOH / g or less, 150 mg KOH / g or less, 140 mg KOH / g or less, 130 mg KOH / g or less, 120 mg KOH / g or less, 110 mg KOH / g or less, or 100 mg KOH / g or less. Herein, the amine value refers to the value obtained by dividing the amino groups (-NH2, -NHR, or -NR2) of the dispersant by the amount of potassium hydroxide (KOH) required for titration with KOH (the value expressed in milligrams (mg) of the amount of titrated KOH required per 1 g of the dispersant).

[0048] The specific gravity of the dispersant at 20 °C can be from 0.5 g / ml to 1.5 g / ml. For example, the lower limit of the specific gravity of the dispersant can be 0.6 g / ml, 0.7 g / ml, 0.8 g / ml, 0.9 g / ml, or 1.00 g / ml or greater. In addition, the upper limit of the specific gravity of the dispersant can 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.

[0049] Relative to the weight of the polyamic acid solution, the amount of the dispersant can be from 0.01 wt% to 5.0 wt%. For example, the lower limit of the amount of the dispersant can be 0.05 wt% or greater, 0.1 wt% or greater, 0.2 wt% or greater, 0.3 wt% or greater, 0.4 wt% or greater, 0.5 wt% or greater, 0.6 wt% or greater, 0.7 wt% or greater, 0.8 wt% or greater, 0.9 wt% or greater, or 1.0 wt% or greater, and the upper limit of the amount of the dispersant can be 4.0 wt% or less, 3.0 wt% or less, 2.0 wt% or less, 1.5 wt% or less, 1.4 wt% or less, 1.3 wt% or less, 1.2 wt% or less, 1.1 wt% or less, or 1.0 wt% or less.

[0050] When the amount of the dispersant exceeds 5.0 wt%, this is not preferred because the thermal stability decreases. On the other hand, when the amount of the additive is less than 0.01 wt%, this is not preferred because there is no effect of improving the dispersibility of the additive.

[0051] Polyimide paint and its cured product

[0052] The solid content of the polyimide paint can be 5 wt% to 40 wt%, preferably 10 wt% to 35 wt%, more preferably 15 wt% to 30 wt%, and even more preferably 20 wt% to 30 wt%. In one embodiment, the solid content of the polyimide paint can be 25 wt%.

[0053] The present invention may include a cured product in the form of a film in which the polyimide paint is imidized.

[0054] In one embodiment, the thickness of the polyimide paint according to the present invention after curing can be 10 μm to 50 μm. For example, the lower limit of the thickness after curing can be 12 μm or greater, 14 μm or greater, 16 μm or greater, 18 μm or greater, 20 μm or greater, 21 μm or greater, 22 μm or greater, 23 μm or greater, or 24 μm or greater, and the upper limit can be 50 μm or less, 48 μm or less, 46 μm or less, 44 μm or less, 42 μm or less, 40 μm or less, 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 thermal conductivity of the polyimide varnish according to the present invention after curing can be from 0.2 W / mK to 10.0 W / mK. For example, the lower limit of the thermal conductivity after curing can be 0.3 W / mK or greater, 0.35 W / mK or greater, 0.4 W / mK or greater, 0.42 W / mK or greater, 0.45 W / mK or greater, 0.47 W / mK or greater, 0.49 W / mK or greater, or 0.5 W / mK or greater. In addition, the upper limit of the thermal conductivity after curing can be 9.0 W / mK or less, 8.0 W / mK or less, 7.0 W / mK or less, 6.0 W / mK or less, 5.0 W / mK or less, 4.0 W / mK or less, 3.0 W / mK or less, 2.0 W / mK or less, 0.9 W / mK or less, 0.8 W / mK or less, 0.7 W / mK or less, 0.65 W / mK or less, 0.63 W / mK or less, 0.60 W / mK or less, 0.58 W / mK or less, 0.57 W / mK or less, 0.56 W / mK or less, 0.55 W / mK or less, or 0.54 W / mK or less. In one embodiment, in order to measure the thermal conductivity, the thermal diffusivity of the cured polyimide varnish in the thickness direction is measured using a thermal diffusivity measuring device (model LFA 447, NETZSCH.GmbH, Selb, Germany) according to the laser flash method, and the thermal conductivity is calculated by multiplying the measured value of the thermal diffusivity by the density (weight / volume) and the specific heat (specific heat measurement value using DSC).

[0056] In one embodiment, the glass transition temperature (Tg) of the polyimide varnish according to the present invention after curing can be in the range of 200 °C to 450 °C. For example, the lower limit of the glass transition temperature can be 250 °C or higher, 300 °C or higher, 350 °C or higher, 355 °C or higher, 360 °C or higher, 365 °C or higher, 367 °C or higher, or 370 °C or higher. The upper limit of the glass transition temperature can be 445 °C or lower, 440 °C or lower, 435 °C or lower, 430 °C or lower, 425 °C or lower, 420 °C or lower, 415 °C or lower, 410 °C or lower, or 405 °C or lower. In one embodiment, the glass transition temperature is determined by measuring the peak of the tangent δ (Tanδ) of the cured polyimide varnish under the condition of raising the temperature to 450 °C at a rate of 10 °C / minute using dynamic mechanical analysis (DMA).

[0057] In one embodiment, the thermal decomposition temperature (Td) at 5% weight loss after curing the polyimide varnish according to the present invention may be from 400 °C to 600 °C. The lower limit of the thermal decomposition temperature may be, for example, 450 °C or higher, 470 °C or higher, 490 °C or higher, 500 °C or higher, 505 °C or higher, 510 °C or higher, 515 °C or higher, or 520 °C or higher. The upper limit of the thermal decomposition temperature may be, for example, 590 °C or lower, 580 °C or lower, 570 °C or lower, or 560 °C or lower. The thermal decomposition temperature can be measured using a TA thermogravimetric analyzer Q50. In a specific example, the cured product of the polyimide varnish (cured polyimide varnish) may be heated to 150 °C at a rate of 10 °C / minute in a nitrogen atmosphere and then isothermally held for 30 minutes to remove moisture. Then, the temperature can be raised to 600 °C at a rate of 10 °C / minute, and the temperature at which 5% weight loss occurs can be measured.

[0058] In one embodiment, the dielectric breakdown voltage (BDV) of the polyimide varnish according to the present invention after curing may be from 50 kV / mm to 350 kV / mm. For example, the lower limit of the dielectric breakdown voltage may be 60 kV / mm or greater, 65 kV / mm or greater, 70 kV / mm or greater, 75 kV / mm or greater, 77 kV / mm or greater, 80 kV / mm or greater, or 82 kV / mm or greater, and its upper limit may be 300 kV / mm or lower, 250 kV / mm or lower, 220 kV / mm or lower, 200 kV / mm or lower, 198 kV / mm or lower, 195 kV / mm or lower, 194 kV / mm or lower, 193 kV / mm or lower, 192 kV / mm or lower, 191 kV / mm or lower, 190 kV / mm or lower, 189 kV / mm or lower, or 188 kV / mm or lower. In one embodiment, the dielectric breakdown voltage (BDV) of the cured product of the polyimide varnish is measured according to the ASTM D149 standard.

[0059] In another aspect of the present invention, a polyimide coating material comprising a cured product of a polyimide varnish is provided.

[0060] In one embodiment, a method for producing a polyimide coating material may include coating a polyimide varnish on a conductor surface; and imidizing the polyimide varnish coated on the surface of the conductor.

[0061] The conductor can be a copper wire made of copper or a copper alloy, but can also include conductors made of other metallic materials such as silver wires, etc., or wires coated with various metals (such as aluminum-coated or tin-coated wires, etc.). The conductor and the coating material can have a thickness according to the KS C3107 standard. The diameter of the conductor can be in the range of 0.3 mm to 3.2 mm, and the standard film thickness (average of the maximum film thickness and the minimum film thickness) of the coating material can be 21 μm to 194 μm for type 0, 14 μm to 169 μm for type 1, and 10 μm to 31 μm for type 2. Depending on the cross-sectional shape of the conductor, the conductor can be a round wire, a rectangular wire, a hexagonal wire, etc., but is not limited thereto.

[0062] In another aspect of the present invention, there is provided an electric wire including a polyimide coating material.

[0063] Specifically, the wire material can be a coated wire including a polyimide coating material produced by coating a polyimide varnish on the surface of the wire material and then imidizing it. In one embodiment, the coated wire can include an electric wire; and a coating material in which the above polyimide is coated on the surface of the wire material and imidized.

[0064] Furthermore, the present invention can provide an electronic device including the above coated wire. The electronic device can be, for example, an electric motor.

[0065] Advantageous Effects

[0066] The polyimide varnish of the present invention and the polyimide coating material containing the same can contain additives and dispersants, thereby maintaining excellent heat dissipation characteristics over time and providing excellent dispersibility of the additives.

[0067] In addition, the improvement of the heat dissipation characteristics can also increase the service life of the motor and can have excellent usability in coating conductors for windings used in electric vehicles (EVs). Brief Description of the Drawings

[0068] Figure 1 The appearance of the additive containing boron nitride according to the type of the dispersant is shown to determine the dispersibility of the additive. Detailed Description of the Embodiments

[0069] The following examples are presented to assist in understanding the present invention. The following examples are provided only for easier understanding of the present invention, but the content of the present invention is not limited by these examples.

[0070] <Examples>

[0071] Example 1. Polyimide Varnish

[0072] Example 1-1

[0073] 99.5 mol% to 100 mol% of pyromellitic dianhydride (PMDA), which is a dianhydride compound, and 100 mol% of 4,4'-diaminodiphenyl ether (ODA), which is a diamine compound, are dispersed in a mixed solvent of N,N'-dimethylacetamide (DMAc) and naphtha mixed at a ratio of 85:15 (weight / weight) to prepare a polyamic acid solution, where the target polyimide solid content is 25 wt%.

[0074] 5 wt% of boron nitride (BN) additive with a particle size (D90) of 1 μm to 10 μm and 0.1 wt% of a polyurethane-based dispersant (amine value 48 mgKOH / g, specific gravity (20 °C) 1.05 g / ml) are added to the polyamic acid solution to produce a polyimide paint.

[0075] Example 1-2

[0076] A polyimide paint is prepared in the same manner as in Example 1-1, except that 1 wt% of the polyurethane-based dispersant is added instead of 0.1 wt% of the polyurethane-based dispersant in Example 1-1.

[0077] Example 1-3

[0078] A polyimide paint is prepared in the same manner as in Example 1-1, except that 1.5 wt% of the polyurethane-based dispersant is added instead of 0.1 wt% of the polyurethane-based dispersant in Example 1-1.

[0079] Comparative Example 1-1

[0080] A polyimide paint is prepared in the same manner as in Example 1-1, except that in Example 1-1, instead of adding 5 wt% of boron nitride (BN) additive and 0.1 wt% of the polyurethane-based dispersant, neither 5 wt% of boron nitride (BN) additive nor 0.1 wt% of the polyurethane-based dispersant is added.

[0081] Comparative Example 1-2

[0082] A polyimide paint is prepared in the same manner as in Example 1-1, except that in Example 1-1, only 5 wt% of boron nitride (BN) additive is added instead of adding 5 wt% of boron nitride (BN) additive and 0.1 wt% of the polyurethane-based dispersant.

[0083] Table 1 below shows the composition and content of the polyimide varnishes according to Examples 1-1 to 1-3 and Comparative Examples 1-1 and 1-2. Here, in Table 1 below, the percentage (%) by weight of the additive (% (wt)) represents the total content of the additive relative to the total weight of the polyamic acid solution, and the wt% of the dispersant represents the total content of the dispersant relative to the total weight of the polyamic acid solution.

[0084] [Table 1]

[0085]

[0086] Example 2. Polyimide Cured Product

[0087] Example 2-1

[0088] The polyimide varnish prepared according to Example 1-1 was rotated at a high speed of 2,000 rpm to remove air bubbles. Then, the degassed polyimide varnish was applied onto a glass substrate (230 mm × 230 mm, thickness: 0.55 mm t) using a spin coater.

[0089] Subsequently, a cured polyimide product in the form of a film was obtained by curing under the conditions of 110 °C (20 minutes) → 150 °C (20 minutes) → 200 °C (20 minutes) → 300 °C (20 minutes) in a nitrogen atmosphere.

[0090] Example 2-2

[0091] A cured polyimide product was prepared in the same manner as in Example 2-1, except that the polyimide varnish according to Example 1-2 was used instead of the polyimide varnish according to Example 1-1 in Example 2-1.

[0092] Example 2-3

[0093] A cured polyimide product was prepared in the same manner as in Example 2-1, except that the polyimide varnish according to Example 1-3 was used instead of the polyimide varnish according to Example 1-1 in Example 2-1.

[0094] Comparative Example 2-1

[0095] A cured polyimide product was prepared in the same manner as in Example 2-1, except that the polyimide varnish according to Comparative Example 1-1 was used instead of the polyimide varnish according to Example 1-1 in Example 2-1.

[0096] Comparative Example 2-2

[0097] A cured polyimide product was prepared in the same manner as in Example 2-1, except that the polyimide varnish according to Comparative Example 1-2 was used instead of the polyimide varnish according to Example 1-1 in Example 2-1.

[0098] Example 3. Polyimide Coating Material

[0099] Example 3-1

[0100] A wire (coated wire) containing a polyimide coating material with a coating thickness of 33 μm to 35 μm was prepared as follows: The polyimide varnish according to Example 1-1 was applied to a copper wire with a conductor diameter of 1 mm in a coating curing furnace, where the coating thickness per pass was adjusted to 2 μm to 6 μm, the minimum and maximum temperatures of the coating curing furnace were adjusted to 350 °C to 550 °C, and the coating speed of the copper wire was adjusted to 12 m / min to 32 m / min, and the coating, drying, and curing processes were repeated a total of 7 times.

[0101] Example 3-2

[0102] A cured polyimide product was prepared in the same manner as in Example 3-1, except that the polyimide varnish according to Example 1-2 was used instead of the polyimide varnish according to Example 1-1 in Example 3-1.

[0103] Example 3-3

[0104] A cured polyimide product was prepared in the same manner as in Example 3-1, except that the polyimide varnish according to Example 1-3 was used instead of the polyimide varnish according to Example 1-1 in Example 3-1.

[0105] <Experimental Example>

[0106] Experimental Example 1. Evaluation of Dispersibility

[0107] 1 wt% of different types of dispersants was mixed in an N,N'-dimethylacetamide (DMAc) solvent containing 1 wt% of boron nitride (BN), and after each mixture was allowed to stand at 23 °C for a certain period of time, the dispersibility of boron nitride (BN) was evaluated by comparing the appearances. Here, the dispersants used were fatty acids A and B, hyperbranched agents C and D, phosphate ester E, and a polyurethane-based dispersant F. Figure 1 The appearance is shown in to determine the dispersibility according to the dispersant.

[0108] According to Figure 1 , when the polyurethane-based dispersant was used, it was determined that the dispersibility of boron nitride (BN) was excellent, and it was considered that due to the strong polarity of the polyurethane-based dispersant, the dispersibility of boron nitride was improved.

[0109] Experimental Example 2. Evaluation of Physical Properties

[0110] The physical properties of the cured products of Examples 2-1 to 2-3 and Comparative Examples 2-1 and 2-2 obtained by curing the polyimide varnishes prepared according to Examples 1-1 to 1-3 and Comparative Examples 1-1 to 1-2 were determined in the following manner, and the results are shown in Table 2 below.

[0111] (1) Glass transition temperature (Tg)

[0112] Using dynamic mechanical analysis (DMA), the peak of the tangent δ (Tanδ) of the cured polyimide varnish was measured under the condition of increasing the temperature to 450 °C at a rate of 10 °C / min.

[0113] (2) Thermal decomposition temperature at 5% weight loss (Td 5%)

[0114] Using TA's thermogravimetric analyzer Q50, the cured polyimide varnish was heated to 150 °C at a rate of 10 °C / min in a nitrogen atmosphere, and then isothermally held for 30 minutes to remove moisture. Then, the temperature was increased to 600 °C at a rate of 10 °C / min, and the temperature at which 5% weight loss occurred was measured.

[0115] (3) Dielectric breakdown voltage (BDV)

[0116] The BDV value of the cured product of the polyimide varnish was measured according to ASTM D149 standard. Specifically, the cured product was pre-treated in an oven at 100 °C to remove moisture, and then the cured product was fixed to the TECHNOLOGIES 6CCE50-5 testing machine of PHENIX set in a room temperature atmosphere and placed on the lower sample stage. Then, the BDV was measured by applying a voltage of 10 KVAc (increasing the voltage from 0 at a constant rate) using the upper electrode fixture.

[0117] (4) Thermal conductivity

[0118] According to the laser flash method, the thermal diffusivity of the cured polyimide varnish in the thickness direction was measured using a thermal diffusivity measurement device (model LFA 447, NETZSCH GmbH, Selb, Germany), and the thermal conductivity was calculated by multiplying the measured value of the thermal diffusivity by the density (weight / volume) and specific heat (specific heat measurement value using DSC). In addition, the thermal conductivity after 6 days was also determined to check the change over time.

[0119] [Table 2]

[0120]

[0121] As can be determined from Table 2, compared with the thermal conductivity (0.28 W / mK) of Comparative Example 2-1 which does not contain additives and dispersants, the thermal conductivities of Examples 2-1 to 2-3 are significantly increased to 0.51 W / mK to 0.54 W / mK. In addition, the initial thermal conductivity and the thermal conductivity after 6 days were compared to determine the change over time. As a result, it was determined that the dispersibility and physical properties of Example 2-2 were maintained. Based on these results, an appropriate combination of dispersants and additives enables the obtainment of a polyimide varnish that maintains heat dissipation characteristics over time and has dispersibility with respect to the additive (BN).

[0122] In this specification, details that can be fully recognized and inferred by those skilled in the art of the present invention are omitted, and various modifications can be made within the scope without changing the technical spirit or basic configuration of the present invention, except for the specific examples described in this specification. Therefore, the present invention can be practiced in a manner other than the manner specifically described and illustrated herein, which is understandable to those skilled in the art.

Claims

1. A polyimide paint, comprising: A polyamic acid solution containing diamine monomers and dianhydride monomers as polymerization units; An additive containing boron nitride; and A dispersant.

2. The polyimide paint according to claim 1, wherein the amount of the additive is 0.1% by weight to 20% by weight based on the weight of the polyamic acid solution.

3. The polyimide paint according to claim 1, wherein the particle size (D90) of the additive is 1 μm to 10 μm.

4. The polyimide paint according to claim 1, wherein the boron nitride is at least one selected from cubic boron nitride (cBN), amorphous boron nitride (aBN), and hexagonal boron nitride (hBN).

5. The polyimide paint according to claim 1, wherein the dispersant includes at least one selected from the following: polyvinyl-based dispersants, polyethylene-based dispersants, polyester-based dispersants, polycarboxylate-based dispersants, unsaturated polyamide-based dispersants, polycarboxylic acid-based dispersants, polycarboxylic acid alkyl salt dispersants, polyacrylic acid-based dispersants, polyethyleneimine-based dispersants, and polyurethane-based dispersants.

6. The polyimide paint according to claim 1, wherein the amount of the dispersant is 0.01% by weight to 5.0% by weight based on the weight of the polyamic acid solution.

7. The polyimide paint according to claim 1, wherein the dianhydride monomer comprises at least one selected from the following: pyromellitic dianhydride (PMDA), biphenyltetracarboxylic dianhydride (BPDA), benzophenone tetracarboxylic dianhydride (BTDA), oxydiphthalic dianhydride (ODPA), diphenyl sulfone-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'-benzophenone tetracarboxylic dianhydride, bis(3,4-dicarboxyphenyl) methane dianhydride, 2,2-bis(3,4-dicarboxyphenyl) propane dianhydride, p-phenylene bis(trimellitic monoester anhydride), p-phenylenebis(trimellitic monoester anhydride), m-terphenyl-3,4,3',4'-tetracarboxylic dianhydride, p-terphenyl-3,4,3',4'-tetracarboxylic dianhydride, 1,3-bis(3,4-dicarboxyphenoxy) benzene dianhydride, 1,4-bis(3,4-dicarboxyphenoxy) benzene dianhydride, 1,4-bis(3,4-dicarboxyphenoxy) biphenyl dianhydride, 2,2-bis[(3,4-dicarboxyphenoxy)phenyl] propane dianhydride (BPADA), 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, and 4,4'-(2,2-hexafluoroisopropylidene) diphthalic dianhydride.

8. The polyimide paint according to claim 1, wherein the diamine monomer comprises at least one selected from the following: 1,4-diaminobenzene (PPD), 4,4'-diaminodiphenyl ether (ODA), 2,2-bis(aminophenoxy)benzene propane (BAPP), m-phenylenediamine, 3,3'-dimethylbenzidine, 2,2'-dimethylbenzidine, 2,4-diaminotoluene, 2,6-diaminotoluene, 3,5-diaminobenzoic acid (DABA), 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane (4,4'-methylenedianiline), 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'-dimethoxybiphenylamine, 2,2'-dimethoxybiphenylamine, 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-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-phenylphenoxy)benzophenone, 3,3'-diamino-4,4'-bis(4-phenylphenoxy)benzophenone, 1,3-bis(3-aminophenylthio)benzene, 1,3-bis(4-aminophenylthio)benzene, 1,4-bis(4-aminophenylthio)benzene, 1,3-bis(3-aminophenylsulfone)benzene, 1,3-bis(4-aminophenylsulfone)benzene, 1,4-Bis(4-aminophenyl)sulfone, 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]sulfide, bis[3-(4-aminophenoxy)phenyl]sulfide, bis[4-(3-aminophenoxy)phenyl]sulfide, bis[4-(4-aminophenoxy)phenyl]sulfide, bis[3-(3-aminophenoxy)phenyl]sulfone, bis[3-(4-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(4-aminophenoxy)phenyl]sulfone, bis[3-(3-aminophenoxy)phenyl]methane, bis[3-(4-aminophenoxy)phenyl]methane, bis[4-(3-aminophenoxy)phenyl]methane, bis[4-(4-aminophenoxy)phenyl]methane, 2,2-bis[3-(3-aminophenoxy)phenyl]propane, 2,2-bis[3-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(3-aminophenoxy)phenyl]propane, 2,2-bis[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., 9. The polyimide varnish according to claim 1, wherein the polyamic acid solution contains 90 mol% to 110 mol% of the diamine monomer.

10. The polyimide varnish according to claim 1, wherein the polyamic acid solution contains 90 mol% to 110 mol% of the dianhydride monomer.

11. The polyimide varnish according to claim 1, wherein the polyamic acid solution contains the dianhydride monomer and the diamine monomer in a molar ratio of 6:4 to 4:

6.

12. The polyimide varnish according to claim 1, wherein the polyamic acid solution further contains an organic solvent.

13. The polyimide paint according to claim 12, wherein the organic solvent includes at least one selected from the following: N-methylpyrrolidone (NMP), N,N'-dimethylformamide (DMF), N,N'-diethylformamide (DEF), N,N'-dimethylacetamide (DMAc), dimethylpropionamide (DMPA), naphtha, diethylpropionamide (DEPA), N-ethylpyrrolidone (NEP), xylene, γ-butyrolactone, γ-valerolactone, and N,N-diethylacetamide (EAc).

14. The polyimide paint according to claim 1, wherein the solid content of the polyimide paint is 5% by weight to 40% by weight.

15. The polyimide paint according to claim 1, wherein the thermal conductivity after curing the polyimide paint is 0.2 W / mK to 10.0 W / mK.

16. The polyimide paint according to claim 1, wherein the glass transition temperature (Tg) after curing the polyimide paint is 200 °C to 450 °C.

17. The polyimide paint according to claim 1, wherein the thermal decomposition temperature (Td) at 5% weight loss after curing the polyimide paint is 400 °C to 600 °C.

18. A polyimide coating material comprising a cured product of the polyimide paint according to any one of claims 1 to 17.

19. A wire comprising the polyimide coating material according to claim 18.

20. An electronic device comprising the wire according to claim 19.

Images