PURPOSE: To make it possible to obtain predetermined strength during preparatory drying, by impregnating or coating filter paper with a reinforcing composition prepared by dissolving phenolic resin, urethane resin and vinyl acetate resin in a solvent.
CONSTITUTION: Filter paper is impregnated or coated with a filter reinforcing composition prepared so as to adjust the mixing ratio of phenolic resin and urethane resin to a range of (20:80)W(80:20) or the mixing ratio of a mixture of urethane resin and vinyl acetate resin and urethane resin to a range of (20:80)W (80:20). Vinyl acetate resin is used in order to enhance the processing performance during filter manufacturing and the mixing ratio of phenolic resin may be arbitrary. As an impregnating method, a two-stage impregnating method wherein phenolic resin is at first impregnated and urethane resin is subsequently impregnated or one-stage impregnating method may be used. As the solvent, acetone is pref. used.
ITOU MOTOYOSHI
SEKINE SHINICHI
