Syringe for the controlled discharge of viscous materials

Claim 1

A syringe for the controlled discharge of a pasty material, comprising: a cartridge for holding the material; a cup-shaped stopper having an open end and having a base surface configured as an elastically deformable disc-shaped membrane surface; and a rotary piston having an inserted end, with the rotary piston configured to be inserted into one end of the cartridge, with the rotary piston, on the inserted end, pressing against the membrane surface, with the stopper having an exterior configuration which tightly closes an inside cross section of the cartridge, and with the membrane surface of the stopper configured as a plastic membrane surface which, in a depressurized state, is prestressed and assumes a stable position with respect to a longitudinal insertion direction of the rotary piston, so that after a displacement of the membrane surface by the rotary piston, the disc-shaped membrane surface returns reversibly to the stable position in the depressurized state, wherein the membrane surface in the depressurized state is configured as a curvature, wherein a concavity of the curvature faces in a direction opposite to the longitudinal direction of insertion of the rotary piston, wherein the cartridge includes an inside wall and the stopper includes a sealing lip in contact with the inside wall of the cartridge, wherein the sealing lip is configured in an encircling manner, wherein the sealing lip includes an outer end which, prior to insertion into the cartridge, has a diameter larger than an inside diameter of the cartridge, wherein the stopper includes a side wall, wherein the sealing lip projects downward beyond the prestressed membrane surface and outward beyond the side wall, and wherein the sealing lip, which is in contact under tension against the inside wall of the cartridge, exerts a bending moment on the membrane surface which is directed opposite to the longitudinal direction of insertion of the rotary piston.