Process for changing material in injection molding and sandwich-shaped molded article

Abstract

When a first molten plastic plasticized by a first injection unit 41 is changed to a third molten plastic by using a sandwich molding nozzle capable of using first and second molten resins, which are plasticized by first and second injection units 41 and 42 , for any one of skin and core layers, a mixed resin of the first and third molten resins supplied from the first injection unit 41 is fed to the sandwich molding nozzle so as to be used for the core layer to carry out a sandwich molding process.

What is claimed is:  
     
         1 . A material changing process for an injection molding, said method comprising the steps of; 
 providing a first injection unit for plasticizing and injecting a first molten material and a second injection unit for plasticizing and injecting a second molten material and an injection nozzle connected to the first and second injection unit so that either of the first molten material or the second molten material selectively is injected into a mold;    changing the first molten material being plasticized in the first injection unit to a third molten material;    injecting the second molten material in the second injection unit into the mold to form a skin layer of a sandwich-shaped article;    injecting a mixed molten material being mixed the first molten material with the third molten material in the first injection unit into the mold to form a core layer of the sandwich-shaped article; and    repeating a injection molding cycle for molding the sandwich-shaped article until the mixed molten material in the first injection unit is completely replaced with the third molten material.    
     
     
         2 . A process according to  claim 1 , wherein said material changing process is included in a injection molding process for the sandwich-shaped molded article.  
     
     
         3 . A process according to  claim 1 , wherein said material changing process is included in a injection molding process for a molded article made of single plastic material.  
     
     
         4 . A process according to  claim 2  or  3 , wherein said material changing process is introduced between the injection molding process for the sandwich-shaped molded article and the injection molding process for the molded article made of single plastic material.  
     
     
         5 . A sandwich shaped-molded article formed by a injection molding, said article comprising; 
 a skin layer; and    a core layer confined in the skin layer, wherein said core layer is made of mixed plastic material generated during a material changing process in a injection unit.