Patent ID: 6878670

Claim:
A heat-sensitive recording material comprising (a) a supporting and (b) a heat-sensitive recording layer formed on the support and containing a leuco dye, a developer and a binder, the heat-sensitive recording layer containing a mixture of 4-hydroxy-4′-isopropoxy-diphenylsulfone and at least one member selected from the group consisting of 2,4′-dihydroxy-diphenylsulfone and 4,4′-dihydroxy-diphenylsulfone as the developer and a black-color-forming leuco dye and a red-color-forming leuco dye as the leuco dye, the red-color-forming leuco dye being present in an amount of 0.5 to 3.5 wt. % relative to the black-color-forming leuco dye, the black-color-forming leuco dye being at least one member selected from the group consisting of 3-di(n-butyl)amino-6-methyl-7-anilinofluoran, 3-di(n-pentyl)amino-6-methyl-7-anilinofluoran and 3-di (n-butyl)amino-7-(o-chloroanilino)fluoran, and the red-color-forming leuco dye being 3-diethylamino-7-chiorofluoran.