PURPOSE: To suppress bleeding of a plasticizer by using a sealing composition, which is a vinyl chloride-based plastisol composition consisting of vinyl chloride resin and a plasticizer as main agents and containing a filler and using a substance whose surface tension is a specified value for the plasticizer.

CONSTITUTION: In a powder paint coating method involving applying a powder paint to a joining part, etc., of a steel sheet to be coated after applying a sealing composition, which is a vinyl chloride-based plastisol composition containing vinyl chloride resin and a plasticizer as main agents and then baking and curing the paint, a plasticizer e.g. BBP, etc., having 39-46dyn/cm2 surface tension is used for the plastisol. The mixing ratio of the plasticizer is preferably 13-19wt.% of the whole composition. Consequently, compatibility of the plasticizer to the powder paint is made excellent and the plasticizer bled out of the sealing composition at the time of baking and curing is absorbed in the powder paint and the plasticizer is thus effectively prevented from bleeding out of the surface of the powder paint coating.