JPH11209664A - Matte electrodeposition coating material and electrodeposition coating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a matte electrodeposition coating material by using an imino-group-contg. alkyl-etherified methylolmelamine resin as a part of a melamine resin component and forming electrodepositable fine microgel particles in water and to provide a matte electrodeposition coating method using the electrodeposition coating material. SOLUTION: This coating material contains a resin compsn. which is prepd. by mixing 100 pts.wt. acrylic resin having an acid value of 20-150, a hydroxyl value of 40-160, and a wt. average mol.wt. of 20,000-100,000, 5-30 pts.wt. alkyl- etherified methylolmelamine resin having, on average, 1-2.5 imino groups per melamine nucleus, and 40-100 pts.wt. alkyl-etherified methylolmelamine resin having substantially no imino group, neutralizing the mixture with a base, and subjecting the resultant aq. resin dispersion to microgelation reaction at 50-120 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a matte electrodeposition paint and a matte electrodeposition coating method. More specifically, a matte electrodeposition paint in which imino group-containing alkyl etherified methylol melamine resin is used as a part of the melamine resin and fine electrodepositable microgel particles are formed in water, and the electrodeposition paint is used The present invention also relates to a matte electrodeposition coating method characterized by obtaining a coating film by an electrodeposition coating method using an object to be coated as an anode.

[0002]

2. Description of the Related Art Heretofore, as a matte paint which does not obscure the hue and fine pattern of the object to be coated itself, one in which micro silica is dispersed in the paint has been generally used.
However, microsilica is inferior in chemical resistance, especially in alkali resistance, and a coating film having good transparency cannot be obtained. There are drawbacks such as a difference in gloss, particularly on the upper and lower surfaces, depending on the part to be coated.

On the other hand, there is known a method of dispersing organic fine particles having a small specific gravity in a coating material. However, this method, for example, one in which organic fine particles are dispersed in a paint as described in JP-B-51-8975 has practical utility as a general solvent-type spray paint or immersion paint, It was unsuitable as an electrodeposition paint. The reason for this is that since the electrophoretic properties of the organic fine particles are not considered at all, the organic fine particles do not have the characteristic of electrophoresis at a constant rate when energized, and sometimes fall off by washing with water.

In the electrodeposition paints and coatings, the viscosity of the electrodeposition bath is set to be substantially the same as the viscosity of water from the viewpoint of diffusion of generated Joule heat and washing properties. The body has such a low viscosity (usually a water content of 80-9
5%) in an electrolyte bath, the uniform dispersibility is poor, and in the electrodeposition coating, a solvent used for the purpose of adjusting gloss, improving washability, lowering the coating film resistance, and other components other than the essential components of the coating are used. There were drawbacks such as the elimination of contaminating electrolytes was not considered.

[0005]

On the other hand, there has been proposed a method in which an alkoxysilyl group is introduced into a base resin and an insoluble intra-particle microgel is formed in the copolymer resin by a condensation reaction with the alkoxysilyl group. For example, JP
JP-A-9-67396, JP-A-64-14281 and JP-A-05-263296 correspond to this technique, but are affected by the fluctuation of the gloss value depending on the coating conditions and the washing step after electrodeposition. For example, there are restrictions on the electrodeposition coating workability, such as ease of use.

The present inventors have conducted intensive studies on a method for forming a microgel that does not depend on an alkoxysilyl group. As a result, by combining a specific acrylic resin and a specific melamine resin, there is little variation in gloss value due to coating conditions. We have found a matte electrodeposition coating method that is also excellent in electrodeposition coating workability.

[0007]

That is, the present invention provides:
(A) an acrylic resin having an acid value of 20 to 150, a hydroxyl value of 40 to 160, and a weight average molecular weight of 20,000 to 100,000;
(B) Average imino groups of 1 to 2.5 per melamine nucleus
Group containing three components of an imino group-containing alkyl etherified methylol melamine resin and (C) an alkyl etherified methylol melamine resin having substantially no imino group, and based on the above (A) 100 in a weight ratio. The mixture in which (B) is 5 to 30 and (C) is 40 to 100 is neutralized with a base to obtain an aqueous resin dispersion, and the aqueous resin dispersion is subjected to a microgelation reaction at 50 to 120 ° C. The present invention relates to a matte electrodeposition paint containing the resin composition obtained as described above and an electrodeposition coating method thereof.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The acrylic resin (A) used in the present invention has an acid value of 20 to 150, preferably 40 to 100, and a hydroxyl value of 40 to 160, preferably 60 to 130,
(A1) an α, β ethylenically unsaturated carboxylic acid monomer;
(A2) a hydroxy group-containing ethylenically unsaturated monomer;
(A3) It can be produced by copolymerizing other α, β ethylenically unsaturated monomers.

The above-mentioned component (a1) mainly imparts water dispersibility, electrophoresis, catalytic action at the time of baking, etc. to the copolymer resin. Examples thereof include acrylic acid, methacrylic acid, and the like.
Crotonic acid, vinyl acetic acid, itaconic acid, maleic acid, maleic anhydride, fumaric acid, citraconic acid and the like. These may be used alone or in combination of two or more.

The amount of component (a1) used is such that the acid value of the acrylic resin is from 20 to 150, preferably from 40 to 100. If the acid value of the acrylic resin is less than 20, sufficient water dispersion stability and matting properties cannot be obtained.
If it exceeds 50, the electrophoretic properties will be poor, and the water resistance and weather resistance will decrease.

The component (a2) reacts with the imino group-containing alkyl etherified methylol melamine resin to form a microgel, and upon baking of the coating film, the alkyl etherified methylol melamine resin having substantially no imino group. And imparts curability.
Examples thereof include 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate, and the like, and lactone-modified products thereof. Species or a mixture of two or more species can be used.

The component (a2) is used in such a range that the hydroxyl value in the copolymer resin is 40 to 160, preferably 60 to 130. If the hydroxyl value is less than 40, the curability is insufficient, and if it exceeds 160, the coating film becomes brittle, the water resistance is reduced, and sufficient performance cannot be obtained.

Further, as the component (a3) which forms the skeleton of the copolymer resin, an alkyl ester of acrylic acid or methacrylic acid or other vinyl monomers can be used. Specific compounds include, for example, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-propyl acrylate, n-propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl acrylate, isobutyl Methacrylate, t-butyl acrylate, t-butyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, lauryl acrylate, lauryl methacrylate, stearyl acrylate, stearyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, heptyl acrylate, heptyl methacrylate, diethylene glycol monoacrylate Over DOO, acrylic acid and diethylene glycol monomethacrylate, esters of methacrylic acid, styrene, alpha-methyl styrene,
Vinyl monomers such as vinyltoluene, vinyl acetate, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, methylolacrylamide, methylolmethacrylamide, methoxymethylacrylamide,
Amide monomers such as n-butoxymethylacrylamide, diacetone acrylamide, diacetone meacrylamide and the like can be mentioned. These can be used alone or in combination of two or more.

Such an acrylic resin has a weight average molecular weight of 20,000 to 100,000. When the weight average molecular weight is 20,000 or less, the coating film durability cannot be sufficiently obtained, and when it is 100,000 or more, the water dispersibility decreases, and the handling property of the paint becomes poor. In particular, in terms of matting properties and paint stability, the weight average molecular weight is 30,000 to 700.
00 is preferred. Further, the glass transition temperature of the acrylic resin is preferably from -10 to 60C, more preferably from 10 to 4C.
0 ° C. is preferred in terms of matting and flexibility.

The above-mentioned acrylic resin can be prepared by subjecting the monomers (a1), (a2) and (a3) to known methods such as solution polymerization, non-aqueous dispersion polymerization, bulk polymerization, emulsion polymerization and suspension polymerization. , But particularly preferred is solution polymerization, and the reaction temperature is usually 40 to 1
70 ° C. is chosen.

As the reaction solvent, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol,
Isobutyl alcohol, sec-butyl alcohol, t
-It is preferable to use a hydrophilic solvent such as butyl alcohol, methyl cellosolve, ethyl cellosolve, propyl cellosolve, butyl cellosolve, propylene glycol monomethyl ether, propylene glycol monoethyl ether, and propylene glycol monobutyl ether. Known polymerization initiators such as organic peroxides, azo compounds, ammonium persulfate, and potassium persulfate can be used as the polymerization initiator.

In order to disperse the obtained acrylic resin in water, at least a part of the carboxyl groups in the resin is neutralized with a basic substance, for example, an organic amine or an inorganic base.
Such basic substances include monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, monoisopropylamine, diisopropylamine, triisopropylamine,
Monobutylamine, dibutylamine, alkylamines such as tributylamine, diethanolamine, diisopropanolamine, triethanolamine, dimethylethanolamine, alkanolamines such as diethylethanolamine, ethylenediamine, propylenediamine,
Examples thereof include alkylene polyamines such as diethylenetriamine and triethylenetetramine, ammonia, ethyleneimine, pyrrolidine, piperidine, piperazine, morpholine, sodium hydroxide, and potassium hydroxide. The neutralization ratio with such a basic substance is suitably from 30 to 100%, and particularly preferably from 50 to 80%, since water dispersibility is good and gloss unevenness does not occur.

The (B) imino group-containing alkyl etherified methylol melamine resin used in the present invention is an alkyl etherified methylol melamine resin having an average of 1 to 2.5 imino groups per melamine nucleus. The amount is 5 to 30 with respect to 100 acrylic resin by weight. When the imino group content or the amount of the melamine resin used is less than the above range, a favorable matting effect cannot be obtained due to insufficient microgel formation reaction. Conversely, when the amount is too large, the microgel is excessively generated, so that the fluidity of the coating material is reduced, and a large number of pinholes are formed in the coating film, and the chemical resistance is reduced. Further, the surface roughness of the coating film is remarkable, which is not preferable. In addition to the imino group, a melamine resin containing a non-alkyl etherified methylol group can also be used. In this case, the content of the methylol group is preferably 0.1 to 1 per melamine nucleus.

(B) Examples of the imino group-containing alkyl etherified melamine resin include Cymel 325, 701, 370, 254, 202, 272 manufactured by Mitsui Cytec.
204, and these are used alone or in combination of two or more, but are not limited thereto.

The (C) alkyl etherified methylol melamine resin containing no imino group used in the present invention is basically obtained by converting all hydrogens bonded to amino groups present in one molecule of melamine to methylol, and then converting the methylol to methylol. An alkyl etherified methylol melamine resin substantially free of an imino group, wherein the group is alkyl etherified with a lower alcohol, wherein the lower alcohol is one or two of methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol and the like. More than species can be used.

(C) The amount of the imino group-free alkyl etherified methylol melamine resin to be used is 40 to 100 in terms of weight ratio with respect to the acrylic resin 100. If the amount is less than this range, the gloss reduction is insufficient. Insufficient cross-linking of the coating, mechanical properties, solvent resistance, chemical resistance, etc. are reduced,
On the other hand, when the amount is large, problems such as poor stability of the aqueous dispersion, nonuniformity of the dispersed particle size, poor water washability after electrodeposition, water repellency, unevenness in gloss of the coating film, and milkiness are caused.

(C) Examples of the imino group-free alkyl etherified methylol melamine resin include Cymel 300, 303, 350, 266 and 26 manufactured by Mitsui Cytec.
7, 235, 236, 232, 238, My Court 50
6, Sumitomo Chemical's Sumimar M-100, M-100
C, M-66B, Nikarac MW- manufactured by Sanwa Chemical Co., Ltd.
40, MW-22, MX-40, and MX-45, and one or more of these are used as a mixture, but are not limited thereto.

In addition to the melamine resin, a conventionally known benzoguanamine resin, urea resin or the like can be used in combination.

Regarding the microgel formation reaction, it is considered that a hydroxyl group of (A) an acrylic resin and an imino group of (B) a melamine resin mainly react. The specific conditions of the gelation reaction are as follows: (A) an acrylic resin and (B) a melamine resin are mixed and dispersed in water, and then the reaction is carried out at 40 to 120 ° C, preferably 60 to 100 ° C. When the temperature is lower than 40 ° C., the microgelation reaction hardly proceeds, and a sufficient matting effect cannot be obtained. On the other hand, when the temperature is higher than 120 ° C., the microgelation reaction proceeds too much, the fluidity of the coating material is reduced, and a large number of pinholes are formed in the coating film to lower the chemical resistance. Further, the surface roughness of the coating film is large, and the surface roughness is remarkable, which is not preferable. The amount of microgel formed is determined by measuring the gel fraction, and a specific method is obtained by subtracting the tetrahydrofuran-soluble component from the solid content of the coating film dried at 40 ° C., as described in Examples. The preferred gel fraction is 20-60%.

The microgel formation reaction can be carried out without using a catalyst, but it is also possible to use an acid catalyst in combination. For example, formic acid, acetic acid, oxalic acid,
There are sulfonic acid, hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid and the like, and sulfonic acid is particularly preferable. As the sulfonic acid, methanesulfonic acid, ethanesulfonic acid, toluenesulfonic acid, isopropylbenzenesulfonic acid, nonylbenzenesulfonic acid, decylbenzenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, dinonyldinaphthalenesulfonic acid, Examples include dihexyldinaphthalenesulfonic acid and didecyldinaphthalenesulfonic acid.

Depending on the required performance, workability, cost and the like, if necessary, for example, xylene resin, epoxy resin, polyester resin, urethane resin, etc. can be used in combination. In this case, it is used in the same manner as the melamine resin.

Further, the electrodeposition paint obtained by the present invention is
If necessary, it is diluted with deionized water or deionized water partially containing a hydrophilic solvent, and then subjected to electrodeposition coating. For electrodeposition coating, an object to be coated is used as an anode, an electrodeposited deposition film is obtained by applying a predetermined voltage, and if necessary, washed by a conventional method, and then, through a baking process, low gloss, mechanical properties, A coating film excellent in solvent resistance, chemical resistance, weather resistance, workability and the like can be obtained.

[0028]

The present invention will be described below with reference to examples. Parts are parts by weight unless otherwise indicated.

Production Example 1 A reactor having a stirring device, a thermometer, a monomer dropping device, and a reflux cooling device is prepared. (1) ethylene glycol monobutyl ether 10.2 parts (2) isopropyl alcohol 40.7 parts (3) 2-ethylhexyl methacrylate 3.2 parts (4) n-butyl acrylate 27.5 parts (5) methyl methacrylate 30. 2 parts (6) Styrene 13.9 parts (7) 2-hydroxyethyl acrylate 18.1 parts (8) Acrylic acid 7.1 parts (9) Azobisisobutyronitrile 1.0 part (10) Azobisiso 0.5 parts of butyronitrile (1) and (2) were charged into a reactor, the mixture was heated to the reflux temperature with stirring, (3) to (9) were uniformly mixed in advance, and then added dropwise over 3 hours. . The temperature was maintained at 90 ± 3 ° C. 1.5 hours after the completion of the dropwise addition, (10) was charged, and the reaction was further continued at 90 ± 3 ° C. for 1.5 hours, followed by cooling.
Resin solid content = 65%, acid value = 55 mg KOH / g resin solid content, hydroxyl value = 87 mg KOH / g resin solid content, transparent and viscous acrylic resin liquid A having a weight average molecular weight of 51,000
1 was obtained.

Production Example 2 (1) Ethylene glycol monobutyl ether 10.2 parts (2) Isopropyl alcohol 40.7 parts (3) 2-ethylhexyl methacrylate 9.9 parts (4) n-butyl acrylate 22.9 parts ( 5) Methyl methacrylate 24.7 parts (6) Styrene 17.3 parts (7) 2-hydroxyethyl acrylate 16.6 parts (8) Acrylic acid 8.6 parts (9) Azobisisobutyronitrile 1.0 part (10) Azobisisobutyronitrile 0.5 part A reaction similar to that of Production Example 1 was performed with the above composition, and the resin solid content was 65%, the acid value was 67 mgKOH / g resin solid content,
A transparent and viscous acrylic resin liquid A2 having a hydroxyl value of 80 mg KOH / g resin solid content and a weight average molecular weight of 42,000 was obtained.

Production Example 3 (1) Ethylene glycol monobutyl ether 10.2 parts (2) Isopropyl alcohol 40.7 parts (3) 2-ethylhexyl methacrylate 11.7 parts (4) n-butyl acrylate 27.2 parts ( 5) Methyl methacrylate 29.3 parts (6) Styrene 20.5 parts (7) 2-hydroxyethyl acrylate 2.7 parts (8) Acrylic acid 8.6 parts (9) Azobisisobutyronitrile 1.0 part (10) Azobisisobutyronitrile 0.5 part A reaction similar to that of Production Example 1 was performed with the above composition, and the resin solid content was 65%, the acid value was 67 mgKOH / g resin solid content,
A transparent and viscous acrylic resin liquid A3 having a hydroxyl value of 13 mg KOH / g resin solid content and a weight average molecular weight of 46,000 was obtained.

Preparation of Aqueous Resin Dispersion Two reactors having a stirrer, a thermometer, a monomer dropping device, and a reflux cooling device are prepared. Table 1 shows one reactor
(1) to (7) were charged in accordance with the amounts of Production Examples 4 to 10 shown in (1), and the mixture was kept at 50 ° C. for 1 hour, heated to 60 ° C., and charged with (8) and (9) in advance. An aqueous resin dispersion was obtained by slowly dropping the mixture into the apparatus. This aqueous resin dispersion was kept at 80 ° C. for 6 hours to terminate the microgelation reaction, and after cooling to 30 ° C., (10) was charged to obtain resin compositions 1 to 7 having a solid content of 30%.

[0033]

[Table 1]

Preparation of paint and electrodeposition coating Examples 1, 2, 3, 4 Comparative Examples 1, 2, 3 Using the resin compositions obtained in Production Examples 4 to 10, Table 2 was used.
The electrodeposition bath liquid was obtained with the composition shown in Table 1. This electrodeposition bath solution was put in a PVC tank, the cathode was made of SUS304 steel plate, and the 6063S aluminum alloy plate was subjected to alumite treatment (alumite film thickness = 9 μm).
m), and further subjected to electrolytic coloring to black, followed by electrodeposition coating using an aluminum material washed by a conventional method as an anode (object to be coated).

[0035]

[Table 2]

Evaluation of coating film performance The specific conditions of electrodeposition coating are as follows: bath temperature 22 ° C., distance between electrodes 12c
m, the pole ratio (+/-) 2/1, and 130
Energize to 10 μm with V, wash after electrodeposition,
Subsequently, after baking was performed at 185 ° C. for 30 minutes, the coating film performance was evaluated. Table 3 shows the results.

[0037]

[Table 3]

(Note) Evaluation method (1) Gel fraction: The obtained dispersion resin solution was applied on a glass plate and dried by ventilation at 40 ° C. for 24 hours, and then the solid content α% of the dried coating film (105 ° C.) × 3 hour method) and β% dissolved in tetrahydrofuran (calculated by measuring the solid content in tetrahydrofuran after 2 hour refluxing dissolution by 105 ° C. × 3 hour method), and (α−β) / α × 100 = It is defined as the gel fraction (%). (2) Gloss: Measure 60 ° gloss with a gloss meter. (3) Pencil hardness: JIS-K-5400 Judgment of tear. (4) Adhesive force: 100 grids are formed on the coating film with a cutter knife, and after sticking a cellophane tape on it, observe the state of adhesion when the cellophane tape is quickly peeled off. 100/100: No peeling 0/100: All peeling (5) Alkali resistance: After immersion in 1% NaOH at 20 ° C. for 48H, the state of the coated surface was observed. (6) Acid resistance: After immersion in 5% sulfuric acid at 20 ° C for 48H, the state of the coated surface was observed. (7) Ra (center line average roughness): The surface roughness is measured, a portion having a measurement length l is extracted from the roughness curve in the direction of the center line, and the center line of this portion is defined as the X axis and the direction of the longitudinal magnification. Is represented by the Y-axis and the roughness curve is represented by y = f (x), Ra = ∫ | f
(X) | dx / l. The larger the Ra, the greater the roughness of the coated surface.

[0039]

Efficient electrophoresis is achieved by using an acrylic resin containing an acid group and a hydroxyl group and an alkyl etherified methylol melamine resin containing an imino group to form fine electrodepositable microgel particles in water. Further, a matte electrodeposition paint having excellent uniform dispersibility in a bath and uniform design was obtained.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C25D 13/06 C25D 13/06 B

Claims (1)

[Claims] (A) an acid value of 20 to 150 and a hydroxyl value of 40
-160, an acrylic resin having a weight average molecular weight of 20,000-100,000, (B) an imino group-containing alkyl etherified methylol melamine resin having an average of 1-2.5 imino groups per melamine nucleus, and (C) substantially (A) containing an alkyl etherified methylol melamine resin having no imino group, and
The mixture in which (B) is 5 to 30 and (C) is 40 to 100 is neutralized with a base to obtain an aqueous resin dispersion, and then the aqueous resin dispersion is microgeled at 50 to 120 ° C. A matte electrodeposition paint and a method of electrodeposition coating the same, which contain a resin composition obtained by a chemical reaction.