Method of injection molding closure with continuous internal rigid rib, mold for use therein and product made thereby

Abstract

An injection molded container closure with a continuous internal projection, in particular a rib having a length-to-width ratio of at least one and one-half, is formed with a mold cavity between a pair of mold halves. One mold half includes a core forming the interior of the closed annular structure of the container closure, wherein the core is separated into a movable core portion and a remaining core portion at a separating line defined at the internal rib for forming the same.

1 . A method of injection molding a mold part in the form of a closed annular structure having a continuous internal rib having a length-to-width ratio of at least one and one-half, the method comprising the steps of: 
 A) providing a mold with a mold cavity between a pair of mold halves with one mold half including a core forming the interior of the closed annular structure, wherein the core is separated into a movable core portion and a remaining core portion at a separating line defined at the internal rib;    B) injecting resin into the mold cavity;    C) opening the mold cavity;    D) moving the moveable core and molded part away from the remaining core during ejection of the mold part following the injection molding to form a space beneath the rib of the molded part; and    E) ejecting the molded part from the moveable core wherein the rib is moved into the space formed by the movement of the moveable core.    
   
   
       2 . The method as claimed in  claim 1  further comprising the steps of molding internal threads onto the molded part and unthreading the molded part from the moveable core during the ejection process.  
   
   
       3 . The method as claimed in  claim 1  wherein the molded part is a flat cap container closure.  
   
   
       4 . A product formed by the process of  claim 1 .  
   
   
       5 . The method of  claim 1  further including the step of scoring a side wall of the injected molded part at a position between the closed top surface and the rib, wherein the scoring defines a tamper-evident portion for the mold part.  
   
   
       6 . The method of  claim 1  wherein the rib is substantially rectangular in cross-section and has a length-to-width ratio of at least two.  
   
   
       7 . The method of  claim 1  wherein the injection molded part is a container closure and further comprising the steps of molding internal threads onto the container closure and of unthreading the molded part from the moveable core during the ejection process.  
   
   
       8 . The method of  claim 7  further including the step of scoring a side wall of the injected molded container closure at a position between the closed top surface and the rib, wherein the scoring defines a tamper-evident portion for the container closure, and wherein the rib is substantially rectangular in cross-section and has a length-to-width ratio of at least two.  
   
   
       9 . An injection mold for forming a mold part in the form of a closed annular structure having a continuous internal rib having a length-to-width ratio of at least one and one-half, the mold comprising: 
 A) a core generally forming the interior of the closed annular structure, wherein the core is separated into 
 (i) a movable core portion, and  
 (ii) a remaining core portion at a separating line defined at the internal rib, wherein the movable core portion is moveable relative to the remaining core portion, wherein the moveable core is moveable away from the remaining core during ejection of the mold part following the molding process whereby a space is formed for the rib to move into during the ejection process by the movement of the moveable core; and  
   B) an outer mold generally forming the exterior of the closed annular structure, wherein the outer mold is moveable relative to the core.    
   
   
       10 . The mold as claimed in  claim 9  wherein the core includes an impression of a thread for forming internal threads on the molded part.  
   
   
       11 . The mold as claimed in  claim 10  wherein the core is structured to form a tamper-evident portion in the molded part.  
   
   
       12 . The mold as claimed in  claim 11  wherein the rib is a retaining element for the tamper-evident portion.  
   
   
       13 . The mold claimed in  claim 10  wherein the molded part is a flat cap with internal threads and a tamper-evident portion and wherein the core forms the internal threads and leaders for the tamper-evident portion, and the rib is part of the tamper-evident portion.  
   
   
       14 . A method of injection molding a flat cap container closure having an internal continuous rib in a mold having (A) a core generally forming the interior of the flat cap, wherein the core is separated into (i) a movable core portion and (ii) a remaining core portion at a separating line defined at the internal rib of the flat cap, wherein the movable core portion is moveable relative to the remaining core portion and B) an outer mold generally forming the exterior of the flat cap, wherein the outer mold is moveable relative to the core, the method comprising the steps of: 
 A) injecting resin into a mold cavity formed by the core and the outer mold;    B) opening the mold cavity by moving the outer mold away from the core;    C) forming a rib ejection space in the mold cavity beneath the rib of the molded flat cap following the injection molding of the flat cap by moving the moveable core and molded flat cap away from the remaining core during ejection of the molded flat cap; and    E) moving the rib into rib ejection space during the ejecting the molded flat cap from the moveable core.    
   
   
       15 . The method as claimed in  claim 14  further comprising the steps of molding internal threads onto the molded flat cap and unthreading the molded flat cap from the moveable core during the ejection process.  
   
   
       16 . A product formed by the process of  claim 14 .  
   
   
       17 . The method of  claim 14  further including the step of scoring a side wall of the injected molded flat cap at a position between the closed top surface and the rib, wherein the scoring defines a tamper-evident portion for the mold part.  
   
   
       18 . The method of  claim 14  wherein the rib is substantially rectangular in cross-section and has a length-to-width ratio of at least two.  
   
   
       19 . The method of  claim 14  further comprising the steps of molding internal threads onto the flat cap container closure; unthreading the flat cap from the moveable core during the ejection process; and scoring a side wall of the injected molded flat cap container closure at a position between the closed top surface and the rib, wherein the scoring defines a tamper-evident portion for the flat cap container closure, and wherein the rib is substantially rectangular in cross-section and has a length-to-width ratio of at least one and one half.  
   
   
       20 . The product formed by the process of  claim 19.