Patent ID: 6054530
Filing Date: 2000-04-25
Classification: B29C,C08F

Abstract:
A continuous process for the preparation of poly(vinyl alcohol) from poly(vinyl acetate) paste, said poly(vinyl acetate) paste comprising poly(vinyl acetate), vinyl acetate monomer, and solvent, the steps which comprise:a) conveying the poly(vinyl acetate) paste to an extruding devolatilization apparatus comprising a flashing area and a mixing area, at a temperature above the glass transition temperature of the poly(vinyl acetate) and below a temperature that causes degradation or decomposition of the poly(vinyl acetate);b) conveying the poly(vinyl acetate) paste into the flashing area;c) flashing the vinyl acetate and solvent from the flashing area to produce a substantially pure poly(vinyl acetate) melt containing less than about 1 wt % vinyl acetate, based on the weight of poly(vinyl acetate);d) conveying the substantially pure poly(vinyl acetate) melt from the flashing area into the mixing area of the extruding devolatilization apparatus such that the poly(vinyl acetate) melt forms a seal between the flashing area and the mixing area;e) mixing the substantially pure poly(vinyl acetate) melt with a hydrolytic alcohol-containing solvent to form a homogenous poly(vinyl acetate) solution; andf) conveying the homogeneous poly(vinyl acetate) solution to a saponification process and effecting saponification.