JPH0819310B2 - Method for producing aqueous dispersion of anionic gel particles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Background and Problem 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-58-93
762 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, in the present invention, the core is made of a thermosetting cross-linking resin, and the shell is made of an aqueous resin having a negative charge and a hydrophilic group necessary for electrodeposition, and a new type of anionic gel fine particle having a core / shell structure. There is provided a method for producing the water dispersion liquid.

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 melamine resin as a cross-linking agent at a solid content of 10 to 25 parts by weight.
Emulsifying a resin composition containing 0 part by weight and an organic solvent in an aqueous medium, removing the organic solvent from the resulting emulsion, and then heating the emulsion at a temperature equal to or higher than the crosslinking temperature of the crosslinking agent (B). Provided is a method for producing an aqueous dispersion of characteristic anionic gel particles.

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

Preferred Embodiment A water-based acrylic resin (A) having a negative charge in water is used as a film-forming resin in the production of an anionic electrocoating paint. 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, 2-ethylhexyl (meth) acrylate, and (meth ) Lauryl acrylate, 2-hydroxyethyl (meth) acrylate, glycidyl (meth) acrylate and the like.

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

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.

The melamine resin is a methylol compound obtained by reacting melamine, benzoguanamine, acetoguanamine or a mixture thereof with formaldehyde, or a part or all of the methylol group is etherified with C _1-4 lower alkanol, and C _1-4 Lower alkanol preferably has a large C number in order to render it insoluble in water.

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, if the reaction is carried out under pressure in an autoclave, it is also possible to use crosslinking agents which react at temperatures above 100 ° C.

The water-based resin (A) and the cross-linking agent (B) 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 solvent such as acetone, methyl ethyl ketone, methoxybutanol, dioxane, ethylene glycol monoethyl ether acetate, xylene,
There are water-immiscible organic solvents such as toluene, methyl isobutyl ketone, hexane, carbon tetrachloride, 2-ethylhexanol, isophorone, cyclohexane and benzene.

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. Examples of the catalyst include dinonylnaphthalene sulfonic acid and dinonyl naphthalene disulfonic acid.

To emulsify a resin composition containing an aqueous resin (A) and a cross-linking agent (B) in an aqueous medium to prepare an emulsion, at least 20 mol% of acid groups in the aqueous resin (A) are treated with a base. The mixture may be added, and the crosslinking agent (B) and an 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 so on.

The aqueous medium is water and may include a surfactant to promote emulsification. Examples of nonionic surfactants include:
Examples include polyethylene glycol alkyl phenyl 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.

The cross-linking reaction is promoted by removing the solvent in the emulsion by azeotropic distillation after preparing the emulsion and before heating.

The emulsion thus obtained is heated at a temperature equal to or higher than the crosslinking temperature under normal pressure or under pressure depending on the crosslinking temperature of the crosslinking agent (B) to obtain the desired anionic gel particles having a core / shell structure. An aqueous dispersion is obtained.

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 crosslinking 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.

Examples of the present invention will be shown below. In these, parts and percentages are by weight.

Examples Resin emulsion parts by weight Solid content Cotax WE-804 * 1) 91 50 U-Van 22R 100 50 Triethylamine 1.4 Deionized water 308 * 1) 91 of water-soluble anionic acrylic resin Cotax WE-804 manufactured by Toray Industries, Inc. 100 parts of Euban 22R and 1.4 parts of triethylamine were added to the above parts, and the mixture was thoroughly stirred, and deionized water was gradually added to emulsify. 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, the resin emulsion was kept warm at 55 ° C. for 1 week and cooled to obtain an anionic gel particle dispersion liquid. 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 nm or less were observed.

Comparative Example Resin emulsion parts by weight Solids Cotax WE-804 * 1) 91 50 U-Van 22R 100 50 Triethylamine 1.4 Deionized water 308 * 1) 91 of water-soluble anionic acrylic resin Cotax WE-804 manufactured by Toray Industries, Inc. 100 parts of U-Van 22R and 1.4 parts of triethylamine were added to the above parts and stirred sufficiently, and deionized water was gradually added to emulsify 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, the resin emulsion was sealed, kept warm at 55 ° C. for 1 week and cooled, and a part thereof was taken and added to 100 times amount of tetrahydrofuran, and it was dissolved transparently. Further, the mixture was kept warm at 55 ° C. for 1 week and cooled, and a part thereof was taken and added to 100 times amount of tetrahydrofuran, and it was transparently dissolved.

Incubate at 55 ℃ for 1 week, cool and take a part of it.
When it was added to 100 times the amount of tetrahydrofuran, it did not dissolve transparently and became cloudy, and an anionic gel fine particle dispersion liquid was obtained, but resin-like precipitation was observed more than in the examples.

Claims (3)

[Claims] 1. A water-based acrylic resin having a negative charge in water (A) as a solid content of 100 parts by weight, and (B) a melamine resin as a cross-linking agent as a solid content of 10 to 25.
Emulsifying a resin composition containing 0% by weight and an organic solvent in an aqueous medium, removing the organic solvent from the resulting emulsion, and then heating the emulsion at a temperature equal to or higher than the crosslinking temperature of the crosslinking agent (B). A method for producing an aqueous dispersion of anionic gel particles, which is characterized. 2. The method for producing an aqueous dispersion of anionic gel particles according to claim 1, wherein the emulsion is heated at atmospheric pressure. 3. The method for producing an aqueous dispersion of anionic gel particles according to claim 1, wherein the emulsion is heated under pressure.