GB2187465A

GB2187465A - Aqueous coating composition containing resin particles

Info

Publication number: GB2187465A
Application number: GB08622582A
Authority: GB
Inventors: Teruaki Kuwajima; Hiroshi Miwa; Hideyoshi Noda; Shinich Ishikura
Original assignee: Nippon Paint Co Ltd
Current assignee: Nippon Paint Co Ltd
Priority date: 1986-02-05
Filing date: 1986-09-19
Publication date: 1987-09-09
Also published as: CA1324224C; AU6269386A; GB8622582D0; DE3632617A1; AU593282B2; GB2187465B

Abstract

An aqueous coating composition comprises, as resinous vehicle, (1) an aqueous composition containing resin particles obtained by polymerizing at least one ???,???-ethylenically unsaturated monomer in an aqueous medium and in the presence of an aqueous resin (A) with the help of an organic initiator, and (2) an aqueous resin (B) having a water tolerance of 4 or more and a surface tension of 1% aqueous resin varnish of 51 dyne/cm or less, the solid weight ratio of said resin particles to the total aqueous resins (A)+(B) being 70-1:30-99. The monomer may be in admixture with a hydrophobic solvent and/or a hydrophobic resin during the polymerization. The coating composition has excellent storage stability and application characteristics and is capable of forming a coating with excellent film properties, and hence is particularly useful as a top coat for automobile bodies and the like.

Description

SPECIFICATION An aqueous coating composition The present invention relates to an aqueous coating composition which is useful as a top coat. More specifically, the invention concerns an aqueous coating composition comprising as resinous vehicle (a), an aqueous resin particles containing composition obtained by the polymerization of a,(3-ethylenically unsaturated monomer(s) in an aqueous medium and in the presence of a largeramountofa watersoluble resin, and (b) a particular water soluble resin, which is excellent in storage stability and application characteristics and is capable of resulting a coating with excellent film properties and especially improved gloss and smoothness, and hence is specifically useful as a top coat for automobile bodies and the like.

An aqueous coating composition is generally inferior to a solvent type composition in durability and water resistance of theformed coating and since it is unableto get a composition with a higher non-volatile content, application characteristics are rather poor. Even if an amount of water insoluble resin powders are compounded with said aqueous composition with the hope for increasing the non-volatile contentthereof, viscosity of the compounded system is inevitably increased therewith and hence, a practical coating composition cannot be obtained.

The inventors had formerlyfound that by the selective use of a particular water soluble resin which will fulfil the requirements that the water tolerance, expressed in terms of water dilution multiplicand ofthe resin for the solution incapable of reading out the defined type in the test wherein 5g of aqueous varnish having a common viscosity usually employed in the manufacture of a coating composition are correctly weighed in a 100 ml beaker, diluted with an increasing amountofdeionized water,and a No. 1 type (26 pointtype) is read through the said beaker, is 4 or more, and the surface tension calculated for a 1%w/waqueous solution is 51 dyne/cm or less, it is possible to formulate an aqueous coating composition comprising said water soluble resin and water insoluble resin powders uniformly dispersed therein having a wider solid weight ratio of 98:2 to 45:55, withoutthe fear of undesired increase in viscosity of the system, and it is thus able to increase the resinous content of a coating composition and have the composition with excellent application characteristics, as well as the improved dispersion stability and film properties. On the basis of these findings, a patent application was filed, which is now publicly opened as Japanese Patent Application Kokai No. 15567/83.Though the resinous powders used in that invention were prepared by pulverizing a solidified resin and shieving the same, various technique have been developed to obtain the better quality powdersto be compounded with a water soluble resin since then. In facts, certain improvements have been attained with these products in respect of application characteristics and storage stability of the coating composition and film properties including gloss and smoothness, of the formed coating.However, in most of the heretofore proposed processes, the water insoluble resin powders were advantageously prepared by an emulsion polymerization of oL,ss-ethylenically unsaturated monomer(s) in an aqueous medium containing a surfactant or emulsifier and in the presence of a polymerization initiator, and therefore, it was unavoidablethatthe surfactant used was always remained on the surfaces of the formed particles, giving undesired effect on the film properties and especially on water resistance of the film and that when a water soluble radical initiator was selected, said initiator was likewise remained atthe end portions of the polymer chain, giving undesired effect on film properties, too. Thus, an additional improvement has been longed for.

Moreover, with an increasing demand for high-grade articles, an aqueous type, top-coat composition capable of resulting a coating with far improved gloss and smoothness has been required, especially in an automobile and an electric appliance industries.

It is, thereore, an object ofthe invention to provide a high quality, aqueous coating composition which is excellent in storage stability and application characteristics and capable of resulting a coating with excellent film properties including water resistance and the like and having far improved gloss and smoothness and which is specifically useful as a top coat for automobile bodies and other articles.

According to the invention, the abovesaid object can be attained with an aqueous coating composition comprising as resinous vehicle, (1) an aqueous, resin particles containing composition obtained by polymerizing at least one a,ss-ethylenically unsaturated monomer in an aqueous medium and in the presence of a water soluble resin (A) with the help of an organic initiator, in which the solid weight ratio of said water soluble resin to said monomer is 35-95:65-5, and (2) a water soluble resin (B) having awatertolerance of 4 or more and a surface tension for a 1%w/w aqueous resin solution of 51 dyne/cm or less, the solid weight ratio of said resin particles to the total of said water soluble resins (A) and (B) being 70-1:30-99.

The present aqueous, resin particles containing composition should be prepared by the polymerization of at least one a,ss-ethylenically unsaturated monomer in an aqueous medium and in the presence of a water soluble resin (A), with the help of an organic initiator. The solid weight ratio of said water soluble resintosaid monomer should be in a rage of 35:65 to 95:5.

As the water soluble resin (A), any of the members customarily used in a coating composition area may be satisfactorily used, including polyester resin, alkyd resin, acryl resin, acryl modified polyester resin, acryl modified alkyd resin and the like. Since they have, in general, an amount of acidic groups are carboxyl group, they are neutralized with a basic material so that solubility is given to them.

However, in the present invention, the water soluble resins (A), as well as the water soluble resins (B) hereinafter mentioned, do not absolutely necessary be offully soluble type and they may be of partly soluble and partly dispersible type. Therefore, the term "water soluble resin" as used herein denotes either of water soluble resin and water reducible or dilutable resin.

As already mentioned, the present resin particles are prepared by the polymerization of a,s-ethylenically unsaturated monomer(s) in an aqueous medium and in the presence of a comparatively large amountofsaid water soluble resin (A) in place ofa surfactantoremulsifieras used in a conventional emulsion polymerization.

Atthis time, the solid weight ratio of said water soluble resin (A) to said monomer is determined in a range of 35:65 to 95:5. This is because, if the amount of said water soluble resin (A) is less than 35 wt% ofthe total of said resin and monomers, it is very hard to obtain a stable aqueous composition containing the resin particles and if the amount of said monomer is less than 5 wt%, it is unable to carry out an emulsion polymerization smoothly and effectively.

As the a,(3-ethylenically unsaturated monomer, any ofthe members customarily used in the preparation of acryl resins may be satisfactorily used, each in singularily-or combination of two or more. Examples ofthese monomers are as follows.

1 ) carboxyl containing monomer: for example, acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid and the like, 2) hydroxyl containing monomer: for example, 2-hydroxyethyl acrylate, hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, al lyl alcohol, methallyl alcohol and the like, 3) nitrogen containing alkyl (meth) acrylates: for example, diemthyl aminoethyl acrylate, dimethyl aminoethyl methacrylate and the like, 4) polymerizable amides: for example, acrylamide, methacrylamide and the like, 5) polymerizable nitriles: for example, acrylonitrile, methacrylonitrile and the like, 6) alkyl acrylates and alkyl methacrylates:: for example, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-butyl acrylate, n-butyl methacrylate, 2-ethyl hexyl acrylate and the like, 7) polymerizable aromatic compounds: for example, styrene, dimethyl styrene, vinyl toluene, t-butyl styrene and the like, 8) a-olefins: for example, ethylene, propylene and the like, 9) vinyl compounds: for example, vinyl acetate, vinyl propionate and the like, 10) dienecompouns: for example, butadiene, isoprene and the like.

As a part of said a,ss-ethylenically unsaturated monomers, one may use a crosslinking monomer having 2 or more radically polymerizable, ethylenic bonds per molecule. Examples of such crosslinking monomers are polymerizable unsaturated monocarboxylic acid esters of polyhydric alcohols, polymerizable unsaturated alcohol esters of polycarboxylic acids, and aromatic compounds substituted with 2 or more vinyl groups and the like, including ethylene glycol diacrylate, ethylene glycol dimethacrylate,triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, 1 ,3-butylene glycol dimethacrylate,trimethylol propane triacrylate, trimethylol propane trimethacrylate, 1 ,4-butanediol diacrylate, neopentyl glycol diacrylate, 1 ,6-hexanediol diacrylate, pentaeryth ritol diacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, pentaerythritol dimethacrylate, pentaerythritol trimethacrylate, pentaerythritol tetramethacrylate, glycerol dimethacrylate, glycerol diacrylate, glycerol allyloxy dimethacrylate, 1,1 ,1-trishydroxymethylethane diacrylate, 1,1,1 -trishydroxymethylethane triacrylate, 1,1,1 -trishydroxymethylethane dimethacrylate, 1,1,1 -trishydroxymethylethane trimethacrylate, 1,1,1 -trishydroxymethylpropane diacrylate, 1,1,1-trishydroxymethyl propanetriacrylate, 1,1,1 -trishydroxymethyl propanedimethacrylate, 1,1,1-trishydroxymethyl propanetrimethacrylate, triallyl cyanurate,triallyl isocyanurate,triallyl trimellitate, diallyl terephthalate, diallyl phthalate, divinyl benzene and the like. By using such a crosslinking monomer, particles of crosslinked copolymer can be obtained. The abovesaid monomers are polymerized in an aqueous medium and in the presence of a water soluble resin (A) and atthattime, an organic initiator may advantageously be used. As the organic initiator use can be made of such members as diacyl peroxides (e.g. acetyl peroxide, lauroyl peroxide, benzoyl peroxide and the like), hydroperoxides (e.g. cumene hydroperoxide and the like), alkyl peroxides (e.g.

di-t-butyl peroxide, t-butyl peroxy 2-ethyl hexanoate, t-butyl perpiperate, t-butyl perbenzoate and the like), azo compounds (e.g. 2,2-azobis isobutyronitrile and the like), disulfides (e.g. tetramethyl thiuram disulfide and the like), and sulfinic acids (e.g. p-toluene sulfinic acid and the like).

Among them, particular preference is giventto a water insoluble organic initiator as azobis isobutyronitrile, benzoyl peroxide, di-t-butyl-peroxide, cumene hydroperoxide and the like.

Usually, water is used as a reaction medium, but in a more preferable embodimentofthe invention,a mixture of water and an organic solvent is selectively used. The inventors have found that when an aqueous composition (1) is prepared by a method wherein a,P-ethylenically unsaturated monomers are polymerized in a mixture ofwaterand an organic solvent and in the presence of a large quantity ofwatersoluble resin (A) and a water insoluble organic initiator, and thus obtained composition (1) is compounded with a water soluble resin (B) hereinafter mentioned, a particularly useful aqueous coating composition can be obtained, which is less foaming, hardly give pinholes, less sagging and capable of resulting a coating with highergloss and far improved smoothness. Therefore, in a perferred embodiment of the invention, the aqueous composition (1 ) is prepared in a reaction medium comprising water and an appropriate amount of a common organic solvent customarily used in the preparation of solvent type coating composition.

Thus, in the present invention, it is essential that an aqueous composition containing resin particles be prepared by the polymerization of at least one a,ss-ethylenical Iy unsaturated monomer in an aqueous medium optionally blended with an organic solvent and in the presence of a large quantity of a watersoluble resin (A) and in the presence of an organic initiator, preferably a water insoluble organic initiator. Inthis aqueous composition, the water soluble resin (A) is physically adsorped on or bound with the resin particles and the particles are stably dispersed in the medium by the high moleculareffectofthewatersoluble resin (A) used.

Since the aqueous composition does not include any of the undesired water-soluble by-products, ionic substances and other impurities, and the water soluble resin per se is useful as a binder resin, there are not undesired effects on the properties of the formed coating mainly due to the emulsifier or surfactant usually presented in a conventional coating composition.

The inventors have also found thatwhen ee,ss-ethylenically unsaturated monomer(s) is (are) used in the form of mixture with at least one hydrophobic solvent or with at least one hydrophobic solvent and at least one hydrophobic resin, hydrophobic solvent and/or hydrophobic resin encapsulated resin particles can be obtained and far improved coating composition can be formulated with thus obtained aqueous composition and an aqueous resin (B) hereinafter defined. At this time, outstanding improvements are realized in respect of application characteristics of the coating composition and gloss and smoothness of the formed coating.

Therefore, in a particularly preferred embodiment of the present invention used is made of an aqueous composition containing solvent encapsulated resin particles obtained by the polymerization of a mixture of at least one a,ethylenically unsaturated monomer and at least one hydrophobic solvent in an aqueous medium and in the presence of a water soluble resin (A) and an organic initiator, or an aqueouscomposition containing hydrophobic resin encapsulated resin particles obtained by the polymerization of a mixture of at least one a,ss-ethylenically unsaturated monomer and a hydrophobic resin or both hydrophobic resin and hydrophobic organic solvent, in an aqueous medium and in the presence of a water soluble resin (A) and an organic initiator.

In the abovesaid embodiment, as the hydrophobic solvent, any ofthe organic solvents having solubility in 200Cwater of 10 weight % or less may satisfactorily used, providing having an optimum evaporation rate and boiling point seing from the view point of application characteristics ofthe coating composition. Examples of such organic solvents are heptane, hexane, n-octane, iso-octane, decane, ligroin, kerosine, toluene, xylene, naphthalene, isobutanol, n-butanol, n-hexanol, methyl-n-butyl ketone, butyl acetate, Solvesso 150 (trademark, Esso Petroleum) and other aliphatic or aromatic hydrocarbons, petroleum cuts, alcohols, esters, ketones and the like.

As already stated, the reaction medium may be water alone or a mixture of water and an organic solvent.

The latter solvent may be of the same or different type from the abovesaidhydrophobic organic solvent to be encapsulated in the resin particles, and it may be of water miscible or immiscible nature. By the inclusion of said solvent in a reaction medium, it is possibleto obtain an aqueous coating composition which is lowin foaming, hardly form pinholes and is excellent in gloss, smoothness and sag resistance. When a mixture of hydrophobic solvent and polymerizable monomer(s) is used, the mixing rate of said solvent and monomer(s) may be varied in awiderrange.

It is, however, generally determined in 80:20to 3:97, preferably 60:40 to 10:90, on weight basis. This is because ifthe solvent to be encapsulated is more than 80 wt %, there is a tendency that stability of the coating composition be lowered and ifthe solvent is less than 3%, there is no significant improvement in smoothness of the coating.

As already stated, inclusion of a hydrophobic solvent in the resin particles is effective for the control of viscosity of the coating composition at the application and the baking stages, and hence considerable improvements in application characteristics and coating appearance and especially smoothness can be attained therewith.

a, & thylenically unsaturated monomers may also be used in the form of mixture with a hydrophobic resin or a combination of hydrophobic resin and hydrophobic solvent, to obtain the hydrophobic resin encapsulated resin particles. In this particular embodiment, any of the known hydrophobic resins may be satisfactorily used provided that they are insoluble in water. Examples of such resins are an alkyd resin, a polyester resin, an acryl resin, an acryl modified alkyd resin, an acryl modified polyester resin, an epoxy resin, an aminoplast resin, a polyether resin, a petroleum resin, a silicone resin, a polyurethane resin, a fluorine plastic, a cellulosic resin and the like.

The hydrophobic solvents are the same members as stated hereinbefore.

The mixing ratio of said hydrophobic resin and polymerizable monomer(s) may be varied in a considerable range. It is, however, determined in 1-70:99-30, preferably 5-50:95-50, on weight basis. This is because ifthe amount of said hydrophobic resin is too large, there is a tendency that stability of the resin particles in an aqueous composition be lowered and if the amount ofthe hydrophobic resin is too small, the desired effect of improvement in smoothness of coating cannot be attained therewith.

The inventors have now found that inclusion of hydrophobic resin or a combination of hydrophobic resin and hydrophobic solvent in resin particles is very effective forthe improvements in coating appearance and especially smoothness and gloss, and in application chracteristics and sag resistance of the coating composition.

That is, the presence of hydrophobic resin in the resin particles may contribute to the formation of coating wherein comparatively small size of aggregates of resin particles are stably and uniformly distributed in a water soluble resin phase, for which a highly glossy coating can be obtained. Both of the hydrophobic resin and hydrophobicsolventare effectiveforthe improvement in smoothness of the coating.When a hydrophobic melamine is used, yield value ofthe coating composition is markedly increased and hence, a sag resistance is greatly improved.The presence of a hydrophobic solvent in the resin particles is effective in the control of viscosity of coating composition at the coating and baking stages, which may attribute to the marked improvement in application characteristics such as pinholing and smoothness of coating.

In the present invention, thus obtained aqueous composition containing resin particles is compounded with a particular water soluble resin (B) having a water tolerance of or more and a surface tension for 1% w/w aqueous varnish of 51 dyne/cm or less, which is minutely stated in Japanese Patent Application Kokai No.15567/83.

That is, the water soluble resin (B) must fulfil the requirements: (1) thatthewatertolerance, expressed in terms of the water dilution multiplicand of the water soluble resin for the solution incapable of reading outthe defined type in the test wherein 5g of aqueous varnish having a common viscosity usually employed in the manufacture of a coating composition are correctly weighed in a 100 ml beaker, diluted with an increasing amount of deionized water, and a No. 1 type (26 point type) is read through the said beaker, is 4 or more, and (2) thatthe surface tension of the solution obtained by dissolving the abovesaid aqueous varnish with deionized waterto 1 wt% solid content, is 51 dyne/cm or less.

Any of the known water soluble resins customarily used in a water soluble type coating composition may be satisfactorily used providing fulfilling the requirements stated hereinabove, and examples of such resins are an alkyd resin, a polyester resin, maleic oil, maleic polyalkadiene, and epoxy resin, an acrylic resin,a urethane resin, an aminoplast resin and the like.

However, in the present invention, the solid weight ratio of the abovementioned resin particles to the total of water soluble resins (A) and (B) should be in a range of70:30to 1 :99, preferably 60:40 to 1:99.

This is because, if the amount of water soluble resin is too low, it will cause deterioration of the dispersion stability ofthe resin powders and will damagethe leveling properties of the coated film and if the amount of water soluble resin it too high, it will cause an excessive increase in the viscosity ofthe composition and give rise to a decrease in water resistance ofthe coated film.

However, in the abovementioned compounding ratio,there is no undesired increase in the viscosity ofthe composition. Therefore, in the present invention, it is possible to increase in the solid content of an aqueous coating composition and obtain the product which is excellent in application characteristics and storage stability and capable of resulting the coating with excellent film properties, gloss and smoothness.

The reasons why the present coating composition can give a coating which is far superior to the heretofore proposed aqueous coating compositions in respect of gloss and smoothness have not been fully understood at the moment, but the following might have a close connection therewith. That is, since a particularwater soluble resin (B) is selected and compounded with the aforesaid resin particles, the particles are floated on the surface layer of the water soluble resin varnish and a uniform coating is easily obtained therefrom.

The present coating composition is, therefore, particularly useful as a top coat in an automobile or other industries where a higher level of gloss, e.g. 80 or more of 20 " gloss, or smoothness ofthe coating is required.

The present coating composition may be used as a clear coating composition as desired, and however, in most applications, it is used as a color lacquer. In that case, coloring matter, crosslinking agent and other additives, including antisagging agent, antiflooding agent1 anticratering agent, surface conditioner, antioxidant, light stabilizer, UV absorber, antisettle agent and the like, may be added thereto.

The coating composition can be applied, as it is or after being diluted with water, in a conventional way, e.g. spraying, dipping, brushing or the like, and dried or baked at an elevated temperature to give the coating with excellent properties as hereinbefore stated.

The invention shall be now more fully explained in thefollowing Examples. Unless otherwise being stated, all parts and % are by weight.

Synthetic Example 1 Preparation of water soluble resin varnish-1 Into a 1 liter flask fitted with a stirrer, a thermoregulator and a condenser, were placed 76 parts of ethyleneglycol monobutyl ether, added with 61 parts of a monomer mixture comprising 45 parts of styrene, 63 parts of methyl methacrylate, 48 parts of 2-hydroxyethyl methacrylate, 117 parts of n-butyl acrylate, 27 parts of methacryl acid, 3 parts of lauryl mercaptane, and 3 parts of azobisiisobutyronitrile and the combined mixture was heated under stirring to 1 200C. Thereafter, the remaining 245 parts of the abovesaid monomer mixture were dropwise added in 3 hours and then the mixture was stirred for 1 hour.Next, 28 parts of dimethyl ethanolamine and 200 parts ofdionized waterwere added to obtain an aqueous acrylic resin varnish having a non-volatile content of 50%. Number average molecularweight of the contained resin was 6000.

Synthetic Example 2 Preparation of water soluble resin varnish-2 Into a 2 liter glass reactorfitted with a stirrer, a thermoregulator, and a decanter, were placed 69 parts of trimethylol propane, 297 parts of neopentyl glycol, 91 parts of hydrogenated bisphenol A, 201 parts of tetrahydrophthalicacid, 155 parts oftrimelliticanhydride, and 10 parts ofxylene and the mixturetemperature was raised under stirring condition.The reaction was continued, while maintaining the temperature at 180" to 210"C and removing the formed water from the reaction mixture, for 5 hours to obtain a polyester resin having an acid value of 55, a hydroxyl value of100 and a number average molecularweightofl500. Then, 183 parts ofethyleneglycol monobutyl ether and 82 parts of dimethyl ethanol amine were added and the combined mixture was diluted with 851 parts of deionized water to obtain an aqueous varnish having a non-volatile content of 45%.

Synthetic Example 3 Preparation of resin particles containing composition-l Into a 1 liter reaction vessel fitted with a stirrer, a thermoregulator and a condenser, were placed 320 parts of the water soluble resin varnish-1 obtained in Synthetic Example 1,300 parts of deionized water and 20 parts of butyl diglycol and the mixture was heated, under stirring, to 85'C.To this, a monomer solution of40 parts of styrene, 40 parts of methyl methacrylate, 60 parts of 2-ethyl hexyl acrylate, 20 parts of 2-hydroxyethyl methacrylate, and 4.0 parts of t-butyl peroxy 2-ethyl hexanate was dropwise added in 2 hours and thereafter, the reaction was continued, understirring,for additional 2 hoursto obtain an aqueouscomposition containing resin particles whose non-volatile content was 40.0%.

Synthetic Example 4 Into the similar reaction vessel as used in Synthetic Example 3, were placed 356 parts of the water soluble resin varnish-2 obtained in Synthetic Example 2,264 parts of deionized water and 20 parts of butyl diglycoi and the mixture was heated, u nder stirring, to 85"C. Thereafter, the same monomer solution as used in Synthetic Example 3 were added and reacted as in Synthetic Example 3 to obtain an aqueous composition containing resin particles, whose non-volatile content was 40.1 %.

Synthetic Example 5 Preparation of resin particles containing composition-3 Into the similar reaction yessel as used in Synthetic Example 3,were placed 576 parts of water soluble resin varnish obtained in Synthetic Example 1 and 192 parts of deionized water and the temperature was raised, under stirring, to 85"C. Next, a monomer solution of 8 parts of styrene, 8 parts of methyl methacrylate, 14 parts of 2-ethyl hexyl acrylate, 2 parts of 2-hydroxyethyl methacrylate and 0.4 parts of azobisisobutyronitrile was dropwise added in 2 hours and the combined mixture was reacted, under stirring, for 2 hours, to obtain an aqueous composition containing resin particles, whose non-volatile content was 40.0%.

Synthetic Example 6 Preparation of resin particles containing composition-4 Following the procedures of Synthetic Example 3,256 parts of the water soluble resin varnish-l , 322 parts of deionized water and 30 parts of butyl diglycol were placed in a reactor, the mixture was, understirring, heated to 85 C, a monomer solution consisting of 48 parts of styrene, 48 parts of methyl methacrylate, 80 parts of 2-ethyl hexyl acrylate, 16 parts of 2-hydroxyethyl methacrylate and 2 parts of azobisisobutyronitrile was dropwise added in 2 hours and the combined mixture was reacted, under stirring, for 2 hours, to obtain an aqueous composition containing resin particles.

Synthetic Example 7 Preparation of resin particles contining composition-5 The same procedures as stated in Synthetic Example 3 were repeated excepting substituting the following for the monomer solution of Synthetic Example 3.

styrene 40 parts methyl methacrylate 40 2-ethyl hexyl acrylate 60 2-hydroxyethyl methacrylate 15 ethyleneglycol dimethacrylate 5 azobisisobutyronitrile 2 An aqueous composition containing resin particles and having a non-volatile content of 40.1% was obtained.

Synthetic Example 8 Preparation of resin particles containing composition-6 (comparative composition) Following the procedures of Synthetic Example 3, 128 parts ofthe water soluble resin varnish-1,400 parts of deionized water and 16 parts of butyl digylcol were placed in a reactor, the mixture was heated, under stirring, to 85"C, a monomer solution consisting of 64 parts of styrene, 64 parts of methyl methacrylate, 100 parts of 2-ethyl hexyl acrylate, 28 parts of 2-hydroxyethyl methacrylate and 3 parts of azobisisobutyronitrile was dropwise added in 2 hours and the combined mixture was reacted, under stirring, for 2 hours, to obtain an aqueous composition containing resin particles, whose non-volatile content was 40%.

(Outside ofthe invention, because the weight ratio of water soluble resin (solid) to monomers is 20:80.) Synthetic Example 9 Preparation of comparative resin particles-1 Into a 2 liter glass made reaction vessel fitted with a stirrer, a thermoregulator, and a condenser,were placed 1100 parts of deionized water, which was then heated to 80'C. To this, an aqueous solution of 6 parts of ammonium persulfate in 100 parts ofdionized waterand 5 parts of a monomer solution of210 parts of methyl methacrylate, 75 parts of 2-ethyl hexyl acrylate and 15 parts of n-dodecyl mercaptane were dropwise added, under stirring, and thereafter, stirring was continued for5 minutes.Then, the remaining parts, i.e. 259 parts, of the monomer solution were dropwise added under stirring, and after stirring for 15 minutes, an aqueous solution of 1 part of ammonium persulfate in 10 parts of deionized water was added and the reaction was continued for 1 hour to obtain a seed emulsion having a non-volatile content of 20%.

Into the similar reaction vessel as used in the preparation of said seed emulsion, were placed 300 parts of deionized water and 25 parts of said seed emulsion, and the mixture was heated to 80"C. To this, an aqueous solution of 0.1 part of ammonium persulfate in 20 parts of deionized water was added, under stirring, and then a pre-emulsion of 360 parts of methyl methacrylate, 105 parts of 2-ethyl hexyl acrylate, 35 parts of 2-hydroxyethyl acrylate, 5 parts of n-dodecyl mercaptane, 200 parts of deionized water, 0.4 part ofsodium dodecyl benzenesulfonate and 0.8 part of ammonium persulfate was dropwise added in 2 hours.After completion of said addition, the mixture was stirred for 30 minutes, added with an aqueous solution of 0.2 part of ammonium persulfate in 20 parts of deionized water and further stirred for 1 hour. Thus obtained emulsion had a non-volatile content of 48.5%, and the resin particles separated from the emulsion had an average diameter (measured by electron microscope) of 0.7 ii. The maximum grain diameter was 1 .4 and number average molecular weight of the resin was 9800.

Synthetic Example 10 Preparation of comparative resin particles-2 Into the similar reaction vessel as used in Synthetic Example 9, were placed 700 parts of deionized water and 10 parts of sodium dodecyl benzene sulfonate and the temperature was raised to 80"C. To this, under stirring, 4.5 parts of ammonium persulfate were added and then a monomer mixture of 360 parts of methyl methacrylate, 105 parts of ethyl hexyl acrylate, 35 parts of hydroxyethyl acrylate and 10 parts of n-dodecyl mercaptanewas dropwise added in 2 hours. After elapsing 15 minutes from the completion of said addition, an aqueous solution of 0.5 part of ammonium persulfatein 50 parts of deionized water was added and the reaction was further continued, under stirring, for 1 hour.Thus obtained emulsion had a non-volatile content of 40% and the average grain diameter ofthe resin particles separated from the said emulsion was 0.1 9;i, and number average molecularweight ofthe resin was 8200.

Synthetic Example ii Preparation of comparative resin particles-3 Into the similar reaction vessel as used in Synthetic Example 9, were placed 900 parts of deionized water, 1.5 parts of Metrose 60 SH-50 (methyl cellulose, trade mark, Shinetsu Kagaku Co.), 216 parts of methyl methacrylate, 63 parts of 2-ethyl hexyl acrylate, 21 parts of 2-hydroxyethyl acrylate, 6 parts of n-dodecyl mercaptane, and 6 parts of azobisisobutyronitrile, and the mixture was reacted, under stirring (rotation speed 250 rpm), at65 Cfor7 hours. Thus obtained suspension was filtered through 200 mesh wire net to obtain pearl particles having 20to 6001J, diameters, which wasthen pulverized in a ball mill for 24 hours to obtain resin microparticles having an average diameter of 18 and the maximum grain diameter of i Number average molecularweight of the resin was 7600.

Example 1 Into a 500 cc stainless steel beaker, were placed 10 parts of the water soluble resin varnish 3 shown in the following Table 1,1160 parts ofthe resin particles containing composition-1 obtained in Synthetic Example3, and 15 parts of hexamethoxymethylol melamine and the mixture was stirred well to obtain a clear coating composition.

This composition was flow-coated on a glass plate and heat-treated at 1 200C for 20 minutes to obtain a clear coating, which had a smooth surface and showed no change even after dipping in a top waterfor 24 hours.

The abovesaid composition was diluted with water to a Ford Cup #4viscosity of 30 seconds and then spraycoated on a test plate. The maximum film thickness showing no sagging in this test was 43.

Comparative Example 1 A comparative clear coating composition was prepared as in Example 1, using 100 parts ofthewater soluble resin varnish 3 and 15 parts of hexamethoxymethylol melamine, and diluted with waterandspraycoated. The maximum film thickness showing no sagging with this coating composition was less than 15p.

The characteristics of the water soluble resins (B) used in this and subsequent Examples and Comparative Examples are shown below.

Table 1 water soluble composition water surface acid HO neutra- non-volatile Molecular resin (B) No. tolerance tension value value lization content weight dyne/cm % 3 acrylic resin 10 < 42 70 60 100 40 8200 4 polyester resin 5 49 15 100 100 45 1480 5 acrylic resin 2 54 15 60 100 25 4500 (for Comp.Ex.) Water tolerance: 5 g of aqueous resin varnish were weighed in a 100 ml beaker, diluted with an increasing amount of deionized water and No. 1 type was read through the beaker.

Watertolerancewas a measure of water dilution limitforthewater-soluble resin and expressed asthe water dilution factor at the stage when No. 1 type can no longer be correctly read through the beaker.

Surface tension: An aqueous resin varnish was diluted with deionized water to obtain a 1% w/w aqueous solution. Surface tension was determined with this solution by using a tensiometer (CB-VP typetensiometer, manufactured by Kyowa Kagaku K.K.).

Examples2 to 9 (Preparation of pigment paste) Into a 1.5 liter stainless steel vessel with a closed cover, were placed 36 parts of the water soluble resin varnish 3,320 parts of Rutile type titanium dioxide and 60 parts of deionized water and the mixture was, after being predispersed in a stirrer with 500 ce of glass beads, dispersed well in a paint conditioner for 2 hours to obtain a pigment paste-1.

Another pigment paste-2 was prepared in a same way, by substituting the water soluble resin varnish-4for the abovesaid varnish-3.

(Preparation of coating composition) Into a stainless steel vessel, the materials shown in thefollowing Table 2 were placed in and the mixture was stirred well in a stirrer at a room temperature to obtain the respective coating composition of Examples 2 to9.

Table2 Example pigment paste water soluble resin particles containing MF resin (B) varnish composition 1 2 3 4 1 2 3 4 5 2 133 52 150 14 3 133 52 150 14 4 133 65 125 19 5 133 78 125 14 6 133 52 150 14 7 133 52 168 12 8 133 142 50 18 9 133 5 208 10 Comparative Examples 2 to 8 Using the same procedures as stated in Examples 2 to 9, but substituting the following materials forthose of Examples 2to 9, comparative coating compositions were prepared.

Table3 Comparative pigment watersoluble Comparative resin resin particles MF Example paste resin (B) varnish particles containing composition 1 3 5 1 2 3 1 3 6 2 133 250 10 3 133 250 15 4* 133 125 90 14 5 133 83 14 6 133 140 62 14 7 133 140 75 14 8 133 140 30 14 +... Afterthe preparation of coating composition, the resin particles had been coagulated.

Each of the coating compositions of Examples 2 to 9 and Comparative Examples 2 to 8 was diluted with deionized water to a Ford Cup #4 viscosity of 30 seconds and the diluted composition was spray-coated on a steel plate. After setting for 5 minutes, the coating was baked at 1 50'Cfor 15 minutes to obtain a crosslinked coating.

The maximum film thickness showin no pinholes and the maximum film thickness showing no sagging were determined forthe respective composition, and gloss value and smoothness of thus obtained coating were evaluated.

Evaluation standards are as follows: Application characteristics: Mark film thickness showing film thickness showing no pinholes (ism) no sagging (,um)

morethan 50 morethan 50 morethan 40 to 50 more than 40 to 50 more than 30 to 40 more than 30 to 40 30 or less 30 or less gloss: Mark 60'gloss 20'gloss

morethan 93 more than 85 more than 90 to 93 more than 75 to 85 morethan 80 to 90 more than 65to 75 80 or less 65 or less Smoothness:: excellent good no good Table 4 coating appearance pinhole sagging 60 gloss 20' gloss smoothness resistance resistance

Example 2 Q 8 excellent &commat; 3 4 Q Qo 5 Q Q Q 6 O 7 Q 8 8 8 Q Q Q 9 Q Q Q Q Comp. Ex. 2 0 0 no good X Q 3 0 0 good 0 0 4 - - - - 5 A A good X O 6 0 0 good 0 Q 7 A A nogood X A 8 X X nogood X A Synthetic Example 12 Preparation of resin particles containing composition-7 Into a 1 liter reaction vessel fitted with a stirrer, a thermoregulator and a condenser, were placed 320 parts of the water soluble resin varnish-1 obtained in Synthetic Example 1,300 parts of deionized water and 20 parts of butyl diglycol and the mixture was heated under stirring to 85 C. To this, a monomer solution consisting of 50 parts of styrene, 50 parts of methyl methacrylate, 40 parts of 2-ethyl hexyl acrylate, 20 parts of 2-hydroxyethyl methacrylate, 2 parts of azobisisobutyronitrile and 100 parts of xylene was dropwise added in 2 hours, and the mixture was stirred for additional 2 hours to obtain a composition containing resin particles and having a non-volatile content of 35.5%.

Synthetic Example 13 Preparation of resin particles containing composition-8 Into a similar reaction vessel as used in Synthetic Example 12, were placed 356 parts ofthe water soluble resin varnish 2 obtained in Synthetic Example 2,264 parts of deionized water and 20 parts of butyl diglycol and the mixture was heated, under stirring, to 85 C.

To this, the same monomer solution as used in Synthetic Example 12 was dropwise added in 2 hours and the mixture was further stirred for 2 hours to obtain a composition (8)containing resin particles.

Synthetic Example 14 Preparation of resin particles containing composition-9 Using the same procedures of Synthetic Example 12,576 parts of the water soluble resin varnish 1 and 192 parts of deionized water were placed in a reactor and heated, under stirring,to 85"C. To this, the monomer solution consisting of 8 parts of styrene,8 8 parts of methyl methacrylate, 14 parts of 2-ethyl hexyl acrylate, 2 parts of 2-hydroxyethyl methacrylate, 0.4 parts of azobisisobutyronitrile and 80 parts ofxylene was dropwise added in 2 hours and the reaction was continuedforadditional 2 hours to obtain a composition (9) containing resin particles and having a non-volatile content of 36.3%.

Synthetic Example 15 Preparation of resin particles containing composition-10 Using the same procedures of Synthetic Example 12,320 parts of the water soluble resin varnish 1,322 parts of deionized water and 20 parts o butyl diglycol were placed in a reactor and the mixture was heated under stirring, to 85"C. To this, a monomer solution consisting of 50 parts of styrene, 50 parts of methyl methacrylate, 40 parts of 2-ethyl hexyl acrylate, 20 parts of 2-hydroxyethyl methacrylate, 3 parts of azobisisobutyronitrile and 10 parts of isophoronewas dropwise added in 2 hours and the reaction was furthercon- tinued for 2 hours to obtain a composition (10) containing resin particles. A non-volatile content of this composition was 38.4%.

Synthetic Example 16 Preparation of resin particles containing composition-1 1 Using the same procedures of Synthetic Example 12, 150 parts of the water soluble resin varnish 1 and 150 parts of deionized water were placed in a reactor and heated, under stirring, to 85"C. To this, a monomer solution consisting of 40 parts of styrene, 30 parts of methyl methacrylate, 50 parts of 2-ethyl hexyl acrylate, 10 parts of 2-hydroxyethyl methacrylate, 1.5 parts of azobisisobutyronitrile and 20 parts of xylene was dropwise added in 2 hours and the reaction was further continued, under stirring, for 2 hours to obtain a composition (11) containing resin particles. The non-volatile content of the composition was 45.5%.

Synthetic Example 17 Preparation of comparative resin particles containing composition-1 2 Using the same procedures of Synthetic Example 12,320 parts of the water soluble resin varnish 1,400 parts of deionized water and 20 parts of butyl diglycol were placed in a reactor and the mixture was heated, under stirring, to 850C. To this, a monomer solution consisting of 50 parts of styrene, 50 parts of methyl methacrylate, 40 parts of 2-ethyl hexyl acrylate, 20 parts of 2-hydroxyethyl methacrylate, and 2 parts of azobisiso butyronitrile was dropwise added in 2 hours and the reaction was continued, under stirring, for additional 2 hours to obtain a composition (12) containing resin particles. The non-volatile content ofthe composition was 35.5%.

Synthetic Example 18 Preparation of comparative resin particles-4 Into a 2 liter glass reaction vessel fitted with a stirrer, a thermoregulator, and a condenser, were placed 1100 parts of deionized water and the temperature was raised to 80 C. To this, an aqueous solution of 6 parts of ammonium persulfate and 100 parts of deionized water and 5 parts of a monomer mixture consistintg of210 parts of methyl methacrylate, 75 parts of 2-ethyl hexyl acrylate and 15 parts of n-dodecyl mercaptanewere added and the combined mixture was stirred for 5 minutes. Thereafter, the remaining 259 parts of said monomer mixture were dropwise added to the reactor in 1 hour.After completion of said addition, the mixture was stirred for additional 15 minutes, added with an aqueous solution of 1 part of ammonium persulfate and 10 parts of deionized water, and the combined mixture was further stirred and reacted for 1 hour to obtain a seed emulsion having a non-volatile content of 20%.

Into a similar reaction vessel as used herein, were placed 300 parts of deionized water and 25 parts ofthe aforesaid seed emulsion, and the mixture was heated to 80"C. To this, an aqueous solution of 0.1 part of ammonium persulfate and 20 parts of deionized water was added and then a pre-emulsion consisting of 155 parts of styrene, 155 parts of methyl methacrylate, 125 parts of 2-ethyl hexyl acrylate, 65 parts of 2hydroxyethyl methacrylate,0.4 part of sodium n-dodecylbenzene soTulfonate, 0.8 part of ammonium persulfate and 180 parts ofxylene was dropwise added in 2 hours.After completion of said addition, stirring was continued for 30 minutes and at this stage, an aqueous solution of 0.2 part of ammonium persulfate and 20 parts of deionized water was added and the combined mixture was further stirred and reacted for 1 hourto obtain an emulsion having a non-volatile content of 41.2%. The mean diameter of the resin particles contained was 0.7 > (by electromicroscopic determination) and the maximum grain diameter was 0A. . The number average molecular weight of the resin was 9800.

Examples lOto 15 Into a stainless steel vessel, the materials shown in thefollowing Table Swere placed and stirred at room temperature to obtain the respective coating compositions of Examples 10 to 15.

TableS Example pigment paste * water soluble resin particles MF ** resin (B) containing composition 1 2 3 4 7 8 9 10 11 10 52 25 85 10 11 52 22 85 12 12 52 5 100 15 13 52 20 85 12 14 52 75 28 12 15 52 5 83 10 f... water soluble resin (A) and pigment **... hexamethoxy methylolmelamine resin Comparative Examples 9 to 11 Using the same procedures of Example 10, but using the materials shown in thefollowing Table 6, compar- ativecoating compositions were prepared.

Table 6 Comparative pigment paste water soluble resin particles (4) resin particles MF * Example resin varnish (B) obtained in containing SyntheticEx.18 composition 1 3 5 4 7 12 9 52 25 85 10 10 52 50 85 10 11** 52 63 37 12 *... hexamethoxy methylolmelamine resin **... afterthe preparation of coating composition, the resin particles contained were agglomerated and separated in the composition.

Each ofthe coating compositions obtained in Examples 1 Oto 15 and Comparative Examples 9to 11 was diluted with deionized water to a Ford Cup #4viscosity of 30 seconds, and the diluted composition was spray-coated onto a steel plate, and after setting for 5 minutes, baked at 1 50"C for 15 minues to obtain a cured coating. The gloss value, and smoothness of the coating and time stability of the respective coating composition were evaluated and the results were shown in Table 7.

Table7 coating appearance timestability 600 gloss 200 gloss smoothness Example 10 Q Q excellent excellent 11 t

12 8 8 13 6 0 t t 14 Q Q 15 O t t Comp. Ex. 9 0 A no good excellent 10 A X good good 11 - - - nogood Synthetic Example 19 Preparation of hydrophobic resin varnish Into a 1 liter reaction vessel fitted with a stirrer, a thermoregulator and a condenser, were placed 25 parts of xylene and the temperature was raised, under stirring, to 1 25"C. To this, a monomer solution consisting of 30 parts of styrene,15 parts of methyl methacrylate, 40 parts of 2-ethyl hexyl methacryalte, 15 parts of 2hydroxyethyl methacrylate and 4 parts of azobisisobutyronitrilewas dropwise added in 2 hours and thereaf tes, the combined mixture was stirred for 2 hours to obtain an acrylic hydrophobic resin varnish having a non-volatile content of 80%. The number average molecular weight of the formed resin was 5000.

Synthetic Example 20 Preparation of hydrophobic resin encapsulated resin particles containing composition-13 Into a 1 liter reaction vessel fitted with a stirrer, a thermoregulator and a condenser, were placed 320 parts ofthe water soluble resin varnish 1 obtained in Synthetic Example 1,300 parts of deionized water and 20 parts of butyl diglycol, and the mixture was heated, under stirring, to 85"C. To this, a monomersolution consisting of 50 parts of styrene, 50 parts of methyl methacrylate, 40 parts of 2-ethyl hexyl acrylate, 20 parts of 2-hydroxyethyl methacrylate, 2 parts of azobisisobutyronitrile and 60 parts of the hydrophobic resin varnish obtained in Synthetic Example 19 was dropwise added in 2 hours and the combined mixture was stirred for2 hours to obtain a composition containing hydrophobic resin encapsulated resin particles. The non-volatile content of the composition was 42.6%.

Synthetic Example 21 Preparation of hydrophobic resin encapsulated resin particles containing composition-14 Using the same procedure as stated in Synthetic Example 20,356 parts ofthe water soluble resin varnish obtained in Synthetic Example 2. 264 parts of deionized water and 20 parts of butyl diglycol were placed in a reactor and the mixture was heated to 85"C. Then, the similar monomer solution as used in Synthetic Example 1 9was dropwise added in 2 hours and the combined mixture was stirred for 2 hours to obtain a composition containing hydrophobic resin encapsulated resin particles. The non-volatile content of the composition was 42.6%.

Synthetic Example 22 Preparation of hydrophobic resin encapsulated resin particles containing composition-l 5 As in Synthetic Example 20,320 parts ofthewater soluble resin varnish-1,300 parts of deionized water and 20 parts of butyl diglycol were placed in a reactor and the mixture was heated, u nder stirring, to 85"C. Then, a monomer solution consisting of 8 parts of styrene, 8 parts of methyl methacrylate, 10 parts of 2-ethyl hexyl methacrylate, 6 parts of 2-hydroxyethyl methacrylate, 1.5 parts of azobisisobutyronitrile and 20 parts of hexamethoxy methylol melamine resin was dropwise added in 2 hours and the combined mixture was stirred for 2 hours to obtain a composition containing hydrophobic resin encapsulated resin particles.The non-volatile content of the composition was 49.0%.

Synthetic Example 23 Preparation of hydrophobic resin encapsulated resin particles containing composition-1 6 As in Synthetic Example 20.320 parts of the water soluble resin varnish 1,400 parts of deionized water and 10 parts of butyl diglycol were placed in a reactor and the mixture was heated, under stirring,to 85"C. To this, a monomer solution consisting of 75 parts of styrene, 75 parts of methyl methacrylate, 60 parts of 2-ethyl hexyl methacrylate, 30 parts of 2-hydroxyethyl methacrylate, 3 parts of azobisisobutyronitrile and 24 parts of Epicoat 1001 (Shell Chemical) was dropwise added in 2 hours and the combined mixture was stirred for2 hours to obtain a composition containing hydrophobic resin encapsulated resin particles. The non-volatile content ofthe composition was 42.6%.

Synthetic Example 24 Preparation of comparative resin particles containing composition-17 As in Synthetic Example 20,320 parts of water soluble resin varnish 1,400 parts of deionized water and 20 parts of butyl diglycol were placed in a reactor and the mixture was heated, under stirring, to 85"C. To this, a monomer solution consisting of 50 parts of styrene, 50 parts of methyl methacrylate, 40 parts of 2-ethyl hexyl acrylate, 20 parts of 2-hydroxyethyl methacrylate, and 2 parts of azobisisobutyronitrile was dropwise added in 2 hours and the combined mixture was stirred for 2 hours to obtain a composition containing resin part- icles. The non-volatile content ofthe composition was 35.5%.

Synthetic Example 25 Preparation of comparative resin particles 5 Into a 2 liter glass reaction vessel fitted with a stirrer, a thermoregulator and a condenser, were placed 1100 parts of deionized water and the content was heated, under stirring to 80 C. To this, an aqueous solution of 6 parts of ammonium persulfate in 100 parts of deionized water and 5 parts of the monomer mixture of 210 parts of methyl methacrylate, 75 parts of 2-ethyl hexyl acrylate and 15 parts of n-dodecyl mercaptanewere added, under stirring, and the combined mixture was stirred for5 minutes. While stirring, the remaining 259 parts of the monomer mixture were dropwise added and the combined mixture was stirred for additional 15 minutes.

Thereafter, an aqueous solution of 1 part of ammonium persulfate in 10 parts of deionized water was added and the mixture was reacted, under stirring, for 1 hour to obtain a seed emulsion having a non-volatile content of 20%.

Into a similar reaction vessel as stated hereinabove, were placed 200 parts of deionized water and 25 parts of the abovesaid seed emulsion, and the temperature was raised to 80"C. To this, an aqueous solution of 0.1 part of ammonium persulfate in 20 parts of deionized water was added and then a pre-emulsion consisting of 155 parts of styrene, 155 parts of methyl methacrylate, 125 parts of 2-ethyl hexyl acrylate, 65 parts of 2- hydroxyethyl methacrylate,5 parts of n-dodecyl benzene sulfonate, 0.8 parts of ammonium persulfate and 150 parts of the hydrophobic resin varnish obtained in Synthetic Example 19 was dropwise added in 2 hours.

After stirring for 30 minutes, an aqueous solution of 0.2 part of ammonium persulfate in 20 parts of deionized water was added and the combined mixture was reacted under stirring for 1 hourto obtain an emulsion containing resin particles. The non-volatile content of the emulsion was 41.2%. The resin particles were separated from thus obtained emulsion. by an electron microscopic examination, it was found thatthe average grain diameter of said particles was 0.7p and the maximum grain diameter was 1.4F.The number aver age molecularweightofthe resin was 9800.

Examples 16to20 Into a stainless steel vessel, the materials shown in thefollowing Table 8 were placed in and the mixture was stirred well in a stirrer at a room temperature to obtain the respective coating composition of Examples 16to 20.

Table8 Example pigment paste water soluble resin particles MF* resin (B) varnish containing composition 1 2 3 4 13 14 15 16 16 52 20 81 12 17 52 22 81 10 18 52 10 72 7 19 52 7 81 12 20 52 40 32 15 *... hexamethylol melamine Comparative Examples 12to 14 Using the same procedures as stated in Examples 16 to 20, but substituting the following materials for those of Examples 16 to 20, comparative coating compositions were prepared.

Table9 Comp. Ex. pigment water soluble Comparative resin resin particles (5) MF paste resin (B) varnish particles obtained in Synth. Ex. 25 1 3 S 13 17 5 12 52 20 85 12 13 52 40 81 12 14* 52 50 37 10 +... Afterthe preparation of coating composition, the resin particles contained were agglomerated and separated.

Each ofthe coating compositions of Examples 16 to 20 and Comparative Examples 12 to 14was diluted with deionized water to a Ford Cup #4viscosity of 30 seconds and the diluted composition was spray-coated on a steel plate. After setting for 5 minutes, the coating was baked at 1 50"C fo r 15 minutes to obtain a crossli- nked coating. The maximum film thickness showing no pinholes and the maximum film thickness showing no sagging were determined forthe respective composition, and gloss value and smoothness ofthus ob- tained coating were evaluated. The results are shown in Table 10.

Table 10 coating appearance time stability 60"gloss 20"gloss smoothness

Example 16 8 8 excellent excellent 17 Q 1 18 8 Q 1 19 (Q) 0 t t 20 Q Q T Comp.Ex. 12 0 A no good excellent 13 A X good good 14 - - - no good

Claims

1. An aqueous coating composition comprising as resinous vehicle (1) an aqueous composition containing resin particles obtained by polymerizing at least one a,ss- ethylenically unsaturated monomer in an aqueous medium and in the presence of an aqueous resin (A) with the help of an organic initiator, in which the solid weight ratio of said aqueous resin to said monomer is 35-95:65-5, and (2) an aqueous resin (B) having a water tolerance of 4 or more and a surface tension for a 1 %w/waqueous resin solution of 51 dyne/cm or less,the solid weight ratio of said resin particlestothetotal of said aqueous resins (A) and (B) being 70-1 :30-99.

2. A composition according to claim 1, wherein the aqueous resins (A) and (B) each is selected from the group consisting of a polyester resin, an alkyd resin, an acryl resin, an acryl modified polyester resin, an acryl modified alkyd resin;

3. A composition according to claim 1, wherein the organic initiator is selected from the group consisting of a diacyl peroxide, a hydroperoxide, an alkyl peroxide, an azo compound, a disulfide, and a sulfinic acid.

4. Acomposition according to claim 1,wherein the aqueous medium contains an organicsolvent.

5. A composition according to claim 1, wherein the a,ss-ethylenically unsaturated monomer includes a crosslinking monomer having in its molecule at least 2 radiclly polymerizable, ethylenically unsaturated bondings.

6. An aqueous coating composition comprising as resinous vehicle (1) an aqueous composition containing solvent encapsulated resin particles obtained by polymerizing a mixture of at least one a,ss-ethylenically unsaturated monomer and at least one hydrophobic solvent in an aqueous medium and in the presence of an aqueous resin (A) with the help of an organic initiator, in which the weight ratio of said aqueous resin solid to the monomer is 35-95:65-6,and (2) an aqueous resin (B) having awatertolerance of 4 or more and a surface tension for 1 %w/waqueous resin solution of 51 dyne/cm or less,the solid weight ratio of said resin particles to the total of said aqueous resins (A) and (B) being 70-1:30-99.

7. A composition according to claim 6, wherein the weight ratio of said hydrophobic solvent to a,ss- ethylenically unsaturated monomer is 80-3:20-97.

8. A composition according to claim 6, wherein the aqueous resins (A) and (B) each is selected from the group consisting of a polyester resin, an alkyd resin, an acryl resin, an acryl modified polyester resin, an acryl modified alkyd resin.

9. A composition according to claim 6, wherein the organic initiator is selected from the group consisting of a diacyl peroxide, a hydroperoxide, an alkyl peroxide, an azo compound, a disulfide, and a sulfinicacid.

10. A composition according to claim 6, wherein the aqueous medium contains an organic solvent.

11. A composition according to claim 6, wherein the a,(S-ethylenically unsaturated monomer includes a crosslinking monomer having in its molecule at least 2 radically polymerizable, ethylenically unsaturated bondings.

12. An aqueous coating composition comprising as resinous vehicle (1) an aqueous composition containing hydrophobic resin encapsulated resin particles obtained by polymerizing a mixture of at least one a,ss-ethylenicaily unsaturated monomer and a hydrophobic resin or both hydrophobic resin and hydrophobic organic solvent, in an aqueous medium and in the presence of an aqueous resin (A), with the help of an organic initiator, theweight ratio of said aqueous resin solid to the monomer being 35-95:65-5, and (2) an aqueous resin (B) having a watertolerance of 40r more and a surface tension for 1 %w/waqueous resin solution of 51 dyne/cm or less, the solid weight ratio of said particles to the total of said aqueous resins (A) and (B) being 70-1:30-99.

13. A composition according to claim 12, wherein the aqueous resins (A) and (B) each is selected from the group consisting of a polyester resin, an alkyd resin, an acryl resin, an acryl modified polyester resin, an acryl modified alkyd resin.

14. A composition according to claim 12, wheren the organic initiator is selected from the group consisting of a diacyl peroxide, a hydroperoxide, an alkyl peroxide, an azo compound, a disulfide, and a sulfinic acid.

15. A composition according to claim 12, wherein the hydrophobic resin is selected from the group consisting of an alkyd resin, a polyester resin, an acryl resin, an acryl modified alkyd resin, an acryl modified polyester resin, an epoxy resin, an aminoplast resin, a polyether resin, a petroleum resin, a silicon resin, a polyurethane resin, a fluorinated resin, and a cellulose series resin.

16. A composition according to claim 12, wherein the aqueous medium contains an organic solvent.

17. A composition according to claim 12, wherein the or,P-ethylenically unsaturated monomer includes a crosslinking monomer having in its molecule at least 2 radically polymerizable, ethylenically unsaturated bondings.

18. A composition according to claim 12, wherein the solid weight ratio of said hydrophobic resin to said unsaturated monomer is 1/99 to 70/30.

19. An aqueous coating composition according to claim 1, substantially as herein described in any ofthe foregoing Examples.