JP2809592B2 - Corrosion resistant paint composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention can improve the corrosion resistance and cationic electrodeposition coating property of a surface-treated steel sheet, and can prevent the elution of chromium in the pretreatment step of cationic electrodeposition of a surface-treated steel sheet subjected to chromate conversion treatment. The present invention relates to a water-based corrosion-resistant coating composition for surface-treated steel sheet (that is, excellent in chromium elution resistance).

[0002]

2. Description of the Related Art In recent years, surface-treated steel sheets having good corrosion resistance have been increasingly used as steel sheets for various uses such as automobile bodies and home electric appliances. A typical example of such a surface-treated steel sheet is a galvanized steel sheet that has been subjected to a chromate conversion treatment or the like. However, such a surface-treated steel sheet cannot sufficiently meet the required performance when applied to, for example, an inner plate of an automobile body, a bag structure part, and a hemming part. A method of improving the corrosion resistance by applying an organic coating film and further applying a cationic electrodeposition coating film has been adopted. Therefore, a surface-treated steel sheet is required to have a high corrosion resistance and a good cationic electrodeposition coating property.

[0003] Further, since these surface-treated steel sheets are used after being subjected to forming by press forming or bonding by welding, etc., there is a tendency that those having good corrosion resistance and good welding characteristics in the formed parts are required. is there. In recent years, air pollution,
From the viewpoint of resource saving, there is a strong demand for a water-based paint for a surface-treated steel sheet that forms the organic coating film. However,
The surface-treated steel sheet coated with the conventional water-based paint is not only inferior in corrosion resistance than the surface-treated steel sheet coated with the organic solvent type paint, but also in the pre-cation electrodeposition pretreatment process such as alkali degreasing and zinc phosphate conversion treatment. Hexavalent chromium is more easily eluted from the surface-treated steel sheet subjected to chromate conversion treatment. As a result, the corrosion resistance of the surface-treated steel sheet is reduced, and the alkali degreasing solution and the zinc phosphate chemical conversion treatment solution are contaminated by hexavalent chromium. There was a problem.

[0004]

SUMMARY OF THE INVENTION In view of the above situation, the present invention provides a surface-treated steel sheet which is excellent in corrosion resistance, cationic electrodeposition coating property, chromium elution resistance, etc., and is advantageous in preventing air pollution and saving resources. An object of the present invention is to provide an aqueous corrosion-resistant coating composition.

[0005]

Means for Solving the Problems The present inventors have made intensive studies to achieve the above object, and as a result, have found that a corrosion-resistant coating composition containing the following components gives good results, and completed the present invention. did. That is, the present invention provides (i) a water-dilutable organic resin, (ii) silica particles, (iii) hydrazine,
It contains at least one reducing agent selected from the group consisting of tannic acid and gallic acid, and (iv) if necessary, at least one chelating agent selected from the group consisting of titanium-based and zirconium-based, and / or (v) 5 in the molecule
The present invention relates to a water-based corrosion-resistant coating composition having a membered or six-membered ring structure and containing an organic adhesion improver having a nitrogen atom in the ring structure.

Hereinafter, the present invention will be described in detail: As the water-dilutable organic resin (i) constituting the coating composition of the present invention, a basic group or an acidic group is introduced into the resin. A resin which can be dissolved or stably dispersed in water by neutralizing with a wetting agent; a resin which is dissolved or stably dispersed in water since a hydrophilic group is introduced into the resin;
Various resins commonly used for aqueous coatings such as emulsion type resins by the forced emulsification method can be used, for example, epoxy resin type, acrylic resin type, urethane resin type, polyester resin type or modified products of these resin types are typical. It is mentioned as a thing. In the present invention, the resins described below can be suitably used.

(A) Water dilution by neutralization with a neutralizing agent
Possible acrylic-modified epoxy resin acryl-modified epoxy resin in the presence of a catalyst in the bisphenol type epoxy resin and the polymerizable unsaturated group-containing polybasic acid or solvent and its anhydride, bisphenol type epoxy resin allowed heating reaction To introduce a polymerizable unsaturated group,
Next, a bisphenol-type epoxy resin having a polymerizable unsaturated group introduced therein and a polymerizable unsaturated monomer component containing a carboxyl group-containing polymerizable unsaturated monomer are subjected to a heat reaction to undergo graft polymerization.

As the bisphenol type epoxy resin, bisphenol A type epoxy resin, bisphenol F type epoxy resin or a mixture thereof can be used.
Epoxy equivalent is 170-3500, preferably 800-
A value of 2500 is suitable. As the polymerizable unsaturated group-containing polybasic acid or acid anhydride thereof, maleic acid,
Typical examples thereof include fumaric acid, itaconic acid, citraconic acid and acid anhydrides thereof.

The polymerizable unsaturated monomer component includes:
Carboxyl group-containing polymerizable unsaturated monomers such as (meth) acrylic acid, maleic acid, fumaric acid, itaconic acid and maleic anhydride are used as essential constituent monomers, and hydroxyethyl (meth) acrylate, (meth) acrylic acid Hydroxyl-containing monomers such as hydroxypropyl and hydroxybutyl (meth) acrylate; acetoacetyl-containing monomers such as acetoacetoxyethyl (meth) acrylate; methyl (meth) acrylate, ethyl (meth) acrylate, (meth) acryl Propyl acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrysate,
(Meth) acrylate monomers such as lauryl (meth) acrysate and cyclohexyl (meth) acrylate;
Substituted styrene monomers such as styrene, vinyltoluene and methylstyrene; one or more comonomers such as (meth) acrylonitrile, vinyl chloride, vinyl acetate, vinyl propionate and dialkyl maleate are typical examples.

As described above, the reaction between the bisphenol type epoxy resin and the polybasic acid containing a polymerizable unsaturated group or an acid anhydride thereof is carried out on the bisphenol type epoxy resin so that the polymerizable unsaturated monomer component can be grafted. In order to introduce a polymerizable unsaturated group, the equivalent ratio of the epoxy group of the bisphenol-type epoxy resin to the carboxyl group of the polymerizable unsaturated group-containing polybasic acid or its acid anhydride is 1: 0. 05-0.8, preferably 1: 0.1
~ 0.3 is appropriate.

A bisphenol type epoxy resin is reacted with a polybasic acid containing a polymerizable unsaturated group or an acid anhydride thereof to introduce a polymerizable unsaturated group, and a polymerizable unsaturated monomer component is added to the polymerizable unsaturated group. An acrylic modified epoxy resin is produced by grafting, and a carboxyl group-containing polymerizable unsaturated monomer is used as an essential component as a polymerizable unsaturated monomer component used at that time.

The carboxyl group-containing polymerizable unsaturated monomer is provided with a carboxyl group in the resin so that the resulting acrylic-modified epoxy resin can be dissolved or stably dispersed in water as a solvent by neutralizing with a neutralizing agent. Use to The carboxyl group also has the effect of contributing to the improvement of the adhesion and spot weldability of the obtained coating film.

Accordingly, the amount of the carboxyl group-containing polymerizable unsaturated monomer used is suitably such that the acid value of the obtained acrylic-modified epoxy resin is about 20 or more, preferably 40 to 200. Further, as a polymerizable unsaturated monomer component, the hydroxyl value of the polymerizable unsaturated monomer component side of the acrylic-modified epoxy resin is about 10 to 50 in order to improve the adhesion of the resulting coating film and the storage stability of the coating composition. It is desirable to use a hydroxyl group-containing monomer in such an amount as to be used in combination. Further, as a polymerizable unsaturated monomer component, in order to improve the adhesion, corrosion resistance, boiling water resistance, alkali resistance, and the like of the obtained coating film, an acetoacetyl group-containing polymerizable unsaturated monomer is added to the polymerizable unsaturated monomer component 1 to 4. Desirably, the content is 20% by weight.

The acrylic modified epoxy resin used in the present invention has a weight average molecular weight of about 2,000 to 100,
000, preferably 4,000 to 70,000. The ratio of the bisphenol-type epoxy resin to the polymerizable unsaturated monomer component graft-polymerized thereto is suitably from 4: 6 to 9: 1 by weight. The acrylic-modified epoxy resin is used in such a state that it can be neutralized with a neutralizing agent and diluted with water so as to be dissolved or stably dispersed in water.

Representative examples of the neutralizing agent include ammonia, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, dimethylethanolamine, monoethanolamine, diethanolamine, triethanolamine, morpholine and the like. . (B) Basicity that can be diluted with water by neutralizing with a neutralizing agent
The nitrogen compound or the polybasic acid compound-modified epoxy resin- modified epoxy resin is a bisphenol-type epoxy resin having an epoxy equivalent of 300 to 2500 such as a bisphenol A-type epoxy resin or a bisphenol F-type epoxy resin, or the epoxy resin in the epoxy resin. A resin obtained by modifying an epoxy resin polymerized to a weight average molecular weight not exceeding 100,000 with a basic nitrogen compound or a polybasic acid compound via a polyfunctional compound having reactivity with a hydroxyl group or a hydroxyl group. .

The polyfunctional compound includes tolylene diisocyanate, hexamethylene diisocyanate,
Representative examples include polyisocyanate compounds such as 4,4-diphenylmethane diisocyanate, xylene diisocyanate, isophorone diisocyanate, and trimethylhexamethylene diisocyanate, and amine compounds such as xylylenediamine, diaminodiphenylmethane, diaminodiphenylsulfone, and toluidine.

Examples of the basic nitrogen compound include, for example, n
-Propylamine, iso-propylamine, n-butylamine, sec-butylamine, tert-butylamine, diethylamine, ethylenediamine, diethylenetriamine, triethylenediamine, tetraethylenediamine,
Representative examples include propylenediamine, N-methylpiperazine, ethanolamine, diethanolamine, N-methylethanolamine, iso-propanolamine, diisopropanolamine, n-propanolamine, ethylethanolamine, 3-methanolpiperidine and the like. .

Examples of polybasic acid compounds include isophthalic acid, terephthalic acid, succinic acid, adipic acid, fumaric acid,
Typical examples thereof include maleic acid, itaconic acid, citraconic acid, trimellitic acid, azelaic acid, sebacic acid, hymic acid or acid anhydrides thereof, rosin maleic anhydride, benzenetricarboxylic anhydride and the like.

The modification of the epoxy resin with a basic nitrogen compound or a polybasic acid compound improves the coating properties such as alkali resistance and water-resistant secondary adhesion as compared with the case where an unmodified epoxy resin is used. By neutralizing with a neutralizing agent, it can be dissolved or stably dispersed in water as a solvent. As the modified epoxy resin, an amine value of about 30 to 100% of an epoxy group of a bisphenol type epoxy resin modified with a basic nitrogen compound is about 20 or more, preferably 40 to 200, or modified with a polybasic acid compound. Suitable are those having an acid value of about 20 or more, preferably 40 to 200. The modified epoxy resin is used in a state where it can be neutralized with a neutralizing agent and diluted with water so as to be dissolved or stably dispersed in water.

In the case of an epoxy resin modified with a basic nitrogen compound, for example, formic acid, acetic acid, lactic acid,
Representative examples include organic acids such as propionic acid and butyric acid; and inorganic acids such as phosphoric acid, hydrochloric acid and sulfuric acid. On the other hand, in the case of an epoxy resin modified with a polybasic acid compound, the same as the above-described neutralizing agent for the acrylic-modified epoxy resin can be used.

(C-1) Water by neutralizing with a neutralizing agent
Urethane resin that can be diluted This urethane resin is a resin obtained by heating and reacting a polyester polyol having an acid value of about 20 to 200 with a polyisocyanate in a solvent. The polyester polyol is a polybasic acid such as phthalic acid, isophthalic acid, trimellitic acid, adipic acid, sebacic acid, maleic acid, fumaric acid or their acid anhydrides and ethylene glycol, diethylene glycol, propylene glycol, glycerin, pentaerythritol And a polyhydric alcohol such as hydrogenated bisphenol A and, if necessary, an esterification reaction of a monobasic acid such as benzoic acid by a conventional method.

Typical examples of the polyisocyanate include tolylene diisocyanate, diphenylmethane diisocyanate, p-phenylene diisocyanate, xylylene diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, isophorone diisocyanate, hydrogenated diphenylene diisocyanate, and hydrogenated xylylene diisocyanate. It is mentioned as a thing.

The reaction between the polyester polyol and the polyisocyanate is suitably carried out at a ratio of an equivalent ratio of the former hydroxyl group to the latter isocyanate group of 1: 0.2 to 1: 1. The weight average molecular weight of the resin is 5,000 to 100,000, preferably 1
A suitable range is from 0000 to 60,000. This urethane resin is used in such a state that it can be neutralized with a neutralizing agent and diluted with water so as to be dissolved or stably dispersed in water. Examples of the neutralizing agent include the same neutralizing agents as those described above for the acrylic-modified epoxy resin.

(C-2) Water by neutralizing with a neutralizing agent
Urethane resin that can be diluted This urethane resin is a resin having an acid value of about 20 to 200 obtained by dissolving or dispersing a polyether polyol and an oxyacid in a solvent, and then adding and reacting a polyisocyanate. The polyether polyol is a homopolymer or copolymer of ethylene oxide, propylene oxide, and butylene oxide, and has a weight average molecular weight of 20.
A value of 0 to 2000 is suitable.

The oxyacid is typically dimethylolpropionic acid, lactic acid, glycolic acid, hydroxybutyric acid, hydroacrylic acid, malic acid, hydroxyphthalic acid or a low condensate thereof. Examples of the polyisocyanate include those similar to the polyisocyanate described in (C-1). The reaction between the polyether polyol and the oxyacid and the polyisocyanate is suitably carried out at a ratio where the equivalent ratio of the former total hydroxyl groups to the latter isocyanate groups is 1: 0.5 to 1: 1; The resulting urethane resin has a weight average molecular weight of 5,000 to 100,000, preferably 10, 000.
000-60,000 is suitable. This urethane resin is used in such a state that it can be neutralized with a neutralizing agent and diluted with water so as to be dissolved or stably dispersed in water. Examples of the neutralizing agent include the same neutralizing agents as those described above for the acrylic-modified epoxy resin.

Silica particles constituting the coating composition of the present invention
(ii) is used to further improve the high corrosion resistance of the coating film, and examples thereof include water-dispersible colloidal silica having a particle diameter of 1 μm to 500 μm and powdered fumed silica. Commercially available water-dispersible colloidal silica includes, for example, Snowtex 20, 30, 40,
C, N, O, S, 20L, OL (all trade names manufactured by Nissan Chemical Industry Co., Ltd.), Adekalite 20N (trade name manufactured by Asahi Denka Kogyo KK) and the like.

Commercial products of powdered fumed silica include R974, R811, R812, R972, and R80.
5, T805, R202, RX200, RY200, R
Y300, RY380, RY180, OX50, 13
0, 200, 200V, 200CF, 300, 300C
F, 380, TT600, MOX80, MOX170,
COK84 (the above-mentioned trade name made by Nippon Aerosil Co., Ltd.) and the like.

When a coating film is formed by blending the silica particles (ii), a dehydration condensation reaction of silanol groups on the surface of the silica particles occurs, and the electrodeposition coating film-silica-steel plate is integrated, and the corrosion resistance is remarkably improved. improves. The silica particles (ii) are suitably blended in an amount of 5 to 400 parts by weight, particularly preferably 30 to 300 parts by weight (in terms of solid content), based on 100 parts by weight of the resin (i). If the amount is less than the above range, the corrosion resistance tends to decrease. On the other hand, if the amount is excessive, the processability, alkali resistance, and adhesion to the electrodeposition coating film tend to decrease.

At least one reducing agent (iii) selected from the group consisting of hydrazine, tannic acid and gallic acid constituting the coating composition of the present invention prevents chromium from eluting from the surface-treated steel sheet subjected to chromate conversion treatment. It is blended for the purpose. Conventionally, a surface-treated steel sheet coated with a water-based paint tends to elute hexavalent chromium from the chromate layer in the pretreatment liquid for cationic electrodeposition used in the next step such as alkali degreasing treatment and zinc phosphate conversion treatment. Not only the treatment liquid was contaminated, but also the corrosion resistance of the surface-treated steel sheet was reduced, but by adding the reducing agent (iii), a part of hexavalent chromium was reduced to trivalent chromium, The effect of preventing the elution of chromium is exhibited.

The reducing agent (iii) is suitably added in an amount of 0.5 to 10 parts by weight, preferably 1 to 5 parts by weight, per 100 parts by weight of the resin (i). If the amount is less than the above range, the effect tends not to be sufficiently exerted. On the other hand, if the amount is excessive, the amount of hexavalent chromium reduced increases, the self-healing action is lost, and the corrosion resistance tends to decrease. At least one chelating agent selected from the group consisting of titanium-based and zirconium-based constituents of the coating composition of the present invention (iv)
Is coordinated with the chromate layer and silica particles (ii), etc., and densifies the resulting coating film, which serves as a barrier effect, preventing chromium elution and preventing corrosion factors from entering from the outside. Contribute to improvement.

Specific examples of the chelating agent (iv) include isopropyl tri (N-aminoethyl-aminoethyl) titanate, tetraethyl titanate, tetrapropyl titanate, tetraisopropyl titanate, tetrabutyl titanate, tetra-2-ethylhexyl titanate, Titanium-based metal chelating agents such as allyl titanate, di-n-butoxy bis (triethanolamine) titanate, dihydroxy bis (lactiquaside) titanate; zirconium oxychloride, zirconyl sulfate, zirconyl nitrate, zirconyl acetate, zirconyl carbonate And zirconium-based metal chelators such as zirconyl hydroxide, zirconyl ammonium carbonate, and zirconyl octylate.

In particular, a chelating agent which is water-soluble or can be stably dispersed in water is desirable from the viewpoint of storage stability of the paint.
The chelating agent (iv) is suitably added in an amount of 0 to 10 parts by weight, preferably 0.5 to 5 parts by weight, based on 100 parts by weight of the resin (i). If the amount is more than the above range, the flexibility of the coating film is reduced, so that the moldability tends to be reduced.

The organic adhesion improver (v) having a 5- or 6-membered cyclic structure in the molecule constituting the coating composition of the present invention and having a nitrogen atom in the cyclic structure is used for coating. Since it has the property of orienting to the substrate when it is done,
Form a uniform barrier layer on the substrate surface. Therefore, it greatly contributes to corrosion resistance. Furthermore, the organic adhesion improver (v) was found to react with the silica particles (ii) during bake hardening, and thus contributed to the adhesion between the formed film and the substrate and to the fixation of the silica particles. I do.

Therefore, by using the organic adhesion improver (v) as a component of the coating composition of the present invention, the corrosion resistance and water-resistant secondary adhesion of the molded portion, which is the object of the present invention, can be greatly improved. You can level up. The organic adhesion improver (v), a hydrogen ion in the coating is coordinated with a lone pair of electrons having a nitrogen atom to become an ammonium ion,
This is adsorbed to the metal cathode as a positively charged hydrophilic group, and the lone pair of electrons of the nitrogen atom is coordinated and covalently bonded to the metal itself due to the difference in electronegativity between the metal atom and the nitrogen atom. This improves the adhesion.

Specific examples of the organic adhesion improver (v) include, for example, 2-mercaptobenzothiazole, benzotriazole, 1-hydroxy-benzotriazole,
-Mercaptobenzimidazole, benzimidazole, 2-mercaptobenzoselenazole, 2-mercaptobenzoxazole, 5-mercapto-3-phenylthiadiazole-2-thione, 2- (O-hydroxyphenol) benzothiazole, 2,2 ′ -Dithiobis-
(Benzothiazole), phenociazoline, dipyridylamine, dipyridyl, dimethylhydantoin, pyrrole-2-carboxaldehyde, 2,5-dimercapto-
1,3,4-thiazole, 5-amino-1,3,4-thiadiazole-2-thiol, 3-amino-1,2,4
-Triazole, 4-amino-1,2,4-triazole, 3-amino-5-mercapto-1,2,4-triazole, 2-mercapto-1-methylimidazole, 2
-Mercaptothiazoline, 2-aminothiazole, 3,
5-dimethylpyrazole, histidine, 1,10-phenanthroline, 1,8-diazabicyclo (5,4,0)
Undecene-7 and the like can be mentioned.

In the coating composition of the present invention, the organic adhesion improver (v) is used in an amount of 0 to 10 parts by weight, particularly preferably 0.5 to 6 parts by weight, based on 100 parts by weight of the resin (i). It is appropriate to mix at a ratio of (solid content). If the amount is more than the above range, the stability of the paint tends to decrease. The coating composition of the present invention comprises the water-dilutable organic resin (i), silica particles (ii), and the reducing agent (iii).
And water (vi) as essential components, and more desirably contains the chelating agent (iv) and / or the organic adhesion improver (v), and optionally makes the organic resin (i) water-dilutable. A solid content of 10 to 60% by weight containing a neutralizing agent as an essential component.

With respect to the coating composition of the present invention, if necessary,
Other conventionally known components are appropriately blended. Specifically, various hydrocarbon-based, ester-based, ketone-based, alcohol-based, and amide-based organic solvents, particularly preferably water-soluble organic solvents; melamine resins, benzoguanamine resins, and cross-linking agents such as polyblocked isocyanate compounds; Or an inorganic pigment; a lubricant powder such as a synthetic wax; an additive such as a dispersant, an anti-settling agent, a leveling agent, or various improved resins.

The coating composition of the present invention can be used for automobiles, home appliances,
Hot-dip galvanized steel sheet, hot-dip zinc-aluminum alloy-plated steel sheet, electro-galvanized steel sheet, electro-zinc-nickel alloy-plated steel sheet, electro-zinc-iron alloy-plated steel sheet, electric-zinc-iron double-layer-plated steel sheet, cold-rolled steel sheet used for building materials, etc. It can be suitably applied as an undercoat paint of various surface-treated steel sheets or of the above-mentioned surface-treated steel sheets which have been subjected to a pretreatment such as a chromate conversion treatment or a phosphate conversion treatment. However, it is not limited to these objects to be coated.

The coating composition of the present invention is applied to these surface-treated steel sheets by means such as spraying, roll coating, shower coating, etc., and reaches a maximum temperature of 100 to 300 ° C.
By curing at the above temperature, a surface-treated steel sheet having excellent corrosion resistance, cationic electrodeposition coating property, and the like can be obtained. Although a thin film having a thickness of about several μm can sufficiently exhibit the performance, it may be thicker.

[0040]

The present invention will be described below in more detail with reference to examples and comparative examples. In Examples and Comparative Examples, "parts"
"%" Is shown on a weight basis: [Preparation of Aqueous Solution of Acrylic-Modified Epoxy Resin Aqueous Solution (A)] A bisphenol A type epoxy resin [Epicoat] 1007 (trade name, manufactured by Yuka Shell Epoxy Co., Ltd., epoxy equivalent: 1750-2200), 696 parts and ethylene glycol monobutyl ether (350 parts) were charged and dissolved by heating. Then, while stirring and introducing nitrogen gas, 4 parts of fumaric acid and 0.1 part of triethylamine is added, and
The reaction was carried out for a period of time to obtain a polymerizable unsaturated group-containing epoxy resin solution having a solid content of 67%. The equivalent ratio of the epoxy group of the epoxy resin to the carboxyl group of the polybasic acid was 1: 0.
2.

Into the reactor, 105 parts of a polymerizable unsaturated group-containing epoxy resin solution were charged and heated to 90 ° C., and styrene 16.2 parts, butyl acrylate 8 parts, acrylic acid 5.8 parts, azobis A mixture consisting of 2.4 parts of isobutyronitrile and 20 parts of ethylene glycol monobutyl ether was added dropwise with stirring over 2 hours, and further reacted at the same temperature for 4 hours. After cooling to 50 ° C., a mixture of 5.7 parts of dimethylethanolamine and 170 parts of ion-exchanged water was added dropwise with stirring over 30 minutes, and an acrylic-modified epoxy resin having a solid content of 30% (acid value 45, weight average molecular weight) 42,000, epoxy resin / polymerizable unsaturated monomer component = 7/3) water diluent (A) was obtained.

[Preparation of basic nitrogen compound-modified epoxy resin water diluent (B-1)] In a three-necked flask equipped with a reflux condenser, a thermometer and a stirrer, a bisphenol A type epoxy resin [Epicoat 1001] (Trade name of Yuka Shell Epoxy Co., Ltd.), epoxy equivalent 450-500] 40
0 parts and 243 parts of ethylene glycol monoethyl ether, and heated to 60 ° C.
The mixture was added dropwise over 2 hours, further heated to 65 ° C., and reacted for 3 hours. After cooling to 50 ° C., a mixture consisting of 52 parts of acetic acid and 350 parts of ion-exchanged water was added dropwise with stirring,
A basic nitrogen compound-modified epoxy resin (amine value: 100, weight average molecular weight: 20,000) diluted with water (B-1) having a solid content of 43% was obtained.

[Preparation of polybasic acid compound-modified epoxy resin aqueous diluent (B-2)] In the above-mentioned three-necked flask, bisphenol A type epoxy resin ["Epicoat 1004"
(Trade name of Yuka Shell Epoxy Co.), epoxy equivalent 90
[0-1000] and 900 parts of ethylene glycol monobutyl ether, heated to 90 ° C., added with 148 parts of phthalic anhydride, and reacted for 3 hours. 50 ℃
After cooling, 73 parts of diethylamine and 10 parts of ion-exchanged water
A mixture consisting of 00 parts was added dropwise with stirring to give a solid content of 4.
A 2% polybasic acid compound-modified epoxy resin (acid value: 50, weight-average molecular weight: 25,000) water dilution (B-2) was obtained.

[Preparation of Urethane Resin Water Diluent (C-1)] In the above-mentioned three-necked flask, phthalic anhydride 292.
1 part, adipic acid 252.8 parts, trimellitic anhydride 9
5.5 parts, 241.6 parts of ethylene glycol, 118.0 parts of trimethylolpropane, and 30.0 parts of xylene are added, and reacted while heating to 220 ° C. over 4 hours to obtain a polyester polyol resin having an acid value of 40. The reaction was terminated when was obtained, and then 86
6 parts were added to prepare a polyester polyol resin liquid having a solid content of 50%. 1000 parts of the resin solution was placed in the above-mentioned three-necked flask, 58 parts of hexamethylene diisocyanate was added dropwise over 1 hour while maintaining the temperature at 70 ° C., 36 parts of triethylamine was added, and 900 parts of ion-exchanged water were further added. Was added. Then, methyl ethyl ketone was distilled off by a vacuum distillation method to obtain a urethane resin (weight average molecular weight: 25,000) aqueous dilution (C-1) having a solid content of 50%.

[Preparation of urethane resin water diluent (C-2)] In the above-mentioned three-necked flask, the weight-average molecular weight was 1000
700 parts of polyethylene glycol, 14 parts of dimethylolpropionic acid, 540 parts of methyl ethyl ketone and N-
After adding 320 parts of methylpyrrolidone and dropping 86 parts of hexamethylene diisocyanate over 1 hour while maintaining the temperature at 70 ° C., 10 parts of triethylamine was added,
Further, 600 parts of ion-exchanged water was added. Then, methyl ethyl ketone was distilled off by a vacuum distillation method, and a urethane resin having a solid content of 50% (weight average molecular weight: 45,000, acid value: 70)
A water dilution (C-2) was obtained.

Examples 1 to 13 and Comparative Examples 1 to 2 A mixture prepared by mixing a resin water diluent, silica particles, a reducing agent, a chelating agent, and an organic adhesion improver in the proportions (parts by weight) shown in Table 1 was used. A coating composition was prepared by mixing with an amount of ion-exchanged water in which the amount became 15%. The obtained coating composition was treated with a chromate treatment shown in Table 2 (chromium equivalent: 50 mg /
m ² ) Roll-coated on various surface-treated steel sheets having a dry film thickness of 1 μm, and baked so that the maximum sheet temperature reaches 150 ° C. in 30 seconds. Under the conditions, corrosion resistance, molded part corrosion resistance, cationic electrodeposition coating property, adhesion, top coat adhesion, water resistance secondary adhesion, alkali resistance, chromium elution resistance, weldability, boiling water resistance were tested, and the results were Are shown in Table 2.

Corrosion resistance: A cross cut was made on the test painted surface, and a salt spray test based on JIS-Z-2371 was carried out for 75 times.
The test was conducted for 0 hour to observe the occurrence of red rust: ◎: no red rust ○: less than 1% of red rust △: red rust 1 to 5
%: Red rust: 5% or more Corrosion resistance of the molded part: A test plate punched into 90 mmφ has a diameter of 5 mm.
0mmφ cylindrical drawing (BHF = 1t)
A salt spray test based on IS-Z-2371 was performed for 750 hours, and the occurrence of red rust was observed:: no red rust ○: less than 1% of red rust △: red rust 1 to 5
%: Red rust 5% or more Cathodic electrodeposition paintability: Cationic electrodeposition coating with an amine-added epoxy resin-blocked isocyanate-based cationic electrodeposition paint on a test plate coated surface at a bath temperature of 28 ° C. and 100 V × 3 minutes, Baking at 165 ° C for 20 minutes, the coating film (area 100
cm ²⁾ Appearance was observed: ◎: gas-pinhole and craters occur 0 points ○: gas-pinhole and craters occur 1-5 points △: gas-pinhole and craters occur 6 to 19 points ×: gas-pinhole and craters generated 20 or more points Adhesion Test Based on JIS-K-5400 based on JIS-K-5400, cut 100 goban eyes with a gap of 1 mm with a cutter knife and perform a peeling test using cellophane tape.
The residual ratio of the coating film was measured: ◎: No peeling ○: Peeling less than 5% △: Peeling less than 5% to 35% ×: Peeling 35% or more Topcoat adhesion: Cationic electrodeposition obtained by cationic electrodeposition coating test 100 goban eyes with a gap of 1 mm were cut into the coated plate with a cutter knife, a peeling test was performed using a cellophane tape, and the residual ratio of the electrodeposited coating film was measured: ：: no peeling ○: less than 5% peeling Δ: peeling ×: less than 5 to 35% ×: Peeling 35% or more Water resistant secondary adhesion: The cationic electrodeposition coated plate obtained in the cationic electrodeposition coating test was immersed in water at 40 ° C. for 400 hours, dried, and then adhered to the top coat. A peeling test was carried out in the same manner as in the peeling test, and the residual ratio of the electrodeposition coating film was measured: ：: No peeling ○: Peeling less than 5% △: Peeling less than 5% 35% ×: Peeling 35% or more Alkali resistance: Test Place the plate at 45 ° C Cali degreasing solution "Granda cleaner 26F" (Million Chemical Co., Ltd. trade name)
After immersion in water for 5 minutes, washing with water, and drying, a peeling test was performed in the same manner as the top coat adhesion test to measure the residual ratio of the coating film: ：: no peeling off: less than 5% peeling off: 5 to less than 35% peeling off ×: Peeling 35% or more Chromium elution resistance: The amount of chromium before and after alkali degreasing and chemical conversion treatment was measured by X-ray fluorescence analysis, and the difference was determined to be the amount of chromium elution: ◎: less than 1 mg / m ² ： １: 1 or more and less than 2 mg / m ² △: 2 or more and less than 5 mg / m ² ×: 5 mg / m ² or more Weldability: Welding force: 200 kgf, welding tip made of Al ₂ O ₃ dispersed steel alloy with 6 mmφ tip Current 9 KA,
Continuous welding was performed at a welding time of 10 hours, and the number of continuous welding points until the nugget diameter became smaller than the reference diameter was measured: ：: 3000 points or more ○: 2000 to 2999 Δ: 1000 to 1999 ×: 999 or less Boiling water resistance: boiling water After immersion for 2 hours, a peeling test was performed in the same manner as the topcoat adhesion test to measure the residual ratio of the coating film. %that's all

[0048]

[Table 1]

[0049]

[Table 2]

As is clear from the data in Table 2, Examples 1 to 13 using the coating composition of the present invention all had excellent coating performance. On the other hand, Comparative Examples 1 and 2, which did not contain a reducing agent and the like, all had poor chromium elution resistance and the like.

[0051]

The coating composition of the present invention is advantageous in preventing air pollution and saving resources because water is used as a solvent.
In addition, the surface-treated steel sheet coated with the coating composition has a corrosion resistance, cationic electrodeposition coating property, adhesion, workability and the like which is not inferior to those of the surface-treated steel sheet coated with the conventional organic solvent type paint. In addition, since the elution of chromium from the surface-treated steel sheet in the pre-treatment for cationic electrodeposition can be prevented, the problem of pollution control can be solved.

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Masanori Nagai 1926-9 Usaba, Otawara-shi, Tochigi Prefecture (72) Inventor Osamu 3-1172-4, Shimonagata, Nishinasuno-cho, Nasu-gun, Tochigi Prefecture (58) Field surveyed (Int .Cl. ⁶ , DB name) C09D 5/00 C09D 5/08 C09D 163/00-163/10 C09D 175/00-175/16

Claims (3)

(57) [Claims] 1. It comprises (i) a water-dilutable organic resin, (ii) silica particles, and (iii) at least one reducing agent selected from the group consisting of hydrazine, tannic acid and gallic acid. Water-based corrosion-resistant coating composition. 2. A reducing agent selected from the group consisting of (i) an organic resin dilutable in water, (ii) silica particles, (iii) hydrazine, tannic acid and gallic acid, and (i)
v) A water-based corrosion-resistant coating composition comprising at least one chelating agent selected from the group consisting of titanium-based and zirconium-based. 3. The method according to claim 1, further comprising: (v) an organic adhesion improver having a 5-membered or 6-membered ring structure in the molecule and having a nitrogen atom in the ring structure. 3. The water-based corrosion-resistant coating composition according to 1 or 2.