Method of producing air pervious material by treating with gas evolving blowing agent and coacting with a washable salt layer

Claim 1

A METHOD OF MAKING A FLEXIBLE, STRETCHABLE AND BREATHABLE FABRIC COMPRISING MIXING TOGETHER POLYVINYL CHLORIDE AND A SUBSTANTIALLY EQUAL AMOHT OF AN ALKYL PLASTICIZER, A STABILIZER AGENT AND A DRIER AGENT, ABOUT 15% OF A GRANULAR WATER SOLUBLE MATERIAL AND A NITROGEN TYPE BLOWING AGENT IN A PROPORTION OF 1/2 TO 1% WEIGHT OF THE TOTAL MIXTURE, MILLING THE RESULTANT MIXTURE TO A HONOGENEOUS CONSISTENCY OF VERY FINE PARTICLES, APPLYING AND SPREADING THE MIXTURE ONTO A STRETCHABLE KNITTED CLOTH BACKING AT A TEMPERATURE BELOW THE ACTIVATION TEMPERATURE OF THE BLOWING AGENT TO FORM A CONTINUOUS COATING ON SAID BACKNG, ADJUSTING THE THICKNESS OF SAID COATING TO A UNIFORM, CONSTANT VALUE SUBSTANTIALLY EQUAL TO THE THICKNESS OF SAID BACKING, SPRINKLING ONTO THE OUTER FACE OF THE UNCURED COATING AN INERT, GRANULATED, WATER-SOLUBLE MATERIAL OF FINE PARTICLE SIZE AND TO A DEPTH OF FROM 15 TO 20 TIMES THE THICKNESS OF THE COATING, STRETCHING SAID FABRIC WIDTHWISE IN THE DIRECTION OF THE COURSES OF THE KNITTED BACKING, WHILE TENSIONING SAID BACKING LENGTHWISE AND HEATING SAID DIMENSIONALLY STABILIZED COATED BACKING IN SUCCESSIVE STEPS OF SUBSTANTIALLY 25*F., FROM 250*F. TO 375*F. TO FUSE AND DRY SAID COATING, WHILE CAUSING SAID BLOWING AGENT TO PRODUCE GAS EVOLUTION THROUGH THE MASS OF SAID COATING, REMOVING THE INERT MATERIALS SPRINKLED ON THE OUTER FACE OF THE COATING, WASHING THE RESULTING COATED FABRIC IN WATER, DRYING THE SAME WHILE IN STRETCHED CONDITION, SANDING THE OUTER FACE OF THE CURED COATING.