Water-resistant polyvinyl alcohol filament and process for producing same

Claim 1

A PROCESS FOR THE PREPARATION OF IMPROVED POLYVINYL ALCOHOL FIBERS WHICH COMPRISES POLYMERIZING VINYL ACETATE IN A LIQUID SOLVENT FOR VINYL ACETATE MONOMER AND POLYMER, INTERRUPTING THE POLYMERIZATION (A) BEFORE THE CONCENTRATION OF THE POLYMER IN THE POLYMERIZATION SOLUTION EXCEEDS 60% OF THE WEIGHT OF THE SOLUTION, (B) BEFORE THE CONVERSION OF MONOMER TO POLYMER EXCEEDS 75%, AND (C) BEFORE THE VISCOSITY OF THE POLYMERIZATION SOLUTION EXCEEDS ABOUT 75 POISES, HYDROLYZING THE POLYMER TO POLYVINYL ALCOHOL OF SAPONIFICATION NUMBER NOT EXCEEDING 10, SPINNING AN AQUEOUS SOLUTION OF THE POLYVINYL ALCOHOL TO FORM A FILAMENT, ORIENTING SAID FILAMENT TO A DRY ORIENTED LENGTH AT LEAST THREE TIMES AS LONG AS THAT OF THE SPUN FILAMENT, WASHING AND DRYING, FURTHER ORIENTING THE DRY FILAMENTS BY STRETCHING THE SAME AT A TEMPERATURE BETWEEN 200* AND 240* C. TO A FINAL LENGTH AT LEAST TWO AND ONE-HALF TIMES THE LENGTH AFTER THE FIRST ORIENTATION, AND RELAXING SAID FURTHER ORIENTED FIBERS BY HEATING THE SAME AT A TEMPERATURE BETWEEN 210* AND 255* C. BUT NOT MORE THAN 10* C. BELOW THE TEMPERATURE AT WHICH THEY WERE FURTHER ORIENTED AND UNDER TENSION CONTROLLED TO PREVENT SHRINKAGE OF MORE THAN 35% OF SAID FURTHER ORIENTED LENGTH AND UNTIL THE FILAMENTS SHRINK LESS THAN 10% OF THEIR LENGTH WHEN IMMERSED FOR SIX MINUTES IN WATER AT 100* C.