PURPOSE: To enhance coloring properties in printing, resistance to plasticizer, and the like, by a method wherein a polyvinyl alcohol (PVA) resin modified by an ethylene-type unsaturated dicarboxylic monoester having specific ester groups is used as a processing aid.

CONSTITUTION: A PVA is produced by a method in which; an ethylene-type unsaturated dicarboxylic monoester wherein one of two carboxyl groups forms an ester shown by a formula (here, R1 represents hydrogen, alkyl, or aryl, and R2 and R3 represent alkyl and aryl) and the other one forms free carboxyl group or the salt thereof is copolymerized with a vinyl acetate, thereafter being saponified. In the application of this modified PVA as a thermal recording paper, the following methods can be employed alternatively; the PVA is applied on a thermal color-forming layer made of a color-forming substance, a color developer, and a binder, as a protective film, the PVA is used as a binder content of the thermal color-forming layer, or the aforesaid methods are simultaneously carried out. In this manner, a thermal recording paper superior in printing density, resistance to plasticizer, water resistance, etc. can be obtained.