H Yari - Amirkabir University
S Moradian
N Tahmasebi - Color engineering group, Azad Islamic University of mahshahr

In recent years, increase in surface area of fillers together with their and interaction with polymer matrices as a consequence of decrease in particle size of such fillers, has become an interesting field of research in composite and coating technology[1,2]. Decrease in particle size of a filler, especially when nano-sized particles are considered, can lead to significant changes in mechanical, rheological and thermal properties of the matrix. To date several researches have shown that addition of different nano particles such as silica (SiO2) and alumina (Al2O3) improve mechanical properties especially scratch resistance of automotive clear coats [3,4]. But the effect of this nano addition on other properties such as appearance and curing process of these automotive coatings less have attracted less attention.Due to importance of aesthetic characteristics in the automotive industry, appearance of an automotive coating has a crucial role in inviting a customer to purchase a car. Therefore, investigation regarding decisive appearance parameters for such a purpose is inevitable. The curing process of a coating in addition to affecting its final mechanical properties would also indirectly influence its appearance. Incomplete curing of a coating could lead to insufficient crosslink density and residual functional groups remaining in the coating. Low crosslink density would decrease coating's resistance to water and electrolytes whereas residual functional groups could act as entities which can absorb the harmful part of incident radiations leading to decrease weathering resistance of the coating [5]. Low weathering resistance of the coating affects appearance during service life