The Pigment Modiifcation And Its Application In The Electrophoretic Coating

Electrophoretic coating is a kind of novel water-soluble anticorrosive coatings, owningsuch advantanges as high throwing power, high utilization efficiency, pyknotic and uniformfilm, pollution-free and so on. At present, electrophoretic paint has been widely applied inautomobile, electrical hardware, metal spectacle frame, ornaments, medical equipment, toysand other industry required electrophoresis. However, the stability and compatibility of thecolor paste in coatings impose restrictions on the development of color electrophoretic coating.In the article, the pigments were modified by surfactant and microencapsulation, respectively.The modified pigments were used in the electrophoretic coating, in order to improve thestability of pigments in the coatings and the properties of the film.The ultrafine paste, which was used in cathodic electrophoretic coating, was prepared viaultrasonic method with pigment yellow83, benzyldimethylstearylammonium chloride anddeionized water. The average particle size, zeta potential and the conductivity and stability ofthe ultrafine paste were discussed. The differences of the cathodic electrophoretic coatingcontaining ultrafine paste or common paint in stability of bath, deposition amount, color depthand appearance of film were also investigated. The results showed that the average particlesize of the ultrafine paste was only196nm and Zeta potential was30mV with ultrasound for30min and2%cationic dispersant. The bath containing ultrafine paste had larger centrifugalstability. The conductivity of the bath was improved as the paste dosage increased. The filmwith ultrafine paste was not only fine and smooth, the deposit amount was also larger thanthat of film with common paste. The deposit amount was increased from11.05g/m2to71.45g/m2and K/S value was ascended from10.69to11.05as the dosage of ultrafine paste in therange from4%to20%. However, the film became rough due to the extract ultrafine paste.The appearance of the film was smooth and neat, the deposit amount and K/S value increasedgradually in the lower voltage. As the voltage was in the higher range, the film had defects asbubble and orange peel, the deposit amount sharply rose while K/S value suddenly declined.The blue, yellow, red, black and green pastes prepared by ultrasonic method withphthalocyanine blue15:3, pigment yellow83, pigment red1701, carbon black7,phthalocyanine green G were used in the electrophoretic coating. The properties of the fivecolor paints were discussed and were compared with the film of electrophoretic coating thatcontaining commercial pastes. The blue, yellow, red and black films were smooth, fine anduniform. Besides, there were no evident differences in the flatness and smoothness ofhorizontal and vertical plane. The deposit amounts of these films with excellent adhesiveforce were about14~19g/m2. However, the electro-film of the modified phthalocyanine greenwas rough, uneven. Its deposit amount was56g/m2and the adhesive force was one grade.The electrophoretic coatings containing modified paste and commercial paste had good acid and alkali resistance.The ultrafine yellow paste was added into cationic resin and anionic resin to prepare thecathodic and anodic electrophoretic coating, respectively. The performances of cathodic andanodic electrophoretic coating were compared. With0.5%cationic dispersant in the ultrafineyellow paste, the film on the anode was smooth, neat and even. However, the rough film withparticles and pinhole was obtained as cationic dispersant in the ultrafine yellow paste was2%.The deposit amount of the anodic electrophoretic coating was27g/m2, which was higher thanthat of cathodic electrophoretic coating. The Gel ratio was77.69%, having no obviousdifference with that of cathodic electrophoretic coating. However, the drying property,adhesion, and acid and alkali resistance of the anodic electrophoretic coating were not as goodas those of cathodic electrophoretic coating.The pigment microcapsules had been prepared via interfacial polymerization. The corematerial of the microcapsules was pigment phthalocyanine green G modified withoctadecylamine. The wall of the polyamide was synthesized from paraphthaloyl chloride anddiethylenetriamine. The influencing factors that affected the particle size, morphology andencapsulation yield of microcapsules, such as the emulsifier dosage, the core/wall ratio, pHvalue as well as reaction temperature, were investigated. FTIR indicated that octadecylaminewas bonded to pigment phthalocyanine green G with the hydrogen bond. The modifiedpigment migrated to the positive electrode under the direct voltage reversibly and the electricresponse time was about85s in20V/mm. The average particle size of microcapsulesdecreased from834.5nm to258.2nm as the dosage of OP-10increased，and the microcapsuleyield reached maximum of83.5%at the OP-10concentration of1.5wt%. With the reductionof the core/wall weight ratio in the range from1:6to1:14, the average particle size improvedfrom267.4nm to554.4nm. However, the maximum of the microcapsule yield was87.6%atthe core/wall weight ratio of1:10. In addition, with the increase of the pH value, the averagesize of microcapsules decreased to271.0nm. The microcapsule yield reached a peak of87.6%as the pH value was12. The average particle size of the microcapsules that obtained at25℃was327.4nm, which was smaller than those prepared in other temperatures. The formedphthalocyanine green microcapsules had a regular spherical shape and thick wall.The prepared microcapsules were added into the anionic resin to obtain the anodicelectrophoretic coating. The influences of voltage, time, temperature of the bath, distancebetween cathode and anode and baking temperature on the appearance and performances offilm were studied. The results demonstrated that the obtained light green film was neat,smooth and uniform, with high deposit amount and good comprehensive properties.