Piston for pressure dispensers of the barrier piston type

Claim 1

For use in a pressure dispensing can of generally cylindrical cross-section, a barrier pack piston, comprising an inverted cup-like shell molded of a bendable plastic and having an imperforate top portion and a generally cylindrical wall of generally constant thickness joining the top portion, the diameter of the outer surface of said cylindrical wall being sufficiently smaller in diameter than the interior diameter of such can to permit sliding therein, said wall having spaced between its top and bottom extremities a circumferential sealing provision comprising a circumferential groove defining a hinge line, constant thickness perimetrical portions of said wall above and below said groove and there adjoining each other, and a circumferential wiping rib molded to project perpendicularly from the outer surface of the upper of said perimetrical portions immediately adjacent to said groove to a diameter which exceeds that of the interior of such can, whereby when the piston is in place within such can the wiping rib is pressed inward by its contact with the inner can wall, causing said perimetrical portions to deflect inward at said groove, the said upper perimetrical portion adjacent said hinge line thereby assuming an inward and downward slope and thus positioning the wiping rib slopingly outward and downward.