hydroxyl groups; and q is an integer of 1 to 50.(6) The surface-treated powder set forth in any one of claims (1) to (5), wherein the weight average molecular weight of the fluorine-containing copolymer is about 1,000 to about 1,000,000. (7) The surface-treated powder set forth in any one of (1) to (6), wherein the alkoxy group-containing monomer (b) is 10 to 400 parts by weight relative to 100 p