JPH0621238B2 - Method for producing acrylic cationic electrodeposition coating - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a novel acrylic cation-type electrodeposition coating composition, and in particular, to a coating surface having excellent properties such as solvent resistance on the coated surface of an object to be coated. The present invention relates to a method for producing an acrylic cationic type electrodeposition coating composition that can be formed.

(Prior art and its problems) As is well known, electrodeposition coating involves putting a water-soluble paint or a water-dispersible paint in a paint bath, dipping a metallic object to be coated, and coating the object. There is a method of forming a coating film on the surface of an object to be coated by electroplating by passing a direct current with one of the tank and the electrode of the bath as an anode and the other as a cathode. The case in which such an article to be coated is an anode is called an anion type, and the case in which it is a cathode is called a cation type. Even the paint used for such electrodeposition coating exists as ions in the paint bath, and is called an anionic paint or a cationic paint depending on the kind of the ions.

By the way, various types of electrodeposition paints in such electrodeposition coatings have been developed so far, for example, as one-coat finish electrodeposition paints, as of now,
Anion-type electrodeposition paint mainly composed of acrylic resin paint is used. However, in this method, since the object to be coated becomes an anode, there is a problem that the material (object to be coated) elutes due to an electrode reaction, which causes deterioration of appearance and deterioration of corrosion resistance.
In the field of anti-corrosion coating such as unpainted automobile body, anion type is changing to cation type. Thus, in this field, since the main purpose is rust prevention, epoxy resin with poor weather resistance is mainly used as the basic resin, and therefore it can be used for one-coat finish. Therefore, it is desired to develop an acrylic cation resin coating which can be used for one-coat finish.

However, conventionally, as the acrylic cationic electrodeposition coating composition, a copolymer containing an acrylic monomer having an amino group as a main component is used, and a melamine resin as a curing agent,
Electrodeposition coatings containing block isocyanate resins, etc. have been developed. In this electrodeposition coating, the presence of alkalis due to amino groups remaining in the coating film and acrylic copolymer Due to its poor reactivity with the curing agent itself, sufficient crosslinking could not be obtained, and the properties such as solvent resistance were poor, and it was not always possible to meet various required properties.

(Solution) Here, the present invention has been made in view of such circumstances, and is not inferior to a conventional anion-type acrylic electrodeposition coating composition, and has a higher coating performance. It is an object of the present invention to provide a method for producing a novel acrylic cationic electrodeposition coating composition which can be provided, and therefore, (a) the following structural formula: (However, R ₁ is a hydrogen atom or a methyl group, R ₂ and R ₃ are each an alkyl group having 1 to 4 carbon atoms, and R _2
4 is a hydrogen atom, an alkyl group, a hydroxyalkyl group, a cycloalkyl group, an aryl group, an aralkyl group or an alkaryl group), and an ethylenically unsaturated monomer having an amine imide group represented by (b) an amino group. An ethylenically unsaturated monomer and (c) one or two of hydroxyalkyl or amide or amide derivative of acrylic acid or methacrylic acid
At least one α, β-ethylenically unsaturated monomer selected from the group consisting of (d) alkyl esters of acrylic acid and methacrylic acid and aromatic vinyl monomers in a water-soluble organic solvent. A vinyl-based copolymer obtained by polymerization, or a vinyl-based copolymer blended with a non-yellowing modified block isocyanate compound, or if necessary, the vinyl-based copolymer and / or yellow-free modified An organic acid and / or a mineral acid is added to a mixture of a curing agent that reacts with a blocked isocyanate compound to cure, and the vinyl copolymer is neutralized to be water-soluble or water-dispersible. I have done so.

In the present invention, an ethylenically unsaturated monomer (a component) having an amine imide group represented by the above structural formula is used, and this is copolymerized with a predetermined acrylic vinyl monomer (b to d components). The vinyl copolymer thus obtained is characterized in that it is used as a main resin of an electrodeposition coating composition, and such a copolymer has a predetermined amine imide group in its side chain. And, this amine imide group, when the coating material adhered to the surface of the object to be coated is heated and baked to form the target coating film,
As shown by the following formula, isocyanate and amine are produced, And the isocyanate group hanging from the main chain of the copolymer, a hydroxyl group or an amide group present in the copolymer, other hydroxyl compounds, amine compounds,
By reacting with a compound having active hydrogen such as an amide compound to cause cross-linking, durability properties such as solvent resistance of the formed coating film can be effectively improved.

Incidentally, the ethylenically unsaturated monomer (a component) having an amine imide group represented by the above structural formula used in the present invention is addition-polymerized as disclosed in Japanese Patent Publication No. 46-34686. Possible unsaturated compounds, generally, R ₄ in the above structural formula is a hydrogen atom, a phenyl group, or an alkyl group, particularly lower (C ₁
-C ₄₎ so that the compound is an alkyl group it is suitably used. More specifically, in addition to dimethyl-2-hydroxypropylamine methacrylimide and dimethyl- (2-hydroxy-3-butoxypropyl) amine methacrylimide, dimethyl-1,2-dihydroxypropylamine methacrylimide and dimethyl-2- Hydroxy-1
-Phenylpropylamine methacrylimide, dimethyl-2-hydroxy-1-cyclohexylpropylamine methacrylimide and the like. As described above, the (a) component monomer having an amine imide group functions as a curing component in the electrodeposition coating composition, and is generally 10
It will be used in a copolymerization amount of ˜40% by weight. If the copolymerization amount is lower than 10% by weight, the crosslink density may be low and the solvent resistance of the electrodeposition coating film may be deteriorated. On the other hand, if the copolymerization amount exceeds 40% by weight. In that case, the balance with the OH value is lost, and problems such as a decrease in boiling water resistance of the coating film occur.

Further, the ethylenically unsaturated monomer having an amine group as the component (b) monomer is an essential component for ensuring the water dispersion performance of the obtained copolymer, and generally,
Copolymerization will occur at a ratio of 3 to 15% by weight. If the copolymerization amount is lower than 3% by weight, the water dispersibility becomes poor, and problems such as deterioration of bath stability and deterioration of the appearance of the coating film occur.
If the amount of copolymerization exceeds the range, problems such as deterioration of acid resistance of the coating film occur. Examples of such an ethylenically unsaturated monomer having an amino group include dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylate, dimethylaminopropyl acrylate, dimethylaminopropyl methacrylate, etc. There is.

Furthermore, the hydroxyalkyl or amide or amide derivative of acrylic acid or methacrylic acid, which is the component (c) component monomer according to the present invention, functions as a curing component, and partly plays a role of imparting water dispersibility. 2-hydroxyethyl acrylate, hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 3-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate, diethylene glycol monoacrylate and methacrylate, acrylamide, methylol acrylamide , Methacrylamide, methylol methacrylamide,
Alkoxymethylol acrylamide, alkoxymethylol methacrylamide, diacetone acrylamide,
One kind or two or more kinds such as diacetone methacrylamide will be used. The copolymerization amount of the component (c) monomer is generally about 10 to 40% by weight, and if the copolymerization ratio is too low, the water dispersibility of the coating composition may decrease or the coating film If the copolymerization ratio exceeds 40% by weight, problems such as deterioration of appearance and solvent resistance may occur, and problems such as deterioration of alkali resistance may occur.

Further, the (a) component monomer, the (b) component monomer and the (c) component monomer are copolymerized, and as the fourth component (d) component monomer, an alkyl ester of acrylic acid and methacrylic acid and an aromatic compound. At least one α, β- selected from the group consisting of vinyl monomers
It is an ethylenically unsaturated monomer, and these monomers harden the formed coating film and improve its chemical resistance performance such as salt water resistance. Then, the component (d) will be copolymerized in a proportion such that the total amount becomes 100% in addition to the proportions of the (a), (b) and (c) component monomers used. However, in general, the copolymerization ratio is about 40 to 80% by weight, preferably 50 to 70% by weight.
If the copolymerization ratio of the component (d) is too low, the chemical resistance of the coating film will be deteriorated, while if the copolymerization ratio is too high, the adhesion and impact resistance of the coating film will be reduced. However, problems such as deterioration of weather resistance will occur. Particularly, as the component (d) monomer,
It is desirable to select to include at least an aromatic vinyl monomer, in which case such an aromatic vinyl monomer will be used in the range of 5 to 30% by weight.

Examples of the alkyl ester of acrylic acid and methacrylic acid as the component (d) monomer include methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, methacrylic acid. There are ethyl, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-hexyl methacrylate, lauryl methacrylate and the like, and aromatic vinyl monomers include styrene and vinyltoluene.

Further, such a copolymer composed of the component monomers (a) to (d) is used to form a predetermined electrodeposition coating composition having an appropriate molecular weight, but generally, the weight average molecular weight thereof is 5,000 to 5,000. A material of about 60,000 is preferably used. When the weight average molecular weight is lower than 5,000, solvent resistance, boiling water resistance and other performances are deteriorated and the water dispersibility of the curing agent is deteriorated.
If it has a weight average molecular weight of more than 000, uniform electrodeposition property is deteriorated, which causes problems such as deterioration of gloss and rough skin.

Then, in the copolymerization of such component monomers (a) to (d), as a polymerization medium, a water-soluble organic solvent such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol, t-butanol, furfuryl alcohol. , Tetrahydrofurfuryl alcohol, dioxane, tetrahydrofuran, methyl lactate, ethyl lactate, γ-butyrolactone, ethylene glycol and its monoether (cellosolve), diethylene glycol and its monoether, triethylene glycol,
There are propylene glycol, dimethylformamide, dimethylacetamide, sulfolane, dimethyl sulfoxide, etc., and in such a water-soluble organic solvent, a suitable radical polymerization catalyst (addition polymerization catalyst) such as azobisisobutyronitrile, benzoyl peroxide, Copolymerization is allowed to proceed in the presence. The copolymerization is generally carried out at a temperature of 0 to 150 ° C, preferably 30 to 100 ° C.
It will be carried out for 0 minutes to 24 hours, preferably for 30 minutes to 6 hours.

The solution of the vinyl-based copolymer comprising the components (a) to (d) thus obtained is blended with a suitable non-yellowing modified block isocyanate compound, or is not blended, An acid and / or a mineral acid is added to neutralize such a vinyl-based copolymer, thereby making it water-soluble or water-dispersible in the form of a neutralized salt. Thus, the electro-deposition paint is formed.

The non-yellowing modified block isocyanate compound to be blended with the vinyl copolymer is generally used as a cross-linking agent, and in the present invention, it can be blended as necessary, , About 5 to 40% by weight in the total solid content after blending, preferably 1
It is mixed in a ratio of about 5 to 30% by weight. If the amount of the yellow-free modified isocyanate compound is too large, it becomes difficult to make it water-soluble. The non-yellowing modified blocked isocyanate compound is preferably an aliphatic or cycloaliphatic isocyanate compound having two or more isocyanate groups, such as hexamethylene diisocyanate, lysine diisocyanate, 4,4′-methylenebis (cyclohexyl isocyanate). , Methylcyclohexane-2,4 (2,6)-
Diisocyanate, 1,3- (isocyanatomethyl)
Compounds such as cyclohexane, isophorone diisocyanate, trimethylhexamethylene diisocyanate and dimer acid diisocyanate, whose isocyanate groups are substantially all blocked with a suitable blocking agent such as monohydric alcohol.

Further, in producing the acrylic cation type electrodeposition coating composition according to the present invention as described above, a curing agent which reacts with the vinyl copolymer and / or the yellow-free modified blocked isocyanate compound to cure them, if necessary. Is blended. As the compounding amount of the curing agent, a ratio of about 10 to 30% by weight in the total solid content after compounding is generally used. As the curing agent, specifically, an amine compound containing two or more amino groups having activated hydrogen, a polyamine resin, an acrylic type, an epoxy type, an alkyd type, a polyester type or a polyol type hydroxyl group is used. There are known polyol resins contained.

Furthermore, the acrylic cation-type electrodeposition coating material according to the present invention contains ethylene alcohols, diethylene monoalkyl ethers, aliphatic alcohols, acetic acid esters, and ketones as auxiliary solvents that help water-solubilize the coating components, if necessary. In some cases, a water-soluble solvent such as is added and compounded.

(Effect of the invention) The acrylic cation-type electrodeposition coating composition obtained according to the method of the present invention as described above has excellent coating film performance, good transparency of the coating film, and further, the coating film turns yellow during baking, It gives a coating film which is not colored and is excellent in durability such as weather resistance, and can be suitably applied to coating of various conductive materials.

(Examples) Some examples of the present invention will be shown below to clarify the present invention in more detail, but it goes without saying that the present invention is not limited by the description of the examples. It's a place. Further, it should be understood that the present invention can be implemented in various forms other than the combinations and techniques illustrated in such embodiments. The parts and percentages in the examples are
Unless otherwise specified, all are indicated by weight.

Example 1 10 parts of butyl cellosolve and 40 parts of isopropanol were placed in a reactor equipped with a stirrer, a condenser, a dropping funnel and a thermometer.
While stirring, the mixture was added dropwise from a dropping funnel at a reflux temperature of about 85 ° C. with stirring.

Dimethylaminoethyl methacrylate 5 (part) dimethyl-2-hydroxypropyl amine methacrylimide 15 2-hydroxyethyl acrylate 20 n-butyl acrylate 20 styrene 15 2-ethylhexyl acrylate 5 methyl methacrylate 20 azobisisobutyronitrile 1 After the addition of the above mixture was completed, the reaction was continued for 3 hours at the reflux temperature as it was to obtain a desired acrylic copolymer solution (nonvolatile component: 66.7%).

Then, 1 of the acrylic copolymer solution thus obtained
To 56 parts, 4 ml of 1N-hydrochloric acid and 0.8 part of acetic acid were added, respectively, and the mixture was stirred for about 1 hour to neutralize it, and then 839 parts of ion-exchanged water was added thereto to obtain a cationic electrodeposition coating composition having a nonvolatile content of 10%. Obtained. The pH of the obtained cationic electrodeposition coating composition was 5.4.

Comparative Example 1 In Example 1 above, 15 parts of dimethyl-2-hydroxypropylamine methacrylimide was not added, and instead of this, 10 parts of dimethylaminoethyl methacrylate,
Copolymerization was carried out according to Example 1 using 30 parts of methyl methacrylate, further neutralized with hydrochloric acid and acetic acid, and then ion-exchanged water was added to prepare a cationic electrodeposition coating composition having a nonvolatile content of 10%.

Example 2 10 parts of butyl cellosolve and 40 parts of isopropanol were placed in a reactor equipped with a stirrer, a condenser, a dropping funnel and a thermometer.
And a mixture having the following formulation was continuously added dropwise from a dropping funnel over 3 hours at a reflux temperature of about 85 ° C. with stirring.

Dimethylaminoethyl methacrylate 10
(Part) dimethyl- (2-hydroxy-3-butoxypropyl) amine methacrylimide
25 2-Hydroxyethyl acrylate 15 n-Butyl acrylate 15 2-Ethylhexyl acrylate 5 Styrene 15 Methyl methacrylate 15 Azobisisobutyronitrile 1 After the addition of the compounded mixture was completed, the reaction was continued for 3 hours at the reflux temperature. Then, the desired acrylic copolymer solution (nonvolatile component: 66.7%) was obtained.

Then, the acrylic copolymer solution 15 thus obtained
After adding 2 parts of acetic acid to 6 parts and stirring for about 1 hour to neutralize, 842 parts of ion-exchanged water was added thereto to obtain a cationic electrodeposition coating composition having a nonvolatile content of 10%. The pH of the obtained cationic electrodeposition coating composition was 6.5.

Comparative Example 2 In the above Example 2, dimethyl- (2-hydroxy-
Without adding 25 parts of 3-butoxypropyl) amine methacrylimide, the amount of methyl methacrylate was increased to 40 parts and the copolymerization was carried out according to the method of Example 2 to prepare the target acrylic copolymer solution. Further, the same operation as in Example 2 was performed on this solution to obtain a cationic electrodeposition coating having a nonvolatile content of 10%.

Example 3 To 156 parts of the acrylic copolymer solution in Example 1,
Block isophorone diisocyanate (Block IPD
I) 33 parts, 10 parts of methyl isobutyl ketone and 23 parts of isopropanol were added, 6 ml of 1N-hydrochloric acid and 1 part of acetic acid were further added, and after neutralization by stirring for about 1 hour, 1101 parts of ion-exchanged water was added. Non-volatile component 1
A 0% cationic electrodeposition coating was obtained. The pH of the obtained cationic electrodeposition coating composition was 5.5.

Comparative Example 3 A predetermined cationic electrodeposition coating composition was produced in the same manner as in Example 3 except that the acrylic copolymer solution obtained in Comparative Example 1 was used.

Example 4 10 parts of a fatty acid-modified polyester (OH value = 90) was added to 156 parts of the acrylic copolymer solution obtained in Example 1.
Xylol (6 parts) and butyl cellosolve (10 parts) were further added, 1N-hydrochloric acid (6 ml) and acetic acid (1 part) were added, and the mixture was stirred for about 1 hour for neutralization, and then 912 parts of ion-exchanged water were added to remove non-volatile components. A 10% cationic electrodeposition coating was obtained. The pH of the obtained cationic electrodeposition coating composition was 5.3.

Comparative Example 4 A predetermined cationic electrodeposition coating composition was obtained in the same manner as in Example 4 except that the acrylic copolymer solution obtained in Comparative Example 1 was used.

Performance test 16 Using a steel plate of 16 cm × 10 cm, each of the paints prepared in Example 1 and Comparative Example 1 was subjected to cathodic electrodeposition coating, followed by washing with water, further draining with air spray, and then drying. , Baked. In addition, as electrodeposition conditions, voltage: 30 V, time: 1 minute, bath temperature: 22 ° C.,
Anode: carbon plate, distance between electrodes: 10 cm, and baking conditions were 175 ° C. × 25 minutes in a hot air drying oven.

The appearances after baking were both smooth, and no abnormalities were found in the coating film.

Performance Test 2 In the coating materials prepared in Example 2 and Comparative Example 2 using a 6 cm × 10 cm brass plate, cathodic electrodeposition coating was performed, followed by washing with water, draining, and baking.
The electrodeposition conditions are: voltage: 40 V, time: 1 minute,
A bath temperature of 25 ° C. and a distance between the electrodes of 15 cm were adopted, and a baking condition of 175 ° C. × 30 minutes was adopted.

Performance test 36 In a coating material prepared in Example 3 and Comparative Example 3 using a 6 cm × 10 cm brass plate, cathodic electrodeposition coating was performed, followed by washing with water and draining, followed by predetermined baking. The electrodeposition conditions and baking conditions were the same as those in Performance Test 1. The baked coating films both had a good appearance.

Performance test 4 Using a commercially available Bonderite steel plate of 7 cm × 15 cm, after degreasing and washing with water, cathodic electrocoating was carried out in each of the paints prepared in Example 4 and Comparative Example 4, followed by washing with water and draining. After that, predetermined baking was performed. In addition,
The electrodeposition conditions and baking conditions were the same as those in Performance Test 1.

For each of the coated plates obtained in the above performance tests 1 to 4, a pencil hardness test (JIS-K-540) was conducted.
0), an eye peel test (JIS-K-5400), an acetone immersion test (reagent first-grade acetone at 25 ° C x 48).
Time immersion), boiling water test (distilled water, 100 ° C. × 2 hours immersion), salt spray test (JIS-H-8617) 72 hours, Cass test (JIS-H-8617) 48 hours, and the results are The results are shown in Table 1 below.

As is clear from the results shown in Table 1, it is understood that the coating films obtained by using the acrylic cation type electrodeposition coating composition according to the present invention all have excellent coating film performance.

Claims (5)

[Claims] 1. (a) The following structural formula: (However, R ₁ is a hydrogen atom or a methyl group, R ₂ and R ₃ are each an alkyl group having 1 to 4 carbon atoms, and R _2
4 is a hydrogen atom, an alkyl group, a hydroxyalkyl group, a cycloalkyl group, an aryl group, an aralkyl group or an alkaryl group), and an ethylenically unsaturated monomer having an amine imide group represented by (b) an amino group. An ethylenically unsaturated monomer and (c) one or two of hydroxyalkyl or amide or amide derivative of acrylic acid or methacrylic acid
At least one α, β-ethylenically unsaturated monomer selected from the group consisting of (d) alkyl esters of acrylic acid and methacrylic acid and aromatic vinyl monomers in a water-soluble organic solvent. The vinyl-based copolymer obtained by polymerization, or the vinyl-based copolymer blended with a non-yellowing modified block isocyanate compound, or if necessary, the vinyl-based copolymer and / or non-yellowing modified An organic acid and / or a mineral acid is added to a mixture of a curing agent that reacts with a blocked isocyanate compound to cure, and the vinyl copolymer is neutralized to be water-soluble or water-dispersible. A method for producing an acrylic cation-type electrodeposition coating composition, which comprises: 2. The vinyl-based copolymer comprises 10 to 40% by weight of the component (a), 3 to 15% by weight of the component (b), and 10 to 10% of the component (c). 40
The production method according to claim 1, wherein the weight-average molecular weight is 5,000 to 60,000, and the balance is a copolymer containing the component (d) monomer. 3. The non-yellowing blocked isocyanate compound is an aliphatic or cycloaliphatic isocyanate compound having two or more isocyanate groups, and the isocyanate groups are substantially all blocked by a blocking agent. The manufacturing method according to claim 1 or 2. 4. The curing agent is an acrylic type, an epoxy type,
The method according to any one of claims 1 to 3, which is an alkyd-based, polyester-based, or polyol-based polyol resin containing a hydroxyl group. 5. The method according to any one of claims 1 to 4, wherein the curing agent is an amine or polyamine compound having activated hydrogen.