PAINT DRYING 1-9 Generally, a coat having a larger and denser net yields better coat performance such as greater resis- tance against weathering and solvents, than a coat having a smaller and open net structure . • '--- __ C_o_a_t _P_e_r_fo_rm_a_n_c_e __ ) Greater Reaction type paints are designed in such a way that they do not start hardening until a reaction starting agent is added to the paint immediately before or after application. Heat, light, water, or chemicals are such agents. In most reaction type paints for automobiles, hardening is started by heat or chemicals. (1) Heat polymer drying paints (baked finish paints) This type of paints is called baked finish paints.
These paints start a chemical reaction when heated (120 to 160°C for 20 to 30 minutes) after application, form net-like structures and become hard. They form large and dense nets that ensure outstanding coat performance and are highly resistant against solvents once they are dried completely. Most paints that are used in carmakers' assembly lines fall in this group. But this type of paints is not used often for repainting needs because plastic parts and electric com- ponents need to be removed from the affected area in the car, or otherwise protected from heat, before application. The table below lists heat polymer drying paints that are commonly used with automobiles.
- 11 - Paint name Main use Thermosetting amino alkyd (baking melamine) Second coat and top coat (solid color) of new vehicles Thermosetting acrylics (baking acrylics; Top coat (meta!!ic co!or) of new vehicles Polyurethane Bumper paints for new vehicles Epoxy Undercoat of new vehicles