Manufacture of polyvinyl aromatic acetals and pigments therefrom

Claim 1

IN THE MANUFACTURE OF FINELY-DIVIDED POLYVINYL AROMATIC ACETALS, THE PROCESS WHICH COMPRISES MIXING UNDER AGITATING CONDITIONS A DILUTE AQUEOUS POLYVINYL ALCOHOL SOLUTION, CONTAINING DISSOLVED THEREIN FROM ABOUT 1 TO 20 PER CENT OF A POLYVINYL ALCOHOL IN WHICH AT LEAST ABOUT 35 PER CENT OF THE THEORETICALLY POSSIBLE HYDROXYL GROUPS ARE UNSUBSTITUTED, WITH AN AROMATIC ALDEHYDE OF THE BENZENE AND NAPHTHALENE SERIES IN THE PROPORTIONS OF AT LEAST ABOUT 0.1 MOLE OF ALDEHYDE TO 1 MOLE OF POLYVINYL ALCOHOL, CAUSING THE ALDEHYDE TO CONDENSE WITH THE POLYVINYL ALCOHOL IN AN AQUEOUS REACTION MEDIUM IN WHICH THE ACETAL REACTION PRODUCT IS SO INSOLUBLE THAT IT WILL PRECIPITATE AS FAST AS IT IS FORMED, IN THE PRESENCE OF AN ACETALIZING CATALYST AND WHILE THE ALDEHYDE IS IN A HIGHLY DISPERSED STATE, AT TEMPERATURES ABOVE THE FREEZING POINT OF THE SOLUTION BUT AT LEAST ABOUT 20* C. BELOW THE SOFTENING RANGE OF THE RESULTING POLYVINYL AROMATIC ACETAL, AND RECOVERING THE FINELY DIVIDED SOLID POLYVINYL AROMATIC ACETAL FROM THE REACTION MIXTURE.