JP2001288598A - Cation electrodeposition coating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrodeposition film excellent in the weather resistance of an outer panel portion of a car body, and the finishing property and the throwing power of electrolytic coloring of an inner panel portion (a tubular area), and the corrosion resistance. SOLUTION: This cation electrodeposition coating method comprises a step (1) of forming an electrodeposition coating by applying an electrodeposition coating composition 1 with high weather resistance and finishing property to a metal work having a tubular structure such as the car body, a step (2) of water-rinsing the work having the electrodeposition coating obtained in the above step, removing the excessively adhered electrdeposition coating composition 1, pre-heating the obtained electrodeposition film at 60-120 deg.C, and removing water and bubbles included in the film, a step (3) of forming the electrodeposition film by applying the electrodeposition coating composition 2 to the work having the electrodeposition film obtained in the above step, a step (4) of water- rinsing the work having the electrodeposition film obtained in the above step to remove the excessively adhered electrodeposition coating composition 2, and removing water or performing the air blow, and a step (5) of simultaneously heating and solidifying the film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cationic electrodeposition coating method and, more particularly, to an electrodeposition coating composition having excellent weather resistance for an article having a bag structure such as an automobile body or an automobile part. 60 after applying about 30μm
Preheating is performed at a temperature of up to 120 ° C., and then an electrodeposition paint having excellent anticorrosion properties is applied to a surface not formed by the electrodeposition coating of the electrodeposition coating composition (for example, a bag structure of an inner plate). By applying the composition by electrodeposition coating, high weather resistance of the outer plate part, high finishability and high throwing power of the inner plate part (bag part),
The present invention relates to a coating method that has both high anticorrosion properties and has improved anticorrosion properties at a coating film boundary, which is a portion where a first electrodeposition coating film and a second electrodeposition coating film are applied repeatedly.

[0002]

[Prior art and its problems] Vehicles manufactured and consumed in the Asian region are considered to be cost-effective,
It is often manufactured from a cold-rolled steel sheet containing iron as a main component without using an intermediate coating paint and an intermediate coating less in which the intermediate coating step is omitted, and without using a rust-preventive steel sheet such as galvanized steel. For this reason, functions such as weather resistance to the outer plate portion, high finishability, high throwing power at the inner plate portion, and high anticorrosion properties are required for the electrodeposition coating composition used in the undercoat paint of the vehicle body.

Therefore, in order to sufficiently satisfy this function, a satisfactory result cannot be obtained only by applying one kind of electrodeposition paint, and an electrodeposition coating method in which two kinds of functions having different functions are repeatedly applied. (Hereinafter, it may be abbreviated as “double-coat electrodeposition coating”.) That is, a method of applying a second electrodeposition coating after the first electrodeposition coating is completed while the coating film is uncured is disclosed in Japanese Patent Application Laid-open No. -165098, JP-A-9-324292
Japanese Patent Application No. 11-43233 discloses a method of baking and curing a coating film after the first electrodeposition coating is completed, and applying a second electrodeposition coating. ing. Furthermore, in conventional double-coat electrodeposition coating, the boundary film thickness of the second electrodeposition coating is affected by the first electrodeposition coating, and the deposition of the second electrodeposition coating becomes non-uniform. Therefore, since the thickness of the boundary portion becomes thinner, there is a problem that the anticorrosion property of the portion is reduced and a problem such as peeling of the coating film is caused. Therefore, an immediate improvement has been required.

[0004]

The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and as a result, by adopting a specific coating process, the film thickness is secured at the boundary of the coating film. The present inventors have found that the anticorrosion property is improved, and have completed the present invention. That is, the present invention provides the following steps: Step (1): A step of applying an electrodeposition coating composition having high weather resistance and high finish to a metal object having a bag structure such as an automobile body to form an electrodeposition coating, Next, the object having the electrodeposition coating film obtained above is washed with water to remove an excessively adhered electrodeposition coating composition, and the obtained electrodeposition coating film is preheated at 60 to 120 ° C. (3) removing the water and bubbles contained in the coating film, and applying the electrodeposition coating composition to the object having the electrodeposition coating film obtained in the above step. Step (4) of forming an electrodeposition coating film; the object having the electrodeposition coating film obtained in the above step is washed with water to remove the extra electrodeposition coating composition, and draining or air blowing is performed. And (5) a step of simultaneously heating and curing these coating films. Cation electrodeposition coating method. 2. The above-mentioned electrodeposition coating composition has the following components: acrylic resin (A); 10 to 10 based on the total weight of monomer components (a) to (d) constituting the acrylic resin.
60% by weight of a hydroxyl group-containing acrylic monomer (a), 5
-35% by weight of an amino group-containing acrylic monomer (b),
A resin obtained by a radical copolymerization reaction of 5 to 55% by weight of an aromatic vinyl monomer (c) and, if necessary, another acrylic monomer (d).

Acrylic resin-modified epoxy resin (B);
Based on the total weight of the epoxy resin component (e) and the acrylic resin component (f), it is composed of 10 to 90% by weight of the epoxy resin component (e) and 90 to 10% by weight of the acrylic resin component (f). The resin (h) and the amine compound (g) were mixed with the resin (h) / amine compound (g) in a ratio of 65 to 95/5.
A hydroxyl group-containing resin obtained by reacting to a concentration of about 35% by weight.

It contains an aliphatic and / or cycloaliphatic blocked isocyanate compound (C) and comprises components (A) to
The compounding ratio of (C) is determined based on the total solid content of the components acrylic resin (A), acrylic resin modified epoxy resin (B), and aliphatic and / or alicyclic blocked isocyanate compound (C). A) is 40 to 90% by weight, component (B) is 5 to 55% by weight, and component (C) is 5 to 40% by weight.
2. The cationic electrodeposition coating method according to item 1, wherein the cationic electrodeposition coating method is used. The MEQ (acid concentration) of the electrodeposition coating composition is 5-2.
3. The cationic electrodeposition coating method according to item 1 or 2, wherein the method is 5. The specific conductivity of the electrodeposition coating composition is from 1500 to 28
4. The method as claimed in claim 1, wherein the rate is 00 μS / cm.
4. The cationic electrodeposition coating method according to any one of the above, The cationic electrodeposition coating according to any one of claims 1 to 4, wherein a top coat is directly applied on the electrodeposition coating film obtained in the steps (1) to (5). Method.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The coating of an object having a complicated structure such as a bag structure of an automobile body or the like is performed in such a manner that an outer plate portion has weather resistance and finishability, and an inner plate portion (bag portion) has a throwing power. Corresponding corrosion protection is required. As a coating method having both functions, coating of an electrodeposition coating composition having different functions is performed by two methods.
This has been made possible by double-coating electrodeposition coating with multiple coatings.

However, when a second electrodeposition coating is performed on the first coating film, if the second electrodeposition coating is performed only by washing with water after the first electrodeposition coating, the outer plate portion is not coated at the time of electrodeposition. Since the current is passed through the gas holes, the second electrodeposition coating film covers the first electrodeposition coating film and cannot sufficiently exhibit the function of the highly weather-resistant coating film applied the first time.

Further, preheating after the first electrodeposition coating is performed, and when the temperature exceeds 120 ° C., the inner plate portion (bag portion)
In the portion where the film was thin, the adhesion of the film caused the coating film resistance, and at the time of the second coating, the coating film did not deposit on that portion and the film at this boundary became thinner. The present invention has solved the above problems by the following steps and a coating composition.

Hereinafter, the steps (1) to (5) and the coating composition will be sequentially described in detail. The object to be coated used in the step (1) may be an automobile body, an automobile part, a metal tube, a box of an electric device, or the like. Examples of the material of the object to be coated include a metal, and a material made of a rust-proof treated steel sheet is preferable from the viewpoint of rust prevention.

[0011] As the steel sheet, a hot-dip galvanized steel sheet, an electro-galvanized steel sheet, an electro-galvanized iron double-layered steel sheet, an organic composite coated steel sheet, and the like, and a base material such as these steel sheets and cold-rolled steel sheets may be used, if necessary. After the surface is cleaned by degreasing or the like, a surface treatment such as a phosphate chemical conversion treatment or a chromate treatment may be performed.

Next, as the electrodeposition coating composition used in the first electrodeposition coating, any resin such as an epoxy-based, acrylic-based, polybutadiene-based, alkyd-based, or polyester-based resin can be used as a base resin. For example, an acrylic resin or an epoxy resin modified with an acrylic resin is preferable from the viewpoint of weather resistance.

The electrodeposition coating composition comprises an acrylic resin (A), an acrylic resin-modified epoxy resin (B), an aliphatic and / or alicyclic block polyisocyanate compound (C), a surfactant and a surface conditioner. Neutralizing the resin,
It is composed of a neutralizing agent such as an aliphatic carboxylic acid, a pigment, a catalyst and the like in order to disperse in water and adjust the MEQ.

An acrylic resin (A) used as a base resin, an acrylic resin-modified epoxy resin (B),
The aliphatic and / or alicyclic blocked polyisocyanate compound (C) used as a curing agent will be described.

Acrylic resin (A): Acrylic resin (A) comprises, as monomer components constituting the acrylic resin, a hydroxyl group-containing acrylic monomer (a), an amino group-containing acrylic monomer (b), and an aromatic vinyl resin. It is composed of a monomer (c) and optionally another monomer (d).

Examples of the hydroxyl group-containing acrylic monomer (a) include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate,
4-hydroxybutyl (meth) acrylate, an addition product of 2-hydroxyethyl (meth) acrylate and caprolactone (for example, Placcel FA-2 and FM-3 as trade names of Daicel Corporation).
These can be used alone or in combination of two or more. The content of the hydroxyl group-containing acrylic monomer (a) is 10 to 60% by weight, preferably 30 to 50% by weight, based on the total weight of the monomer components constituting the resin (A). When the content of the acrylic monomer (a) exceeds 60% by weight, the hydrophilicity of the resin (A) increases, and the corrosion resistance of the electrodeposition coating film deteriorates. Conversely, if the content is less than 10% by weight, the water dispersibility of the resin (A) is reduced, so that the stability of the coating material is poor. Examples of the amino group-containing acrylic monomer (b) include N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N , N-di-t-butylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide and the like.
The content of the amino group-containing acrylic monomer (b) is 5 to 5 based on the total amount of the monomer components constituting the resin (A).
35% by weight, preferably 10 to 25% by weight. The content of the amino group-containing acrylic monomer (b) is 35% by weight.
If it exceeds 50%, the weather resistance of the electrodeposition coating film will be poor, while if it is less than 5% by weight, the performance of corrosion resistance will be poor.

The content of the aromatic vinyl monomer (c) is 5% based on the total amount of the monomer components constituting the resin (A).
The content is preferably 55 to 55% by weight, more preferably 10 to 45% by weight. When the content of the aromatic vinyl monomer (c) exceeds 55% by weight, the weather resistance of the electrodeposited coating film is reduced. If the content is less than 5% by weight, sufficient corrosion resistance cannot be obtained.

As the other monomer (d), for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl ( (Meth) acrylate, t-butyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and the like. The content of the other monomer (d) is 0 to 0 based on the total of the monomer components constituting the resin (A).
80% by weight, preferably in the range of 0 to 50% by weight. The acrylic resin (A) of the present invention can be obtained by subjecting the monomers (a) to (d) to a radical copolymerization reaction by a known method. Examples of the organic solvent used for the radical copolymerization reaction include aromatic hydrocarbon solvents such as toluene and xylene; ketone solvents such as methyl isobutyl ketone and cyclohexanone;
Alcohol solvents such as butanol, ethyl cellosolve, methoxypropanol, and diethylene glycol monobutyl ether can be used. Any of these organic solvents may be used alone or in a mixture of two or more.

The radical copolymerization reaction is generally carried out in the following organic solvent maintained at about 50 ° C. to about 300 ° C., preferably about 60 ° C. to 250 ° C. in the presence of an inert gas such as nitrogen. The monomer component can be subjected to a radical copolymerization reaction for about 1 hour to about 24 hours, preferably for about 2 hours to about 10 hours.

The acrylic resin (A) has a hydroxyl value in the range of usually 10 to 300 mgKOH / g, preferably 50 to 300 mgKOH / g.
The range of -200 mgKOH / g is appropriate. When the hydroxyl value exceeds 300 mgKOH / g, the hydrophilicity of the resin (A) increases, and the corrosion resistance of the electrodeposition coating film deteriorates.
If it is less than 0 mgKOH / g, the water dispersibility of the resin (A) decreases, and the coating film performance deteriorates due to a decrease in crosslink density.

The amine value of the acrylic resin (A) is usually in the range of 10 to 125 mg KOH / g, preferably in the range of 15 to 80 mg KOH / g. When the amine value exceeds 125 mgKOH / g, the hydrophilicity of the resin (A) increases, and the performance of the electrodeposition coating film such as weather resistance and corrosion resistance is deteriorated. When the amount is less than 10 mgKOH / g, the water dispersibility of the emulsion of the resin (A) is remarkably reduced. The number average molecular weight of the acrylic resin (A) is 2,000
Suitably, it is in the range of 0-100,000, preferably in the range of 5,000-50,000. If the number average molecular weight is less than 2,000, the emulsion stability is impaired, and conversely, the number average molecular weight is 100,
If it exceeds 000, the smoothness of the coating film surface is impaired, which is not preferred.

Acrylic resin-modified epoxy resin (B):
The acrylic resin-modified epoxy resin (B) is, for example, an α, β-ethylenically unsaturated group-containing epoxy obtained by reacting an epoxy resin (e) component with an α, β-ethylenically unsaturated carboxylic acid (f). As another method, a resin, a hydroxyl group-containing acrylic monomer and, if necessary, a radical copolymerization reaction with another monomer, and then reacting the obtained copolymer with an amine compound (g),
α, β-ethylenically unsaturated carboxylic acid, hydroxyl group-containing acrylic monomer and, if necessary, carboxyl group-containing acrylic resin obtained by copolymerization reaction with epoxy resin and epoxy resin, then react with amine compound (g) Can be obtained.

When the content of the epoxy resin (e) constituting the acrylic resin-modified epoxy resin (B) is less than 10% by weight, the hydrophilicity of the resin (B) is increased, and the electrodeposition coating film cannot have sufficient corrosion resistance. Conversely, if it exceeds 90% by weight, the water dispersibility decreases due to poor compatibility with the acrylic resin (A), so that the paint stability deteriorates and the crosslink density after baking is insufficient, resulting in poor coating film performance. Become.

When the acrylic resin (f) constituting the acrylic resin-modified epoxy resin (B) is less than 10% by weight, water dispersibility is deteriorated due to poor compatibility with the acrylic resin (A). As a result, the stability of the coating composition deteriorates. On the other hand, if it exceeds 90% by weight, the hydrophilicity of the resin (B) increases and the corrosion resistance of the electrodeposition coating film cannot be obtained, which is not preferable. The amine compound is 5 to 35% by weight, preferably 10 to 20% by weight as a total weight of the acrylic-modified epoxy resin and the amine compound. The mixing ratio of the epoxy resin component (e) and the acrylic resin component (f) is as follows:
The ratio is based on the total weight of both components.

The compounding ratio of the amine compound (g) is 5
When the amount is less than 35% by weight, the water dispersibility of the emulsion is reduced and the stability of the coating is reduced. On the contrary, when the amount is more than 35% by weight, sufficient corrosion resistance and weather resistance of the electrodeposition coating film cannot be obtained, which is not preferable.

As the epoxy resin constituting the epoxy resin component (e), a compound having two or more epoxy groups in one molecule can be used, and it is generally at least 340, preferably 400 to 3,000, more preferably 800 to 1,700. Suitable are those having a number average molecular weight in the range of, especially those obtained by the reaction of a polyphenol compound with epichlorohydrin. As the polyphenol compound used for forming the epoxy resin, for example, bis (4-
(Hydroxyphenyl) -2,2-propane 4,4-dihydroxybenzophenone, bis (4-hydroxyphenyl)-
1,1-isobutane, bis (4-hydroxy-t-butylphenyl) -2,2-propane, bis (2-hydroxynaphthyl) methane, tetra (4-hydroxyphenyl)-
Examples thereof include 1,1,2,2-ethane, 4,4-dihydroxyphenyl sulfone, phenol novolak, and cresol novolak.

The epoxy resin (e) has a number average molecular weight of 34
If it is less than 0, the corrosion resistance of the coating film is insufficient, and conversely 3,000
Exceeding the range is not preferred because the coated surface smoothness is impaired.
The acrylic resin component (f) is composed of an α, β-ethylenically unsaturated carboxylic acid, a hydroxyl group-containing acrylic monomer and, if necessary, other monomers. α, β
-Ethylenically unsaturated carboxylic acid, for example, acrylic acid,
Methacrylic acid, crotonic acid, itaconic acid, maleic acid,
Fumaric acid and the like can be mentioned. Examples of the hydroxyl group-containing acrylic monomer include the same ones as described above.

Other monomers include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate,
Examples thereof include cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and styrene. These may be used alone or in combination.

The acrylic resin component (f) has a hydroxyl value of 30 to 200 mgKOH / g, preferably 50 to 150 mgKOH.
/ G is preferred. When the hydroxyl value exceeds 200 mgKOH / g, the water resistance and corrosion resistance are reduced, and conversely, the hydroxyl value becomes 30%.
If the amount is less than mgKOH / g, the curability is lowered, and the weather resistance and corrosion resistance are lowered.

When the epoxy resin is reacted with the acrylic resin, the acrylic resin (f) has a resin acid value of 1
5050 mgKOH / g, preferably 10-30 mgKOH / g
The value of g is preferably within the range. If the resin acid value is less than 1 mgKOH / g, the amount of the acrylic resin added to the epoxy resin (e) decreases, so that poor compatibility with the acrylic resin (A), poor water dispersibility, poor finish, etc. On the contrary, if the resin acid value exceeds 50 mgKOH / g, gelling occurs during the synthesis of the acrylic resin-modified epoxy resin (B), which is not preferable. The acrylic resin (f) has a number average molecular weight in the range of 2,000 to 10,000, preferably 5,000 to 8,
A range of 000 is appropriate. The number average molecular weight of the acrylic resin (f) can be adjusted by changing the synthesis conditions, but a chain transfer agent such as dodecyl mercaptan, 2-ethylhexyl thioglycolate, or styrene dimer may be used. The number average molecular weight of the acrylic resin (f) is 2,000
If it is less than 0, poor compatibility, poor water dispersibility, and reduced finish will occur. Conversely, if the number average molecular weight exceeds 10,000, it will gel during the synthesis of the acrylic resin-modified epoxy resin (B), which is not preferable. . The above amine compound (g)
As, for example, diethylamine, dibutylamine,
Methylbutylamine, diethanolamine and the like can be mentioned. Also, ketiminated blocks of amine compounds such as diethylenetriamine can be used. These may be used alone or in combination.

In the production of the acrylic resin-modified epoxy resin (B) used in the present invention, the above-mentioned component epoxy resin (e), acrylic resin (f) and other acrylic monomer (d) are conventionally known. It can be produced based on a reaction between a carboxyl group and an epoxy group and a radical copolymerization reaction.

In the above reaction, for example, an aromatic hydrocarbon agent such as toluene and xylene; a ketone solvent such as methyl isobutyl ketone and cyclohexanone; n-butanol, ethyl cellosolve, butyl cellosolve, methoxypropanol, An organic solvent such as an alcohol solvent such as diethylene glycol monobutyl ether can be used. The organic solvent may be used alone or in a mixture of two or more. The reaction conditions between the carboxyl group and the epoxy group are 50-200.
30 minutes to 12 hours at a temperature in the range of ° C. are applicable.

Aliphatic and / or alicyclic blocked polyisocyanate compound (C): The blocked polyisocyanate compound used as a curing agent in the present invention is obtained by blocking an aliphatic and / or alicyclic polyisocyanate compound with a blocking agent. Compound. When the polyisocyanate compound is a non-aliphatic and / or alicyclic polyisocyanate compound, for example, an aromatic polyisocyanate compound, it is not preferable because the weather resistance of the coating film is deteriorated.
Examples of the aliphatic and / or alicyclic polyisocyanate compound include aliphatic or alicyclic diisocyanate compounds such as isophorone diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, and methylene diisocyanate, and dimers and dimers thereof.
And isocyanate-terminated compounds obtained by reacting an excess of these isocyanate compounds with a low molecular active hydrogen-containing compound such as ethylene glycol, propylene glycol, trimethylolpropane, hexanetriol, or castor oil.

On the other hand, the blocking agent is one which blocks by adding to the isocyanate group of the polyisocyanate compound, and the blocked polyisocyanate compound formed by the addition is stable at room temperature and has a viscosity of about 10%.
When heated from 0 ° C. to 200 ° C., it is desirable that the blocking agent be dissociated to regenerate the isocyanate group. Examples of the blocking agent satisfying such conditions include lactam compounds such as ε-caprolactam and γ-caprolactam; oxime compounds such as methyl ethyl ketoxime and cyclohexanone oxime; and aromatic alkyl compounds such as phenylcarbinol and methylphenylcarbinol. Alcohols; ether alcohol compounds such as ethylene glycol monobutyl ether;

Of these, oxime-based and lactam-based blocking agents are dissociating agents at relatively low temperatures, and are therefore particularly suitable from the viewpoint of low-temperature curability of the electrodeposition coating composition. The compounding ratio of the cationic electrodeposition coating composition of the present invention,
Component (A) is 40 to 90%, preferably 55 to 85% based on the total solid content of components (A), (B) and (C).
Component (B) is 5 to 55%, preferably 10 to 30% by weight
Is suitably within the range. If the component (A) exceeds 90% by weight, sufficient corrosion resistance cannot be obtained, and if it is less than 40% by weight, sufficient weather resistance cannot be obtained. If the component (B) exceeds 50% by weight, sufficient weather resistance cannot be obtained, and if it is less than 5% by weight, sufficient corrosion protection cannot be obtained.

The component (C) is an acrylic resin (A)
And the hydroxyl group contained in the acrylic resin-modified epoxy resin (B) should be blended so as to react,
55 of the total solids of components (A), (B) and (C)
When the amount of the component (C) exceeds 40% by weight, the finish of the electrodeposition coating film is impaired. When the amount is less than 5% by weight, insufficient curing is caused. Causes performance degradation. The electrodeposition coating composition may contain a surface conditioner, a repellent, a surfactant, a plasticizer, and other additives in addition to the components (A), (B), and (C).

The base resin is usually neutralized and dispersed in water by dispersing the base resin in an aliphatic carboxylic acid such as glycolic acid, glyceric acid, lactic acid, dimethylolpropionic acid, dimethylolbutyric acid, dimethylolvaleric acid, tartaric acid, and apple. acid,
It is carried out by neutralizing with a water-soluble organic acid such as hydroxymalonic acid, dihydroxysuccinic acid, trihydroxysuccinic acid, methylmalonic acid, acetic acid and formic acid, followed by dispersing in water. When acetic acid and / or formic acid are used as a neutralizing agent,
It is preferable because it has excellent finishability, throwing power, and low-temperature curability.

When the aqueous dispersion is carried out, the MEQ (acid concentration) of the electrodeposition coating composition is in the range of 5 to 25, preferably 15 to 25.
It is also possible to determine the amount of the neutralizing agent to be added so that it can be adjusted to the range of 20 to 20, and in some cases, improve the water dispersibility of the resin with a dispersing agent such as a surfactant to adjust the MEQ.

Here, if the MEQ is less than 5, poor stability with time of the coating composition and poor deposition of the formed coating film are caused. On the other hand, if the MEQ exceeds 25, the amount of gas generated during electrodeposition coating increases and the first electrodeposition coating is performed. Some of the deposited coating film is fused, and thus the outer plate portion has a reduced finish. In addition, at the boundary between the first electrodeposition coating film and the second electrodeposition coating film, the first coating film does not adhere. Due to the thinness, partial fusion of the coating film causes non-uniformity of the film resistance.
It is not preferable because it causes a problem of the second electrodeposition coating film.

Here, MEQ is an abbreviation for mg equivalent, and is defined as m of neutralizing agent (acid) per 100 g of solid content of the paint.
g equivalent. About 10 g of the electrodeposition coating composition is precisely weighed to about 50 g.
After dissolving in 1 ml of solvent (THF), 1 / 10N Na
It is calculated by quantifying the acid content in the electrodeposition coating composition by performing potentiometric titration using an OH solution.

The electrodeposition coating composition may contain, if necessary, a coloring pigment, an anticorrosive pigment, an extender pigment, a dye, an additive and the like in addition to the above components. It is also possible to use as a clear paint without blending pigments.

The coloring pigment is not particularly limited, but inorganic pigments such as titanium oxide, carbon black, iron chromic acid, and lead; organic pigments such as aniline black, vermilion red, lake red, phthalocyanine blue, and fast sky blue Can be used. As the anticorrosion pigment, a basic lead silicate, a bismuth compound, a zinc type or the like can be used. As the extender, kaolin, barium sulfate, or the like can be used.

The electrodeposition coating composition can further contain a tin compound. Examples of the tin compound include organic tin oxides such as dibutyltin oxide and dioctyltin oxide: dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin diacetate, dioctyltin benzoateoxy, dibutyltin benzoateoxy, dioctyltin dibenzoate, Examples thereof include aliphatic or aromatic carboxylate salts of dialkyltin such as dibutyltin dibenzoate. Of these, dialkyltin aromatic carboxylate salts are preferred from the viewpoint of low-temperature curability.

The tin content in the cationic electrodeposition paint is not strictly defined, and can be varied over a wide range according to the performance required for the electrodeposition paint. It is suitable that the tin content is in the range of 0.05 to 8 parts by weight, preferably 1 to 5 parts by weight per 100 parts by weight of the resin solid content therein.

The electrodeposition coating composition is not particularly limited, and a usual coating production method can be applied. One example of the method is described below. As the electrodeposition coating method, a general cationic electrodeposition coating method can be applied. For example, the solid content concentration is about 5 to 40% by weight, preferably 15 to 25% by weight.
The cation electrodeposition coating composition diluted with deionized water or the like so as to have a pH of 4.0 to 9.0 is used as an electrodeposition bath, and the bath temperature is usually 15 to 35 ° C. After adjustment, coating object (cathode) in the range of load voltage 50-400V
And an electrode plate (anode). The coating thickness is 10 to 50 μm, preferably 25 to
45 μm is preferred also from the viewpoint of weather resistance and finish.

In the step (2), an ultrafiltration solution is used to remove excess electrodeposition coating composition.
It is preferable to sufficiently wash with water such as RO permeated water and pure water so that the electrodeposition coating composition does not remain on the surface of the coated object. Further, this water washing equipment can be carried out by dipping water washing in which the body is immersed or spray water washing. Then 60-120
Preheat at a temperature of ° C. Preheat temperature is 60
When the temperature is lower than ℃, moisture and bubbles contained in the coating film cannot be sufficiently removed, and the finish property is lowered. The preheat temperature is 120 ° C
In the case described above, since the coating film is partially cured, a problem occurs in the recoating of the electrodeposition coating composition, and the anticorrosion property at the boundary portion is reduced. Preheating time is 1 to 30 minutes, preferably 5 to 2 minutes.
0 minutes may be good in terms of production efficiency of the line.

In the outer plate portion, the film thickness of the electrodeposition coating composition is preferably formed to be 25 μm or more, so that the coating film is fused by preheating, and the coating film resistance is reduced. The weathering function of the electrodeposition coating composition is effectively used on the outer plate surface without being formed on the upper layer of the coating composition.

Further, since the foam and moisture contained in the inner plate portion are removed to form a uniform coating resistance, the efficiency of the electrodeposition coating composition to be coated next is increased, and the electrodeposition coating composition is improved. The film thickness of the boundary portion where the product and the electrodeposition coating composition are coated with the electrodeposition coating film is secured, and the anticorrosion property is improved.

Step (3) is a step of applying an electrodeposition coating composition to the object having the electrodeposition coating film obtained in the above step to form an electrodeposition coating film. Conventional electrodeposition coating compositions can be used.

The electrodeposition coating composition will be described below. As the base resin, any resin such as epoxy-based, acrylic-based, polybutadiene-based, alkyd-based, and polyester-based resins can be used, but the main purpose is to prevent corrosion at the inner plate (bag). Thus, an epoxy resin is preferable, and an amine is added to the epoxy resin to be used as an electrodeposition coating composition. Examples of the amine-added epoxy resin (D) used in the electrodeposition coating composition include (i) an adduct of a polyepoxy compound and a primary mono- and polyamine, a secondary mono- and polyamine, or a primary and secondary mixed polyamine. (E.g., U.S. Pat. No. 3,984,299); (ii) adducts of polyepoxide compounds with secondary mono- and polyamines having a ketiminated primary amino group (e.g., U.S. Pat. No. 4,017,438); (iii) polyepoxide compounds Reaction product obtained by etherification of a ketimine-containing hydroxy compound having a primary amino group (for example,
No. 59-43013).

The polyepoxide compound used for producing the above amine-added epoxy resin is a compound having two or more epoxy groups in one molecule, and generally has at least 20 epoxy groups.
0, preferably 400-4000, more preferably 80
Those having a number average molecular weight in the range of 0 to 2,000 are suitable, and particularly those obtained by reacting a polyphenol compound with epichlorohydrin are preferable. Examples of the polyphenol compound that can be used for forming the polyepoxide compound include bis (4-hydroxyphenyl) -2,2-propane, 4,4-dihydroxybenzophenone, and bis (4-hydroxyphenyl) -1,1.
-Ethane, bis (4-hydroxyphenyl) -1,1-
Isobutane, bis (4-hydroxy-tert-butyl-phenyl) -2,2-propane, bis (2-hydroxynaphthyl) methane, tetra (4-hydroxyphenyl)-
Examples thereof include 1,1,2,2-ethane, 4,4-dihydroxydiphenylsulfone, phenol novolak, and cresol novolak.

The polyepoxide compound is a polyol,
Polyether polyol, polyester polyol, polyamidoamine, polycarboxylic acid, may be partially reacted with a polyisocyanate compound and the like, furthermore, ε-caprolactone, and those obtained by graft polymerization of acrylic monomers, etc. Is also good.

As the blocked polyisocyanate (C) used as a curing agent for the electrodeposition coating composition, the same ones as used for the electrodeposition coating composition can be used. For example, aromatic, aliphatic or alicyclic polyisocyanate compounds such as tolylene diisocyanate, xylylene diisocyanate, phenylene diisocyanate, bis (isocyanatemethyl) cyclohexane, tetramethylene diisocyanate, hexamethylene diisocyanate, methylene diisocyanate, and isophorone diisocyanate; Those obtained by reacting an excess amount of these isocyanate compounds with a low-molecular-weight active hydrogen-containing compound such as ethylene glycol, propylene glycol, trimethylolpropane, hexanetriol, or castor oil. Here, aromatic, alicyclic and the like are preferable as the electrodeposition coating composition from the viewpoint of anticorrosion properties, but are not limited thereto.

The blocking agent is one that blocks by adding to the isocyanate group of the polyisocyanate compound, and the blocked polyisocyanate compound formed by the addition is stable at room temperature and is about 100 to 20.
When heated to 0 ° C, preferably 120 to 150 ° C, it is desirable that the blocking agent be dissociated to regenerate free isocyanate groups.

As such a blocking agent, for example,
Lactam compounds such as ε-caprolactam and γ-butyrolactam; oxime compounds such as methyl ethyl ketoxime and cyclohexanone oxime; phenol compounds such as phenol, para-t-butylphenol and cresol; fats such as n-butanol and 2-ethylhexanol Aromatic alcohols such as phenylcarbinol and methylphenylcarbinol; ether alcohol compounds such as ethylene glycol monobutyl ether;

The amount of the blocking agent is preferably 1: 1 to 1: 1.3 with respect to the NCO group of the isocyanate. If the ratio exceeds 1.3, the blocking agent remains to lower the corrosion resistance of the coating film, and if the ratio is less than 1.0, NCO groups remain to impair the stability of the coating composition, which is not preferable.

The electrodeposition coating composition may contain, in addition to the above-mentioned amine-added epoxy resin (D) and blocked polyisocyanate compound (C), a surface conditioner, a repellent, a surfactant, a plasticizer, and other additives. An agent can be compounded.

The neutralization of the base resin and the dispersing in water are usually carried out using an aliphatic carboxylic acid such as glycolic acid, glyceric acid, lactic acid, dimethylolpropionic acid, dimethylolbutyric acid, dimethylolvaleric acid, tartaric acid, malic acid. It is carried out by neutralizing with a water-soluble organic acid such as hydroxymalonic acid, dihydroxysuccinic acid, trihydroxysuccinic acid, methylmalonic acid, acetic acid and formic acid, followed by dispersing in water. Use of formic acid as a neutralizing agent is preferable because of excellent throwing power.

In addition to the above components, coloring pigments, anticorrosive pigments, extenders, dyes, additives and the like can be added as required. It is also possible to use as a clear paint without blending pigments. The coloring pigment is not particularly limited, but inorganic pigments such as titanium oxide, carbon black, iron chromic acid, and lead; organic pigments such as aniline black, vermilion red, lake red, phthalocyanine blue, and fast sky blue; anticorrosive pigments as,
Basic lead silicate, bismuth compound, zinc type, etc .; as the extender, kaolin, barium sulfate, etc. can be used.

The electrodeposition coating composition may further contain a tin compound. Examples of the tin compound include organic tin oxides such as dibutyltin oxide and dioctyltin oxide: dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin diacetate, dioctyltin benzoateoxy, dibutyltin benzoateoxy, dioctyltin dibenzoate, Examples thereof include aliphatic or aromatic carboxylate salts of dialkyltin such as dibutyltin dibenzoate. Of these, dialkyltin aromatic carboxylate salts are preferred from the viewpoint of low-temperature curability.

The tin content in the electrodeposition coating composition is not strictly defined, and can be varied over a wide range according to the performance required for the electrodeposition coating composition. It is suitable that the tin content is in the range of 0.05 to 8 parts by weight, preferably 1 to 5 parts by weight per 100 parts by weight of the resin solids in the coating material. The electrodeposition coating composition is not particularly limited, and a usual method for producing a coating can be applied. One example of the method is described below.

As the electrodeposition coating method, a usual cationic electrodeposition coating method can be applied. For example, deionization is performed so that the solid content concentration is about 5 to 40% by weight, preferably 10 to 25% by weight. Dilute with water etc. and further increase the pH to 4.0
The electrodeposition coating composition of the cation adjusted to a range of ~ 9.0 was used as an electrodeposition bath, and the bath temperature was usually adjusted to 15 to 35 ° C.
It can be carried out by applying a voltage between the object to be coated (cathode) and the electrode plate (anode) in a load voltage range of 50 to 400V. The coating film thickness is 10 to 50 μm, preferably 20 to 40
μm is also preferred from the viewpoint of corrosion protection.

Step (4) is a step of washing the object having the electrodeposition coating film obtained in the above step with water, removing excess electrodeposition coating composition adhering thereto, and draining water. ). The washing water is preferably sufficiently washed with an ultrafiltration solution (UF filtrate), RO permeated water, pure water or the like so that the electrodeposition paint does not remain on the surface of the coated object. The water washing equipment can be carried out by dipping water washing in which the body is immersed or spray water washing.

Step (5), a step of simultaneously heating and curing these coating films, can be performed using an electric hot air dryer, a gas hot air dryer, or the like. The drying temperature is 110 ° C. to 200 ° C., preferably 140 to 180 ° C. at the temperature of the surface of the substrate, and the drying time is 10 minutes to 180 °.
Minutes, preferably 20 minutes to 40 minutes.

[0065]

EFFECT OF THE INVENTION By the double-coat electrodeposition coating of the method of the present invention, a coating film having excellent weather resistance and the like is formed on the outer plate portion, and a coating film having excellent corrosion resistance is formed on the boundary coating portion. You.
This is presumed to be due to the following reasons.

1. By using the electrodeposition paint having excellent weather resistance in the first electrodeposition coating, an electrodeposition coating film having excellent weather resistance is formed on the coated portion (outer plate portion) having good electrodeposition efficiency. 2. A coating film is formed by the second electrodeposition coating on a portion to be coated not coated with the electrodeposition coating composition, in particular, on a bag structure portion of the inner plate portion. 3. Since both components contain an epoxy resin as a component of the electrodeposition coating film used in the first and second times, a coating film having excellent adhesion between both the coating films and corrosion prevention at the boundary is formed. 4. By the first pre-heating treatment of the electrodeposition coating film, moisture and bubbles in the electrodeposition coating film are removed and the electrodeposition coating film is fused, so that the resistance value of the electrodeposition coating film becomes moderately high, For this reason, when the first electrodeposition coating film is less than about 25 μm,
Since the second electrodeposition paint is deposited, a coating film having no difference in thickness at the boundary between the two coating films is formed, and the corrosion resistance at the boundary is excellent. 5. If the temperature of the preheat treatment is less than 60 ° C., moisture and bubbles are not removed, and the fusion of the electrodeposited film becomes insufficient. Precipitates, resulting in poor weather resistance and the like.
Since the resistance of the second electrodeposition coating film becomes too high, the film thickness at the boundary portion is not sufficiently secured, and the anticorrosion property is reduced. 6. In order to achieve the objectives of paragraphs 4 and 5,
As the second electrodeposition coating composition, those having an MEQ in the range of 5 to 25 are preferable because they exhibit an excellent effect of the balance between the amount of generated bubbles and the deposition of the coating film. 7. In order to achieve the objectives of paragraphs 4 and 5,
As the second electrodeposition coating composition, the specific conductivity was 1500 to
Since the throwing power is excellent in the range of 2800 μS / cm, an electrodeposition coating film is formed on the inner plate portion (bag portion) which has not been coated by the first electrodeposition coating, so that it is preferable.

[0067]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited by this. Note that “parts” and “%” indicate “parts by weight” and “% by weight”.

Production Example of Acrylic Resin (A-1) 246 parts of propylene glycol monomethyl ether was charged into a 2 liter four-necked flask, and purged with nitrogen.
Maintained at 110 ° C. The following mixture was added dropwise thereto over 3 hours. Styrene 25 parts Methyl methacrylate 18 parts n-butyl acrylate 6 parts 2-hydroxyethyl methacrylate 12 parts Praxel FM-3 (trade name, manufactured by Daicel Chemical Industries, Ltd.) 24 parts Dimethylaminoethyl methacrylate 15 parts Azobisisobutylnitrile 3 parts After dropping, After 1 hour, 8 parts of 2,2 * -azobis (2-methylbutyronitrile) was dissolved in 56 parts of propylene glycol monomethyl ether.
It was dropped over time. After completion of the dropwise addition, the mixture was kept at 110 ° C. for another hour, and then methyl isobutyl ketone 44 was added.
Then, an acrylic resin (A-1) having a solid content of 67% and a Gardner viscosity of Z3 was obtained.

Production Example of Acrylic Resin (A-2) The same operation as in Production Example 1 was carried out, except that the mixture to be dropped was changed to the following composition, to obtain a solid content of 67%.
%, An acrylic resin (A-2) having a Gardner viscosity of Z3. Styrene 45 parts n-butyl acrylate 4 parts 2-hydroxyethyl methacrylate 12 parts Praxel FM-3 (trade name, manufactured by Daicel Chemical Industries, Ltd.) 24 parts Dimethylaminoethyl methacrylate 15 parts Azobisisobutylnitrile 3 parts.

Production Example of Acrylic Resin-Modified Epoxy Resin (B) Reaction 1: 200 parts of propylene glycol monomethyl ether and 50 parts of ethylene glycol butyl ether were charged into a two-liter four-necked flask, and purged with nitrogen.
It was kept at 120 ° C. A mixture having the following composition was dropped therein over 4.5 hours. Styrene 50 parts 2-Hydroxymethacrylate 19 parts Praxel FM-3 24 parts Acrylic acid 2 parts AMSD-GRH (manufactured by Gonka Kasei Co., Ltd., trade name, chain transfer agent) 5 parts 2,2'-azobis (2-methylbutyro) 5 parts of nitrile) One hour after the completion of the dropwise addition, a solution of 5 parts of 2,2′-azobis (2-methylbutyronitrile) dissolved in 25 parts of propylene glycol monomethyl ether was added thereto.
It was dropped over time. After completion of the dropwise addition, the mixture was kept at 120 ° C. for another hour, and an acrylic resin solution having a solid content of 75% a
I got Reaction 2: "Epicoat 828" (manufactured by Yuka Shell Epoxy Co., Ltd., epoxy equivalent: 1)
90 bisphenol A type epoxy resin) 375 parts,
Bisphenol A (150 parts) and diethanolamine (2.05 parts) were added, and reacted at 120 ° C. for 2 hours.
00 was obtained. To this, 650 parts of the acrylic resin solution a obtained in Reaction 1 was added and reacted at 120 ° C. The reaction temperature was lowered to 100 ° C., 54 parts of a solution of methyl isobutyl ketone ketimine of diethylene triamine (70% solid content) was added, and the mixture was allowed to react for 2 hours. The acrylic resin-modified epoxy resin (B) had a solid content of 76%. I got

Production Example of Amine-Added Epoxy Resin (D) 1010 g of Epikote 828EL (trade name, epoxy resin manufactured by Yuka Shell Co., Ltd.), 390 g of bisphenol A, and 0.2 g of dimethylbenzylamino are added, and the epoxy equivalent becomes 800 at 130 ° C. Until the reaction. Next, 260 g of ε-caprolactone and 0.03 g of tetrabutoxytitanium were added, the temperature was raised to 170 ° C., sampling was performed over time while maintaining this temperature, and the amount of unreacted ε-caprolactone was traced in the infrared absorption spectrum measurement. , The reaction rate is 98
%, The temperature was lowered to 120 ° C. Next, 160 g of diethanolamine and 65 g of methyl isobutyl diketimine of diethylenetriamine were added,
For 4 hours, and 420 g of butyl cellosolve was added.
An amine-added epoxy resin (D) having an amine value of 58 and a resin solid content of 80% was obtained.

The blocked isocyanate compound (C-
Production Example 1) After 50 parts of hexamethylene diisocyanurate was dropped into 40 parts of methyl ketoxime at 40 to 60 ° C., the mixture was heated at 80 ° C. for 1 hour to obtain a blocked isocyanate compound (C-1) having a resin solid content of 90%. I got

The blocked isocyanate compound (C-
Production Example 2) 250 g of MDI and 44 g of methyl isobutyl ketone were added, and the temperature was raised to 70 ° C. After slowly adding 146 g of methylacetamide, the temperature was raised to 90 ° C. While maintaining this temperature, sampling was conducted over time, and infrared absorption spectrum measurement confirmed that the absorption of unreacted isocyanate had disappeared, whereby a blocked polyisocyanate compound (C-2) having a solid content of 90% was obtained. .

Production Example of Pigment Dispersion Paste (F) 4.7 parts of a tertiary amine acid neutralized dispersion resin having a solid content of 85%,
After mixing 1.4 parts of 0% acetic acid, deionized water was further added and mixed and stirred. Then, JR-600E14 part (manufactured by Teica, trade name, titanium white), hydride PXN
10 parts (Takehara Chemical Co., trade name, refined clay), C-1
00 0.5 part (manufactured by Kikuchi Color Co., trade name, lead-based rust-preventive pigment), carbon MA-7B 3 parts (manufactured by Mitsubishi Kasei Co., Ltd., trade name, carbon black), DOTO (manufactured by Sankyoki Gosei Co., Ltd.) Product name, dioctyltin oxide)
0.5 part of KP-152K (Daiichi Kogyo Seiyaku Co., Ltd., trade name, surfactant) was added and dispersed in a ball mill for 40 hours to obtain a 50% pigment dispersion paste (F).

Clear emulsions EM-1 to EM-4
After uniformly stirring each component and the composition shown in Table 1 below, deionized water was added, and the mixture was added dropwise over about 15 minutes with vigorous stirring to give a cationic electrodeposited clear emulsion EM having a solid content of 32.0%. -1 to EM-4 were obtained.

[0076]

[Table 1]

Production Examples of Electrodeposition Coating Composition-32% Clear Emulsion EM-1 318.5
To this part, 70 parts of a 50% pigment-dispersed paste (F) and 296 parts of pure water were added to obtain a coating composition having a solid content of 20% and applied for the first time. The MEQ at that time was 19.

Similarly, a coating composition to be applied for the first time was obtained with the composition shown in Table 2. In addition, ME of the coating composition
Q was 18. The composition as shown in Table 2 was used to obtain an electrodeposition coating composition to be applied for the second time. At that time, the specific conductivity was 2000 μS / cm. Similarly, an electrodeposition coating composition was obtained with the composition shown in Table 2, and the specific conductivity at that time was 1
It was 650 μS / cm.

[0079]

[Table 2] Example 1 Bath temperature 2 using the electrodeposition composition obtained by the above formulation
A cold rolled steel sheet (70 × 150 × 0.8 mm) treated at 8 ° C. and chemically converted with Palbond # 3020 (trade name, manufactured by Nippon Parker Rising Co., Ltd., zinc phosphate treatment) was put together as shown in FIG. Processed into a test plate having a clearance, immersed in 13 cm of electrodeposition bath paint, and applied at 230 V-
Coating was performed for 2 minutes with a power-on time, and an electrodeposited film was obtained on the outer and inner plate surfaces of the two sheets together. After washing with water, preheat to 80 ° C
-10 minutes, and the coated plate is further coated with the electrodeposition composition for 2 minutes.
The coating was carried out at 80 V for 2 minutes with an electric current applied, and an electrodeposition film was further applied to the inner plate surfaces of the two sheets together, washed with water, baked and dried. Table 3 shows the thickness of the outer plate and the thickness of the boundary at that time. Examples 2 to 5 and Comparative Examples 1 to 5 The thickness of the outer plate and the thickness at the boundary were obtained by the same operation as in Example 1, the combination of the electrodeposition coating compositions shown in Table 3, and the coating conditions. Performance test results at that time are also shown.

[0080]

[Table 3]

(Note 1) Boundary film thickness: This is the film thickness of the portion of the inner plate portion in FIG. 1 where the second electrodeposition coating film is applied over the first electrodeposition coating film. (Note 2) Finishing property of the outer plate part: The surface roughness of the electrodeposited coating film on the outer plate part was measured by a surf test 301 (trade name, manufactured by MITSUTOYO Co., Ltd., surface roughness meter). (Note 3) Weather resistance (gloss retention): Remove the clip from the electrodeposited and baked test plate, and attach the outer plate of the test plate to J
IS K-5400 A weather resistance test was performed using an accelerated weather resistance tester (manufactured by Suga Test Instruments Co., Ltd.) specified in 9.8.1.
The 60 ° specular reflectance (60 ° gloss) of the test plate was 20
The measurement was performed at intervals, and the time when the gloss retention (%) was less than 50% was defined as the test end time. (Note 4) Weather resistance (clear adhesion): The clip was removed from the electrodeposited and baked test plate, and the UV absorber was removed from the acrylic melamine clear paint used for metallic coating on the outer plate of the test plate. The test plate coated with the clear paint and baked was subjected to a SWOM accelerated weathering test. At that time, the adhesion is checked over time. Each time, each check is immersed in warm water of 40 ° C. for 20 hours, then cross-cut with a cutter knife, and a peeling test is performed with Cellotape (registered trademark). At this time, the limit time during which the clear coating film is adhered without peeling is displayed. (Note 5) Corrosion protection at the boundary: Electrodeposition coating, electrodeposition coating part of inner plate after baking (uncoated part and part of the second electrodeposition coating film with thickness of 5 μm or less are masked and excluded from the test) Was subjected to a salt spray test for 480 hours using a 35 ° C. salt spray tester. After the test, check for rust and blisters at the boundary. ○ indicates no rust and blistering. × is rust,
There are blisters. (Note 6) The throwing power was tested by a four-sheet box method. 4
L PVC ED tank, magnetic stirrer used to create 4 boxes with a PVC jig for 4 boxes of paint agitation, 3 test plates with 8 mm diameter holes, set the box as shown in Fig. 2, Second electrodeposition coating → water washing → preheating → second time coating → water washing → electrodeposition coating in a baking process at 170 ° C for 20 minutes, and measure the film thickness of the A to H surfaces. At the time of preheating, the coated plate is disassembled from a PVC box making jig and washed with water.
After preheating, reassemble the box to its initial state with a PVC jig. The throwing power in Table 3 indicates the average film thickness of the F and G surfaces.

[Brief description of the drawings]

FIG. 1 shows a model diagram of a “two-folded” test plate having a clearance portion used in a coating test of the present invention and a state of a coating film when a clip is removed after baking.

FIG. 2 shows a model diagram and a test method of “four-box throwing power” used in the throwing power test of the present invention.

[Explanation of symbols]

1. Assuming the outer panel of the car body facing outward with the "two-piece" test panel. 2. This is a clip for closing the painted plate of the "two-piece" test plate. The clearance is 3.1 mm, and the spacer is sandwiched between both ends. 4. Unelectrodeposited part 5. This is the part that was painted by the second electrodeposition coating. 6. This is the portion where the first electrodeposition paint and the second electrodeposition paint are applied and overlapped. 7. This is the part painted by the first electrodeposition coating. (The second electrodeposition paint is not applied.) This is a boundary portion where the first electrodeposition paint is applied over the second electrodeposition paint. There is no electrodeposition coating at the spacer.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) C09D 5/44 C09D 5/44 A 175/04 175/04 C25D 13/06 C25D 13/06 E (72) Inventor Mitsuyoshi Kitano 1st floor, Azaji, Miyoshi-cho, Nishi-kamo-gun, Aichi Prefecture Kansai Paint Co., Ltd.F-term (reference) NA12 NA23 PA04 PB07 PC02

Claims (5)

[Claims] 1. The following step: Step (1): forming an electrodeposition coating film by coating a metal coating object having a bag structure such as an automobile body with an electrodeposition coating composition having high weather resistance and high finish. Step (2): Next, the object to be coated having the electrodeposition coating film obtained above is washed with water to remove an excessively adhered electrodeposition coating composition, and the obtained electrodeposition coating film is washed with water. A step of preheating at ~ 120 ° C to remove moisture and bubbles contained in the coating; Step (3); and further applying an electrodeposition coating to the object having the electrodeposition coating obtained in the above step. A step of coating the composition to form an electrodeposition coating film; step (4); washing the object having the electrodeposition coating film obtained in the above step with water to remove excess electrodeposition coating composition And draining or air blowing, step (5); and simultaneously heating and curing these coatings. Cationic electrodeposition method characterized in that it comprises a. 2. The electrodeposition coating composition according to claim 1, wherein said acrylic resin (A) and said monomer components (a) to (d) constituting said acrylic resin are in a total amount of 10 to 10.
60% by weight of a hydroxyl group-containing acrylic monomer (a), 5
-35% by weight of an amino group-containing acrylic monomer (b),
A resin obtained by a radical copolymerization reaction of 5 to 55% by weight of an aromatic vinyl monomer (c) and, if necessary, another acrylic monomer (d); an acrylic resin-modified epoxy resin (B); an epoxy resin component Based on the total weight of (e) and the acrylic resin component (f), a resin composed of 10 to 90% by weight of the epoxy resin component (e) and 90 to 10% by weight of the acrylic resin component (f) ( h) a hydroxyl-containing resin obtained by reacting the amine compound (g) with the amine compound (g) such that the ratio of the resin (h) / amine compound (g) becomes 65 to 95/5 to 35% by weight;
An aliphatic and / or alicyclic blocked isocyanate compound (C) is contained, and the mixing ratio of the components (A) to (C) is as follows: component acrylic resin (A), acrylic resin modified epoxy resin (B) And the total solid content of the aliphatic and / or alicyclic blocked isocyanate compound (C),
40 to 90% by weight of component (A) and 5 to 55 of component (B)
The cationic electrodeposition coating method according to claim 1, wherein the component (C) is blended so as to be 5 to 40% by weight. 3. MEQ (acid concentration) of the electrodeposition coating composition
The cationic electrodeposition coating method according to claim 1 or 2, wherein the number is from 5 to 25. 4. The specific conductivity of the electrodeposition coating composition is 150.
The cationic electrodeposition coating method according to any one of claims 1 to 3, wherein the coating pressure is 0 to 2800 µS / cm. 5. The method according to claim 1, wherein an overcoat is applied directly on the electrodeposition coating film obtained in the steps (1) to (5). Cation electrodeposition coating method.