Paint compositions for electrostatic coating

Abstract

It can improve coating efficiency. [Solution] The electrostatic coating paint composition contains an epoxy resin lacquer, a diluting organic solvent, and one or more thickeners selected from the group consisting of calcium carbonate, magnesium silicate, silica, mica, amide wax, and cellulose-based materials, and has a viscosity in the range of 10s to 60s.

Description

[Technical Field]

[0001] The present invention relates to an electrostatic coating composition that can be used, for example, as an insulating coating or rust-preventive coating for various automobile parts, and more particularly to an electrostatic coating composition that can improve coating efficiency. [Background technology]

[0002] Vehicle bodies and parts, such as those of automobiles, are painted for purposes such as protecting the base material, enhancing aesthetics, and providing functionality (corrosion prevention, etc.). In particular, with the recent proliferation of electric vehicles (BEVs), the need for insulating properties in their parts has increased, leading to a rise in the use of insulating paints. Furthermore, electrostatic painting is used as a painting method for insulating paints, rust-preventive paints, etc., with the aim of improving coating efficiency (paint yield) by reducing the amount of paint used and waste paint, making the equipment more compact by reducing the number of coats, and preventing contamination of the paint booth.

[0003] As disclosed in Patent Documents 1 and 2, in insulating coatings, epoxy resin coatings with excellent electrical insulation properties are used. Furthermore, in these epoxy resin coatings, layered clay minerals such as clay are incorporated into the epoxy resin coating to improve thixotropy, mechanical strength, and heat resistance. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2005-251543 [Patent Document 2] Japanese Patent Publication No. 2008-201823 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, according to the inventors' experimental research, epoxy resin paints containing layered viscous minerals such as clay experienced a significant decrease in liquid resistance (paint resistance) due to the addition of these minerals. As a result, electrostatic coating would result in electrical leakage and a significantly lower coating efficiency, making them unsuitable for electrostatic coating.

[0006] Therefore, the object of the present invention is to provide a coating composition for electrostatic coating that can improve coating efficiency. [Means for solving the problem]

[0007] The electrostatic coating paint composition of the invention of claim 1 contains an epoxy resin lacquer, a diluting organic solvent, and one or more thickeners selected from the group consisting of calcium carbonate, magnesium silicate, silica, mica, amide wax, and cellulose-based materials, and has a viscosity in the range of 10s to 60s, preferably 15s to 55s, and more preferably 20s to 55s.

[0008] The epoxy resin lacquer mentioned above is a one-component type made by dissolving epoxy resin in a solvent. The above-mentioned diluting organic solvent dilutes the solution concentration of the epoxy resin lacquer and reduces its viscosity, and preferably contains at least acetone. The above-mentioned thickening agents are used to increase viscosity or adjust thixotropy, and one or more selected from the group consisting of calcium carbonate, magnesium silicate, silica, mica, amide wax, and cellulose-based materials are used. The above viscosity was measured (at 20°C) using a Ford Cup viscometer No. 4 (made of stainless steel, conforming to standard: ASTM D1200-10 (2018)).

[0009] The electrostatic coating paint composition of the invention according to claim 2 has a liquid resistance within the range of 0.03 MΩ or more and 10.0 MΩ or less, preferably 0.03 MΩ or more and 5.0 MΩ or less, and more preferably 0.04 MΩ or more and 1.0 MΩ or less. The above liquid resistance (paint resistance) was measured using a Landsburg paint tester (at 20°C).

[0010] The electrostatic coating paint composition of the invention of claim 3 contains an epoxy resin lacquer, a diluent organic solvent, and a thickener, and has a viscosity in the range of 10s to 60s, preferably 15s to 55s, more preferably 20s to 55s, and a liquid resistance in the range of 0.03MΩ to 10.0MΩ, preferably 0.03MΩ to 5.0MΩ, more preferably 0.04MΩ to 1.0MΩ.

[0011] The epoxy resin lacquer mentioned above is a one-component type made by dissolving epoxy resin in a solvent. The above-mentioned diluting organic solvent dilutes the solution concentration of the epoxy resin lacquer and reduces its viscosity, and preferably contains at least acetone. The above-mentioned thickening agents are used to increase viscosity or adjust thixotropy, and one or more selected from the group consisting of calcium carbonate, magnesium silicate, silica, mica, amide wax, and cellulose-based materials are used. The above viscosity was measured (at 20°C) using a Ford Cup viscometer No. 4 (made of stainless steel, conforming to standard: ASTM D1200-10 (2018)). The above liquid resistance (paint resistance) was measured using a Landsburg paint tester (at 20°C).

[0012] The diluting organic solvent in the electrostatic coating paint composition of the invention of claim 4 contains at least acetone.

[0013] The epoxy resin in the epoxy resin lacquer of the electrostatic coating paint composition of the invention of claim 5 preferably has a glass transition temperature in the range of 40°C or higher and 100°C or lower, more preferably 50°C or higher and 100°C or lower, and even more preferably 60°C or higher and 95°C or lower. The above glass transition point (Tg) is determined by measurement using the DSC method.

[0014] In the electrostatic coating composition of the invention according to claim 6, the epoxy resin lacquer is preferably within the range of 30 to 70% by mass, more preferably 30 to 65% by mass, still more preferably 35 to 60% by mass, the diluting organic solvent is preferably within the range of 30 to 70% by mass, more preferably 30 to 65% by mass, still more preferably 35 to 60% by mass, and the thickener is preferably within the range of 0.1 to 20% by mass, more preferably 0.3 to 20% by mass, still more preferably 0.5 to 18% by mass in terms of formulation.

[0015] The epoxy resin of the epoxy resin lacquer in the electrostatic coating composition of the invention according to claim 7 is a modified epoxy resin. The above modified epoxy resin is preferably one obtained by polymerizing a bisphenol A type epoxy resin with a modifier to increase its molecular weight, and examples thereof include amine-modified epoxy resin, aliphatic amine-modified epoxy resin, urethane-modified epoxy resin, acrylic-modified epoxy resin, polyester-modified epoxy resin, isocyanate-modified epoxy resin, modified phenoxy resin, and the like.

Advantages of the Invention

[0016] The electrostatic coating composition according to the invention of claim 1 contains an epoxy resin lacquer, a diluting organic solvent, and at least one thickener selected from the group consisting of calcium carbonate, magnesium silicate, silica, mica, amide wax, and cellulose-based materials, and has a viscosity within the range of 10 s or more and 60 s or less, preferably 15 s or more and 55 s or less, more preferably 20 s or more and 55 s or less.

[0017] Through diligent experimental research by the inventors, we have discovered that by blending epoxy resin lacquer, a diluting organic solvent, and one or more thickeners selected from the group consisting of calcium carbonate, magnesium silicate, silica, mica, amide wax, and cellulose-based materials, and by setting the viscosity of the composition within the range of 10s to 60s, the coating efficiency can be improved, thus completing the present invention. In other words, by combining epoxy resin lacquer, a diluting organic solvent, and one or more thickeners selected from the group consisting of calcium carbonate, magnesium silicate, silica, mica, amide wax, and cellulose-based materials, the viscosity can be set to a range of 10s to 60s, preferably 15s to 55s, and more preferably 20s to 55s, making it suitable for electrostatic coating and allowing it to be sprayed in a mist from an electrostatic coating machine and reach the workpiece. Furthermore, if the thickener is one or more selected from the group consisting of calcium carbonate, magnesium silicate, silica, mica, amide wax, and cellulose-based materials, a significant decrease in liquid resistance due to the addition of the thickener is suppressed. Therefore, the coating efficiency can be improved.

[0018] According to the electrostatic coating paint composition of the invention of claim 2, the liquid resistance is in the range of 0.03 MΩ or more and 10.0 MΩ or less, preferably 0.03 MΩ or more and 5.0 MΩ or less, and more preferably 0.04 MΩ or more and 1.0 MΩ or less. Therefore, when electrostatic coating is performed, electricity is less likely to leak, and the amount of charge of the particles is moderately large, making it easy to adhere to the object to be coated. In addition to the effects described in claim 1, high adhesion efficiency can be obtained.

[0019] According to the electrostatic coating paint composition of claim 3, it contains an epoxy resin lacquer, a diluent organic solvent, and a thickener, and has a viscosity in the range of 10s to 60s, preferably 15s to 55s, more preferably 20s to 55s, and a liquid resistance in the range of 0.03MΩ to 10.0MΩ, preferably 0.03MΩ to 5.0MΩ, more preferably 0.04MΩ to 1.0MΩ.

[0020] Through diligent experimental research by the present inventors, it has been found that coating efficiency can be improved if the viscosity of an electrostatic coating paint composition containing epoxy resin lacquer, a diluent organic solvent, and a thickener is in the range of 10s to 60s, preferably 15s to 55s, more preferably 20s to 55s, and the liquid resistance is in the range of 0.03MΩ to 10.0MΩ, preferably 0.03MΩ to 5.0MΩ, more preferably 0.04MΩ to 1.0MΩ, thus completing the present invention. In other words, if the viscosity is within the range of 10s to 60s, preferably 15s to 55s, and more preferably 20s to 55s, it can be made suitable for electrostatic coating by being sprayed in a mist from an electrostatic coating machine and reaching the object to be coated. Furthermore, if the liquid resistance is within the range of 0.03MΩ to 10.0MΩ, preferably 0.03MΩ to 5.0MΩ, and more preferably 0.04MΩ to 1.0MΩ, it will be less prone to electrical leakage, and the particles will have an appropriate amount of charge, making it easy to adhere to the object to be coated. Thus, the coating efficiency can be improved.

[0021] According to the electrostatic coating paint composition of claim 4, since the diluting organic solvent contains at least acetone, in addition to the effects described in claim 1 or claim 3, the desired viscosity can be easily adjusted without significantly reducing the liquid resistance.

[0022] According to the electrostatic coating paint composition of claim 5, the epoxy resin lacquer has a glass transition temperature of preferably 40°C or higher and 100°C or lower, more preferably 50°C or higher and 100°C or lower, and even more preferably 60°C or higher and 95°C or lower, so that the coating strength can be maintained even in areas used in high-temperature environments. Therefore, in addition to the effects described in claim 1 or claim 3, it is also suitable for coating areas used in high-temperature environments.

[0023] According to the electrostatic coating paint composition of claim 6, the epoxy resin lacquer is preferably in the range of 30 to 70% by mass, more preferably 30 to 65% by mass, and even more preferably 35 to 60% by mass; the diluting organic solvent is preferably in the range of 30 to 70% by mass, more preferably 30 to 65% by mass, and even more preferably 35 to 60% by mass; and the thickening agent is preferably in the range of 0.1 to 20% by mass, more preferably 0.3 to 20% by mass, and even more preferably 0.5 to 18% by mass. Therefore, in addition to the effects described in claim 1 or claim 3, the desired viscosity can be easily adjusted.

[0024] According to the electrostatic coating paint composition of claim 7, since the epoxy resin of the epoxy resin lacquer is a modified epoxy resin, in addition to the effects described in claim 1 or claim 3, it is possible to improve adhesion to metals and rust prevention. [Brief explanation of the drawing]

[0025] [Figure 1] Figure 1 is a graph showing the relationship between liquid resistance (MΩ) and coating efficiency (%) for samples A to H containing epoxy resin lacquer, a diluting organic solvent, and a thickener. [Modes for carrying out the invention]

[0026] [Embodiment] Embodiments of the present invention will be described below. The electrostatic coating paint composition according to an embodiment of the present invention contains an epoxy resin lacquer, a diluting organic solvent, and a thickener, and is a solvent-based paint composition.

[0027] Epoxy resin lacquers are prepared by dissolving a one-component lacquer-type epoxy resin in a solvent. Examples of epoxy resins include bisphenol-based epoxy resins (including phenoxy resins) such as bisphenol A and bisphenol F, glycidyl ester-based epoxy resins, glycidylamine-based epoxy resins, phenol novolac-based epoxy resins, and cresol-based epoxy resins. Preferably, bisphenol A-type epoxy resins are modified epoxy resins obtained by increasing their molecular weight or adding functional groups using a modifying agent. Examples include aliphatic-modified epoxy resins, amine-modified epoxy resins, aliphatic amine-modified epoxy resins, urethane-modified epoxy resins, acrylic-modified epoxy resins, polyester-modified epoxy resins, isocyanate-modified epoxy resins, alkyl-modified epoxy resins, alkyl ether-modified epoxy resins, alkylphenol novolac-modified epoxy resins, hydroxyl-modified epoxy resins, and modified phenoxy resins (e.g., hydroxyl-containing modified phenoxy resins). Modification of bisphenol-based epoxy resins, etc., to increase molecular weight or add functional groups makes it possible to improve adhesion to metals (aluminum, stainless steel, steel plates, non-ferrous metals, etc.) and corrosion resistance.

[0028] Furthermore, organic solvents are preferred as solvents for epoxy resin lacquers, such as hydrocarbons like toluene and xylene; ketones like methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), and cyclohexanone; esters like propyl acetate, butyl acetate, and ethyl acetate; cellosolve acetates like propylene glycol monomethyl ether acetate (PMA), methyl cellosolve acetate, and cellosolve acetate; cellosolves like methyl cellosolve and ethyl cellosolve; alcohols like isopropyl alcohol (IPA) and butanol; cyclohexane; and propylene glycol monomethyl ether (PM).

[0029] In addition, such epoxy resin lacquers have a solid content (non-volatile content) of epoxy resin of, for example, 30 to 80% by mass, preferably 35 to 50% by mass, and more preferably 35 to 45% by mass, and a solvent (volatile content) of, for example, 20 to 70% by mass, preferably 50 to 65% by mass, and more preferably 55 to 65% by mass. Furthermore, the weight-average molecular weight of the epoxy resin (polystyrene equivalent value obtained by gel permation chromatography) is preferably 5,000 to 150,000, more preferably 15,000 to 100,000, and even more preferably 15,000 to 80,000.

[0030] Examples of commercially available epoxy resin lacquers include Arakid 9201N, 9203N, 9205, 9208, KA-1439A, 1439A, Modipix 401, 408, 409 from Arakawa Chemical Industries, Ltd., and EPICLON® H-303-45M, H-360, EXA-192 from DIC Corporation.

[0031] Preferably, the epoxy resin of the epoxy resin lacquer has a glass transition temperature (Tg) measured by DSC method within the range of 40°C to 100°C, more preferably 50°C to 100°C, and even more preferably 60°C to 95°C. This allows the coating strength to be maintained even when the coated object is used in a high-temperature environment, such as 40°C to 80°C, making it suitable for coating parts used in high-temperature environments.

[0032] Preferably, one or more of the following solvents are used as the diluent organic solvent: ketone-based, aromatic hydrocarbon-based, non-aromatic hydrocarbon-based, alcohol-based, ether-based, and ester-based solvents, and more preferably, at least acetone is used. If acetone is used, it can be diluted to a predetermined viscosity with a small amount of addition, making viscosity adjustment easy, and it does not reduce liquid resistance to any significant degree. The acetone content of the diluent organic solvent is preferably 5% by mass or more and 70% by mass or less, more preferably 5% by mass or more and 60% by mass or less, and even more preferably 10% by mass or more and 55% by mass or less. In the entire paint composition, the acetone content is preferably 3% by mass or more and 20% by mass or less, more preferably 4% by mass or more and 15% by mass or less, and even more preferably 5% by mass or more and 10% by mass or less.

[0033] Examples of ketone-based solvents include acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone, and cyclohexanone. Examples of aromatic hydrocarbon solvents include benzene, toluene, xylene, ethylbenzene, naphthalene, styrene monomer, and aromatic hydrocarbon mixtures. Examples of non-aromatic aqueous carbonized solvents include hexane and cyclohexane. Examples of alcohol-based solvents include methanol (methyl alcohol), ethanol (ethyl alcohol), butanol (butyl alcohol), isopropyl alcohol (IPA), n-propyl alcohol, isobutyl alcohol, n-butyl alcohol, 2-ethylbutyl alcohol, 2-ethylhexyl alcohol, cyclohexanol, methylamyl alcohol, phenol, ethylene glycol, and propylene glycol. Examples of ether-based solvents include dimethyl ether, THF, propylene glycol monomethyl ether (1-methoxy-2-propanol), ethylene glycol monomethyl ether, ethylene glycol monoethyl ether (Cellosolve), ethylene glycol monobutyl ether (butyl cellosolve), 3-methoxy-3-methyl-1-butanol, and ethylene glycol monopropyl ether. Examples of ester-based solvents include ethyl acetate and butyl acetate.

[0034] The thickening agent functions as a viscosity-enhancing agent and also as a thixotropic agent that imparts thixotropic fluidity. One or more of the following are used: calcium carbonate, magnesium silicate, silica, mica, amide wax, and cellulose-based materials. Adding calcium carbonate, magnesium silicate, silica, mica, amide wax, or cellulose-based thickeners can suppress a significant decrease in liquid resistance. Preferably, if calcium carbonate, magnesium silicate, silica, mica, or cellulose-based thickeners are used, they will also have high adhesion to metals such as aluminum.

[0035] Among these, calcium carbonate is preferred due to its low cost and availability. The calcium carbonate can be light calcium carbonate (synthetic calcium carbonate, precipitated calcium carbonate) or heavy calcium carbonate (natural calcium carbonate). In particular, surface-treated calcium carbonate (surface-treated calcium carbonate) is preferable because it can impart appropriate viscosity and thixotropy as ultrafine precipitated calcium carbonate (UFPCC), and its viscosity can be controlled by selecting the primary particle size (BET specific surface area) of the surface-treated calcium carbonate, and its thixotropy can be controlled by selecting the surface treatment agent for the calcium carbonate. Examples of surface treatment agents for calcium carbonate include fatty acids such as abietic acid, stearic acid, and 12-hydroxystearic acid. For example, calcium carbonate surface-treated with a fatty acid can be used as the surface-treated calcium carbonate.

[0036] From the viewpoint of dispersibility, such calcium carbonate is used, preferably having a primary particle size (median diameter) in the range of 10 to 150 nm, more preferably 30 to 120 nm, and even more preferably 80 to 110 nm, and a BET specific surface area of ​​preferably 5 to 40 m². 2 / g, comfortable, 10-35m 2 / g, more preferably 13-20m 2 Products within the range of / g are used. The shape of the calcium carbonate is not particularly important, but from the standpoint of low cost, cubic calcium carbonate is preferred. Examples of commercially available calcium carbonates include Viscoexcel 30, 30HV, Shirotsuya CC, CCR-S510, CC-R, CCR-S, Viscolite-EL10, EL20, OS, RC10, RC20, HL, and Vigot-10, all manufactured by Shiraishi Kogyo Co., Ltd.

[0037] Furthermore, according to the definitions of terms in the text and commentary of JIS Z 8901 "Test Powders and Test Particles," "median diameter" refers to the particle size (diameter) at which the number (or mass) of particles larger than a certain particle size accounts for 50% of the total particle size distribution of the powder; that is, the 50% oversize particle size, and is usually called the median diameter or 50% particle size.50 This is expressed as follows. By definition, the size of the particle group is expressed by the average particle diameter and the median diameter, but here, it is the value displayed in the product description and measured by the laser diffraction and scattering method. And this "median diameter measured by the laser diffraction and scattering method" is the particle diameter (D) at which the cumulative weight parts account for 50% of the particle size distribution obtained by the laser diffraction and scattering method using a laser diffraction particle size distribution analyzer. 50 This refers to [the specified value]. Note that the above figures are not strictly accurate, and there are variations between products. Including measurement errors, this does not rule out the possibility of errors of approximately 10% or less. From the perspective of this error, the distribution is normal, and particle size follows a normal distribution. Therefore, even if we consider the median diameter to be approximately equal to the average particle diameter, the difference between the two is within a few percent, which is considered within the margin of error.

[0038] Furthermore, magnesium silicate is generally a compound represented as xMgO·ySiO2·nH2O (n≧0, for example, 2MgO·6SiO2·nH2O), and may be synthetic magnesium silicate or natural magnesium silicate, and may be either heavy or light. Additionally, hydrated magnesium silicate (3MgO·4SiO2·H2O), such as talc, may be used, or silicate minerals such as apatalgite or sepiolite may be used. Examples of commercially available magnesium silicate products include MICRO ACE D-600, D-800, D-1000, P-2, P-3, P-4, P-6, P-8, SG-95, and Talc MS from Nippon Talc Co., Ltd.; LMS-100, LMS-200, LMS-300, LMS-350, LMS-400, LMP-100, PKP-53, PKP-80, PKP-81, FH104A, and PK-C from Fuji Talc Industrial Co., Ltd.; GH7 and MST from Hayashi Chemical Co., Ltd.; P Talc, PH Talc, PS Talc, TTK Talc, TT Talc, T Talc, ST Talc, Hytron, Microlight, Hylac, and Hymicron from Takehara Chemical Industry Co., Ltd.; and Crown Talc (registered trademark) from Matsumura Sangyo Co., Ltd.

[0039] As the silica, preferably, it is fumed silica produced by a dry method as amorphous silica, and it may be hydrophobic (for example, hydrophobized with halogenated silane, silazane such as hexamethyldisilazane, low molecular weight siloxane, organopolysiloxane, organopolysilazane, chlorosilane, alkoxysilane, etc.) or hydrophilic. From the viewpoint of the thickening effect, the primary particle diameter (median diameter) is preferably in the range of 4 to 100 nm, more preferably 5 to 50 nm, and still more preferably 5 to 35 nm, and the BET specific surface area is preferably 30 to 800 m 2 / g, more preferably 50 to 700 m 2 / g, and still more preferably 100 to 500 m 2 / g within the range is used. Examples of commercially available fumed silica include AEROSIL (registered trademark) 50, 90, 130, 200, 300, 380, R974, R972, R972V, 972F, R805, R812, R812S, R816, R8200, RY200, RX200, RY200S, R202, R7200, R8200, R9200 manufactured by EVONIK INDUSTRIES and Nippon Aerosil Co., Ltd.; Rheoseal (registered trademark) QS30, QS102, QS103, MT10, MT30 manufactured by Tokuyama Corporation; WACKER HDK (registered trademark) manufactured by Asahi Kasei Wacker Silicone Co., Ltd.; Cab-O-Sil (registered trademark) M-5, MS-5, MS-7, H-300, TS-720, TS-530, TG-308F manufactured by Cabot Japan Ltd. and Cabot Corporation; Nipsil SS series manufactured by Tosoh Silica Corporation, etc.

[0040] As mica, it may be natural mica (natural mica) of a scaly substrate obtained by pulverizing ore mica, or fluorophlogopite (KMg3AlSi3O 10 F2), potassium tetrasilicate mica (KMg 2.5 AlSi4O 10 F2), sodium tetrasilicate mica (NaMg 2.5 AlSi4O 10 F2), Na teniolite (NaMg2LiSi4O 10F2), LiNa teniolite (LiMg2LiSi4O 10 It may also be synthetic mica (synthetic mica) based on F2) etc. (for example, muscovite, sericite, phlocopite, biotite, fluorinated phlocopite, red mica, soda mica, vanadine mica, illite, tin mica, paragonite, brittle mica, etc.). Commercially available mica products include, for example, wet mica 100M, 300M, and 1000M from Osaka Mica Industry Co., Ltd.; Repco Mica S-200HG, S-325, S-400, M-200, M-325, and M-400 from Repco Co., Ltd.; mica powder from Fukuoka Talc Industry Co., Ltd.; mica A-21S, AB-25S, A-41S, YM-21S, YM-31S, SYA-21R, and SB-061R from Yamaguchi Mica Co., Ltd.; and Suzoraite 350-PO, 325-PO, 325-HK, 325-S, 80-SF, 200-PO, 200-S, 200-HK, 150-NY, 150-PO, and 150-S from Imerys Specialties Japan. Examples include MICA WG-160, WG-325, 4-K, C-1000, C-3000, and C-4000 from Minerals.

[0041] Amid waxes consist of fatty acids (such as lauric acid, myristic acid, palmitic acid, stearic acid, linoleic acid, linolenic acid, coconut oil fatty acid, castor oil fatty acid, and other higher fatty acids) and amines (such as N,N-dimethylaminopropylamine, N,N-diethylaminopropylamine, N,N-diethylaminoethylamine, N-aminoethylmorpholine, and N-methylpiperazine). Examples include fatty acid amide waxes such as stearate amide, oleate amide, palmitate amide, ethylenebisoleate amide, and hexamethylenebisoleate amide, as well as polyamide waxes. Examples of commercially available amide waxes include Talen 7200-20 from Kyoeisha Chemical Co., Ltd., DISPARLON (registered trademark) 3500, 6650, 6900-20X, RE-8000, 305, 4200-20, and A630-20X from Kusumoto Kasei Co., Ltd., Monoral 3300 from HS CHEM, and Recolb FA1 from Clariant Chemicals Co., Ltd.

[0042] Cellulose-based thickeners include cellulose ethers such as methylcellulose, hydroxyethylcellulose, hydroxypropylmethylcellulose, carboxymethylcellulose, ethylcellulose, butylcellulose, hydroxypropylcellulose, carboxyethylcellulose, and ethylhydroxyethylcellulose. Commercially available cellulose-based thickeners include SANHEC L from Sansho Co., Ltd. and hydroxypropylcellulose (HPC-H) from Nippon Soda Co., Ltd.

[0043] Here, electrostatic painting (also called electrostatic atomization painting or electrostatic micro-atomization painting) is a painting method in which the electrode pin (corona pin) at the tip of an electrostatic painting machine (such as an electrostatic spray gun) is used as the negative (-) pole, and the object to be painted is grounded (earthed) as the positive (+) pole, causing it to be electrostatically charged by the electrostatic sensing phenomenon, and a voltage is applied to the electrostatic painting machine. Specifically, a high voltage (for example, -30,000 to -150,000V) from a DC current is applied to the electrode pin of the electrostatic painting machine, ionizing the surrounding air through corona discharge, forming an electrostatic field between the two electrodes (for example, with an inter-electrode distance of 50 to 300 mm), and paint particles atomized from the electrostatic painting machine within the electrostatic field are negatively charged and allowed to ride on the electrostatic field (fly along the electric field lines), utilizing the Coulomb force of static electricity to adhere the paint to the object to be painted. This electrostatic coating method creates an electrostatic field that extends to the sides and back of the object to be coated. This allows paint particles to wrap around and adhere to these areas, resulting in better adhesion to the back of the object, higher coating efficiency, and a simpler coating process. Methods for atomizing the paint include air-based, airless, and rotary atomization (such as the bell type). Electrostatic coating machines come in stationary, automatic, and handheld types. The bell rotary atomization method generates a liquid column of paint using the centrifugal force of a rapidly rotating bell cup, which can then be atomized using shaping air (atomizing air) or electrostatic force.

[0044] The electrostatic coating composition of this embodiment is suitable for insulating coatings for automotive parts, such as insulating coatings for temperature control units in electric vehicles, and for rust-preventive coatings. The substrates to which the electrostatic coating composition of this embodiment is applied are not particularly limited, but for example, it can be applied to steel sheets such as galvanized steel sheets, zinc alloy plated steel sheets, cold-rolled steel sheets, stainless steel sheets, and tin-plated steel sheets, metal substrates such as aluminum sheets and aluminum alloys, and plastic substrates. These substrates are painted after being degreased and surface-treated as necessary, and in the case of resin substrates (for example, polyolefin-based or polyurethane-based), a conductive primer or the like is applied as an undercoat as necessary before painting. In the case of electrostatic painting of automotive parts, the coating is applied to the workpiece after it has been degreased, static-free, and dust-free, or after it has been degreased, static-free, and dust-free, and a conductive primer or similar undercoat has been applied as needed. The coating is then cured by drying (baking) in a drying oven at a predetermined temperature above the boiling point of the solvent for a predetermined time.

[0045] Furthermore, the electrostatic coating composition of this embodiment, which contains epoxy resin lacquer, a diluting organic solvent, and one or more thickeners selected from the group consisting of calcium carbonate, magnesium silicate, silica, mica, amide wax, and cellulose-based materials, uses a one-component epoxy resin lacquer in which the epoxy resin is dissolved in the solvent. As a result, a hardener for the epoxy resin is not required, as is the case with two-component types. Moreover, high-temperature baking is not required because a hardener is not used, and the complicated process of mixing the epoxy resin and hardener is eliminated. The coating film is formed by the vaporization of the solvent and diluting organic solvent in the lacquer.

[0046] In this embodiment, the electrostatic coating composition consists of epoxy resin and thickeners in the lacquer, which are non-volatile components that form the coating film, while the solvent and diluent organic solvent in the lacquer are volatile components. That is, the coating film formed from the electrostatic coating composition by the evaporation of the solvent and diluent organic solvent in the lacquer contains epoxy resin and thickener components. In the case of electrostatic coating of automobile parts, the coating is applied to the object to be coated so that the cured film thickness after coating is, for example, 10 to 100 μm, preferably about 10 to 50 μm. When implementing the present invention, additives (for example, pigments, dispersants, thickeners, defoaming agents, preservatives, fungicides, matting agents, surfactants, anti-sagging agents, anti-color separation agents, plasticizers, anti-skinning agents, leveling agents, etc.) may be added as needed.

[0047] In particular, the electrostatic coating paint composition of this embodiment uses an epoxy resin lacquer, and its resin concentration is diluted with a diluting organic solvent. Furthermore, the viscosity is set to a range of 10s to 60s, preferably 15s to 55s, and more preferably 20s to 55s, by adding one or more thickeners selected from the group consisting of calcium carbonate, magnesium silicate, silica, mica, amide wax, and cellulose-based materials. If the viscosity is too high, it is difficult to spray it in a mist from the electrostatic coating machine, and if the viscosity is too low, it will leak and flow out even if filled into the electrostatic coating machine, making it difficult to spray it in a mist and reach the object to be coated. If the viscosity is within the range of 10s to 60s, preferably 15s to 55s, and more preferably 20s to 55s, a large proportion can be sprayed in a mist from the electrostatic coating machine and reach the object to be coated, resulting in a viscosity suitable for electrostatic coating. The thixotropic index (Ti value) at this time is preferably in the range of 1.5 to 8.0, more preferably in the range of 1.5 to 7.0. Furthermore, if one or more thickening agents selected from the group consisting of calcium carbonate, magnesium silicate, silica, mica, amide wax, and cellulose-based materials are used, a significant decrease in liquid resistance is suppressed. Therefore, the coating efficiency can be improved.

[0048] Here, the electrostatic coating composition according to this embodiment will be specifically described with reference to examples. The electrostatic coating compositions according to Examples 1 to 5 are composed of epoxy resin lacquer, a diluting organic solvent, and a thickening agent. The electrostatic coating compositions according to Examples 1 to 5 are prepared by mixing and dispersing the epoxy resin lacquer and the diluting organic solvent, and then further mixing and dispersing the thickening agent.

[0049] The electrostatic coating compositions of Examples 1 to 5 use a modified epoxy resin, obtained by modifying bisphenol A type epoxy resin, as the epoxy resin lacquer, dissolved in an organic solvent (toluene, methyl ethyl ketone, isopropyl alcohol, propylene glycol monomethyl ether acetate) (glass transition temperature (Tg) by DSC method: 94°C, non-volatile content (resin solids): 39-41%, molecular weight (MV): 50,000), and also use a diluent organic solvent containing 15.5% by mass of acetone, differing only in the type of thickener used.

[0050] In Example 1, 43 parts by mass of epoxy resin lacquer (non-volatile content (resin solids): 39-41% by mass, volatile content (solvent): 59-61% by mass), 47 parts by mass of a diluted organic solvent containing 15.5% by mass of acetone, and surface-treated calcium carbonate A with a primary particle size of 100 nm as a thickener (treatment agent: fatty acid, BET specific surface area: 14.0 m²) were used. 2 A coating composition for electrostatic painting was prepared by blending 10 parts by mass of ( / g) with a viscosity of 35s.

[0051] In Example 2, 43 parts by mass of epoxy resin lacquer (non-volatile content (resin solids): 39-41% by mass, volatile content (solvent): 59-61% by mass), 47 parts by mass of a diluted organic solvent containing 15.5% by mass of acetone, and surface-treated calcium carbonate B with a primary particle size of 80 nm as a thickener (treatment agent: fatty acid, BET specific surface area: 18.0 m²) were used. 2 A coating composition for electrostatic painting was prepared by blending 10 parts by mass of ( / g) with a viscosity of 50s.

[0052] In Example 3, 43 parts by mass of epoxy resin lacquer (non-volatile content (resin solids): 39-41% by mass, volatile content (solvent): 59-61% by mass), 47 parts by mass of a diluted organic solvent containing 15.5% by mass of acetone, and surface-treated calcium carbonate C (treatment agent: fatty acid, BET specific surface area: 33.0 m²) with a primary particle size of 30 nm as a thickener. 2 A coating composition for electrostatic painting was prepared by blending 10 parts by mass of ( / g) with a viscosity of 50s.

[0053] In Example 4, 46 parts by mass of epoxy resin lacquer (non-volatile content (resin solids): 39-41% by mass, volatile content (solvent): 59-61% by mass), 51 parts by mass of a dilution organic solvent containing 15.5% by mass of acetone, and 10 parts by mass of hydrophilic fumed silica as a thickener were blended to create an electrostatic coating composition with a viscosity of 35s.

[0054] In Example 5, 43 parts by mass of epoxy resin lacquer (non-volatile content (resin solids): 39-41% by mass, volatile content (solvent): 59-61% by mass), 47 parts by mass of a diluted organic solvent containing 15.5% by mass of acetone, and 10 parts by mass of an amide wax-based thickener were blended to create an electrostatic coating composition with a viscosity of 34s.

[0055] In addition, paint compositions related to Comparative Example 1 and Comparative Example 2 were also prepared as comparative examples. In Comparative Example 1, no thickening agent was added, and only 48 parts by mass of epoxy resin lacquer (non-volatile content (resin solids): 39-41% by mass, volatile content (solvent): 59-61% by mass) and 52 parts by mass of a diluted organic solvent containing 15.5% by mass of acetone were added to create a paint composition with a viscosity of 30s.

[0056] In Comparative Example 2, 48 parts by mass of epoxy resin lacquer (non-volatile content (resin solids): 39-41% by mass, volatile content (solvent): 59-61% by mass), 51 parts by mass of a dilution organic solvent containing 15.5% by mass of acetone, and 3 parts by mass of smectite as a thickening agent were blended to create a paint composition with a viscosity of 36s.

[0057] The viscosity measurements mentioned above were performed using a Ford Cup viscometer No. 4 (made of stainless steel, conforming to ASTM D1200-10 (2018)) at 20°C. In addition, the thixotropic index (Ti value) is also determined here as an indicator of thixotropy. The Ti value was calculated using a B-type viscometer with rotor No. 7, at a temperature of 20°C, from the ratio of the viscosity (mPa·S) at 2 rpm to the viscosity (mPa·S) at 2 rpm (2 rpm / 20 rpm).

[0058] The liquid resistance (paint resistance) of the paint compositions of Examples 1 to 5 and Comparative Examples 1 and 2 was measured (at 20°C) using a Landsberg paint tester. The liquid resistance of the paint composition of Example 1 was 0.15 MΩ, the liquid resistance of the paint composition of Example 2 was 0.15 MΩ, the liquid resistance of the paint composition of Example 3 was 0.15 MΩ, the liquid resistance of the paint composition of Example 4 was 0.14 MΩ, the liquid resistance of the paint composition of Example 5 was 0.14 MΩ, the liquid resistance of the paint composition of Comparative Example 1 was 0.30 MΩ, and the liquid resistance of the paint composition of Comparative Example 2 was 0.01 MΩ.

[0059] Then, for each of the coating compositions of Examples 1 to 5 and Comparative Example 2, each coating composition was electrostatically coated onto an aluminum test panel under the same conditions, and the coating efficiency on the test panel was measured.

[0060] Here, coating efficiency is expressed as a percentage, representing the ratio of the mass of solids in the paint used for coating to the mass of the dry coating film (mass of solids) applied to the object being coated. Here, each paint composition was electrostatically applied to a pre-weighed flat substrate (an aluminum test panel) using electrostatic atomization (a bell rotation atomization method in which a liquid column of paint is generated by the centrifugal force of a rapidly rotating bell cup and then atomized by shaping air). After baking at 110°C for 60 minutes, the painted substrate was weighed to determine the dry film weight, and the coating efficiency was calculated using the following formula (1). Coating efficiency (%) = W / (F × NV) × 1000 ... (1) W(g): Mass of applied coating (dry coating mass) = Mass of substrate after coating - Mass of substrate before coating NV (%): Dry solids content of paint = Non-volatile content F(g): Paint output = Mass of spray gun before painting - Mass of spray gun after painting = Paint output per unit time (g / min) × Time spent painting the object (spraying time) (s) / 60

[0061] Table 1 shows the measured results for the formulation composition (parts by mass), viscosity (s), thixotropy (Ti value), liquid resistance (MΩ), and coating efficiency (%) of the paint compositions of Examples 1 to 5 and Comparative Examples 1 and 2.

[0062] [Table 1]

[0063] As shown in Table 1, Comparative Example 1 (blank), which did not contain a thickening agent, had low viscosity and Ti value, making electrostatic coating difficult. However, in Comparative Example 2, the inclusion of smectite as a thickening agent resulted in a suitable viscosity and thixotropy for electrostatic coating. Nevertheless, in Comparative Example 2, the inclusion of smectite as a thickening agent significantly reduced the liquid resistance to 0.01 MΩ compared to Comparative Example 1, resulting in an extremely low coating efficiency of 35%.

[0064] In contrast, the paint composition of Example 1, which contains surface-treated calcium carbonate A with a primary particle size of 100 nm as a thickener and has a viscosity of 30 s; the paint composition of Example 2, which contains surface-treated calcium carbonate B with a primary particle size of 80 nm as a thickener and has a viscosity of 50 s; the paint composition of Example 3, which contains surface-treated calcium carbonate C with a primary particle size of 30 nm as a thickener and has a viscosity of 50 s; the paint composition of Example 4, which contains fumed silica as a thickener and has a viscosity of 35 s; and the paint composition of Example 5, which contains amide wax as a thickener and has a viscosity of 34 s, all had a moderate viscosity and thixotropy suitable for electrostatic coating, and the liquid resistance was 0.14 to 0.15 MΩ without a significant decrease compared to Comparative Example 1, and the coating efficiency was extremely high at 90% or more.

[0065] This suggests that the smectite in Comparative Example 2, being layered and having an organically treated surface with a high concentration of cations, significantly reduces liquid resistance. In contrast, calcium carbonate, magnesium silicate, silica, mica, amide wax, and cellulose-based thickeners do not have organically treated surfaces, so adding them does not significantly reduce liquid resistance, and therefore, it is presumed that this improved coating efficiency. Although not described in the above examples, our experimental research has confirmed that magnesium silicate, mica, and cellulose-based thickeners can also improve coating efficiency without significantly reducing liquid resistance.

[0066] Incidentally, when the dielectric breakdown voltage of the paint compositions of Examples 1 to 5 was measured, it was all within the range of 7.5kV / mm to 9kV / mm. Therefore, the paint compositions of Examples 1 to 5 have high liquid resistance, but also ensure electrical strength against voltage, making them suitable as insulating paints. The dielectric breakdown voltage was measured in accordance with JIS C 2110-1:2016 "Solid electrical insulating materials - Test methods for dielectric breakdown strength - Part 2: Test by DC voltage application," using an dielectric withstand voltage tester (YHTA / D-30K-2KDR manufactured by YAMABISHI) and the automatic withstand voltage method (heating rate 500V / sec, interruption current value: 10mA, electrodes used: disc-shaped electrodes with an outer diameter of 25mmf and a radius of curvature of 2.5mmf at the periphery of both electrodes). Specifically, the dielectric breakdown strength (kV / mm) was determined by gradually increasing the applied voltage until a current of 10mA or more was generated and the voltage application was interrupted, and then dividing the voltage at that moment by the distance between the electrodes.

[0067] Furthermore, according to the inventors' experimental research, the proportions of epoxy resin lacquer, diluent organic solvent, and thickener used in the examples are such that, when the total paint composition is considered as 100% by mass, the epoxy resin lacquer is preferably in the range of 30-70% by mass, more preferably 30-65% by mass, and even more preferably 35-60% by mass; the diluent organic solvent is preferably in the range of 30-70% by mass, more preferably 30-65% by mass, and even more preferably 35-60% by mass; and the thickener is preferably in the range of 0.1-20% by mass, more preferably 0.3-20% by mass, and even more preferably 0.5-18% by mass. Within this range, the desired viscosity can be easily adjusted, and a predetermined viscosity suitable for electrostatic coating can be ensured.

[0068] Furthermore, the epoxy resin (resin solids, non-volatile content) used in the examples is preferably in the range of 5 to 40 parts by mass, more preferably 10 to 35 parts by mass, and even more preferably 10 to 30 parts by mass, per 100 parts by mass of the entire paint composition. The total amount of solvent (volatile matter) in the lacquer and diluent organic solvent used in the examples is in the range of 50 to 90 parts by mass, more preferably 55 to 90 parts by mass, and even more preferably 60 to 85 parts by mass, per 100 parts by mass of the entire paint composition. The amount of the thickening agent used in the examples is preferably 0.1 to 20 parts by mass, more preferably 0.5 to 20 parts by mass, and even more preferably 0.8 to 15 parts by mass, per 100 parts by mass of the entire paint composition. Within this range, the desired viscosity can be easily adjusted, and a predetermined viscosity suitable for electrostatic coating can be ensured.

[0069] Incidentally, the inventors of this invention have conducted measurement experiments on the relationship between liquid resistance and coating efficiency. Specifically, paint compositions containing epoxy resin lacquer, a diluent, and a thickener were prepared with different liquid resistances, and the coating efficiency when these were electrostatically applied was measured.

[0070] Here, the same epoxy resin lacquer as in Examples 1 to 5 above was used, and the same surface-treated calcium carbonate A as in Example 1 was used as a thickener. Furthermore, although acetone was included as a diluent organic solvent, samples A to F (paint compositions) with different liquid resistances were prepared by varying the amount of acetone and the types and amounts of other solvent components (butyl cellosol, xylol, etc.).

[0071] Furthermore, samples G and H (paint compositions) with different liquid resistances were prepared by combining the same epoxy resin lacquer as samples A to F with a diluting organic solvent containing acetone and smectite as a thickening agent, while varying the amount of acetone and the types and amounts of other solvent components (butyl cellosol, xylol, etc.). Samples A to H (paint compositions) all have a viscosity within the range of 10s to 60s.

[0072] Figure 1 shows the relationship between the liquid resistance (MΩ) of these samples A to H (paint compositions) and the coating efficiency (%) when each sample A to H was electrostatically coated onto an aluminum test panel. The conditions for measuring liquid resistance and electrostatic coating were the same as in the above-described embodiment.

[0073] As shown in Figure 1, samples A to F (paint compositions) with a liquid resistance of 0.03 MΩ or higher showed excellent coating efficiency of 90% or more, while samples G and H (paint compositions) with a liquid resistance of less than 0.03 MΩ showed a significant decrease in coating efficiency to less than 50%.

[0074] Furthermore, when sample E (paint composition) with a liquid resistance of 0.15 MΩ and sample G (paint composition) with a liquid resistance of 0.02 MΩ were electrostatically coated onto an aluminum test panel and baked, the adhesion of the paint to the back of the test panel was observed. With sample E, the paint wrapped around and adhered to the back of the test panel, demonstrating high adhesion, which was visually confirmed. In contrast, with sample G, the paint hardly adhered to the back of the test panel. It should be noted that good adhesion allows for the securing of the required film thickness even on objects with complex shapes, thus eliminating the need for repair work and improving the quality of the painted surface.

[0075] When the liquid resistance fell below 0.03 MΩ, the coating efficiency decreased significantly. This is presumed to be because, when the liquid resistance of the paint becomes too low, the paint leaks electricity, meaning that electricity leaks to the paint side connected to ground. This prevents high voltage from being applied to the electrode pins of the electrostatic coating machine, reducing the ionization of the air in the space of the electrostatic field formed between the grounded workpiece (aluminum test panel) on the positive side and the electrostatic coating gun on the negative side. As a result, the charge amount of the paint particles decreases, becoming close to uncharged (charged). Consequently, it is speculated that paint particles sprayed from the electrostatic coating machine either flow back into the machine and adhere to it, or escape the electrostatic field formed between the grounded workpiece (aluminum test panel) on the positive side and the electrostatic coating machine on the negative side and float in the space outside of it.

[0076] On the other hand, if the liquid resistance of the paint composition is 0.03 MΩ or higher, the amount of charge (charge) of the paint particles is high, and the paint particles atomized in the electrostatic field become one with air ions and fly toward the object to be painted by the Coulomb force, making it easier to adhere. On the other hand, paint particles that adhere to an earthed object easily release their charge to the earth, reducing the amount of charge of the paint particles that adhere to the object, and the paint particles that are painted on top of them will experience less charge repulsion, that is, the electrostatic repulsion force decreases, and the sprayed particles adhere within the range where the Coulomb force acts, so it is presumed that the adhesion efficiency will be higher. Furthermore, it is presumed that the higher the amount of charge (charge) of the paint particles, the better their adherence to the object to be painted, which also contributes to the higher adhesion efficiency.

[0077] Furthermore, according to experimental research by the present inventors, it has been confirmed that in an electrostatic coating paint composition containing epoxy resin lacquer, a diluting organic solvent, and one or more thickeners selected from the group consisting of calcium carbonate, magnesium silicate, silica, mica, amide wax, and cellulose-based materials, the liquid resistance is 10.0 MΩ or less, preferably 5.0 MΩ or less, and more preferably 1.0 MΩ or less.

[0078] Therefore, an electrostatic coating composition containing epoxy resin lacquer, a diluting organic solvent, and one or more thickeners selected from the group consisting of calcium carbonate, magnesium silicate, silica, mica, amide wax, and cellulose-based materials will have extremely high coating efficiency if the liquid resistance is 0.03 MΩ or more and 10.0 MΩ or less, preferably 0.03 MΩ or more and 5.0 MΩ or less, and more preferably 0.04 MΩ or more and 1.0 MΩ or less. Note that liquid resistances of 0.03 MΩ or more and 10.0 MΩ or less correspond to electrical resistivity (volume electrical resistance) of 0.1 MΩ·cm or more and 20.0 MΩ·cm or less.

[0079] As described above, the electrostatic coating composition of this embodiment can improve coating efficiency, thereby reducing the amount of paint used and paint residue, and consequently reducing the amount of volatile organic compounds (VOCs) used as solvents, thus reducing the environmental burden. Furthermore, by reducing airborne mist and paint waste, it is possible to reduce running costs and energy required for cleaning work by preventing contamination of paint booths and equipment, and for the collection and post-treatment of waste paint, as well as improve painting speed (productivity), reduce the number of coats and make the paint booth more compact, thereby reducing the energy used for temperature and humidity control in the paint booth, and also contribute to reducing carbon dioxide emissions and carbon neutrality through energy savings.

[0080] As described above, the electrostatic coating paint composition according to the above embodiment contains an epoxy resin lacquer, a diluting organic solvent, and one or more thickeners selected from the group consisting of calcium carbonate, magnesium silicate, silica, mica, amide wax, and cellulose-based materials, and has a viscosity in the range of 10s to 60s, preferably 15s to 55s, and more preferably 20s to 55s.

[0081] By combining epoxy resin lacquer, a diluting organic solvent, and one or more thickeners selected from the group consisting of calcium carbonate, magnesium silicate, silica, mica amide wax, and cellulose-based materials, the viscosity can be set to a range of 10s to 60s, preferably 15s to 55s, and more preferably 20s to 55s, making it suitable for electrostatic coating and allowing it to be sprayed in a mist from an electrostatic coating machine and reach the workpiece. Furthermore, if the thickener is one or more selected from the group consisting of calcium carbonate, magnesium silicate, silica, mica amide wax, and cellulose-based materials, a significant decrease in liquid resistance due to the addition of the thickener is suppressed, and the liquid resistance can be increased. Therefore, it is possible to reduce electrical leakage during electrostatic coating and improve coating efficiency.

[0082] Furthermore, if the electrostatic coating paint composition according to the above embodiment has a liquid resistance within the range of 0.03 MΩ or more and 10.0 MΩ or less, preferably 0.03 MΩ or more and 5.0 MΩ or less, and more preferably 0.04 MΩ or more and 1.0 MΩ or less, then electricity is less likely to leak during electrostatic coating, and the amount of charge of the paint particles is appropriately large, making it easy to adhere to the object to be coated, thereby achieving high adhesion efficiency.

[0083] In the electrostatic coating paint composition according to the above embodiment, the diluting organic solvent contains at least acetone, which allows for easy adjustment of viscosity without significantly reducing liquid resistance.

[0084] In the electrostatic coating paint composition according to the above embodiment, if the epoxy resin in the epoxy resin lacquer has a glass transition temperature preferably in the range of 40°C to 100°C, more preferably 50°C to 100°C, and even more preferably 60°C to 95°C, the coating strength can be maintained even in areas used in high-temperature environments, making it suitable for coating areas used in high-temperature environments.

[0085] In the electrostatic coating paint composition according to the above embodiment, the desired viscosity can be easily adjusted if the epoxy resin lacquer is preferably in the range of 30 to 70% by mass, more preferably 30 to 65% by mass, and even more preferably 35 to 60% by mass, the diluting organic solvent is preferably in the range of 30 to 70% by mass, more preferably 30 to 65% by mass, and even more preferably 35 to 60% by mass, and the thickener is preferably in the range of 0.1 to 20% by mass, more preferably 0.3 to 20% by mass, and even more preferably 0.5 to 18% by mass.

[0086] In the electrostatic coating paint composition according to the above embodiment, if the epoxy resin of the epoxy resin lacquer is a modified epoxy resin, it is possible to improve adhesion to metals and rust prevention because the modification process increases the molecular weight and imparts functional groups.

[0087] The electrostatic coating paint composition according to the above embodiment is suitable for electrostatic coating, as long as its thixotropic index (Ti value) is preferably in the range of 1.5 to 8.0, more preferably in the range of 1.5 to 7.0, and can be sprayed in a mist from an electrostatic coating machine to reach the object to be coated, thereby ensuring high coating efficiency.

[0088] Furthermore, the electrostatic coating paint composition according to the above embodiment contains an epoxy resin lacquer, a diluent organic solvent, and a thickener, and has a viscosity in the range of 10s to 60s, preferably 15s to 55s, more preferably 20s to 55s, and a liquid resistance in the range of 0.03MΩ to 10.0MΩ, preferably 0.03MΩ to 5.0MΩ, more preferably 0.04MΩ to 1.0MΩ. If the viscosity is within the range of 10s to 60s, preferably 15s to 55s, and more preferably 20s to 55s, it can be made suitable for electrostatic coating, allowing it to be sprayed in a mist from an electrostatic coating machine and reach the object to be coated. Furthermore, if the liquid resistance is within the range of 0.03MΩ to 10.0MΩ, preferably 0.03MΩ to 5.0MΩ, and more preferably 0.04MΩ to 1.0MΩ, then electrical leakage during electrostatic coating is less likely, and the amount of charge in the paint particles is appropriately high, making it easy to adhere to the object to be coated, thereby improving the coating efficiency.

[0089] Furthermore, when implementing the present invention, the other components, formulations, manufacturing methods, etc., of the electrostatic coating composition are not limited to the embodiments described above. Also, not all of the numerical values ​​given in the embodiments and examples of the present invention represent critical values; some values ​​represent suitable values ​​for implementation, and therefore, slightly changing the above values ​​does not negate the possibility of implementation.

Claims

1. A paint composition for electrostatic coating containing epoxy resin lacquer, a diluting organic solvent, and a thickener, The viscosity is within the range of 10s or more and 60s or less. The electrostatic coating composition is characterized in that the thickening agent is one or more selected from the group consisting of calcium carbonate, magnesium silicate, silica, mica, amide wax, and cellulose-based materials.

2. The electrostatic coating composition according to claim 1, characterized in that the liquid resistance is in the range of 0.03 MΩ or more and 10.0 MΩ or less.

3. A paint composition for electrostatic coating containing epoxy resin lacquer, a diluting organic solvent, and a thickener, The viscosity is within the range of 10s or more and 60s or less. A coating composition for electrostatic painting, characterized in that its liquid resistance is in the range of 0.03 MΩ or more and 10.0 MΩ or less.

4. The electrostatic coating composition according to claim 1 or 3, characterized in that the diluting organic solvent contains at least acetone.

5. The electrostatic coating composition according to claim 1 or 3, characterized in that the epoxy resin lacquer has a glass transition temperature of 40°C or higher and 100°C or lower.

6. The electrostatic coating composition according to claim 1 or 3, characterized in that the epoxy resin lacquer is in the range of 30 to 70% by mass, the diluting organic solvent is in the range of 30 to 70% by mass, and the thickener is in the range of 0.1 to 20% by mass.

7. The electrostatic coating paint composition according to claim 1 or 3, characterized in that the epoxy resin in the epoxy resin lacquer is a modified epoxy resin.

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