Process for making polyvinylbutyracetal resins which are capable of being cast

Claim 1

IN A PROCESS FOR THE PRODUCTION OF POLYVINYLBUTYRAL SUBSTANTIALLY FREE OF COLOR BY THE SAPONIFICATION OF POLYVINYL ACETATE IN A NON-AQUEOUS LOWER ALIPHATIC ALCOHOL CONTAINING FROM 5% TO 7% OF SULFURIC ACID ON THE WEIGHT OF THE POLYVINYL ACETATE AND THE SUBSEQUENT ACETALIZATION OF THE POLYVINYL ALCOHOL FORMED WITH BUTYRALDEHYDE IN THE SAPONIFICATION REACTION MEDIUM, THE STEPS WHICH COMPRISE CARRYING OUT THE SAPONIFICATION IN SAID NON-AQUEOUS LOWER ALIPHATIC ALCOHOL AT A TEMPERATURE OF ABOUT 65*C. UNTIL THE RESIDUAL UNSAPONIFIED ACETATE GROUPS ON THE POLYVINYL ALCOHOL FORMED ARE AT MOST 1% BY WEIGHT, ADDING FROM 13% TO 16% BY WEIGHT OF WATER ON THE WEIGHT OF THE LOWER ALCOHOL PRESENT TO THE ACID LOWER ALIPHATIC ALCOHOL SOLUTION POLYVINYL ALCOHOL OBTAINED TOGETHER WITH AN AMOUNT OF BUTYRALDEHYDE ABOUT EQUAL IN WEIGHT TO THE POLYVINYL ALCOHOL FORMED AND REACTING THE POLYVINYL ALCOHOL WITH THE ADDED BUTYRALDEHYDE IN SAID ACID REACTION MEDIUM FOR 5 TO 6 HOURS AT A TEMPERATURE OF ABOUT 65*C. TO FORM POLYVINYLBUTYRAL HAVING ABOUT 19% TO 23% FREE HYDROXYL GROUPS.