JP2000204299A - Cation electrodeposition paint composition and method of forming coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress development of gas pinholes in zinc steel sheets or galvanized steel sheets and improve the throwing power of a film by specifying a conductivity of a diluted paint and a Coulomb effect in electrodeposition. SOLUTION: A cationic resin having an epoxy equivalent of 180-1200, especially 375-1,000, 10-50 wt.%, preferably 15-40 wt.% of a block polyisocyanate having a dissociation temperature of 100-180 deg.C, 0.1-6 wt.% of a dissociation catalyst such as dibutyltin laurate and N-methylmorpholine as needed, 0.1-15 wt.%, especially 0.1-5 wt.% of additives such as acids such as formic acid, lactic acid, acetic acid and sulfamic acid and surfactants, 1-35 wt.%, especially 10-30 wt.% of a pigment, 1-20 wt.%, especially 1-15 wt.% of a pigment dispersing resin are dispersed in an aqueous medium to obtain a cation electrodeposition paint composition having a conductivity of a diluted paint of 1,000-1,300 μS/cm2 and a Coulomb efficiency of 40 mg/Coulomb or more in three-minute electrodeposition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a cationic electrodeposition coating composition and a method for forming a coating film using the same. More specifically, the present invention relates to a cationic electrodeposition coating composition capable of suppressing generation of gas pinholes on a zinc steel sheet or a galvanized steel sheet and obtaining a coating film having high throwing power, and a coating film forming method using the same.

[0002]

2. Description of the Related Art A cationic electrodeposition coating composition used for coating an automobile body or the like is generally a resin dispersion (emulsion) containing a cationic resin, a curing agent and a neutralizing agent.
And a pigment dispersion paste containing a pigment dispersion resin and a pigment are provided in a form dispersed in an aqueous medium.

When a galvanized steel sheet is subjected to cationic electrodeposition coating, a crater-like abnormality may occur on the coating film surface. In the cationic electrodeposition paint, hydrogen gas generated by electrolysis of water is present between the deposited films in the initial stage of coating, and the film resistance increases as the electrodeposition proceeds, and the voltage applied to the coated film is reduced by hydrogen gas discharge. When the voltage becomes higher than the voltage, spark discharge occurs, and the heat at that time hardens the resin of the coating film near the discharge, and the heat flow of the coating film in the subsequent steps becomes insufficient and remains as a crater. This crater is called a gas pinhole, and the tendency to suppress the generation of the gas pinhole is called gas pinhole property.

[0004] The gas pinhole property is particularly problematic when a zinc steel sheet, a galvanized steel sheet, or an alloyed hot-dip galvanized steel sheet plated with a metal having a low spark voltage, such as zinc, is used as an object to be coated.

Conventionally, in order to improve the gas pinhole property, there has been a method of adding a solvent, a plasticizer, or the like to form a soft deposited film, thereby facilitating the escape of generated hydrogen gas. This causes a problem that the turning property is reduced. The throwing power refers to a performance in which an unpainted portion may remain without sufficiently forming an electrodeposition film far from the electrode portion, and the unpainted portion may be reduced.

[0006] In addition, by forming a thick electrodeposition coating film,
Although there was a method of repairing pinholes generated at the time of deposition, there was a problem that the amount of paint used was increased.

Therefore, it is desired to develop a measure for preventing gas pinholes from occurring without adversely affecting other performances such as throwing power.

[0008]

DISCLOSURE OF THE INVENTION The present invention relates to a cationic electrodeposition coating composition which suppresses the generation of gas pinholes on a steel sheet, especially a zinc steel sheet or a galvanized steel sheet, and which can provide a high throwing power coating film. It is an object of the present invention to provide a coating film forming method used.

[0009]

According to the present invention, there is provided a cationic electrodeposition wherein the electric conductivity of the diluted paint is 1000-1300 μS / cm ² , and the coulombic efficiency at the time of electrodeposition coating for 3 minutes is 40 mg / coulomb or more. A coating composition is provided.

The conductivity of the diluted paint is preferably 1050
１２1250 μS / cm ² .

The coulomb efficiency at the time of electrodeposition coating of the diluted paint for 3 minutes is preferably 45 to 55 mg / coulomb.

The diluted paint has a neutralizing agent concentration of 20 mg equivalent /
It is preferably 100 g solids or less, more preferably 10 to 20 mg equivalent / 100 g solids.

The reaction equivalent ratio of the glycidyl group to the amine of the resin dispersion (emulsion) is preferably from 1 / 0.7 to
1 / 0.9.

[0014] The present invention also provides a method for forming a coating film, comprising forming a coating film on a steel sheet using the above-mentioned cationic electrodeposition coating composition.

The steel sheet is, for example, a zinc steel sheet or a galvanized steel sheet.

[0016]

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

In the cationic electrodeposition coating composition of the present invention, the conductivity of the diluted coating must be 1000 to 1300 μS / cm ² . If the electric conductivity exceeds 1300 μS / cm ² , the gas pinhole property deteriorates. When a voltage is applied to the electrodeposition paint at the time of electrodeposition coating, a large current flows immediately after the voltage is applied, and then suddenly decreases, and thereafter gradually decreases to a steady current. It has been confirmed that the discharge caused by hydrogen gas is more likely to occur as the amount of current flowing immediately after the application of the voltage increases. Therefore, the generation of gas pinholes can be suppressed by reducing the amount of current flowing by lowering the conductivity of the diluted paint. However, when the electric conductivity is less than 1000 μS / cm ² , it becomes difficult for a current to flow far from the electrode portion, and the throwing power becomes poor. More preferred conductivity is 1050-12
50 μS / cm ² .

The conductivity is 1000 to 1300 μS / cm ²
As a method for adjusting the amount of unreacted amine, unreacted amine (free amine) is reacted when the cationic resin is cationized.
To decrease and adjust. For example, when using an amino-modified epoxy resin obtained by amination of an epoxy resin,
The reaction equivalent ratio of glycidyl group to amine is 1 / 0.7 to 1
/0.9. After the addition of the amine, for example, one equivalent of
Even better results are obtained if half-blocked isocyanate blocked with a blocking agent such as ethylhexyl cellosolve is added to eliminate free amines.

Further, the cationic electrodeposition coating composition has a coulomb efficiency of 40 minutes at the time of electrodeposition coating for 3 minutes when used as a diluted coating.
It is necessary to be at least mg / coulomb. here,
The Coulomb efficiency indicates the ratio of the amount of paint (mg) deposited to the amount of electric charge (Coulomb) consumed by passing an electric current. In the present invention, since the electric conductivity of the diluted paint is lower than before, the amount of current flowing during electrodeposition coating is smaller than before, and the current is particularly small in areas far from the electrode portion, so that the throwing power is significantly reduced. Become. Therefore, if a large amount of paint can be deposited with a small current (amount of charge) during the three-minute electrodeposition coating, in other words, if the Coulomb efficiency is increased, the throwing power can be improved. That is, sufficient throwing power can be obtained by setting the Coulomb efficiency during electrodeposition coating for 3 minutes to 40 mg / Coulomb or more. The coulomb efficiency at the time of electrodeposition coating for 3 minutes is more preferably 45 to 55 mg / coulomb.

Coulomb efficiency during electrodeposition coating for 3 minutes is 40 m
Examples of the method for adjusting the concentration to g / coulomb or more include, for example, setting the concentration of the neutralizing agent in the diluted paint to 20 mg equivalent / 100 g solid content or less, and more preferably 10 to 20 m.
g equivalent / 100 g solids. Specifically, the cationic group of the cationic resin is neutralized with one or a combination of two or more of acetic acid, lactic acid, formic acid, and sulfamic acid. In particular, it is preferable to use a strong acid such as formic acid or sulfamic acid.

The cationic electrodeposition coating composition of the present invention is characterized in that a coating film is formed on a steel sheet, particularly a zinc steel sheet plated with a metal having a low spark voltage such as zinc, a galvanized steel sheet, and a galvannealed alloy. It is useful when forming a coating on a steel sheet.

Next, examples of components constituting the cationic electrodeposition coating composition of the present invention will be described.

The cationic resin used in the present invention is not particularly limited, but a preferred cationic resin is an amine-modified resin, particularly preferably an amino-modified epoxy resin. Examples of the amino-modified epoxy resin include those obtained by aminating a bisphenol A type epoxy resin with a secondary amine.

The epoxy resin used in the present invention is generally a polyepoxide. This polyepoxide has an average of one or more 1,2-epoxy groups in one molecule. These polyepoxides have an epoxy equivalent of 180-1200,
It is particularly preferred to have an epoxy equivalent of 375 to 1000.

Useful classes of such polyepoxides include the polyglycidyl ethers of polyphenols (eg, bisphenol A). These are prepared, for example, by etherifying a polyphenol with epichlorohydrin or dichlorohydrin in the presence of an alkali. This polyphenol is bis (4-hydroxyphenyl) -2,2-propane, 4,
It can be 4'-dihydroxybenzophenone, bis (4-hydroxyphenyl) -1,1-ethane or an analog thereof.

These epoxy resins may be modified with a suitable resin such as polyester polyol, polyether polyol or monofunctional alkylphenol. Examples of the resin used for this modification include polycaprolactone diol, ethylene oxide addition polymer and the like.

The secondary amine used for amination of the epoxy resin includes alkanolamines such as n-methylethanolamine, diethanolamine and diisopropanolamine; and alkylamines such as diethylamine and dibutylamine. Further, a polyamine having at least one primary amino group such as diethylenetriamine and aminoethylethanolamine may be used as a ketimine compound in which the primary amino group is blocked with a ketone such as methyl isobutyl ketone and methyl ethyl ketone. These amines may be used as a mixture of two or more.

As the curing agent used in the present invention, a blocked polyisocyanate is preferable. Particularly preferred blocked polyisocyanates are those having a dissociation temperature of 100 to 180 ° C. The blocked polyisocyanate may be present in the composition as a separate component, or may be integrated with other components. For example, a half-blocked polyisocyanate may be reacted with a cationic resin to impart a crosslinking ability to the cationic resin. When the block polyisocyanate is not contained, the curability is insufficient, and if the dissociation temperature of the block polyisocyanate is less than 100 ° C., the fluidity of the coating film is extremely poor, so that the smoothness of the plane portion is reduced, which is not preferable. . There is also a problem with the stability of the paint. On the other hand,
If the dissociation temperature exceeds 180 ° C., the curability will be insufficient under the baking conditions of many current coating lines, and the corrosion resistance will decrease.

As the blocked polyisocyanate having a dissociation temperature of 100 to 180 ° C., all polyisocyanates conventionally used as a vehicle component for electrodeposition coatings can be used. Representative polyisocyanates include, for example, toluene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, 1,2-propylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate Aliphatic cyclic isocyanates such as 1,3-butylene diisocyanate, ethylidene diisocyanate, butylidene diisocyanate, 1,3-cyclopentane diisocyanate, 1,4-cyclohexane diisocyanate, 1,2-cyclohexane diisocyanate and isophorone diisocyanate Diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 4 Aromatic diisocyanates such as 4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 1,4-naphthalene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4- or 2,6-toluene diisocyanate or mixtures thereof; Aliphatic-aromatic diisocyanate such as 4,4'-toluidine diisocyanate, 1,4-xylene diisocyanate, nucleus-substituted aromatic diisocyanate such as 4,4'-diphenylether diisocyanate, chlorodiphenyl diisocyanate, triphenylmethane-4 , 4 ', 4 "-triisocyanate, 1,
3,5-triisocyanate benzene, triisocyanates such as 2,4,6-triisocyanate toluene,
4,4'-diphenyl-dimethylmethane-2,2 ',
Examples thereof include tetraisocyanates such as 5,5′-tetraisocyanate, and polymerized polyisocyanates such as toluene diisocyanate dimer and toluene diisocyanate trimer.

The blocking agent that dissociates at 100 to 180 ° C. may be in the presence of a catalyst. Examples of such a blocking agent include lower and higher alcohols such as methanol, ethanol, butanol and 2-ethylhexanol, cellosolves such as ethyl cellosolve, butyl cellosolve and hexyl cellosolve, furfuryl alcohol, and alkyl group-substituted furfuryl. Aliphatic or heterocyclic alcohols such as alcohol, phenol, m-
Phenols such as cresol, p-nitrophenol, p-chlorophenol and nonylphenol, oximes such as methyl ethyl ketone oxime, methyl isobutyl ketone oxime, acetone oxime and cyclohexane oxime, and active methylene compounds such as acetylacetone, ethyl acetoacetate and ethyl malonate And caprolactam.

When a dissociation catalyst is used as the blocked polyisocyanate curing agent, an organic tin compound such as dibutyltin laurate, dibutyltin oxide, dioctyltin or the like,
Amines such as methyl morpholine and metal salts such as lead acetate, strontium, cobalt and copper can be used. The concentration of the catalyst is usually 0.1 to 6% by weight based on the solid content of the film-forming resin in the cationic electrodeposition paint.

The compounding amount of the blocked polyisocyanate curing agent in the composition is from 10 to 15% by weight, preferably from 15 to 40% by weight, based on the solid content of the coating composition. If the amount is less than 10% by weight, the curability is insufficient. If the amount is more than 50% by weight, a large amount of debris is generated at the time of baking of the coating film. There are problems such as occurrence.

The resin dispersion may contain various additives and solvents as required in addition to the above components. Examples of the additives include acids such as formic acid, acetic acid, lactic acid, and sulfamic acid and a surfactant, which are used as a neutralizing agent when the film-forming component is dispersed in an aqueous medium. The concentration of these additives is usually 0.1 to 15% by weight, preferably 0.1 to 5% by weight, based on the resin solid content in the electrodeposition paint. However, as described above, the amount of the acid added is desirably 20 mg equivalent / 100 g solid content or less as a neutralizing agent concentration.

The pigment dispersion paste used in the present invention is a mixture of a pigment dispersion resin and a suitable pigment. Pigment dispersion resins that can be used include known resins such as the above-mentioned cationic resins. Examples of pigments that can be used include carbon black, graphite, titanium oxide, coloring pigments such as zinc oxide, extenders such as aluminum silicate and kaolin, strontium chromate, basic lead silicate, basic lead sulfate, and phosphomolybdenum. Synthetic pigments such as aluminum oxide can be used. The concentration of this pigment is 1 to 35% by weight, preferably 10 to 30% by weight, based on the solid content of the entire electrodeposition paint. The amount of the pigment-dispersed resin used depends on the amount of the pigment, but is 1 to 20% by weight, preferably 1 to 15% by weight, based on the total solid content of the electrodeposition paint.

In the present invention, a lead-based rust-preventive pigment is not used at all to reduce the lead content, or even if used, the total metal ion concentration of the diluted paint (the state added to the electrodeposition bath) is 500 ppm.
It is preferable to use the following amount. If the concentration of metal ions is high, the smoothness may decrease.

The cationic electrodeposition coating composition of the present invention is obtained by dispersing the above components in an aqueous medium. In the aqueous medium, various organic solvents may be used in addition to water to adjust the dissolution and viscosity of the resin. Examples of solvents that can be used include hydrocarbons (eg, xylene or toluene), alcohols (eg, methyl alcohol, n
-Butyl alcohol, isopropyl alcohol, 2-ethylhexyl alcohol, ethylene glycol, propylene glycol), ethers (eg, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, propylene glycol monoethyl ether, 3-methyl) -3-methoxybutanol, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether), ketones (eg, methyl isobutyl ketone, cyclohexanone, isophorone, acetylacetone), esters (eg, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate) And mixtures thereof. The amount of these solvents used is about 0.1
-5% by weight, preferably 0.2-3% by weight.

[0037]

EXAMPLES Next, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples.

(Production Example 1) 168 parts of hexamethylene diisocyanate and methyl isobutyl ketone (hereinafter abbreviated as "MIBK") are placed in a five-necked flask equipped with a reflux condenser, a stirrer, a dropping funnel and a nitrogen inlet tube. 2 parts and 0.2 parts of dibutyltin dilaurate were charged at 50 ° C.
, And 34.6 parts of trimethylolpropane was gradually added dropwise while maintaining the internal temperature not to exceed 60 ° C.
Next, 106.7 parts of methyl ethyl ketoxime was added dropwise while keeping the internal temperature not exceeding 70 ° C. After the completion of the dropwise addition, the mixture was kept at 70 ° C. for 1 hour until the peak of the isocyanate group disappeared in the IR spectrum, and 3.9 parts of butanol was added.
Then, the mixture was cooled and a blocked isocyanate curing agent was prepared. The solids content was 80%.

(Production Example 2) A liquid epoxy resin having an epoxy equivalent of 188 (trade name “DER-331J”, manufactured by Dow Chemical Co., Ltd.) was placed in the same reaction vessel as that of Production Example 1 prepared separately.
81 parts by weight, 269 parts of bisphenol A, 88 parts of nonylphenol and 115 parts of MIBK were charged at 140 ° C.
And completely dissolved. As a reaction catalyst, a 2-% solution of 2-ethyl-4-methylimidazole (xylene 98
%), And reacted at 140 to 150 ° C. After adding 146 parts of MIBK with epoxy equivalent 1210 as an end point, the mixture was cooled to 105 ° C. Next, 47 parts of n-methylethanolamine and 54 parts of 73% of methyl isobutylene ketimine of diethylenetriamine (MIBK solution) were added, and the mixture was kept at 120 ° C. for 1 hour, and cationic resin A was added.
I got

(Production Example 3) To 1405 parts of the cationic resin A obtained in Production Example 2, 692 parts of the curing agent obtained in Production Example 1 and 59 parts of n-hexyl cellosolve were mixed at 90 ° C. for 30 minutes, and 88% formic acid was added. After neutralization with 14.6 parts, a plasticizer (trade name "New Pole YG-1" manufactured by Sanyo Chemical Industries, Ltd.) was slowly diluted with 18 parts and 3113 parts of deionized water, and the organic solvent was removed under reduced pressure. Thus, an epoxy emulsion X having a solid content of 36.0% was obtained.

(Production Example 4) To 1405 parts of the cationic resin A obtained in Production Example 2, 692 parts of the curing agent obtained in Production Example 1 and 59 parts of n-hexyl cellosolve were mixed, and 90% acetic acid 2
After neutralization with 5.1 parts, a plasticizer (trade name "New Pole YG-1" manufactured by Sanyo Chemical Industries, Ltd.) was slowly diluted with 18 parts and 3100 parts of deionized water, and the organic solvent was removed under reduced pressure. Thus, an epoxy emulsion Y having a solid content of 36.0% was obtained.

(Production Example 5) A liquid epoxy resin having an epoxy equivalent of 188 (trade name “DER-331J”, manufactured by Dow Chemical Company) was placed in the same reaction vessel as that of Production Example 1 prepared separately.
81 parts by weight, 269 parts of bisphenol A, 88 parts of nonylphenol and 115 parts of MIBK were charged at 140 ° C.
And completely dissolved. As a reaction catalyst, a 2-% solution of 2-ethyl-4-methylimidazole (xylene 98
%), And reacted at 140 to 150 ° C. After adding 146 parts of MIBK with epoxy equivalent 1210 as an end point, the mixture was cooled to 105 ° C. Next, 43 parts of n-methylethanolamine and 54 parts of a 73% MIBK solution of diethylenetriamine in methyl isobutylene ketimine were added, and the mixture was kept at 120 ° C. for 1 hour to obtain a cationic resin B.

(Production Example 6) The cationic resin B1405 parts obtained in Production Example 5 was combined with 503 parts of the curing agent obtained in Production Example 1 and n-
63 parts of a half-blocked isocyanate solution (solid content: 80%) obtained by blocking 57 parts of hexyl cellosolve and 1 equivalent of isophorone diisocyanate with 2-ethylhexyl cellosolve was mixed at 90 ° C. for 30 minutes, and neutralized with 15.2 parts of 88% formic acid. After that, a plasticizer (manufactured by Sanyo Kasei Co., Ltd., trade name “New Pole YG-1”) was slowly diluted with 18 parts and 3113 parts of deionized water, and the organic solvent was removed under reduced pressure to obtain a solid content of 36.0%. Epoxy emulsion Z was obtained.

(Production Example 7) A liquid epoxy resin having an epoxy equivalent of 188 (trade name “DER-331J”, manufactured by Dow Chemical Co., Ltd.) was placed in the same reaction vessel as in Preparation Example 1 separately prepared.
81 parts by weight, 269 parts of bisphenol A, 77 parts of nonylphenol and 114 parts of MIBK were charged at 140 ° C.
And completely dissolved. As a reaction catalyst, a 2-% solution of 2-ethyl-4-methylimidazole (xylene 98
%), And the mixture was reacted at 140 to 150 ° C., 144 parts of MIBK was added with an epoxy equivalent of 1180 as an end point, and then cooled to 105 ° C. Next, 55 parts of n-methylethanolamine and 54 parts of a 73% MIBK solution of diethylenetriamine in methyl isobutylene ketimine were added, and the mixture was kept at 120 ° C. for 1 hour to obtain a cationic resin D.

(Production Example 8) 500 parts of the curing agent obtained in Production Example 1 and 54 parts of n-hexyl cellosolve were mixed with 1400 parts of the cationic resin D obtained in Production Example 7 at 60 ° C. for 30 minutes. After neutralizing with a solvent, a plasticizer (manufactured by Sanyo Kasei Co., Ltd., trade name “New Pole YG-1”) was slowly diluted with 76 parts and 3426 parts of deionized water, and the organic solvent was removed under reduced pressure. An epoxy emulsion U of 36.0% was obtained.

(Production Example 9) 500 parts of the curing agent obtained in Production Example 1 and 54 parts of n-hexyl cellosolve were mixed with 1400 parts of the cationic resin D obtained in Production Example 7 at 60 ° C. for 30 minutes, and 88% formic acid 27 was added. After neutralizing with a solvent, the plasticizer (manufactured by Sanyo Kasei Co., Ltd., trade name “New Pole YG-1”) was slowly diluted with 76 parts and 3419 parts of deionized water, and the organic solvent was removed under reduced pressure. An epoxy emulsion V of 36.0% was obtained.

(Production Example 10) 503 parts of the curing agent obtained in Production Example 1 were added to 1405 parts of the cationic resin B obtained in Production Example 5,
63 parts of a half-blocked isocyanate solution (80% solids MIBK) obtained by blocking 57 parts of hexyl cellosolve and 1 equivalent part of isophorone diisocyanate with 2-ethylhexyl cellosolve were mixed at 90 ° C. for 30 minutes,
After neutralizing with 18 parts of 90% acetic acid, a plasticizer (trade name "Newpol YG-1", manufactured by Sanyo Chemical Industries, Ltd.) is slowly diluted with 18 parts and 3100 parts of deionized water, and the organic solvent is removed under reduced pressure. Thus, an epoxy emulsion W having a solid content of 36.0% was obtained.

(Production Example 11) Component Weight part Solid content 2-ethylhexanol half-blocked 320.0 304 Toluene diisocyanate (in MIBK) Dimethylethanolamine 87.2 87.2 Lactic acid aqueous solution 117.6 88.2 Ethylene glycol Monobutyl ether 39.2-According to the above composition, use a suitable reaction vessel at room temperature
Ethylexanol half-blocked toluene diisocyanate (in MIBK) was added to dimethylethanolamine. The mixture exothermed and was stirred for 1 hour. Next, lactic acid was charged, and butyl cellosolve was further stirred at 65 ° C. for about half an hour to obtain a quaternizing agent.

Ingredient Parts by weight Solid content Bisphenol A type epoxy resin 710.0 681.2 (Epoxy equivalent 193 to 203, manufactured by Shell Chemical Company, trade name “Epon 829”) Bisphenol A 289.6 289. 6 2-ethylhexanol half-blocked 406.4 386.1 Toluene diisocyanate (in MIBK) Quaternizing agent 496.3 421.9 Deionized water 71.2 Ethylene glycol monobutyl ether 1584.1-bisphenol A according to the above composition The epoxy resin and bisphenol A were charged into a suitable reaction vessel and heated to 150 to 160 ° C. under a nitrogen atmosphere. An initial exothermic reaction occurred. The reaction mixture was reacted at 150 to 160 ° C. for about 1 hour, and then cooled to 120 ° C., and then 2-ethylhexanol half-blocked toluene diisocyanate was added. Keeping the reaction mixture at 110-120 ° C. for about 1 hour,
Then, butyl cellosolve was added. Then, 85-9
After cooling to 5 ° C., the mixture was homogenized, and a quaternizing agent was further added. The mixture was kept at 85 to 95 ° C. until the acid value became 1, to obtain a pigment dispersion varnish C. The resin solid content was 50%.

(Production Example 12) Varnish C50 for dispersing pigment
Parts, 93 parts of deionized water, 1.8 parts of carbon black, 7 parts of dibutyltin oxide, 20 parts of kaolin, 6 parts of lead silicate
And 72.2 parts of titanium dioxide were mixed, dispersed by a sand grind mill, and pulverized until the particle size became 10 μm or less, to obtain a pigment-dispersed paste P.

(Production Example 13) A bisphenol-type epoxy resin having an epoxy equivalent of 450 was reacted with 2-ethylhexanol half-blocked isophorone diisocyanate, and reacted with 1- (2-hydroxyethylthio) -2-propanol and dimethylolpropionic acid. 135.3 g of a resin varnish for pigment dispersion which has been converted to grade sulfonium (tertiary sulfonium conversion rate: 70.6%, resin solid content: 60%), 435.0 g of ion-exchanged water, 8.5 g of carbon black, 72.0 g of kaolin, titanium dioxide 345.0 g, 75.0 g of aluminum phosphomolybdate and 41 g of dibutyltin oxide were dispersed in a sand grind mill, and this was further pulverized until the particle size became 10 μm or less to obtain a pigment dispersion paste Q.

(Examples 1 to 5, Comparative Examples 1 to 4) The emulsions X and Y, the pigment dispersion pastes P and Q, and the deionized water obtained in the above production examples were blended according to the compositions shown in Tables 1 and 2. The diluted paints of Examples 1 to 5 and Comparative Examples 1 to 4 were obtained. Table 3 shows the electrical conductivity, coulomb efficiency, neutralizer concentration, solid content of each diluted paint, and the evaluation results of gas pinhole properties and throwing power of each diluted paint. In addition, the evaluation method by gas pinhole property and throwing power is as follows.

(Gas pinhole property) 200 V, 220 V, 24 V
After increasing the pressure to 0 V and 260 V in 5 seconds, the paint of each Example or Comparative Example was electrodeposited in 175 seconds, washed with water, and washed with water.
It was baked at 10 ° C. for 10 minutes and the state of the coated surface was observed. It can be evaluated that the higher the voltage at which the crater is generated, the better the gas pinhole property.

(Throwing power) The throwing power was evaluated by a so-called four-box method. That is, as shown in FIG. 1, four zinc phosphate treated steel sheets (JIS G 3
141 Surfdyne SD-5000 of SPCC-SD
Treatment) A box 10 is used in which 11 to 14 are arranged in parallel in an upright state at an interval of 20 mm, and the lower part and the bottom part on both sides are sealed with an insulator such as cloth adhesive tape. In addition, the steel plates 11 to 13 other than the steel plate 14 are provided with 8 mmφ through holes 15 in the lower part. This box 10 is immersed in an electrodeposition coating container 20 containing the diluent paint 21 of each example or comparative example as shown in FIG.
1 to enter the box 10. Then, each steel plate is electrically connected, and the distance to the nearest steel plate 11 is 1
The counter electrode 22 was arranged so as to be 50 mm. A voltage was applied to each of the steel sheets as a cathode and the counter electrode 22 as an anode to perform cation electrodeposition coating on the steel sheets. The coating was performed by increasing the voltage of the coating film formed on the side A of the steel sheet 11 to a voltage of 20 μm within 5 seconds from the start of the application, and thereafter maintaining the voltage for 175 seconds. The bath temperature at this time was adjusted to 28 ° C. Each coated steel sheet is washed with water, baked at 160 ° C. for 20 minutes, and air-cooled, after which the thickness of the coating film formed on the surface A of the steel sheet 11 closest to the counter electrode 22 and the steel sheet 14 farthest from the counter electrode 22 are reduced. The film thickness of the coating film formed on the G surface was measured, and the throwing power was evaluated based on the ratio (G / A value) of the film thickness (G surface) / film thickness (A surface). The larger this value, the better the throwing power.

[0055]

[Table 1]

[0056]

[Table 2]

[0057]

[Table 3]

[0058]

As described above, according to the present invention, there is provided a cationic electrodeposition coating composition which suppresses the generation of gas pinholes particularly on a zinc steel sheet or a galvanized steel sheet and can provide a coating film having high throwing power. Can be provided.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of a box used for evaluating throwing power.

FIG. 2 is an explanatory diagram showing a method for evaluating throwing power.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Ken Ishiwatari 4-1-1-15 Minamishinagawa, Shinagawa-ku, Tokyo Japan Paint Co., Ltd. Tokyo Office F-term (reference) 4D075 BB87X BB89X BB89Y BB89Z DB02 DB05 DC12 4J038 EA011 NA20 PA04 PC02

Claims (3)

[Claims] 1. The diluted paint has an electric conductivity of 1,000 to 1,300.
μS / cm ² , Coulomb efficiency during electrodeposition coating for 3 minutes is 40
mg / Coulomb or more. 2. A method for forming a coating film, comprising forming a coating film on a steel sheet using the cationic electrodeposition coating composition according to claim 1. 3. The method according to claim 2, wherein the steel sheet is a zinc steel sheet or a galvanized steel sheet.