A resin composition comprises (A) hydroxyl group containing acrylic resin having a hydroxyl group value of from 5 to 200 mgKOH/g and a number average molecular weight of from 500 to 20,000, (B) hexakisalkoxymethylated melamine resin, (C) de-watering agent, (D) blocked sulfonic acid compound, (E) silicate compound and (F) at least one type of material selected from among (a) organic resin particle of average particle diameter not more than 40 μm, (b) inorganic glass particles of average particle diameter not more than 100 μm and (c) inorganic fibers of average length not more than 300 μm.