Patent ID: 8492308

Claim:
A thermosensitive recording medium having a thermosensitive color developing layer comprising a colorless or pale colored electron donating leuco dye and an electron accepting color developing agent on a substrate, wherein the thermosensitive color developing layer contains, as electron accepting color developing agent(s), (a) a phenol derivative represented by the chemical formula 1: wherein R 1 represents a hydrogen atom or a linear or branched, saturated or unsaturated hydrocarbon containing 1 to 4 carbon atoms, R 2 -R 4 independently represent alkyl groups containing 1 to 5 carbon atoms, alkenyl groups containing 1 to 5 carbon atoms, alkoxy groups containing 1 to 5 carbon atoms, aryl groups, aralkyl groups, halogen atoms, hydroxyl groups, cyano groups or nitro groups, X represents —SO 2 —, —C(R 5 ) 2 —, wherein R 5 independently represents hydrogen atoms, alkyl groups or aryl groups, or —NHCOCH 2 S—, m, n and o each represents an integer of 0 to 3, and p represents an integer of 0 to 3, and (b) a diphenyl sulfone derivative represented by the chemical formula 2: wherein R 6 represents a linear or branched, saturated or unsaturated hydrocarbon containing 1 to 12 carbon atoms, R 7 -R 12 independently represent halogen atoms, or alkyl or alkenyl groups containing 1 to 12 carbon atoms, q, r, s, t, u and v each represent integers of 0 to 4, w represents an integer of 0 to 5, and Y independently represents a linear or branched, saturated or unsaturated hydrocarbon groups containing 1 to 12 carbon atoms that may contain ether linkages; wherein the ratio for the phenol derivative and the diphenyl sulfone derivative in the thermosensitive color developing layer (phenol derivative:diphenyl sulfone derivative (weight ratio) is 3/1 to 8/1.