A rubber-made syringe piston with a film laminated on it includes a plurality of annular ridges of different outer diameters formed continuously and integrally on a sliding surface of a liquid-contacting, leading end portion of the piston. The annular ridges may preferably be different by from 0.01 to...http://www.google.com/patents/US7766882?utm_source=gb-gplus-sharePatent US7766882 - Syringe piston
