Heat-sensitive recording sheets having improved stability

Claim 1

Heat-sensitive recording sheets having an improved stability comprising a colorless or pale-colored chromogenic compound and an organic acid for coloring said chromogenic compound by heating, which contain at least one phenol derivative different from said chromogenic compound and said organic acid, which phenol derivative is present in an amount of 10 to 500 wt % based on the weight of chromogenic compound and increases the stability of the colored reaction product of the chromogenic compound and is selected from the group consisting of ##SPC20## (wherein R 1 represents a branched alkyl group having 3 to 8 carbon atoms, R 2 and R 3 represent each a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and R 4 represents a hydroxyl group, an alkyl group having 1 to 8 carbon atoms or an alkoxy group), ##SPC21## (wherein R 1 and R 5 represent each a branched alkyl group having 3 to 8 carbon atoms, R 4 and R 6 represent each an alkyl group having 1 to 8 carbon atoms, and X represents S, O, SO 2 , S 2 or ##EQU6## wherein n is an integer of 0 to 3, and R 7 and R 8 represent each a hydrogen atom or an alkyl group having 1 to 8 carbon atoms or R 7 and R 8 form a cyclopentamethylene group by binding together) ##SPC22## (wherein R 1 and R 11 represent each a branched alkyl group having 3 to 8 carbon atoms, R 2 , R 3 , R 12 and R 13 represent each a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and Y represents S, O, SO 2 , S 2 or ##EQU7## wherein m represents an integer of 0 to 3, and R 14 and R 15 each represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, or R 14 and R 15 form a cyclopentamethylene group by binding together), ##SPC23## (wherein R 1 and R 9 represent each a branched alkyl group having 3 to 8 carbon atoms, and R 4 , R 6 and R 10 represent each an alkyl group having 1 to 8 carbon atoms), ##SPC24## (wherein R 1 represents a branched alkyl group having 3 to 8 carbon atoms, R 17 represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and R 18 and R 19 represent each an alkyl group having 1 to 8 carbon atoms), ##SPC25## (wherein R 20 , R 21 , R 22 and R 23 represent each a hydrogen atom or an alkyl group having 1 to 18 carbon atoms, and R 1 represents a branched alkyl group having 3 to 8 carbon atoms, R 2 represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms), and ##SPC26## (wherein R 1 and R 2 represent each a branched alkyl group having 3 to 8 carbon atoms, and R 16 represents an alkyl group having 1 to 18 carbon atoms).