Linear polyester films having surfaces suitable for writing thereon

Claim 1

THE PROCESS OF MAKING A SURFACE OF A BIAXIALLY STRETCHED AND HEAT-SET FILM OF POLYETHYLENE TEREPHTHALATE RECEPTIVE TO PENCIL-MARKINGS WHICH PROCESS COMPRISES: COATING SAID SURFACE WITH A SOLUTION OF A POLYESTER MADE BY ESTERIFICATION AND POLYCONDENSATION OF A MIXTURE OF TEREPHTHALIC ACID, A DICARBOXYLIC ACID, AND A DIHYDROXY ALCOHOL HAVING UP TO 10 CARBON ATOMS, IN AN ORGANIC SOLVENT, AND DRYING SAID COATING, SAID SOLUTION HAVING SUSPENDED IN ITSELF AN INORGANIC ABRASIVE MATERIAL INCLUDING ESSENTIALLY SUCH SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF SILICON DIOXIDE, ALUMINUM OXIDE, TITANIUM OXIDE, SILICON CARBIDE, TALCUM, CHALK AND GLASS, SAID ABRASIVE MATERIAL HAVING AN AVERAGE PARTICLE SIZE BELOW 30 U.