KR20010020716A - Coating method for car body - Google Patents

Abstract

PURPOSE: To form a coating film free from the generation of sag, each of hiding, popping, or the like, and exhibiting uniform metallic feeling by uniformly and regularly orienting a metallic pigment in parallel to the coating surface when the coating film is metallic. CONSTITUTION: An organic solvent based thermosetting 1st colored coating material B containing a neutralized material of a polycarboxylic acid resin having 5-100 mgKOH/g acid value and an amino resin is applied on the outside and inside both plates of an automobile body having a coating film formed by applying a cationic electrodeposition coating material A and hardening by heating and, after a thermosetting 2nd colored coating material C and a thermosetting aq. transparent coating material D are successively applied on the outside plate, the coating material B, C and D are hardened at the same time by heating and a thermosetting transparent coating material E is applied further on the outside plate and the coating film is hardened by heating.

Description

Coating method for car body

The present invention relates to a coating method of the inner plate portion and the outer plate portion of the vehicle body.

The vehicle body is mainly composed of inner plate parts such as a trunk room, engine room, and door interior, and outer plate parts such as a roof, a bonnet, a trunk lid, a door panel, and a fender, and both inner and outer plates are, for example, by the method described below. The painting is done.

That is, (1) after coating the organic solvent-based intermediate coating material on the outer plate of the car body which has been electrodeposited and heat-hardened and heat-hardened, the organic solvent-based coloring coating material is coated on both inner and outer plates, and the organic solvent-based A method of coating both clear coats and heating and curing both coats simultaneously; (2) An organic solvent-based coloring paint is applied to the inner plate of the car body which has been electrodeposited and heat cured, and then an organic solvent-based intermediate paint is coated on the outer plate and heat cured, and then the water-based colored paint and the outer plate are hardened. A method of coating an organic solvent-based clear paint and simultaneously heating and curing these coating films; (3) After the intermediate coating is applied to the outer plate of the car body by electrodeposition and heat curing, and after heat curing, the aqueous coating is coated on both sides of the inner and outer plates, and the organic solvent-based clear coating is coated on the outer plate to coat the coating film. Hardening method.

However, these coating methods have various problems, and the solution of these problems is strongly desired. For example, (1) the coating method is not preferable from the viewpoint of pollution prevention and resource saving because both the coloring paint and the clear paint are organic solvent type, and (2) the coating method must separately prepare the organic solvent type paint for the inner plate, and The external appearance of the coating film by the water-based coloring paint is not enough, and the method (3) has a problem that the external appearance of the coating film by the water-based coloring paint coated on both inner and outer plates is insufficient.

An object of the present invention is to provide a novel coating method for the inner plate and outer plate of an automobile body in which these problems in the above (1) to (3) coating methods are eliminated.

According to the present invention, a neutralized product of a polyvalent carboxylic acid resin having an acid value of 5 to 100 mgKOH / g on both inner and outer plates of an automobile body formed by coating a cationic electrodeposition paint (A) and heating and curing the coating film; An organic solvent-based thermosetting first coloring paint (B) containing an amino resin is applied, and then a thermosetting aqueous second coloring paint (C) and a thermosetting aqueous transparent coating (D) are sequentially coated on the outer plate, and then the paint The three-layer coating film of (B), (C) and (D) is simultaneously heat-hardened, and the thermosetting transparent paint (E) is again coated on the outer plate, and the coating method of the automobile body is provided by heat-curing the coating film. do.

Next, the coating method (henceforth a method) of the automobile body of this invention is demonstrated in detail.

Examples of automobiles to which the present invention is subject to painting include, for example, passenger cars, RV cars, light cars, wagon cars, buses, trucks, and the like, and these car bodies are mainly exteriors such as trunk rooms, engine rooms, door interiors, and the like. Is comprised of an "inner plate part" which is hard to see, and an "outer plate part" exposed to the outside, such as a roof, a bonnet, a trunk lid, a door panel, a fender, and a bumper. Both of these materials are mainly metals, but plastic parts may coexist. In this specification, these inner plate parts and outer plate parts of a motor vehicle are named generically "car body."

According to this method, first, the cationic electrodeposition paint (A) is coated on the metal parts of both inner and outer plates of the vehicle body. The said cationic electrodeposition coating (A) is an aqueous supercoat, and what is known by itself can be used. Specifically, it is a paint containing an aqueous resin obtained by neutralizing a cationic resin such as an epoxy resin modified with an amino group-containing compound, an acrylic resin, a polybutadiene resin with a neutralizing agent, and a crosslinking agent (e.g., a block polyisocyanate, an alicyclic epoxy). Resin, etc.), a coloring pigment, an rust preventive pigment, a sieving pigment, a hydrophilic organic solvent, etc. are mix | blended as needed, and the electrodeposition paint formed. Examples of the neutralizing agent include organic acids such as acetic acid, hydroxyacetic acid, propionic acid, butyric acid, lactic acid and glycine, and inorganic acids such as sulfuric acid, hydrochloric acid and phosphoric acid.

The coating of the cationic electrodeposition coating (A) on the vehicle body is, for example, a cationic electrodeposition coating (A) bath made by adjusting the solid content concentration to about 5 to about 40% by weight, preferably about 10 to about 30% by weight, pH 5.5 to 8. It can carry out by immersing a vehicle body in (iv) and electrodeposition-coating by a conventional method. The coating film thickness is preferably about 10 to about 60 µm, particularly about 15 to about 30 µm, as the cured coating film, and the coating film can be cured by heating at about 140 to about 210 ° C. for about 5 to 40 minutes.

According to the present method, the organic solvent-based first coloring paint (B) is coated on the vehicle body coated with the cationic electrodeposition paint (A) by the above-described method. The organic solvent-based first coloring paint (B) is a neutralizer (B-1), amino resin (B-2) and coloring pigment (B-3) of a polyhydric carboxylic acid resin having an acid value of 5 to 100 mgKOH / g. It is an organic solvent-based paint containing, and it is advantageously used to form a solid color or metal-like coating film having underlying hiding properties. The organic solvent-based first coloring paint (B) is coated on the cured coating film surface of the cationic electrodeposition paint (A) before the thermosetting aqueous second coloring paint (C).

The coating film of the below-mentioned 2nd coloring paint (C) coat | covered by the drawing by the use of the said 1st coloring paint (B) can be finished by a uniform and smooth drawing, without being influenced by the painting atmosphere humidity.

The polyhydric carboxylic acid resin in the component (B-1) of the organic solvent-based first coloring paint (B) is a resin having an acid value of 5 to 100 mgKOH / g containing an average of at least two carboxyl groups in one molecule. For example, the following various resins already known per se can be used.

i) Acrylic resin or vinyl resin obtained by copolymerizing a carboxyl group-containing polymerizable monomer, a hydroxyl-containing polymerizable monomer, and other polymerizable monomers.

The carboxyl group-containing polymerizable monomer is a compound having a carboxyl group and a polymerizable unsaturated bond in one molecule, and examples thereof include acrylic acid, methacrylic acid, maleic acid, itaconic acid and crotonic acid. The hydroxyl group-containing polymerizable monomer is a compound having a hydroxyl group and a polymerizable unsaturated bond in one molecule, for example, the number of carbon atoms of (meth) acrylic acid such as 2-hydroxyethyl (meth) acrylate and hydroxypropyl (meth) acrylate. 1-8 hydroxyalkyl ester etc. are mentioned. The other polymerizable monomer is a compound having a polymerizable unsaturated bond in one molecule which can be copolymerized with a carboxyl group-containing polymerizable monomer and a hydroxyl group-containing polymerizable monomer, such as methyl (meth) acrylate, ethyl (meth) acrylate, Of (meth) acrylic acid such as butyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, and decyl acrylate Alkyl or cycloalkyl ester having 1 to 24 carbon atoms; Functional such as (meth) acrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, diacetone acrylamide, N-methylol (meth) acrylamide, N-butoxymethyl acrylamide, etc. (Meth) acrylamide; Glycidyl group-containing vinyl monomers such as glycidyl (meth) acrylate, glycidyl (meth) acrylamide, allyl glycidyl ether and the like; Vinyl monomers such as styrene, vinyltoluene, vinyl propionate, α-methylstyrene, vinyl acetate, (meth) acrylonitrile, vinyl propionate, vinyl pibarate, beobamonomer (manufactured by Shell Chemical), and the like.

The acrylic resin or vinyl resin may generally have a number average molecular weight in the range of 5000 to 40000, preferably 8000 to 30000.

ii) A polyester resin obtained by esterifying a polyhydric alcohol and a polybasic acid in excess of an acid component.

Polyhydric alcohols are compounds having two or more alcoholic hydroxyl groups in one molecule, such as ethylene glycol, diethylene glycol, propylene glycol, butanediol, pentanediol, 2,2-dimethylpropanediol, glycerin, trimethylolpropane, pentaerythritol, and the like. Can be mentioned. Polybasic acids are compounds having two or more carboxyl groups in one molecule, such as phthalic acid, isophthalic acid, tetrahydrophthalic acid, hexahydroxyphthalic acid, maleic acid, succinic acid, adipic acid, sebacic acid, trimellitic acid, pyromellitic acid, anhydrides thereof Etc. can be mentioned. In the esterification reaction between these polyhydric alcohols and polybasic acids, monoepoxy compounds having a monohydric alcohol and a glycidyl group are used as part of the alcohol component, if necessary, and / or benzoic acid and t-butyl as part of the acid component. Monobasic acids, such as benzoic acid, can be used. The polyester resin also includes a polyester resin modified with oil components such as castor oil, paulownia oil, sunflower oil, soybean oil, linseed oil, tor oil, palm oil, or fatty acids thereof. These polyester resins can generally have a number average molecular weight within the range of 500-10000, preferably 1000-5000.

These polyhydric carboxylic acid resins may have an acid value in the range of 5 to 100 mgKOH / g, preferably 10 to 50 mgKOH / g, more preferably 30 to 50 mgKOH / g. When the acid value is less than 5, the coating of the second colored paint (C) is not carried out because it does not blend well with the second colored paint (C) coated in the drawing and there is no water intake in the second colored paint (C). Defects, such as a deviation and a run down generate | occur | produce, and the plastering property of a coating film worsens. Moreover, when acid value is larger than 100, since the water resistance of the coating film itself of a 1st coloring paint (B) falls, it is unpreferable.

It is preferable that the polyhydric carboxylic acid resin in the said (B-1) component has a hydroxyl group in order to accelerate crosslinking reaction with amino resin (B-2), and the hardness, water resistance, weather resistance, etc. of the coating film formed from it are Performance is improved. It is preferable that content of the said hydroxyl group is 10-200 mgKOH / g, especially 25-70 mgKOH / g in a hydroxyl value.

These polyhydric carboxylic acid resins can be made water-soluble or water dispersible by neutralizing with a basic substance. As the basic substance, various basic substances such as ammonia, methylamine, ethylamine, dimethylamine, diethylamine, trimethylamine, triethylamine, dimethylethanolamine, diethanolamine and triethanolamine can be used. The amount used is preferably in the range of about 0.1 to about 2 equivalents, particularly about 0.3 to about 1.2 equivalents, relative to the carboxyl groups in the resin.

The amino resin (B-2) is a crosslinking agent for curing the polyhydric carboxylic acid resin, and can be obtained by condensation or co-condensation of formaldehyde with melamine, benzoguanamine, triazine-based compound, urea, dicyandiamide and the like. And those modified with these modifiers. Among these, melamine-formaldehyde resin is preferable.

The compounding ratio of the neutralizing agent (B-1) and the amino resin (B-2) of the polyhydric carboxylic acid resin is 50 to 90%, particularly 60 to 85%, based on the total weight of both solids. The component (B-2) is preferably 10 to 50%, particularly preferably in the range of 15 to 40%.

The first coloring paint (B) contains the components (B-1) and (B-2), and is an organic solvent system formed by dissolving or dispersing them in an organic solvent together with a coloring pigment (B-3), in particular, coating When the solid content is adjusted to about 35% by weight or more, particularly about 40 to about 60% by weight, the so-called high solid type is preferable from the viewpoint of pollution prevention and the like.

The coloring pigment (B-3) imparts a solid color or metallic wind-like concealment to the coating film of the first coloring paint (B). Specifically, for example, titanium dioxide, zincation, carbon black, bengal, cadmium red, or mol Budenred, Cadmium Yellow, Chrome Yellow, Titanium Yellow, Phthalocyanine Blue, Phthalocyanine Green, Carbazole Violet, Untrapyridin, Azo Orange, Pravan Sloan Yellow, Isoindolin Yellow, Azo Yellow, Inderslo Blue, Dibrom Anza Solid color pigments such as slon red, perylene red, azo red, unsluquinone red, knaclidon red and violet; And metallic pigments such as flake aluminum, mica and mica coated with metal oxides. These can be used alone or in combination of two or more.

As for the compounding quantity of a coloring pigment (B-3), the light transmittance in wavelength 400-700 nm of the single coating film (30 micrometers in thickness of a cured coating film) of a 1st coloring paint (B) is 5% or less, Preferably it is 3% or less The amount that is done is reasonable. Although it changes with the coloring power of a pigment specifically, it can usually be in the range of 1-250 weight part per 100 weight part of resin solid content (total amount of a base resin and a hardening | curing agent), Preferably it is in the range of 5-150 weight part. The light transmittance of the coating film of the 1st coloring paint (B) coats the coating material (B) so that it may become a predetermined | prescribed cured film thickness on a glass plate, and hardens | cures it, and after immersing in 60-70 degreeC warm water, peeling, and drying, it is isolated as a sample. It is an average spectral transmittance measured at a wavelength of 400-700 nm using a magnetic spectrophotometer (Hitachi Seisakusho, EPS-3T type).

As the organic solvent in the first coloring paint (B), conventional paint solvents can be used, and examples thereof include ester solvents, ether solvents, alcohol solvents, amide solvents, ketone solvents, aliphatic hydrocarbon solvents and alicyclic solvents. Hydrocarbon solvents, aromatic hydrocarbon solvents, and the like. In particular, among these, ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, dioxane, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, and diethylene Glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monodiethyl ether, diethylene glycol monobutyl ether, methyl alcohol, ethyl alcohol, allyl alcohol, n-propyl alcohol, isopropyl alcohol, tert-butyl alcohol, ethylene Glycol, 1,2-propylene glycol and its monoether, 1,3-butylene glycol, 2,3-butylene glycol, hexylene glycol, hexanediol, dipropylene glycol and this monoether, acetone, diacetone alcohol, etc. It is preferable to use the same hydrophilic organic solvent as at least part of the organic solvent. As a hydrophilic organic solvent, the organic solvent which melt | dissolves 50 weight part or more per 100 weight part of water at 20 degreeC is preferable. The ratio of the hydrophilic organic solvent to the total organic solvent is suitably in the range of 20% by weight or more, particularly in the range of 40 to 100% by weight, based on the total weight of the organic solvent contained in the first coloring paint (B) when coating.

The color tone of the first colored paint (B) is a multilayer coating film composed of a first colored paint (B), an aqueous second colored paint (C), an aqueous transparent paint (D), and a transparent paint (E) coated on the outer plate part. It is preferable to approximate the color tone.

The first coloring paint (B) is coated on both the electrodeposited coating film surfaces of the inner and outer plate portions of the vehicle body formed by coating the cationic electrodeposition coating (A) and heat curing the coating film. For coating, for example, air spray, airless spray, electrostatic coating, etc., the viscosity is adjusted to about 15 to about 60 seconds, in particular 15 to 35 seconds (20 ° C) with a pod cup # 4, and based on the cured coating film. It is preferable to carry out so that it may become 2 to about 60 micrometers, especially about 5 to 25 micrometers film thickness.

In this method, the first colored paint (B) is applied to both electrodeposited coating surfaces of the inner and outer shell portions of the vehicle body in the same manner as described above, and left at room temperature to 100 ° C. or lower for 1 to 10 minutes, and the first colored coating of the outer shell portion. The thermosetting aqueous second colored coating (C) is coated on the uncured drawing of (B).

As the thermosetting aqueous second colored coating (C), an aqueous liquid coating containing water as its main solvent or dispersion medium and containing a water-soluble or water dispersible thermosetting resin composition is used to form a solid color or metal-like coating film.

Examples of the thermosetting resin composition include a base resin such as a water-soluble or water-dispersible acrylic resin having a crosslinkable functional group such as a hydroxyl group, a vinyl resin, a polyester resin, and an amino resin as a crosslinking agent.

As the water-soluble acrylic resin and vinyl resin, an acid value obtained by copolymerizing a carboxyl group-containing polymerizable monomer, a hydroxyl group-containing polymerizable monomer and other polymerizable monomers is 20 to 100 mgKOH / g, in particular 30 to 80 mgKOH / g. And resins having a hydroxyl value in the range of 20 to 200 mgKOH / g, in particular 30 to 120 mgKOH / g.

As these polymerizable monomers, the polymerizable monomer illustrated by i) of (B-1) component can be used preferably, The polymerization reaction of these monomers uses the said polymerizable monomer as azobisisobutyronitrile, benzoyl peroxide, di It can be performed in an organic solvent compatible with water, such as butyl cellosolve, using radical polymerization initiators, such as butyl peroxide.

Water-soluble acrylic resins and vinyl resins are neutralized using basic materials such as ammonia or triethylamine, monoethanolamine, diethanolamine, triethanolamine, amines such as dimethylaminoethanol or alkali metal hydroxides such as sodium hydroxide, and the like. Later, the water is diluted by adding water and an organic solvent compatible with water as necessary to obtain a suitable solid.

Water-dispersible acrylic resins can be produced, for example, by using ionic or nonionic low-molecular or polymer surfactants, water-soluble resins, or the like as dispersion stabilizers and emulsifying the polymerizable monomer in an aqueous medium by a method known per se.

The water-soluble polyester resin has, for example, an acid value of 15 to 100 mgKOH / g, especially 20 to 80 mgKOH / g, and a hydroxyl value of 20 to 200 mgKOH / g, especially 40, of the polyester resin described in the first coloring paint (B). It can obtain by using what exists in the range of -150 mgKOH / g, and neutralizing it with a basic substance by the same method as the said water-soluble acrylic resin.

It is preferable to use amino resin as the crosslinking agent, which is reacted with the gas resin by heating to form a three-dimensional cured coating film. Examples of such amino resins include those obtained by condensation or copolymerization of melamine, benzoguanamine, urea, dicyandiamine and the like with formaldehyde, and those modified with C1-8 alcohols or carboxyl-containing amino resins. Can be. These amino resins can usually be prepared by reacting about 0.5 to about 2 equivalents of formaldehyde with one equivalent of an amino group by using a pH adjusting agent (e.g., ammonia, sodium hydroxide, amines) and alkali or acidic by a method already known per se. . Preferred crosslinking agents in the second coloring paint (C) are water-soluble melamine-formaldehyde resins.

The mixing ratio of the gaseous resin and the crosslinking agent in the second coloring paint (C) is about 50 to about 90% by weight, in particular about 60 to about 85% by weight, based on the total solid weight of both components, and about 10 to about It is preferred to range from about 50% by weight, in particular from about 15 to about 40% by weight.

The second coloring paint (C) is an aqueous coating obtained by blending a solid color pigment and / or a metallic pigment with these thermosetting resin compositions. The pigments that can be blended are preferably the same as those described for the first coloring paint (B). Is used. These pigments may be used independently or may be used together 2 or more types.

These pigment compounding amounts colorize the coating film of the second coloring paint (C) and impart color cosmetic properties to the multilayer coating film formed on the outer plate part by the present method, and simultaneously illuminate the coating film to make the first coloring paint (B) thereunder. It is preferable to set it as the amount which imparts the lower extremity concealability to the extent that the coating film color tone of? Therefore, it is preferable that the light transmittance in the wavelength 400-700 nm range of the single coating film (15 micrometers in thickness of a cured coating film) of a 2nd coloring paint (C) is 5% or less, especially 3% or less.

The second coloring paint (C) has a solid content of 15 to 65% by weight, preferably 18 to 40% by weight, and a viscosity of 15 to 60 seconds, preferably 20 to 50 seconds / pod cup # 4 /. A film of about 5 to about 25 µm, particularly about 10 to about 20 µm, in a cured coating film by means of air spray, airless spray, electrostatic coating, etc. It is preferable to make it so that it may become thickness.

In this method, after coating the second coloring coating (C) on the outer plate, the thermosetting aqueous transparent coating (D) is coated on the uncured drawing. In addition, before coating of the said thermosetting aqueous transparent paint (D), both the 1st coloring (B) and the 2nd coloring (C) coating film may be pre-dried at about 50-about 100 degreeC temperature. The preliminary drying is such that the crosslinking reaction between the two coating films is little or no progress (gel fraction is 0 to 5%), and almost or all of the volatile components such as organic solvent and water contained in both coating films are evaporated. It is desirable to.

Subsequently, the thermosetting aqueous transparent paint (D) is coated on the uncured drawing of the second coloring paint (C) coated on the outer plate portion of the vehicle body. As the aqueous transparent paint (D), an aqueous liquid paint containing a water-soluble or water-dispersible thermosetting resin composition and forming a colorless transparent or colored transparent film formed by blending a solid color pigment or a metallic pigment, etc., if necessary, is used. do.

The transparent paint (D) can be prepared by excluding some or all of the solid color pigments or metallic pigments in the second coloring paint (C) composition, and the content of these pigments is that the single coating film of the transparent paint (D) is transparent. It is preferable that it is about the color of the 2nd coloring paint (C) visually, and is less than content of a pigment in a 2nd coloring paint (C).

Specifically, the light transmittance in the wavelength range of 400 to 700 nm of the single coating film (15 µm thick of the cured coating film) of the transparent paint (D) is within the range of 6 to 95%, particularly 10 to 90%, and more particularly 20 to 80%. It is preferable to blend the pigment in an amount.

When the transparent coating (D) is applied, the viscosity is adjusted to about 10 to about 50 seconds, preferably 20 to 40 seconds (20 ° C) with a pod cup # 4, and air spray coating, airless spray coating, rotary electrostatic coating, or the like. It is preferable to apply | coat to the uncured drawing of the 2nd coloring paint (C) so that it may become a film thickness of about 5 to about 30 micrometers, especially about 10 to about 25 micrometers based on a cured coating film.

In this method, it is preferable that the second coloring paint (C) and the transparent paint (D) have affinity, and specifically, even if some or all of the thermosetting resin compositions contained in the two paints are common, similar or different. It is desirable to have affinity for the liver.

In this method, the cationic electrodeposition paint (A) is applied to the inner and outer shell parts of the automobile body, and the coating film is heated and cured, and the first colored paint (B) is applied to the inner and outer parts, and the cured coating film is not cured. After the second coloring paint (C) and the transparent paint (D) are sequentially coated on the outer surface without heating, the heating is generally performed at a temperature of about 100 to about 170 ° C., preferably at about 130 to about 150 ° C. for about 10 to 40 minutes. After the three-layer coating film is cured at the same time, the thermosetting transparent paint (E) is coated on the curing drawing of the transparent paint (D).

Thermosetting transparent paint (E) is a paint which forms a colorless transparent or colored transparent coating, for example, contains little or no liquid paints or solvents such as organic solvent solution type, non-aqueous dispersion type (NAD), powder slurry type, etc. already known per se. Powder coating which is not done can be used. And when apply | coating, the solid content paint which is 35 weight% or more, Preferably it is 40-80 weight% can also be used preferably.

The transparent paint (E) is a transparent paint (D) for the purpose of further improving the plastering, finishing appearance, weather resistance, chemical resistance, water resistance, moisture resistance, and stiffness of the multilayer coating film formed on the outer plate portion. It is coated with the uppermost coating film in the cured drawing, and specifically, as a crosslinking agent such as an acryl resin or a vinyl resin having a crosslinkable functional group such as a hydroxyl group or a carboxyl group, an amino resin, a block polyisocyanate compound, an epoxy group-containing compound, etc. The coating material containing the formed thermosetting resin composition is mentioned.

When the liquid transparent coating (E) is coated, the viscosity is adjusted to about 10 to about 60 seconds, preferably 20 to 50 seconds (20 ° C.), with a pod cup # 4, and a method such as air spray, airless spray or electrostatic coating It is preferable to coat the cured drawing of the transparent paint (D) with a film thickness of about 5 to about 60 µm, particularly about 10 to about 50 µm, based on the cured coating film. The coating film of the transparent paint (E) can be hardened | cured by heating for about 10 to 40 minutes normally at about 100-about 170 degreeC, Preferably it is about 130 to about 150 degreeC temperature.

According to the method of the present invention described above, the effects described below can be obtained.

(1) Since the neutralized polyhydric carboxylic acid resin contained in the uncured coating film of the first coloring paint (B) exhibits strong absorbency, moisture in the coloring paint (C) coated in the drawing is absorbed and the viscosity is rapidly increased. Is raised. As a result, there is no occurrence of dripping, cracking, swelling, etc. of the coating film of the coloring paint (C). If the coating film is metallic, the metallic pigment is oriented parallel and uniformly with respect to the drawing, and there is no metallic deviation. The coating film which has a uniform metallic feeling can be formed.

(2) Since the first colored paint (B) coating film is excellent in concealment under the ground, in the multilayer coating film formed on the outer plate portion of the vehicle body, sunlight from the outside can improve the interlayer adhesion without reaching the electrodeposition coating film. .

(3) Since the second coloring paint (C) has good wettability with the first coloring paint (B), even when coated in a low temperature atmosphere, no defect such as surface roughness is generated.

(4) Since the transparent paint (E) is coated in the drawings of the cured transparent paint (D), the selection range is not limited without causing defects such as mixed layers.

(5) Transparent paint (D) has transparency, and can finish with drawings with excellent appearance such as thickness, smoothness, clarity, depth, high gloss and high metallic feeling.

(6) Since both parts of the inner plate and outer plate of the vehicle body are coated with the first coloring paint (B) having a hydrophilic coating film, no gap is generated or stretched even when the inner plate is complicated in shape. .

(7) By coating and heat-curing the transparent paint (D), even if the defects such as garbage and unevenness generated before the process are polished and removed, the multilayer coating film formed by coating the paint (E) afterwards has a sensibility or gloss. Etc. are remarkably excellent.

Hereinafter, the present invention will be described in more detail in Examples and Comparative Examples. In addition, part and% are weights as a reference | standard, and a coating film thickness is with respect to a cured coating film.

1. Preparation of Sample

1) Electrodeposition Painted Steel Sheet

Electron # 9400 (manufactured by Kansai Into Co., Ltd., trade name, polyamide-modified epoxy resin and block polyisocyanate electrodeposition coating) was diluted with deionized water so that the solid content concentration was 16%, and the pH was within the range of 5.5 to 8.0. The steel sheet (size 10x10x0.8mm) is immersed in the adjusted electrodeposition bath, electrodeposition-coated according to a conventional method, and it heats at about 175 degreeC for 30 minutes, and hardens a coating film. The film thickness is 20 micrometers.

2) Organic solvent-based thermosetting first coloring paint (B)

Gas resin (B1): 30 parts of methyl methacrylate, 23 parts of ethyl acrylate, 30 parts of butyl acrylate, 12 parts of hydroxyethyl methacrylate, 12 parts of acrylic acid in a reaction vessel obtained by adding 60 parts of ethyl cellosolve and heating to 120 ° C. A monomer mixture consisting of 5 parts and 2 parts of α, α'-azobisisobutyronitrile was added and polymerized over 3 hours using a metering pump to give an acid value of 40 mgKOH / g, a hydroxyl value of 52 mgKOH / g, and a number average molecular weight. An acrylic resin solution of about 10000 and a resin solid content of 60% is obtained. To 100 parts of the acrylic resin solution, 3.5 parts of 2-amino-2-methylpropanol are added and neutralized, and then diluted with isopropyl alcohol to obtain an acrylic resin neutralizing solution (B1) having a resin solid content of 50%.

Gas resin (B2): 0.7 mol of neopentylglycol, 0.3 mol of trimethylolpropane, 0.4 mol of phthalic anhydride and 0.5 mol of adipic acid were added to the reaction vessel and reacted at 200 to 230 DEG C for 5 hours, followed by 0.03 trimellitic anhydride. After adding molar, it was made to react at 180 degreeC again for 1 hour, and butyl cellosolve was added after that, and the polyester resin solution of 40 mgKOH / g of acid value, the number average molecular weight about 6000, and 70% of resin solid content was obtained. To 100 parts of the polyester resin solution, 4 parts of 2-amino-2-methylpropanol are added and neutralized. Thereafter, the mixture is diluted with isopropyl alcohol to obtain a polyester resin neutralizing solution (B2) having a solid content of 60%.

Preparation of 1st coloring paint (B):

The said component is mixed in the compounding ratio shown in Table 1 below, and 1st coloring paint (a, b, c) is obtained.

First Color Paint (B) a b c Gas balance (B1) 140 140 - (B2) - - 117 Cymel 370 (Note 1) 34 34 34 Titanium White Pigment 75 75 75 Blue G316 (Note 2) 5 5 5 Carbon black 3 3 3 Isopropyl Alcohol 140 150 125 Paint Solids (%) 36 35 38 Viscosity (sec) (Note 3) 25 25 25 Light transmittance (Note 4) 0.1> 0.1> 0.1> Note 1) Trade name, manufactured by Mitsui Cytec Co., Ltd., water-soluble melamine liquor 2) Trade name, Sanyo Shikisosha Co., Ltd., Blue Pigment Note 3) Pod cup # 4/20 ° C Note 4) Measured value in a coating film having a film thickness of 20 µm.

3) Thermosetting Aqueous Secondary Color Coating (C)

Preparation of 20% acrylic resin emulsion (C1): 140 parts of deionized water, 30% `` Newcol 707SF '' (Surfactant, manufactured by Nippon Nyusai Co., Ltd.) 2.5 parts and the following monomer mixture (1) (Note 5) 1 3 parts of 3% aqueous ammonium persulfate solution were added at 60 ° C while stirring and mixing in a nitrogen gas atmosphere. Subsequently, after raising the temperature to 80 ° C., a monomer emulsion consisting of 79 parts of the monomer mixture (shareholder 5), 2.5 parts of 30% “Newcol 707SF”, 4 parts of 3% aqueous ammonium persulfate solution and 42 parts of deionized water was added. Add to reaction vessel using metering pump over time. After the addition is completed, it is aged for 1 hour. Then, 20.5 parts of the following monomer mixture (2) (Note 6) and 4 parts of an aqueous 3% ammonium persulfate solution were simultaneously added dropwise to the reaction vessel at 80 ° C. for 1.5 hours. After completion of the addition, the mixture was aged for 1 hour, diluted with 30 parts of deionized water, and filtered through a nylon mesh of 200 mesh at 30 ° C. Deionized water was further added to the filtrate to adjust pH to 7.5 with dimethylaminoethanol to obtain an acrylic resin emulsion (C1) having an average particle diameter of 0.1 µm and a nonvolatile content of 20%.

(5) Monomer mixture (1): 55 parts of methyl methacrylate, 8 parts of styrene, 9 parts of n-butyl acrylate, 5 parts of 2-hydroxyethyl acrylate, 2 parts of 1,6-hexanediol diacrylate and meta A mixture consisting of 1 part of krylic acid.

(Note 6) Monomer mixture (2): A mixture consisting of 5 parts of methyl methacrylate, 7 parts of n-butyl acrylate, 5 parts of 2-ethylhexyl acrylate, 3 parts of methacrylic acid and 0.5 parts of 30% "Newcol 707SF".

Preparation of Aqueous Second Coloring Paint (C): The above components are mixed in an arrangement ratio shown in Table 2 below to obtain thermosetting second coloring paints (a, b).

Second Color Paint (C) a b Gas balance (B1) 50 50 (B2) 50 50 Emulsion (C1) 100 100 Cymel 370 (Note 1) 34 34 Alpaste 504AR (Note 7) - 5 Blue G316 5 - Deionized water 220 220 Paint Solids (%) 25 25 Viscosity (sec) (Note 3) 30 30 Light transmittance (Note 8) 40 40 Note 7) manufactured by Toyo Aluminum Co., Inc., flaky aluminum paste. Note 8) Light transmittance is measured on a coating film with a thickness of 15 µm.

4) Thermosetting Water-based Transparent Paint (D)

What was prepared by the same method except the "blue G316" from the composition of the said thermosetting aqueous 2nd coloring paint (a) is made into the transparent paint (d).

5) Thermosetting Waterborne Transparent Paint (E)

Gas resin (E1): 30 parts of styrene, 35 parts of butyl acrylate, 10 parts of 2-ethylhexyl acrylate, 10 parts of hydroxy acrylate in a reaction vessel heated to 120 ° C by adding 40 parts of Swasol # 1000 (manufactured by Maruzen Seiko Oil Co., Ltd.) A monomer mixture consisting of 25 parts of ethyl and 4 parts of α, α'-azobisisobutyronitrile is added and polymerized over 3 hours using a metering pump. As a result, an acrylic resin solution (E1) having a hydroxyl value of 120 mgKOH / g, a number average molecular weight of about 6000 and a resin solid content of 70% was obtained.

60% acrylic resin non-aqueous dispersion (E2): 60% breast 28-60 (Mitsuido Atsuga Chemical Co., Ltd., melamine resin solution) in a reaction container, 58 parts of n-heptane and 0.15 parts of benzoyl peroxide were added thereto, and 95 ° C Heated to 15 parts of styrene, 9 parts of acrylonitrile, 13 parts of methyl methacrylate, 15 parts of methyl acrylate, 1.8 parts of n-butyl acrylate, 10 parts of 2-hydroxyethyl methacrylate, 1.2 of acrylic acid Part, a mixture of 0.5 parts of benzoyl peroxide, 5 parts of n-butanol, 30 parts of Shelzol 140 (Note 9) and 9 parts of n-heptane was added dropwise over 3 hours, and t-butylperoctoate was passed for 1 hour at the same temperature. A mixture of 0.65 parts and 3.5 parts of Shelzol 140 (Note 9) is added dropwise over 1 hour. Thereafter, stirring is continued for 2 hours while maintaining the temperature at 95 ° C. Subsequently, 34 parts of solvents are removed under reduced pressure, and acrylic resin non-aqueous dispersion (E2) of 60% of resin solid content and varnish viscosity A (Gardner bubble viscosity) is obtained.

(Note 9): Shell Seki Yusha, trade name, hydrocarbon solvent

Preparation of Thermosetting Transparent Paint (E):

57 parts of 70% acrylic resin solution (E1), 50 parts of 60% acrylic resin non-aqueous dispersion (E2), 30 parts of Cymel 303 (Note 10), 4 parts of 25% dodecylbenzenesulfonic acid solution and BYK-300 (Note 11) 0.5 parts are mixed and adjusted to a viscosity of 30 seconds (Pod Cup # 4/20 ° C) in Swasol # 1000 (Note 12) to obtain a transparent paint (e) having a resin content of 55%.

(Note 10): Mitsui Cytec Co., Ltd., brand name, mono melamel melamine resin

(Note 11): Big Chemistry Fan Shasa, brand name, surface conditioner

(Note 12): Cosmo Sekiyusha Co., Ltd., trade name, aromatic hydrocarbon solvent

2. Example

Examples 1-3

The first colored paints (B) -a, b, c adjusted to a viscosity of 25 seconds (pod cup # 4/20 ° C) on the entire surface of the electrodeposited coated steel sheet were each air at a relative humidity of 75% RH so as to have a thickness of 20 µm. Paint with a spray and leave for about 5 minutes at room temperature. Subsequently, on the uncured coating film surface of the first colored paint, which is the lower half of the coated steel sheet, the second colored paints (C) -a, b adjusted to a viscosity of 30 seconds (pod cup # 4/20 ° C) were each 15 µm. After coating with air spray at 75% RH for relative film thickness, and leaving it at room temperature for about 5 minutes, the thermosetting water-based transparent paint (D) -d was sprayed with air spray at 75% RH for a relative thickness of 5 μm. After the coating was allowed to stand at room temperature for about 3 minutes, it was heated at 140 ° C. for 30 minutes to simultaneously crosslink and cure the three-layer coating film consisting of the first, second, and transparent paints.

Thereafter, the thermosetting transparent coating material (E) -e adjusted to a viscosity of 30 seconds (pod cup # 4/20 ° C) was coated on the cured coating film surface of the transparent coating with an air spray so as to be about 45 µm based on the cured film thickness. It is left to stand at room temperature for about 5 minutes and then heated at 140 ° C. for 30 minutes to be cured by heating.

3. Performance test result

The performance of the multilayer coating film obtained in the above example is tested. The test results are shown in Table 3.

The test method is as follows.

Smoothness: Measured with a tension meter (RENAULY company). Larger value means better smoothness.

Sensitivity: It is measured by the sedimentation measuring instrument NSIC (made by Sugashion Kisha). Larger value means better sensibility.

Water resistance: After immersing a sample plate in 40 degreeC warm water for 240 hours, the drawing state is visually evaluated. 0: No abnormality is observed, Δ: defects such as glossiness and swelling are seen slightly, ×: defects such as glossiness and swelling are remarkable.

Example One 2 3 Electrodeposition Paint (A) Electron # 9400 Baking Condition 175 ℃ 20 minutes Film thickness (㎛) 20 20 20 First Color Paint (B) a b c Drying condition Room temperature, 5 minutes Film thickness (㎛) 20 20 20 Second Color Paint (C) a a b Drying condition Room temperature, 5 minutes Film thickness (㎛) 15 15 15 Clear Paint (D) d d d Baking Condition 140 ° C, 30 minutes Film thickness (㎛) 5 5 5 Clear Paint (E) e e e Baking Condition 140 ° C, 30 minutes Film thickness (㎛) 45 45 45 Performance test results Smoothness 20 21 21 Sunyoung Sung 78 80 81 Water resistance 0 0 0

The method of the present invention prevents pollution, saves resources, does not separately prepare an organic solvent type paint for inner plates, and provides a good appearance of the finished film by water-based colored paints coated on both inner and outer plates.

Claims (20)

Organic solvent-based thermosetting containing a neutralized polyhydric carboxylic acid resin having an acid value of 5 to 100 mgKOH / g and an amino resin on both inner and outer plates of a car body formed by coating a cationic electrodeposition paint (A) and heat-curing the coating film. The first coloring paint (B) is applied, and then the thermosetting aqueous second coloring paint (C) and the thermosetting aqueous transparent coating (D) are sequentially coated on the outer plate, and then the paints (B), (C) and ( The three-layer coating film of D) is heat-hardened simultaneously, and a thermosetting transparent paint (E) is apply | coated to an outer-plate part, and the coating film is heat-hardened, The coating method of the automobile body body characterized by the above-mentioned. The method according to claim 1, wherein the first coloring paint (B) forms a solid color or metal-like coating film having lower concealment properties. The number average molecular weight according to claim 1, wherein the polyvalent carboxylic acid resin in the first coloring paint (B) is obtained by copolymerizing i) a carboxyl group-containing polymerizable monomer, a hydroxyl group-containing polymerizable monomer and another polymerizable monomer. Phosphorus acrylic resin or vinyl resin and ii) a polyhydric alcohol and a polybasic acid. The method according to claim 1, wherein the polyvalent carboxylic acid resin in the first coloring paint (B) has an acid value in the range of 10 to 50 mgKOH / g. The method according to claim 1, wherein the polyhydric carboxylic acid resin in the first coloring paint (B) has a hydroxyl group and the content of the hydroxyl group is in the range of 10 to 200 mgKOH / g as the hydroxyl value. 2. What is obtained by condensation or co-condensation of melamine, benzoguanamine, triazine-based compound, urea, dicyandiamide and the like with formaldehyde in the first coloring paint (B) and those modified with a modifier Selected method. The method according to claim 6, wherein the amino resin in the first coloring paint (B) is melamine-formaldehyde resin. The method of claim 1, wherein the first coloring paint (B) is 50 to 90% of the neutralization of the polyhydric carboxylic acid resin and the amino resin by 10 based on the total solid weight of the neutralization of the polyhydric carboxylic acid resin and the amino resin. The method contained in the range of-50%. The method according to claim 1, wherein the first colored paint (B) forms a coating film having a light transmittance of 5% or less in a wavelength range of 400 to 700 nm of a single coating film (thickness 30 μm of the cured coating film). The method according to claim 1, wherein the coating of the first coloring paint (B) is performed so as to have a film thickness of about 2 to about 60 µm based on the cured coating film. The first coloring paint (B) according to claim 1, wherein the first coloring paint (B) is applied to the electrodeposition coating surfaces on both inner and outer plates of the vehicle body, and left at a temperature of room temperature to 100 DEG C for 1 to 10 minutes. A method of coating a thermosetting aqueous second colored coating (C) on an uncured drawing of the sheet. 2. The second coloring paint (C) comprises a water-soluble or water-dispersible acrylic resin, a vinyl resin or a polyester resin and an amino resin having a crosslinkable functional group, and forms a solid color or metal-like coating film. How to do. The method according to claim 1, wherein the second coloring paint (C) forms a coating film having a light transmittance of 5% or less in a wavelength range of 400 to 700 nm of a single coating film (15 µm thick of the cured coating film). The method according to claim 1, wherein the coating of the second colored paint (C) is performed so as to have a film thickness of about 5 to about 25 µm based on the cured coating film. The method according to claim 1, wherein the two coating films of the first color paint (B) and the second color paint (C) are pre-dried at a temperature of about 50 to about 100 ° C. prior to the coating of the thermosetting aqueous transparent paint (D). The method according to claim 1, wherein the transparent paint (D) is an aqueous liquid paint which forms a colorless transparent or colored transparent coating. The method according to claim 1, wherein the coating of the transparent paint (D) is performed so as to have a film thickness of about 5 to about 30 mu m based on the cured coating film. The method according to claim 1, wherein the transparent paint (E) is an organic solvent solution type, a non-aqueous dispersion type (NAD), or a powder slurry type liquid paint or powder paint which forms a colorless transparent or colored transparent coating film. The method according to claim 1, wherein the coating of the transparent paint (E) is performed so as to have a film thickness of about 5 to 60 µm based on the cured coating film. An automobile body coated with the method according to any one of claims 1 to 19.