Mold and method for manufacturing two-layered preforms by injection overmolding, and two-layered preform

Abstract

The mold includes a first molding cavity connected to a first hot channel for supplying a primary molding material, a second overmolding cavity connected to a second hot channel for supplying an overmolding material; and a core configured to be first introduced in the first cavity for a molding operation of a first layer, and to then be introduced, with the first layer thereon, in the second cavity for an overmolding operation of a second layer. At least one supporting member is arranged to support the core with respect to the first cavity during the entire molding operation of the first layer. An opening left in the first layer by the supporting member is filled and/or covered by the second layer.

1 . A method for manufacturing two-layered preforms by injection overmolding, said two-layered preforms comprising a tubular body with a mouth providing a neck at a first end and a closed bottom at an opposite second end, at least part of said tubular body being formed by a first layer of a primary molding material and a second layer of an overmolding material, the method comprising the steps of:
 first introducing a core in a primary molding cavity connected to a first hot channel through which a primary molding material is injected to perform a molding operation of said first layer;   then introducing said core with the first layer formed thereon in an overmolding cavity connected to a second hot channel through which an overmolding material is injected to perform an overmolding operation of a second layer;   forming the first layer with the primary molding material covering a region of the preform including said closed bottom and excluding said neck of the preform while supporting a free end of the core with respect to said primary molding cavity during the entire molding operation of the first layer by means of at least one supporting member; and   forming the second layer with the overmolding material covering all the first layer and forming the neck, thus filling and/or covering a corresponding opening left by said supporting member in the first layer with the overmolding material of the second layer.   
     
     
         2 . The method according to  claim 1 , further comprising supporting the core by means of at least one supporting member fixed to the primary molding cavity and projecting from an inner surface thereof to make contact with the core. 
     
     
         3 . The method according to  claim 2 , further comprising supporting the core by means of at least three of said supporting members arranged in a closed bottom of the primary molding cavity around a primary molding material injection nozzle. 
     
     
         4 . The method according to  claim 1 , further comprising supporting the core by means of at least one supporting member fixed to the core and projecting from an outer surface thereof to make contact with the primary molding cavity. 
     
     
         5 . The method according to  claim 4 , further comprising forming a bulge in a region of the second layer to cover the corresponding opening in the first layer by means of a depression formed in the overmolding cavity and facing the supporting member of the core. 
     
     
         6 . The method according to  claim 5 , further comprising supporting the core by means of at least three of said supporting members arranged at a free end of the core to be around a primary molding material injection nozzle in the primary molding cavity, and forming at least three of said corresponding bulges in the second layer by means of at least three of said depressions arranged in a closed bottom of the overmolding cavity around an overmolding material injection nozzle. 
     
     
         7 . The method according to  claim 1 , further comprising using a synthetic polymer as common base material for both the first and second layers, said synthetic polymer being mixed with one or more coloring agents in each of the first and second layers, and at least one of said coloring agents being common in both the first and second layers. 
     
     
         8 . The method according to  claim 7 , wherein said synthetic polymer is selected from the group consisting of polyethylene terephthalate (PET), polypropylene (PP), and high density poliethylene (HDPE), and said coloring agents are selected from the group consisting of titanium oxide (TiO 2 ) in solid or liquid form, and carbon black or activated carbon in solid, powder or liquid form. 
     
     
         9 . A mold for manufacturing two-layered preforms by injection overmolding, said two-layered preforms comprising a tubular body with a mouth providing a neck at a first end and a closed bottom at an opposite second end, at least part of said tubular body being formed by a first layer of a primary molding material and a second layer of an overmolding material, the mold comprising:
 a primary molding cavity connected to a first hot channel for supplying a primary molding material;   an overmolding cavity connected to a second hot channel for supplying an overmolding material;   a core configured to first be introduced in said primary molding cavity for a molding operation of a first layer of said primary molding material, and to then be introduced, with said first layer formed thereon, in said overmolding cavity for an overmolding operation of a second layer of said overmolding material; and   a pair of neck half-molds forming at least an external configuration of said neck,   wherein said core has a surface in a region corresponding to said neck of the two-layered preform configured to make contact with a corresponding surface of the primary molding cavity to form the first layer with the primary molding material covering a region of the preform including said closed bottom and excluding said neck of the preform,   said neck half-molds are associated with said overmolding cavity to form the neck with the overmolding material of the second layer not coated by the first layer,   at least one supporting member is arranged between a free end of said core and the primary molding cavity to support the core in the primary molding cavity during the entire mentioned molding operation of the first layer, and   said second cavity is configured to make the overmolding material of the second layer fill and/or cover an opening left in the region of the closed bottom of the first layer by said supporting member.   
     
     
         10 . The mold according to  claim 9 , wherein said supporting member is fixed to the primary molding cavity and projects from an inner surface thereof to make contact with the core. 
     
     
         11 . The mold according to  claim 10 , wherein at least three of said supporting members are arranged in a closed bottom of the primary molding cavity around a primary molding material injection nozzle. 
     
     
         12 . The mold according to  claim 9 , wherein said supporting member is fixed to the core and projects from an outer surface thereof to make contact with an inner surface of the primary molding cavity. 
     
     
         13 . The mold according to  claim 12 , wherein a depression is formed in an inner surface of the overmolding cavity facing the supporting member of the core, said depression being configured to form a bulge in a region of the second layer which covers the mentioned opening in the first layer of the two-layered preform. 
     
     
         14 . The mold according to  claim 13 , wherein at least three of said supporting members are arranged at a free end of the core to make contact with the primary molding cavity around a primary molding material injection nozzle, and at least three of said depressions are correspondingly arranged in a closed bottom of the overmolding cavity around an overmolding material injection nozzle. 
     
     
         15 . A two-layered preform obtained by injection overmolding, comprising a tubular body with a mouth providing a neck at a first end and a closed bottom at an opposite second end, at least part of said tubular body being formed by a first layer of a primary molding material and a second layer of an overmolding material,
 wherein said first layer, or inner layer, is made of a material providing a barrier effect against light by absorption,   said second layer, or outer layer, is made of a material providing a barrier effect against light by reflection, and   said neck is formed with said overmolding material of the second layer not coated by the first layer.   
     
     
         16 . The preform according to  claim 15 , wherein said primary molding material of the first layer is polyethylene terephthalate (PET), polypropylene (PP) or high density poliethylene (HDPE) with from 0.01% to 2% by weight of carbon black or activated carbon and from 3% to 10% by weight of active ingredients of titanium oxide (TiO 2 ), and
 the overmolding material of the second layer is polyethylene terephthalate (PET), polypropylene (PP) or high density poliethylene (HDPE) with from 3% to 10% by weight of active ingredients of titanium oxide (TiO 2 ).   
     
     
         17 . The preform according to  claim 15 , wherein the first layer includes at least one opening in the region of said closed bottom of the two-layered preform, and said second layer covers completely the region of the closed bottom, with said at least one opening being filled or covered with the overmolding material of the second layer. 
     
     
         18 . The preform according to  claim 17 , wherein the first layer comprises three of said openings arranged at angular intervals of 120 degrees around the longitudinal central axis of the two-layered preform. 
     
     
         19 . A two-layered preform obtained by injection overmolding, wherein said two-layered preform is obtainable by the method of  claim 1 .