wherein the ink layer comprises a coloring material and a homopolymer or a copolymer comprising a repeating unit derived from a monomer represented by the following formula 1 or a phthalic polyester formed by polymerization of phthalic acid and a polyol; ##STR2## wherein R1 is a hydrogen atom or an alkyl group having 1 to 12 carbon atoms; R2, R3 and R4 are each a hydrogen atom, an alkyl group havi