JP2003165946A - Electrodeposition coating material composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an electrodeposition coating material composition having low temperature curability which does not cause cissing and excels in the gloss and mar resistance of a cured coating film. <P>SOLUTION: This clear electrodeposition coating material composition comprises a resin composition composed of (a) an acrylic resin having carboxyl groups in an amount so as to render the acid value 70-130 mgKOH/g and hydroxy groups in an amount so as to render the hydroxy number 90-160 mgKOH/g and (b) a hydrophilic melamine resin at a weight ratio of the acrylic resin (a) to the hydrophilic melamine resin (b) of 60-80:40-20 (based on the solid content). The clear electrodeposition coating material composition has a methyl/butyl mixed ether-modified melamine resin having a molar ratio of the methoxy group to the butoxy group of 6/4 to 9/1 as the hydrophilic melamine resin. The clear electrodeposition coating material composition is obtained by dispersing the above resin composition in an aqueous medium so as to make the concentration of the resin composition 5-20 wt.%. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an electrodeposition coating composition,
In particular, the present invention relates to a low temperature curable electrodeposition coating composition having no cissing property and excellent in scratch resistance of a cured coating film.

[0002]

2. Description of the Related Art As an electrodeposition coating composition, an acrylic resin having an acid group and a hydroxyl group, an amino resin, and / or
Further, those containing an isocyanate resin as a main component are widely used because not only the physical properties and appearance of the coating film are excellent, but also the stability of the coating is excellent. Acrylic resins that have been used in the electrodeposition paints of this system so far are designed to have low acid groups and hydroxyl groups. The reason is that even if only one of the acid group and the hydroxyl group is designed to be high, the performance cannot be balanced, and if both are increased, the viscosity of the acrylic resin becomes high, which makes production difficult. Therefore, conventional ones with low acid groups and hydroxyl groups do not have very high curability of the coating film,
There was a problem in low temperature curability and coating film hardness. Further, when both the acid group and the hydroxyl group are low, the compatibility between the acrylic resin and the amino resin is inferior, which causes a problem of cissing.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a low temperature curable clear electrodeposition coating composition having no cissing property and excellent in scratch resistance of a cured coating film.

[0004]

[Means for Solving the Problems] In the present invention, the above-mentioned problems were solved by using an acrylic resin having a high acid value and a high hydroxyl value as the main component of the resin composition constituting the paint. . That is, the present invention is
a) Carboxyl group and hydroxyl value of 90 to 160 mgK in such an amount that the acid value becomes 70 to 130 mgKOH / g.
An acrylic resin having a hydroxyl group in an amount of OH / g, and b) a hydrophilic melamine resin, and
The present invention relates to a clear electrodeposition coating composition containing a resin composition in which the weight ratio of acrylic resin to b) hydrophilic melamine resin is 60 to 80:40 to 20 (based on solid content, the same applies hereinafter). Particularly, the present invention relates to the above-mentioned clear electrodeposition coating composition, wherein the hydrophilic melamine resin is a methyl / butyl mixed ether modified melamine resin having a methoxy group / butoxy group molar ratio of 6/4 to 9/1. The present invention also relates to the above-mentioned clear electrodeposition coating composition which is dispersed in an aqueous medium so that the concentration of the resin composition is 5 to 20% by weight. further,
The present invention relates to a method for electrodeposition coating a conductive substrate with the above-mentioned clear electrodeposition coating composition. In particular, it relates to the above method, wherein the conductive substrate is aluminum.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION One of the characteristics of the electrodeposition coating composition of the present invention is that it has a low temperature curability. It means that a cured state of about 4H to 5H can be developed in a baking time of minutes.

The electrodeposition coating composition of the present invention has an acid value of 70 to 1 as the acrylic resin which is the main component of the coating resin composition.
It is characterized in that it has a carboxyl group in an amount of 30 mgKOH / g and a hydroxyl group in an amount of 90 to 160 mgKOH / g. In the present invention, the acid value means the number of mg of potassium hydroxide required to neutralize the carboxyl groups contained in 1 g of the acrylic resin. Further, the hydroxyl value means the mg number of potassium hydroxide required to neutralize the acetic acid required to acetylate 1 g of the acrylic resin.

The acrylic resin in the resin composition constituting the coating composition of the present invention is not particularly limited as long as the acid value and the hydroxyl value are within the above ranges, more preferably the acid value is 80 to 120 mgKOH / g, hydroxyl value is 100 to 150 mg KOH / g. The weight average molecular weight of the acrylic resin is preferably 5000.
To 100,000, particularly preferably 10,000 to 7,000
It is 0. The scale of the molecular weight distribution represented by the ratio of the weight average molecular weight and the number average molecular weight is preferably 1-6, more preferably 1-4. The molecular weight of acrylic resin is 5000
Below, the emulsion becomes unstable, and when it exceeds 100,000, the flowability of the electrodeposition coating film deteriorates.

The acrylic resin is blended in an amount of 60 to 80% by weight, preferably 65 to 75, based on the total solid content of the resin composition in the coating material. When the content of the acrylic resin is less than 60% by weight, a coating material having excellent surface hardness and adhesiveness to a substrate cannot be obtained. On the other hand, if it exceeds 80% by weight, the amount of the curing agent becomes relatively small, and a coating film excellent in weather resistance, water resistance and surface hardness cannot be obtained.

Polymerizable monomers for introducing a carboxyl group into an acrylic resin include acrylic acid, methacrylic acid, maleic acid, maleic anhydride, fumaric acid, maleic acid monoester, itaconic acid, itaconic acid monoester, crotonic acid. , A vinyl-polymerizable α, β-unsaturated fatty acid such as citraconic acid, and mixtures thereof. The carboxyl group has an acid value of the acrylic resin of 70 to 130 mgKOH / g, preferably 80.
Introduced to be ~ 120 mg KOH / g. Acid value is 7
When it is less than 0, the low temperature curability is lost, and the physical properties of the coating film after curing, especially the hardness, are not sufficiently high. If the acid value exceeds 130 mgKOH / g, the water resistance of the coating film becomes poor, which is not preferable.

The reason why the hydroxyl group is introduced into the acrylic resin is to improve the compatibility with the melamine resin which is a curing agent and to enhance the reactivity. This is also to increase the degree of crosslinking and scratch resistance. To introduce a hydroxyl group, a polymerizable monomer having a hydroxyl group, such as β-hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, allyl alcohol,
A monomer selected from the group consisting of hydroxybutyl (meth) acrylate, trademark Praxel FM1-5 (Daicel Chemical) and mixtures thereof may be copolymerized.

In the acrylic resin of the present invention, the hydroxyl group is introduced so that the hydroxyl value is 90 to 160 mgKOH / g, more preferably 100 to 150 mgKOH / g. When the hydroxyl value is less than 90 mgKOH / g, the curing reaction does not sufficiently occur, the hardness is lowered, and the chemical resistance becomes poor. On the other hand, when it exceeds 160 mgKOH / g, unreacted hydroxyl groups remain in the coating film, resulting in poor water resistance and weather resistance.

Further, N-methylol acrylamide and / or N-butoxymethyl acrylamide may be copolymerized with the acrylic resin of the present invention. These amide components are added in an amount of 2 to 10% by weight, preferably 3 to 5% by weight, based on the total weight of the monomers forming the acrylic resin. By copolymerizing these amide components,
Since a cross-linking reaction occurs between the acrylic resins, the cross-link density is increased, and the water resistance and chemical resistance are improved.

As the acrylic component of the acrylic resin of the present invention, methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, isobutyl (meth) acrylate, normal butyl (meth) are used.
Any of acrylate, cyclohexyl (meth) acrylate, lauryl (meth) acrylate, glycidyl (meth) acrylate and the like are preferably used. Further, the acrylic resin of the present invention, styrene, α-methylstyrene, in the range that does not impair the characteristics of the electrodeposition coating composition of the present invention,
You may copolymerize vinyl acetate, vinyl propionate, vinyl chloride, vinylidene chloride, (meth) acrylonitrile, vinyl fluoride, vinylidene fluoride, 2-ethylhexyl (meth) acrylate and the like. The content of these monomer components is preferably 20% by weight or less in the acrylic resin.

The acrylic resin may be produced by any known method such as solution polymerization, emulsion polymerization and suspension polymerization. Especially alcohol-based solvent, cellosolve-based solvent,
It is preferable to use a solution polymerization method in which a water-miscible solvent such as a carbitol-based solvent, a glyme-based solvent, and a cellosolve acetate-based solvent is used, and each monomer and an initiator are added for polymerization. As the initiator used when preparing the acrylic resin, any of those used in ordinary synthesis is preferably used, and examples thereof include azo compounds, disulfide compounds, sulfide compounds, sulfine compounds, diazo compounds, and nitroso. Examples thereof include compounds and peroxide compounds.

In the coating material of the present invention, the acrylic resin has a carboxyl group as an alkaline substance such as ammonia; trimethylamine, monoethylamine, diethylamine,
Triethylamine, tripropylamine, triisopropylamine, monobutylamine, dibutylamine, tributylamine, cyclohexylamine, dicyclohexylamine, diethylcyclohexylamine, methoxyisopropylamine, 2-amino-2-methylpropanol, 2-dimethylamino-2-methyl -1-Propanol,
Aliphatic amines such as morpholine and N-ethylmorpholine; neutralized with alkanolamines such as ethanolamine, diethanolamine, triethanolamine, monomethylethanolamine, dimethylethanolamine, dibutylethanolamine, etc., and used as a water-soluble resin Good.

In the present invention, a hydrophilic melamine resin is added as a curing agent in an amount of 20 to 40% by weight, preferably 25 to 35% by weight, based on the total solid content of the resin composition. If the amount of the curing agent is less than 20% by weight, a sufficient curing reaction does not occur, while if it exceeds 40% by weight, the coating film becomes too hard and the adhesion and flexibility are deteriorated.

As a hydrophilic melamine resin used as a curing agent, a methyl / butyl mixed ether modified type melamine resin is usually preferably used. At this time, methyl /
The ratio of methoxy group / butoxy group in the butyl mixed ether modification is 6: 4 or more, preferably 7: 3 or more,
It is preferred to use modified methoxy resins up to 9: 1. If the ratio is less than 6: 4, the cissing property is adversely affected.

The melamine resin is a high imino type alkyl etherified melamine resin, a methylol type alkyl etherified melamine resin, an alkyl etherified melamine resin,
Although they are classified into mixed alkyl etherified melamine resins and the like, any of them can be used and can be appropriately selected depending on the baking temperature and the physical properties of the coating film. Since those having an imino group or a methylol group generally have low water resistance, an alkyl etherified melamine resin and a mixed alkyl etherified melamine resin are preferable from the viewpoint of water resistance of the coating film.

Examples of the alkyl etherified melamine resin include butylated melamine resin etherified with n-butyl group, iso-butyl group, methylated melamine resin etherified with methyl group, and methyl group, n-butyl. Group, methyl / etherified by i-butyl group
There is a butyl mixed etherified melamine resin. The commercially available methylated melamine resin has, for example, a methoxy group / isobutoxy group molar ratio of 60/4.
0 CYMER 238, methoxy group / butoxy group molar ratio 60/40 CYMER 235, methoxy group / butoxy group molar ratio 65/35 CYMER 231, methoxy group / butoxy group molar ratio 40/60 Cymel 236,
Examples thereof include Cymel 266 and 277 having a methoxy group / butoxy group molar ratio of 70/30 (all of which are manufactured by Mitsui Cytec Co., Ltd.) and Sumimar 50B (manufactured by Sumitomo Chemical Co., Ltd.).

As the commercially available butylated melamine resin, for example, Mycoat 506 (manufactured by Mitsui Cytec Co., Ltd.), Uban 20SE, Uban 20N.
-60 (manufactured by Mitsui Toatsu Chemicals, Inc.) and the like.
Examples of commercially available methylated melamine resins include Cymel 303 (manufactured by Mitsui Cytec Co., Ltd.), Sumimar M30W, M40S, M50W (all manufactured by Sumitomo Chemical Co., Ltd.), and Melan 622 and 623 (both Hitachi Chemical Co., Ltd.). Manufactured by the company) and the like.

In the coating material of the present invention, the above resin composition is used by being dispersed in an aqueous medium, and the solid content in the coating material is 5 to 20% by weight, preferably about 7 to 15% by weight. The coating composition of the present invention is a clear electrodeposition coating composition.
Here, the term "clear" refers to a coating material that does not contain a pigment such as an extender pigment or a coloring pigment. If necessary, the electrodeposition coating composition of the present invention may further contain a dye, a colorant and other commonly used additives.

The present invention also provides a method for electrodeposition coating in which the above-mentioned clear electrodeposition coating composition is applied to a conductive substrate. In the electrodeposition coating method of the present invention, although not particularly limited, the temperature of the electrodeposition tank is preferably 10 to 30 ° C., the applied voltage is preferably 50 to 300 V, and the coating time is preferably 1 to 10. Minutes. Examples of the conductive base material that is the material to be coated include an iron plate, a steel plate, an aluminum plate, and a surface-treated product of these, or a molded product thereof, but is not particularly limited as long as it has conductivity. Aluminum is particularly preferred.

[0023]

Example (Synthesis of Acrylic Resin 1) 32 parts by weight of isopropyl alcohol and butyl cellosolve 3 which are solvents
3 parts by weight were charged into a reaction vessel, heated to 90 to 100 ° C., and gently refluxed while 10 parts by weight of styrene, 27 parts by weight of methyl methacrylate, 15 parts by weight of isobutyl acrylate, 8 parts by weight of ethyl acrylate, and hydroxyethyl. 24 parts by weight of acrylate, 13 parts by weight of methacrylic acid and N-butoxymethylacrylamide 4
A mixture of parts by weight of the monomer and 2.0 parts by weight of azobisisobutyronitrile as a polymerization initiator was added dropwise over 3 hours. After the reaction was continued for another 1 hour after the completion of dropping, 0.5 part by weight of azobisisobutyronitrile as an initiator and 1.0 part by weight of isopropyl alcohol were added dropwise over 1.5 hours, and the reaction was continued for another 2 hours. Let The obtained acrylic varnish has a nonvolatile content of 60% and a hydroxyl value of 100.
mgKOH / g, acid value was 80 mgKOH / g, and weight average molecular weight was 30,000.

(Synthesis of Acrylic Resin 2) 32 parts by weight of isopropyl alcohol and 33 parts by weight of butyl cellosolve were placed in a reaction vessel, heated to 90 to 100 ° C., and gently refluxed, while 13 parts by weight of styrene and 10 parts of methyl methacrylate were added thereto. Parts by weight, isobutyl acrylate 2
2 parts by weight, 33 parts by weight of hydroxyethyl acrylate,
A mixture of 18 parts by weight of methacrylic acid and 4 parts by weight of N-butoxymethylacrylamide and 2.0 parts by weight of azobisisobutyronitrile as a polymerization initiator was added to a mixture of 3 parts.
It dripped over time. After the completion of dropping, the reaction was continued for another hour, and then the initiator, azobisisobutyronitrile, was added.
5 parts by weight and 1.0 part by weight of isopropyl alcohol were added dropwise over 1.5 hours, and the reaction was further continued for 2 hours.
The obtained acrylic varnish has a nonvolatile content of 60%, a hydroxyl value of 150 mgKOH / g, and an acid value of 120 mgKO.
H / g, the weight average molecular weight was 35,000.

(Synthesis of Acrylic Resin 3) 32 parts by weight of isopropyl alcohol and 33 parts by weight of butyl cellosolve were placed in a reaction vessel, heated to 90 to 100 ° C., and gently refluxed, while 6 parts by weight of styrene and 50 parts of methyl methacrylate were added thereto. Parts by weight, isobutyl acrylate 10
By weight, 10 parts by weight of hydroxyethyl acrylate, 12 parts by weight of ethyl acrylate, 8 parts by weight of methacrylic acid and 4 parts by weight of N-butoxymethylacrylamide, and 2.0 parts by weight of azobisisobutyronitrile as a polymerization initiator. The mixture of was added dropwise over 3 hours. After the reaction was further continued for 1 hour after the completion of dropping, 0.5 part by weight of azobisisobutyronitrile as an initiator and 1.0 part by weight of isopropyl alcohol were added dropwise over 1.5 hours.
The reaction was continued for 2 hours. The resulting acrylic varnish has a nonvolatile content of 60% and a hydroxyl value of 40 mgKOH /
g, acid value 50 mgKOH / g, weight average molecular weight 30
It was 000.

(Synthesis of Acrylic Resin 4) 32 parts by weight of isopropyl alcohol and 33 parts by weight of butyl cellosolve were placed in a reaction vessel, heated to 90 to 100 ° C., and gently refluxed, while 6 parts by weight of styrene and 23 parts of methyl methacrylate were added thereto. Parts by weight, isobutyl acrylate 28
Parts by weight, 33 parts by weight of hydroxyethyl acrylate, 6 parts by weight of methacrylic acid and 4 parts by weight of N-butoxymethylacrylamide, and a mixture of 2.0 parts by weight of azobisisobutyronitrile as a polymerization initiator for 3 hours. Was dropped. After the addition was completed, the reaction was continued for 1 hour, and then 0.5 parts by weight of azobisisobutyronitrile as an initiator and 1.0 part by weight of isopropyl alcohol were added to 1.5 parts by weight.
After that, the solution was added dropwise over a period of time and reacted for 2 hours. The obtained acrylic varnish has a nonvolatile content of 60%, a hydroxyl value of 150 mgKOH / g, an acid value of 50 mgKOH / g,
The weight average molecular weight was 35,000.

(Synthesis of Acrylic Resin 5) 32 parts by weight of isopropyl alcohol and 33 parts by weight of butyl cellosolve were placed in a reaction vessel, heated to 90 to 100 ° C., and gently refluxed, while 12 parts by weight of styrene and 26 parts of methyl methacrylate were added thereto. Parts by weight, isobutyl acrylate 3
2 parts by weight, 17 parts by weight of hydroxyethyl acrylate,
A mixture of 9 parts by weight of methacrylic acid and 4 parts by weight of N-butoxymethylacrylamide and 2.0 parts by weight of azobisisobutyronitrile as a polymerization initiator was added dropwise over 3 hours. After the reaction was continued for an additional 1 hour after the completion of dropping, the initiator was azobisisobutyronitrile 0.5.
1 part by weight and 1.0 part by weight of isopropyl alcohol.
The mixture was added dropwise after 5 hours and reacted for 2 hours. The obtained acrylic varnish has a nonvolatile content of 60%, a hydroxyl value of 80 mgKOH / g, an acid value of 80 mgKOH / g,
The weight average molecular weight was 30,000.

Example 1 Triethylamine was added to 81 parts by weight of the acrylic resin 1 varnish synthesized above so as to have a neutralization ratio of 35% (0.35 equivalent to a carboxyl group), and mixed uniformly.
In this, Cymel 285 (manufactured by Mitsui Cytec Co., Ltd .;
19 parts by weight of melamine resin and methoxy / butoxy ratio = 7/3 (weight ratio)) were added and stirred for 10 minutes. While stirring, deionized water was gradually added to this to prepare an aqueous dispersion having a solid content of 50% by weight, which was used as an electrodeposition coating solution. In addition, triethylamine and deionized water were added to this stock solution to give a neutralization rate of 70% and a solid content of 8% by weight, which was subjected to electrodeposition. This electrodeposition paint was adjusted to 20 ° C., and the 6063S aluminum alloy plate was anodized (alumite film thickness: 9μ
m) and then sealing treatment (immersing in hot water at 80 ° C. for 3 minutes) to obtain a dry film thickness of 8 to 10 μm.
A direct current voltage of 00 V was applied for 3 minutes for electrodeposition coating. After electrodeposition coating, the coated aluminum alloy plate was immersed in a washing bath adjusted to 20 ° C. for 3 minutes and then baked and dried at 160 ° C. for 30 minutes to obtain a cured coating film.

Example 2 An electrodeposition coating composition was prepared in the same manner as in Example 1 except that acrylic resin 2 was used as the acrylic resin, and electrodeposition coating, washing with water and baking were performed.

Comparative Example 1 An electrodeposition coating composition was prepared in the same manner as in Example 1 except that acrylic resin 3 was used as the acrylic resin, and electrodeposition coating, washing with water and baking were performed.

Comparative Example 2 An electrodeposition coating composition was prepared in the same manner as in Example 1 except that acrylic resin 4 was used as the acrylic resin, and electrodeposition coating, washing with water and baking were performed.

Comparative Example 3 An electrodeposition coating composition was prepared in the same manner as in Example 1 except that acrylic resin 5 was used as the acrylic resin, and electrodeposition coating, washing with water and baking were performed.

Comparative Example 4 In the same manner as in Example 1 except that acrylic resin 4 was used as the acrylic resin and Cymel 235 (manufactured by Mitsui Cytec Co .; methoxy / butoxy ratio = 4/6 (weight ratio)) was used as the melamine resin. Prepare electrodeposition paint, electrodeposition coating and washing with water,
Baking was performed.

Using the electrodeposition paints prepared in Examples 1 and 2 and Comparative Examples 1 to 4, the stability of the paints during operation was determined by pump shear property, and the hardness of the cured coating film was evaluated by pencil hardness and pencil hardness. Scratch resistance, curability were evaluated as hydrochloric acid resistance and strong alkali resistance, and cissing resistance was evaluated by the uniformity of the coating film when a melamine resin was dropped onto the uncured coating film.
Table 1 shows the properties of each resin used in Examples and Comparative Examples. Next, the evaluation method is shown in Table 2 as well.

Evaluation method for cured coating film [Hardness] A scratch value test with a pencil was carried out in accordance with JIS K5400, and the hardness was expressed as the maximum pencil hardness at which the coating film was not scraped off.

[Curability] 1. Hydrochloric acid resistance: According to JIS K8602, the coating film surface was visually observed after being contacted with a 5% hydrochloric acid aqueous solution at 20 ° C. for 192 hours, and the rating number (J
IS K8681: Corrosion area ratio to test surface). 2. Strong alkali resistance: 2 according to JIS K8602
After being contacted with a 5% aqueous sodium hydroxide solution at 0 ° C. for 192 hours, the coating film surface was visually observed and expressed by a rating number (JIS K8681: corrosion area ratio to the test surface).

[Scratch resistance] 800 using a Gakushin type dyed friction fastness tester (manufactured by Daiei Kagaku Seiki Co., Ltd.)
After the corrugated board under a load of g was reciprocated 200 times, the state of the coating film surface was visually evaluated. ○: There are no scratches or marks. Δ: There are about 1 to 3 scratches. X: There are several noticeable scratches. XX: There are band-like scratches.

[Repelling property (compatibility with melamine resin)] Aluminum test piece (JIS H4000: A6063)
The alumite treated product of S) was energized at a predetermined voltage for 2 minutes, washed with water and then left at room temperature for 30 minutes to dry the coating film surface. Then, a melamine resin (Cymel 285: manufactured by Mitsui Cytec Co., Ltd.) was dropped on the surface of the coating film, and 1
Baking was performed at 60 ° C., and the state of the coating film after baking was visually evaluated. ○: No cissing or dents occurred. Δ: Very few cissing, dents, etc. were observed. X: Repelling, dents, etc. occur.

Method for Evaluating Stability of Electrodeposition Paint During Operation [Pump Share Property] 1 L of paint was circulated for 1 hour by an Iwaki magnet pump (MD-15-RN), and then electrodeposition coating was carried out by the following procedure. 1. The coating was vigorously stirred before electrodeposition coating. 2. An aluminum test piece (JIS H4000: A6063) bent into an L-shape in the electrodeposition bath containing the above electrodeposition paint.
The alumite-treated product of S) was added and stirring was stopped for 5 minutes. 3. Electricity was applied for 2 minutes at a predetermined voltage to perform electrodeposition coating, washing with water and baking. The coating film baked and cured in this way is visually repellant,
It was evaluated whether there were any abnormalities such as dents and used as a measure of the stability of the paint during operation. Judgment is 10 points, no problem,
The level was evaluated in 10 steps.

[0040]

[Table 1]

[0041]

[Table 2]

[0042]

The electrodeposition coating composition of the present invention is 140 to 16
Hardness at low temperature such as 0 ° C is possible, and the cured coating film obtained by curing this coating material in the above temperature range has excellent hardness and is evaluated from the viewpoint of cissing property evaluated by dropping the melamine resin. The paintability is also good, and there is no problem with the stability of the paint itself during operation.

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4J038 CG141 CH031 CH041 CH171                       DA162 DB221 GA03 GA06                       GA09 JB01 JB09 MA08 MA10                       MA12 MA14 NA03 NA04 NA11                       NA25 PA04 PC02

Claims (5)

[Claims] 1. A) acid value of 70 to 130 mg KOH / g
The amount of carboxyl group and hydroxyl value is 90
To 160 mgKOH / g of an acrylic resin having a hydroxyl group, and b) a hydrophilic melamine resin, and the ratio of the a) acrylic resin to the b) hydrophilic melamine resin is 60 to 80:40 by weight. A clear electrodeposition coating composition containing a resin composition of 20 (based on solid content, the same applies hereinafter). 2. The clear electrodeposition coating composition according to claim 1, wherein the hydrophilic melamine resin is a methyl / butyl mixed ether-modified melamine resin having a methoxy group / butoxy group molar ratio of 6/4 to 9/1. 3. The clear electrodeposition coating composition according to claim 1, wherein the resin composition is dispersed in an aqueous medium so that the concentration of the resin composition is 5 to 20% by weight. 4. A method of electrodeposition coating the electro-conductive substrate with the clear electrodeposition coating composition according to claim 1. 5. The method of claim 4, wherein the electrically conductive substrate is aluminum.