Synthetic resin cap, synthetic resin cap liner, closure device and beverage-contained closure device

摘要

A synthetic resin cap provided with a main cap body having a cylindrical part extending down from a top plate and the rim thereof, and a liner provided on the lower surface of the top plate. The liner has a flat part, an inner sealing protrusion that abuts the open end from the internal circumferential side thereof, and an outer sealing protrusion that abuts the open end from the outer circumferential side. The outer circumference of the liner is formed so as to be separate from the cylindrical part on the inside thereof and secure a space between the liner and the cylindrical part. The outer diameter of the outer sealing protrusion is smaller than the outer diameter of the open end.