Method for multilayer molding of thermoplastic resins and multilayer molding apparatus

Abstract

A multilayer-molding method includes the steps of mixing at least one thermoplastic resin selected from a plurality of types of thermoplastic resins with a bubble-nucleating agent and a foaming gas, injecting the plurality of types of thermoplastic resins into a mold cavity such that the thermoplastic resins are layered in the mold cavity, and then, after increasing the volume of the mold cavity, foaming the at least one thermoplastic resin mixed with the bubble-nucleating agent and the foaming gas. The multilayer-molding method is characterized in that the foaming gas is supplied at a pressure of 0.1 MPa or more but less than 1.0 MPa to at least one injection-molding machine selected from a plurality of injection-molding machines, and that the thermoplastic resin plasticized in the injection-molding machine is mixed with the foaming gas.

1 . A multilayer-molding method of molding thermoplastic resins, which includes the use of: a plurality of injection-molding machines that plasticize and inject a plurality of types of thermoplastic resins as molding materials; a mold that has a cavity as a molding space to be filled with the thermoplastic resins injected by the plurality of injection-molding machines; and a clamping apparatus that can clamp the mold and open or close the mold to increase or decrease the volume of the cavity,
 the method comprising the steps of: mixing at least one thermoplastic resin selected from the plurality of types of thermoplastic resins with a foaming gas; injecting the plurality of types of thermoplastic resins into the mold cavity such that the thermoplastic resins are layered in the mold cavity; and then, after increasing the volume of the mold cavity, foaming the at least one thermoplastic resin mixed with the foaming gas,   wherein the foaming gas is supplied at a pressure of 0.1 MPa or more but less than 1.0 MPa to at least one injection-molding machine selected from the plurality of injection-molding machines, and the thermoplastic resin plasticized in the injection-molding machine is mixed with the foaming gas.   
     
     
         2 . The multilayer-molding method of molding thermoplastic resins according to  claim 1 , wherein the pressure of the foaming gas supplied to the injection-molding machine is in the range of 0.5 MPa or more but less than 1.0 MPa. 
     
     
         3 . The multilayer-molding method of molding thermoplastic resins according to  claim 1 , wherein a bubble-nucleating agent is premixed with the foaming gas to be supplied into the injection-molding machine, thereby allowing the thermoplastic resin injected into the mold cavity to contain the bubble-nucleating agent. 
     
     
         4 . The multilayer-molding method of molding thermoplastic resins according to  claim 1 , wherein a bubble-nucleating agent is premixed with a thermoplastic resin serving as a molding material, thereby allowing the thermoplastic resin injected into the mold cavity to contain the bubble-nucleating agent. 
     
     
         5 . The multilayer-molding method of molding thermoplastic resins according to  claim 1 , wherein the bubble-nucleating agent is one or a mixture of at least two selected from the group consisting of iron oxides, calcium silicate, zinc stearate, magnesium stearate, organic acids, aluminum silicate, glass fiber, and talc. 
     
     
         6 . The multilayer-molding method of molding thermoplastic resins according to  claim 1 , wherein the foaming gas is supplied to the injection-molding machine under controlled pressure. 
     
     
         7 . The multilayer-molding method of molding thermoplastic resins according to  claim 1 , wherein the foaming gas is supplied to a hopper of the injection-molding machine, the hopper serving as a charge port of a thermoplastic resin to be plasticized, or into a plasticized thermoplastic resin in a plasticizing cylinder of the injection-molding machine. 
     
     
         8 . The multilayer-molding method of molding thermoplastic resins according to  claim 1 , wherein the foaming gas is one inorganic gas or a mixture of at least two inorganic gases selected from the group consisting of air, carbon dioxide, and nitrogen. 
     
     
         9 . An automotive interior multilayer-molded product manufactured by the multilayer-molding method of molding thermoplastic resins according to  claim 1 . 
     
     
         10 . A multilayer-molding apparatus for manufacturing a multilayer-molded product that contains a multilayer of a plurality of types of thermoplastic resins, one layer of which is foamed and composed of at least one thermoplastic resin selected from the plurality of types of thermoplastic resins,
 the apparatus comprising: a plurality of injection-molding machines that plasticize and inject the plurality of types of thermoplastic resins as molding materials; a mold that has a cavity as a molding space to be filled with the thermoplastic resins injected by the plurality of injection-molding machines; a clamping apparatus that can clamp the mold and open or close the mold to increase or decrease the volume of the cavity; and a unit for supplying a foaming gas and a unit for supplying a bubble-nucleating agent each for use in the foaming.