Abstract: A reusable thermal ink sheet used for thermal printing has a thermal ink composition layer formed on a substrate. The thermal ink composition is a mixture of ink material and filler. The ink material includes a coloring agent and a low temperature melting compound which is a solid at room temperature and is melted during thermal printing in response to a printing image to be transferred. The low temperature melting compound contains a urethane compound as a base material and additive materials as viscosity modulators thereof which lower the viscosity of the ink material at printing temperature. The additive materials contain at least one material selected from the group consisting of fatty acid compounds, fatty acid amide compounds and ester compounds. The improved ink sheet assures a high quality printing image is transferred to a plain paper having a rough surface when thermal printing occurs ten times or more. In addition, ghost images are not formed and background noise is eliminated.

Abstract: An ink sheet including an ink layer composed of 10 weight part of urethane wax, 1 weight part of ester wax, 5 weight part of paraffin wax, 5 weight part of dyestuff and 2 weight part of carbon black, on a polyester resin film substrate through an adhesive layer composed of 15 weight part of a (vinyl chloride)-(vinyl acetate) copolymerized resin, 15 weight part of carbon black and 48 weight part of polyester mixture composed of two kinds of polyester resin one of which has a glass transition temperature of 67.degree. C. and the other of which has a glass transition temperature of -20.degree. C., mixed in a weight ratio of 75/25.