JPH0794584B2 - Method for producing aqueous dispersion of anionic gel particles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Background and Problems of the Invention Conventionally, fine resin particles (microgel) made of a polymer of an ethylenically unsaturated monomer internally cross-linked are added to an electrodeposition paint to obtain a matte coating film. This is well known. JP-A-58-937
62 and JP-A-56-49766. The addition of microgel to the electrodeposition coating is effective not only for the purpose of matting but also for coating performance and throwing power.

However, since these microgels do not have the electric charge necessary for electrodeposition, are insoluble in an aqueous medium, and do not heat-fuse at the baking temperature of the coating film, they cannot be electrodeposited by themselves, and are soluble in water or dispersed in water. Must be used in combination with a water-based resin that has the necessary electric charge for positive electrodeposition. However, in that case, since the microgel impairs the storage stability of the paint and the workability of electrodeposition due to the above-mentioned properties, it cannot be added in a large amount.

Therefore, the present invention, the core is made of a thermosetting cross-linking resin,
Ciel provides a method for producing an aqueous dispersion of fine particles of anionic gel of a new type having a core / shell structure, which comprises an aqueous resin having a negative charge and a hydrophilic group necessary for electrodeposition.

Solution The present invention provides (A) 100 parts by weight of an aqueous acrylic resin having a negative charge in water as a solid content, and (B) a methylolphenol or an etherified methylolphenol as a solid content as a crosslinking agent.
To 250 parts by weight of a resin composition is emulsified in an aqueous medium, and the resulting emulsion is heated at a temperature equal to or higher than the crosslinking temperature of the crosslinking agent (B) to produce an aqueous dispersion of anionic gel particles. Provide a way.

The aqueous dispersion of the anionic gel particles of the present invention has a negative charge that allows the particles themselves to be electrodeposited, and the hydrophilic resin serves as a shell to cover the core of the insoluble thermosetting crosslinked resin. Therefore, when it is added to the anion electrodeposition coating, it does not impair the electrodeposition workability and coating film performance, and does not adversely affect the storage stability of the coating.

Preferred Embodiment Aqueous acrylic resin (A) having a negative charge in water
Is used as a film-forming resin in the production of anionic electrocoating paints. They are resins obtained by introducing an acid group such as a carboxyl group, a sulfonic acid group or a phosphate group into the resin. These resins form an aqueous solution or dispersion by neutralizing their acid groups with a base and diluting with water.

The anionic acrylic resin can be obtained by copolymerizing a (meth) acrylic acid ester, an ethylenically unsaturated monomer having an acid group, and optionally an ethylenically unsaturated monomer other than these.

Examples of the (meth) acrylic acid ester include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, and (meth).
2-ethylhexyl acrylate, lauryl (meth) acrylate, 2-hydroxyethyl (meth) acrylate,
Glycidyl (meth) acrylate and the like.

Examples of the ethylenically unsaturated monomer having an acid group include (meth) acrylic acid, crotonic acid, itaconic acid, carboxylic acids such as maleic anhydride, sulfo acids such as sulfoacrylate, and mono (2-hydroxyethyl acrylate).
Examples include phosphates such as acid phosphates.

Examples of the ethylenically unsaturated monomer other than the above, which is an optional component, include styrene, vinyltoluene, acrylonitrile, acrylamide, and vinyl acetate. A commercially available water-soluble acrylic resin, for example, Cotax WE-804 or Cotax WE-832 manufactured by Toray Industries, Inc. may be used.

Methylolphenols that are cross-linking agents are phenol,
p-cresol, pt-butylphenol, aminophenol, p-phenylphenol, bisphenol A
It can be obtained by reacting phenols such as and the like with formaldehyde in the presence of an alkali catalyst. Methylol phenols and etherification, phenolic OH group a suitable etherifying agent methylol phenols, e.g., RX (R is _{-CH 3, -CH 2 -CH = CH} 2, -CH 2 C 6 H 5, X can be obtained by etherifying a part or all of X with a halogen) or a monoepoxy compound. When the etherifying agent is a monoepoxy compound, the etherified methylolphenols are β-hydroxyphenol ether compounds and are highly reactive, which is preferable.

The cross-linking agent (B) does not form a core of fine particles because it is difficult to form an emulsion in an aqueous medium unless it is water-insoluble.
Therefore, methylolphenols that do not etherify phenolic OH groups are nearly water-soluble and are not very preferable.

Since the cross-linking agent (B) undergoes a cross-linking reaction in water, it must be cross-linkable at a temperature of 100 ° C. or lower when it is reacted at atmospheric pressure. However, when the reaction is carried out under pressure in an autoclave, it is also possible to use crosslinking agents which react at temperatures of 100 ° C. and above.

The water-based resin (A) and the cross-linking agent (B) can contain an organic solvent in order to reduce the viscosity and facilitate emulsion formation. Examples of such solvents are ethyl cellosolve, propyl cellosolve, butyl cellosolve, methanol, ethanol, isopropyl alcohol, n-butanol, isobutanol, ethylene glycol dimethyl ether, diacetone alcohol, 4-methoxy-4-methylpentanone-2- , Water-miscible organic solvents such as acetone, methyl ethyl ketone, methoxybutanol, dioxane, ethylene glycol monoethyl ether acetate, xylene, toluene, methyl isobutyl ketone, hexane, carbon tetrachloride, 2-ethylhexanol, isophorone, cyclohexane, benzene, etc. There are water-immiscible organic solvents.

The aqueous resin (A) and the cross-linking agent (B) may contain a catalyst in order to accelerate the reaction of the cross-linking agent.

To emulsify a resin composition containing an aqueous resin (A) and a crosslinking agent (B) in an aqueous medium and prepare an emulsion, at least 20 mol% of acid groups in the aqueous resin (A) are neutralized with a base. Then, the crosslinking agent (B) and the aqueous medium may be added and emulsified. The ratio of the aqueous resin (A) to the cross-linking agent (B) is 10 to 250 parts by weight of the latter per 100 parts by weight of the solid content.

As a base for neutralizing the aqueous resin (A), ammonia,
Diethanolamine, triethanolamine, methylethanolamine, N, N-dimethylethanolamine, N, N
-Diethylethanolamine, diethylamine, triethylamine, morpholine, potassium hydroxide and the like.

The aqueous medium is water and may include a surfactant to promote emulsification. Examples of nonionic surfactants include polyethylene glycol alkylphenol ether, polyethylene glycol alkyl ether, polyoxyalkylene alkyl ether, polyethylene glycol sorbitan monostearate, polypropylene glycol polyethylene glycol ether and the like. Examples of the anionic surfactant include polyoxyethylene alkylphenyl ether sulfate ammonium salt, polyoxyethylene alkyl ether sulfate ammonium salt and the like.

It is desirable that the solvent in the emulsion be removed by azeotropic distillation after preparing the emulsion and before heating. This accelerates the crosslinking reaction.

The emulsion thus obtained contains the crosslinking agent (B)
Depending on the crosslinking temperature, heating under normal pressure or under pressure at a temperature equal to or higher than the crosslinking temperature gives a desired aqueous dispersion of anionic gel particles having a core / shell structure.

The core / shell type emulsion of the present invention has good thermal stability because it is stably dispersed in water due to the repulsive force of the charges of the same sign, and therefore the thermal crosslinking reaction of the crosslinking agent (B) in the emulsion form. proceed. The cross-linking reaction in the form of such an emulsion can be confirmed by adding a large amount of a resin-melting solvent such as tetrahydrofuran to the emulsion before and after heating. If it is not crosslinked, the emulsion is transparently dissolved in the solvent, and if it is crosslinked, it becomes insoluble and the solvent becomes cloudy. The aqueous dispersion of the anionic gel particles can be air-dried and dried under reduced pressure, and the particles can be observed with an electron microscope.

The aqueous dispersion of anionic gel particles obtained by the present invention can be added to a known anionic electrodeposition coating composition for the purposes of matting and improving the performance of the electrodeposition coating film. In that case, even if added in a relatively large amount, the workability of electrodeposition, coating film performance, storage stability and the like do not deteriorate. Further, the above-mentioned dispersion liquid can be added to a general water-based coating composition for the same purpose.

The production examples and examples of the present invention are shown below. In these, parts and percentages are by weight.

Production example β-hydroxyphenol ether compound Tamanol 722 * 1) 60 parts Butyl glycidyl ether * 2) 23 parts n-Butanol 10 parts Methoxybutanol 10 parts Dimethylbenzylamine 0.4 parts * 1) Arakawa Chemical Industries, Ltd., resole type Phenolic resin * 2) Monoepoxy compound manufactured by Tohto Kasei Co., Ltd. 60 parts of Tamanol 722 is charged, 10 parts of n-butanol and 10 parts of methoxybutanol are added, and further 23 parts of butyl glycidyl ether is added. While uniformly stirring this, the temperature was raised to 100 ° C., and 0.4 g of dimethylbenzylamine was added. 100 ° C while paying attention to heat generation
After keeping the temperature for 3 hours and keeping the mixture for 3 hours with sufficient stirring, the content of glycidyl group in the reaction product was measured and found to be 5% or less with respect to the charged amount. As a result of analysis of the obtained compound, a β-hydroxyphenol ether compound in which the phenolic OH group disappeared and which had a methylol group and a secondary alcohol group was obtained.

Example resin emulsion * 3) Toray Co., Ltd., water-soluble anionic acrylic resin Cotax WE-804, was added 91 parts of β-hydroxyphenol ether compound 73.5 parts and triethylamine 1.4 parts, and sufficiently stirred, and deionized water was gradually added. In addition, it was emulsified. The solvent was removed under reduced pressure while adding deionized water to this to obtain a resin emulsion.

A part of this was taken and added to 100 times the amount of tetrahydrofuran, whereupon it dissolved transparently.

Next, heat the resin emulsion at 55 ° C for 1 week to cool it,
An anionic gel particle dispersion liquid was obtained. This product did not dissolve transparently in tetrahydrofuran and became cloudy. When observed with an electron microscope, fine particles with a particle size of 100 mm or less were observed.

Claims (5)

[Claims] 1. (A) 100 parts by weight of an aqueous acrylic resin having a negative charge in water as a solid content, and (B) 10 parts by weight of a methylolphenol or an etherified methylolphenol as a crosslinking agent as a solid content.
To 250 parts by weight of a resin composition is emulsified in an aqueous medium, and the resulting emulsion is heated at a temperature equal to or higher than the crosslinking temperature of the crosslinking agent (B) to produce an aqueous dispersion of anionic gel particles. Method. 2. The method for producing an aqueous dispersion of anionic gel particles according to claim 1, wherein the etherified methylolphenols are β-hydroxyphenol ether compounds. 3. A method for producing an aqueous dispersion of anionic gel fine particles according to claim 1 or 2, wherein the emulsion is heated at normal pressure. 4. The method for producing an aqueous dispersion of anionic gel particles according to claim 1 or 2, wherein the emulsion is heated under pressure. 5. The method for producing an aqueous dispersion of anionic gel particles according to any one of claims 1 to 4, wherein the emulsion contains an organic solvent, and the step of removing the organic solvent before heating.