JP2002224613A - Method of forming multilayer coating film and multilayer coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of forming a multilayer coating film, by which coating film smoothness as a multilayer coating film in a 3 coat 1 bake system on a electrodeposition coating film is attained, and the multilayer coating film. SOLUTION: The method of forming the multilayer coating film is performed by applying successively an intermediate coating material, a top coating base coating material and a top coating clear coating material on the surface of the cured electrodeposition coating film film-formed on the base material by a cation electrodeposition coating material and having >=110 deg.C glass transition point and <=0.3 μm surface roughness (Ra) to form a 3 layer coating film of an uncured intermediate coating film, top base coating film and top clear coating film and heating and curing simultaneously the 3 layer coating film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a multilayer coating film having a good finished appearance and a multilayer coating film.

[0002]

2. Description of the Related Art Automobile bodies, motorcycles, electric products and the like, in which the appearance of a coating film such as a design property is regarded as important, and the finishing of these parts are usually performed by using heat having excellent smoothness, sharpness and weatherability. A multilayer coating film is formed by the curable paint. The method of forming this multilayer coating film is to form a cationic electrodeposition coating film on a substrate, and then prevent deterioration of the electrodeposition coating film surface due to light transmission of the overcoat due to exposure, and to conceal the base. To form a gray or white intermediate coating film. Next, on the heat-cured intermediate coating film, a top coating material containing a glitter pigment and / or a coloring pigment is applied, and without heat-curing the top coating base film,
An overcoat clear coating is applied by so-called wet-on-wet (W / W), and finally both the overcoat base coating and the overcoat clear coating are heat-cured at once. The method of heating and curing both the overcoat base coating film and the overcoat clear coating film at a time is called a three-coat two-bake method.

On the other hand, as a method of forming a multi-layer coating film, from the viewpoint of saving energy required for baking and drying, an object to be coated is colored base paint (A), metallic paint (B) and clear paint (C). Has been proposed in Japanese Patent Application Laid-Open No. Hei 10-277474, for example, in which a three-layer coating is simultaneously coated by wet-on-wet coating and then heated to simultaneously cure the three-layer coating film. Such a method of simultaneously curing the three-layer coating film is called a three-coat one-bake method.

[0004] However, in order to keep the finished appearance of the multi-layer coating film good, the properties of the electrodeposition coating film are important. However, in the above prior art, there is no mention of the electrodeposition coating film. There is a concern that the appearance of the coating film due to the smoothness of the coating film as a multilayer coating film in a three-coat one-bake system on the coating film cannot be sufficiently obtained.

[0005]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for forming a multilayer coating film capable of obtaining a coating film smoothness as a multilayer coating film in a three-coat one-bake system on an electrodeposition coating film. It is to provide a multilayer coating.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies in view of the above-mentioned problems, and as a result, have reached the present invention. 1. The glass transition temperature of the cured electrodeposition coating film formed on the substrate by the cationic electrodeposition coating material is 110 ° C. or higher,
An intermediate paint, a top coat base paint and a top coat clear paint are sequentially applied to the electrodeposited coat surface having a surface roughness (Ra) of 0.3 μm or less, and an uncured middle coat coat, a top coat base coat and A method for forming a multi-layer coating film, in which after forming a three-layer coating film of a top-coat clear coating film, the three-layer coating film is simultaneously heated and cured. 2. The glass transition temperature of the cured electrodeposition coating film is 110 to 1
50 ° C. and a surface roughness (Ra) of 0.1 to 0.3
The above-mentioned method for forming a multilayer coating film having a thickness of μm. 3. The above method for forming a multilayer coating film, wherein the intermediate coating film is formed by a thermosetting intermediate coating material containing a polyester resin and an amino resin as a vehicle component. 4. The above method for forming a multilayer coating film, wherein the top clear coating film is formed by a coating material containing a carboxyl group-containing polymer and an epoxy group-containing polymer. 5. A multilayer coating film formed by a coating method according to the above multilayer coating film forming method.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described below in detail. In the method for forming a multilayer coating film of the present invention, the glass transition temperature of a coating film formed on a substrate by a cationic electrodeposition paint is 11
A three-layer coating of an uncured intermediate coating film, a top coating base coating film and a top coating clear coating film on the surface of the cured electrodeposition coating film having a surface roughness (Ra) of 0 ° C. or more and a surface roughness (Ra) of 0.3 μm or less. Is formed, the three-layer coating film is simultaneously heated and cured.

The base material is not limited as long as it is a base material capable of electrodeposition coating. Iron, steel, aluminum, tin, zinc, etc., alloys containing these metals, and metals Plating or vapor deposition products. Specifically, the body and parts of automobiles such as passenger cars, trucks, motorcycles, and buses manufactured by using these metal members are exemplified. In addition, plastics such as polyethylene resin, polypropylene resin, ethylene-vinyl acetate copolymer resin, polyamide resin, acrylic resin, vinylidene chloride resin, polycarbonate resin, polyurethane resin, epoxy resin, etc. It can be applied to materials and the like.

In the method for forming a multilayer coating film according to the present invention, an electrodeposition coating film is formed on the substrate directly or through a base treatment such as degreasing or chemical conversion treatment.

Electrodeposition Coating In the method for forming a multilayer coating film of the present invention, the electrodeposition coating film is formed by
The glass transition temperature of the cured electrodeposition coating film formed by the cationic electrodeposition coating material is 110 ° C. or higher, and the surface roughness (R
a) is applied by a cationic electrodeposition paint having a size of 0.3 μm or less.

The above electrodeposition paint has a cured electrodeposition coating having a glass transition temperature of 110 ° C. or higher and a surface roughness (Ra) of 0.1.
The following cationic base resin so as to be 3 μm or less,
It is a paint containing a crosslinking agent and a solvent. When the glass transition temperature of the cured electrodeposition coating film is less than 110 ° C., the surface roughness (R
If a) exceeds 0.3 μm, after forming the three-layer coating film, in the step of simultaneously baking these three-layer coating films, the surface roughness of the electrodeposition coating film cannot be sufficiently hidden. In addition, the solvent of the intermediate coating film is easily sucked into the electrodeposition coating film, the fluidity of the coating film is impaired, and the appearance of the composite coating film is deteriorated. The glass transition temperature of a preferred cured electrodeposition coating film is 110 to 150 ° C. The preferable surface roughness (Ra) is 0.1 to 0.3 μm.

The above-mentioned glass transition temperature is measured, for example, using a dynamic viscoelasticity measuring device, for example, Leo Vibron manufactured by Orientik. Specifically, the dynamic Young's modulus (E ') and the dynamic loss (E ") obtained by applying a vibration at a frequency of 11 Hz to the coating film at a rate of temperature increase of 2 ° C. per minute based on the following equation. It is obtained as the temperature that gives the maximum value of the calculated mechanical loss (Tan δ) Tan δ = E ″ / E ′ The surface roughness Ra is the center line average roughness Ra defined in JIS-B0601. And is an index of two-dimensional roughness.

The glass transition temperature of the electrodeposited coating is 110 ° C.
As described above, in order to make the surface roughness (Ra) 0.3 μm or less, for example, in a system comprising (1) a cationic base resin and a curing agent, an aromatic ring such as a benzene ring or a complex such as an oxazolidone ring is used. Heavy use of rigid structures such as rings,
(2) It can be obtained by increasing the rigidity of the components constituting the electrodeposition coating film and increasing the crosslink density by a technique such as increasing the blending amount of the curing agent.

As the above-mentioned cationic base resin, those giving higher corrosion resistance are preferred, and examples thereof include amino-epoxy resins, amino-containing acrylic resins, amino-containing polyester resins, and the like. Preferably, amino-epoxy resins are used. No. Amino-epoxy resins are obtained by opening the epoxy ring of an epoxy resin with an amine such as an acid salt of a primary amine, a secondary amine or a tertiary amine, and cationizing it.

Examples of the epoxy resin which is a starting material of the above-mentioned cationic base resin are a reaction product of a polycyclic phenol compound such as bisphenol A, bisphenol F, bisphenol S, phenol novolak, cresol novolak and epichlorohydrin. A polyphenol polyglycidyl ether type epoxy resin and a modified epoxy resin containing an oxazolidone ring in the molecule are exemplified. It is preferable to use a modified epoxy resin containing an oxazolidone ring in the molecule. This modified epoxy resin is subjected to a dealcoholization reaction between a bisurethane compound obtained by reacting a diisocyanate compound with a single active hydrogen compound or a heterourethane compound obtained by reacting two or more active hydrogen compounds with an epoxy resin. Can be obtained. When a modified epoxy resin containing an oxazolidone ring is used as a base resin, an electrodeposition coating film having excellent corrosion resistance can be obtained, and thinning of the electrodeposition coating film due to loss on heating is less likely to occur.

The preferred cationic base resin has an amine value of 30 to 130, more preferably 40 to 130.
80 and a number average molecular weight of 1,000 to 20,000. When the amine value is less than 30, it is difficult to make water soluble, and when it exceeds 130, the conductivity becomes high and the gas pinning property is lowered, and there is a problem in the workability of the electrodeposition coating such as a decrease in Coulomb efficiency and resolubility. Might be. Water-soluble organic acids used for neutralization include formic acid, acetic acid, propionic acid, lactic acid, citric acid, malic acid, tartaric acid, acrylic acid, etc.
Examples of the inorganic acid include hydrochloric acid, phosphoric acid, and sulfamic acid. Preferred water-soluble organic or inorganic acids include acetic acid, lactic acid, propionic acid, formic acid, sulfamic acid and the like.

The crosslinking agent contained in the cationic electrodeposition paint used in the method for forming a multilayer coating film of the present invention is preferably a block polyisocyanate compound or an etherified melamine resin. A blocked polyisocyanate compound is obtained by completely blocking or partially blocking an isocyanate group contained in a polyisocyanate compound such as an aromatic polyisocyanate or an aliphatic or alicyclic polyisocyanate, and dissociating the blocking agent. At a temperature, the blocking agent is dissociated to generate an isocyanate group, which reacts with the functional group in the cationic base resin and cures. The etherified melamine resin can be obtained by etherifying melamine with an alcohol such as methanol or butanol.

The polyisocyanate compounds preferably used in the synthesis of the blocked isocyanate used together with the cationic base resin include trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, and 1,2-propylene diisocyanate. Aliphatic compounds such as 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, ethylidene diisocyanate, butylidene diisocyanate, 1,3-cyclopentane diisocyanate, 1,4-cyclohexane diisocyanate, , 2-cyclohexanediisocyanate,
Aliphatic cyclic compounds such as isophorone diisocyanate and norbornane diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 4,
Aromatic compounds such as 4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 1,4-naphthalene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4- or 2,6-toluene diisocyanate or a mixture thereof; Aliphatic-aromatic compounds such as 4,4'-toluidine diisocyanate and 1,4-xylene diisocyanate; nuclear-substituted aromatic compounds such as dianisidine diisocyanate, 4,4'-diphenyl ether diisocyanate and chlorodiphenyl diisocyanate; triphenylmethane-4 , 4 ',
Triisocyanates such as 4 "-triisocyanate, 1,3,5-triisocyanatebenzene, 2,4,6-triisocyanatetoluene, 4,4'-diphenyl-dimethylmethane-2,2 ', 5,5'- Examples include tetraisocyanates such as tetraisocyanate, and polymerized polyisocyanates such as toluene diisocyanate dimer and toluene diisocyanate trimer.
Preferably, they are isophorone diisocyanate, norbornane diisocyanate, and 4,4'-diphenylmethane diisocyanate.

Examples of the blocking agent include halogenated hydrocarbons such as 1-chloro-2-propanol and ethylene chlorohydrin, aliphatic and heterocyclic rings such as n-propanol, furfuryl alcohol and alkyl-substituted furfuryl alcohol. Formula alcohols, phenol, m-
Phenols such as cresol, p-nitrophenol, p-chlorophenol, nonylphenol, methyl ethyl ketoxime, methyl isobutyl ketone oxime,
Oximes such as acetone oxime and cyclohexanone oxime; active methylene compounds such as acetylacetone, ethyl acetoacetate and diethyl malonate; aliphatic alcohols such as ε-caprolactam, methanol, ethanol and isopapropanol; and aromatic alcohols such as benzyl alcohol And glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether and diethylene glycol monomethyl ether. Preferred are methyl ethyl ketoxime and ε-caprolactam.

The cationic electrodeposition paint preferably has a solid content ratio of cationic base resin / crosslinking agent of 50/5.
0 to 90/10, more preferably 60/40 to 80/2
0. If the ratio is out of the range of 50/50 to 90/10, there is a possibility that a problem may occur in curability.

The above cationic electrodeposition coating composition contains water as a solvent, and methoxypropanol,
Ethyl cellosolve, propyl cellosolve, butyl cellosolve, 2-ethylhexyl cellosolve, n-hexyl cellosolve, methanol, ethanol, isopropyl alcohol, n-butanol, isobutanol, ethylene glycol dimethyl ether, diacetone alcohol, acetone, methyl ethyl ketone, methoxybutanol, dioxane, ethylene Water-miscible organic solvents such as glycol monoethyl ether acetate, xylene, toluene,
Methyl isobutyl ketone, hexane, carbon tetrachloride, 2-
Water-immiscible organic solvents such as ethylhexanol, isophorone, cyclohexane, and benzene can be included.
From the viewpoint of film forming properties, preferred organic solvents are butyl cellosolve, 2-ethylhexyl cellosolve, and n-hexyl cellosolve, and the amount of the organic solvent is 0.1% per 100 parts by mass of the solid content of the cationic base resin and the crosslinking agent. 1 to 10
Parts by weight are preferred.

When the cationic electrodeposition coating composition contains a dissociation catalyst for dissociating the blocking agent of the crosslinking agent in addition to the above components, an organic tin compound such as dibutyltin laurate, dibutyltin oxide, dioctyltin oxide or the like can be used. , N-
Amines such as methylmorpholine, lead acetate, and metal salts such as strontium, cobalt, and copper can be used. The concentration of the dissociation catalyst is 0.1 to 6 with respect to 100 solid parts by mass of the total of the cationic base resin and the crosslinking agent in the cationic electrodeposition paint.
Parts by weight.

In addition, the composition may contain, if necessary, crosslinkable resin particles, pigments and various additives. By adding the crosslinkable resin particles, the effect of maintaining the thickness of the edge portion of the substrate to be coated can be promoted. As the cross-linkable resin particles, any resin such as an acrylic resin, an epoxy resin, a phenol resin, and a melamine resin may be used, but it is particularly preferable that the cross-linkable particles using an acrylic resin be used for ease of production. preferable. The average particle size is 0.
Particles of from 02 to 30 μm are preferred.

The above pigments include coloring pigments such as titanium oxide, red iron oxide and carbon black; extender pigments such as aluminum silicate and precipitated barium sulfate; and phosphomolybdic acid and aluminum, ferric iron, titanium, zirconium, manganese and cobalt. Phosphomolybdate, which is a salt with a divalent or trivalent metal salt of nickel, copper, zinc, silicon, etc., and a salt of the above-mentioned divalent or trivalent metal salt with tripolyphosphoric acid, metaphosphoric acid, pyrophosphoric acid or the like In addition, a rust-preventive pigment such as a condensed phosphate, specifically, aluminum dihydrogen triphosphate, aluminum metaphosphate, and ferric pyrophosphate can also be added.

The cationic electrodeposition coating used in the method for forming a multilayer coating film of the present invention can be obtained by dispersing the above components in an aqueous medium containing the above water-soluble organic acid or inorganic acid as a neutralizing agent. it can. The preferred dry film thickness of the electrodeposition coating film is 10 to 40 μm, more preferably 15 to 30 μm.

The conditions for the electrodeposition coating include a coating voltage;
100 to 450 V, coating time: 1 to 5 minutes, electrodeposition liquid temperature:
20-35 ° C, electrodeposition liquid solid content: 5-40%, electrodeposition liquid p
H: 5.5 to 8.5, curing temperature of electrodeposited coating: 100 to 2
It is preferable to set 50 ° C. and the curing time of the electrodeposition coating film: 5 to 60 minutes.

Intermediate coating film The intermediate coating film in the method for forming a multilayer coating film of the present invention can be obtained by applying an intermediate coating material on the cured electrodeposition coating film. This intermediate coating is for forming a coating film for concealing the electrodeposition coating film, imparting chipping resistance, and ensuring adhesion with the overcoated base coating film to be applied in the next step.

The intermediate coating is a colored coating containing a vehicle and various pigments. The vehicle contained in the intermediate coating material is a vehicle in which various pigments are dispersed, and is composed of a resin for forming a coating film and, if necessary, a crosslinking agent.

Examples of the coating film forming resin constituting the vehicle include (a) an acrylic resin, (b) a polyester resin, (c) an alkyd resin, (d) a fluororesin,
(E) epoxy resin, (f) polyurethane resin, (g)
Polyether resins are mentioned, and these can be used in combination of two or more.

The resin for forming a coating film has an acid value of 3 to 200,
A hydroxyl value of 30 to 200, and a number average molecular weight of 500 to
50,000 are preferable, and particularly, an acid value of 3 to 200,
A hydroxyl value of 30 to 200, and a number average molecular weight of 2,000
Acrylic resin having an acid value of 3 to 200, a hydroxyl value of 30 to 200, and a number average molecular weight of 500 to 2
0000 polyester resins are preferred. When the intermediate coating is prepared as an aqueous solution or an aqueous dispersion, the acid value of the resin for forming a coating film is preferably 10 to 10.
It is preferably in the range of 200 and a hydroxyl value of 30 to 200.

The resin for forming a coating film includes a curable type and a lacquer type. Usually, a curable type is used. In the case of a type having curability, it is used by being mixed with a cross-linking agent such as an amino resin or a (block) polyisocyanate compound, an amine-based, a polyamide-based, or a polyvalent carboxylic acid. Let it proceed. It is also possible to use a non-curable type coating film forming resin and a curable type together. Particularly, as the vehicle, a polyester resin / amino resin is preferably used from the viewpoints of film forming properties and weather resistance.

As the acrylic resin (a), a copolymer of an acrylic monomer and another ethylenically unsaturated monomer can be exemplified. Acrylic monomers that can be used in the above copolymerization include acrylic acid or methacrylic acid methyl, ethyl, propyl, n-butyl, i
-Butyl, t-butyl, 2-ethylhexyl, lauryl, phenyl, benzyl, 2-hydroxyethyl, 2-
Esterified products such as hydroxypropyl, ring-opened adducts of caprolactone of acrylic acid or 2-hydroxyethyl methacrylate, glycidyl acrylate, glycidyl methacrylate, acrylamide, methacrylamide and N-methylolacrylamide, polyhydric alcohol (meth) ) Acrylic esters and the like. Examples of the other ethylenically unsaturated monomers copolymerizable therewith include styrene, α-methylstyrene, itaconic acid, maleic acid, and vinyl acetate.

Examples of the polyester resin (b) include saturated polyester resins and unsaturated polyester resins, and examples include condensates obtained by heat-condensing a polybasic acid and a polyhydric alcohol. Examples of the polybasic acids include saturated polybasic acids and unsaturated polybasic acids. Examples of the saturated polybasic acids include succinic acid, adipic acid, azelaic acid, sebacic acid, hexahydrophthalic acid, and 1,4- Examples include cyclohexanedicarboxylic acid, and examples of the unsaturated polybasic acid include maleic acid, maleic anhydride, fumaric acid, phthalic anhydride, terephthalic acid, and isophthalic acid. Examples of the polyhydric alcohol include dihydric alcohols and trihydric alcohols. Examples of the dihydric alcohol include ethylene glycol, diethylene glycol, neopentyl glycol, 1,5-pentanediol, and 1,6-hexanediol. Examples of the trihydric alcohol include glycerin and trimethylolpropane.

The alkyd resin (c) includes, in addition to the above polybasic acids and polyhydric alcohols, fats and oils and fatty acids (soybean oil, linseed oil, coconut oil, stearic acid, etc.), and natural resins (rosin, amber, etc.). An alkyd resin obtained by reacting the above-mentioned denaturing agent can be used.

The (d) fluororesin may be any one of vinylidene fluoride resin and ethylene tetrafluoride resin or a mixture thereof, a fluoroolefin and a hydroxy-containing polymerizable compound, and other copolymerizable vinyl resins. Examples include resins made of various fluorine-based copolymers obtained by copolymerizing monomers made of compounds.

Examples of the epoxy resin (e) include resins obtained by the reaction of bisphenol and epichlorohydrin. Examples of the bisphenol include bisphenols A and F. Examples of the bisphenol type epoxy resin include, for example, Epicoat 828, Epicoat 1001, Epicoat 100
4, Epicoat 1007, Epicoat 1009 (all manufactured by Shell Chemical Co., Ltd.), and those obtained by chain-extending these with an appropriate chain extender can also be used.

Examples of the polyurethane resin (f) include resins having a urethane bond obtained by various polyol components such as acryl, polyester, polyether and polycarbonate and a polyisocyanate compound. Examples of the polyisocyanate compound include 2,4-tolylene diisocyanate (2,4-TD
I), 2,6-tolylene diisocyanate (2,6-T
DI), and mixtures thereof (TDI), diphenylmethane-4,4′-diisocyanate (4,4′-MD
I), diphenylmethane-2,4'-diisocyanate (2,4'-MDI), and mixtures thereof (MDI)
Naphthalene-1,5-diisocyanate (NDI),
3,3'-dimethyl-4,4'-biphenylene diisocyanate (TODI), xylylene diisocyanate (XDI), dicyclohexylmethane diisocyanate (hydrogenated HDI), isophorone diisocyanate (I
PDI), hexamethylene diisocyanate (HD
I), hydrogenated xylylene diisocyanate (HXDI)
And the like.

The (g) polyether resin is a polymer or copolymer having an ether bond, and is a polyoxyethylene polyether, polyoxypropylene polyether, polyoxybutylene polyether, or bisphenol. A polyether resin having at least two hydroxyl groups per molecule, such as a polyether derived from an aromatic polyhydroxy compound such as A or bisphenol F, can be mentioned. Further, the polyether resin and succinic acid, adipic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, polyvalent carboxylic acids such as trimellitic acid, or a reactive derivative of these acid anhydrides and the like. Carboxyl group-containing polyether resin obtained by the above method.

When the vehicle contains a cross-linking agent, the ratio of the resin for forming a film to the cross-linking agent is 90 to 50% by mass and the content of the cross-linking agent is 10 to 50% by mass in terms of solid content. Yes, preferably 85 to 60% by mass of the resin for forming the coating film and 15 to 40% by mass of the crosslinking agent. If the amount of the crosslinking agent is less than 10% by mass (the amount of the resin for forming a coating film exceeds 90% by mass), the crosslinking in the coating film may not be sufficient. On the other hand, if the cross-linking agent exceeds 50% by mass (the resin for forming a coating film is less than 50% by mass), the storage stability of the coating composition decreases and the curing speed increases, so that the coating film appearance may be deteriorated. There is.

As the color pigment used in the intermediate coating,
For example, azo lake pigments, phthalocyanine pigments, indico pigments, berylen pigments, quinophthalone pigments,
Organic pigments such as dioxazine pigments, quinacridone pigments, isoindolinone pigments, metal complex pigments and carbon black, and inorganic pigments such as graphite, yellow iron oxide, red iron oxide and titanium dioxide. The amount of the coloring pigment to be added can be set arbitrarily according to the desired hue. Further, various extender pigments such as barita powder, precipitated barium sulfate, barium carbonate, gypsum, clay, silica, talc, magnesium carbonate, and alumina white can be used in combination.

The total pigment content (PW)
C) is preferably from 10 to 50%, more preferably from less than 10 to 30%.

In addition to the above-mentioned components, the above-mentioned intermediate coating composition comprises a polyamide wax as a lubricating dispersion of an aliphatic amide, a polyethylene wax as a colloidal dispersion mainly composed of polyethylene oxide, a curing catalyst, an ultraviolet absorber, Inhibitors, leveling agents, surface conditioners such as silicon and organic polymers, anti-sagging agents, thickeners, defoamers, lubricants, crosslinkable polymer particles (microgels) and the like can be added as appropriate. The performance of paints and coatings can be improved by blending these additives at a ratio of 15 parts by mass or less based on 100 parts by mass of the vehicle (based on solid content).

The intermediate coating composition is usually provided in a form in which the above components are dissolved or dispersed in a solvent. Any solvent may be used as long as it dissolves or disperses the vehicle, and an organic solvent and / or water may be used. Examples of the organic solvent include those commonly used in the field of coatings. For example, toluene, hydrocarbons such as xylene, acetone, ketones such as methyl ethyl ketone, ethyl acetate, butyl acetate, cellosolve acetate,
Esters such as butyl cellosolve and alcohols can be exemplified. When the use of an organic solvent is regulated from the viewpoint of the environment, it is preferable to use water. in this case,
An appropriate amount of a hydrophilic organic solvent may be contained.

The viscosity of the intermediate coating at the time of application is determined by using the above-mentioned organic solvent and / or water and a mixture thereof.
It is preferable to adjust to 10 to 30 seconds (Ford cup # 4/20 ° C). If the above viscosity is lower than the above range, there is a possibility that it will be mixed with the top coating base paint to be applied next, and if it exceeds the above range, it is difficult to handle, and the coating film is dried early, and There is a possibility that surface irregularities that cannot be covered or repaired by the coating film may occur.

The method for forming the intermediate coating film is not particularly limited, but a spray method, a roll coater method and the like are preferable. The preferred dry film thickness of the intermediate coating film is 5 to 80 μm, more preferably 10 to 50 μm. After the formation of the intermediate coating film, setting is performed, and the process proceeds to the next step of forming the top coating base film without heating and curing.

Top coat base coat The top coat base coat in the method for forming a multilayer coat of the present invention is obtained by applying a top coat base coat on the uncured intermediate coat by a wet-on-wet method. Can be This top coat base coating forms a coating film for the purpose of imparting a design, ensuring adhesion with the intermediate coating film formed in the previous step, and ensuring adhesion with the clear top coating film to be applied in the next step. It is.

The top coating base paint is formed from a glitter paint or a solid paint containing a vehicle, a glitter pigment and / or a color pigment, an extender pigment, various additives and a solvent. The overcoat base paint is aqueous or organic solvent-based, including aqueous dispersions and organic solvent dispersions.

As the vehicle, coloring pigment, extender, various additives and solvent contained in the above-mentioned base coating, any of those described for the above-mentioned intermediate coating can be used. The vehicle contained in these base paints
In the glittering base paint, the glittering pigment and the coloring pigment as necessary are dispersed, and in the solid base paint, the coloring pigment is dispersed, and it is composed of a resin for forming a coating film and, if necessary, a crosslinking agent. The combination of the vehicle-forming resin and the cross-linking agent may be at least one kind of coating selected from acrylic resin, polyester resin, fluororesin, epoxy resin, polyurethane resin, polyether resin, and modified resins thereof. A mixture of the reactive resin and the above-mentioned crosslinking agent can be used. Preferably, an acrylic resin / melamine resin system is used. In this case, the acrylic resin has an acid value of 10 to 200 and a hydroxyl value of 30 to 20.
Those having 0 and a number average molecular weight of 2,000 to 50,000 are preferred.

Among the pigments contained in the overcoat base paint, the glitter pigments include, for example, aluminum flake pigment, colored aluminum flake pigment, interference mica pigment, colored mica pigment, metal oxide-coated alumina flake pigment, metal oxide Coated glass flake pigment, metal plated glass flake pigment, metal oxide coated glass flake pigment, metal oxide coated silica flake pigment, metal titanium flake pigment, graphite pigment, stainless flake pigment, plate-like iron oxide pigment, phthalocyanine flake pigment or hologram Pigments can be mentioned. When using the above-mentioned glitter pigment and / or coloring pigment, the total content (PWC) of the entire pigment is preferably 1 to 50%, more preferably 5 to 30%. If it is less than 1%, the design is not sufficiently imparted, and if it exceeds 50%, the appearance of the coating film may be deteriorated.

The above-mentioned top coat base paint has a viscosity of 1% at Ford cup # 4/20 ° C. using a suitable diluent.
It is desirable to adjust to 0 to 30 seconds. If the viscosity is lower than the above range, there is a risk of mixing with the overcoat clear coating to be applied next, and, if it exceeds the above range, it is difficult to handle, and the coating film solidifies early, and There is a possibility that surface irregularities that cannot be covered or repaired by the coating film may occur.

The method for forming the above-mentioned base coat is not particularly limited, but a spray method, a roll coater method and the like are preferable. It is also possible to paint a plurality of times. The dry film thickness of the above top coat base film is 5 to 5 per coat.
50 μm is preferable, and 10 to 30 μm is more preferable.

Top clear coating film The top clear coating film in the method for forming a multilayer coating film of the present invention is obtained by applying the top clear coating film on the uncured top coating base film by a W / W method. Can be The clear topcoat coating forms a coating film for protecting the basecoat base coating film and imparting a sense of design depth.

The above-mentioned clear top coating is formed from a clear coating containing a vehicle, various additives and a solvent. The clear top coating is water-based or organic solvent-based, including aqueous dispersions and organic solvent dispersions.

As the vehicle, various additives and the organic solvent contained in the clear top coating, any of those described for the intermediate coating can be used. Is preferably an acrylic resin / melamine resin type. In this case, the acrylic resin has an acid value of 10 to 20.
0, hydroxyl value 30 to 200, and number average molecular weight 200
Those having 0 to 50,000 are preferred.

From the viewpoint of preventing acid rain and increasing the difference in solubility between the base coat and the base coat in W / W, the clear paint does not disturb the orientation of the brilliant pigment in the base coat. A clear coating containing a carboxyl group-containing polymer and an epoxy group-containing polymer described in JP-A-8-19315 is preferably used. Also, these clear paints, if necessary,
As long as the transparency is not impaired, coloring pigments, extender pigments,
Additives such as a modifying agent, an ultraviolet absorber, a leveling agent, a dispersant, and an antifoaming agent can be blended.

The method for forming the above clear top coat is not particularly limited, but a spray method, a roll coater method and the like are preferable. The dry film thickness of the top clear coating film is 1
20 to 50 μm is preferable per coat, and 25 to 40 μm
m is more preferred. After the formation of the above-mentioned top coat, the intermediate coat, top coat base coat and top coat clear coat
The coating film of the layers is baked at 120 to 160 ° C. for a predetermined time to obtain a multilayer coating film.

Composite Coating The composite coating obtained by the method of forming a multilayer coating according to the present invention has a cured electrodeposition coating having a glass transition temperature of 11
An uncured intermediate coating film, a top coating base coating film and a top coating clear coating film are coated on the electrodeposited coating surface having a temperature of 0 ° C. or more and a surface roughness (Ra) of 0.3 μm or less. After the formation, it is obtained by simultaneously heating and curing the three-layer coating film.

[0058]

EXAMPLES Next, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples. In addition, the compounding amount represents a mass part unless there is particular notice.

Preparation of cationic electrodeposition coatings A to F Preparation example 1: Preparation of pigment paste (1) Isophorone diisocyanate (hereinafter referred to as IPDI)
222.0 parts), diluted with 39.1 parts of methyl isobutyl ketone (hereinafter abbreviated as MIBK), and then 0.2 parts of dibutyltin laurate was added. Then 50 ° C
To 2-ethylhexanol (hereinafter 2EH)
131.5 parts were stirred in a dry nitrogen atmosphere under stirring.
It was dropped over time. The reaction temperature was maintained at 50 ° C. by cooling appropriately. As a result, 2-ethylhexanol half-blocked IPDI was obtained (resin solid content: 90%). (2) Dimethylethanolamine 87.2 was added to the reaction vessel.
, A 75% aqueous lactic acid solution (117.6 parts) and ethylene glycol monobutyl ether (39.2 parts) were added in order.
The mixture was stirred at about half an hour to prepare a quaternizing agent. (3) Next, 710.0 parts of EPON 829 (manufactured by Shell Chemical Company; bisphenol A type epoxy resin, epoxy equivalent 193 to 203) and 289.6 parts of bisphenol A were charged into an appropriate reaction vessel.
It heated to 150-160 degreeC under nitrogen atmosphere. An initial exothermic reaction occurred. The reaction mixture was reacted at 150 to 160 ° C. for about 1 hour, and then cooled to 120 ° C., and then 498.8 parts of 2-ethylhexanol half-blocked IPDI (MIBK solution) prepared in the above (1) was added.
The reaction mixture is kept at 110-120 ° C. for about 1 hour, then ethylene glycol monobutyl ether 1390.
2 parts were added, the mixture was cooled to 85 to 95 ° C., and after homogenization, 196.7 parts of the quaternizing agent prepared in the above (2) was added. The reaction mixture is heated to 85 to 95 ° C. until the acid value becomes 1.
And then add 37.0 parts of deionized water to terminate quaternization in the epoxy-bisphenol A resin,
A pigment dispersion resin having a quaternary ammonium group was used (resin solid content: 50%). (4) 19.1 parts of a pigment dispersion resin having a quaternary ammonium group prepared in the above (3), titanium dioxide 30.4
Parts, kaolin 15.4 parts, carbon black 0.9 parts,
A mixture of 34.3 parts of ion-exchanged water was dispersed in a sand grind mill to prepare a pigment paste (solid content: 56%) pulverized to a particle size of 10 μm or less.

Production Example 2: Polyurethane crosslinking agent (IPDI
Preparation of System) 222 parts of isophorone diisocyanate was placed in a reaction vessel equipped with a stirrer, a thermometer, a cooling pipe, and a nitrogen introduction pipe.
After diluting with 56 parts of methyl isobutyl ketone, 0.2 parts of dibutyltin dilaurate was added, and after raising the temperature to 50 ° C, 174 parts of methyl ethyl ketoxime was added so that the temperature did not exceed 70 ° C. The mixture was kept at 70 ° C. for 1 hour until the absorption of isocyanate groups substantially disappeared by infrared absorption spectrum, and then diluted with 43 parts of n-butanol to prepare a polyurethane crosslinking agent (solid content: 80%).

Production Example 3: Polyurethane crosslinking agent (NBDI)
Preparation of system) 206 parts of norbornane diisocyanate was placed in a reaction vessel equipped with a stirrer, a nitrogen inlet tube, a cooling tube and a thermometer, diluted with 55 parts of methyl isobutyl ketone, and then 0.2 parts of dibutyltin laurate was added. After the temperature rises,
Then, 174 parts of methyl ethyl ketoxime were added at a temperature of 70.
It was added not to exceed ° C. The mixture was kept at 70 ° C. for 1 hour until the absorption of isocyanate groups substantially disappeared by an infrared absorption spectrum, and then diluted with 40 parts of n-butanol to prepare a polyurethane crosslinking agent (solid content: 80%).

Production Example 4: Polyurethane crosslinking agent (HMDI
Preparation of system) A reaction vessel equipped with a stirrer, a thermometer, a cooling pipe and a nitrogen introduction pipe was charged with 840 parts of hexamethylene diisocyanate, diluted with 609 parts of methyl isobutyl ketone, and then 0.9 parts of dibutyltin dilaurate was added. After raising the temperature to 223.5 parts of trimethylolpropane at a temperature of 60
C. was added slowly so as not to exceed .degree. Then 435 parts of methyl ethyl ketoxime were added so that the temperature did not exceed 70 ° C. The mixture was kept at 70 ° C. for 1 hour until the absorption of isocyanate groups substantially disappeared by an infrared absorption spectrum, and then diluted with 32 parts of n-butanol to prepare a polyurethane crosslinking agent (solid content: 70%).

Production Example 5 Preparation of Amino Group-Containing Acrylic Copolymer 1500 parts of butyl cellosolve was charged into a reaction vessel equipped with a stirrer, thermometer, decanter, reflux condenser, nitrogen inlet tube and dropping funnel, and nitrogen gas was introduced. While increasing the temperature to 120 ° C., 627 parts of methyl methacrylate, 191 parts of lauryl methacrylate, 4-hydroxybutyl acrylate 1
A mixture of 82 parts, 300 parts of 2-methoxyethyl acrylate, 200 parts of dimethylaminoethyl methacrylate and 50 parts of t-butylperoxy-2-ethylhexanoate was dropped at a constant speed over 3 hours. After completion of the dropwise addition, the mixture was further reacted at 120 ° C. for 3 hours and then cooled to obtain an amino group-containing acrylic copolymer. The obtained resin had a number average molecular weight of 10,000 and an amine value of 48 at a solid content of 50%.

Production Example 6 Preparation of Aqueous Dispersion of Cationic Resin In a reaction vessel, 633 parts of Epicoat 828 (Yukaka Epoxy Co., Ltd .; bisphenol A type epoxy resin, epoxy equivalent: 188), 633 parts, methanol 65 parts, methyl isobutyl ketone 169 parts and 0.3 parts of dibutyltin dilaurate were stored and stirred at room temperature to obtain a homogeneous solution.
When 147 parts of a 2,6-tolylene diisocyanate 80/20 (weight ratio) mixture was added dropwise over 50 minutes, the temperature in the system reached 70 ° C. due to heat generation. The IR spectrum showed a disappearance of the absorption at 2280 cm ^-1 based on the isocyanate and an absorption at 1730 cm ^-1 based on the carbonyl group of the urethane. After adding 2 parts of N, N-dimethylbenzylamine, the temperature of the system was raised to 120 ° C., and the reaction was carried out until the epoxy equivalent reached 463 while distilling off by-produced methanol by a decanter. The IR spectrum showed the disappearance of the absorption at 1730 cm ^-1 based on the urethane carbonyl group and the appearance of an absorption at 1750 cm ^-1 based on the carbonyl group of the oxazolidone ring. 185 parts of p-nonylphenol and 70 parts of methyl isobutyl ketone were added, and while maintaining the temperature at 125 ° C., the epoxy equivalent was 11 parts.
The reaction was run until 46 was reached. The temperature in the system is 110 ℃
And cooled to a ketimine of aminoethylethanolamine (79% by mass solution in methyl isobutyl ketone).
After adding 0 parts, 35 parts of diethanolamine, 25 parts of N-methylethanolamine and 15 parts of methyl isobutyl ketone, the mixture was heated and reacted at 120 ° C. for 2 hours. Thus, a cationic epoxy resin having an amine value of 54 was obtained, and then the polyurethane crosslinking agent of Production Example 2 (IPDI
System) 330 parts, 90 parts of the amino group-containing acrylic copolymer of Production Example 5, ethylene glycol monohexyl ether 1
40 parts were mixed. 1800 parts of the obtained cationic resin was added to a mixed solution of 29 parts of glacial acetic acid and 414 parts of ion-exchanged water, and the mixture was sufficiently stirred.
Parts were added slowly. Then, the organic solvent and water were removed under reduced pressure until the solid content became 36% to obtain an aqueous dispersion of a cationic resin.

Production Example 7: Preparation of cationic electrodeposition paint A Aqueous dispersion 1346 of the cationic resin obtained in Production Example 6
The mixture was mixed with 1744 parts of ion-exchanged water and 371 parts of the pigment paste of Production Example 1 to obtain a cationic electrodeposition coating material A.

Production Example 8: Preparation of cationic electrodeposition coating material B The same procedure as in Production Example 7 was carried out except that the polyurethane crosslinking agent (IPDI type) of Production Example 2 was replaced with the polyurethane crosslinking agent (NBDI type) of Production Example 3. A coating material B was obtained.

Production Example 9 Preparation of Cationic Electrodeposition Coating C The same procedure as in Production Example 7 was repeated except that the polyurethane crosslinking agent (IPDI type) in Production Example 2 was replaced with the polyurethane crosslinking agent (HMDI type) in Production Example 4. A coating material C was obtained.

Production Example 10: Preparation of cationic electrodeposition paint D The amount of the polyurethane crosslinking agent (HMDI system) of Production Example 4 was changed to 3
30 to 495 parts, the amount of hexyl cellosolve is 140
Cationic electrodeposition coating material D was obtained in the same manner as in Production Example 9 except that the parts were changed to 130 parts.

Production Example 11: Preparation of cationic electrodeposition paint E The amount of the polyurethane crosslinking agent (IPDI system) of Production Example 2 was changed to 3
30 to 250 parts, the amount of hexyl cellosolve is 140
A cationic electrodeposition coating material E was obtained in the same manner as in Production Example 7, except that the parts were changed to 160 parts.

Production Example 12: Preparation of cationic electrodeposition paint F A cationic electrodeposition paint F was obtained in the same manner as in Production Example 7, except that the amount of the pigment paste was changed from 371 parts to 500 parts.

Examples 1 to 10 and Comparative Examples 1 to 4 Preparation of Substrates Dull steel plates (length 300 mm, width 100 mm and thickness 0.8 mm) were treated with a zinc phosphate treating agent ("Surfdyne SD2
000 "(manufactured by Nippon Paint Co., Ltd.), and the cationic electrodeposition coatings A to F prepared as described above were electrodeposited in a combination shown in Table 1 so that the dry film thickness was 25 μm. . Then bake at 160 ° C for 30 minutes,
The substrate was used.

Formation of Intermediate Coating Film The above substrate is air-sprayed with a polyester / amino resin-based intermediate coating material (“Olga S-90 Sealer Gray”, manufactured by Nippon Paint Co., Ltd.) to a dry film thickness of 40 μm. After coating, the coating was set at room temperature for 3 minutes to form an intermediate coating film.

Top coat base coat and top coat clear coat
The formation and then the intermediate coating film surface of the fee, a base top coating material shown below in combination shown in Table 1, dry thickness was coated so that the 15 [mu] m. After coating, set at room temperature for 3 minutes, apply a clear top coating so that the dry film thickness becomes 35 μm, set at room temperature for 10 minutes, and apply at 140 ° C.
For 30 minutes. The clear top paint used was acrylic / melamine resin clear paint 1.
(“Super Lac O-130 Clear”, manufactured by Nippon Paint Co., Ltd.) or a clear paint 2 containing a carboxyl group-containing polymer and an epoxy group-containing polymer (“Macflow O-520 Clear”, manufactured by Nippon Paint Co., Ltd.) Kind. The Tg and Ra of the electrodeposition coating film and the coating film appearance of the obtained composite coating film were evaluated by the following evaluation methods. Table 1 shows the results.

Overcoat base paint 1: Acrylic amino resin-based overcoat base paint containing aluminum flake pigment;
(“Superlac M-180 Silver”, manufactured by Nippon Paint Co., Ltd.), Topcoat basecoat 2: acrylic-amino resin-based topcoat basecoat containing interference mica pigment;
180 mica base ", manufactured by Nippon Paint Co., Ltd.)

Evaluation method Tg of electrodeposited coating film: Tg was measured using Reovibron (manufactured by Orientic). The measurement conditions were as follows: dynamic Young's modulus (E ′) and dynamic loss (E ″) obtained by applying vibration of a frequency of 11 Hz to the coating film at a rate of temperature increase of 2 ° C. per minute.
Is used to calculate the mechanical loss (Tan
δ) was determined as the temperature giving the maximum value. Tan δ = E ″ / E ′

Ra of electrodeposited film: The surface roughness Ra (center line average roughness) of the electrodeposited film after drying was measured in accordance with JIS-B0601, using a surface roughness meter (type: Surf Test 211, Mi).
(manufactured by Tsutoyo).

Appearance of composite coating film: The appearance of the formed composite coating film was visually evaluated according to the following criteria. 3: No poor coating appearance of composite coating due to electrodeposited coating 2: Slight poor coating appearance of composite coating due to electrodeposition coating 1: Composite coating due to electrodeposition coating Coating appearance defect is remarkable

[0078]

[Table 1]

As is evident from the results shown in Table 1, Examples 1 to 10 were obtained by forming a coating film by the coating film forming method of the present invention, and did not have any coating film defect due to the electrodeposition coating film. A good composite coating film could be formed. On the other hand, Comparative Examples 1 to 4
In the case of (2), poor appearance of the coating film caused by the electrodeposition coating film occurred, and a desired composite coating film could not be formed.

[0080]

According to the method for forming a coating film of the present invention, a cured electrodeposition coating film formed on a substrate with a cationic electrodeposition coating material has a glass transition temperature of 110 ° C. or more and a surface roughness ( R
a: center line average roughness) is 0.3 μm or less, an intermediate coating, a top coating base coating, and a top coating clear coating are sequentially applied to the electrodeposited coating surface, and an uncured intermediate coating film and a top coating base coating are applied. Further, after forming a three-layer coating film of a clear top coating film, the above-mentioned three-layer coating film is simultaneously heated and cured to form a good composite coating film without a coating appearance defect caused by an electrodeposition coating film. Was possible.

The composite coating film obtained by the present invention has a good coating appearance and can save energy required for baking and drying in the coating process. Therefore, the outer coating of vehicles such as automobiles and motorcycles, outer surfaces of containers, coil coating, etc. It is preferably used in fields requiring high appearance and energy savings during painting, such as the home appliance industry.

 ──────────────────────────────────────────────────続 き Continuing on the front page F term (reference) 4D075 AE03 AE08 AE09 AE10 BB89X CA48 DC12 EA19 EA43 EB32 EB33 EB35 4F100 AA03B AA21B AA37B AB03A AB10D AK24E AK25D AK25E AK35C CCB AK36E AK36 CC03A03 CCB GB32 GB48 JA05B JK15 JK15B JL00 JL09 YY00B

Claims (5)

[Claims] 1. A cured electrodeposition coating film formed by coating a cationic electrodeposition coating material on a substrate has a glass transition temperature of 110 ° C. or higher and a surface roughness (Ra: center line average roughness). 0.
An intermediate paint, a top coat base paint, and a top clear coat are sequentially applied to the electrodeposited coat surface of 3 μm or less, and a three-layer coat of an uncured intermediate coat, a top coat base coat, and a top coat clear coat is applied. After the formation, a method for forming a multilayer coating film in which the three-layer coating film is simultaneously heated and cured. 2. The cured electrodeposition coating film having a glass transition temperature of 1
10 to 150 ° C. and a surface roughness (Ra) of 0.1
The method for forming a multilayer coating film according to claim 1, wherein the thickness is from 0.3 to 0.3 m. 3. The method for forming a multilayer coating film according to claim 1, wherein said intermediate coating film is formed of a thermosetting intermediate coating material containing a polyester resin and an amino resin as a vehicle component. 4. The method for forming a multilayer coating film according to claim 1, wherein said clear top coating film is formed by a coating material containing a carboxyl group-containing polymer and an epoxy group-containing polymer. 5. A multilayer coating film formed by a multilayer coating film forming method according to any one of claims 1 to 4.