JPH11207252A - Multiple-layer coating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve finish appearance (smoothness, gloss and the like), interlaminar adhesion and the like and lower VOC(content of volatile organic compound) and shorten a coating process. SOLUTION: A cation electrodeposition coat (A) adjusted so as to start crosslinkage curing reaction of a coating film before than of an intermediate coat adjacent thereto starts is applied on a coating object matter, an aqueous intermediate coat (B) containing a block polyisocianate compound as a crosslinking agent is applied on its uncured coating face. After the coating (A), (B) are cured by heating, a coloring finish coat (C) excellent in substrate concealing property and a transparent coat forming water-based finish coat (D) are applied sequentially, and the both coats (C) and (D) are cured by heating and then a clear coat is further applied on the cured coating film face and curing by heating is effected.

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 multi-layer coating film by sequentially applying a cationic electrodeposition coating, an aqueous intermediate coating, a colored top coating, an aqueous top coating and a clear coating on an object to be coated. In particular, the formation of a novel multi-layer coating film in which the finished appearance (smoothness, glossiness, etc.) and interlayer adhesion are improved, the VOC (volatile organic compound content) is low, and the coating process is shortened. About the method.

[0002]

2. Description of the Related Art A cationic electrodeposition coating material and a liquid coating material containing a block polyisocyanate as a curing agent are applied to a metal substrate by wet-on-wet, and the two coating films are simultaneously cured by heating. A method for forming a two-layer coating film is known (for example, see Japanese Patent Publication No. 56-20073).
However, the two-layer coating film formed by this method has a drawback that the finished appearance such as smoothness and luster is not sufficient. Furthermore, even if a top coat is applied to this coated surface, these drawbacks cannot be eliminated, and if pebbles or the like hit these coated surfaces, the interlayer between the electrodeposition coating film and the liquid coating film will be lost. This also has a disadvantage that chipping peeling (pilling) easily occurs.

[0003] Further, the intermediate coating, which comprises the steps of electrodeposition coating, heat curing, first intermediate coating, heat curing, second intermediate coating, heat curing, colored top coating, clear coating, and heat curing, is performed in two steps. Or two or more clear coatings consisting of electrodeposition coating-heat curing-intermediate coating-heating curing-colored top coating-first clear coating-heat curing-second clear coating-heat curing However, these coating systems are all five-coat and four-bake systems, and although the finished appearance of the coating film is excellent, it cannot be said that it is sufficient. Since the paint, the top coat and the clear paint are all organic solvent-based, they are not preferable from the viewpoint of pollution prevention and resource saving, and reduction in the number of heating steps is also desired.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to improve the finished appearance and chipping-off resistance of a two-layer coating film formed from the above-mentioned cationic electrodeposition coating material and liquid coating material. To provide a novel method for forming a multilayer coating film in which the finish appearance in a 4-bake type coating system is improved, the VOC (volatile organic compound content) is low, and the coating process is shortened. .

The present inventors have proposed a process of cationic electrodeposition coating-aqueous intermediate coating-heat curing-colored top coating-aqueous top coating-heat curing-clear coating-heat curing (5 coats 3).
By applying a coating system consisting of a bake system) and adjusting the cross-linking curing reaction of the cationic electrodeposition coating film to start earlier than that of the intermediate coating film, the above object can be sufficiently achieved. We have found and completed the present invention.

Thus, according to the present invention, a block polyisocyanate is used as a cross-linking agent, which is adjusted so that the cross-linking and curing reaction of the coating starts earlier than that of an adjacent intermediate coating. A cationic electrodeposition paint (A) containing a compound is applied, an aqueous intermediate coating (B) containing a block polyisocyanate compound as a cross-linking agent is applied to the uncured coated surface, and then the paint (A) is heated. After curing both coating films A) and (B), a colored top coating material (C) and a transparent film-forming water-based top coating material (D) having excellent base concealment properties
Are sequentially coated and heated to cure both coatings (C) and (D), and then the clear coating (E) is applied to the cured coating surface and cured by heating. A film forming method is provided.

[0007] In the present specification, the timing of the start of crosslinking and curing of the coating film of the cationic electrodeposition coating material (A) and the aqueous intermediate coating material (B) is measured by a pendulum type viscoelasticity meter (manufactured by Toyo Boldwin, Leo Vibron DDV). -OPA type). Specifically, using a pendulum having a weight of 22 g and an inertial moment of 850 g · cm ² , these paints were applied to a steel plate so that the film thickness based on the cured film was 30 μm. When the pendulum is heated at a predetermined temperature (for example, 140 to 180 ° C.) for crosslinking and curing the coating film while the pendulum is vibrated, the value of the logarithmic attenuation rate of the vibration of the pendulum starts to increase. Is referred to as “crosslinking curing start time”. And the time required from the start of heating of the coating film to the time of the start of crosslinking and curing is referred to as `` curing start time ''
A shorter time means that the crosslinking curing reaction starts earlier. The comparison of the crosslinking curing start times of the coating films (A) and (B) is carried out at the same temperature.

Hereinafter, the method for forming a multilayer coating film of the present invention will be described in more detail.

[0009] article to be coated: coating objects which can be painted by the method of the present invention is not particularly limited as long as the product cation electrodeposition coating capable at least the surface is metal, such as iron, copper,
Examples include aluminum, tin, zinc and alloys containing these metals, and products plated or deposited with these metals. In particular, automobile bodies such as passenger cars, trucks, buses, and motorcycles made of these metals are suitable. It is preferable that the surface of these objects to be subjected to a chemical conversion treatment with a phosphate, a chromate or the like before the cationic electrodeposition coating.

[0010] Cationic electrodeposition paint (A): The cationic electrodeposition paint (A) contains a block polyisocyanate compound as a cross-linking agent, and specifically includes, for example, a hydroxyl group and a cationic group. A known cationic electrodeposition paint containing the base resin (a-1) and the block polyisocyanate compound (a-2) can be used.

In the base resin (a-1), the hydroxyl group is involved in a crosslinking reaction with the block polyisocyanate compound, and the cationic group is for forming a stable aqueous dispersion. Examples of the base resin (a-1) having such a group include the following.

I): a reaction product of a polyepoxy resin and a cationizing agent; ii): a polycondensation product of a polycarboxylic acid and a polyamine (see US Pat. No. 2,450,940), which is protonated with an acid; iii): a polyisocyanate compound or a polyadduct of a polyol and a mono- or polyamine protonated with an acid; iv): a copolymer of an acrylic or vinyl monomer containing a hydroxyl group and an amino group with an acid. Protonated (JP-B-45-12395, JP-B-45-123)
No. 96), v): A product obtained by protonating an adduct of a polycarboxylic acid resin and an alkyleneimine with an acid (US Pat. No. 34030).
No. 88).

Specific examples and production methods of these cationic resins are described, for example, in JP-B-45-12395, JP-B-45-12396, and JP-B-49-23.
No. 087, U.S. Pat. No. 2,450,940, U.S. Pat. No. 3,403,088, U.S. Pat.
No. 529, U.S. Pat. No. 3,963,663, and the like, and the detailed description will be replaced with reference to these documents.

As a particularly preferred base resin (a-1), a cationizing agent is added to the epoxy group of the polyepoxide resin excellent in anticorrosion obtained by the reaction between the polyphenol compound and epichlorohydrin, which is included in the above i). Resins obtained by the reaction can be mentioned.

The polyepoxide resin has one epoxy group.
Compounds having two or more in the molecule, particularly those having a number average molecular weight of at least 200, preferably 400 to 4,000, more preferably 800 to 2,000 are suitable. As such a polyepoxide resin, those known per se can be used.For example, polyglycidyl of a polyphenol compound which can be produced by reacting a polyphenol compound with epichlorohydrin in the presence of an alkali can be used. Ethers are included. Examples of the polyphenol compound usable here include, for example, bis (4-hydroxyphenyl)
-2,2-propane, 4,4'-dihydroxybenzophenone, bis (4-hydroxyphenyl) -1,1-ethane, bis- (4-hydroxyphenyl) -1,1-isobutane, bis (4-hydroxy- tert-butyl-
Phenyl) -2,2-propane, bis (2-hydroxybutyl) methane, 1,5-dihydroxynaphthalene, bis (2,4-dihydroxyphenyl) methane, tetra (4-hydroxyphenyl) -1,1,2,2 2-ethane, 4,4'-dihydroxydiphenyl ether, 4,
4'-dihydroxydiphenyl sulfone, phenol novolak, cresol novolak and the like.

Among these polyepoxide resins, those particularly suitable for producing the base resin (a-1) have a number average molecular weight of at least about 380, preferably from about 800 to about 2.0.
It is a polyglycidyl ether of a polyphenol compound having a molecular weight of 00 and an epoxy equivalent of 190 to 2,000, preferably 400 to 1,000. This may be modified by partially reacting with a polyol, a polyether polyol, a polyester polyol, a polyamidoamine, a polycarboxylic acid, a polyisocyanate compound, etc., and further, ε-caprolactone, An acrylic monomer or the like may be graft-polymerized.

The above i) included in the base resin (a-1)
Is a product obtained by reacting a cationizing agent with an epoxy group of a polyepoxide resin obtained by reacting the above-mentioned polyphenol compound with epichlorohydrin, and the cationizing agent is almost all of the epoxy groups of the polyepoxide resin. Alternatively, it is preferable to react with all.

Examples of the cationizing agent include amine compounds such as primary amines, secondary amines, tertiary amines and polyamines, which are reacted with the epoxy groups of the polyepoxide resin by a method known per se. Then, a base resin having a hydroxyl group and a cationic group can be obtained by introducing a cationic group such as a secondary amino group, a tertiary amino group, and a quaternary ammonium base into the resin.

Examples of the primary amine compound as a cationizing agent include methylamine, ethylamine, n-propylamine, isopropylamine, monoethanolamine, n-propanolamine, isopropanolamine and the like. As the secondary amine compound, for example, diethylamine, diethanolamine, din
-Propanolamine, diisopropanolamine, N
-Methylethanolamine, N-ethylethanolamine and the like. Examples of the tertiary amine compound include triethylamine, triethanolamine, and the like.
N, N-dimethylethanolamine, N-methyldiethanolamine, N, N-diethylethanolamine, N
-Ethyldiethanolamine and the like, and polyamines include, for example, ethylenediamine, diethylenetriamine, hydroxyethylaminoethylamine, ethylaminoethylamine, methylaminopropylamine, dimethylaminoethylamine, dimethylaminopropylamine and the like.

Further, ammonia, hydroxyamine,
A basic compound such as hydrazine, hydroxyethylhydrazine, N-hydroxyethylimidazoline or the like may be used as a cationizing agent, and the basic group formed by the reaction with the epoxy group may be protonated with an acid to form a cationic group. As the acid that can be used, a water-soluble organic carboxylic acid such as formic acid, acetic acid, glycolic acid, and lactic acid is preferable.

The hydroxyl groups in the base resin (a-1) include:
For example, a primary hydroxyl group introduced into a resin by a reaction with an alkanolamine as a cationizing agent, a ring opening reaction with caprolactone which may be introduced into an epoxy resin, or a reaction with a polyol; And secondary hydroxyl groups in the resin. Of these, primary hydroxyl groups introduced by reaction with an alkanolamine are preferred because of their excellent crosslinking reactivity with a block polyisocyanate compound (crosslinking agent).

The base resin (a-1) in the cationic electrodeposition coating composition (A) has a hydroxyl group in an amount of generally from 20 to
It is preferably contained in an amount within the range of 5,000, particularly 100 to 1,000 mg KOH / g, and particularly preferably one having a primary hydroxyl group equivalent in the range of 200 to 1,000 mg KOH / g. The content of the cationic group is preferably at least the minimum necessary for stably dispersing the base resin in water, and is generally 3 to 3 in terms of KOH (mg / g solid content) (amine value). 200, especially 10
It is preferably in the range of 80. Base resin (a-
1) desirably does not contain a free epoxy group in principle.

On the other hand, the block polyisocyanate compound (a-2) as a crosslinking agent is obtained by blocking all of the isocyanate groups of the polyisocyanate compound with a volatile active hydrogen compound (blocking agent). When heated to a predetermined temperature or higher, the blocking agent is dissociated and the original isocyanate group is regenerated to participate in a crosslinking reaction with the base resin (a-1).

The polyisocyanate compound is a compound having two or more free isocyanate groups in one molecule, for example, hexamethylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate. To
Aliphatic diisocyanates such as dimer acid diisocyanate and lysine diisocyanate; isophorone diisocyanate, methylene bis (cyclohexyl isocyanate)
A) alicyclic diisocyanates such as methylcyclohexane diisocyanate, cyclohexane diisocyanate, and cyclopentane diisocyanate; xylylene diisocyanate, tolylene diisocyanate, and diphenylmethane diamine. Isocyanate, naphthalene diisocyanate,
Aromatic diisocyanate such as toluidine diisocyanate
G; urethanized adducts, biuret type adducts, and isocyanuric ring type adducts of these polyisocyanate compounds.

As the blocking agent, for example, pheno-
, Cresol, xylenol, p-ethylphenol
, O-isopropylphenol, p-tert-butylphenol, p-tert-octylphenol, thymol, p-naphthol, p-nitrophenol, p-
Phenol blocking agents such as chlorophenol; methanol, ethanol, propanol, butanol, amyl alcohol, ethylene glycol, ethylene glycol
Monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, propylene glycol monomethyl ether, methyl cellosolve, butyl cellosolve, methyl carbitol, benzyl alcohol
Alcohol-based blocking agents such as toluene, phenyl cellosolve, furfuryl alcohol, cyclohexanol, methyl glycolate, butyl glycolate, diacetone alcohol, methyl lactate, and ethyl lactate; acetylacetone; Active methylene blocking agents such as dimethyl malonate, diethyl malonate and ethyl acetoacetate; mercaptan blocking agents such as butyl mercaptan, hexyl mercaptan, thiophenol, methylthiophenol, ethylthiophenol, and tert-dodecyl mercaptan Acid amide blocking agents such as acetanilide, acetaniside, acetate amide and benzamide; succinimide;
Imide-based blocking agents such as maleic imide; amine-based blocking agents such as diphenylamine, xylidine, dibutylamine, phenylnaphthylamine, aniline and carbazole; imidazole-based blocking agents such as imidazole and 2-ethylimidazole Urea-based blocking agents such as urea, thiourea and ethylene urea; carbamic acid-based blocking agents such as phenyl N-phenylcarbamate and 2-oxazolidone; imine-based blocking agents such as ethyleneimine and propyleneimine; formamide oxime, formaldehyde Oxime blocking agents such as oxime, acetoaldoxime, acetoxime, methyl ethyl ketoxime, diacetyl monooxime, cyclohexanone oxime; sulfite blocking agents such as sodium bisulfite and potassium bisulfite; ε-cap Lactam, δ- valerolactam,
Lactam-based blocking agents such as γ-butyrolactam and β-propiolactam are exemplified.

The block polyisocyanate compound (a-
The reaction between the polyisocyanate compound and the active hydrogen compound (blocking agent) for preparing 2) can be carried out by a known method, and the obtained blocked polyisocyanate compound is substantially free isocyanate. Desirably, it does not contain any groups.

In the cationic electrodeposition paint (A), the base resin (a-1) and the block polyisocyanate compound (A
The composition ratio with -2) is not particularly limited, but the former is 40 to 90%, based on the total solid weight of these two components,
In particular, 50 to 80%, the latter being 60 to 10%, especially 50 to 2%.
It is preferably within the range of 0%.

The cationic electrodeposition coating material (A) comprises a base resin (a)
-1) is prepared by neutralizing the cationic group in acetic acid, formic acid, lactic acid, phosphoric acid and the like with an acidic compound such as acetic acid, formic acid, lactic acid, and phosphoric acid, and then dispersing and mixing in water with the block polyisocyanate compound (a-2). And the pH of the aqueous dispersion is generally in the range of 3 to 9, especially 5 to 7,
Further, the resin solid concentration is suitably in the range of 5 to 30% by weight.

The cationic electrodeposition paint (A) may include aluminum, nickel, zinc, strontium,
A rust-proofing curing catalyst such as a hydroxide, oxide, organic acid salt or inorganic acid salt of a metal selected from zirconium, molybdenum, tin, antimony, lanthanum, tungsten, bismuth, etc .; Rust-preventing pigments; anti-settling agents and the like can be appropriately compounded.

Further, in order to promote a crosslinking reaction between the base resin (a-1) and the block polyisocyanate compound (a-2), tin octoate, Dibutyltin dilaurate, manganese, cobalt,
Lead, bismuth stannate, lead stannate, zirconium octoate, zinc octoate, dibutyltin-bis-O-phenylphenylene, dibutyltin-S, S-dibutyldithio-carbonate, triphenyl Antimony dichloride, dibutyltin maleate, dibutyltin diacetate
, Dibutyltin dilaurate mercaptide, triethylenediamine, bismuth stearate, lead stearate,
A curing catalyst such as dimethyltin dichloride can be blended. Usually, the compounding amount is suitably in the range of 0.1 to 10 parts by weight per 100 parts by weight of the total of the base resin (a-1) and the block polyisocyanate compound (a-2).

In the present invention, the cationic electrodeposition paint (A)
Is required to start earlier than the coating of the intermediate coating (B) adjacent to the upper layer. Therefore, the curing of the coating of the cationic electrodeposition coating (A) requires It is preferable to start at a lower temperature as compared with the intermediate coating (B) coating film. For example, the cationic electrodeposition coating is cured at 1 to 20 ° C., particularly 5 to 15
It is preferred to start at a lower temperature. When the onset of curing of the cationic electrodeposition coating (A) is slower than that of the intermediate coating (B), the finished appearance (smoothness, gloss, etc.) of the multilayer coating composed of both coatings and the interlayer adhesion of both coatings It becomes difficult to improve such.

The initiation time of the crosslinking curing reaction of the coating film of the cationic electrodeposition coating material (A) may be, for example, a polyisocyanate compound,
It can be easily controlled by appropriately selecting the type and amount of the blocking agent, curing catalyst, etc., and the “curing start time” from the start of heating to the start of crosslinking curing.
Is suitably in the range of about 3 to about 20 minutes, especially about 5 to about 15 minutes.

The coating of the cationic electrodeposition paint (A) is performed, for example, by using the above-mentioned object to be treated as a cathode and a carbon plate as an anode.
Bath temperature 20-35 ° C, voltage 100-400V, current density O. 01 to 5 A and energization time of 1 to 10 minutes. The coating thickness of the cured coating film is generally preferably about 10 to 40 μm.

In the present invention, the cationic electrodeposition coating material (A) is applied, and the water-based intermediate coating material (B) is applied to the uncured coating surface without curing the coating film. At this time, the coating film of the cationic electrodeposition coating material (A) can be left at room temperature and then coated with an aqueous intermediate coating (B).
The following temperatures, e.g.
After heating for about a minute to remove some of the water in the coating,
Preferably, after substantially removing the moisture in the coating film, it is desirable to apply the aqueous intermediate coating material (B) to the uncured coated surface.

Aqueous intermediate coating (B): The intermediate coating used in the present invention is an aqueous coating containing a block polyisocyanate compound as a curing agent, and specifically, an isocyanate such as a hydroxyl group. A base resin (b) having a functional group capable of undergoing a cross-linking reaction with a
-1) and the block polyisocyanate compound (b-
This is a paint containing 2) and mixing and dispersing them in water.

The base resin (b-1) contains two or more functional groups capable of cross-linking with an isocyanate group such as a hydroxyl group in one molecule in an amount necessary to make the resin water-soluble or water-dispersible. A resin having a hydrophilic group, particularly a polyester resin or an acrylic resin having a hydroxyl group and a carboxyl group is particularly suitable.

The hydroxyl group-containing polyester resin can be produced by subjecting a polybasic acid and a polyhydric alcohol to an esterification reaction, and has a number average molecular weight of 1,000.
５０50,000, especially 2,000〜20,000, hydroxyl value 20２０200 mg KOH / g, especially 50〜150.
mgKOH / g, and the acid value is 1-100 mgKOH / g.
g, particularly preferably in the range of 10 to 70 mgKOH / g.

The polybasic acid is a compound having two or more carboxyl groups in one molecule, for example, phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, tetrahydrophthalic acid, hexa Examples thereof include hydrophthalic acid, heptic acid, maleic acid, fumaric acid, itaconic acid, trimellitic acid, pyromellitic acid and anhydrides thereof. The polyhydric alcohol is a compound having two or more hydroxyl groups in one molecule. Examples thereof include ethylene glycol, propylene glycol, diethylene glycol, butylene glycol, hexanediol, diethylene glycol, diethylene glycol, and the like. Propylene glycol, neopentyl glycol, hydrogenated bisphenol A, triethylene glycol, glycerin, trimethylolethane,
And trimethylolpropane and pentaerythritol.

The introduction of the hydroxyl group into the polyester resin is carried out by adding a trihydric or higher alcohol such as glycerin, trimethylolethane, trimethylolpropane, or pentaerythritol as a polyhydric alcohol component in the production of the polyester resin. It can be carried out by using together with alcohol. The carboxyl group can be introduced by subjecting a part of the hydroxyl group of the obtained polyester resin having a hydroxyl group to a half-esterification reaction of the above polybasic acid.

The hydroxyl group-containing acrylic resin is copolymerized under ordinary conditions using a hydroxyl group-containing monomer and an acrylic monomer, a carboxyl group-containing monomer and other monomer components as required (for example, a solution). Polymerization, emulsion polymerization)
The number average molecular weight is 1,000 to 50,000, especially 2,000 to
20,000, hydroxyl value is 20-200 mgKOH /
g, especially 50-150 mg KOH / g, and the acid value is 1
-100 mgKOH / g, especially 10-70 mgKOH / g
It is preferably within the range of g.

The hydroxyl group-containing monomer is a compound having at least one hydroxyl group and at least one polymerizable unsaturated bond in one molecule, for example, hydroxyethyl (meth) acrylic acid.
, Hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate and the like having 2 to 20 carbon atoms
Glycolide - such as Le and (meth) C ₂ -C ₂₀ hydroxyalkyl esters of acrylic acid. The acrylic monomers include C ₁ -C ₂₂ alkyl esters of (meth) acrylic acid, such as methyl (meth) acrylate, ethyl (meth) acrylate, and propyl (meth) acrylate.
Acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, octyl (meth) acrylate
And lauryl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and the like.

The carboxyl group-containing monomer is a compound having at least one carboxyl group and at least one polymerizable unsaturated bond in one molecule, such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, fumaric acid, and mesacon. Examples thereof include acids, anhydrides and half-esterified products thereof.

Other polymerizable monomers are monomers other than these monomers which can be copolymerized with the above-mentioned hydroxyl group-containing monomer, acrylic monomer and carboxyl group-containing monomer. , methoxybutyl acrylate les - DOO, methoxybutyl methacrylate - DOO, methoxyethyl acrylate les - DOO, methoxyethyl methacrylate - C ₂ -C of (meth) acrylic acid, such as preparative ₁₈ alkoxyalkyl ester; N, N-dimethyl Aminoethyl acrylate, N, N-dimethylaminoethyl methacrylate, N, N-diethylaminoethyl acrylate, N, N-diethylaminoethyl methacrylate, Nt-butylaminoethyl acrylate −
, Nt-butylaminoethyl methacrylate, N,
N, N-dialkylaminoalkyl esters of (meth) acrylic acid such as N-dimethylaminopropyl acrylate and N, N-dimethylaminopropyl methacrylate; acrylamide, methacrylamide, N-methylacrylamide, N- Methyl methacrylamide, N-ethyl acrylamide, N-ethyl methacrylamide, N-
Butyl acrylamide, N-butyl methacrylamide,
Acrylamide monomers such as N-dimethylacrylamide and N-dimethylmethacrylamide; glycidyl group-containing monomers such as glycidyl acrylate and glycidyl methacrylate; vinyl such as styrene, α-methylstyrene and vinyltoluene Aromatic compounds; acrylonitrile, vinyl acetate, vinyl chloride and the like.

The block polyisocyanate compound (b-
2) is a cross-linking agent for the base resin (b-1), and the block polyisocyanate compound (a-2) described as the cross-linking agent in the cationic electrodeposition paint (A) can be used in the same manner.

In the aqueous intermediate coating composition (B), the base resin (b-1) and the block polyisocyanate compound (b-
The composition ratio with 2) is not particularly limited, but the base resin (b-1) is 4% based on the total solid weight of these two components.
0 to 90%, particularly 50 to 80%, and the block polyisocyanate compound (b-2) is 60 to 10%, especially 50 to 2%.
It is preferably within the range of 0%.

The aqueous intermediate coating composition (B) is a base resin (b-
1) and the block polyisocyanate compound (b-
In addition to 2), a curing catalyst, an extender, a coloring pigment, and a surface conditioner may be further contained to promote a crosslinking reaction between these two components. Among them, as the curing catalyst, those exemplified for the above-mentioned cationic electrodeposition coating material (A) can be used in the same manner.
The range of 0.1 to 10 parts by weight per 100 parts by weight of the total of the block polyisocyanate compound (b-2) is suitable.

The cross-linking and curing start time of the coating of the aqueous intermediate coating (B) is determined by the cationic electrodeposition coating (A) adjacent to the lower layer.
It is preferable that the cross-linking curing is started later than the coating film of (A), specifically, about 0.5 to about 10 minutes later than the curing start time of the coating film of the cationic electrodeposition paint (A). That is, the cross-linking and curing of the coating of the cationic electrodeposition coating (A) starts, and after about 0.5 to about 10 minutes have elapsed, the cross-linking and curing of the coating of the aqueous intermediate coating (B) may start. preferable. In particular, the timing of the initiation of crosslinking and curing of the coating film of the aqueous intermediate coating composition (B) is preferably from about 3.5 to about 30 minutes, particularly from about 5.5 to about 25 minutes after the start of heating.

The timing of the start of crosslinking and curing of the coating film of the aqueous intermediate coating composition (B) can be easily controlled, for example, by appropriately selecting the types and amounts of the polyisocyanate compound, the blocking agent, the curing catalyst, and the like. Can be.

The aqueous intermediate coating (B) is obtained by uniformly mixing and dispersing the above-mentioned components in water.
The solid concentration at the time of coating is preferably in the range of 20 to 70% by weight. The aqueous intermediate coating (B) can be applied by, for example, electrostatic coating, airless spraying, air spraying, etc., and its film thickness is about 5 based on the cured coating film.
Suitably in the range from about 15 to about 35 μm.

The heating temperature for cross-linking and curing both the coating film of the cationic electrodeposition coating material (A) and the coating film of the aqueous intermediate coating material (B) is determined by the block polyisocyanate contained in both coating films. Above the dissociation temperature of the
0 to about 180 ° C is suitable, at which temperature about 10 to about 40 ° C
The coating film can be cured by heating for minutes.
The multilayer coating film composed of the cationic electrodeposition coating material (A) and the aqueous intermediate coating material (B) has excellent finished appearance (smoothness and glossiness, etc.), and also has remarkably excellent interlayer adhesion between both coating films. I have.

Colored topcoat (C): Colored topcoat (C) applied to the surface of the intermediate coating film cured according to the present invention.
Is a paint that forms a colored top coat having excellent base concealing properties.

The colored topcoat paint (C) is designed so that the light transmittance at a wavelength of 400 to 700 nm in a single coating film having a thickness of 30 μm (as a cured coating film) is 5% or less, preferably 3% or less. A liquid paint excellent in concealing property of a base and containing a coloring pigment is suitable.

For the light transmittance, the top coat (C) was coated on a smooth glass plate with a cured coating film to a thickness of 30 μm, cured by heating under predetermined conditions, immersed in warm water at 60 to 70 ° C. A self-recording spectrophotometer (type EPS-3T, manufactured by Hitachi, Ltd.) was used as a sample with the free coating film peeled off and dried at room temperature.
Is the spectral transmittance when measured at a wavelength of 400 to 700 nm using. Measurement wavelength (400-700nm)
When there is a difference in transmittance in the same sample, the maximum numerical value (maximum transmittance) is adopted as the light transmittance.

Wavelength 4 of single coating film of colored top coat (C)
When the light transmittance at a wavelength of from 00 to 700 nm is more than 5%, the aesthetic properties of the obtained multilayer coating film generally deteriorate.

The composition of the colored topcoat paint (C) is not particularly limited as long as it is a liquid paint that forms a colored coating film having excellent light-transmittance within the above range and excellent in base concealment property.
Various solid color paints or metallic paints known per se can be used.

In the present invention, the colored top coat (C)
In particular, an organic solvent-based thermosetting colored coating material having excellent base concealing properties containing a neutralized product of a carboxyl group-containing resin having an acid value of 5 to 100 mgKOH / g and a crosslinking agent as essential components (C-1) It is preferable to use a water-based thermosetting colored paint (C-2) having excellent base concealing properties.

The coloring paint (C-1) has an acid value of 5 to 100.
The light transmittance at a wavelength of 400 to 700 nm in a single coating film containing a neutralized product of a carboxyl group-containing resin (mgKOH / g), a crosslinking agent, a coloring pigment, and an organic solvent and having a thickness of 30 μm (as a cured coating film) is obtained. It can be a solid color or metallic organic solvent-based paint having an excellent concealing property adjusted to 5% or less, preferably 3 or less.

As the carboxyl group-containing resin having an acid value of 5 to 100 mgKOH / g, for example, a carboxyl group-containing vinyl resin or polyester resin having an acid value in such a range can be suitably used.

As the carboxyl group-containing vinyl resin,
(Co) polymerization of at least a carboxyl group-containing unsaturated monomer together with an acrylic unsaturated monomer, a hydroxyl group-containing unsaturated monomer, and other unsaturated monomers as required. And a resin obtained by the above method.

The carboxyl group-containing unsaturated monomer is a compound having at least one carboxyl group and at least one polymerizable unsaturated group in one molecule, for example, acrylic acid, methacrylic acid, maleic acid, itaconic acid, crotonic acid. And the like.

The acrylic unsaturated monomer includes a C ₁ -C ₂₄ alkyl ester of (meth) acrylic acid. Specifically, for example, methyl (meth) acrylate, (meth) acrylate
Ethyl acrylate, propyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate,
2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, lauryl (meth) acrylate,
And stearyl (meth) acrylate.

The hydroxyl group-containing unsaturated monomer is a compound having at least one hydroxyl group and at least one polymerizable unsaturated group in one molecule. Examples thereof include 2-hydroxyethyl (meth) acrylate and hydroxy (meth) acrylate. C ₂ -C ₁₂ hydroxyalkyl esters of (meth) acrylic acid, such as propyl and the like.

The other unsaturated monomer is a polymerizable unsaturated monomer other than the above-mentioned carboxyl group-containing unsaturated monomer, acrylic unsaturated monomer and hydroxyl group-containing unsaturated monomer. For example, functional (meth) acrylamides such as (meth) acrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, diacetoneacrylamide, N-methylol (meth) acrylamide, N-butoxymethylacrylamide, etc. ; (Meta)
Glycidyl group-containing vinyl monomers such as glycidyl acrylate, glycidyl (meth) acrylamide, and allyl glycidyl ether; vinyl aromatic compounds such as styrene, α-methylstyrene, and vinyl toluene; vinyl propionate, vinyl acetate, ) Acrylonitrile, vinyl pivalate, veova monomer (trade name, manufactured by Shell Chemical Co., Ltd.) and the like.

The above carboxyl group-containing vinyl resin is
5-100 mgKOH / g, preferably 10-50 mg
KOH / g, more preferably 30 to 50 mg KOH / g
The hydroxyl value is preferably 10 to 200 mgKOH / g, and more preferably 25 to 70 mKOH / g.
gKOH / g, and number average molecular weight is about 2,000-
1,000,000, especially about 3,000-100,00
It is preferably in the range of 0.

The carboxyl group-containing polyester resin is
It can be produced by using a polybasic acid and a polyhydric alcohol and, if necessary, further using a monobasic acid and the like, and subjecting them to an esterification reaction.

The polybasic acid is a compound having two or more carboxyl groups in one molecule, for example, phthalic acid, isophthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, maleic acid, succinic acid, adipic acid, sebacic acid ,
Trimellitic acid, pyromellitic acid and anhydrides thereof are exemplified. Polyhydric alcohols are compounds having two or more hydroxyl groups in one molecule, for example, ethylene glycol, diethylene glycol, propylene glycol.
, Butanediol, pentanediol, 2,2-dimethylpropanediol, glycerin, trimethylolpropane, pentaerythritol and the like. Further, as the monobasic acid, benzoic acid, t-butylbenzoic acid and the like can be mentioned. Also, castor oil, tung oil, safflower oil,
Oil components such as soybean oil, linseed oil, tall oil, coconut oil and their fatty acids can also be used in combination.

The introduction of a carboxyl group into a polyester resin can be performed, for example, by adding glycerin, trimethylolethane,
By using a trihydric or higher alcohol such as trimethylolpropane or pentaerythritol in combination with a dihydric alcohol to produce a polyester resin having a hydroxyl group,
Next, half-esterification reaction of the above polybasic acid with at least a part of the hydroxyl groups of the polyester resin can be performed.

The carboxyl group-containing polyester resin is
5-100 mgKOH / g, preferably 10-50 mg
KOH / g, more preferably 30 to 50 mg KOH / g
The hydroxyl value is preferably 10 to 200 mgKOH / g, and more preferably 25 to 70 mKOH / g.
gKOH / g, and number average molecular weight is about 1,000 to 1
It is preferably in the range of from about 000, especially about 2,000 to 500,000.

The acid value as described above is 5 to 100 mgK
Basic substances that can be used to neutralize the OH / g carboxyl group-containing resin include, for example, ammonia,
Examples include methylamine, ethylamine, dimethylamine, diethylamine, trimethylamine, triethylamine, dimethylethanolamine, diethanolamine, triethanolamine and the like. The amount of these neutralizing agents (basic substances) used is generally in the range of about 0.1 to about 2.0 equivalents, preferably about 0.3 to about 1.2 equivalents, based on the carboxyl group in the resin. Are suitable.

The crosslinking agent used in the coloring paint (C-1) is for crosslinking and curing the above carboxylic acid resin, and may be an amino resin, a block polyisocyanate compound or the like. it can.

As the amino resin, for example, a condensation reaction product (a methylol compound) of one or more compounds selected from melamine, benzoguanamine, urea, dicyandiamide and the like with formaldehyde, or a mixture of the condensation reaction product and a carbon atom having 1 carbon atom To 8 monovalent alcohols and the like. In particular, a condensation reaction product of melamine and formaldehyde (methylolated melamine) and an etherified product of this condensation reaction product with a monovalent alcohol having 1 to 8 carbon atoms (alkyl etherified methylol melamine)
Is preferred.

As the block polyisocyanate compound, the block polyisocyanate compound (a) described as a crosslinking agent in the cationic electrodeposition coating composition (A) is used.
-2) can be used similarly.

In the coloring paint (C-1), the composition ratio of the carboxyl group-containing resin and the crosslinking agent is about 50 to about 90 parts by weight, based on the total solid content of these two components, Preferably from about 60 to about 85 parts by weight, and the crosslinker may range from about 50 to about 10 parts by weight, preferably from about 40 to about 15 parts by weight.

The coloring pigment is for imparting a base layer concealing property to a single coating film of the coloring paint (C-1) and for imparting color and beauty to the formed multilayer coating film. ,
An amount such that the light transmittance at a wavelength of 400 to 700 nm of a single coating film (thickness: 30 μm, as a cured coating film) of the colored coating (C-1) gives a base concealing property of 5% or less, preferably 3% or less. It can be.

As the color pigment, a known solid color can be used.
Pigments, metallic pigments and the like can be used, and specifically, for example, titanium dioxide, carbon black, phthalocyanine blue, phthalocyanine line, carbazole violet, anthrapyridine, azo orange,
Solid color pigments such as flavanthron yellow, isoindolin yellow, azo yellow, indus remble, dibromanzathrone red, perylene red, azo red, anthraquinone red, and quinacridone red; aluminum powder, bronze powder, and copper powder And metallic pigments such as zinc powder, iron phosphide, mica-like iron oxide powder, mica powder, and metal oxide-coated mica powder, but are not limited thereto. These color pigments can be used in an appropriate combination depending on the intended color tone.

As the organic solvent in the coloring paint (C-1), known organic solvents for ordinary paints can be used. Examples thereof include ester solvents, ether solvents, alcohol solvents, and amide solvents. Solvents, ketone solvents, aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, aromatic hydrocarbon solvents, and the like. One or more of these solvents may be used. it can. In particular, among them, ethylene glycol monomethyl ether ether, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, dioxane, ethylene glycol monomethyl ether, ethylene glycol monomethyl ether
Monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether,
Diethylene glycol monoethyl ether, diethylene glycol diethyl ether, diethylene glycol monobutyl ether, methyl alcohol, ethyl alcohol
, Allyl alcohol, n-propyl alcohol, isopropyl alcohol, tertiary butyl alcohol, ethylene glycol, 1,2-propylene glycol and its monoetherified product, 1,3-butylene glycol -Le, 2,
Hydrophilic organic solvents such as 3-butylene glycol, hexylene glycol, hexanediol, dipropylene glycol and its monoethers, acetone, diacetone alcohol, etc., especially at 20 DEG C. A hydrophilic organic solvent that dissolves at least 50 parts by weight per 100 parts by weight of water,
It is preferable to use it as at least a part of the organic solvent. At that time, the ratio of the hydrophilic organic solvent is 2% based on the total amount of the organic solvent contained in the colored paint (C-1) at the time of coating.
The content is desirably 0% by weight or more, particularly preferably 40 to 100% by weight.

The colored top coat (C-1) can be prepared by dispersing the above-mentioned neutralized carboxyl group-containing resin, a crosslinking agent, a coloring pigment and an organic solvent according to a conventional method. Depending on the type, extender pigments, dyes and the like can be blended.

Examples of extenders that can be appropriately compounded include barita powder, precipitated barium sulfate, barium carbonate, gypsum,
Clay, silica, white carbon, diatomaceous earth, talc,
Magnesium carbonate, alumina white, satin white, and the like, and as the dye, those excellent in light resistance and solubility in water and organic solvents are preferable, for example, monoazo dyes, polyazo dyes, metal complex salt azo dyes, and pyrazolone azo dyes. Dyes, stilbene azo dyes and thiazo-
Azo dyes such as luazo dyes; anthraquinone dyes such as anthraquinone derivatives and anthrone derivatives; indigo dyes such as indigo derivatives and thioindigo derivatives; phthalocyanine dyes; diphenylmethane dyes;
Carbonium dyes such as tolphenylmethane dyes, xanthene dyes and acridine dyes; quinone imine dyes such as azine dyes, oxazine dyes and thiazine dyes; methine dyes such as polymethine (or cyanine) dyes and azimethine dyes; quinoline dyes; ;
Nitroso dyes; benzoquinone and naphthoquinone dyes;
Naphthalimide dyes; perinone dyes, etc., each of which can be used alone or in combination of two or more.

The colored top coat (C-1) can be applied by an atomizing type coating machine such as an air spray coating machine, an airless spray coating machine or an electrostatic coating machine. 15 to 60 seconds with cup # 4, especially 1
For 5 to 35 seconds (20 ° C.), the solid content is preferably adjusted within the range of 10 to 80% by weight, particularly 30 to 60% by weight.

On the other hand, a water-based thermosetting colored paint (C-2)
Is a paint obtained by dissolving or dispersing a base resin, a curing agent and a color pigment in water, and having a thickness of 30 μm of a single coating film.
m (as cured coating) wavelength 400-700 nm
Is a solid-color or metallic-color thermosetting aqueous liquid paint excellent in concealing property, in which a color pigment is blended so that the light transmittance of the composition is 5% or less, preferably 3% or less.

As the base resin in the colored coating (C-2), any known coating resin which can be dissolved or dispersed in water and has a crosslinkable functional group such as a hydroxyl group can be used. Specific examples include an acrylic resin, a vinyl resin, and a polyester resin containing a hydrophilic group such as a carboxyl group and a crosslinkable functional group such as a hydroxyl group, which are useful for water-solubilization or water-dispersion. These base resins have a hydroxyl value of 10 to 200 mgKOH / g,
Particularly, the acid value based on the carboxyl group is 200 mgKOH / g or less, particularly 10 to 10 mgKOH / g.
0 mg KOH / g, and a number average molecular weight of about 1,000
About 1,000,000, especially about 2,000 to about 10
It is preferably in the range of 0.000.

The acrylic resin and vinyl resin containing a carboxyl group and a hydroxyl group include carboxyl group-containing unsaturated monomers, hydroxyl group-containing unsaturated monomers, acrylic unsaturated monomers and other unsaturated monomers. Can be prepared by copolymerization using a conventional method. As these monomers, those exemplified in the description of the base resin in the colored coating material (C-1) can be similarly used.

Further, the polyester resin containing a carboxyl group and a hydroxyl group may be a polybasic acid or a polyhydric alcohol.
And, if necessary, an esterification reaction using a monobasic acid or the like in combination. These components are exemplified in the description of the base resin in the colored coating (C-1). Things can be used as well.

Further, as the base resin, a resin obtained by subjecting a part of the hydroxyl groups contained in at least one of these acrylic resins, vinyl resins and polyester resins to a high molecular weight by urethane-forming a polyisocyanate compound. And these can be applied as a water-dispersible resin.

These base resins can be made water-soluble or water-dispersible by neutralizing the carboxyl groups contained therein, and the basic compounds usable therefor include the above-mentioned colored paints (C-1 The basic substances exemplified for use in the neutralization of the carboxyl group of the carboxyl group-containing resin in (1) can be applied.

As the curing agent in the colored paint (C-2), an amino resin or a block polyisocyanate compound which can react with a crosslinkable functional group (for example, a hydroxyl group) of the base resin can be suitably used. Among them, as the amino resin, those exemplified for the above-mentioned colored paint (C-1) can be similarly applied. The block polyisocyanate compound is a polyisocyanate compound having two or more free isocyanate groups in one molecule in which all of the isocyanate groups are blocked with a blocking agent, and has a dissociation temperature of When heated above (eg, 100 ° C.), the blocking agent dissociates and free isocyanate groups are regenerated, causing a crosslinking reaction with the functional groups of the base resin.

Examples of the polyisocyanate compound include aromatic diisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate and naphthalene diisocyanate; tetramethylene diisocyanate. Aliphatic diisocyanates such as neat, hexamethylene diisocyanate, dimer diisocyanate and lysine diisocyanate; methylene bis (cyclohexyl isocyanate), isophorone diisocyanate, methyl Cyclohexane diisocyanate
Cycloaliphatic diisocyanates such as cyclohexane diisocyanate and cyclopentane diisocyanate;
A biuret type adduct, an isocyanuric ring type adduct of the polyisocyanate; and a free isocyanate obtained by reacting the polyisocyanate with a low molecular weight or high molecular weight polyol in excess of an isocyanate group. Group-containing prepolymers. Further, as a blocking agent, for example, phenols, oximes,
Lactams, active methylenes, alcohols, acid amides, imides, amines, imidazoles, ureas, carbamic acids, imines, mercaptans and the like can be mentioned. The reaction between the polyisocyanate compound and the blocking agent can be carried out by a known method, and the molecular weight of the obtained block polyisocyanate compound is 200 to 10,000.
Is preferably within the range.

The composition ratio of the base resin and the crosslinking agent in the colored coating material (C-2) is based on the total solid content of these two components, and is about 50 to about 90 parts by weight, preferably about 60 to 90 parts by weight. About 85 parts by weight, and about 50 to about 10
Parts by weight, preferably in the range of about 40 to about 15 parts by weight.

The coloring pigment used in the coloring paint (C-2) is to impart hiding power to a single coating film and to give a multi-layer coating film formed according to the present invention a colorful cosmetic. And the compounding amount thereof is determined by the amount of the colored paint (C
-2) The light transmittance at a wavelength of 400 to 700 nm of a single coating film (thickness: 30 μm, as a cured coating film) of 5-2 or less, and preferably 3% or less, can be given as an amount that gives a base concealing property. .

As the color pigment, the above-mentioned color paint (C-
Solid color pigments and metallic pigments described in 1) can be used.

The coloring paint (C-2) can be prepared by dissolving or dispersing the above-mentioned base resin, curing agent and coloring pigment in water. If necessary, the above-mentioned extender pigment may be used. Dyes and the like can also be blended.

The coloring paint (C-2) can be applied by an atomizing type coating machine such as an air spray coating machine, an airless spray coating machine, and an electrostatic coating machine. 13 to 60 seconds in # 4, especially 15 to 3
It is preferable to adjust the solid content to 5 seconds (20 ° C.) and the solid content to 10 to 80% by weight, particularly to 30 to 60% by weight.

In the present invention, the object to be coated is coated with the cationic electrodeposition coating material (A), the uncured coating surface is coated with the aqueous intermediate coating material (B), and the coating materials (A) and (B) are heated. Is applied to the cured coating surface of the intermediate coating film obtained by curing both coating films (a) to (c), for example, a colored coating (C-1) or a colored coating (C-2) having excellent base concealing property. ),
10 to 50 μm, preferably 15 to 35 μm in the cured coating
After coating at a room temperature or forcibly drying at a temperature of 120 ° C. or lower to substantially volatilize volatile components such as an organic solvent or water in the coating. An uncured coated surface is coated with a transparent coating film-forming water-based top coating (D).

Transparent film-forming water-based topcoat (D): The topcoat (D) is a colored topcoat (C) as described above.
A water-based paint for forming a colorless transparent or colored transparent coating film to be applied to the uncured coating surface of the above, wherein the color tone of the coating surface of the lower colored overcoating material (C) is visually observed through the coating film. Is what you can do.

The overcoat paint (D) is a thermosetting paint containing a base resin and a curing agent, further adding a coloring pigment as needed, and dissolving or dispersing these in water. The color pigment in the top coat (D) is an optional component, and includes a colorless transparent film-forming paint containing no color pigment, a colored transparent film-forming paint mixed with a color pigment, and the like.

Of these, the colored transparent film-forming coating material has a wavelength of 40 μm at a film thickness of 30 μm (as a cured film).
Those which form a transparent coating film having a light transmittance of 0 to 700 nm exceeding 5%, preferably 10 to 90%, more preferably 20 to 80%, are preferably solid color or metallic. Is included.

The light transmittance of the transparent coating film of the top coat (D) was determined by curing the top coat (D) on a smooth glass plate with a cured coat.
0 μm, heat-cured under the specified conditions, immersed in warm water at 60-70 ° C., peeled off the coating, dried at room temperature as a sample, and used a self-recording spectrophotometer (Hitachi 400 to 7 using the EPS-3T type manufactured by Seisakusho
This is the spectral transmittance when measured at a wavelength of 00 nm. When there is a difference in transmittance depending on the wavelength to be measured (400 to 700 nm), the maximum numerical value (maximum transmittance) is adopted as the light transmittance. The larger the numerical value of the transmittance, the more easily light is transmitted, and the closer to the transparency.

As the base resin in the top coat (D), any known resin for coating which can be dissolved or dispersed in water and has a crosslinkable functional group such as a hydroxyl group can be used. Specific examples include an acrylic resin, a vinyl resin, and a polyester resin containing a hydrophilic group such as a carboxyl group and a crosslinkable functional group such as a hydroxyl group, which are useful for making the resin water-soluble or water-dispersible. These base resins generally have a hydroxyl value in the range from 10 to 200 mg KOH / g, in particular from 20 to 100 mg KOH / g;
00 mg KOH / g or less, especially 10 to 100 mg KOH
Acid number based on carboxyl groups in the range of from about 1,000 to about 1,000,000, especially from about 2,000
Preferably, it has a number average molecular weight in the range of from about to about 100,000.

The acrylic resin and vinyl resin containing a carboxyl group and a hydroxyl group include carboxyl group-containing unsaturated monomers, hydroxyl group-containing unsaturated monomers, acrylic unsaturated monomers, and other unsaturated monomers. Can be prepared by copolymerization using a conventional method. These monomers include the above-mentioned colored paint (C-1)
What is exemplified in the description can be used in the same manner.

Further, the polyester resin containing a carboxyl group and a hydroxyl group may be a polybasic acid or a polyhydric alcohol.
And, if necessary, an esterification reaction with the use of a monobasic acid or the like.
What is exemplified in the description of 1) can be similarly applied.

Further, as the base resin, a resin obtained by subjecting a part of the hydroxyl group contained in one or more of these acrylic resins, vinyl resins and polyester resins to a urethane-forming reaction with a polyisocyanate compound to have a high molecular weight is also used. And these can be applied as a water-dispersible resin.

When the carboxyl groups of the base resin are neutralized, the base resin can be made water-soluble or water-dispersible. The basic compound usable for this purpose is the above-mentioned colored paint (C-1). And the basic substances exemplified for use in neutralizing the carboxyl group of the carboxyl group-containing resin.

As the curing agent in the top coat (D), an amino resin or a block polyisocyanate compound which can react with a crosslinkable functional group (for example, a hydroxyl group) of the base resin can be suitably used. Among them, as the amino resin, those exemplified above for the colored paint (C-1) can be similarly applied. The block polyisocyanate compound is obtained by blocking substantially all of the isocyanate groups of the polyisocyanate compound with a blocking agent. Those which dissociate to regenerate free isocyanate groups and which undergo a crosslinking reaction with the functional groups of the base resin are preferably used. As the polyisocyanate compound and the blocking agent, those exemplified above for the colored coating (C-2) can be similarly applied.

In the top coat (D), the mixing ratio of the base resin and the curing agent is from about 50 to about 90% by weight, especially about 6% by weight, based on the total solid content of these two components.
Preferably, the amount ranges from 0 to about 85% by weight, and the curing agent ranges from about 50 to about 10% by weight, especially from about 40 to about 15% by weight.

Coloring pigments that can be used to make the coating film of the top coating composition (D) colored and transparent include color coating compositions (C-
The solid color pigments and the metallic pigments exemplified above for 1) are exemplified. The amount of the pigment used is, for example, a single coating film (D) having a thickness of 30 μm and a cured coating film containing the coloring pigment. Wavelength of 400 to
The light transmittance at 700 nm exceeds 5%, preferably 10%.
The amount may be such that a transparent coating film is formed within a range of from 90% to 90%, more preferably from 20% to 80%.

The top coat (D) can be prepared by dissolving or dispersing the above-mentioned base resin and curing agent in water together with a coloring pigment, a dye, an extender and the like, if necessary.

The top coat (D) is preferably applied by an atomizing type coating machine such as an air spray coating machine, an airless spray coating machine, and an electrostatic coating machine. 13-60 seconds, especially 1
5 to 35 seconds (20 ° C), and solids content of 10 to 8
It is preferably adjusted to 0% by weight, particularly 30 to 60% by weight.

In the present invention, the top coating (D) is a cured coating of 5 to 50 μm, preferably 10 μm, on the uncured coating surface of the colored top coating (C) applied to the cured coating surface of the intermediate coating film. After coating to a film thickness of ~ 35 μm and leaving it at room temperature, or by forcibly drying at a temperature of 100 ° C or less to volatilize volatile components such as water in the coating film substantially,
Heating at 120 to 160 ° C. for 10 to 40 minutes simultaneously cures both the top coat (C) and the top coat (D).

The multilayer coating film according to the present invention is obtained by simultaneously heating and curing both the top coating (C) and the top coating (D), and then clearing the cured coating surface of the top coating (D). It is formed by applying a paint (E) and curing by heating.

Clear paint (E): Clear paint (E)
A paint that is applied to the cured coating surface of the topcoat paint (D) to impart aesthetics, finished appearance, weather resistance, acid resistance, water resistance, etc., and that forms a substantially colorless coating film Curable organic solvent-based paints, water-based paints, powder paints and the like can be mentioned.

As the clear paint (E), a thermosetting paint for forming a transparent coating film which contains a base resin and a curing agent, and further contains a coloring pigment, an organic solvent, water and the like as necessary. Can be.

Examples of the base resin include acrylic resins, vinyl resins, polyester resins, fluororesins, urethane resins having a functional group such as a hydroxyl group, a carboxyl group, an epoxy group and an isocyanate group, and modified resins thereof (for example, grafts). And the like, and any of these can be known per se. The glass transition temperature of these base resins is usually about 4
It is preferably in the range from 0 to about 120C, especially from about 50 to about 90C.

The curing agent may be any one which reacts with the above-mentioned functional group of the base resin and cross-links and cures three-dimensionally. For example, a part or all of the methylol group of the melamine resin or the urea resin may be used. Monovalent 1 to 8 monovalent alcohols
Resin, polyisocyanate
Compound, block polyisocyanate compound, epoxy group-containing compound (or resin), carboxyl group-containing compound (or resin), hydroxyl group-containing compound (or resin)
And the like, and any known compounds or resins can be used.

The mixing ratio of the base resin and the curing agent is about 50% based on the total solid content of these two components.
Preferably, the curing agent is in the range from about 50% to about 90%, especially about 60% to about 85%, and the curing agent is about 50% to about 10%, especially about 40% to about 15%.

The clear paint (E) is prepared by, for example, adding the base resin and the curing agent to the colored paint (C-1) if necessary.
With respect to solid color pigments such as those exemplified above, color pigments such as metallic pigments, thickeners, defoamers, ultraviolet absorbers, light stabilizers, and the like, dissolved or dispersed in an organic solvent and / or water to obtain a solid content. Content: 10 to 80% by weight, viscosity: 10 to 60 seconds / Ford cup # 4/20 ° C
To obtain a liquid paint.

If necessary, solid color pigments, metallic pigments,
A powder coating obtained by blending an ultraviolet absorber, a light stabilizer, etc., melt-kneading, cooling and pulverizing can also be used as the clear coating (E).

The clear paint (E) is applied on the cured coating surface of the top coat (D) by an atomizing coating machine such as an air spray coating machine, an airless spray coating machine or an electrostatic coating machine to form a cured coating film. To 200 μm, preferably 10 to 150 μm, and left at room temperature, or
After forcibly drying at a temperature of not more than 00 ° C. to substantially volatilize volatile components such as an organic solvent or water in the coating film,
Curing can be accomplished by heating at 20 to about 160 ° C. for about 10 to about 40 minutes.

[0118]

According to the method of the present invention described above,
The finished appearance (smoothness, gloss, etc.) and interlayer adhesion of the multilayer coating film composed of the cationic electrodeposition coating film and the aqueous intermediate coating film are excellent. Can improve the finished appearance and interlayer adhesion of a multi-layer coating film having at least a five-layer structure obtained by applying a transparent coating film-forming aqueous top coating material and a clear coating material,
In addition, VOC (volatile organic compound content) is low, and the coating process can be shortened.

[0119]

The present invention will be described below more specifically with reference to examples and comparative examples. All parts and percentages are based on weight.

[0120] 1. Preparation of sample 1) Cationic electrodeposition paint (A ) 1,260 parts of a bisphenol A type epoxy resin having an epoxy equivalent of 630 (“Epicoat 1002”, trade name, manufactured by Shell Chemical Co., Ltd.) were dissolved in 450 parts of butyl cellosolve, 132 parts of p-nonylphenol and 105 parts of N-methylethanolamine were added, and the mixture was heated to 140 ° C. and reacted at the same temperature to obtain a solid content of 77% and an amine value of 52.
Was obtained. To 130 parts of this resin solution, 2.1 parts of acetic acid was added to protonate. Then, 30 parts of a block polyisocyanate compound (curing agent) (Note 1), 1.3 parts of lead acetate and 1.3 parts of polypropylene glycol (number average molecular weight 4000) were added to this, and deionized. Water is gradually added and dispersed to form an emulsion having a solid content of 30%. 15 parts of titanium white pigment, Cle-7
Parts, carbon black 0.3 parts and dioctyl tin oxide 3 parts, and further diluted with deionized water to obtain a solid content of 1 part.
A 9% electrodeposition bath was used. The time to start crosslinking of the coating film of the electrodeposition paint (a) is 10 minutes.

The time to start the cross-linking and curing of the coating film was measured using a pendulum type viscoelasticity meter (manufactured by Toyo Boldwin, Leo Vibron DDV-OPA type). Specifically, using a pendulum having a weight of 22 g and an inertial moment of 850 g · cm ² , a paint was applied to a steel plate so that the film thickness based on the cured coating film was 30 μm, and the uncured coating film surface was coated with the paint. Put the pendulum,
While the pendulum is vibrated, the coating film is heated at a predetermined temperature (for example, 140 to 180 ° C.) for crosslinking and curing, and the time at which the value of the logarithmic decrement of the vibration of the pendulum starts to increase is referred to as “crosslink curing start time”. The time required from the start of heating of the coating film to the start of crosslinking and curing is referred to as “curing start time”.

(Note 1) Block polyisocyanate compound: The reaction product of 174 parts of 2,6-tolylene diisocyanate and 85 parts of polycaprolactone diol having a hydroxyl equivalent of 425 was added to the reaction product of ethylene glycol. A compound obtained by reacting 2-ethylhexyl alcohol monoether (blocking agent).

2) Aqueous intermediate coating (B ) (a) Polyester resin (1) (Note 2) 1000 parts (solid content), 2-amino-2-methylpropanol 40
Parts, an aliphatic hexafunctional block polyisocyanate compound (Note 3) (410 parts), titanium white pigment (1400 parts) and carbon black (20 parts) were mixed and dispersed in deionized water (1800 parts) to obtain an aqueous intermediate coating ( a) was obtained. The time to start crosslinking of the coating film of the aqueous intermediate coating material (a) is 12 minutes.

(Note 2) Polyester resin (1): 756 parts of neopentyl glycol, trimethylolpropane 1
09 parts, 370 parts of hexahydrophthalic acid, adipic acid 2
92 parts and 398 parts of isophthalic acid are placed in a reaction vessel,
After reacting at 220 ° C. for 6 hours, trimellitic anhydride 4
A polyester resin having a number average molecular weight of about 8,000, an acid value of 20 mg KOH / g and a hydroxyl value of 95 mg KOH / g, obtained by adding 5 parts and reacting at 170 ° C. for 30 minutes.

(Note 3) Aliphatic hexafunctional block polyisocyanate compound: A trimer adduct of hexamethylene diisocyanate was blocked with methyl ethyl ketoxime.

(B) Polyester resin (1) (Note 2) 1
000 parts (solid content), 40 parts of 2-amino-2-methylpropanol, 410 parts of an aliphatic trifunctional block polyisocyanate compound (Note 4), 1400 parts of titanium white pigment, and carbon black 20 Was mixed and dispersed in 1800 parts of deionized water to obtain an aqueous intermediate coating composition (b). The time to start crosslinking of the coating film of the aqueous intermediate coating material (b) is 13 minutes.

(Note 4) Aliphatic trifunctional block polyisocyanate compound: a compound obtained by blocking hexamethylene diisocyanate trimer with methyl ethyl ketoxime.

(C) Acrylic resin (1) (Note 5) 100
0 parts, 40 parts of 2-amino-2-methylpropanol, 410 parts of aliphatic trifunctional block polyisocyanate compound (Note 4), 1400 parts of titanium white pigment and 20 parts of carbon black It was mixed and dispersed in 1800 parts of water to obtain an aqueous intermediate coating material (c). The time to start crosslinking of the coating film of the aqueous intermediate coating material (c) is 11 minutes.

(Note 5) Acrylic resin (1): styrene 2
10 parts, 294 parts of n-butyl methacrylate, 253 parts of hydroxybutyl acrylate, 200 parts of 2-ethylhexyl methacrylate and 30 parts of acrylic acid are put into a reaction vessel and reacted at 120 ° C. for 5 hours. Acrylic resin having a number average molecular weight of about 20,000, an acid value of 25 mg KOH / g and a hydroxyl value of 95 mg KOH / g.

(D) Polyester resin (1) (Note 2) 1
000 parts, 2-amino-2-methylpropanol 40
Parts, aliphatic trifunctional block polyisocyanate compound (Note 6) 410 parts, titanium white pigment 1400 parts and carbon black 20 parts are mixed and dispersed in deionized water 1800 parts to obtain an aqueous intermediate coating composition ( d) was obtained. The time to start crosslinking of the coating film of the aqueous intermediate coating material (d) is 8 minutes (for comparison).

(Note 6) Aliphatic trifunctional block polyisocyanate compound: A compound obtained by blocking hexamethylene diisocyanate trimer with ethyl malonate.

(E) Polyester resin (1) (Note 2) 1
000 parts, 2-amino-2-methylpropanol 40
Parts, melamine resin (Note 7) 300 parts, titanium white pigment 14
00 parts and 20 parts of carbon black in 18 parts of deionized water.
The resulting mixture was mixed and dispersed in 00 parts to obtain an aqueous intermediate coating composition (e). The time to start crosslinking of the coating film of the aqueous intermediate coating material (e) is 9 minutes (for comparison).

(Note 7) Melamine resin: “CYMER 30
3) (manufactured by Mitsui Cyanamid Co., Ltd., trade name, methanol-modified melamine resin) 3) Colored top coat (C ) (a) 140 parts of acrylic resin neutralizing solution (Note 8), "Cymel 370" (Note 9) ) 34 parts, "Arpest 891
K ”(Note 10) 20 parts and isopropyl alcohol 1
Prepared by mixing 40 parts. The solid content of the colored top coat (a) obtained is 34% and the viscosity (form)
Cup # 4/20 ° C.) for 25 seconds, and the light transmittance of the coating film (cured coating film 30 μm) was 0.1 or less.

(Note 8) Acrylic resin neutralizing solution: 60 parts of butyl cellosolve was added to a reaction vessel and heated to 120 ° C.
A polymerization reaction was carried out by adding the following monomer mixture, and an acid value of 4
An acrylic resin solution having 0, a hydroxyl value of 52, a number average molecular weight of about 10,000 and a resin solid content of 60% was obtained. This acrylic resin solution was neutralized by adding 2-amino-2-methylpropanol, and then diluted with isopropyl alcohol to adjust the resin solid content to 50% to obtain a neutralized acrylic resin solution.

Monomer mixture: methyl methacrylate 30
Parts, ethyl acrylate 23 parts, butyl acrylate 3
A mixture comprising 0 parts, 12 parts of hydroxyethyl methacrylate, 5 parts of acrylic acid and 2 parts of α, α'-azobisisobutyronitrile.

(Note 9) "Cymel 370": trade name, manufactured by Mitsui Cytec, a water-soluble melamine resin.

(Note 10) "Alpaste 891K": trade name, manufactured by Toyo Aluminum Co., Ltd., aluminum flake paste.

(B) Acrylic resin neutralizing solution (Note 8) 14
0 copies, "Symel 370" (Note 9) 34 copies, "Bull-G
316 "(Note 11), 2 parts of carbon black and 150 parts of isopropyl alcohol were mixed to prepare a colored overcoat (b). The colored top coat (b) has a solid content of 33%, a viscosity of 25 seconds (with a feed cup # 4/20 ° C.), and a light transmittance (cured coating of 30 μm) of 0.1 or less. there were.

(Note 11) “Blue-G316”: trade name, manufactured by Sanyo Dyestuffs Co., Ltd., a blue-based pigment.

(C) Neutralizing solution of polyester resin (Note 1)
2) 117 parts, "Symel 370" (Note 9) 34 parts,
A colored top coat (C) was prepared by mixing 10 parts of "Blue-G316" (Note 11), 2 parts of carbon black and 125 parts of isopropyl alcohol. The solid content of the colored top coat (c) is 39%, the viscosity (Ford cup # 4/20 ° C.) is 25 seconds, and the light transmittance of the coating film (cured coating film 30 μm) is 0.1 or less. there were.

(Note 12) Neutralizing solution of polyester resin: 0.7 mol of neopentyl glycol, 0.3 mol of trimethylolpropane, 0.4 mol of phthalic anhydride and 0.5 mol of adipic acid were added to a reaction vessel, and 200 After reaction at ~ 230 ° C for 5 hours, 0.03 mol of trimellitic anhydride was added and the reaction was further performed at 180 ° C for 1 hour, and then butyl cellosolve was added to obtain an acid value of 40 and a number average molecular weight of about 6,6.
000, a polyester resin solution having a resin solid content of 70% was obtained. The polyester resin solution was neutralized by adding 2-amino-2-methylpropanol, and then diluted with isopropyl alcohol to obtain a polyester resin neutralized solution having a resin solid content of 60%.

(D) 140 parts of deionized water was added to the reaction vessel,
2.5 parts of 0% “Newcol 707SF” (surfactant, manufactured by Nippon Emulsifier Co., Ltd.) and 1 part of a monomer mixture (i) having the following composition were added, and the mixture was stirred and mixed in a nitrogen gas stream.
At 0 ° C., 3 parts of a 3% aqueous solution of ammonium persulfate were added. Then, after raising the temperature to 80 ° C., 79 parts of the monomer mixture (i), 30% “Newcol 707SF”
A monomer emulsion consisting of 2.5 parts, 4 parts of a 3% ammonium persulfate aqueous solution and 42 parts of deionized water was added to the reaction vessel over 4 hours using a metering pump. After completion of the addition, aging was performed for 1 hour.

Further, at 80 ° C., 20.5 parts of a monomer mixture (ii) having the following composition and a 3% aqueous solution of ammonium persulfate 4
The parts were simultaneously dropped into the reaction vessel in parallel over 1.5 hours.
After completion of the addition, the mixture was aged for 1 hour, diluted with 30 parts of deionized water, and filtered at 30 ° C. with a 200 mesh nylon cloth. Deionized water was further added to the filtrate, and the pH was adjusted to 7.5 with 2-amino-2-methylpropanol to obtain an acrylic resin emulsion having an average particle diameter of 0.1 μm and a nonvolatile content of 20%.

Monomer mixture (i): 55 parts of methyl methacrylate, 10 parts of styrene, 9 parts of n-butyl acrylate,
A mixture consisting of 5 parts of 2-hydroxyethyl acrylate and 1 part of methacrylic acid.

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

In another reaction vessel, 126 parts of melamine, 80 parts
% Paraformaldehyde (manufactured by Mitsui Toatsu Chemicals Co., Ltd.) (225 parts) and n-butanol (592 parts) were added, and the pH was adjusted to 9.5 to 10.0 with a 10% aqueous solution of caseisoda.
The reaction was performed at 0 ° C. for 1 hour. Thereafter, n-butanol 88
8 parts were added, the pH was adjusted to 5.5 to 6.0 with a 5% aqueous sulfuric acid solution, and the mixture was reacted at 80 ° C. for 3 hours. After the reaction, 20%
Neutralize to pH 7.0-7.5 with aqueous Caseiso-da,
After n-butanol was removed under reduced pressure at 60 to 70 ° C., filtration was performed to obtain a hydrophobic melamine resin. Non-volatile content 80
% And a weight average molecular weight of 800.

Next, 25 parts (solid content) of this melamine resin was placed in a stirring vessel, and an aqueous acrylic resin solution (25% n-butyl acrylate, 20% methyl methacrylate, 30% styrene, 18% 2-hydroxyethyl methacrylate)
20 parts of an aqueous solution containing a polymer having an acid value of 54, a hydroxyl value of 100, and a number average molecular weight of 15,000 and a solid content of 50%) obtained by polymerizing 7% of acrylic acid.
After gradually adding 80 parts of deionized water while stirring with a rotary stirrer at 0 to 1500 rpm, the mixture is further stirred for 30 minutes and dispersed in water to obtain a solid content of 27% and an average particle diameter of 0.11.
A μm aqueous melamine resin dispersion was obtained.

The above 20% acrylic resin emulsion 3
25 parts, 131 parts of a 27% aqueous melamine resin dispersion, 31 parts of a pigment component (Note 13), 171 parts of deionized water, 3 parts of "Akwazol ASE-60" (Note 14) and 2-amino-
0.3 parts of 2-methylpropanol was mixed and then adjusted with deionized water to a viscosity of 30 seconds / Food cup # 4/20 ° C. to obtain a colored top coat (d).

The content of the pigment in the colored top coat (d) was 20 parts by weight per 100 parts by weight of the solid content of the resin, and the light transmittance (cured coating 30 μm) of the coating was 0.1%.
It was less than 1%.

(Note 13) Pigment component: “Aluminum paste A”
W-500B "(trade name, manufactured by Asahi Kasei Metals Co., Ltd., aluminum flake content: 65%) (Note 14)" Akwazol ASE-60 ": trade name, manufactured by Rohm and Haas Co., Ltd., a thickener.

(E) Cymel 350 (trade name, manufactured by Mitsui Cytec Co., Ltd., full methyl ether melamine resin)
25 parts (solid content), 20% of the colored top coat (d)
A mixture of 25 parts of an acrylic resin emulsion (solid content) and 50 parts of an aqueous acrylic resin solution (Note 15) contains 31 parts of a pigment component (Note 13), 171 parts of deionized water,
ASE-60 "(Note 14), 0.3 parts of 2-amino-2-methylpropanol and 4 parts of a 25% dodecylbenzenesulfonic acid solution, and then mixed with deionized water for a viscosity of 30 seconds / form. The temperature was adjusted to # 4/20 ° C. to obtain a colored top coat (e). The content of the pigment in the colored top coat (e) is 2 per 100 parts by weight of the resin solid content.
0 parts by weight, and the light transmittance of the coating film (cured coating film 30
μm) was 0.1% or less.

(Note 15) Acrylic resin neutralizing solution: 60 parts of butyl cellosolve was added to a reaction vessel and heated to 120 ° C., and a monomer mixture having the following composition was added to carry out a polymerization reaction to obtain an acid value of 53 and a hydroxyl value of 50. , Number average molecular weight about 15.0
An acrylic resin solution having a resin solid content of 60% was obtained. The acrylic resin solution was neutralized by adding 2-amino-2-methylpropanol, and then diluted with deionized water to adjust the resin solid content to 50% to obtain an acrylic resin aqueous solution.

Monomer mixture: 30 parts of styrene, 30 parts of butyl methacrylate, 20 parts of 2-ethylhexyl methacrylate, 13 parts of hydroxybutyl acrylate, 7 parts of acrylic acid, and 2 parts of α, α'-azobisisobutyronitrile A mixture consisting of

4) Transparent coating film-forming aqueous top coating (D ) 61% water-soluble acrylic resin [styrene / 2-ethylhexyl methacrylate / isobutyl methacrylate / hydroxybutyl acrylate / Placcel FA2 (Daicel Chemical Industries, Ltd.) (Manufactured by Industrial Company, trade name) / acrylic acid = 30/20 /
Polymer having a weight ratio of 13/10/20, number average molecular weight 10,000] 75 parts (solid content), "CYMER 350"
25 parts (solid content), 0.9 part of pigment component (Note 15), 25
% Dodecylbenzenesulfonic acid solution 4 parts, deionized water 1
71 parts and 2-amino-2-methylpropanol 0.1%.
Mix 3 parts and then use deionized water for a viscosity of 30 seconds / formula.
A water-based topcoat (a) adjusted to 20 ° C
I got

The light transmittance (cured coating: 30 μm) of the single coating of the water-based top coating (a) was 70%.

5) Clear coating (E ) (a) 70% acrylic resin solution (Note 16) 57 parts, 60 parts
50 parts of a 30% acrylic resin non-aqueous dispersion (Note 17), 30 parts of "CYMER 303" (Note 18), 4 parts of a 25% dodecylbenzenesulfonic acid solution, and "BYK-300" (Note 1)
9) Add 0.5 part of the mixture to “Swazol # 100
0 "(Cosmo Oil Co., Ltd., trade name, aromatic hydrocarbon solvent) with a viscosity of 30 seconds / ford cup # 4/20 ° C, and a high solid type clear coating material having a solid content of 55% ( a) was obtained.

(Note 16) 70% acrylic resin solution: Transfer 40 parts of "Swazol # 1000" into a reaction vessel and place at 120 ° C
To the monomer mixture (styrene 30 parts, butyl acrylate 35 parts, 2-ethylhexyl acrylate 1)
0 parts, 25 parts of hydroxyethyl acrylate and α,
α'-azobisisobutyronitrile (4 parts) was added over 3 hours using a metering pump to carry out polymerization.
An acrylic resin solution having 0 mgKOH / g, a number average molecular weight of about 6,000, and a resin solid content of 70% was obtained.

(Note 17) 60% acrylic resin non-aqueous dispersion: 58 parts of "Uban 28-60" (trade name, melamine resin solution, manufactured by Mitsui Toatsu Chemicals) and 30 parts of n-heptane in a reaction vessel And benzoyl peroxide (0.15 part), which was heated to 95 ° C., and a monomer mixture [styrene 15 parts, acrylonitrile 9 parts, methyl methacrylate 13 parts, methyl acrylate 15 parts, n-acrylic acid 1.8 parts of butyl, 2-hydroxyethyl methacrylate 10
Parts, acrylic acid 1.2 parts, benzoyl peroxide 0.1 part.
5 parts, n-butanol 5 parts, "Shellsol 140"
(Trade name, manufactured by Shell Sekiyu KK, 30 parts and n-heptane 9 parts) were dropped over 3 hours. After 1 hour, a mixed solvent consisting of 0.65 parts of t-butyl peroctoate and 3.5 parts of "Shellsol 140" was added.
It was dropped over time. Then keep the temperature as it is 2
After continuing stirring for a period of time, the pressure was reduced to remove 34 parts of the solvent,
An acrylic resin non-aqueous dispersion having a resin solid content of 60% and a varnish viscosity A (Gardona bubble viscometer / 20 ° C.) was obtained.

(Note 18) "Cymel 303": trade name, manufactured by Mitsui Cytec Co., Ltd., a monomeric melamine resin.

(Note 19) "BYK-300": trade name, surface conditioner, manufactured by BYK-Chemie.

(B) 40 parts of methyl methacrylate, 2-
30 parts of ethylhexyl acrylate, 30 parts of glycidyl methacrylate, 10 parts of styrene, 1 part of t-butyl peroxide (polymerization initiator) and 2 parts of potassium oleate soap (surfactant) were charged into a flask and suspended. Heat polymerization was performed by a turbid polymerization method, and the obtained copolymer (glass transition temperature: about 60 ° C) was dried. 100 parts by weight of this copolymer, 25 parts of decamethylene dicarboxylic acid and 1 part of a coating surface modifier were melt-kneaded at 120 ° C. for 10 minutes using a heating kneader. Then, after cooling the kneaded material, it is pulverized to a particle size of 20-1.
A 50 μm clear powder coating was obtained.

(C) 68 parts of the powder clear coating material of (b) was mixed with 100 parts of deionized water and a dispersant (Disperbyk-182 BYK).
1 part of Chemie Co., Ltd. and rheology modifier ("Acrizo-
LE ASE-60 "manufactured by Rom & Haas Co., Ltd.
(Acrysol ASE-60 Rohm & Haas Co.) was mixed with 0.6 parts to obtain a powder slurry paint.

[0163] 2. Examples and Comparative Examples A steel sheet surface-treated with “Bonderite # 3030” (trade name, manufactured by Nippon Parkerizing Co., Ltd., a zinc phosphate treating agent) was subjected to an electrodeposition bath for cationic electrodeposition paints (A) and (a). And electrodeposited by a conventional method. The film thickness of the cured film is about 20 μm. The film is pulled out of the bath, dried at 100 ° C. for 10 minutes, and then subjected to the aqueous intermediate coating composition (B) (a) to (e).
Was applied by air spray, and then heated at 170 ° C. for 30 minutes to crosslink and cure both coating films. The coating thickness of the aqueous intermediate coating is 35 μm in the cured coating.

Then, (a) to (d) of the colored top coat (C) were applied to the cured intermediate coat by air spray so as to have a thickness of 25 μm as a cured coat, and the mixture was coated at room temperature for 5 minutes. After leaving, the uncured coated surface is coated with a water-borne overcoat paint (D) or (a) for forming a transparent coating film by air spraying to form a cured coating film.
The coating was applied to a thickness of μm, left at room temperature for 5 minutes, and then heated at 140 ° C. for 30 minutes to crosslink and cure both coatings. Then, (a) to (c) of the clear coating material (E) are applied to the coated surface of the cured top coating material (D).
The coating was crosslinked and cured by heating for 0 minutes. The coating thickness of the clear paint (E) is also shown in Table 1.

Table 1 shows the results of the coating process and the performance test of the coating film.

The test methods in Table 1 are as follows: Smoothness : Measured with a tension meter (manufactured by RENAULY). The larger the value, the better the smoothness.

Sharpness: the result of measurement with an image clarity measuring device NSIC (manufactured by Suga Test Instruments Co., Ltd.). Larger values indicate better clarity (image clarity).

Water Adhesion Resistance : The test plate was placed in warm water of 40 ° C. for 10 minutes.
After soaking for a day, it is dried, and the coated surface is cut with a cutter-knife at 11 intervals at 2 mm intervals so as to reach the substrate, and at 11 mm intervals at 2 mm intervals in a direction perpendicular to this, and 2 mm × 2 mm Make 100 Goban eyes, 20 ℃
Then, an adhesive cellophane tape is adhered to the coated surface, and after the adhesive cellophane tape is abruptly peeled off, the number of the remaining coated films is examined. ○: 100 remaining, Δ: 99-90 remaining, and ×: 89
This indicates that less than or equal to the number remain.

Chipping resistance : QGR gravelomere
100g of No. 7 crushed stone using tar (Q Panel Co., Ltd.)
Was sprayed at an air pressure of about 3 kg / cm ² at -20 ° C. at a spray angle of 45 ° on the coated surface. Thereafter, the state of the coated surface was visually evaluated. ○: slight impact flaw is observed on the intermediate coated surface, but no peeling of the electrodeposited film is observed. △: slight impact flaw is recognized on the intermediate coated surface, and peeling of the electrodeposited film is also slight. And x indicates that many impact flaws are recognized on the intermediate coated surface, and that the electrodeposition coating film is considerably peeled off.

Weather resistance : After accelerated exposure with a sunshine weatherometer (light quantity: 1100 KJule / m ² ) for 200 hours, the test was immersed in warm water of 40 ° C. for 24 hours as one cycle, and this test was repeated 25 times, followed by JISK
-5400 8.5.2 According to the cross-cut tape method, 2
One hundred squares having a size of 2 mm × 2 mm were prepared, an adhesive cellophane tape was adhered to the coated surface at 20 ° C., and after abruptly peeling off, the number of remaining coated squares was examined. ○ is 100
残存 indicates that 99 to 90 remain, and X indicates that 89 or less remain.

VOC (%): VOC (%) is the percentage of the total amount of the organic solvent to the solid content (resin, pigment, etc.) in all the paints (based on the time of painting) used to form the multilayer coating film.

[0172]

[Table 1]

(Note 20): Organic solvent-based intermediate coating (“HS
-48B ", manufactured by Kansai Paint Co., Ltd., trade name, polyester / melamine resin, gray color (Note 21): Organic solvent-based intermediate coating (" HS-39 ", manufactured by Kansai Paint Co., trade name, polyester / melamine) (Resin-based, gray color) (Note 22): Organic solvent-based topcoat ("Magiclon HM-
32 Silva ", manufactured by Kansai Paint Co., Ltd., trade name, acrylic / melamine resin-based, Silva-metallic) (Note 23): Organic solvent-based topcoat (" Lugagabek HK ")
-4 clearer ", manufactured by Kansai Paint Co., Ltd., trade name, acrylic / melamine resin, clear paint)

Claims (7)

[Claims] 1. A cationic electrodeposition containing a block polyisocyanate compound as a crosslinking agent, wherein a cross-linking and curing reaction of a coating film is started on an object to be coated earlier than that of an adjacent intermediate coating film. The coating material (A) is applied, an aqueous intermediate coating material (B) containing a block polyisocyanate compound as a cross-linking agent is applied to the uncured coated surface, and then the coating materials (A) and (B) are heated. After curing both coatings, a colored topcoat (C) and a transparent coating-forming aqueous topcoat (D) having excellent underlayer concealing properties are sequentially applied, and heated to obtain coatings (C) and (D). A method for forming a multilayer coating film, comprising: after curing both coating films, further applying a clear coating (E) to the cured coating surface and curing by heating. 2. The coating film of the cationic electrodeposition paint (A) is 100
The method for forming a multilayer coating film according to claim 1, wherein the aqueous intermediate coating material (B) is applied after heating at a temperature of not more than ° C to substantially remove moisture in the coating film. 3. The colored top coat (C) is a solid color paint.
The method according to claim 1 or 2, wherein the method is a paint or a metallic paint. 4. The colored top coat (C) has a thickness of 30 μm.
A method for forming a multilayer coating film according to any one of claims 1 to 3, wherein the coating film is a liquid coating material in which a color pigment is blended so that the light transmittance at a wavelength of 400 to 700 nm in the single cured coating film is 5% or less. . 5. The colored top coat (C) has an acid value of 5-1.
The multilayer coating film according to any one of claims 1 to 4, which is an organic solvent-based thermosetting colored coating material having excellent base concealing properties containing a neutralized product of a carboxyl group-containing resin of 00 mg KOH / g and a crosslinking agent. Forming method. 6. The method for forming a multilayer coating film according to claim 1, wherein the colored top coating material (C) is a water-based thermosetting colored coating material having excellent base concealing properties. 7. An object to be coated is coated with a cationic electrodeposition coating material (A), and heated at a temperature of 100 ° C. or less to substantially remove water in the coating film. Coating paint (B)
Is applied and heated to cure both coatings (A) and (B), and then the cured coated surface is coated with a colored top coating (C) having excellent underlayer concealing properties, at a temperature of 120 ° C. or lower. After pre-heating in step (a), the water-based top coating (D) is applied, and after heating to cure both coatings (C) and (D), a clear coating (E) is applied to the cured coating surface. The method for forming a multilayer coating film according to any one of claims 1 to 6, wherein the method is heat-cured.