Aqueous condensation process for the preparation of polyvinyl acetal resins

Claim 1

THE PROCESS COMPRISING (1) PREPARING A MIXTURE OF AN AQUEOUS POLYVINYL ALCOHOL SOLUTION A STRONG ACID CATALYST, AND AN ALIPHATIC ALDEHYDE HAVING 2 TO 6 CARBON ATOMS, SAID ALDEHYDE BEING PRESENT IN AN AMOUNT WHICH IS 5% TO 40% IN EXCESS OVER THE THEORETICAL AMOUNT WHICH WILL CONDENSE WITH THE DESIRED NUMBER OF HYDROXYL GROUPS IN SAID POLYVINYL ALCOHOL, (2) PUMPING THE RESULTANT MIXTURE AT 50* C. TO 95* C. IN A RECIRCULATING LOOP FROM WHICH A CONTINUOUS SIDESTREAM IS DRAWN OFF, THE FLOW RATE OF THE SIDESTREAM BEING NOT MORE THAN ABOUT ONE-TENTH OF THE FLOW RATE IN THE RECIRCULATING LOOP AND THE LINEAR VELOCITY OF THE FLUID IN THE RECIRCULATING LOOP BEING NOT LESS THAN ABOUT 5 FEET PER SECOND, (3) COLLECTING THE MATERIAL FLOWING FROM THE SIDESTREAM AND MAINTAINING IT AT A TEMPERATURE OF ABOUT 60* C. TO 100* C. UNTIL THE DESIRED DEGREE OF ACETALIZATION IS ESSENTIALLY COMPLETED, (4) RAISING THE PH OF THE RESULTING POLYVINYL ACETAL RESIN SLURRY TO SOME VALUE FROM ABOUT 5 TO 7, (5) REMOVING EXCESS ALDEHYDE, (6) STABILIZING THE RESULTING POLYVINYL ACETAL RESIN BY RAISING THE PH TO ABOUT 8 OR MORE, AND (7) RECOVERING A POLYVINYL ACETAL RESIN.