JPS6024194B2 - Cathode electrodeposition coating method - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a cathodic electrodeposition coating method using a paint containing a thermosetting urethane resin. As is conventionally known, the haze coating method involves immersing the object to be coated in ionized water-based or water-dispersible paint and applying a voltage between it and an electrode to generate electricity on the surface of the object. This is a method of coating by depositing paint using chemical phenomena. The paint used for this purpose is one whose resin component contains polycarboxylic acid and is neutralized with amines, and is anodically deposited by anion electrolysis, so this is called anionic electrodeposition coating.On the other hand, the resin component contains basic amine groups. When the coating is neutralized with an acid, it is cathodically deposited using a cationic electrolysis method, so this is called cationic electrodeposition coating to distinguish between the two. However, compared to anionic electrodeposition paints, cationic electrodeposition paints have better coverage, meaning that the paint spreads evenly to every corner of the complex-shaped object, and the resulting paint film is also stronger. Due to its excellent adhesion to substrates and corrosion resistance, it has recently become widely used as a strong anticorrosive paint and as an effective method for preventing rust in automobiles. In actual cationic electrodeposition coating, the paint is continuously circulated in a tank, and while preventing precipitation, a voltage of 150 to 300 V is applied to the object to be coated and electricity is applied for 1 to 5 minutes to deposit the paint. After that, excess paint adhering to the surface is washed away with water, and the paint is finished by passing it through a drying oven and baking the paint at a temperature of 150 to 200 qo for 20 to 30 minutes. In this case, if the applied voltage is low, the coverage of the paint will be poor for objects with complex shapes, and the deposition rate of the paint will decrease, making it take a long time to deposit the desired film thickness, which will reduce the coating efficiency. descend. Therefore, high voltage work of 200V or more is generally performed. However, when performing high-voltage electrodeposition using cationic electrodeposition paint, pinholes are likely to occur on the coating surface, especially when the object to be coated is an alloy or alloy plated material, such as zinc and iron alloy, zinc and nickel. It appears conspicuously in alloys, etc., and is unfavorable from the viewpoint of appearance and corrosion resistance. On the other hand, steel sheets with zinc-containing alloy plating films have excellent corrosion resistance and are promising for use in automobiles and other applications. The present inventors investigated a frost coating method that does not generate pinholes even with this alloy plating material and can provide improved corrosion resistance, and found that if a frost coating containing a specific thermosetting resin is used. The inventors found that the above-mentioned drawbacks could be improved and arrived at the present invention. That is, the present invention uses a dew coating containing a urethane resin having a hydroxyl group, a tertiary amyl group, and a blocked isocyanate group that can react with the hydroxyl group at heating temperature, and uses zinc-iron or zinc-nickel. A cathodic electrodeposition coating method is characterized in that coating is performed at an applied voltage of 200 volts or more using a steel plate having an alloy plating film mainly composed of as a cathode. The present invention will be explained in detail below. The steel plate used in the present invention is Zn-Fe or Zn-N
It has an alloy plating film whose basic component is i. It is also effective to add other ingredients for the purpose of improving the workability, corrosion resistance, etc. of the plating film. Zn-Fe
In the case of alloy plating, such components include AI, S
i, Mn, Cr, Ni, V, Ti, 81g, etc. Z
In the case of n-Nj alloy plating, Fe, Cu, Co, Mo,
Examples include Cr, Sn, Mn, Pb, and Sb. The form of the alloy plating film varies depending on the plating conditions, but Zn-Fe
In the case of '1, 6. , Ki, and Ri phases, or a composite phase; in the case of Zn-Nj, it may be any of Q, Q, y, y, and y+Ti phases, or a composite phase. These alloy-plated steel sheets can be obtained directly by electroplating, but Zn-Fe
In the case of alloy plating, it can also be obtained by performing an alloying treatment after zinc plating, and these are respectively known in "Iron and Steel" 1 Satoshi Chuo June issue). For example, for a Zn--Fe alloy plated steel sheet, an alloy plating consisting of six phases can be obtained by cathodic electrolysis from a sulfuric acid grade containing Zn+, FeH, and citric acid as a rusting agent. Further, a similar Zn--Fe alloy plated steel sheet can be obtained by applying hot-dip Zn plating or electrogalvanizing to a steel sheet and then thermally diffusing iron from the base material into the plating layer by heat treatment. Zn-Ni alloy plated steel sheet is ZnH
, Ni+10 by cathodic electrolysis from a sulfuric acid oxide containing Ni+10. Multi-component alloy plating can also be obtained by a method similar to that described above by adding metal ions necessary for plating.
The thickness of the alloy plating film does not matter. Urethane resins having hydroxyl groups, tertiary amino groups, and blocked isocyanate groups capable of reacting with hydroxyl groups at heating temperatures used in the present invention are, for example,
It is described in Japanese Patent Application Laid-open No. 0-17234 and Japanese Patent Application Laid-Open No. 115476-1983. Specifically, 'a' polyisocyanate compound {b} polyhydroxy compound [c} a hydroxy compound having a tertiary amino group and, if necessary, a hydroxy compound having a quaternary amino group 'd- a blocking agent. Urethane resins obtained by this method are preferred. The urethane resin of the present invention is produced by a reaction between an isocyanate group and a hydroxyl group, and a reaction between an isocyanate group and a hydroxyl group. It consists of a reaction with a cooking agent, usually using a solvent inert to isocyanate groups and, if necessary, using a common urethanization catalyst at 10-150°C, preferably 20-150°C.
The reaction is carried out in a temperature range of 10,000 °C. The above c compound may be a tertiary amino group-containing hydroxy compound alone, a partially quaternized tertiary amino group-containing hydroxy compound, or a tertiary amino group-containing hydroxy compound and a quaternary hydroxy compound. It may also be a mixture of hydroxy compounds containing a grade amino group. The above-mentioned compounds [a--] may be mixed at once or may be reacted individually in any order. Although the ratio of these compounds can be adjusted freely, a particularly preferred method will be described below. Polyisocyanate 'a} and polyhydroxy compound 'b
} at NCO/OH (equivalent ratio)>1.0 to obtain polyurethane prepolymer [1] having isocyanate groups at the terminals. Next, this polyurethane prepolymer [1] is reacted with a compound 'c- having a tertiary amino group and, if necessary, a quaternary ammonium group. At this time, isocyanate group 1
The reaction is carried out at a ratio of more hydroxy groups per equivalent than the equivalent amount to obtain a polyurethane (m) having hydroxy groups at the terminals. Meanwhile, in another reaction vessel, polyisocyanate 'a' (which may be the same as or different from the polyisocyanate used to obtain the polyurethane prepolymer [1]) and a monofunctional blocking agent [d- An average of 0.8 to 1. A compound [m] having preferably one free isocyanate group is obtained. Then, for the hydroxyl group of the product [b]

The final product [W] is obtained by reacting the isocyanate [0] in a proportion that does not reach an equivalent amount. Another preferable production method is to react all the polyisocyanates and polyhydroxy compounds to be used at the same blending ratio as above, then add the blocking agent to the reaction system, and finally add the 'c} compound. There is a way to react. A final required amount of blocking agent is added to all the polyisocyanate compounds used and reacted with some of the polyisocyanate compounds, and then reacted with the polyhydroxy compound, and then the compound (c) is A reaction method is also preferred.The urethane resin of the present invention obtained by the method described above has a molecular weight of 300 to 100,000, a basic nitrogen atomic weight of 0.01 to 10 milliequivalents/unit in the resin, The amount of hydroxyl group is 0.005 to 50 milliequivalents/unit, and the amount of flocked isocyanate group is 1/5 to 4 to hydroxyl group.
A range of double equivalents is preferred. The basic nitrogen atom refers to a nitrogen atom in a hydroxy compound having a tertiary or quaternary amino group, and does not include a nitrogen atom forming a urethane bond. It is desirable to use an organic solvent for the reaction, and preferred organic solvents include polyisocyanate and inert ethyl acetates such as ethyl acetate and butyl acetate, ethyl acetates such as dioxane and tetrahydrofuran, ketones such as acetone and methyl ethyl ketone, Examples include aromatic solvents such as benzene and toluene, and dimethylformamide and dimethyl sulfoxide. {As polyisocyanate for a1, 2
Examples include aromatic and aliphatic polyisocyanates having isocyanate groups. For example, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, naphthalene-1,5-diisocyanate, xylylene diisocyanate, 4,4'
-diphenylmethane diisocyanate, 4,4'-diphenyldimethylmethane diisocyanate, di- and tetraalkyldiphenylmethane diisocyanate, 4,4'
- Aromatic diisocyanates such as dibenzylisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, and their chlorinated isocyanates, brominated isocyanates, and phosphorus-containing Isocyanates, tetramethylene diisocyanate, hexamethylene diisocyanate, dicyclohexyl diisocyanate, cyclohexane-1,4-diisocyanate,
Examples include aliphatic diisocyanates such as lysine diisocyanate and isophorone diisocyanate. Prepolymers having isocyanate groups at both ends obtained by reacting these diisocyanates with polyols preferably having a molecular weight of 1000 or less at an NCO/OH (molar ratio) of 1 to 2 can also be used. A mixture of two or more types may be used. Furthermore, diisocyanates containing an amide group obtained by modifying the above diisocyanates with polyfunctional carboxylic acids, polyamines, water, etc., diisocyanates containing an oxazolidone ring modified with a compound having an epoxy group, diisocyanates modified with carbodimide, etc. good. Furthermore, polymerized polyisocyanates such as tolylene diisocyanate 2-done and Mitoyo-tai, 1,3,5-triisocyanate benzene, 2,4,6-triisocyanate toluene, or tolylene diisocyanate It is also possible to use a mixture of triisocyanates such as an adduct of trimethylolpropane and an adduct of hexamethylene diisocyanate and water. The polyhydroxy compound {b} to be reacted with the polyisocyanate 'a} usually has a molecular weight of 50 to 10,00.
0 and is generally used for polyurethane production, such as known polyhydroxy compounds such as low molecular weight glycols, polyethers, polyesters,
Polyacetals, polythioethers, polybutadiene glycols, silicon-containing polyols, phosphorus-containing polyols, and the like can be used. Examples of low molecular weight glycols include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-phthanediol, bentamethylene glycol, hexamethylene glycol, neobentyl glycol, 2 -Ethyl-1,3-hexanediol, N-alkyldiethanolamine, bisphenol-
A etc. are used. Furthermore, it is also possible to partially mix and use diols having a carboxyl group such as diphenolic acid. Examples of polyethers include polymerization products or copolymers of ethylene oxide, propylene oxide, butylene oxide, tetrahydrofuran, and the like. Further, polyethers or mixed ethers obtained by condensation of the above-mentioned low molecular weight glycols, and furthermore ethylene oxide and oxidized polyethers. Products obtained by addition polymerization of pyrene, butylene oxide, etc. can also be used. As the polythioethers, it is particularly suitable to use thioglycol alone or a condensation product of thioglycol and other glycols. Examples of polyacetals include water-impregnable polyacetals obtained from 1,4-phthanediol and formaldehyde, or from 4,4'-dioxyethoxydiphenyldimethylmethane and formaldehyde. Typical examples of polyesters include polyester glycols obtained by dehydration condensation reaction from the above-mentioned low molecular weight glycols and dibasic acids, and polyester glycols obtained by ring-opening polymerization of cyclic ester compounds. In addition to the above-mentioned polyhydroxy compounds, it is also possible to partially mix and use a trifunctional or higher functional polyhydroxy compound. Furthermore, in addition to the above-mentioned polyhydroxy compound, it is also possible to partially use a polyamine, water, an epoxy group-containing compound, a polyfunctional carboxylic acid, etc. in a mixed manner. {The hydroxy compound having a tertiary amino group of c- is preferably a tertiary amine having at least two hydroxyl groups in one molecule,
These amines include N-methyldiethanolamine, N-ethyldiethanolamine, N-butyldiethanolamine, N-oleyldiethanolamine, N-cyclohexyldiethanolamine, and N-methyldiisopropylene. /gunolamine, N-cyclohexyldiisopropanolamine, N,N-bishydroxyethylaniline,
N,N-bishydroxyethyl-m-toluidine, N,
N-bishydroxyethyl-p-toluidine, N,N-bishydroxypropylnaphthylamine, N,N-bis(dihydroxyethyl)-Q-aminopyridine, N,N
'-bishydroxyethylpiverazine, polyethoxylated butylgetanolamine, polypropoxylated-methylgetanolamine, tertiary amine/group-containing polyester, N,N'-dimethyl-N,N'-bishydroxypropylethylenediamine, N,N'-dimethyl-N,N'
-bishydroxyethylethylenediamine, N,N-dialkyl-N',N'-bishydroxyethylethylenediamine, N,N-dialkyl-N',N'-bishydroxypropylethylenediamine, N,N-dialkyl-N',N'- Bishydroxyethylpropylene diamine, N,N'-dialkyl-N', N'-bishydroxypropylpropylene diamine, triethanolamine, triisopro/gnolamine, N-alkyl-N,
N',N'-trishydroxyethylethylenediamine, N-alkyl-N,N',N'-trishydroxypropylethylenediamine, N,N,N',N'-tetrakishydroxyethylethylenediamine, N,N,N'
, N'-tetrakishydroxypropylethylenediamine, and products obtained by the addition reaction of a compound having an epoxy group with a secondary amine, etc. can be used, and these amines can be used alone or as a mixture of two or more. You can also use Preferably, the number of hydroxyl groups per molecule of the hydroxy compound having a tertiary amino group is 2.3 on average.
Hyde having a tertiary amino group in the range of 2.5 or more, more preferably 2.5 or more. Preference is given to using xy compounds. Of course, it is also possible to partially mix and use a tertiary amino group-containing compound having one hydroxyl group. As a hydroxyl compound having a quaternary ammonium group, which is used in combination with a hydroxyl group having a tertiary amino group as required, the above-mentioned hydroxyl compound having a tertiary amino group can be quaternized with various quaternizing agents. It can be obtained by converting As a quaternizing agent, 1,2 in the presence of an acid or an acid and water
- Epoxy-containing compounds are the most preferred example. 1,2
- Epoxy compounds include ethylene oxide, propylene oxide, 1,2-butylene oxide, styrene oxide, alkylene oxides such as glycidol, monobasic glycidyl esters such as glycidyl acrylate, glycidyl esters of alcohols or phenols. Tels and the like are preferred. When a 1,2-epoxy group-containing compound is used as a quaternizing agent, a hydroxyl group can be introduced by quaternization. A quaternary amine compound can also be used as a hydroxy compound having a quaternary ammonium group by quaternization. Other quaternizing agents include alkyl halites such as methyl chloride, ethyl furomide and butyl bromide, dialkyl sulfates such as dimethyl sulfate and dibutyl sulfate, penzyl chloride, and ethylene halohydrin. These quaternization reactions involve ethanol, isopropanol,
Alcohols such as butanol and ethylene glycol monoethyl ether, ethers such as dioxane and butrahydrofuran, ketones such as acetone and methyl ethyl ketone, esters such as ethyl acetate and butyl acetate,
Preferably, a solvent such as water or dimethylformamide is used. The reaction conditions are the same as the usual quaternization conditions, and the reaction temperature is preferably 3000 to 1500C. When a quaternizing agent and a tertiary amine compound are used together, the molar ratio of quaternizing agent/tertiary amino group is preferably 0.01 to 2.0. {d
) is a compound having one active hydrogen that can be measured by the Cherevitinoff method. Specifically, the following can be mentioned. Sulfites such as acidic potassium sulfite, acidic sodium sulfite, etc., secondary amines such as diethylamine, dibutylamine, diphenylamine, butylphenylamine, phenylnaphthylamine, methyl alcohol, ethyl/real alcohol, chloroethyl alcohol, propyl alcohol , aliphatic alcohols such as butyl alcohol, amyl alcohol, hexyl alcohol, heptyl alcohol, octyl alcohol, nonyl alcohol, decyl alcohol and lauryl alcohol, alicyclic alcohols such as cyclobentanol and cyclohexanol, phenyl carbinol, methyl Aromatic alkyl alcohols such as phenyl carbinol, ethylene glycol monomethyl ether, ethylene glycol mole ethyl ether, ethylene glycol monobutyl ether, ethylene glycol moleamyl ether, ethylene glycol molehexyl ether, ethylene glycol monophenyl ether,
Monoalkyl or free ethers of alkylene glycol such as diethylene glycol monomethyl ether and diethylene glycol monobutyl ether, phenol, o-cresol, p-cresol, m-cresol, rt-butylphenol, p-ethylphenol, o-isof. Phenols such as ropinolephenol, p-nitrophenol, p-chlorophenol, dimethylethanolamine, jetylethanolamine, N
, N,N'-trimethyl-N'-hydroxyethylethylenediamine, N-alkyl-N'-hydroxyethylpiverazine, N-alkyl-N'-hydroxyisopropylpiverazine, etc. Functional alcohols, trialkylhydroxyalkylammonium salts such as triethylhydroxyethylammonium acetate and trimethylhydroxypropylammonium lactate, oximes such as acetoxime, methylethylketoxime, cyclohexanoneoxime,
Lactams such as -caprolactam, y-butyrolactam, 6-valerolactam, and pyrrolidone, imides such as succinimide and maleic acid imide, imidazole, 2-
Examples include imidazoles such as ethylimidazole, active methylene compounds such as dimethyl malonate, jetyl malonate, methyl acetoacetate, and ethyl acetoacetate.
The resin for cathodic electrodeposition coating of the present invention can be made into a stable aqueous solution or aqueous dispersion by adding water or an aqueous acid solution to the resin obtained by the method described above and thoroughly mixing the resin. As the acid, organic acids such as formic acid, acetic acid, propionic acid, hydroxyacetic acid, lactic acid, and citric acid, or inorganic acids such as hydrochloric acid, sulfuric acid, and phosphoric acid are used. The amount used is usually 0.2 to 1 per mole of tertiary amino group.
．． 5 equivalents, preferably 0.3 to 1.0 equivalents. 0.
If the amount is less than 2 equivalents, the water-removal property will be poor, which is undesirable, and if it is more than 1.5 equivalents, undesirable phenomena such as re-dissolution of the tortoise coating and an increase in the amount of hydrogen gas generated at the cathode will occur. The aqueous solution or aqueous dispersion obtained as described above is used to form an electrodeposited coating film on the object to be coated by cathodic electrodeposition. A coating composition can be prepared by containing agents, surfactants, coupling solvents, curing catalysts, crosslinking agents, and the like. Pigments include iron oxide, lead oxide, carbon black, strontium chromate, titanium dioxide, talc,
One or more clays and the like are used. As curing catalysts, customary urethanization catalysts such as dibutyltin dilaurate, dibutyltin diacetate, dioctyltin dilaurate, dibutyltin oxide, and dioctyltin oxide are particularly preferred. As the crosslinking agent, for example, completely blocked polyisocyanates, aminoblast condensates, phenoplast condensates, etc. are preferable. In the exposure coating, an exposure coating film is deposited on the cathode by passing an electric current between the cathode and the anode in an electrodeposition made of the above-mentioned aqueous composition. The conditions for conducting the hexagonal deposition are generally similar to those used for debonding other types of coatings. The applied voltage can vary widely, ranging from low voltages to high voltages, but is usually 200 volts or more, usually 200 to 500 volts. The temperature for kametsuzoku is preferably 10 to 70 qo, and usually 10 to 350 qo. According to the present invention, an excellent coating film without pinholes can be obtained especially at high voltages of 200 V or more.
After electrodeposition, the electrodeposited coating film is washed with water and heated to 80 to 250°C, preferably 120 to 200°C, in an ordinary brazing oven or infrared heating lamp.
Cure in the temperature range of °C. As detailed above, according to the present invention, by coating a steel plate with a Zn-containing alloy plating film with a specific urethane resin, a pinhole-free coating film with excellent corrosion resistance can be obtained. . The present invention will be explained below with reference to Examples. Examples and Comparative Example 1 Production of Resin'1) Production of Resin Solution [A] A resin was synthesized according to the following formulation according to Hakama Ko No. 17234/1983. 4,4'-diphenylmethane diisocyanate (4,4'-diphenylmethane diisocyanate
(hereinafter referred to as MDI) was taken at 12.5 pm (1 equivalent) and the internal temperature was set at 60 pm. To this, polypropylene glycol (molecular weight 400) 1
A solution containing 96 grams of acetone (1/2 equivalent) dissolved therein was gradually added dropwise from the sample dropping funnel. After the dropwise addition was completed, a heating reaction was carried out at 6,000 ℃ for 3 hours. Next, I lowered my daily intake to 4.0 pm and started taking 75 pm of trietanoamine (
A solution prepared by dissolving 32 ml of acetone (3/2 equivalent) in acetone was gradually added dropwise, and a heating reaction was further carried out at 50 to 60°C for 2 hours. This reaction product is referred to as [1]. Take MDI125 (1 equivalent) in another four-bottle flask and adjust the internal temperature to 60qC.
Worship as a hina. To this, 65 g of 2-ethylhexanol (1/2 equivalent)
This reaction product was obtained by gradually dropping a solution in which 81% of acetone was dissolved at 50°C over 3 hours, and after the dropwise addition was completed, heating at 5000°C for 1 hour was carried out.

Set to [0]. Reaction product [m] was gradually added dropwise to reaction product [1] at room temperature, and then heated at 40°C for 2 hours at 5000 °C.
Let it react for 1 hour. Next, 209 g of ethylene glycomonoethyl ether was added and mixed thoroughly, and then acetone was distilled off under reduced pressure to obtain the final resin solution [A]. The basic nitrogen atom content, hydroxyl group content, and blocked isocyanate group content of the resin are 1.02 milliequivalents per solid resin content. ■ Production of resin solution [B] Into a four-necked flask equipped with a thermometer, a rope strainer, a sample dropping funnel, a dryer, a cooler, etc., put 219 mm (1.75 equivalents) of MDI. The temperature was set at 6-0 and we worshiped with candles. A solution of ADEKA Polyether BPX-$ (manufactured by Asahi Denka Kogyo Co., Ltd., hydroxyl value 197) dissolved in 114 parts of acetone (1/2 equivalent) was gradually added dropwise to this solution from a sample dropping funnel. After the dropwise addition was completed, heating was carried out at 60°C for 3 hours. Next, ethylene glycol monobutyl ether 44
．． A solution prepared by dissolving 59 ounces of acetone (3/8 equivalent) was added dropwise at 60° C., and a heating reaction was carried out for 2 hours. After cooling the reaction product to 3000 ml, triethanolamine 3
A solution of 7.5 liters (3/4 equivalent) and 29.6 liters (1/2 equivalent) of N-methyljetanolamine dissolved in 28.8 liters of acetone was gradually added dropwise, and the mixture was allowed to react at 30° C. for 4 hours. Next, ethylene glycomonoethyl ether 202
After thoroughly mixing, the acetone was removed under reduced pressure to obtain a resin solution [B]. The basic nitrogen atom content is 1.06 milliequivalents per resin solids. The hydroxyl group content and the blocked isocyanate group content are each 0.794 milliequivalents per resin solid content. '3'
Comparative Example Production of resin (i) Production of quaternizing agent Using the same four-necked flask as in Example 1, 2-ethylhexanol semi-capped toluene diisocyanate (methyl lysoptyl ketone solution, solid) was added at room temperature. 320.0 minutes (95%) was added dropwise to 87.2 hours of dimethylethanolamine. After stirring the mixture at 8000 for 1 hour, add 75% lactic acid aqueous solution 1
A mixture of 17.6 and 39.2 hours of ethylene glycol monobutyl enal was added dropwise and heated at 65q0 for about 30 minutes to obtain a quaternizing agent. Let this reaction product be [m]. Manufacture of resin solution for pigment dispersion Epon 82 (bisphenol type epoxy resin, manufactured by Shell Chemical Company, epoxy equivalent approximately 193-2
03) 177.5 liters and bisphenol A 72.4 liters were charged into a four-necked flask similar to Example 1, and reacted by heating at 150 to 160 ounces in a nitrogen atmosphere for about 1 hour, then cooled to 120 quarts, and then mixed with 2-ethyl 101.6 hours of hexanol semi-capped toluene diisocyanate (methyl isobutyl ketone solution, 95% solids) was added. After heating and reacting at an internal temperature of 110 to 120°C for about 1 hour,
141.9 tons of ethylene glycomonobutyl ether were added. It was then cooled to 85-95°C, and after homogenization, 1 part of deionized water was added.
7.8 minutes was added, and further, the reaction product [m] 124
．． Added one evening. The temperature of the reaction mixture was maintained at 80 to 85 qo until the acid value reached 1 to obtain a pigment dispersion resin solution [C]. (iii) Production of base resin solution Epon 829 139.0 and bisphenol A4
4.9 minutes into a flask similar to Example 1 and 150~1
Approximately 1.60 qo. After an immediate heating reaction, the internal temperature was reduced to 125 oo.
Then, 99.92 g of 2-ethylhexanol half-capped toluene diisocyanate (methyl imptyl ketone solution/liquid, solid content 95%) was added. After holding the reaction mixture at 12 psi for about 1 hour, PCP020
0 (polycaprolactone diol, manufactured by Union Carbide Corporation, molecular weight 540) 36.5 and 2,2,4-trimethylbentanediol-1,3
-29.7 hours of monoisoptylate was added. Next, add 0.7 liters of dimethylethanolamine and
Donner-Holdt viscosity is N (5 wt% ethylene glycol)
This temperature was maintained for approximately 7 hours until a solution of 25° C.) was obtained. To this reaction mixture were added 46.9 mols of ethylene glycol monophenyl ether, 21.8 mols of ethylene glycol monoethyl ether and 5.2 mols of tetramethyldescinediol, and then 75% of
% lactic acid aqueous solution and 41.0 hours of dimethylcyclohexylamine lactate solution (75% isopropanol solution) were added, and the resin solution (
D) was obtained. 2 Preparation of paint {1' Adjustment of paint [1] Pigment paste [E] was kneaded and dispersed in the following composition. Varnish base [F] was mixed and manufactured with the following composition. Next, paint [1] was prepared by mixing the following composition. The state of this paint was 5.3. (2} Paint

Preparation of [0] Using the resin solution [B], paint

[0] was manufactured using exactly the same composition and method as paint [1]. The pH of this paint was 5.7. '3} Comparative Example Paint preparation pigment paste [G] was kneaded and dispersed in the following composition. Varnish base [H] was mixed and manufactured with the following composition. Next, a paint was prepared by mixing the following composition. The pH of this paint was 6.5. 3. Adjustment of alloy-plated steel sheets Various types of Zn--Fe alloy-plated steel sheets and Zn-Ni-based alloy-plated steel sheets were prepared by electroplating or hot-dip plating. In order to further improve paint adhesion, phosphate treatment agent Bt3
A chemical conversion treatment was performed using 030 (manufactured by Nihon Parkerizing Co., Ltd.). The types of steel sheets tested are shown in Table 1 below. -1 The dimensions of the sample are 0.8 x 50 x 15 pieces. 4. Drop-on coating A haze-on coating was performed under the following conditions, washed with water, heated at 180oC for 20 minutes in a hot air drying oven, and pinholes on the coating surface were measured. The results are shown in Table-2. Table-2 Pinholes: ○ Not at all, △ Slight occurrence, × Electrodeposition conditions Bath temperature = 2900 Electrode distance = 15 arcs Applied voltage = 240 V and 280 V Current application time = 2 to 4 minutes Coating film thickness = 20 ± 1 French Energization method = Energization after full immersion 5 Corrosion resistance JIS Z-2371 salt water light fog test test plate 6
The state of corrosion after 7 hours of incubation was evaluated in the following four grades. The results are shown in Table-3. ◎ No abnormalities ○ Rust or blisters are less than 5% of the painted area △ Rust or blisters are less than 20% of the painted area × Rust or blisters are more than 20% of the painted area Table-3

Claims (1)

[Scope of Claims] 1. Using an electrodeposition paint containing a urethane resin having a hydroxyl group, a tertiary amino group, and a blocked isocyanate group that can react with the hydroxyl group at heating temperature, zinc-iron or zinc - A cathodic electrodeposition coating method characterized in that the coating is applied at an applied voltage of 200 volts or more using a steel plate having an alloy plating film mainly composed of nickel as a cathode. 2 The molecular weight of the urethane resin is 300 to 100,000
, the basic nitrogen atomic weight in the resin is 0.01 to 10 milliequivalents/g, and the hydroxyl group is 0.005 to 50 milliequivalents/g.
g. The cathodic electrodeposition coating method according to claim 1, wherein the amount of the blocked isocyanate group is 1/5 to 4 times equivalent to the hydroxyl group.