US Patent 7378374 Thermally sensitive recording medium

A thermally sensitive recording medium containing a thermally sensitive recording medium providing an undercoating layer containing a pigment and a binder as main components and a thermally sensitive recording layer containing a colorless or pale colored basic leuco dye and a color developing agent, which reacts with said basic leuco dye, as main components on a substrate, wherein the undercoating layer contains carboxymethyl cellulose having an etherification degree of from 0.55 to 0.75 and hydroxyethyl cellulose from the view point of high effectiveness.