JPS624429B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a replenishment paint for electrodeposition coating. To explain in detail, among the coating film forming components, α,
Stable aqueous emulsion type electrodeposition made by adjusting the number of moles of the basic compound to be neutralized (hereinafter referred to as degree of neutralization) to 0.2 moles or less per mole of carboxyl group of β-ethylenically unsaturated polycarboxylic acid resin The present invention relates to a method for producing replenishment paint for painting. Paints used for electrodeposition generally use polycarboxylic acid resins and crosslinking resins containing carboxyl groups in their molecules as film-forming components, and the carboxyl groups are partially neutralized with a basic compound. It is water-dispersed. It is well known that when electrodeposition coating is performed using such an electrodeposition paint, basic compounds accumulate in the paint bath, making it impossible to achieve uniform coating. In order to eliminate such drawbacks, various methods have been implemented in the past. For example, (1) cation exchange treatment of electrodeposition paint containing an excess of basic compounds,
Method of removing basic compounds. (2) In order to replenish the resin solid content of the electrodeposition paint, which is gradually decreasing, a method of adding a replenishment paint with a higher resin solid content and a lower amount of basic compounds than the composition of the electrodeposition paint bath, or a combination of both. methods etc. are being implemented. However, in order to carry out the cation exchange resin treatment in (1), operations such as regenerating, washing, and replacing the cation exchange resin are required, which results in poor work efficiency, and it is difficult to reduce or eliminate the number of cation exchange treatments as much as possible. This has become an issue. On the other hand, the method (2) of adding replenishment paint with a low degree of neutralization to the electrodeposition bath has the advantage of improving on-site work efficiency without requiring the complicated operations of (1), and has been widely used in recent years. has been done. Furthermore, since the basic compounds accumulated in the electrodeposition paint bath are effectively utilized without being removed, it is an advantageous method that also leads to cost reduction. There are two types of replenishment paints with a low degree of neutralization: solvent-based paints and emulsion-based paints. Solvent-based paints can produce stable paints even with very low amine molar ratios, but electrodeposition paints When added to a bath, it is difficult to dissolve and requires a step of forcibly mixing and stirring using a disperser or other means. Furthermore, since solvent-based paints require a large amount of organic solvent, they also increase costs. On the other hand, emulsion-type paints are easily dispersed in an electrocoating paint bath, so there is no need to install a special dispersion machine, and they require only a small amount of organic solvent, making them inexpensive and economical. However, emulsion-type paints have a limit in maintaining a stable state by reducing the amine molar ratio. That is, when the amine molar ratio is reduced to about 0.3, stability begins to deteriorate, and when the amine molar ratio is less than 0.25, there is a problem that gelation or separation of the paint occurs, so that it has not been put into practical use yet. In view of the above points, the present inventors set out to obtain an emulsion-type replenishment paint that is stable even when the amine molar ratio is reduced, and as a result of repeated research, they first developed an emulsion type paint that is stable and has a low amine molar ratio (approximately 0.3). By preparing a mold coating and further subjecting it to cation exchange treatment, we were able to do something that was beyond conventional wisdom. It was discovered that a stable replenishment paint that does not cause gelation or separation can be obtained even in the region of extremely low amine molar ratios, and the present invention was completed. To outline the present invention, the coating film forming components are (a) α, β
-Ethylenically unsaturated polycarboxylic acid resin and (b) alkoxylated methylol melamine, partially neutralized with a basic compound and dispersed in water so that the amount is 0.25 mol or more per 1 mol of carboxyl group of component (a). This is a method for producing a replenishing paint for electrodeposition coating, which comprises subjecting a stable aqueous emulsion obtained by cation exchange treatment to reduce the amine molar ratio to 0.2 or less. The reason why the aqueous emulsion type replenishing paint obtained by the present invention is stable even in the extremely low amine ratio region of 0.2 or less is that in the manufacturing process, first, a stable aqueous emulsion with a relatively higher amine molar ratio than the desired amine molar ratio is used. To adjust the emulsion,
This is presumed to be because the initially formed emulsion particles are strong and will not be destroyed even if the amine molar ratio is reduced to an extremely low amine molar ratio by cation exchange treatment. To explain the present invention in more detail, the replenishment paint for electrodeposition uses a resin composition of an α,β-ethylenically unsaturated polycarboxylic acid resin and an alkoxylated methylol melamine as a film-forming component. The α,β-ethylenically unsaturated polycarboxylic acid resin includes (a) α,β-ethylenically unsaturated carboxylic acid 3-
30% by weight, (b) 5-30% by weight of a hydroxyalkyl-containing ester or amide or amide derivative of α,β-ethylenically unsaturated carboxylic acid, (c) α,β-
Alkyl esters of ethylenically unsaturated carboxylic acids
30-80% by weight, (d) other copolymerizable monomers 0-20
It is obtained by reacting a monomer composition blended so that the total amount is 100% by weight, and preferably has an acid value of 10 to 200. Suitable (a) α,β-ethylenically unsaturated carboxylic acids include acrylic acid, α-chloroacrylic acid,
Methacrylic acid, itaconic acid, maleic anhydride, maleic acid, fumaric acid, crotonic acid, citraconic acid, mesaconic acid, etc. alone or in mixtures, or their functional derivatives having at least one carboxyl group, such as unsaturated polymerizable Partial esters or amides of di- or poly-carboxylic acids. Next, (b) hydroxyalkyl-containing esters or amides or amide derivatives of α,β-ethylenically unsaturated carboxylic acids include 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate,
2-hydroxypropyl methacrylate, 3-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate, diethylene glycol monoacrylate, diethylene glycol monomethacrylate, acrylamide, methacrylamide, methylol, acrylamide, methylolmethacrylamide, alkoxymethylol acrylamide,
Examples include alkoxymethylol methacrylamide, diacetone acrylamide, and diacetone methacrylamide. (c) Examples of alkyl esters of α,β-ethylenically unsaturated carboxylic acids include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-propyl acrylate, n-propyl methacrylate, isopropyl acrylate, isopropyl methacrylate,
Butyl acrylate, butyl methacrylate, lauryl methacrylate, lauryl methacrylate, stearyl acrylate, stearyl methacrylate, hexyl acrylate, 2-ethylhexyl methacrylate, heptyl acrylate,
Similar esters having up to about 20 carbon atoms in the alkyl group can be used, such as heptyl methacrylate. (d) Other copolymerizable monomers include styrene, α-alkylstyrene, α-chlorostyrene, vinyltoluene, acrylonitrile, vinyl acetate, and the like. On the other hand, the alkoxylated methylol melamine may be one in which at least a portion of the methylol group is alkoxylated with a lower alcohol. As the lower alcohol, one or more of methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol, etc. is used. The above α in the replenishment paint for electrodeposition coating of the present invention,
The composition ratio of β-ethylenically unsaturated polycarboxylic acid resin and alkoxylated methylolmelamine is as follows:
α,β-ethylenically unsaturated polycarboxylic acid resin 5
~95 parts by weight, alkoxylated methylolmelamine
It can be used in a range of 95 to 5 parts by weight. In the present invention, a replenishment paint for electrodeposition coating is manufactured by the method shown below. First, a stable aqueous emulsion containing (a) an α,β-ethylenically unsaturated polycarboxylic acid resin and (b) an alkoxylated methylolmelamine is prepared. A suitable monomer composition for producing component (a) is charged together with an organic solvent into a reaction vessel equipped with a stirrer, a thermometer, and a reflux condenser, and the reaction is carried out at reflux temperature for 2 to 5 hours. After the reaction was completed, the mixture was cooled to 50 to 80°C, the alkoxylated methylolmelamine and basic compound (component (b)) were added, and after stirring for 1 hour, deionized water was gradually added to form an emulsion.
Prepare a stable aqueous emulsion. Examples of organic solvents include methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butanol, isobutanol,
Alcohols such as sec-butanol, t-butanol, pentanol, etc., cellosolves such as methyl cellosolve, ethyl cellosolve, isopropyl cellosolve, butyl cellosolve, sec-butyl cellosolve, etc. are used. Basic compounds include ammonia, monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, monoisopropylamine, diisopropylamine, triisopropylamine, monobutylamine, dibutylamine, alkylamines such as tributylamine, and monoethanol. amine,
Diethanolamine, triethanolamine, mono(2-hydroxypropyl)amine, di(2-
Examples include alkanolamines such as hydroxypropyl)amine, tri(2-hydroxypropyl)amine, dimethylaminoethanol, and diethylaminoethanol, and alkylene polyamines such as ethylenediamine, propylenediamine, diethylenetriamine, and triethylenetetramine. The higher the resin solid content of this aqueous emulsion, the more convenient it is to use as a refill paint, but it is necessary to select a concentration that is stable even after the subsequent cation exchange treatment. According to experiments by the inventors, the resin solid content was 40
It was confirmed that when the amount exceeds the weight percentage, stable cation exchange treatment is not performed and gelation tends to occur. In the present invention, the stable aqueous emulsion prepared as described above is treated with a cation exchange resin. As for the type of cation exchange resin (to be used), either a strong acid type or a weak acid type can be used. It was confirmed that the passing rate of the aqueous emulsion in the cation exchange treatment has a correlation with the amine molar ratio of the emulsion after the treatment, and that the slower the passing rate, the lower the amine molar ratio. The preferred liquid passing rate in the present invention is SV=5 to 250
is within the range of When the SV is less than 5, the amine molar ratio decreases too much and the aqueous emulsion becomes unstable.
On the other hand, if it is larger than 250, the effect of lowering the amine molar ratio is small and it is difficult to adjust the amine molar ratio to the desired value, which is not preferred in the present invention. It was confirmed that by repeating this cation exchange resin treatment, the amine molar ratio decreased depending on the number of times. By the method described above, we have succeeded in producing an aqueous emulsion with a high solids content that is stable even at an extremely low amine molar ratio of 0.2 or less, which could not be obtained using conventional methods. If this water-based emulsion is used as a replenishment paint for electrodeposition coating, it has the excellent effect of efficiently consuming the basic compounds that accumulate in the electrodeposition bath, and thus greatly reducing the number of cation exchange resin treatments. shows. Examples are shown below to explain the present invention in more detail. However, the present invention is not limited thereto. Parts mean parts by weight. Example 1 8 parts of acrylic acid, 15 parts of 2-hydroxyethyl acrylate, 10 parts of styrene, 20 parts of 2-ethylhexyl acrylate, and 47 parts of methyl methacrylate were placed in a reaction vessel equipped with a stirrer, a thermometer, and a reflux condenser.
1.5 parts of azobisisobutyronitrile, 10 parts of ethylene glycol monobutyl ether, and 30 parts of isopropyl alcohol.
℃) for 5 hours, and α,β-ethylenically unsaturated polycarboxylic acid resin solution (acid value 62KOH
mg/g solid) was prepared. Next, this was cooled to 65°C, and 30 parts of alkoxylated methylolmelamine (trade name MX-40, manufactured by Sanwa Chemical Co., Ltd.) and 3 parts of dimethylaminoethanol were added.
After stirring for 1 hour, 250 parts of pure water was gradually added to prepare an aqueous emulsion type stock solution-1 having a resin solid content of 30% by weight and an amine molar ratio of 0.3. The aqueous emulsion type stock solution-1 was mixed with H-type weakly acidic cation exchange resin (trade name Imac Z-5 Netherlands).
Space velocity SV=
When the solution was passed through the solution at a concentration of 20, an aqueous emulsion type stock solution-2 with an amine molar ratio of 0.12 was obtained. Example 2 In the method of Example 1, an H-type strongly acidic cation exchange resin (trade name SK-1A manufactured by Mitsubishi Chemical Industries, Ltd.) was used instead of the H-type weakly acidic cation exchange resin, and SV-
As a result of passing through the solution at 30° C., an aqueous emulsion stock solution-3 with an amine molar ratio of 0.2 was obtained. Example 3 The aqueous emulsion stock solution-1 obtained in Example 1 was
When the cation exchange treatment was further repeated twice under the same conditions, the amine molar ratio became 0.06. Comparative Example 1 An aqueous emulsion stock solution-5 having an amine molar ratio of 0.15 was prepared in the same manner as in Example 1 except that the amount of dimethylaminoethanol used was 1.5 parts. The average particle diameter and stability over time of the aqueous emulsion stock solutions obtained in Examples 1 to 3 and Comparative Example 1 were compared, and the results are shown in Table 1.

[Table] Comparative Example 2 In the method of Example 1, the amount of pure water used was reduced to 100%.
The same method was carried out except for the resin solid content.
An aqueous emulsion stock solution-6 of 46% and amine molar ratio of 0.3 was prepared. When the aqueous emulsion stock solution-6 was subjected to cation exchange treatment under the same conditions as in Example 1, it gelled in the cation exchange resin and became impossible to pass through. Example 4 In the method of Example 1, when the flow rate of the cation exchange treatment was changed, the amine molar ratio changed as shown in Table 2.

【table】

Claims (1)

[Scope of Claims] 1. The coating film-forming component consists of (a) an α,β-ethylenically unsaturated polycarboxylic acid resin and (b) an alkoxylated methylolmelamine, and the carboxyl group of the component (a) 1
An aqueous emulsion prepared by partially neutralizing it with a basic compound and dispersing it in water so that the molar ratio is 0.25 mol or more is treated with cation exchange to adjust the molar ratio.
A method for producing a replenishing paint for electrodeposition coating, characterized in that the concentration is reduced to 0.2 or less. 2. The method for producing a replenishing paint for electrodeposition coating according to claim 1, wherein a weakly acidic cation exchange resin, a strongly acidic cation exchange resin, or a mixture thereof is used in the cation exchange treatment. 3 For cation exchange treatment, space velocity SV = 5 ~
2. The method for producing a replenishment paint for electrodeposition coating according to claim 1, characterized in that the liquid is passed through at a rate of 250 mL.