Method of producing pierceable stopper

A method of producing a pierceable stopper, said pierceable stopper having:

• a pierceable part pierceable with a hollow needle, said pierceable part being made of a thermoplastic synthetic resin elastic material;
• and
• a stopper body made of a thermoplastic synthetic resin material having a higher rigidity than that of the material of said pierceable part, said stopper body having an outer peripheral portion for preventing a stress from propagating to an outside when said pierceable part is pierced with the hollow needle and for defining said pierceable part;
• said method comprising the steps of:
• injection-molding said pierceable part in an injection mold;
• injecting a melt of a thermoplastic synthetic resin material into a cavity defined by said injection mold and said pierceable part to mold said stopper body at a melt injection pressure not lower than 500 kgf/cm2;
• and
• thermowelding said stopper body to said pierceable part in said injection mold by the melt heat of either said thermoplastic synthetic resin material or said thermoplastic synthetic resin elastic material.