Patent ID: 7766882

Claim:
A syringe piston composed of a rubber material having a film laminated thereon, wherein said syringe piston comprises a liquid-contacting leading end portion, a trailing end portion opposite said liquid-contacting leading end portion, a sliding surface extending from the liquid-contacting leading end portion to the trailing end portion, and a plurality of annular ridges of different outer diameters formed integrally on the sliding surface at said liquid-contacting leading end portion, and wherein said outer diameters of said plurality of annular ridges sequentially increase, from said liquid-contacting leading end portion toward said trailing end portion, in a manner such that at least one of said plurality of annular ridges has an outer diameter greater than an inner diameter of a syringe barrel configured to receive the syringe piston to retain a sealing property, wherein at least one of said plurality of annular ridges has a larger diameter than the remainder of the sliding surface, and wherein a difference between said outer diameters of adjacent annular ridges is from 0.01 mm to 0.2 mm.