JP2002066440A - Method for forming double-layered coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a double-layered coating film using a cationic electrodeposi tion paint and an aqueous topcoating paint. SOLUTION: The aqueous topcoating paint is applied to the surface of the uncured coating film of the cation electrodeposition paint and both coating films are cured at the same time under heating to form the double-layered 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 using a cationic electrodeposition paint and an aqueous topcoat.

[0002]

2. Description of the Related Art Conventionally, as a method of coating a metal object such as an automobile body, an aqueous top coat is applied to a heat-cured coating surface of a cationic electrodeposition coating without using an intermediate coating. The so-called two-coat two-bake system (2C2B) in which a multilayer coating film is formed by heating and curing is already known. However, this method requires at least two heating steps to cure the coating film, and has a defect that the coating step is extremely complicated.

[0003]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned deficiencies in a method of forming a multilayer coating film using a cationic electrodeposition paint and an aqueous topcoat paint. Omit the heating process of the coating film, apply the water-based top coat, then heat and cure both the coatings simultaneously, heating in one step, and reduce the performance of the multilayer coating Finding that there is no
The present invention has been completed. That is, according to the present invention, the water-based overcoat paint (B) is applied to the uncured coating surface of the cationic electrodeposition paint (A).
And heating the two coatings simultaneously to provide a multilayer coating film forming method.

[0004]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

[0005] The cationic electrodeposition paint (A) is used for directly electrodepositing a conductive metal product such as an automobile body or an electric product, which is an object to be coated, prior to the water-based overcoat paint (B). And a known cationic electrodeposition paint can be used. In particular, a cationic electrodeposition paint using a block polyisocyanate compound as a crosslinking agent is preferable. Specific examples include a cationic electrodeposition paint containing a base resin (A-1) having a hydroxyl group and a cationic group and a block polyisocyanate compound (A-2).

The hydroxyl group of the base resin (A-1) participates in a crosslinking reaction with the block polyisocyanate compound, and the cationic group is for forming a stable aqueous dispersion, and is exemplified below. To do.

(A): A reaction product of a polyepoxy resin and a cationizing agent.

(B): Polycondensate of polycarboxylic acid and polyamine (see US Pat. No. 2,450,940) protonated with an acid.

(C) A polyisocyanate compound or a polyadduct of a polyol and a mono- or polyamine, which is protonated with an acid.

(D): A copolymer of an acrylic or vinyl monomer containing a hydroxyl group and an amino group, which is protonated with an acid (JP-B-45-12395, JP-B-45-19545)
-12396).

(E): A product obtained by protonating an adduct of a polycarboxylic acid resin and an alkyleneimine with an acid (see US Pat. No. 3,403,088).

Among these, the products obtained by reacting a cationizing agent with an epoxy group of a polyepoxide resin obtained from a polyphenol compound and epichlorohydrin, which are included in (a), have excellent corrosion resistance of the coating film. Is particularly preferred.

This polyepoxide resin is a known compound having two or more epoxy groups in one molecule.
As described above, those having a number average molecular weight of preferably 400 to 4000, more preferably 800 to 2000 are suitable, and can be produced, for example, by reacting a polyphenol compound with epichlorohydrin in the presence of an alkali. Polyglycidyl ethers of polyphenol compounds are included. Examples of the polyphenol compound usable here include bis (4-hydroxyphenyl) -2,2-propane, 4,4'-dihydroxybenzophenone, and 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'-dihydroxydiphenylsulfone, 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 200.
0 and an epoxy equivalent of 190-2000, preferably 4
It is a polyglycidyl ether of a polyphenol compound having a molecular weight of 00 to 1000. These are polyols, polyethers
Also included are those obtained by partially reacting with terpolyol, polyester polyol, polyamidoamine, polycarboxylic acid, polyisocyanate compound, etc., and those obtained by graft polymerization of ε-caprolactone, acrylic monomer, etc. .

The reaction product (a) can be obtained by reacting most or all of the epoxy groups of these polyepoxide resins with a cationizing agent.

Examples of the cationizing agent include amine compounds such as primary amines, secondary amines, tertiary amines, and polyamines, which are reacted with these epoxy groups to form secondary amino groups, tertiary amines, and tertiary amines. A cationic group such as a quaternary amino group or a quaternary ammonium base is introduced into a cationized resin. Specifically, as the primary amine compound, for example, methylamine, ethylamine, n-propylamine, isopropylamine, monoethanolamine, n-amine
Primary compounds such as propanolamine and isopropanolamine;
Secondary amine compounds; examples of the secondary amine compound include secondary amines such as diethylamine, diethanolamine, di-n-propanolamine, diisopropanolamine, N-methylethanolamine and N-ethylethanolamine.
Tertiary amine compounds such as triethylamine, triethanolamine, N, N-dimethylethanolamine, N-methyldiethanolamine, N, N-diethylethanolamine and N-ethyldiethanolamine; , For example, ethylenediamine,
Examples thereof include polyamines such as diethylenetriamine, hydroxyethylaminoethylamine, ethylaminoethylamine, methylaminopropylamine, dimethylaminoethylamine, and dimethylaminopropylamine.

In addition to these amine compounds, a basic group formed by using a basic compound such as ammonia, hydroxyamine, hydrazine, hydroxyethylhydrazine, N-hydroxyethylimidazoline as a cationizing agent is protonated with an acid. May be a cationic group. Acids that can be used include formic acid, acetic acid, glycolic acid,
Water-soluble organic carboxylic acids such as lactic acid are preferred.

The hydroxyl group of these cationic resins may be, for example, a reaction of an alkanolamine in the above-mentioned cationizing agent, a reaction of a ring-opened product of caprolactone which may be introduced into an epoxy resin and a reaction of a polyol. Primary hydroxyl groups to be introduced; secondary hydroxyl groups in an epoxy resin; and the like. Among these, the primary hydroxyl groups to be introduced by the reaction of the alkanolamine are a block polyisocyanate compound (crosslinking agent). ) Is preferred because of its excellent cross-linking reactivity with).

The base resin (A-1) in the cationic electrodeposition coating composition (A) has a hydroxyl group and a cationic group,
The content of the hydroxyl group is preferably from 20 to 5,000, particularly preferably from 100 to 1,000 mgKOH / g in terms of the hydroxyl equivalent, and particularly preferably from 200 to 1,000 mgKOH / g in terms of the primary hydroxyl equivalent.
Is preferred. The content of the cationic group is preferably at least the minimum necessary to stably disperse the base resin in water, and is generally 3 to 200, particularly preferably 10 to 100 in terms of KOH (mg / g solid content) (amine value). It is preferably in the range of ~ 80. The base resin (A-1) does not contain free epoxy groups in principle.

The block polyisocyanate compound (A-
2) is a reaction in which all of the isocyanate groups of the polyisocyanate compound are reacted with a volatile active hydrogen compound (blocking agent) and blocked, and rendered inactive at room temperature. The blocking agent is dissociated and the original isocyanate group is regenerated, and participates 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. Diisocyanates such as diisocyanate, dimer acid diisocyanate and lysine diisocyanate; isophorone diisocyanate
G, methylene bis (cyclohexyl isocyanate),
Alicyclic diisocyanates such as methylcyclohexane diisocyanate, cyclohexane diisocyanate and cyclopentane diisocyanate; xylylene diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate Aromatic diisocyanates such as naphthalene diisocyanate and toluidine diisocyanate; urethanized adducts of these polyisocyanate compounds;
Biuret type adducts, isocyanuric ring type adducts; and the like.

Examples of the blocking agent include phenol-based blocking agents, alcohol-based blocking agents, active methylene-based blocking agents, mercaptan-based blocking agents, acid amide-based blocking agents, imide-based blocking agents, and amine-based blocking agents. And imidazole-based blocking agents, urea-based blocking agents, carbamic acid-based blocking agents, imine-based blocking agents, oxime-based blocking agents, sulfite-based blocking agents, and lactam-based blocking agents.

The block polyisocyanate compound (A-
2) can be obtained by reacting these polyisocyanate compounds with an active hydrogen compound (blocking agent) by a known method, and there is substantially no free isocyanate group.

In the cationic electrodeposition coating material (A), the base resin (A-1) and the block polyisocyanate compound (A
The composition ratio with -2) is not particularly limited, but based on the total solid weight of both components, the former is 40 to 90%, particularly 50 to 80%, and the latter is 60 to 10%, particularly 50 to 90%. 20
% Is preferred.

The cationic electrodeposition coating composition (A) contains the base resin (A-1) and the block polyisocyanate compound (A-2), and further contains the cationic resin in the base resin (A-1). The group can be prepared by neutralizing the group with an acidic compound such as acetic acid, formic acid, lactic acid, or phosphoric acid, and then dispersing and mixing in water.
The resin solid content concentration is suitably from 5 to 30% by weight.

It is more preferable to use a bismuth-containing compound in addition to the above-mentioned components in the cationic electrodeposition coating composition (A) because the corrosion resistance and the curability of the electrodeposition coating film are improved. In particular, when the electrodeposition coating film and the water-based topcoat film are cured with 2C1B as in the present invention, if the curability of the electrodeposition coating film is improved by using a bismuth-containing compound together, It has the effect of improving the adhesion between the layer and the water-based overcoat, the chipping resistance of the multi-layer paint, and the finished appearance such as the smoothness, sharpness, and gloss of the water-based overcoat. Moreover, it is no longer necessary to include harmful substances such as lead compounds in the cationic electrodeposition paint (lead free).

Examples of the bismuth-containing compound include, for example,
Bismuth hydroxide, bismuth trioxide, bismuth nitrate, bismuth benzoate, bismuth citrate, bismuth oxycarbonate, bismuth silicate and the like are particularly preferred, and bismuth hydroxide is particularly preferred. 0.1 to 10 parts by weight, especially 0.2
-5 parts by weight is preferred.

Further, as the bismuth-containing compound, bismuth lactate using lactic acid containing 80% or more of the L-form among the optical isomers can also be used successfully. Specifically, an aqueous bismuth lactate solution obtained by reacting lactic acid containing 80% or more of the L-form with 1 mol of bismuth oxide in the presence of water at a ratio of 2 to 10 mol is preferable. The compounding amount of bismuth lactate is preferably 0.1 to 10 parts by weight, particularly preferably 0.2 to 5 parts by weight, per 100 parts by weight of the electrodeposition coating resin solids.

As lactic acid used for preparing bismuth lactate,
Of the optical isomers, L-form is 80% or more (that is, D-form is 20% or more).
%), Preferably 85% or more, more preferably 8% or more.
A material containing 0% or more is used. If the L-form is less than 80%, the water solubility may decrease. L-lactic acid is preferably produced by a fermentation method. As the bismuth compound used for preparing bismuth lactate, bismuth hydroxide, basic bismuth carbonate, and the like are also suitable in addition to bismuth oxide.

The reaction between the bismuth compound and lactic acid is suitably carried out at a ratio of 2 to 10 mol, particularly 3 to 8 mol, of lactic acid containing 80% or more of L-form per mol of bismuth compound. For example, in the presence of water, 2 to 10 mol, particularly 3 to 8 mol, of lactic acid containing 80% or more of the L-form per 1 mol of bismuth oxide is allowed to react at room temperature to 90 ° C. for about 1 to 30 hours to form a homogeneous solution. A bismuth lactate aqueous solution is obtained. If the amount of lactic acid is less than 2 mol, it is difficult to make water soluble, and if it exceeds 10 mol, the electrodeposition coatability may be reduced. When bismuth hydroxide is used, bismuth lactate can be obtained by reacting 1 to 5 mol, particularly 1.5 to 4 mol, of lactic acid containing 80% or more of the L-form per 1 mol of bismuth hydroxide. The concentration of these reaction solids is usually 0.1 to 8
0% by weight, preferably 0.5 to 70% by weight, more preferably 1 to 60% by weight is suitable.

The bismuth lactate aqueous solution may be blended before or after the cationic electrodeposition paint is dispersed in water. The solid content concentration at the time of mixing the bismuth lactate aqueous solution is not particularly limited before being dispersed in water, but when blended after being dispersed in water, it is suitably adjusted to 60% by weight or less. This is because bismuth lactate is uniformly dispersed in the electrodeposition coating composition,
Considering the ease of coating formulation, storage stability, etc., it is preferable to add the electrodeposition coating composition after dispersion.

As the bismuth-containing compound, water-insoluble bis
Mass compounds and R₁ C (H) (OR _Two ) (CH_Two ) NCO
OH [wherein R₁ Is a hydrogen atom or an alkyl having 1 to 3 carbon atoms
R group, R_Two Is a hydrogen atom or an alkyl having 1 to 10 carbon atoms
And n is 0 or 1.]
Are mixed and dispersed in an aqueous medium in the presence of a dispersant.
Carboxylic acid modified bismuth obtained by
Compounds can also be used, which are water-insoluble
And a water dispersion of bismuth that is uniformly and stably dispersed
-Can be used as a strike.

This paste is a water-dispersed paste,
Water-insoluble bismuth compound and R ₁ C (H) (OR ₂ )
It is obtained by mixing and dispersing an aliphatic carboxylic acid represented by (CH ₂ ) n COOH [wherein R ₁ , R ₂ and n are the same as above] in an aqueous medium in the presence of a dispersant. The aliphatic carboxylic acid of the above formula is used in such a ratio that a water-insoluble aliphatic carboxylic acid-modified bismuth compound is mainly produced. By incorporating such an aqueous dispersion paste into the cationic electrodeposition coating composition, curability and anticorrosion properties can be improved without lowering throwing power and finished appearance.

The aqueous dispersion paste was centrifuged (1200).
(At 0 rpm for 30 minutes), the content of the water-soluble bismuth compound present in the supernatant obtained in the weight of the metal bismuth compound is about 40% by weight or less, particularly about 30% by weight of the total amount of the water-insoluble bismuth compound used as the raw material. It is desirable that the content be less than about 20% by weight.

Examples of the water-insoluble bismuth compound include bismuth oxide, bismuth hydroxide, and tribasic bismuth carbonate. These compounds have a solubility in water at 20 ° C. of 0.001 g / 100 g or less, with bismuth oxide being preferred. It is. The aliphatic carboxylic acid represented by the above formula is used for the purpose of converting the water-insoluble bismuth compound into a sufficiently uniform dispersion in an aqueous medium, and specifically, hydroxyacetic acid, lactic acid, Aliphatic hydroxycarboxylic acids such as hydroxypropionic acid; and aliphatic alkoxycarboxylic acids such as methoxyacetic acid, ethoxyacetic acid and 3-methoxypropionic acid. Of these, lactic acid, particularly L-lactic acid and methoxyacetic acid, are preferred. These aliphatic carboxylic acids can be used in combination with other organic acids such as acetic acid.

The amount of the aliphatic carboxylic acid used is within a range in which the obtained aliphatic carboxylic acid-modified bismuth compound may be in a water-insoluble state, and it depends on the type of the aliphatic carboxylic acid used. For lactic acid, the molar ratio to the amount of bismuth in the water-insoluble bismuth compound is usually in the range of 0.5 to 1.7, preferably 0.75 to 1.3, and for methoxyacetic acid, the bismuth in the water-insoluble bismuth compound is 0.25 to 2.5 in molar ratio to the amount,
Preferably, it can be in the range of 0.5 to 1.3.

As the dispersing agent used for preparing the aqueous dispersion paste of bismuth, any cationic dispersing resin or surfactant known per se in the field of cationic electrodeposition coatings can be used without any limitation. The dispersing resin can be appropriately selected from those described above and used. For example, resins of tertiary amine type, quaternary ammonium salt type, tertiary sulfonium salt type and the like can be mentioned. As the surfactant, for example, HLB is 3 to 18, preferably 5 to 15
Nonionic surfactants such as acetylene glycols, polyethylene glycols, and polyhydric alcohols in the range of the above. The amount of the dispersant can be changed depending on the type and the amount of the water-insoluble bismuth compound used, and is usually in the range of 1 to 150 parts by weight, particularly 10 to 100 parts by weight per 100 parts by weight of the water-insoluble bismuth compound. It is suitable.

The production of a water-dispersed paste of bismuth using a water-insoluble bismuth compound, an aliphatic carboxylic acid and a dispersant is carried out by using a pigment paste used in a cationic electrodeposition paint.
This can be carried out in the same manner as in the production of a strike.Specifically, an aliphatic carboxylic acid and a water-insoluble bismuth compound are added to water containing a dispersant, and dispersion treatment is performed in a dispersion mixer such as a ball mill or a sand mill. Thus, an aqueous dispersion paste of bismuth can be produced. The resulting aqueous dispersion paste is
In general, it can have a solids content of from 10 to 70% by weight, in particular from 30 to 60% by weight. Further, this water-dispersed paste may be prepared as a pigment paste by adding a pigment used in a usual cationic electrodeposition coating.

Specifically, for example, a pigment paste is prepared by blending a pigment dispersing resin, a neutralizing agent, and pigments and subjecting them to a dispersion treatment in a dispersion mixer such as a ball mill or a sand mill. This can be added with the above-mentioned aqueous dispersion paste of bismuth. Organic acids such as acetic acid, formic acid, and lactic acid can be used as the neutralizing agent. As the pigment dispersing resin, known resins can be used without any limitation. For example, the same cationic dispersing resin as used in preparing the above-mentioned dispersion paste can be used. As the pigments, any pigments which are usually used in cationic electrodeposition paints can be used without any particular limitation. For example, coloring pigments such as titanium oxide, carbon black, red iron, etc .; clay, mica, barita, talc Extenders such as calcium phosphate, calcium carbonate and silica; rust preventive pigments such as aluminum phosphomolybdate and aluminum tripolyphosphate. These bismuth dispersion pastes are:
Generally, the content of bismuth metal per 100 parts by weight of the resin solid content in the cationic electrodeposition paint is 0.1 to 10 parts by weight, preferably 0.3 to 7 parts by weight, more preferably 0.5 to 10 parts by weight.
It is within the range of 5 parts by weight.

In the cationic electrodeposition coating composition (A), in addition to the above-mentioned components, if necessary, a curing catalyst, aluminum, nickel, zinc, strontium, zirconium,
Rust-preventing curing catalyst such as hydroxide, oxide, organic acid salt, inorganic acid salt of a metal selected from molybdenum, tin, antimony, lanthanum, tungsten, etc .; extender pigment; coloring pigment; An anti-settling agent;

Among them, the curing catalyst is a base resin (A-
It is effective for accelerating the crosslinking reaction between 1) and the block polyisocyanate compound (A-2). Examples thereof include tin octoate, dibutyltin dilaurate, manganese, cobalt, lead, and bismuth stannate. Salt, lead stannate, zirconium octoate, zinc octoate, dibutyltin-bis-
O-phenylphenylene, dibutyltin-S, S-dibutyldithio-carbonate, triphenylantimony-dichloride, dibutyltin maleate, dibutyltin diacetate, dibutyltin dilaurate mercaptide, triethylenediamine, bismuth Stearate, lead stearate
And dimethyltin dichloride. The compounding amounts thereof are based on the base resin (A-1) and the block polyisocyanate.
Per 100 parts by weight in total with the compound (A-2).
A range of 1 to 10 parts by weight is suitable.

In the present invention, the cationic electrodeposition paint (A)
For example, the object to be coated is a cathode, and the bath temperature is 20 to
35 ° C., voltage 100 to 400 V, current density O. 01-5
A, It is preferable to perform the energization for 1 to 10 minutes. The coating film thickness is preferably about 10 to 40 μm for the cured coating film.

The method of the present invention comprises a cationic electrodeposition coating (A)
After coating, the coating film is forcibly dried at a temperature of 100 ° C. or lower as required without curing, and then the uncured coating surface is coated with an aqueous overcoating material (B), and then heated. This is a method of forming a multilayer coating film by simultaneously curing the coating films.

The water-based top coating (B) is a coating for forming a top coating film to be applied to the uncured coating surface of the cationic electrodeposition coating (A), and a conventionally known coating can be used. it can. Specifically, it contains a base resin (B-1) having a crosslinkable functional group such as a hydroxyl group and a crosslinker (B-2), and further contains a color pigment (B-3) mixed and dispersed in water. Water-based paints can be applied.

The base resin (B-1) having a crosslinkable functional group such as a hydroxyl group in the aqueous intermediate coating composition (B) includes:
For example, a polyester resin or an acrylic resin having two or more hydroxyl groups in one molecule is particularly suitable.

The hydroxyl group-containing polyester resin can be prepared by subjecting a polybasic acid and a polyhydric alcohol to an esterification reaction, and has a number average molecular weight of 1,000 to 5,000.
0, especially 2000 to 20000, and the hydroxyl value is 20 to 20
0 mgKOH / g, especially 50-150 mgKOH / g,
Acid value is 100 mgKOH / g or less, especially 10 to 70 mg
KOH / g is preferred.

Polybasic acids are compounds having two or more carboxyl groups in one molecule, such as 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.
Propylene glycol, diethylene glycol, butylene glycol, hexanediol, diethylene glycol, dipropylene glycol, neopentyl glycol, hydrogenated bisphenol A, triethylene glycol.
, Glycerin, trimethylol-ethane, trimethylo-
Lepropane and pentaerythritol.

The hydroxyl group-containing acrylic resin can be prepared by copolymerizing a hydroxyl group-containing polymerizable monomer and a polymerizable monomer component containing an acrylic monomer under ordinary conditions, and has a number average molecular weight of 1,000. ~ 50,000, especially 2000-20,000, hydroxyl value is 20 ~ 200mg
KOH / g, especially 50 to 150 mg KOH / g, acid value is 100 mg KOH / g or less, especially 20 to 70 mg KOH
/ G is preferred.

The hydroxyl group-containing polymerizable monomer is a compound having at least one hydroxyl group and at least one polymerizable unsaturated bond in one molecule. Examples thereof include hydroxyethyl (meth) acrylate and hydroxypropyl (meth) acrylate. C2, such as hydroxybutyl (meth) acrylate
Monoesters of glycol 20 and (meth) acrylic acid. The acrylic monomer is a monoester of (meth) acrylic acid and a monovalent alcohol having 1 to 22 carbon atoms, for example, methyl acrylate.
, Methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, hexyl acrylate, hexyl methacrylate
Octyl acrylate, octyl methacrylate,
Lauryl acrylate, lauryl methacrylate, 2-
Ethylhexyl acrylate, 2-ethylhexyl methacrylate and the like can be mentioned.

In preparing the hydroxyl group-containing acrylic resin,
Other polymerizable monomers other than these hydroxyl group-containing polymerizable monomers and acrylic monomers can be used in combination. As other monomers, for example, (meth) acrylic acid such as methoxybutyl acrylate, methoxybutyl methacrylate, methoxyethyl acrylate, methoxyethyl methacrylate and the like having 2 to 18 carbon atoms. Alkoxy ester; N, N-dimethylaminoethyl acryle
N, N-dimethylaminoethyl methacrylate,
N, N-diethylaminoethyl acrylate, N, N-
Diethylaminoethyl methacrylate, Nt-butylaminoethyl acrylate, Nt-butylaminoethyl methacrylate, N, N-dimethylaminopropyl acrylate, N, N-dimethylaminopropyl Aminoacrylic monomers such as methacrylate; acrylamide, methacrylamide, N-methylacrylamide, N
Acrylamide monomers such as -methylmethacrylamide, N-ethylacrylamide, N-ethylmethacrylamide, N-butylacrylamide, N-butylmethacrylamide, N-dimethylacrylamide, N-dimethylmethacrylamide; acrylic acid, methacrylic acid Glycidyl acrylate, maleic acid, itaconic acid, fumaric acid, mesaconic acid, and compounds having at least one carboxyl group and one polymerizable unsaturated bond in one molecule such as anhydrides and half esterifications thereof; Glycidyl group-containing monomers such as glycidyl methacrylate; styrene, α-methylstyrene, vinyltoluene, acrylonitrile, vinyl acetate, vinyl chloride and the like.

The crosslinking agent (B-2) is a base resin (B-1)
And a three-dimensionally cross-linkable hardening by reacting with a cross-linkable functional group, such as a blocked polyisocyanate compound and a melamine resin.

As the blocked polyisocyanate compound, those exemplified as the blocked polyisocyanate compound (A-2) described as a crosslinking agent in the cationic electrodeposition coating composition (A) can be suitably used. As the melamine resin, known ones can be used, and examples thereof include an alkyl etherified melamine resin obtained by fully or partially etherifying a monoalcohol having 1 to 10 carbon atoms to methylolated melamine.

The composition ratio of the base resin (B-1) and the crosslinking agent (B-2) in the water-based overcoating material (B) is not particularly limited, but is based on the total solid weight of both components. The former is 40-90%, especially 50-80%, and the latter is 6%
0-10%, especially 50-20% is preferred.

As the color pigment (B-3) in the water-based overcoat paint (B), ordinary paint pigments can be used, for example, titanium oxide, zinc white, lead white, basic lead sulfate, lead sulfate, lithopone, Zinc sulfide, antimony white, carbon black, acetylene black, lamp black, bone black, graphite, iron black, aniline black, naphthol yellow S, Hansa yellow, pigment yellow L, benzidine yellow, permanent yellow, chrome orange, chrome vermillion, permanent Orange, iron oxide, amber, red iron, lead red, permanent red, quinacridone red pigment, cobalt purple, fast violet, methyl violet lake, ultramarine, navy blue, cobalt blue, phthalocyanine blue, indigo, chrome green, pigment green Or solid color pigments such as phthalocyanine green; metallic pigments such as aluminum powder, aluminum oxide powder, evaporated aluminum powder, bronze powder, copper powder, tin powder, iron phosphide, metal oxide-coated mica powder, mica-like iron oxide or light Interference pigments and the like. The mixing amount of these coloring pigments (B-3) is
Although it can be arbitrarily selected depending on the purpose, a range of 0.1 to 150 parts by weight per 100 parts by weight (solid content) of the base resin (B-1) and the crosslinking agent (B-2) is suitable.

It is preferable that the single coating film of the water-based top coating material (B) is colored in any of a solid color tone, a metallic tone and a light interference tone with these coloring pigments, and has excellent hiding properties and is adjacent to the lower layer. It is preferred that the electrodeposition coating film cannot be seen through.

In addition to the above-mentioned components, the water-based top coat (B) includes, for example, an organic solvent, a filler, a fluidity adjuster, an anti-bake agent, an antioxidant, a curing accelerator, a charge controlling agent, and other paints. Additives can be added as needed.

The water-based top coat (B) is obtained by uniformly mixing and dispersing the above-mentioned components in water, and it is preferable to adjust the solid content concentration at the time of coating to 20 to 70% by weight.

According to the present invention, the cationic electrodeposition coating composition (A) is applied and, without curing, forcibly dried at 100 ° C. or lower, if necessary. This is achieved by simultaneously crosslinking and curing the two coating films.

The aqueous intermediate coating composition (B) can be applied by, for example, electrostatic coating, airless spraying, air spraying, or the like.
８０80 μm, especially about 15-35 μm, are suitable. The heating temperature for crosslinking and curing both the cationic electrodeposition coating (A) coating and the aqueous intermediate coating (B) coating is usually 130 to 200 ° C. for 10 to 40 minutes. .

[0061]

EXAMPLES Examples and comparative examples according to the present invention will be described below. All parts and percentages are based on weight, and the thickness of the coating is for the cured coating.

1. Preparation of sample 1) Cathodic electrodeposition paint (A) (A-1): 1,260 parts of bisphenol A type epoxy resin having epoxy equivalent of 630 (trade name of “Epic Coat 1002”, manufactured by Shell Chemical Co., Ltd.) is butyl cellosolve 450 And 132 parts of p-nonylphenol and 105 parts of N-methylethanolamine. The mixture was heated to 140 ° C. and reacted at the same temperature to give a solid content of 77% and an amine value of 52.
Was obtained. To 130 parts of this resin, 2.1 parts of acetic acid was added to protonate. Then this one 7
To 0 parts (solid content), 30 parts of a block polyisocyanate compound (curing agent), 1 part of bismuth hydroxide and 1.3 parts of polypropylene glycol (number average molecular weight 4000) are added, and deionized water is gradually added. And an emulsion having a solid content of 30%. To this, 15 parts of titanium white pigment, 7 parts of clay, 0.3 part of carbon black and 3 parts of dioctyltin oxide were added, and further diluted with deionized water to obtain an electrodeposition bath having a solid content of 15%. The above block polyisocyanate
The compound is 2,6-tolylene diisocyanate 174
Part and polycaprolactone diol 8 having a hydroxyl equivalent of 425
The reaction product with 5 parts is reacted with 2-ethylhexyl alcohol monoether (blocking agent) of ethylene glycol.

(A-2): The above cationic electrodeposition paint (A-
Except that "1 part of bismuth hydroxide" in 1) was replaced with "1 part of bismuth lactate (as the amount of metal bismuth)", all were prepared in the same manner as the cationic electrodeposition paint (A-1). Here, “bismuth lactate” is placed in a flask and 300 g of 90% lactic acid.
(3 mol as lactic acid) and 658 g of deionized water were charged and heated to 60 ° C. Next, 233 g of bismuth oxide
(0.5 mol) was added slowly, and the mixture was stirred at 60 ° C. for 3 hours. It is a bismuth lactate aqueous solution having a solid content of 10%, which is obtained by confirming that the reaction solution has become clear of yellow solid content and has become transparent, and then adding 3572 g of deionized water.

(A-3): The cationic electrodeposition paint (A-
Except that "1 part of bismuth hydroxide" in 1) was replaced with "1 part of bismuth dispersion paste (as the amount of metallic bismuth)", all were prepared in the same manner as the cationic electrodeposition paint (A-1). Here, "dispersion paste of bismuth" is as follows: 133.3 parts of an epoxy-based tertiary amine-type pigment dispersion resin (amine value 100) having a solid content of 75%, methoxyacetic acid 81.
After mixing 1 part of the mixture and stirring to make it uniform, 233.5 parts of deionized water was dripped into the mixture with vigorous stirring, and 111.5 parts of bismuth oxide was added.
Bismuth dispersion paper with 50% solids content
Is.

(A-4): The cationic electrodeposition paint (A-
Except for removing "1 part of bismuth hydroxide" in 1), all were prepared in the same manner as the cationic electrodeposition coating composition (A-1).

2) Aqueous top coating (B) (B-1): 1000 parts of acrylic resin (Note 1), 40 parts of dimethylaminoethanol, 40 parts of aliphatic trifunctional block polyisocyanate compound (Note 2) ) 410 parts, 1400 parts of titanium white pigment and 20 parts of carbon black were mixed and dispersed in 1800 parts of deionized water to obtain an aqueous top coat (B-1).
I got

(Note 1) Acrylic resin: styrene 210
Parts, 294 parts of n-butyl methacrylate, 253 parts of hydroxybutyl acrylate, 200 parts of 2-ethylhexyl methacrylate, and 30 parts of acrylic acid were placed in a reaction vessel, and reacted at 120 ° C. for 5 hours. Number average molecular weight about 20
000, acid value 25mgKOH / g, hydroxyl value 95mgK
An OH / g acryl resin was obtained.

(Note 2) Aliphatic trifunctional block polyisocyanate compound: A trimer adduct of hexamethylene diisocyanate was blocked with methyl ethyl ketoxime.

2. Examples and Comparative Examples Example 1 A dull steel sheet treated with zinc phosphate was immersed as a cathode in an electrodeposition bath of a cationic electrodeposition coating composition (A-1), and was immersed at 30 ° C and 200 ° C.
V for 3 minutes (film thickness 25 μm for cured coating), 10
After drying at 0 ° C for 10 minutes, an aqueous topcoat (B-1)
Is applied by air spray (the thickness of the cured coating is 30 to 35).
μm) and then heated at 170 ° C. for 30 minutes to crosslink and cure both coatings.

Example 2 A dull steel sheet treated with zinc phosphate was immersed in an electrodeposition bath of a cationic electrodeposition coating composition (A-2) as a cathode,
V for 3 minutes (film thickness 25 μm for cured coating), 10
After drying at 0 ° C for 10 minutes, an aqueous topcoat (B-1)
Is applied by air spray (the thickness of the cured coating is 30 to 35).
μm) and then heated at 170 ° C. for 30 minutes to crosslink and cure both coatings.

Example 3 A dull steel sheet treated with zinc phosphate was immersed as a cathode in an electrodeposition bath of a cationic electrodeposition paint (A-3),
V for 3 minutes (film thickness 25 μm for cured coating), 10
After drying at 0 ° C for 10 minutes, an aqueous topcoat (B-1)
Is applied by air spray (the thickness of the cured coating is 30 to 35).
μm) and then heated at 170 ° C. for 30 minutes to crosslink and cure both coatings.

COMPARATIVE EXAMPLE 1 A dull steel plate treated with zinc phosphate was immersed in an electrodeposition bath of a cationic electrodeposition coating composition (A-4) as a cathode.
V for 3 minutes (film thickness 25 μm for cured coating), 17
After heating at 0 ° C. for 30 minutes to cure the coating, an aqueous overcoat (B-1) is applied by air spray (thickness of the cured coating is 30 to 35 μm), and then heated at 170 ° C. for 30 minutes. And cured.

3. Performance test results Table 1 shows the performance test results of the multilayer coating films formed in Examples and Comparative Examples.

[0074]

[Table 1]

The test method is as follows.

Gloss: 60 ° specular reflectance.

Sharpness: The sharpness of the multilayer coating film was measured by an image clarity meter (IMAGE CLARITY METER, manufactured by Suga Test Instruments Co., Ltd.). The numbers in the table are ICM values, from 0 to 100.
The value of the range of, the larger the numerical value is sharpness (image clarity)
And an ICM value of 80 or more indicates that the sharpness is extremely good.

Chipping resistance: QGR gravelomer
15 to 20 m in diameter using a tar (manufactured by Q Panel Co., Ltd.)
100 g of crushed stone with air pressure of about 4 kg / cm2
The spraying was performed at 20 ° C. at a spray angle of 90 ° on the surface of the multilayer coating film. Thereafter, the state of the coated surface was visually evaluated. ○: slight impact flaw is observed on the overcoated surface, but no peeling of the electrodeposited film is observed. △: slight impact flaw is recognized on the overcoated surface, and slight peeling of the electrodeposited film is observed. Many impact flaws are observed on the overcoated surface, and the electrodeposition coating film is considerably peeled off.

Impact resistance: Using a DuPont impact tester, with a hammer of 1/2 inch and a load of 5
A weight of 00 g was dropped, and the falling distance (height cm) at which the coating film did not crack was measured.

Smoothness: The multilayer coating film was visually judged.は indicates good without any swelling and dents, 少 し indicates slightly poor swelling and dents, and X indicates poor with many swelling and dents.

Adhesion: Cut with a cutter so as to reach the substrate, make 100 gobangs with a size of 1 mm × 1 mm, apply an adhesive tape to the coated surface, and apply the tape at 20 ° C.
The tape was peeled off, and the number of remaining streaks was determined. ○ is 98
以上 indicates that 90 to 97 remain, and X indicates that 96 or less remain.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) C25D 13/00 308 C25D 13/00 308C 13/10 13/10 F term (reference) 4D075 AE12 BB26Z BB89Y CA04 CA13 CA33 CA48 CB04 DA06 DB01 DC11 DC18 EA06 EA10 EB20 EB22 EB32 EB33 EB35 EB38 EB45 4J038 DG161 DG171 DG191 DG301 GA03 HA216 HA296 HA336 HA456 JA50 KA02 KA03 LA03 LA06 MA08 MA10 NA03 NA24 NA25 PA04 PA12 PA19 PC

Claims (6)

[Claims] 1. A method for forming a multilayer coating film, comprising applying an aqueous overcoating material to the uncured coating surface of a cationic electrodeposition coating material, and heating and curing both coating films simultaneously. 2. The method according to claim 1, wherein the cationic electrodeposition coating further contains a bismuth-containing compound. 3. A bismuth-containing compound, comprising: bismuth hydroxide;
3. The method according to claim 2, wherein the method is selected from bismuth trioxide, bismuth nitrate, bismuth benzoate, bismuth citrate, bismuth oxycarbonate, and bismuth silicate. 4. The method for forming a multilayer coating film according to claim 2, wherein the bismuth-containing compound is bismuth lactate obtained by using lactic acid containing at least 80% of an L-isomer among optical isomers. 5. A bismuth-containing compound comprising, in the presence of water, 2 to 3 moles of lactic acid containing at least 80% of an L-form in 1 mol of bismuth oxide.
The method for forming a multilayer coating film according to claim 4, which is an aqueous solution of bismuth lactate obtained by reacting at a ratio of 10 mol. 6. The bismuth-containing compound is a water-insoluble bismuth compound and R ₁ C (H) (OR ₂ ) (CH ₂ ) nCOO.
H wherein R ₁ is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, R ₂ is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms,
n is 0 or 1];
An aqueous dispense paste of bismuth in which the aliphatic carboxylic acid-modified bismuth compound obtained by mixing and dispersing in the presence of a dispersant in an aqueous medium is in a water-insoluble state and is uniformly and stably dispersed. Item 3. The method for forming a multilayer coating film according to Item 2.