Leak stop plug against needle piercing and method of manufacturing the leak stop plug

Abstract

A pierceable stopper enhanced in elasticity so that the liquid in a container will not leak even after a hollow needle inserted into the container through the pierceable stopper has been removed therefrom and a method of producing the pierceable stopper are provided. A pierceable part ( 11 ) through which a hollow needle is inserted into a container ( 2 ) is molded from a thermoplastic synthetic resin elastic material. The pierceable part is heat-treated with heated air at a temperature of from 80 to 120° C. to remove the internal stress. The heat-treated pierceable part ( 11 ) is inserted into an injection mold ( 20, 21 ). A molten thermoplastic synthetic resin is injected into a cavity ( 26 ) corresponding to a stopper body ( 10 ), which is defined by the injection mold ( 20, 21 ) and the pierceable part ( 11 ), to form a pierceable stopper ( 5 ).

What is claimed is:  
     
         1 . A pierceable stopper comprising: 
 a pierceable part pierceable with a hollow needle, said pierceable part being formed by using a thermoplastic synthetic resin elastic material as a base polymer, said thermoplastic synthetic resin elastic material being a styrene elastomer consisting essentially of a hydrogenated product of a styrene-conjugated diene block copolymer having a weight-average molecular weight not less than 150,000, wherein said conjugated diene is at least one selected from isoprene and butadiene, said pierceable part having a hardness in a range of from 20 to 80 in terms of JIS(A) hardness and a thickness in a range of from 2 millimeters to 8 millimeters;    a stopper body formed from a thermoplastic synthetic resin 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 said hollow needle and for defining said pierceable part; and    a thermowelded joint at which said pierceable part and said stopper body are thermowelded together;    wherein said pierceable part, which has been molded, is heated to perform a heat treatment for removing an internal stress and then inserted into an injection mold, and a melt of the thermoplastic synthetic resin is injected into a cavity defined by said injection mold and said pierceable part at an injection pressure not lower than 59 MPa to mold said stopper body, and further, said pierceable part and said stopper body are thermowelded together in said injection mold to form the thermowelded joint.    
     
     
         2 . A pierceable stopper according to  claim 1 , wherein said heat treatment is carried out for a period of time in a range of from 30 minutes to 12 hours by using heated air at a temperature of from 80 to 120° C.  
     
     
         3 . A pierceable stopper according to  claim 1  or  2 , wherein said thermoplastic synthetic resin elastic material is a styrene elastomer consisting essentially of a hydrogenated product of a styrene-conjugated diene block copolymer having a weight-average molecular weight of from 270,000 to 400,000, wherein said conjugated diene is at least one selected from isoprene and butadiene.  
     
     
         4 . A pierceable stopper according to  claim 1  or  2 , wherein said thermoplastic synthetic resin elastic material is a hydrogenated product of a styrene-isoprene-butadiene-styrene block copolymer having a weight-average molecular weight of from 270,000 to 400,000.  
     
     
         5 . A pierceable stopper according to  claim 4 , wherein said pierceable part is formed from a mixture of said hydrogenated product of a styrene-isoprene-butadiene-styrene block copolymer, a paraffin oil, and a polyolefin resin.  
     
     
         6 . A pierceable stopper according to  claim 4 , wherein said thermoplastic synthetic resin is at least one selected from polypropylenes, polyethylenes, and ABS resins.  
     
     
         7 . A method of producing a pierceable stopper, said pierceable stopper having: 
 a pierceable part pierceable with a hollow needle, said pierceable part being formed by using a thermoplastic synthetic resin elastic material as a base polymer, said thermoplastic synthetic resin elastic material being a styrene elastomer consisting essentially of a hydrogenated product of a styrene-conjugated diene block copolymer having a weight-average molecular weight not less than 150,000, wherein said conjugated diene is at least one selected from isoprene and butadiene, said pierceable part having a hardness in a range of from 20 to 80 in terms of JIS(A) hardness and a thickness in a range of from 2 millimeters to 8 millimeters;    a stopper body formed from a thermoplastic synthetic resin 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 said hollow needle and for defining said pierceable part; and    a thermowelded joint at which said pierceable part and said stopper body are thermowelded together;    said method comprising the steps of heating said pierceable part, which has been molded, to perform a heat treatment for removing an internal stress; inserting said pierceable part, which has been heat-treated, into an injection mold; injecting a melt of the thermoplastic synthetic resin into a cavity defined by said injection mold and said pierceable part at an injection pressure not lower than 59 MPa to mold said stopper body; and thermowelding together said pierceable part and said stopper body in said injection mold to form the thermowelded joint.    
     
     
         8 . A method of producing a pierceable stopper according to  claim 7 , wherein said heat treatment is carried out at a temperature of from 80 to 120° C. for a period of time in a range of from 30 minutes to 12 hours.  
     
     
         9 . A method of producing a pierceable stopper according to  claim 7  or  8 , wherein said thermoplastic synthetic resin elastic material for forming said pierceable part is a styrene elastomer consisting essentially of a hydrogenated product of a styrene-conjugated diene block copolymer having a weight-average molecular weight of from 270,000 to 400,000, wherein said conjugated diene is at least one selected from isoprene and butadiene.  
     
     
         10 . A method of producing a pierceable stopper according to  claim 7  or  8 , wherein said thermoplastic synthetic resin elastic material for forming said pierceable part is a styrene elastomer consisting essentially of a hydrogenated product of a styrene-isoprene-butadiene-styrene block copolymer having a weight-average molecular weight of from 270,000 to 400,000.  
     
     
         11 . A method of producing a pierceable stopper according to  claim 10 , wherein said thermoplastic synthetic resin for forming said stopper body is at least one selected from polypropylenes, polyethylenes, and ABS resins.  
     
     
         12 . A pierceable stopper according to  claim 10 , wherein said pierceable part is formed from a mixture of said hydrogenated product of a styrene-isoprene-butadiene-styrene block copolymer, a paraffin oil, and a polyolefin resin.