Direct color thermal printing method preventing yellow stains

Abstract

A color thermosensitive recording sheet is formed by sequentially laying a cyan thermosensitive coloring layer, a magenta thermosensitive coloring layer, and a yellow thermosensitive coloring layer on a base. On this color thermosensitive recording sheet, a color image is printed with a thermal head by a three-color image sequential printing method. Each thermosensitive coloring layer develops color by a bias heating and an image heating. A bias heat energy slightly short of the coloring of a thermosensitive coloring layer to be colored and an image heat energy corresponding to the coloring density are used. A blank area is formed in the background of a binary image such as characters and line drawings. A blank frame is formed surrounding a half tone image area, Rearing elements facing such a blank area and a blank frame make a bias heating at a heat energy approximate to the magenta bias heat energy, for printing to the lowermost cyan thermosensitive coloring layer. The heating elements for printing the binary image or the half tone image make the bias heating at the cyan bias heat energy. For a postcard having a half tone image area and a binary image area juxtaposed with the half tone image area, the first several lines of the binary image area are inhibited from being printed for yellow and magenta, and the cyan image is dummy-printed at the magenta bias heat energy, so as to avoid a color registration shift of the binary image.