PURPOSE: To prevent chemicals in a vessel from contaminating by eliminating wear at the time of plugging by sticking strongly a sheet and rubber layer to each other, by laminating a specific polyethylene sheet to the rubber.
CONSTITUTION: Synthetic rubber such as butyl rubber or natural rubber is used as a material for a rubber plug main body 1 and a matter whose mean molecular weight is 1300000-8000000 is used as a material for a polyethylene sheet 3 which is laminated to the rubber plug main body 1. Then a polyethylene sheet 3 molded by a lower mold is loaded into parts 4, 5 corresponding to a mouth part and the surface of a contacting parts of chemicals of the lower part mold having, for example, a W-shaped recessed part. After unvulcanized rubber is filled into a cavity part of the mold on the polyethylene sheet 3 and the same is placed between the lower part mold and an upper part mold, the unvulcanized rubber is vulcanized by heating and pressurizing the same from the upper part with the upper part mold having a recessed part in a form of a conical trapezoid. In this instance, a part of a molecular chain of the polyethylene is pyrolyzed and ramified, which is bonded to the rubber by crosslinking with the rubber and a rubber plug where the polyethylene sheet 3 is laminated to the rubber plug main body 1 is manufactured.
MATSUZAKI MASARU
AOKI RYOEI
