The isocyanate functional group can be blocked through one of the several methods. Commonly, one thinks of a blocked isocyanate as one in which the isocyanate group is reacted with an active hydrogen compound. Oxime blocked isocyanate, particularly using butanone oxime are widely used for cross linking hydroxy-functional resins. For exmaple, Oxime blocked 1,6-diisocyanatohexane and 1-isocyanato-3-aminomethyl-3,5,5-trimethylcyclohexane with a combination of hydroxy-functional acrylic and polyester resins give etch resistant and mar resistance clear top coats that can be cured at 130 ℃ ~ 150 ℃. However, Oxime blocking agent cured coatings tend to yellow during curing and exposure. So this paper attempts to reduce yellowing and improve environmental etch resistance (acid rain spotting), scratch resistance, long term durability etc.