JPH0539446A - Method for forming matte electrodeposition coating film - Google Patents

Abstract

PURPOSE:To form a coating film having excellent appearance, not causing luster unevenness, providing a thick film by electrodeposition coating once by using a coating compound composition comprising a specific acrylic resin and a specific alkyl etherified methylol resin. CONSTITUTION:A coating compound composition comprising (A) an acrylic resin having 20-150 (preferably 30-100) acid value and 30-150 (preferably 40-100) hydroxyl number and (B) a substantially water-insoluble alkyl etherified methylolmelamine resin containing >=3.5 (preferably >=4.5) ether groups on the average per melamine nucleus, wherein 70-100 (preferably 80-100%) of the ether group is butoxy group, in a ratio of 40/60 to 80/20 (preferably 50/50 to 70/30) by weight is diluted and applied by electrodeposition to form a matte coating film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a matte electrodeposition coating film, and in particular, by using a specific melamine resin as a curing agent, gloss unevenness does not occur and it is possible to obtain a thick coating after one electrodeposition coating. The present invention relates to a method for forming a matte electrodeposition coating film capable of forming a film and forming a good appearance.

[0002]

2. Description of the Related Art Conventionally, many methods have been proposed as a method for matting an electrodeposition coating film. For example, a method of incorporating an inorganic pigment such as silica fine powder or fine powder such as polyethylene or polypropylene (see, for example, JP-A-56-16569 and JP-A-
56-75596, JP-A-60-135466), a method of post-treating an electrodeposition coating film with an acidic treatment liquid (for example, JP-A-52-137444).
No.) etc. have been proposed. However, in these methods, a uniform matte coating film cannot be obtained due to sedimentation of the matting agent or the like, and the number of post-treatment steps increases, resulting in uneven luster during withdrawal from the treatment solution or washing with water. There are drawbacks such as side effects in terms of membrane performance.

[0003]

As a method for matting an electrodeposition coating composition which has overcome the above-mentioned drawbacks, an electrodeposition method in which a base resin and a melamine resin which is a curing agent are preliminarily heated in the presence of an acid to have a high molecular weight A method using a paint (see, for example, JP-A-58)
No. 215466) and a method of forming an insoluble intragranular gel structure in the copolymer resin by introducing an alkoxysilane group into the main resin (Japanese Patent Publication No. 62-24519).
However, these methods have a problem that the raw material resin needs to have a high molecular weight, the gloss value varies depending on the degree, and it is difficult to control the matting degree. Further, when coated on an aluminum material, the hiding property of the underlayer is not always sufficient, and there is a problem that the die marks of the aluminum material are conspicuous. Furthermore, since it contains a highly reactive high molecular weight component as a matting component,
The coating film resistance during electrodeposition coating is large, the coating voltage is high,
There is a problem that it is difficult to obtain a thick film.

On the other hand, a method of reacting a butylated melamine resin and an acrylic resin under a specific condition to use as a composition for electrodeposition coating is disclosed in JP-A-58-147467. However, the improvement in solvent resistance, chemical resistance, hardness, low-temperature bakeability, etc. was limited, and it was difficult to obtain a coating film having a good matte appearance.

Therefore, an object of the present invention is to provide a method for forming a matte electrodeposition coating film capable of forming a thick film by one-time electrodeposition coating and forming a good appearance in which the underlying die marks are not conspicuous. Is to provide.

[0006]

As a result of earnest research in view of the above object, the present inventors have found that the structure of a melamine resin used as a curing agent in the formation of a matte electrodeposition coating film containing an acrylic resin as a main component is However, it has been found that the matting effect is greatly affected. Furthermore, the present inventors have found that if a specific melamine resin is used as a curing agent, a thick film can be obtained by a single electrodeposition coating, and the underlying die marks are not conspicuous, and a good matte coating is stable. It was found that it can be formed by. The present invention has been made based on the above.

That is, the method for forming a matte electrodeposition coating film of the present invention is to form a matte coating film by electrodeposition from an aqueous paint prepared by diluting a matte electrodeposition coating composition.
The matte electrodeposition coating composition has (I) an acrylic resin having an acid value of 20 to 150 and a hydroxyl value of 30 to 150, and (II) an average of 3.5 or more ether groups per melamine nucleus. A substantially water-insoluble alkyl etherified methylol melamine resin in which 70 to 100% of the ether groups are butoxy groups, and the weight ratio of (I) to (II) is 40/60.
It is characterized by being ~ 80/20.

The present invention is described in detail below. (I) Acrylic resin The acrylic resin used in the method of the present invention has an acid value of
20 to 150, preferably 30 to 100, and a hydroxyl value of 30 to 150
, Preferably 40 to 100, (a) an ethylenically unsaturated carboxylic acid monomer, (b) a hydroxyl group-containing polymerizable unsaturated monomer, and (c) an ethylenically unsaturated carboxylic acid ester. It can be produced by copolymerizing a monomer and / or a vinyl monomer.

The above-mentioned component (a) mainly imparts water-diluting property, electrophoretic property, catalytic action at the time of curing, etc. to the copolymer resin, and examples thereof include acrylic acid, methacrylic acid, crotonic acid, vinyl acetic acid, and itacone. Examples thereof include acids, maleic acid, maleic anhydride, fumaric acid and the like. These may be used alone or in combination of two or more.

The component (a) is used in such a range that the acrylic resin (copolymer resin) has an acid value of 20 to 150, preferably 30 to 100. If the acid value of the acrylic resin is less than 20, the water-diluting property and the matting property are deteriorated, and if it exceeds 150, the water resistance and weather resistance are deteriorated.

The component (b) mainly imparts curability with a melamine resin which is a curing agent, and is, for example, 2-
Examples thereof include hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate and the like. These may be used alone or in combination of two or more.

The component (b) is used in such a range that the hydroxyl value in the copolymer resin is 30 to 150, preferably 40 to 100. When the hydroxyl value is less than 30, the curability is insufficient, and when it exceeds 150, the coating film becomes brittle and the water resistance is lowered.

Further, the component (c) is a component which mainly forms the skeleton of the copolymer resin, and in addition to alkyl esters such as acrylic acid and methacrylic acid, ordinary vinyl monomers can be used. Examples of these 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. Acrylic acid such as 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, dimethylaminoethyl methacrylate, methacrylic In addition to esters such as acids, styrene and methyl Styrene, vinyltoluene, vinyl acetate, acrylonitrile,
Examples thereof include vinyl monomers such as acrylamide, methacrylamide, methylol acrylamide, methylol methacrylamide, and n-butoxymethyl acrylamide. These may be used alone or in combination of two or more.

The preferred number average molecular weight of such an acrylic resin is 3,000 to 70,000. Number average molecular weight is 3,000
If it is above, sufficient coating durability can be obtained, and 70,000
If it is below, it is likely to be water-soluble or water-dispersible, has an appropriate viscosity, and is easy to handle. In particular, it is preferable that the number average molecular weight is 10,000 to 50,000 from the viewpoints of matting property and coating stability. The preferred glass transition temperature of the acrylic resin is −10 to 60 ° C., and particularly preferably 20 to 50 ° C. in terms of matteness and flexibility.

The amount of the (a) ethylenically unsaturated carboxylic acid monomer used in the acrylic resin is the amount necessary to give a predetermined acid value as described above. Specifically, (a)
It is preferably 3 to 20% by weight based on 100% by weight of + (b) + (c).

The amount of the (b) hydroxyl group-containing polymerizable unsaturated monomer used is an amount necessary to give a predetermined hydroxyl value as described above. Specifically, (a) + (b) +
The total amount of (c) is preferably 6 to 30% by weight based on 100% by weight.

Further, the amount of the (c) ethylenically unsaturated carboxylic acid ester monomer and / or vinyl monomer used is an amount necessary to form the skeleton of the acrylic resin. Specifically, the total of (a) + (b) + (c) is set to 100% by weight, and 50 to
91% by weight is preferred.

The above-mentioned acrylic resin can be obtained by polymerizing each of the above-mentioned monomers by a known method such as solution polymerization, non-aqueous dispersion polymerization, bulk polymerization, emulsion polymerization, suspension polymerization, etc. It is preferably obtained by a solution polymerization method using a hydrophilic solvent such as alcohol, isobutyl alcohol, ethyl cellosolve or butyl cellosolve.

In order to make the obtained acrylic resin water-soluble or water-dispersible (water-dilutable), at least a part of the carboxyl groups in the resin is neutralized with a basic substance such as an organic amine or an inorganic base. Is preferred. As the basic substance, an organic amine such as monomethylamine, dimethylamine, trimethylamine, diethylamine, triethylamine, monoisopropylamine, diisopropylamine, triethanolamine, dimethylethanolamine, diethylethanolamine, or ammonia is preferable. The neutralization rate with such a basic substance is preferably 30 to 100%, but is particularly preferably 50 to 95% because the water dilutability is good and no uneven gloss occurs.

(II) Melamine Resin The melamine resin used in the present invention is
It is a substantially water-insoluble alkyl etherified methylol melamine resin having an average of 3.5 or more ether groups and 70 to 100% of the ether groups are butoxy groups. The butoxy group in this case may be any of an n-butoxy group, an i-butoxy group and a t-butoxy group. Further, examples of the alkoxy group other than the butoxy group include a methoxy group and an ethoxy group. If the average number of ether groups contained is less than 3.5, a sufficient matting effect cannot be obtained. The average number of preferred ether groups is 4.5 or more. If the butoxy group content is less than 70%, the matting effect is reduced. The butoxy group content is preferably 80% or more. The average degree of polymerization of the melamine resin is preferably 3.0 nuclides or less from the viewpoint of stability of the aqueous solution.

Acrylic resin (I) as the main component as described above
And the mixing ratio of the melamine resin (II) as a curing agent is 40/60 to 80/20, preferably 50/50 to 70/30 in terms of weight ratio ((I) / (II)) based on the solid content. Is. If the weight ratio is less than 40/60, the stability of the coating is impaired, while if it exceeds 80/20, the matte effect is not sufficient and the chemical resistance of the coating film is reduced.

The matte electrodeposition coating used in the present invention can be obtained by mixing the acrylic resin (I) and the melamine resin (II) and diluting the resulting composition. The mixing method of the component (I) and the component (II) is not particularly limited, and it can be performed at room temperature. In order to increase the homogeneity at the time of mixing, it is preferable to heat the components (I) and (II) to such an extent that they do not react with each other to increase the molecular weight. In addition, the component (I) is diluted with water by the addition of the basic substance, and then the component
Water dilutability may be imparted by mixing with (II) or by mixing with component (II) and then adding a basic substance.

Further, if desired, a surface active agent for improving unevenness in dryness and water washability, a pigment for assisting matting and improving smoothness, a wax for improving smoothness and matting, latex, etc. Colorants, plasticizers, acidic / basic substances, etc. can be added as appropriate. These mixtures are diluted with water and used as a matte electrodeposition paint.
If necessary, other acrylic resin or other melamine resin may be added within a range that does not impair the effects of the present invention.

Such an electrodeposition coating composition of the present invention is electrodeposition-coated with the article to be coated as an anode. At this time, the solid content concentration of the coating composition in the electrodeposition coating bath is suitably 5 to 15% by weight. If it is less than 5% by weight, the coating voltage becomes too high,
On the other hand, if it exceeds 15% by weight, the loss to the outside of the coating system is large and it is not economical. In addition, the electrodeposition coating is usually performed at an electrodeposition coating bath temperature of 15-
It can be performed under the conditions of 35 ° C., coating voltage 50 to 250 V, and electrodeposition time 1 to 5 minutes. According to such a method for forming a matte electrodeposition coating film of the present invention, the film thickness of the coating film can be appropriately selected and adjusted within the range of 5 to 60 μm.

If necessary, wash the electrodeposition-coated object with water,
Then, by heat-curing at 140 to 200 ° C. for 10 to 60 minutes, a matte electrodeposition coating film having stable gloss and good appearance is formed.

The object to be coated which can be applied to the matte electrodeposition coating method of the present invention is not particularly limited as long as it has conductivity, but when aluminum or aluminum alloy is used as the object to be coated, smoothness is obtained. It is possible to obtain a uniform matte coating film having excellent properties such as the like, and to obtain a matte coating film having a dull appearance in which die marks and the like of an aluminum material are inconspicuous.

[0027]

[Function] Alkyl-tellated methylol melamine resin
Properties vary depending on the degree of methylolation, degree of etherification, and type of ether group, but especially in the case of electrodeposition coating, it can be applied to other coating methods, such as spray coating or coating with a roll coater, depending on the combination with the resin of the main component. In comparison, there may be a significant difference in appearance and the like.

When the highly butyl etherified specific alkyl etherified methylol melamine resin of the present invention is used as a curing agent, electrodeposition coating is performed with an electrodeposition coating containing a specific acrylic resin as a main component, and bake curing is performed. , Fine irregularities are formed on the surface of the electrodeposition coating film, and a matte coating film is obtained. Although the mechanism of generation of these fine irregularities is not always clear, since it does not occur in spray coating, etc., the water-insoluble property of the melamine resin, the reactivity caused by the deposition of the electrodeposition coating film, or the shrinkage during heat curing It is thought that this is due to distortion.

In electrodeposition coating, the concentration of the curing agent on the surface of the coating film differs from that of the curing agent resin due to the difference in water solubility between the base resin and the curing resin. It is considered to be one of the causes.

Since the method of the present invention uses the electrodeposition coating composition comprising such a composition, it can be coated at a low voltage, a thick film can be obtained by a single electrodeposition coating, and an aluminum material or the like can be applied. When used as a base, a coating film having a good matte appearance in which the die marks of the base are not noticeable and having excellent flexibility and chemical resistance can be stably formed.

[0031]

The present invention will be described in more detail with reference to the following specific examples. The following were used as the alkyl etherified methylol melamine resin which is a curing agent. -Butyl etherified methylol melamine resin BM-1: [Mycoat 506, manufactured by Mitsui Cyanamid Co., Ltd., degree of etherification about 5, ratio of butoxy groups 100]
%, Solid content 98% by weight] BM-2: [Cymel 1156, manufactured by American Cyanamid, degree of etherification about 5, butoxy group ratio 100%,
Solid content 98% by weight] BM-3: [Cymel 1158, manufactured by American Cyanamid Co., degree of etherification about 4, butoxy group ratio 100%,
Solid content 80% by weight] BM-4: [Super Beckamine G-821, manufactured by Dainippon Ink and Chemicals, Inc., degree of etherification about 2.5, butoxy group ratio 100%, solid content 60% by weight] -Butyl / Methyl etherified methylol melamine resin BM-5: [Nikalac MX-40, manufactured by Sanwa Chemical Co., Ltd., degree of etherification about 5, butoxy group ratio 30%,
Methoxy group ratio 70%, solid content 98% by weight)

Synthesis Example 1 Synthesis of acrylic resin (AR-1) 400 parts by weight of isopropyl alcohol and 200 parts by weight of butyl cellosolve were charged into a reaction vessel and the temperature was raised to 80 ° C.
(A) 80 parts by weight of acrylic acid (AA) as a carboxyl group-containing polymerizable acrylic monomer, (b) 150 parts by weight of 2-hydroxyethyl methacrylate (2HEMA) as a hydroxyl group-containing polymerizable acrylic monomer, ( c) 470 parts by weight of methyl methacrylate (MMA), 150 parts by weight of ethyl acrylate (EA) and 150 parts by weight of butyl acrylate (BA), and azobis as the ethylenically unsaturated carboxylic acid ester monomer and / or vinyl monomer A mixture of 4 parts by weight of isobutyronitrile was added dropwise over 4 hours. After 1 hour from the end of the dropping, 10 parts by weight of azobisisobutyronitrile and 50 parts of isopropyl alcohol were further added.
Part by weight of the mixture was added dropwise over 3 hours, and after addition was complete, 2 more
After stirring for a period of time to complete the polymerization, the acrylic resin solution (AR-
1) was obtained.

The resulting acrylic resin (a), (b) and
The types and blending amounts of the component (c) are shown in Table 1 together with the ratio of acid value, hydroxyl value, glass transition temperature and number average molecular weight.

Synthesis Example 2 Synthesis of acrylic resin (AR-2) 450 parts by weight of isopropyl alcohol and 150 parts by weight of butyl cellosolve were placed in a reaction vessel and the temperature was raised to 80 ° C.
50 parts by weight of acrylic acid (AA) and 50 parts by weight of methacrylic acid (MAA) as component (a), 180 parts by weight of 2-hydroxyethyl methacrylate (2HEMA) as component (b), and methyl methacrylate (as component (c) ( MMA) 37
A mixture consisting of 0 parts by weight, 50 parts by weight of styrene (ST), 200 parts by weight of ethyl acrylate (EA) and 100 parts by weight of 2-ethylhexyl acrylate (2EHA), and 3 parts by weight of azobisisobutyronitrile was added dropwise in 4 hours. did. After 1 hour from the end of the dropping, 10 parts by weight of azobisisobutyronitrile and 50 parts of isopropyl alcohol were further added.
Part by weight of the mixture was added dropwise over 3 hours, and after addition was complete, 2 more
After stirring for a period of time to complete the polymerization, the acrylic resin solution (AR-
2) was obtained.

The resulting acrylic resin (a), (b) and
The types and blending amounts of the component (c) are shown in Table 1 together with the ratio of acid value, hydroxyl value, glass transition temperature and number average molecular weight.

[0036]

Example 1 1660 parts by weight of the acrylic resin solution (AR-1) prepared in Synthesis Example 1 was mixed with butyl etherified methylol melamine resin (BM-).
1) Add 680 parts by weight, 220 parts by weight of isopropyl alcohol and 140 parts by weight of butyl cellosolve, stir at 70 ° C for 2 hours, mix, add 75 parts by weight of triethylamine to this, and further stir at 70 ° C for 1 hour. After continuing, water was gradually added and diluted to prepare an electrodeposition paint having a resin solid content concentration of 11% by weight.

This electrodeposition coating material was placed in an electrodeposition tank, and an anodized 6063S aluminum plate was used as an anode for a bath temperature of 22 ° C.
Then, a coated plate was prepared by energizing at a predetermined voltage (80 to 180 V) for 3 minutes. After completion of electrodeposition, these coated plates were washed with washing water containing 3% by weight of isopropanol and 1% by weight of butyl cellosolve, and heat-cured at 180 ° C. for 30 minutes. The performance of the obtained electrodeposition coating film was evaluated. This electrodeposition coating film had a stable matte state, and the die marks on the aluminum plate were inconspicuous. The composition of the electrodeposition coating composition is shown in Table 2 and the performance evaluation results are shown in Table 3.

Example 2 An electrodeposition coating composition was prepared in the same manner as in Example 1 except that the amount of the butyl etherified methylol melamine resin was changed to 340 parts by weight. Similar evaluation was performed. The composition of the electrodeposition paint is shown in Table 2,
The results of performance evaluation are shown in Table 3.

Example 3 An electrodeposition coating composition was prepared in the same manner as in Example 1 except that BM-2 was used instead of BM-1 as the butyl etherified methylol melamine resin.
Electrodeposition coating was carried out in the same manner as above, and the same evaluation was carried out. The composition of the electrodeposition coating composition is shown in Table 2 and the performance evaluation results are shown in Table 3.

Example 4 85 parts by weight of triethylamine was added to 1663 parts by weight of the acrylic resin solution (AR-2) of Synthesis Example 2, and the mixture was stirred at 25 ° C. for 1 hour, and then butyl etherified methylol melamine resin (B
M-3) 550 parts by weight, 220 parts by weight of isopropyl alcohol, and 140 parts by weight of butyl cellosolve were added, and the mixture was stirred at 25 ° C for 4 hours, then diluted by gradually adding water, and an electrodeposition paint having a resin solid content concentration of 11% by weight. Was prepared.

Using this electrodeposition coating composition, electrodeposition coating was carried out in the same manner as in Example 1. The performance of the obtained electrodeposition coating film was evaluated in the same manner as in Example 1. This electrodeposition coating film had a stable matte state, and the die marks on the aluminum plate were inconspicuous. The composition of the electrodeposition coating composition is shown in Table 2 and the performance evaluation results are shown in Table 3.

Example 5 An electrodeposition coating composition was prepared in the same manner as in Example 1, except that the amount of BM-1 was 544 parts by weight and 136 parts by weight of BM-5 was added. Similarly, electrodeposition coating was performed and the same evaluation was performed. The composition of the electrodeposition coating composition is shown in Table 2 and the performance evaluation results are shown in Table 3.

Comparative Example 1 In the method of Example 1, BM-5 was used instead of BM-1.
An electrodeposition coating composition was produced in the same manner as in Example 1 except that the above was used, and electrodeposition coating was performed in the same manner as in Example 1 and the same evaluation was performed.
The composition of the electrodeposition coating is shown in Table 2, and the performance evaluation results are shown in Table 3.
Shown in the table.

Comparative Example 2 85 parts by weight of triethylamine was added to 1663 parts by weight of the acrylic resin solution (AR-2) of Synthesis Example 2, stirred at 25 ° C. for 1 hour, and 900 parts by weight of BM-4 was added, and 25 ° C. After stirring for 4 hours, water was gradually added and diluted to prepare an electrodeposition coating having a resin solid content concentration of 11% by weight.

Using this electrodeposition coating composition, electrodeposition coating was carried out in the same manner as in Example 1. The performance of the obtained electrodeposition coating film was evaluated in the same manner as in Example 1. This electrodeposition coating film did not have good matte properties, had uneven gloss, and had poor paint stability. The composition of the electrodeposition coating composition is shown in Table 2 and the performance evaluation results are shown in Table 3.

Comparative Example 3 The coating material obtained in Example 1 was applied by an applicator so that a predetermined dry film thickness was obtained, and baking was performed in the same manner, instead of electrodeposition. The resulting coating had high gloss and did not become matte. The results of performance evaluation are shown in Table 3.

Comparative Example 4 An electrodeposition coating composition was prepared in the same manner as in Example 1 except that the amount of BM-1 was 136 parts by weight and 544 parts by weight of BM-5 was added. Similarly, electrodeposition coating was performed and the same evaluation was performed. The composition of the electrodeposition coating composition is shown in Table 2 and the performance evaluation results are shown in Table 3.

Table 2 Composition of coating material (parts by weight) Example 1 Example 2 Example 3 Example 4 Example 5 Acrylic resin AR-1 1660 1660 1660-1660 AR-2 --- 1663- alkyl etherified methylol Melamine resin BM-1 680 340 − − 544 BM−2 − − 680 − − BM−3 − − − 550 − BM−4 − − − − − BM-5 − − − − 136 Hydrophilic solvent Isopropyl alcohol 220 220 220 220 220 Butyl Cellosolve 140 140 140 140 140 Amines Triethylamine 75 75 75 85 75

Table 2 (continued) Composition of paint (parts by weight) Comparative Example 1 Comparative Example 2 Comparative Example 3 ^* Comparative Example 4 Acrylic resin AR-1 1660-1660 1660 AR-2-1663- alkyletherified methylol Melamine resin BM-1 − 680 136 BM-2- − − − BM-3 − − − − BM-4- 900 − − BM-5 680 − − 544 Hydrophilic solvent Isopropyl alcohol 220 − 220 220 Butyl cellosolve 140 − 140 140 Amines Triethylamine 75 85 75 75 Note) *: A composition similar to the composition of Example 1.

[0051] Table 3 film properties Example 1 Example 2 Example 3 Example 4 Example 5 Gloss ⁽¹⁾ 14 20 14 16 21 inconspicuous film appearance ⁽²⁾ None None None None None gloss unevenness die marks Inconspicuous Inconspicuous Inconspicuous Inconspicuous Hardness ⁽³⁾ 4H 4H 4H 4-5 4H 4H Alkali resistance ⁽⁴⁾ No abnormality No abnormality No abnormality No abnormality No abnormality No acid resistance ⁽⁵⁾ No abnormality No abnormality Abnormal nothing Abnormal None Absorption Properties ⁽⁶⁾ 100/100 100/100 100/100 100/100 100/100 Flexible ⁽⁷⁾ Good Good Good Good Good Good Thick coatability ⁽⁸⁾ Good Good Good Good Good Good

Table 3 (continued) Coating film characteristics Comparative example 1 Comparative example 2 Comparative example 3 Comparative example 4 Gloss ⁽¹⁾ 87 70 90 80 Appearance of coating ⁽²⁾ No gloss unevenness Yes Yes No No Dice mark Conspicuous Conspicuous Conspicuous hardness ⁽³⁾ 4H 4H 4H 4H Alkali resistance ⁽⁴⁾ No abnormality No abnormality No abnormality No abnormality Abnormality Acid resistance ⁽⁵⁾ No abnormality No abnormality No abnormality No abnormality Adhesion ⁽⁶⁾ 100/100 100/100 100/100 100 / 100 Flexibility ⁽⁷⁾ Good Good Good Good Thick coatability ⁽⁸⁾ Good Good- ^* Good Note) *: Not a coating film by electrodeposition coating, so it was not evaluated.

Evaluation Method and Evaluation Criteria (1) Gloss: The degree of gloss by 60 ° specular reflection is JIS K 5400.
It was measured according to 7.6. (2) Appearance of coating film: The surface of the electrodeposition coating film after baking was visually observed to evaluate whether or not there was uneven gloss and whether or not the die marks were conspicuous. (3) Hardness: The coating film after baking is gradually cooled to 20 ° C, and then JIS K 54
A pencil scratch test was performed according to 00 8.4. The hardness of a coating film is expressed by the hardness of a pencil with scratches. (4) Alkali resistance: Using a 1% aqueous sodium hydroxide solution, the presence or absence of the above on the coating film surface was observed after a 24-hour spot test (temperature 23 ° C). (5) Acid resistance: Using a 5% sulfuric acid aqueous solution, the presence or absence of the above on the coating film surface was observed after a 24-hour spot test (temperature 23 ° C.). (6) Adhesion: 1 × 10 mm 10-inch goggles eye test (JIS
K 5400 compliant), and adhere to the aluminum substrate,
Displayed by the number that does not peel / 100 (7) Flexibility: A coating film scratch test was conducted using an iron claw (manufactured by Okada Kogyo Co., Ltd.), and those with no scratch were evaluated as good, and those with scratch were evaluated as poor. (8) Thick coatability: 20μ by measuring the film thickness at a predetermined coating voltage.
A film having a film thickness of m or more and having no abnormal appearance is evaluated as good, and any other film is evaluated as bad.

As is clear from Table 3, the coating films of Examples 1 to 5 prepared by the method of the present invention had a good matte surface, and the die marks of the aluminum material were not noticeable. On the other hand, the coating films prepared by the methods of Comparative Examples 1 to 4 are
The degree of matting was not sufficient (the gloss value was large), and uneven gloss, die marks, etc. were conspicuous.
In particular, the coating film of Comparative Example 3, which was coated with the same composition as in Example 1 using an applicator, did not have a sufficient degree of matting and the die marks were noticeable.

[0055]

As described above in detail, in the method for forming a matte electrodeposition coating film of the present invention, an acrylic resin having a specific acid value and hydroxyl value has a high degree of etherification and a butoxy group of the ether group. A mixture of a specific alkyl-tellated methylol melamine resin with a high proportion of groups is used as a curing agent to dilute the composition to form an electrodeposition paint, which enables coating at low voltage and a thick film with a single electrodeposition coating. Stable formation of a coating film that is obtained and has a good matte appearance, in which the underlying die marks are not conspicuous when an aluminum material or the like is used as the base, and which has excellent flexibility and chemical resistance. You can

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yukihiro Hara 2-1, Chikusaigan, Ichihara-shi, Chiba Toray Co., Ltd. Chiba factory (72) Inventor Yukihiko Nishitani 4-1-115 Minamishinagawa, Shinagawa-ku, Tokyo Japan Paint Co., Ltd. Tokyo office (72) Inventor Masatoshi Ono 4-15 Minami-Shinagawa, Shinagawa-ku, Tokyo Japan Paint Co., Ltd. Tokyo office

Claims (1)

[Claims] 1. A method for forming a matte coating film by electrodeposition from an aqueous coating composition obtained by diluting a matte electrodeposition coating composition, wherein the matte electrodeposition coating composition comprises (I) acid value. But
Acrylic resin with 20-150 and hydroxyl value of 30-150, and
(II) contains a substantially water-insoluble alkyl etherified methylol melamine resin having an average of 3.5 or more ether groups per melamine nucleus, and 70 to 100% of the ether groups are butoxy groups. A method for forming a matte electrodeposition coating film, wherein the weight ratio of (I) and (II) is 40/60 to 80/20.