JPH0470955B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a coating method that improves the chipping resistance, corrosion resistance, interlayer adhesion, coating surface finish, etc. of a coating film formed by applying a cationic electrodeposition coating powder coating. Both cationic electrodeposition paints and powder paints contain little or no organic solvents and have excellent coating efficiency, making them effective in preventing pollution and conserving resources. Painting systems are being adopted. However, it is desired to improve the performance of the coating film produced by this coating system, such as chipping resistance, corrosion resistance, interlayer adhesion, and coating surface finish. For example, with regard to chipping resistance, in the automobile industry, emphasis is being placed on the durability of coating films, particularly the problem of reduced corrosion resistance of coating films due to impact peeling and progress of corrosion of steel materials. In particular, in cold regions of Europe and America, gravel mixed with a large amount of relatively coarsely crushed rock salt is often laid down to prevent road surfaces from freezing during the winter, and vehicles driving on these types of roads are often covered with gravel mixed with large amounts of rock salt. Rock salt particles and pebbles thrown up by the wheels collide with the paint surface, and the impact often causes the paint film to peel off locally from the car body, a so-called "chipping" phenomenon. As a result of this phenomenon, the metal surface of the impacted portion of the outer surface of the vehicle body is exposed, and rust immediately develops and corrosion progresses. Usually, peeling of the paint film due to chipping occurs more often on the bottom of the vehicle body and around the suspension, but it is known that it also occurs on the hood and roof, and localized corrosion becomes quite noticeable after about six months to one year. In order to prevent this chipping and the progress of corrosion caused by it, various studies have been made on chemical conversion treatments on the surface of the external metal base of the car body, as well as electrocoating paints and powder topcoating paints. For example, in chemical conversion treatments, the use of iron phosphate coatings and zinc phosphate coatings with different crystal forms has been considered, but such chemical conversion treatments cannot sufficiently improve the adhesion of coatings on impact areas. Have difficulty. In addition, various studies have been conducted on the resin and/or pigment contained in electrodeposition paints and powder topcoats, but so far no one has been found that has sufficient adhesion-improving effects to withstand chipping. I haven't reached it yet. Therefore, in order to improve the above-mentioned problems, the present inventors have investigated the chipping resistance, corrosion resistance, and interlayer The present invention has been completed as a result of extensive research aimed at providing a coating method with improved adhesion and surface finish. That is, according to the present invention, a cationic electrodeposition paint is applied to a steel plate, and then a film formed on the coated surface is composed mainly of a modified polyolefin resin having a static glass transition temperature of -30 to -60°C. Provided is a method for painting a steel plate, which comprises applying a barrier coat, applying a liquid paint if necessary, and then applying a powder top coat. The feature of the present invention is that in the process of sequentially applying cationic electrodeposition paint and powder top coat paint to a steel plate,
After applying the electrodeposited paint and before applying the powder top coat, a barrier coat having a specific composition and properties is applied to the electrodeposited surface in advance. As a result, it was possible to form a coating film with outstanding chipping resistance, corrosion resistance, interlayer adhesion, and surface finish. That is, a barrier coating film with a glass transition temperature adjusted to -30 to -60°C (more preferably,
As described below, the tensile strength elongation rate of the coating film is adjusted to 200 to 1000% at -20°C).
It is flexible and has unique viscoelasticity due to the modified polyolefin resin. Therefore, even if a strong impact force from rock salt, pebbles, etc. is applied to the surface of the topcoat film formed through a barrier coat film with such physical properties, most or all of the impact energy will be absorbed by the barrier coating film. It is absorbed into the coating film and does not spread to the underlying electrodeposited coating film, and the top coating film itself is virtually free from physical and intellectual damage. In other words, the above-mentioned barrier coating film layer exhibits a buffering effect against external impact forces, significantly improving the chipping resistance, preventing rusting and corrosion of the steel plate due to chipping, and furthermore preventing the steel plate from colliding with rock salt, pebbles, etc. Deterioration of the top coat itself was also resolved. Additionally, by applying a barrier coat, the interlayer adhesion between the electrodeposition coating and the powder topcoat, as well as the finish quality of the topcoat, were significantly improved, which was an unexpected technical effect. It was hot. The coating method of the present invention will be specifically explained below. Steel plate: Any material to be coated by the method of the present invention is not limited as long as it has a metal surface that can be coated by cationic electrodeposition. Examples include iron, copper, aluminum, tin, zinc, alloys containing these metals, and plated or vapor-deposited products of these metals and alloys, and specifically passenger cars, trucks, and safari cars made using these metals. , the body of a motorcycle, etc. Further, it is preferable that the steel sheet is previously subjected to a chemical conversion treatment with a phosphate or chromate prior to being coated with a cationic electrodeposition paint. Cationic electrodeposition paint: A known electrodeposition paint for coating the above-mentioned steel plate can be used. The cationic electrodeposition paint uses a basic water-dispersed resin that can be neutralized with an organic or inorganic acid, such as an epoxy, acrylic, or polybutadiene resin that has many amino groups in its resin skeleton. It is a water-based paint (the resin is not limited to these), and the resin contains a neutralizing agent, a pigment (coloring pigment,
The content of pigments such as extender pigments and antirust pigments is preferably less than 40 parts by weight per 100 parts by weight of resin solid content),
A hydrophilic solvent, water, and if necessary, a curing agent, a crosslinking agent, additives, etc. are blended to form a coating by a conventional method. Examples of neutralizing agents for neutralizing and water-soluble (dispersing) the above-mentioned basic water-dispersible resin (usually dissolved in a hydrophilic solvent) include acetic acid, hydroxyl acetic acid, propionic powder, butyric acid, lactic acid, glycine, etc. organic acids,
Inorganic acids such as sulfuric acid, hydrochloric acid, and phosphoric acid can be used. The amount of neutralizing agent to be mixed is based on the base number of the above resin (approximately 30 to 200).
A neutralization equivalent range of about 0.1 to 0.4 is suitable.
The solid content is diluted with deionized water to a concentration of about 5 to 40% by weight, the pH is maintained within the range of 5.5 to 8.0, and the steel plate is electrodeposited using a conventional method. The thickness of the electrocoated film is not particularly limited, but it is preferably 10 to 40 μm based on the cured film, and the film is cured by heating to about 140 to 210°C. Barrier coat: A composition to be applied to a cationic electrodeposited surface, containing a modified polyolefin resin whose static glass transition temperature of the formed coating is -30 to -60°C (preferably -40 to -55°C). It is a composition consisting of a main component and further containing an organic solvent or the like as necessary. That is, as a modified polyolefin resin, for example, a propylene-ethylene copolymer (preferably a molar ratio of 40 to 80:60 to 20%) and a chlorinated polyolefin (chlorination rate of about 1 to 60%) are mixed.
A mixture containing 50 parts by weight, preferably 10 to 20 parts by weight (each per 100 parts by weight of the copolymer), or the above propylene-ethylene copolymer
Examples include resins in which 0.1 to 50 parts by weight, preferably 0.3 to 20 parts by weight of maleic acid or maleic anhydride are graft-polymerized per 100 parts by weight.
In the present invention, if these modified polyolefin resins themselves have a static glass transition temperature within the above range, they can be used as a barrier coat by themselves; If it is desired to change the static glass transition temperature, a viscosity imparting agent can be added as necessary. The viscosity imparting agent includes, for example, rosin, petroleum resin (Chroman), ester gum, polybutadiene, epoxy-modified polybutadiene, low molecular weight aliphatic epoxy resin, low molecular weight aliphatic bisphenol, which has good compatibility with the modified polyolefin resin. Examples include type epoxy resin, polyoxytetramethylene glycol, vinyl acetate-modified polyethylene, etc., and the blending amount thereof is preferably 1 to 50 parts by weight per 100 parts by weight of the above-mentioned modified polyolefin resin. In the barrier coat, it is preferable to dissolve or disperse the modified polyolefin resin in an organic solvent in order to improve coating properties. As the organic solvent, most of the organic solvents for paints can be used without any particular restrictions, such as aromatic hydrocarbons such as benzene, toluene, xylene, hexane, heptane, etc.
Aliphatic hydrocarbon solvents such as octane, chlorinated hydrocarbon solvents such as trichlorethylene, perchlorethylene, dichloroethylene, and dichloroethane are used. In addition, as an organic solvent, diisopropylbenzene, tetralin, decalin, o-dichlorobenzene, trichlorobenzene, benzyl alcohol,
Organic solvents such as diisobutyl ketone, isophorone, cellosolve acetate, carbitol acetate, dimethyl phthalate, etc. that have a boiling point of 150°C or higher and that are compatible with powder topcoat paints (hereinafter referred to as "compatible solvents")
(sometimes abbreviated as ) is preferably used in combination. This is because after applying a barrier coat made by dissolving or dispersing the above-mentioned modified polyolefin resin in an organic solvent containing an affinity solvent, a powder topcoat can be applied immediately while the coating is still wet without baking the coating. When the paint is applied and baked, the affinity solvent remaining in the barrier coat film evaporates and reaches the powder topcoat film, promoting heat melting fluidity of the powder resin particles and improving the finish coating surface. This is because smoothness can be significantly improved. The content of the compatible solvent in the organic solvent in the barrier coating paint is not particularly limited, but is 5 to 50% by weight.
The total organic solvent content in the paint is preferably from 15 to 95% by weight. Therefore, in the present invention, it is effective to apply the powder topcoat directly onto the undried wet barrier coat surface containing an compatible solvent in order to obtain a smooth coated surface. In the present invention, it is essential that the static glass transition temperature of the coating film forming the barrier coat is within the above range, and furthermore, the tensile strength elongation at break of the coating film must be within the -20°C atmosphere. 200～
Preferably it is 1000%. Furthermore, if the static glass transition temperature of the formed coating film is higher than -30°C, the above object of the present invention cannot be achieved, and if it is higher than -60°C, the performance of the coating film, particularly water resistance, adhesion, etc., decreases. So I don't like it. Furthermore, in the present invention, it is more preferable to use the barrier coat containing a resin deterioration inhibitor such as an ultraviolet absorber, a light stabilizer, and an antioxidant. The purpose of this is to absorb ultraviolet rays that penetrate through the top coat film, which has low hiding power, and to prevent the oxidation of radicals generated in the resin chain, thereby preventing the barrier coating film itself, the electrodeposition coating film, and the surface of the barrier coat from being exposed to UV rays. The objective is to prevent deterioration over time due to The UV absorber that can be incorporated into the barrier coat absorbs UV energy, is compatible with the barrier coating resin or can be uniformly dispersed in the resin, and is easily decomposed at the baking temperature of the paint. Any one may be used as long as it does not lose its effectiveness. For example, benzophenone,
2,4-dihydroxybenzophenone, 2,2',
4,4'-tetrahydroxybenzophenone, 2-
Hydroxy-4-methoxybenzophenone, 2,
2'-dihydroxy-4,4'-dimethoxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, 2-hydroxy-4-dodecyloxy Benzophenone, 2-hydroxy-4-methoxy-5-sulfobenzophenone, 5-chloro-2-hydroxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxy-5-sulfobenzo Phenone, 2-hydroxy-4-methoxy-
Benzophenone series such as 2'-carboxybenzophenone, 2-hydroxy-4-(2-hydroxy-3-methylacryloxy)propoxybenzophenone; 2-(2'-hydroxy-5'-methyl-phenyl)benzo Triazole, 2-(2-hydroxy-3,5-di(1,1'-dimethylbenzylphenyl)-2H benzotriazole, 2-(2'-hydroxy-3',5'-ditertiary-butyl-phenyl) Benzotriazole, 2-(2'-hydroxy-3'-tertiary-butyl-5'-methyl-
phenyl)benzotriazole, 2-(3,5-
ditertiary-amyl-2-hydroxyphenyl)bendotriazole, 2-(2'-hydroxy-3',5'-ditertiary-butyl-phenyl)
-5-chlorobenzotriazole, 2-(2'-hydroxy-3',5'-ditertiary-isoamyl phenyl)benzotriazole, 2-(hydroxy-5-tert-butyl-phenyl)
Benzotriazole series such as benzotriazole; phenyl salicylate, 4-tertiary-
Salicylic acid esters such as butyl-phenyl salicylate and para-octyl-phenyl salicylate; ethyl-2-cyano-3,3'-diphenyl acrylate, 2-ethylhexyl-2-cyano-3,3'-diphenyl acrylate diphenyl acrylate series such as hydroxy-5-methoxy-acetophenone, 2-hydroxy-naphthophenone, 2-ethoxyethyl-para-methoxycinnamate, nickel-bisoctylphenyl sulfide, [2,2'-thiobis(4 -t-octylphenolate)]-n-butylamine-nickel,
Examples of commercially available benzotriazole UV absorbers include Tinuvin 900 and Tinuvin 328 (CIBA
- Geigy), Uvinur 400 etc. for benzophenones, and Sandoz 3206 for oxalic acid anilides.
(Sandbore Inc.) etc. The blending amount of these ultraviolet absorbers is preferably 0.1 to 10 parts by weight, particularly 0.5 to 5 parts by weight, per 100 parts by weight of the modified polyolefin resin. Examples of light stabilizers include tetrakis(2,2,6,6-tetramethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate, 8-acetyl-3-dodecyl-7, 7,
9,9-tetramethyl-1,3,8-triazaspiro(4,5)decane-2,4-dione, bis(1,2,2,6,6-pentamethyl-4-piperidinyl)sebacate, bis-( 2, 2, 6, 6
-tetramethyl-4-piperidyl) sebacate,
His(1,2,2,6,6-pentamethyl-4-
piperidyl) sebacate, dimethyl-2-(4-
Hydroxy-2,2,6,6-tetramethyl-1
-piperidyl) ethanol condensate, poly[6-
(1,1,3,3-tetramethylbutyl)imino-1,3,5-traazine-2,4-diyl 4-
(2,2,6,6-tetramethylpiperidyl)hexamethylene-4,4-(2,2,6,6-tetramethylpiperidyl)imino], 1-[2-3-
(3,5di-t-butyl-4-hydroxyphenyl)propionyloxyethyl]-4-3-(3,
5-di-t-butyl-4-hydroxyphenyl)
Propionyloxy]-2,2,6,6-tetramethylpiperidine, etc., and antioxidants include, for example, 4,4'-thiobis-(3-methyl-6-t-butylphenyl), 2,2 '-Methylenebis-(4-methyl-6-t-butylphenol), 4,4'-methylenebis-(2,6-di-t-
butylphenol), 1,3,5-trimethyl-
2,4,6-tris(3,5-di-t-butyl-
4-Hydroxybenzyl)benzene, tris-
(2-methyl-4-hydroxy-5-t-butylphenyl)-butane, pentaerythritol tetrakis (3-laurylthiopropionate),
Dilaurylthiodipropionate, distearylthiodipropionate, dimyristylthiodipropionate, triethylene glycol-bis-3
-(3-t-butyl-5-methyl-4-hydroxyphenyl)-propionate, 1,6-hexanediol-bis-3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate ,
2,4-bis-(n-octylthio)-6-(4-
hydroxy-3,5-di-t-butylanilino)
-1,3,5-triazine, pentaerythrityl-tetrokis-[3-(3,5-di-t-butyl-
4-hydroxyphenyl)-propionate],
2,2-thio-diethylenebis-[3-(3,5-
di-t-butyl-4-hydroxyphenyl)-propionate], octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 2,2-thiobis-(4-methyl- 6
-t-butylphenol), N,N'-hexamethylenebis-(3,5-di-t-butyl-4-hydroxy-hydroxynamamide), and the like. It is preferable to use these in combination with the ultraviolet absorber, and the blending amount is determined by the modified polyolefin resin.
Per 100 parts by weight, the light stabilizer is 0.1 to 10 parts by weight (preferably 0.5 to 3 parts by weight), and the antioxidant is 0.1 to 5 parts by weight.
Parts by weight (preferably 0.2 to 3 parts by weight) are suitable. Furthermore, extender pigments, coloring pigments (excluding anticorrosion pigments), etc. may be added to the barrier coat. The blending amount of these pigments is preferably 10 to 100 parts by weight per 100 parts by weight of the modified polyolefin resin. In the present invention, these barrier coats are applied to the cationic electrodeposition coating surface, but the coating method is not limited, and examples include spray coating, brush coating, dipping coating, melt coating, electrostatic coating, etc.
The coating film thickness is preferably 1 to 20 microns, particularly 5 to 10 microns, depending on the coating film formed. Note that the static glass transition temperature of the formed coating film of the barrier coat used in the present invention is a value measured with a differential scanning calorimeter (Model DSC-10 manufactured by Daini Seikosha),
The tensile strength elongation at break is the value measured using a universal tensile testing machine with a constant temperature bath (Shimadzu Corporation, Autograph S-D type), the sample length was 20 mm, and the tensile speed was 20 mm/min. Ta. The samples used for these measurements were coated on a tin plate to a thickness of 25μ based on the film formed by the barrier coat, and heated at 120℃.
After baking for 30 minutes, it was isolated by the mercury amalgam method and used. When applying the top coat to the surface of the barrier coat, the barrier coat may be baked in advance, but the top coat may also be applied wet-on-wet without baking. Baking temperature of barrier coat film is 80 to 160
℃, especially 80-130℃ is suitable. Powder topcoat paint: A paint that is applied to the barrier coated surface and imparts cosmetic properties to the coated object. Preferably, the finished appearance (sharpness,
It already forms a coating film with excellent properties such as smoothness, gloss, etc.), weather resistance (gloss retention, color retention, chalk resistance, etc.), chemical resistance, water resistance, moisture resistance, and hardening properties. Known powder coatings can be used, such as amino/acrylic resin, acid/glycidyl acrylic resin, amino/polyester resin, isocyanate/polyester resin, and isocyanate/polyester resin.
Examples include thermosetting powder paints that use acrylic resin as a vehicle. In the present invention, as a top coating finishing method using a powdered top coating, for example, a powdered enamel solid color coating in which a coloring pigment is blended into the vehicle component of the powder coating is applied to the barrier coating film and baked (1 A solid color finish using a one-coat bake method), and a liquid solid color or metallic paint is applied to the barrier coat film, and after baking (or no baking) the powdered topcoat clear paint containing little or no coloring pigment is applied. Examples include pre-baking (solid color or metallic finish using 2-coat 1-bake or 2-coat 2-bake method). First, regarding the above, after baking the barrier coat film, apply a barrier coat preferably containing the above-mentioned affinity solvent, and apply powdered solid color enamel paint for about 3 to 30 minutes without baking.
Paint to a film thickness of 150μ (based on the coating film after baking, the same applies below), and apply at 120 to 210℃, especially 130 to 180℃.
It is baked at a temperature of If the barrier coat film contains an affinity solvent, minute irregularities on the top coat surface (for example, yuzu skin, tangerine skin)
It is possible to prevent the occurrence of blemishes and to finish the painted surface with excellent smoothness. After applying the barrier coat and baking, or without baking, apply solid color or metallic liquid paint to a film thickness of 10 to 30μ, and then bake (baking temperature 80 to 170℃) or apply the above powder without baking. After applying clear paint to a thickness of 30 to 150 microns, it is heated to 80 to 170 degrees Celsius and baked. Known liquid paints can be used, such as paints whose vehicle component is an acrylate resin, an amino alkyd resin, an amino polyester resin, or the like.
In this case, it is preferable to add an ultraviolet absorber, a light stabilizer, an antioxidant, etc. to the barrier coat because weather resistance and the like will be improved. These powdered top coatings are preferably applied by electrostatic powder coating or the like, and the coating film thickness is preferably 40 to 120 μm based on the cured coating film. Heating conditions can be arbitrarily adopted depending on the vehicle components, but
Preferably, the temperature is 120-210°C, particularly 130-180°C for 10-40 minutes. Cationic electrodeposition coating on steel plate as described above.
Barrier code coating - The performance of coatings formed by powder topcoating is particularly poor in terms of finished appearance (e.g. smoothness, gloss, sharpness, etc.) compared to coatings formed without barrier coating. , chipping resistance, corrosion resistance, interlayer adhesion, etc. were significantly improved. Next, examples and comparative examples related to the present invention will be described. Sample (1) Steel plate: Galvanized steel plate chemically treated with Bonderite #3030 (manufactured by Nippon Parker Rising Co., Ltd., zinc phosphate type) (size 300 x 90 x 0.8
mm) (2) Cationic electrodeposition paint: Elekron #9200
(manufactured by Kansai Paint Co., Ltd., epoxy polyamide-based cationic electrodeposition paint, gray color) (3) Barrier coat (A): Toluene solution (static Glass transition temperature -43℃, -20
Tensile strength elongation rate at ℃ 410%). (B): A mixed organic solvent consisting of cellosolve acetate/toluene = 30/70 (weight ratio) per 100 parts by weight of a modified polyolefin resin made by mixing 10 parts by weight of rosin per 100 parts by weight of the graft resin of (A) above. A liquid made by blending 200 parts by weight of (Static glass drying temperature -52℃, -20
Tensile strength elongation at break 700% at °C) (C): Per 100 parts by weight of the graft polymer of (A),
1 part by weight of 2-(2-hydroxy-3,5-di(1,1-dimethylbenzyl)phenyl)-2H benzotriazole as an ultraviolet absorber and bis(1,
A liquid containing 0.5 parts by weight of 2,2,6,6-pentamethyl-4-piperidinyl)-sebacate and 200 parts by weight of a mixed solvent consisting of carbinol acetate and toluene = 10/90 (weight ratio). (D): Same as (B) except that the mixed solvent in (B) was changed to a mixed solvent consisting of dimethyl phthalate/toluene = 5/95 (weight ratio). (E): 200 parts by weight of a mixed solvent consisting of isophorone/toluene = 20/80 (weight ratio) is blended per 100 parts by weight of the graft resin (A). (F): An organic liquid of a resin made by graft polymerizing maleic acid onto a propylene-ethylene copolymer (static glass transition temperature +5°C). (4) Top coating (4-1) Powder paint (A): Glycidyl group-functional acrylic resin/dodecane 2 acid-based white powder paint (pencil hardness H) (B): Glycidyl group-functional acrylic resin/dodecane 2 Acid-based powder clear paint (Pencil hardness H) (4-2) Liquid metallic paint (C): Magikron Silver (Kansai Paint Co., Ltd.)
manufactured by Amino Acrylic Resin Top Coating Paint, 2
Coat 1 Bake silver metallic paint, pencil hardness H) Example Comparative example Cationic electrodeposition paint on a steel plate using the above sample.
Barrier coats and top coats were applied as shown in Table 1.

[Table] In Table 1, (1) All film thicknesses are based on the dry coating film. (2) The barrier coat was applied using a spray coating machine, and the powder coating was applied using an electrostatic powder coating machine. Performance Test Results A coating film performance test was conducted using the coated plates coated in the above Examples and Comparative Examples. The results are shown in Table 2.

【table】

[Table] The test methods in Table 2 are as follows. (*1) Chipping resistance As described above, the chipping resistance was investigated for the test board immediately after painting and the test board after accelerated exposure. The accelerated exposure test was performed using a Sunshine Weather-Ometer (manufactured by Suga Test Instruments Co., Ltd., WEL-SUN-
HC type) was exposed for 2000 hours. Chipping resistance is as follows: (1) Test equipment: Flying stone testing machine JA-400 model (gravelometer) (product of Suga Test Instruments Co., Ltd.) (2) Stones to be sprayed: Crushed stones with a diameter of approximately 15 to 20 m/m (3 ) Capacity of stone to be blown: Approximately 500ml (4) Blowing air pressure: Approximately 4Kg/cm ² (5) Temperature during test: Approximately 20℃ Mount the test piece on the test piece holder and hold it for approx.
Approximately 500 ml of crushed stone particles were ejected onto the test piece at a blowing air pressure of Kg/cm ² , and then the coated surface condition and salt spray resistance were evaluated. The condition of the painted surface was visually evaluated using the following criteria. ◎ (Good): Only a few scratches due to impact were observed on a part of the top coat, and no peeling of the coat was observed. △ (slightly poor): Many scratches due to impact were observed on the topcoat film, and peeling of the electrodeposited film was also observed here and there. × (Poor): Most of the top coat has peeled off,
The electrodeposited coating on the impact area including the impact area and its surrounding area peeled off. Salt spray resistance was determined by subjecting the test piece to a salt spray test according to JIS Z2371 for 240 hours, and observing the presence or absence of rust from the impact area and the state of corrosion. (*2) Impact resistance: According to JIS K5400-1979 6.13.3 B method,
The test was carried out in an atmosphere of 0°C. weight 500
Damage to the paint film was examined by dropping a 50cm weight from a height of 50cm. (*3) Adhesiveness after accelerated exposure: After 2000 hours of accelerated exposure using a Sunshine Weather-Ometer in the same manner as in (*1) above,
In accordance with JISK5400-1979 6.15, gongs were made on the coating film, adhesive cellophane tape was applied to the surface, and the coated surface was evaluated after it was quickly peeled off. (*4) Water resistance: The coated surface was evaluated after being immersed in water at 40°C for 10 days. (*5) Painted surface smoothness: Judging by visual inspection, ◎ indicates that no or almost no tangerine skin or citrus skin is observed on the painted surface, △ indicates that a little is observed, and △ indicates that much is observed. ×

Claims (1)

[Claims] 1. A steel plate is coated with a cationic electrodeposition paint, and then the static glass transition temperature of the coating film formed on the coated surface is -30 to
A method for coating a steel plate, which comprises applying a barrier coat containing a modified polyolefin resin as a main component at -60°C, applying a liquid paint as necessary, and then applying a powder topcoat.