PROCESS FOR PREPARING A THERMOCHROMIC VARNISH,COATING PREPARED THEREFROM AND UTILIZATION THEREOF

摘要

For the preparation of a thermochromic varnish and appropriate mixture for the serigraphy of two or three storable compounds is used. The first compound is a heavy or noble metal compound dispersed in a resin based solution. The second compound is a compound covalent of sulphur and carbon, dispersable in the resin based solution or into a resin hardener and the third compound is a hardener. The resin and the metal compound are in stoechiometric proportions with respectively the hardener and the compound covalent of sulphur and carbon. The metal compound is a derivative of an oxide, of an inorganic anion or of a mono or dicarboxylic acid, forming with sulphur ions, metal sulphides of irreversible black colour. The resin is a prepolymer of a methacrylic acid or of a glycidyl ether and the hardener is a diol or an amine. The thermochromic coating has a thickness of 10 to 1000`//c and is subjected to an irreversible and local black coloration with a heating element. The varnish coatings are used on credit cards with optical markings which may be thermally erased and of which the erasure may be made visible by blackening.