JPH107976A - Water-dispersible coating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water-dispersible coating compsn. which forms a coating film with improved resistances to water and stain. SOLUTION: This compsn. is obtd. by subjecting a monomer mixture contg. 70-99.9wt.% (based on the resin content, and the same applies hereunder) ethylenically unsatd. monomer and 0.1-10wt.% water-soluble ethylenically unsatd. monomer copolymerizable therewith to emulsion copolymn. in an aq. medium in the presence of a surfactant, contains 0.5-10wt.% mixture of an ethylene glycol deriv. and a diethylene glycol deriv. in a wt. ratio of (2:8)-(8:2) as the film-forming assistant, and has a Tg (the glass transition point of the polymer) of 50 deg.C or higher.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a water-dispersible coating composition, and more particularly to a water-dispersible coating composition for forming a coating film having excellent durability and stain resistance.

[0002]

2. Description of the Related Art In coating agents such as paints, there is a strong demand for non-pollution or safety and hygiene of paints from the viewpoint of environmental protection and safety and health of living bodies (human bodies). The use of emulsion paints is expanding in place of conventional solvent-based paints, and interest is growing. Along with this, a high level of coating performance has been required in these emulsion paints, and improvement in durability and stain resistance of the coating when applied to an inorganic substrate has been recognized as both important issues. I have.

[0003] In the case of an emulsion paint, a uniform coating film is formed only through thermal fusion between emulsion particles, so that the glass transition point (Tg value) of the polymer is set lower or a large amount of film is formed. It is necessary to add auxiliaries, plasticizers and the like. Therefore, a coating film obtained by forming an aqueous emulsion has a drawback in that the coating film is inferior in stain resistance as compared with a coating film using a solvent-based paint.

[0004] In recent years, with respect to these problems, studies have been made on improving the performance of a coating film by an aqueous emulsion obtained by copolymerizing a fluorine-containing monomer or by blending aqueous emulsions. According to this method, the types of copolymerizable monomers are restricted, and there is still a need for improvements in terms of film hardness, film contamination due to high durability, and production cost.

[0005] As a method for obtaining a uniform coating film with a small amount of solvent, there is a method for producing a coating material containing as a main component a blend of two types of polymer emulsions having different Tg values.
In this case, although the amount of the solvent can be reduced and the water resistance can be improved, the problem of contamination resistance is low due to the presence of a polymer having a low Tg value, so that the efficiency of removing contaminants is low and the compatibility between the polymers is further reduced. Is left.

[0006] In the core / shell type emulsion,
Emulsion particles having a high Tg value polymer composition are arranged in the inner layer and low Tg value emulsion particles are arranged in the outer layer, thereby improving the film forming property of the emulsion particles and fusing between the particles. It also aims to improve high Tg value polymer composition driven stain resistance. However, in a coating film obtained using these two types of emulsions, as the difference in Tg value between the inner layer and the outer layer increases,
Although the stain resistance is correspondingly improved, there is a problem that the durability of the coating film is deteriorated due to the poor compatibility of the polymers in both the inner and outer layers. When the difference in Tg value between the inner layer and the outer layer is small, the compatibility of the polymer becomes good, so this method is considered to be an effective means for improving the durability of the coating film. However, the improvement in stain resistance remains as a future problem because the property deteriorates.

As described above, in studies using organic polymers, there is a limit in improvement of stain resistance and the like. Therefore, durability and stain resistance due to the combined use of inorganic polymers such as water glass and colloidal silica and organic polymers are considered. There have also been many studies of improvement.

In practice, coatings obtained from coatings based on water glass or a blend of colloidal silica and an organic polymer emulsion have a high hardness and good stain resistance, but they are inorganic polymer And the emulsion have a weak mutual binding effect, and as a result, there remains a problem in terms of durability such as long-term water resistance and alkali resistance of the coating film. Therefore, in order to strengthen the bond between the inorganic polymer and the organic polymer emulsion, a method of adding alkoxysilanes to a blend of these polymers and a method of using a polymerizable monomer having an alkoxysilane group have been proposed. ing. However, the coating compositions obtained by these methods have poor stability in their own right, and therefore have not yet been able to obtain satisfactory properties such as being unable to withstand long-term storage and storage.

Conventionally, there has been proposed a paint capable of forming a film even at room temperature by adding a large amount of a film forming aid to a polymer emulsion having a relatively high Tg value. In this case, if a film-forming auxiliary having a relatively low boiling point is used, a large amount of solvent needs to be added, and a coating film formed from a relatively small amount of the film-forming auxiliary is liable to crack. In addition, if a film-forming auxiliary having a high boiling point is used, the obtained coating film still has "stickiness" even after several days, and poor stain resistance is exposed. Thus, it was difficult to select a film-forming aid, and it was difficult to achieve both film-forming properties and coating film performance.

[0010]

SUMMARY OF THE INVENTION In view of the above-mentioned problems in the prior art, the present inventors have been keen to obtain a useful water-dispersible coating composition for forming a coating film having excellent durability and stain resistance. As a result of research, the present invention has been completed.

The gist of the present invention is as follows.
Aqueous dispersion having a Tg value of 50 ° C or higher (polymer glass transition point) obtained by emulsion copolymerization with a monomer mixture in an aqueous medium in the presence of an anionic surfactant and / or a nonionic surfactant. A coating composition comprising: (a) 70 to 99.9% by weight of an ethylenically unsaturated monomer based on the amount of resin; and (a) a copolymerizable with the ethylenically unsaturated monomer (b). ) Containing from 0.1 to 10% by weight of a water-soluble ethylenically unsaturated monomer, and wherein the composition is from 0.5 to 10% by weight based on the amount of resin and the mixing weight ratio is from 2/8 to 8/2. A water-dispersible coating composition characterized by further comprising a mixture of an ethylene glycol derivative and a diethylene glycol derivative as a film-forming aid.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The water-dispersible coating composition of the present invention uses a dispersion of a polymer-based dispersoid in a dispersion medium containing water as a main component.

The average particle size of the dispersoid is usually in the range of 10 to 500 nm. This means that, when trying to obtain a particle size of 10 nm or less, it tends to have a low solid content due to viscosity and the like, and it is not practical as a paint base,
Further, when the particle diameter is larger than 500 nm, the durability was determined in consideration of the decrease.

There is no particular limitation on the emulsion polymerization method. For example, (a) an ethylenically unsaturated monomer and (b) a water-soluble polymer which can be radically polymerized in the presence of water, an emulsifier, and an initiator. A monomer dropping method in which a mixture of ethylenically unsaturated monomers is dropped; a radically polymerizable mixture of (a) an ethylenically unsaturated monomer and (b) a water-soluble ethylenically unsaturated monomer is emulsified in the presence of water and an emulsifier. A pre-emulsion method in which the polymerization is carried out while dropping the mixture; or a radical in the presence of water, an emulsifier, an initiator, a mixture of (a) an ethylenically unsaturated monomer and (b) a water-soluble ethylenically unsaturated monomer. A one-bath polymerization method for performing polymerization can be used in the present invention.

In the monomer dropping method and the pre-emulsion method, 1 to 50% by weight, preferably 3 to 30% by weight of the total dropped amount.
% By weight can be added in advance at the start of the polymerization. From the viewpoint of safety, the monomer dropping method and the pre-emulsion method are preferable, and the pre-emulsion method is particularly preferable.

The above-mentioned (a) ethylenically unsaturated monomers applicable to the present invention include, for example, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, hexyl acrylate, cyclohexyl acrylate,
2-ethylhexyl acrylate, lauryl acrylate, stearyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, methacrylic acid C1-C24 alkyl or cycloalkyl esters of (meth) acrylic acid such as stearyl; C2-C8 hydroxyalkyl esters of (meth) acrylic acid such as hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate; Aromatic unsaturated monomers such as styrene, vinyltoluene, α-methylstyrene, N-vinylpyrrolidone and vinylpyridine; Rate, of epoxy groups such as glycidyl methacrylate (meth) acrylic acid ester, acrylic acid 1-methyl 2-imidazolidone, acrylic acid
C1 containing an imidazole ring of (meth) acrylic acid such as 1-ethyl 2-imidazolidone, 1-methyl 2-imidazolidone methacrylate, 1-ethyl 2-imidazolidone methacrylate
Pyrroles of (meth) acrylic acid such as 1-methyl 2-pyrrolidone acrylate, 1-ethyl 2-pyrrolidone acrylate, 1-methyl 2-pyrrolidone methacrylate, 1-ethyl 2-pyrrolidone methacrylate Ring-containing C
1-C24 alkyl ester; 1-methyl 2-oxazolidone acrylate, 1-ethyl 2-oxazolidone acrylate,
1-methyl 2-oxazolidone methacrylate, methacrylic acid
An oxazole ring-containing C1-C24 alkyl ester of (meth) acrylic acid such as 1-ethyl 2-oxazolidone;
Alternatively, there is a combination of one or more of the aforementioned compounds.

Further, as the water-soluble ethylenically unsaturated monomer (b) applicable to the present invention, for example, acrylic acid, methacrylic acid, maleic acid, crotonic acid, (meth) acrylate having a polyoxyethylene chain; Acrylamide, N-methylolacrylamide, N-butoxymethylacrylamide; or a combination of one or more of the foregoing compounds.

Next, the amount of the above-mentioned (a) ethylenically unsaturated monomer and (b) water-soluble ethylenically unsaturated monomer is selected in the following range with respect to the total amount of the resin.
(A) ethylenically unsaturated monomer: 90 to 99.5% by weight, preferably 95 to 99% by weight; and (b) water-soluble ethylenically unsaturated monomer: 0.5 to 10% by weight, preferably 1 to 5% by weight. , And.

The emulsifier used in the present invention includes anionic surfactants, nonionic surfactants, amphoteric surfactants and the like. Specifically, as anionic surfactants, for example, fatty acid ester salts of higher alcohols, alkylbenzene sulfonates, aliphatic sulfonates and the like, and as nonionic surfactants, polyethylene glycol alkyl ester type, Alkyl ether type, alkyl phenyl ether type, etc., and further, as amphoteric surfactants, surfactants in which the anion portion is a carboxylate, sulfonate, sulfate ester salt, and the cation portion is an amine salt, quaternary ammonium salt Agents. Further, a reactive emulsifier in which a polymerizable functional group is introduced into the above-mentioned surfactant can be used. The use ratio of these surfactants is 1.2 to 2.5 with respect to the resin.
It is preferable to set the weight% to obtain good durability.

Examples of the radical polymerization initiator used in the present invention include water-soluble or oil-soluble persulfates, peroxides, which are radically decomposed by heat or a reducing substance to initiate addition polymerization to monomers. Azo compounds and the like can be used. For example, potassium persulfate, sodium persulfate,
Ammonium persulfate, hydrogen peroxide, t-butyl hydroperoxide, t-butyl peroxybenzoate,
There are 2,2-azobisisobutyronitrile, 2,2-azobis (2-diaminopropane) hydrochloride and the like, and water-soluble ones are particularly preferable from the viewpoint of easy handling. An amount of 2% by weight, preferably 0.1-0.5% by weight, is added. In addition, when accelerating the polymerization rate and performing the polymerization at a low temperature, sodium bisulfite, ferrous chloride,
A reducing agent such as ascorbate or Rongalit can be used in combination with the radical polymerization initiator.
It is also possible to add a chain transfer agent such as dodecyl mercaptan for controlling the molecular weight. The aqueous emulsion polymerized in the present invention exhibits stable dispersibility without neutralizing the carboxyl groups in the aqueous emulsion, but in order to maintain the dispersibility over a long period of time, for example, ammonia, sodium hydroxide, hydroxide The pH can be adjusted in the range of 6 to 10 using potassium and amines.

Examples of the film-forming aid used in the present invention include ethylene glycol derivatives such as ethylene glycol monoalkyl ether such as butyl cellosolve and ethyl cellosolve, diethylene glycol monoalkyl ether such as ethyl carbitol and butyl carbitol, and diethylene glycol. Mixtures with diethylene glycol derivatives such as diethylene glycol dialkyl ethers such as diethyl ether. The mixing ratio (weight ratio) of these ethylene glycol derivatives / diethylene glycol derivatives ranges from 2/8 to 8/2,
Preferably, it is 3/7 to 7/3. In addition, several kinds of ethylene glycol derivatives and diethylene glycol derivatives can be used in combination at an arbitrary ratio.

From the viewpoint of obtaining good durability, these are used in an amount of 0.5 to 10% by weight, preferably 1 to 5% by weight, based on the resin.

The aqueous emulsion of the present invention can also contain components usually added to water-based paints, such as thickeners, defoamers, pigments, dispersants, dyes, and preservatives.

[0024]

Next, the present invention will be described in detail with reference to examples and comparative examples. However, it should be understood that the present invention should not be construed as being limited by these disclosures. In the following Examples and Comparative Examples, all parts and percentages are by weight unless otherwise specified.

A. Sample Preparation Example 1 30 parts of water and 0.2 parts of potassium persulfate (KPS) were charged into a 2 liter four-necked flask equipped with a stirrer, a reflux condenser, a dropping funnel, and a thermometer. The gas was replaced, and the temperature was raised to 85 ° C. At the same temperature, 17 parts of water, 4 parts of surfactant, 38 parts of methyl methacrylate, 2-ethylhexyl acrylate 6
And 0.6 parts of acrylic acid, were added dropwise over 3 hours, and the mixture was maintained at 85 ° C. for 2 hours and then cooled to room temperature. Further, a mixed solution of 1.5 parts of butyl cellosolve and 1.5 parts of diethylene glycol diethyl ether was added as a film-forming aid, and the pH was adjusted to 8 with a 25% aqueous ammonia solution to obtain a desired aqueous emulsion (solid content: about 40%). .

Example 2 A sample was prepared in the same manner as in Example 1 except that a mixture of 1.5 parts of butyl cellosolve and 1.5 parts of diethylene glycol ethyl methyl ether was added as a film-forming aid (solid content: about 40%).

Comparative Example 1 The monomer composition was changed to 30 parts of methyl methacrylate, acrylic acid
A sample was prepared in the same manner as in Example 1 except that 14 parts of 2-ethylhexyl was used (solid content: about 40%).

Comparative Example 2 A sample was prepared in the same manner as in Example 1 except that 3 parts of butyl cellosolve was added as a film-forming aid (solid content: approx.
40%).

Comparative Example 3 A sample was prepared in the same manner as in Example 1 except that 3 parts of diethylene glycol diethyl ether was added as a film-forming auxiliary (solid content: about 40%).

The details of the compositions obtained in Example 1-2 and Comparative Example 1-3 are summarized in Table 1 below.

[0031]

[Table 1]

B. Test properties of water-dispersible coating composition then spraying the resulting water dispersible coating composition in Example 1-2 and Comparative Example 1-3, at a coverage of about 100 g / m ² on a slate plate After that, the film was dried at 120 ° C. for 3 minutes to obtain a film sample to be subjected to the following test.

[0033] 1. The presence or absence of cracks in the film formed on the film-forming slate plate was observed with an optical microscope (magnification: 200 times).

[0034] 2. The film formed on the water-resistant slate plate was immersed in warm water at 60 ° C. for 4 hours, then quenched with water and dried at room temperature, and the state of the film was visually determined.

[0035] 3. Contamination resistance of the film (1) About 1 g of contaminants prepared by mixing 10% of carbon black with white petrolatum on the film formed on the slate plate
The degree is applied to a cloth and rubbed 10 times with even force, then cured at 40 ° C for one week. After curing, the contaminants are wiped off with a clean cloth, washed thoroughly with water and dried at room temperature. After drying, the state of the film was visually determined.

[0036] 4. (2) A 10% solution of red ink is spotted on the film formed on the slate plate and left for 1 hour. Thereafter, the ink was wiped off with gauze, and the degree of contamination was visually determined.

Test 1 ~ 4. Table 2 below summarizes the test results.

[0038]

[Table 2]

[0039]

As is clear from the above series of results,
According to the present invention, provision of a water-dispersible coating composition which forms a film having excellent water resistance and stain resistance, which was the intended purpose, has been realized.

Further, the water-dispersible coating composition of the present invention can be easily and inexpensively manufactured on an industrial scale by the same manufacturing apparatus and manufacturing conditions as those of the conventional water-dispersible coating composition.
It also has an effect that it can be stably provided in large quantities to the coating agent market as a substitute for organic solvent type paint.

Claims (8)

[Claims] 1. A water-dispersible coating composition having a Tg value (glass transition point of a polymer) of 50 ° C. or higher, obtained by emulsion-copolymerizing a monomer mixture in an aqueous medium in the presence of a surfactant. Wherein the monomer mixture comprises (a) 70 to 99.9% by weight of an ethylenically unsaturated monomer, and 0.1 to 10% by weight of the (a) ethylenically unsaturated monomer copolymerizable with the ethylenically unsaturated monomer.
(b) a water-soluble ethylenically unsaturated monomer, wherein the composition contains a mixture of an ethylene glycol derivative and a diethylene glycol derivative as a film-forming aid in an amount of 0.5 to 10% by weight based on the resin amount; A water-dispersible coating composition, wherein the mixture weight ratio of the derivative / diethylene glycol derivative is 2/8 to 8/2. 2. The surfactant according to claim 1, wherein the surfactant is an anionic surfactant selected from the group consisting of fatty acid ester salts of higher alcohols, alkylbenzene sulfonates, aliphatic sulfonates, and combinations of at least one of these salts. The water-dispersible coating composition according to claim 1. 3. The surfactant according to claim 1, wherein the surfactant is a nonionic surfactant selected from the group consisting of alkyl ester type, alkyl ether type, alkyl phenyl ether type of polyethylene glycol, and a combination of at least one of these surfactant types. The water-dispersible coating composition according to claim 1. 4. The surfactant according to claim 1, wherein the surfactant is an amphoteric surfactant in which the anion portion is a carboxylate, a sulfonate, a sulfate ester salt, and the cation portion is an amine salt or a quaternary ammonium salt. 3. The water-dispersible coating composition according to 1.). 5. The (a) ethylenically unsaturated monomer is methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, hexyl acrylate, cyclohexyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, C1 of (meth) acrylic acid such as stearyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, stearyl methacrylate, etc. (Meth) acryls such as C24 alkyl or cycloalkyl esters, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate C2-C8 hydroxyalkyl esters of acids, styrene, vinyltoluene, α-methylstyrene, N-
Aromatic unsaturated monomers such as vinyl pyrrolidone and vinyl pyridine, epoxy group-containing (meth) acrylates such as glycidyl acrylate and glycidyl methacrylate, 1-methyl 2-imidazolidone acrylate, 1-ethyl 2-imidazolidone acrylate, methacryl C1-C containing imidazole ring of (meth) acrylic acid such as 1-methyl 2-imidazolidone acrylate, 1-ethyl 2-imidazolidone methacrylate
24 alkyl esters, 1-methyl 2-pyrrolidone acrylate, 1-ethyl acrylate
C1-C24 alkyl esters containing a pyrrole ring of (meth) acrylic acid, such as 2-pyrrolidone, 1-methyl 2-pyrrolidone methacrylate, 1-ethyl 2-pyrrolidone methacrylate, 1-methyl 2-oxazolidone acrylate, acrylic Oxazole ring-containing C1-C of (meth) acrylic acid such as 1-ethyl 2-oxazolidone methacrylate, 1-methyl 2-oxazolidone methacrylate, 1-ethyl 2-oxazolidone methacrylate
The water-dispersible coating composition according to any one of claims 1 to 4, which is a monomer selected from the group consisting of 24 alkyl esters and a combination of at least one of the compounds described above. 6. The water-soluble ethylenically unsaturated monomer (b) is selected from the group consisting of acrylic acid, methacrylic acid, maleic acid, crotonic acid,
(Meth) acrylate having a polyoxyethylene chain, acrylamide, N-methylolacrylamide, N-
The water-dispersible coating composition according to any one of claims 1 to 5, which is a monomer selected from the group consisting of butoxymethylacrylamide and a combination of at least one of the compounds described above. 7. The water dispersibility according to claim 1, wherein the ethylene glycol derivative is an ethylene glycol monoalkyl ether selected from the group consisting of butyl cellosolve, ethyl cellosolve, and a combination thereof. Coating composition. 8. The diethylene glycol derivative is a diethylene glycol dialkyl ether selected from the group consisting of diethylene glycol monoalkyl ethers such as ethyl carbitol and butyl carbitol, diethylene glycol diethyl ether, and combinations thereof. A water-dispersible coating composition according to any one of the above.