Method for preparing polyvinyl acetals

Claim 1

A PROCESS FOR THE PREPARATION OF POLYVINYL ACETALS, WHICH COMPRISES SUBJECTING A SOLID POLYVINYL ESTER IN NON-COLLOIDAL SUBDIVIDED FORM TO THE ACTION OF A HYDROLYZING AGENT CONSISTING OF A 20 TO 25% AQUEOUS SOLUTION OF HYDROCHLORIC ACID IN AN AMOUNT EQUIVALENT TO 10 TO 30% OF ANHYDROUS HYDROCHLORIC ACID RELATIVE TO THE WEIGHT OF THE SOLID ESTER BEING TREATED, UNTIL A HOMOGENEOUS VISCOUS REACTION MASS IS OBTAINED, ADDING TO SAID REACTION MASS THE WATER NECESSARY TO COMPLETE HYDROLYSIS, SAID WATER BEING ADDED IN SMALL SUCCESSIVE PORTIONS AND WITH AGITATION UNTIL HOMOGENEITY OF THE MIXTURE IS REALIZED AFTER THE ADDITION OF EACH PORTION OF WATER, FURTHER DILUTING THE RESULTANT REACTION MIXTURE WITH WATER DOWN TO A CONCENTRATION OF 5 TO 10% OF HYDROLYSIS PRODUCTS AND 3 TO 10% OF ANHYDROUS HYDROCHLORIC ACID, INCORPORATING AN ALDEHYDE INTO THE DILUTED MIXTURE AT A TEMPERATURE AT MOST EQUAL TO AMBIENT TEMPERATURE, AND THEN DIGESTING THE RESULTING PRECIPITATE FOR 3 TO 6 HOURS IN ITS MOTHER LIQUOR.