A powder coating material and a precoat steel plate

摘要

A powder coating composition comprises 100 weight parts of the total of a polyester resin having a hydroxyl value in the range from 20 to 100 KOH mg/g and a blocked polyisocyanate compound, 0.01 to 3 weight parts of an organotin compound and 0.01 to 10 weight parts of a carboxylic acid compound having an acid value of 1000 KOH mg/g or less which can form a complex compound by reaction with the organotin compound. The amount of the polyester resin is in the range from 95 to 50 weight % and the amount of the blocked polyisocyanate compound is in the range from 5 to 50 weight % respectively based on the total of the polyester resin and the blocked polyisocyanate compound. A precoat steel plate is prepared by coating the powder coating composition described above on a steel plate by a electrostatic powder coating method to form a coating layer having a thickness in the range from 20 to 120 mu m and curing the coating composition by baking at a temperature in the range from 190 to 300 DEG C for a time in the range from 20 seconds to 10 minutes. The powder coating composition can be cured without formation of blisters and pin holes under a desired condition by controlling the rate of the curing reaction.