Integrally moulded plastic plug ring cap

Abstract

A screw cap produced by a bi-injection moulding process is disclosed herein in which discrete thermoplastics are moulded sequentially for resulting correspondingly into a soft inner lip and outer hard shell for sealing containers or conduits having an externally threaded neck, said containers or conduits being directed at holding or conveying chemical, food, and pharmaceutical preparations.

I claim: 
     
         1 ) A cap for sealing a container having an externally threaded neck thereon, comprising—
 a) An outer shell of formable material moulded to assume a cylindrical geometry, said outer shell being composed of a flat circular top having a circumferentially-continuous, internally-threaded side wall descending at a right angle from said flat circular top to end in an open mouth to be received on the externally threaded neck of the container for sealing the same; 
 b) An inner plug ring of a formable material moulded to assume an annular geometry and arranged to descend concentrically from underbelly of the flat circular top of the outer shell to an extent sufficient to allow force-fitting onto the externally threaded neck of the container when the cap is screwed home thereon; and 
 c) A tamper-evident means continuous with mouth of the outer shell, said ring being composed of two initially joined, but separable members of which one member is attached at open end of the outer shell and the other member fixedly embraces the externally threaded neck of the container 
 
       Characterized in that—
 i) The formable material of the inner plug ring is selected to be one having less rigidity than that of the outer shell to allow a tight fit and therein accommodating any undulations on lip of the externally threaded neck; 
 ii) The formable material of the inner plug ring is selected to be one having high chemical resistivity to allow inert behavior upon contact with contents of the container; and 
 iii) The outer shell and inner sealing plug ring are integrally moulded together, thereby allowing a leak-proof seal when the cap is received onto the container. 
 
     
     
         2 ) The cap for sealing a container having an externally threaded neck thereon as claimed in  claim 1 , wherein the container is an article for storing or conveying fluids, said article being chosen among a bottle, vial, tube, jerry-can, conduit, tube or equivalent. 
     
     
         3 ) The cap for sealing a container having an externally threaded neck thereon as claimed in  claims 1  and  2 , wherein the cap is a screw-type cap allowing a screw-type fit when received rotatably on the threaded neck of the container. 
     
     
         4 ) The cap for sealing a container having an externally threaded neck thereon as claimed in  claim 1 , further including an aperture passing through the flat circular top of the outer shell for receiving a vent plug. 
     
     
         5 ) The cap for sealing a container having an externally threaded neck thereon as claimed in  claim 4 , wherein the vent plug is a plastic plug with a membrane inside that allows gases, but not liquids, to selectively pass through therein allowing breathability to contents of the container when sealed using the cap. 
     
     
         6 ) The cap for sealing a container having an externally threaded neck thereon as claimed in  claims 1  and  3 , wherein threading on the inner wall of the outer shell and neck of the container have a complementary pitch to thereby allow the cap to assume a sealed, leak-proof fit when received rotatably on the threaded neck of the container. 
     
     
         7 ) The cap for sealing a container having an externally threaded neck thereon as claimed in  claim 1 , wherein the tamper-evident means are selected among a perforated-type and racket type tamper-evidence rings. 
     
     
         8 ) The cap for sealing a container having an externally threaded neck thereon as claimed in  claim 1 , wherein the formable material of the outer shell is selected among the group of thermoplastics including polyethylene, High-density polyethylene, and polypropylene. 
     
     
         9 ) The cap for sealing a container having an externally threaded neck thereon as claimed in  claims 1  and  8 , wherein the formable material of the inner plug ring is selected among flexible sealing materials, a compounded polypropylene thermoplastic in particular, which are compatible with the formable material of the outer shell for adhesion there-with while undergoing injection moulding. 
     
     
         10 ) A method for production of the cap recited at  claim 1 , comprising—
 a) Moulding of formable material at an increased temperature to obtain an outer shell of cylindrical geometry, said outer shell being composed of a flat circular top having a circumferentially-continuous, internally-threaded side wall descending at a right angle from said flat circular top to end in an open mouth to be received on the externally threaded neck of the container for sealing the same; and 
 b) Maintaining the outer shell obtained at step a) at high temperature while moulding of an inner plug ring in form of a skirt integral to the outer shell by injecting the sealing area of the outer shell under high temperature and pressure conditions with a formable material less rigid than that of the outer shell, therein causing the outer shell and inner plug ring to fuse into a unibody construct.