Pressure sensitive record sheet, method of making and composition therefor

Claim 1

POROUS PRESSURE-SENSITIVE, HEAT-RESISTANT RECORDING MATERIAL INCLUDING A BASE SHEET, A NORMALLY OPAQUE COATING HAVING THE PROPERTY OF BECOMING RELATIVELY TRANSPARENT UNDER WRITING PRESSURE WITHOUT BECOMING RELATIVELY TRANSPARENT UNDER HEAT UP TO ABOUT THE CHARRING TEMPERATURES OF PAPER, ADHERED TO SAID BASE SHEET, SAID COATING HAVING FINELY DIVIDED VOIDS AND COMPRISING AND COMPRISING A MATRIC OF AT LEAST ONE THERMOPLASTIC ORGANIC RESIN AND A NON-VOLATILE, WATER-INSOLUBLE COMPATIBLE PLASTICIZER FOR THE ORGANIC RESIN HAVING A PLASTICIZER-RESIN WEIGHT RATIO OF BETWEEN ABOUT 1:3 AND 5:1 AND A PIGMENT, CAPABLE OF FORMING POROSITY IN SAID COATING, HAVING A REFRACTIVE INDEX SUBSTANTIALLY THE SAME AS SAID MATRIX, EMBEDDED IN SAID MATRIX AND HAVING A SUFFICIENTLY LARGE SURFACE AREA SO THAT IT IS CAPABLE OF FORMING A POROUS COATING, THE PROPORTION OF SAID MATRIX TO SAID PIGMENT BEING SUCH THAT THE COATING IS NORMALLY OPAQUE BUT WILL BE RENDERED TRANSPARENT WHEN SUBECTING TO PRESSURE AND A SURFACE UNDER SAID COATING CONTRASTING TO THE COLOR OF SAID PIGMENT.