d, glycols such as ethylene glycol, propylene glycol and butylene glycol, and unsaturated monobasic acids such as acrylic acid and methacrylic acid; and urethane acrylates obtained from diisocyanates such as tolylene diisocyanate, hexamethylene diisocyanate and diphenylmethane diisocyanate and esters of acrylic acid or methacrylic acid having 1 hydroxyl group in the molecule such as 2-hydroxyethyl