Gas-assisted two-shot injection molding process

Abstract

A process for injection molding a composite of rigid thermoplastic and soft thermoplastic, the soft thermoplastic including a cavity established with pressurized assist gas or an assist liquid. The process includes the steps of: injecting a hard molten thermoplastic into a first mold chamber; injecting a soft molten thermoplastic into a second mold chamber; establishing communication between the first chamber and the second chamber so that the rigid thermoplastic and soft thermoplastic integrally bond; and injecting an assist fluid into the soft thermoplastic to form a cavity. In a preferred embodiment, the formed composite is an automotive cowl where the rigid thermoplastic forms the rigid body portion of the cowl and the integrally bonded soft thermoplastic forms a compressible bulb seal.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:  
     
         1 . A process for fluid-assist injection molding and composite article comprising the steps of: 
 providing a mold;    injecting a shot of hard thermoplastic resin in molten form into the mold;    injecting a shot of soft thermoplastic resin in molten form into the mold, a first portion of the soft thermoplastic resin bonding to the hard thermoplastic resin, a second portion of the soft thermoplastic resin having a viscous interior; and    injecting assist fluid into the heated viscous interior to establish a cavity in the second portion of the soft thermoplastic resin.    
     
     
         2 . The process of  claim 1  comprising the step of allowing the hard thermoplastic and soft thermoplastic to cool and solidify.  
     
     
         3 . The process of  claim 2  wherein the hard thermoplastic is polypropylene and the soft thermoplastic is a thermoplastic elastomer.  
     
     
         4 . The process of  claim 1  wherein the mold defines a first chamber and a second chamber selectively separated by a core slide.  
     
     
         5 . The process of  claim 4  wherein the core slide is moveable between a protracted position and retracted position.  
     
     
         6 . The process of  claim 5  wherein the soft thermoplastic is prevented from bonding to the hard thermoplastic when the core slide is in a protracted position and wherein the soft thermoplastic and hard thermoplastic bond to one another when the core slide is in a retracted position.  
     
     
         7 . A process for injection molding a composite article comprising the steps of: 
 injecting a hard thermoplastic into a first mold chamber;    injecting a soft thermoplastic into a second mold chamber;    establishing communication between said first mold chamber and the second mold chamber so that the hard thermoplastic and soft thermoplastic bond to one another; and    introducing a pressurized gas into said soft thermoplastic whereby a cavity is formed in the soft thermoplastic.    
     
     
         8 . The process of  claim 7  wherein the soft thermoplastic with the cavity therein forms a bulb seal.  
     
     
         9 . The process of  claim 7  wherein the first and second mold chambers are selectively separated by a retractable mold insert.  
     
     
         10 . The process of  claim 9  wherein said establishing step includes retracting the mold insert.  
     
     
         11 . The process of  claim 7  wherein the soft thermoplastic is chosen from the group consisting of thermoplastic elastomer, thermoplastic polyurethane, polyvinyl chloride, thermoplastic olefin and ionomers.  
     
     
         12 . The process of  claim 8  wherein the hard thermoplastic is chosen from the group consisting of: polypropylene, polyethylene, acrylonitrile-butadiene-styrene, polystyrene, polycarbonate, thermoplastic olefin, nylon, polyacetal, polyethylene terephthalate, polybutylene terephthalate, acrylonitrile styrene acrylate, polybutylene terephalate and polyester.  
     
     
         13 . A automotive cowl formed by the process of  claim 7 .  
     
     
         14 . A cowl for use in a vehicle between a windshield and a hood of the vehicle, the cowl comprising: 
 a rigid thermoplastic body including a top surface, a bottom surface, an elongated front edge, an elongated back edge, sides extending from said back edge to said front edge;    a compressible bulb seal integrally molded to said rigid thermoplastic body along said front edge, said seal formed from a material that is soft relative to said rigid thermoplastic body and adapted to provide an interface between the cowl and the vehicle hood.    
     
     
         15 . The cowl according to  claim 14  wherein said rigid thermoplastic body is constructed of materials chosen from : polypropylene, polyethylene, acrylonitrile-butadiene-styrene, polystyrene, polycarbonate, thermoplastic olefin, nylon, polyacetal, polyethylene terephthalate, polybutylene terephthalate, acrylonitrile styrene acrylate, polybutylene terephalate and polyester.  
     
     
         16 . A cowl according to  claim 15  wherein the bulb seal is constructed from materials chosen from thermoplastic elastomer, thermoplastic polyurethane, polyvinyl chloride, thermoplastic olefin and ionomers.  
     
     
         17 . An apparatus for injection molding composite articles comprising: 
 a mold including a first chamber and a second chamber;    a retractable insert capable of selectively separating said first chamber from said second chamber;    means for injecting a hard thermoplastic shot into said first chamber;    means for injecting a soft thermoplastic shot into said second chamber;    means for retracting said insert so that the hard thermoplastic and soft thermoplastic communicate with and bond to one another;    means for injecting an assist fluid into the soft thermoplastic in the second chamber to form a cavity in the soft thermoplastic.    
     
     
         18 . The apparatus of  claim 17  wherein the first mold chamber is in of a shape corresponding to an automotive cowl body.  
     
     
         19 . The apparatus of  claim 18  wherein the second mold chamber is of a shape corresponding to an exterior of a bulb seal.