| The cationic electro-deposition coatings formed by bisphenol A epoxy resin have been developed for decades of years. They have many advantages, such as feasible operation, highly automated painting, high utilization of coating, environment friendly, and anti-corrosion. Nowadays they have been widely used in automobile, machinery, hardware, building materials. As users require multiple functions for a cationic electro-deposition coating which is not only anti-corrosive, but also UV-resistant, this work prepared successfully the bisphenol A epoxy resin modified by acrylic resin in two methods as following. Method ⅠThe main body epoxy resin and acrylic resin were blended, while the crosslinking agent resin was maintained. This product has UV-resistant ability. The detailed processes are as follows:The acrylic resins with different hydroxyl values were synthesized by changing the proportion of acrylic monomers. The formula was optimized, and the amine was added to improve the mobility of the high hydroxyl resin.The cationic main body epoxy resin were produced by blending the epoxy resin and polyamine resin with the acrylic resin. The UV-resistant ability on the hydroxyl value and acrylic resin content was investigated for the emulsion formed by the product.Method ⅡThe acrylic resin and crosslinking agent resin were graft-copolymerized, while the main body epoxy resin was maintained. This product has also UV-resistant ability. The detailed processes were as follows:The toluene diisocyanate and polyols were crosslinking-polymerized, and then graft-copolymerized with the acrylic resin. The UV-resistant electro-deposition coating therefore was prepared.The paint films formed by the coatings produced as above methods were cured at 170℃. The performances were compared by ASTM (American Society for Testing Material) test, and then optimized for the process accordingly.Following results were obtained based on the investigation:(1) For method Ⅰ, the mobility can be improved by adding amine compound in the acrylic resin with high hydroxyl value higher than 40, therefore leading to the main body epoxy resin easily blended with the acrylic resin. The improvement is benefit to the good stability of the emulsion and bath solution formed by the electro-deposition coating.(2) The analysis of UV-aging and gloss for the products prepared in method Ⅰ indicate that the products of the main body epoxy resin blended with various acrylic resin in the same content but without amine compound controlling the mobility have good U V-resistant ability.(3) The product of the main body epoxy resin blended with 5% acrylic resin in method Ⅰ has the best UV-resistant ability. While as the acrylic resin was increased up 15%, the UV-resistant ability was decreased gradually..(4) The stability of the emulsion and the paint bath solution of the product prepared in method Ⅱ is better than that in the method I. The stable duration of the emulsion was 3 month for the product prepared in method Ⅰ, while was increased up to 5 month for the product prepared in method Ⅱ, and other performances are comparable between two methods.The paint films formed by the resin emulsion and bath solution prepared in above two methods were tested by ASTM. The anti-salt fog ability is 720 hours shorter than that of 1000 hours for the bisphenol A epoxy resin electro-deposition coating without modification. But other performances including pencil hardness, cupping, impact resistance, ate, are comparable between the modified and original bisphenol A epoxy resin electro-deposition coating. |
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