ELECTRODEPOSITION COATING COMPOSITION

Abstract: An electrodeposition coating composition containing polymer microparticles of 0.01 to 20 microns size is disclosed. The polymer microparticles have a predetermined range of softening point, solubility parameter, refractive index or crosslinking density.

Description: Electrodeposition coating processes have been a wide use for applying anti-corrosive primer coatings to various metallic substrates such as automobile bodies because they are applicable to a variety of substrates regardless of shape or configuration and also hazardless to attendant workers and to the environment. Coating compositions used in the electrodeposition processes are in the form of an aqueous solution or dispersion of electrically charged resin particles. Accordingly, their stability and throwing power are important for the consistent operation of an electrodeposition coating line. With regard to finished coating films, it is desirable to have a large film thickness and high performance properties in such a field as automobile painting where a high corrosion and chipping resistance is essential. Furthermore, there is ever growing needs among users for coated articles having a highly aesthetic appearance in terms of sharpness and gloss. It is known that the throwing power of an electrodeposition coating composition may be improved by incorporating thereto an amount of pigment particles having a suitable particle size. Japanese Laid Open Patent Application 58-47067 discloses the addition of resinous components used in a pulverulent coating composition into electrodeposition coating compositions to improve the throwing power thereof. Japanese Laid Open Patent Application 55-135180 proposes to incorporate an emulsion of polymers having a functional group capable of crosslinking with a base polymer in order to improve the throwing power of the electrodeposition coating composition containing said base polymer. Japanese Laid Open Patent Applications 56-49766 and 58-93762 disclose an electrodeposition coating composition containing crosslinked polymer particles or powder for use in giving a mat finish on a glaring surface such as aluminum or aluminum alloy substrates. These known compositions containing pigment or resin particles suffer from certain disadvantages in that they are not so effective as desirable in enhancing the throwing power, that other properties such as storage stability or film appearance are adversely affected, and that they are not adapted for a wide variety of uses. SUMMARY OF THE INVENTION It is, therefore, a main object of the present invention to provide an electrodeposition coating composition containing an amount of polymer microparticles which can alleviate all or most of the above mentioned disadvantages of known compositions. Other advantages and objects of this invention will become apparent to those skilled in the art as the description proceeds. According to this invention, there is provided an electrodeposition coating composition comprising: (a) an aqueous dispersion of a water-dispersible, electrically depositable cationic resin in an aqueous medium containing an amount of acid sufficient to achieve at least 20 % neutralisation of said resin which is neither soluble nor dispersible in water in its unneutralised form but soluble or dispersible in water in an at least 20 % neutralised form; and (b) 1 to 50 % by weight of the total solid content of the composition of internally crosslinked polymer microparticles having a particle size from 0.01 to 20 microns uniformly dispersed in said aqueous dispersion, said polymer microparticles having been prepared by polymerizing a mixture of ethylenically unsaturated monomers comprising a monomer having at least two ethylenically unsaturated polymerizable sites per molecule, said polymer microparticles being electrically neutral or cationic and having a crosslinking density of 0.01 to 5.05 mmol/g. Electrodeposition coating films are usually subjected to a baking step at an elevated temperature. If the coating film exhibits an excessive fluidity during this baking step, corners or edges of a coated substrate will not be fully covered by the coating film having desirable thickness. Polymer microparticles having a particle size of 0.01 to 20 microns and a crosslinking density of 0.01 to 5.05 mmol/g may be used for controlling the fluidity of electrodeposition coating films during the curing step. The polymer microparticles incorporated to the coating composition of this invention do not adversely affect the stability and the workability of the coating composition. Nor do they have any adverse effect on the finished coating film. They exhibit some advantageous effects on the properties of the resulting coating film. DETAILED DISCUSSION WATER-DISPERSIBLE, ELECTRICALLY DEPOSITABLE RESIN This invention is applicable to cathodic electrodeposition coating compositions. Water-dispersible resins usable in the electrodeposition coating process may be classified, depending upon their dispersed state, into the solution type, the dispersion type, the emulsion type and the suspension type. These types of resins are collectively referred to as "water-dispersible resins" herein. A wide variety of such resins are known and may be used in this invention. Water-dispersible resins used in the cathodic electrodepositin coating process have a cationic functional group such as primary, secondary or tertiary amine moiety as a positively chargeable hydrophilic group. A variety of such resins are konwn including epoxy, polyether, polyester, polyurethane, polyamide, polybutadiene, phenolic and acrylic resins. According to the curing mechanism of particular resins, they may be classified into three classes. The first one is those capable of self-crosslinking through a radical or oxidative polymerization reaction. The second class of resins requires a crosslinking agent such as melamine resins or blocked polyisocyanates. The third one utilizes both the self-crosslinking reaction and the crosslinking agent in combination. According to the type of energy source required for initiating the crosslinking reaction, the water-dispersible, chargeable resins may also be classified into the ambient temperature curing, heat-curing and radiation e.g. UV or electron beam curing types. The water-dispersible resins must be hydrophilic such that they are not soluble or dispersible in water when they are in the form of a free base, but become soluble or dispersible to make a stable aqueous solution or dispersion when at least 20 % of the base function is neutralized. If the water-dispersible resins are too hydrophilic, they fail to form a coating film having satisfactory water- or corrosion resistance and/or the application of electrodeposition coating processes become impossible. In order to enhance various film properties, the water-dispersible resins are often used in the form of an emulsion in which said water-dispersible resin constitutes a continuous phase and a water-insoluble resin free from chargeable hydrophilic groups such as epoxy acrylate resin constitutes a dispersed phase. The term "electrically depositable, water-dispersible resins" as used herein includes all of the aforesaid resins and resin mixtures. Further details of electrically depositable resins are well-known to those skilled in the art and thus need not be discussed herein. POLYMER MICROPARTICLES Several methods are known for preparing the polymer microparticles. One method includes the steps of emulsion or suspension polymerizing a mixture of ethylenically unsaturated monomers in an aqueous medium, and removing water from the emulsion by means of solvent substitution, azeotropic distillation, centrifugation, drying and the like. Another method commonly referred to as the non-aqueous dispersion (NAD) method or precipitation polymerization method comprises polymerizing a mixture of ethylenically unsaturated monomers in a non-aqueous organic liquid such as aliphatic hydrocarbons having low solubility parameters or those solvents having high solubility parameters in which the monomer mixture is soluble but the polymer is insoluble to form a non-aqueous dispersion of the polymeric microparticles. The polymeric micraparticles used in the present invention may be prepared by any of these known methods. The monomer mixture contains, at least as a portion thereof, a monomer having at least two ethylenically unsaturated polymerizable sites per molecule as a cross-linking monomer to give microparticles which are internally cross-linked. Examples of ethylenically unsaturated monomers used for the production of microparticles include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, styrene, α-methylstyrene, vinyltoluene, t-butylstyrene, ethylene, propylene, vinyl acetate, vinyl propionate, acrylonitrile, methacrylonitrile, dimethylaminoethyl (meth)acrylate and the like. Two or more monomers may be combined. Cross-linking monomers include a monomer having at least two ethylenically unsaturated polymerizable sites per molecule. Monomers having at least two ethylenically unsaturated polymerization sites may typically be represented by esters of a polyhydric alcohol with an ethylenically unsaturated monocarboxylic acid, esters of an ethylenically unsaturated monoalcohol with a polycarboxylic acid and aromatic compounds having at least two vinyl substituents. Specific examples thereof incude ethylene glycol diacrylate, ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, 1,4-butanediol diacrylate, neopentyl glycol diacrylate, 1,6-hexanediol diacrylate, pentaerythritol diacrylate, pentaerythritol triacrylate, pentaerythritol tetracrylate, pentaerythritol dimethacrylate, pentaerythritol trimethacrylate, pentaerythritol tetramethacrylate, glycerol diacrylate, glycerol allyloxy dimethacrylate, 1,1,1-tris(hydroxymethyl)ethane diacrylate, 1,1,1-tris(hydroxymethyl)ethane triacrylate, 1,1,1-tris(hydroxymethyl)ethane dimethacrylate, 1,1,1-tris(hydroxymethyl)ethane trimethacrylate, 1,1,1-tris(hydroxymethyl)propane diacrylate, 1,1,1-tris(hydroxymethyl)propane triacrylate, 1,1,1-tris(hydroxymethyl)propane dimethacrylate, 1,1,1-tris(hydroxymethyl)propane trimethacrylate, triallyl cyanurate, triallyl isocyanurate, triallyl trimellitate, diallyl phthalate, diallyl terephthalate and divinyl benzene. Polymer microparticles are recovered by such conventional means as filtration, spray drying or lyophilization. Polymer microparticles in an aqueous or nonaqueous medium may be isolated in a similar manner and used directly without heating or after milling to a suitable particle size. Alternatively, the dispersion containing the polymer microparticles may be subjected to solvent substitution and the resulting suspension in a new medium may be incorporated in the composition of this invention. The average size or diameter of the polymer mlcroparticles may be controlled by selecting an appropriate polymerization method. The emulsion polymerization and NAD method are suited for 0.01 to 0.6 micron range while the precipitation polymerization method is suited for 0.2 to 20 micron range. It is preferable for the polymer microparticles used in the present invention to bear on their surfaces ionic groups having the same polarity as that of the binder resin to be combined i.e. a cationic group such as amino group for cathodic electrodeposition. This may be effected by incorporating a monomer having both ethylenic unsaturation and a basic group such as dimethylaminoethyl (meth)acrylate or vinylpyridines to the monomer mixture constituting the polymer microparticles. Alternatively, the cationic group may be given to the polymer microparticles by using a polymerization initiator which gives the base terminal when polymerizing the monomer mixture. The polymer microparticles having ionic groups may also be prepared by emulsion polymerizing monomer mixtures having no ionic group in the presence of an emulsifier having ionic groups, particularly amphoionic groups such oligosoaps, polysoaps or reactive emulsifiers disclosed in Japanese Laid Open Patent Applications 56-24461, 57-21927 and 57-40522. The polymer microparticles may also be prepared by polymerizing a mixture of ethylenically unsaturated monomers using the solution- or bulk polymerization technique, pulverizing the resulting polymer mass into microparticles and classifying or sieving the microparticles. The crosslinking density of the polymer microparticles may be controlled by varying the molar fraction of crosslinking monomers in the momomer mixture forming the polymer microparticles. ELECTRODEPOSITION COATING COMPOSITION The electrodeposition coating composition of this invention comprises, as essential components, the aforesaid electrically depositable base resin and the polymer microparticles. The proportion of the polymer microparticles ranges from 1 to 50 % by weight of the total solid content of the composition. If this proportion is too low, the effect of polymer microparticles can not be expected. Conversely, excessive addition of the microparticles tend to affect the storage stability and workability of the composition of this invention. The coating composition of this inventin may contain an auxiliary curing agent such as melamine resin, benzoguanamine resin, phenol resin or blocked polyisocyanate compounds, or a metallic dryer compound such as manganese, cobalt, copper, tin or lead compounds. These components are uniformly dispersed in an aqueous medium containing an acid in the case of cathodic electrodeposition in an amount sufficient to neutralize at least 20 % of the binder resin. Examples of acids include phosphoric acid, acetic acid, propionic acid and lactic acid. The aqueous medium is water or a mixture of water and a water-miscible organic solvent such as ethylcellosolve, propylcellosolve, butylcellosolve, ethyleneglycol dimethyl ether, diacetone alcohol, 4-methoxy-4-methylpentanone-2 or methyl ethyl ketone. A small amount of a water-immiscible organic solvent such as xylene, toluene, methyl isobutyl ketone or 2-ethylhexanol may be added to the mixture of water and the water-miscible organic solvent. The electrodeposition coating composition of this invention may further contain conventional pigments such as titanium dioxide, ferric oxide, carbon black, aluminum silicate, precipitated barium sulfate,aluminum phosphomolybdate, strontium chromate, basic lead silicate or lead chromate. The electrodeposition coating composition must have an electroconductivity from 0.1 to 5 mS/cm, preferably from 0.5 to 3 mS/cm. When this value is too low, it is difficult to obtain a film thickness having desired protective and other functions. Conversely, if the composition is too conductive, problems such as the dissolution of substrate or counter electrode in the bath, uneven film thickness or poor water- or corrosion resistance will arise. The electrodeposition coating composition of this invention may be applied on a conductive substrate by the electrodeposition coating process at a nonvolatile content of 10 to 20 % by weight to a dry film thickness of 15 to 30 microns. After applying, the resulting coating film may be cured at ambient or an elevated temperature, or by irradiating with UV or electron beam depending upon the nature of particular base resins. The invention is further illustrated by the following examples in which all parts and percents are by weight unless otherwise specified. Production Example 1 NISSEKI polybutadiene B-2000 ( Mn = 2,000, 1,2-vinyl = 65 %) was epoxidized with peracetic acid to obtain an epoxidized polybutadiene having an oxirane oxygen content of 6.4 %. 1,000 g of the epoxidized polybutadiene, 354 g of ethylcellosolve and 62.1 g of dimethylamine were reacted in a 2 liter autoclave at 150 °C for 5 hours. After unreacted dimethylamine was distilled off the residue was cooled to 120 °C. A mixture of 79.3 g of acrylic acid, 7.6 g of hydroquinone and 26.4 g of ethylcellosolve was added to the residue and reacted therewith at 120 °C for 3 3/4 hours. A cationic resin varnish having an amine number of 85.2 millimoles/100 g, an acid number of 100 millimoles/100 g, and a solid content of 75.0 % was obtained. Production Example 2 1,000 g of bisphenol A epoxy resin (EPIKOTE 1004, epoxy equivalent = 950, Yuka Shell Epoxy Co., Ltd.) was dissolved in 343 g of ethylcellosolve. To the solution was added a mixture of 76.3 g of acrylic acid, 10 g of hydroquinone and 5 g of N,N-dimethylaminoethanol. The mixture was reacted at 100 °C for 5 hours to obtain a solution of epoxy acrylate resin having a solid content of 75 %. Production Example 3 1,000 g of NISSEKI polybutadiene B-1000 ( Mn = 1,000, 1,2-vinyl = 60 %), 265.8 g of maleic anhydride, 1 g of ANTIGEN 6C (Sumitomo Chemical Industry Co., Ltd.) and 10 g of xylene were added to a 2 liter separable flask having a reflux condenser attached thereto. The mixture was reacted at 190 °C for 5 hours under nitrogen gas current. Unreacted maleic anhydride and xylene were distilled off in vacuo to obtain maleinized polybutadiene having an acid number of 214 millimoles/100 g. 1,000 g of the maleinized polybutadiene was reacted with 212.4 g of ethylcellosolve at 120 °C for 2 hours to open the acid anhydride ring. A half ester of maleinized polybutadiene having a solid content of 98 % was obtained. Production Example 4 Epoxydized polybutadiene, E 1800-6.5 (Nippon Petrochemical Co., Ltd.) 1000 g Butylcellosolve 349 g Dimethylamine 46 g 50 % Lactic acid 138 g Deionized water 473 g Phenyl glycidyl ether 117 g An autoclave was charged with epoxidized polybutadiene E 1800-6.5, butylcellosolve and dimethylamine. The mixture was reacted at 150 °C for 5 hours. After unreacted dimethylamine was distilled off, the product was cooled to 60 °C, diluted with a mixture of 50 % lactic acid and deionized water, and then stirred at 80 °C for 30 minutes. Then phenyl glycidyl ether was added and the temperature was raised to 110 °C. The reaction was continued at the same temperature with stirring until the acid number of the reaction product was less than 0.1 when titrating with alcoholic potassium hydroxide using phenolphthalain indicator. A solution of cationic resin having a nonvolatile content of 55 % was obtained. Production Example 5 To a two liter flask having stirring means, a reflux condenser, temperature-control means, a nitrogen gas-introducing tube and a decanter were added 134 parts of N,N-bis(hydroxyethyl)taurine, 130 parts of neopentyl glycol, 236 parts of azelaic acid, 186 parts of phthalic anhydride, and 27 parts of xylene. The mixture was refluxed and water was removed as an azoetropic mixture with xylene. The temperature was raised to 190 °C over 2 hours and the reaction was continued with stirring until an acid number of 145 was reached. The reaction product was cooled to 140 °C and 314 parts of CARDURA E-10 (glycidyl versatate, Shell Chemical Company) was added dropwise over 30 minutes at 140 °C. The reaction was continued for additional two hours with stirring. A polyester resin having an acid number of 59, a hydroxyl number of 90 and a number average molecular weight ( Mn ) of 1054 was obtained. To a one liter flask equipped with stirring means, cooling means and temperature-control means were added 306 parts of deionized water, 45 parts of the above polyester resin and 4.5 parts of dimethylethanolamine. The mixture was stirred at 80 °C to make a solution. To the solution was added a solution of 4.5 parts of azobiscyanovaleric acid in 45 parts of deionized water containing 4.3 parts of dimethylethanolamine. Then a monomer mixture consisting of 55.7 parts of styrene, 41.7 parts of methyl methacrylate, 13.9 parts of n-butyl acrylate, 83.5 parts of ethyleneglycol dimethacrylate and 5.6 parts of dimethylaminopropyl methacrylate was added dropwise over 60 minutes. After addition of monomer mixture, a solution of 1.5 parts of azobiscyanovaleric acid in 15 parts of deionized water containing 1.4 parts of dimethylethanolamine was added. The mixture was stirred for additional 60 minutes at 80 °C. A dispersion of cationic polymer microparticles having a nonvolatile content of 45 %, a particle size of 51 nm and a crosslinking density of 1.562 mmol/g was obtained. Production Example 6 To the same flask as used in Production Example 5 were placed 100 parts of ethyleneglycol monomethyl ether. Two drip funnels were mounted to the flask. A solution of 75 parts of N-methyl-N-(vinylbenzyl) taurine in 100 parts of ethyleneglycol monomethyl ether containing a small amount of dimethylethanolamine was placed into one funnel. A monomer mixture consisting of 50 parts of 2-hydroxyethyl acrylate, 10 parts of acrylic acid, 110 parts of methyl methacrylate, 110 parts of styrene and 145 parts of n-butyl acrylate was placed into the other funnel. A mixture of 10 parts laurylmercaptan and 10 parts of azobisbutyronitrile was dissolved in the monomer mixture. The contents of two funnels were then added dropwise to the flask at 100 °C over 120 minutes. After the addition, the mixture was stirred at 100 °C for 60 minutes and evaporated in a rotary evaporator to remove the solvent. An acrylic resin having a solid content of 96 % and a number average molecular weight of 4500 was obtained. A one liter flask equipped with stirring means, condenser and temperature controlling means was charged with 306 parts of deionized water, 18 parts of the above acrylic resin and 2.6 parts of dimethylethanolamine. The content was heated to 80 °C with stirring to make a solution. A solution of 4.8 paarts of azobiscyanovaleric acid in 48 parts of deionized water containing 4.56 parts of dimethylethanolamine was added with stirring while maintaining the inner temperature at 80 °C. A monomer mixture consisting of 26.6 parts of styrene, 79.8 parts of methyl methacrylate, 53.2 parts of n-butyl acrylate, 53.2 parts of ethylene glycol dimethacrylate, 53.2 parts of ethyl acrylate and 16.0 parts of diethylaminoethyl acrylate was added dropwise over 60 minutes. After the addition, a solution of 1.2 parts of azobiscyanovaleric acid in 12 parts of deionized water containing 1.14 parts of dimethylethanolamine was added at the same temperature. The reaction was continued with stirring for further 60 minutes. A dispersion of cationic polymer dispersion having a particle size of 146 nm, a crosslinking density of 0.953 mmol/g and a nonvolatile content of 45 % was obtained. Example 1 400 parts of the cationic resin solution of Production Example 1, 240 parts of the resin solutin of Production Example 2 and 19.2 parts of the resin solution of Production Example 3 were thoroughly mixed. The mixture was neutralized with 8.1 parts of acetic acid and diluted with 1,835 parts of deionized water. To the mixture were added 200 parts of the dispersion of Production Example 5. This gave a cathodic electrodeposition coating composition having a solid content of about 20 % and a polymer microparticle content of about 3 %. This composition was deposited electrically on a zinc phosphate-treated steel plate used as cathode at 150 V for 3 minutes. The coated plate was then rinsed with water and baked at 175 °C for 30 minutes to give a cured film having a thickness of about 20 microns. Properties of the film are shown in Table 1. Example 2 231 parts of the varnish of production Example 4 were dissolved in 315 parts of deionized water. To the solution was added a pigment mixture consisting of 16 parts of carbon black, 92 parts of titanium dioxide, 220 parts of kaolin, 58 parts of basic lead silicate and an amount of glass beads. The mixture was thoroughly dispersed in a sand mill to a particle size less than 20 microns and filtered to remove glass beads. A pigment paste having a nonvolatile content of 55 % was produced. Example 3 400 parts of the cationic resin solution of Production Example 1, 240 parts of the resin solution of Production Example 2 and 19.2 parts of the resin solution of Production Example 3 were thoroughly mixed. The mixture was neutralized with 8.1 parts of acetic acid and diluted with 1,835 parts of dionized water. To the mixture were added 360 parts of the pigment paste of Example 2, 550 parts of deionized water and 260 parts of the dispersion of Production Example 5. A cathodic electrodeposition enamel having a polymer microparticle content of about 2 % was obtained. Electrodeposition coating was carried out using the above enamel in the same way as Example 1 except that the voltage was 200 V. Properties of the resulting coating film are shown in Table I. Example 4 970 parts EPON 1001 (epoxy resin, sold by Shell Chemical Company, epoxy equivalent 485) and 265 parts of polycaprolactone diol (sold under the name of PCP 0200 by Union Carbide Corporation, M.W. about 543) were placed in a suitable reactor and heated to 100 °C in a nitrogen gas atmosphere. 0.46 parts of dimethylbenzylamine were added to the mixture and allowed to react at 130 °C for 1.5 hours. Then the reaction mixture was cooled to 110 °C. To this were added 110 parts of methyl isobutyl ketone, 39.8 parts of a 73 % solution of diethylenetriamine methyl isobutyl ketimine in methyl isobutyl ketone, and 100 parts of methyl isobutyl ketone. Then the mixture was cooled to 70 °C. After adding 53.1 parts of diethylamine, the mixture was heated at 120 °C for 3 hours to complete the reaction. The resulting solution referred to as "First Liquid" has a nonvolatile content of 75 %. Using a separate reactor, 291 parts of toluenediisocyanate (mixture of 2,4- and 2,6-isomers at a ratio of 80 : 20) were reacted with 218 parts of 2-ethylhexanol for 0.5 hours in a nitrogen atmosphere with stirring at 38 °C while cooling externally. The reaction mixture was then heated to 60 °C. To this were added 75 parts of trimethylolpropane and 0.08 parts of dibutyltin dilaurate. The mixture was allowed to react for 1.5 hours at 121 °C until substantially all isocyanato function disppeared when confirmed IR spectrometrically. This reaction product was diluted with 249 parts of ethyleneglycol monomethyl ether to give a solution referred to as "Second Liquid" having a nonvolatile content of 70 %. 576 parts of First Liquid, 217 parts of Second Liquid, 13.2 parts of dibutyltin dilaurate, 12.3 parts of glacial acetic acid were thoroughly mixed. After diluting the mixture with 705.5 parts of deionized water, 39 parts of ethyleneglycol monohexyl ether, 1,880 parts of deionized water and 145 parts of the dispersion of Production Example 6 were added thereto. A cathodic electrodeposition coating composition having a solid content of about 20 % and a polymer microparticle content of about 2 % was prepared. This composition was deposited on a zinc phosphate-treated steel plate at 60 V for 3 minutes. Then the coated substrate was rinsed with water, and baked at 175 °C for 30 minutes to give a film having a thickness of 20 microns. The coated plate was tested for the smoothness of film surface and the coverage of edge areas. The results are shown in Table I. Example 5 320 parts of Second Liquid prepared in Example 4 and 87.2 parts of dimethylethanolamine were reacted in a suitable reactor exothermally at 80 °C for 1 hour with stirring. Then 117.6 parts of a 75 % aqueous solution of lactic acid and 39.2 parts of butylcellosolve were added thereto. The mixture was stirred at 65 °C for additional 30 minutes to give a quaternizing agent. Using a separate reactor, 710 parts of EPON 829 (reaction product of epichlorhydrine and bisphenol, sold by Shell Chemical Company, epoxy equivalent about 193) and 289.6 parts of bisphenol A were reacted exothermally in a nitrogen gas atomosphere at 150-160 °C for 1 hour. Then the reaction mixture was cooled to 120 °C. A portion of 406.4 parts of Second Liquid of Example 4 was added thereto and allowed to react at 110-120 °C for about 1 hour. After cooling to 85-95 °C, the reaction mixture was diluted with 56.76 parts of butylcellosolve and 71.2 parts of deionized water. Then the remaining portion of Second Liquid of Example 4 was added and allowed to react at 80-85 °C until an acid number 1 was reached. 1,024 parts of the resulting vehicle was diluted to a solid content of 30 % with 241 parts of butylcellosolve and 1,122 parts of deionized water. To this were added 1,666 parts of kaolin, 204.4 parts of lead silicate and 71.4 parts of dibutyltin oxide. After mixing for 1 hour in a disperser, an amount of glass beads was added to the mixture. Then the mixture was dispersed in a sand mill to a particle size of less than 20 microns and filtered to remove glass beads. A pigment paste having a solid content of 55 % was prepared. A mixture of 576 parts of First Liquid of Example 4, 217 parts of Second Liquid of Example 4 and 13.2 parts of dibutyltin dilaurate was neutralized with 12.3 parts of glacial acetic acid and diluted with 705.5 parts of deionized water. After adding 39 parts of ethyleneglycol monohexyl ether and 1,880 parts of deionized water, 360 parts of the above pigment paste, 630 parts of deionized water and 190 parts of the dispersion of Productin Example 6 were mixed to give a cathodic electrodeposition enamel having a polymer microparticle content of about 2 %. This composition was deposited electrically on a zinc phosphate-treated steel plats under the same conditions as Example 4. The electrodeposition voltage was 100 V. Film properties are shown in Table I. Comparative Example 1 Example 4 was followed except that the polymer microparticles of Production Example 6 were not added and the voltage was 50 V. Comparative Example 2 Example 5 was followed except that the polymer microparticles of Production Example 6 were not added and the voltage was 80 V.

Claims: An electrodeposition coating composition comprising: (a) an aqueous dispersion of a water-dispersible, electrically depositable cationic resin in an aqueous medium containing an amount of acid sufficient to achieve at least 20 % neutralisation of said resin which is neither soluble nor dispersible in water in its unneutralised form but soluble or dispersible in water in an at least 20 % neutralized form; and (b) 1 to 50 % by weight of the total solid content of the composition of internally crosslinked polymer microparticles having a particle size from 0.01 to 20 microns uniformly dispersed in said aqueous dispersion, said polymer microparticles having been prepared by polymerizing a mixture of ethylenically unsaturated monomers comprising a monomer having at least two ethylenically unsaturated polymerizable sites per molecule to effect internal crosslinking, said polymer microparticles being electrically neutral or cationic and having a crosslinking density of 0.01 to 5.05 mmol/g. A coating composition as claimed in claim 1, wherein said aqueous dispersion is an emulsion of said water-dispersible resin, and wherein said particle size of said polymer microparticle is greater than the particle size of said emulsion. A coating composition as claimed in claim 1, wherein said aqueous dispersion is an emulsion of said water-dispersible resin, and wherein said particle size of said polymer microparticles is less than the particle size of said emulsion. A coating composition as claimed in any of the preceding claims, wherein said monomer mixture is polymerized by the emulsion, NAD or precipitation polymerization method. The use of a coating composition as claimed in claim 1 in coating a substrate by electrodeposition.

Inventors: ISHII, KEIZOU, NISHIKAWA, SHIGEO, SAITO, KOICHI, TOBINAGA, KENSHIRO, TSUCHIYA, YASUYUKI
Applicants: NIPPON PAINT CO., LTD.
Application year: 1987
Main classification: C09D5
IPC codes: C09D5