Filter start-up in dry spinning acrylonitrile copolymer

Claim 1

In a process wherein a heated solution of an acrylonitrile polymer containing at least about 85 percent by weight of acrylonitrile and up to about 15 percent of another ethylenically unsaturated compound in a volatile organic liquid is extruded from a supply where it is maintained under pressure into an evaporative atmosphere after passage through an apparatus comprising at least one filter wherein solution flow through at least one filter is periodically terminated, and is thereafter resumed, the improvement in the process of resuming flow of solution through said filter which comprises positioning said filter in the path of flow of said solution from said supply to the point of extrusion without establishing communication therebetween, filling said filter with solvent for said polymer, establishing a predetermined superatmospheric pressure-responsive normally closed outlet for solvent in said filter, heating said filter to approximately the temperature of said solution during filtration, establishing communication between said supply and said filter whereby the superatmospheric pressure builds up in said filter and bleeding solvent and solution from said filter through said outlet, continuing to bleed solution through said outlet for a period of time sufficient to reestablish equilibrium conditions with said supply, and establishing communication between said filter and said point of extrusion, whereby solution passes through said filter to said extrusion point into the evaporative atmosphere.