Patent ID: 6030573
Filing Date: 2000-02-29
Classification: B29C

Abstract:
A process for manufacturing thermoplastic resin moldings from molten thermoplastic resin and a mold assembly, said mold assembly comprising a male mold and a female mold, said male and female molds each having opposing mold surfaces, said mold assembly being able to open and close and define a mold cavity between said opposing mold surfaces, said mold cavity defining a cavity clearance which can be greater than, less than, or approximately equal to a final thickness of a molding of said thermoplastic resin, at least one of said male or female mold containing at least first and second thermoplastic resin feeding gates wherein said first thermoplastic resin feeding gate is adjacent to said second thermoplastic resin feeding gate, said thermoplastic resin feeding gates individually being in an opened or closed communicating relationship with respect to said mold cavity, said thermoplastic resin feeding gates including a device or devices for controlling timing and feeding of a quantity of said molten thermoplastic resin from each of said feeding gates into said mold cavity, said process comprising the steps of:(a) feeding a first portion of said molten thermoplastic resin into said mold cavity from said first feeding gate while said first feeding gate is open and said mold assembly is open;(b) spreading said first portion of said molten thermoplastic resin in said mold cavity, whereby a flow front is created in said first portion of said molten thermoplastic resin, by partially closing said mold assembly, said cavity clearance being kept greater than said cavity clearance defining said final thickness of said molding;(c) feeding a second portion of said molten thermoplastic resin from said second feeding gate when said second feeding gate is open and about when said flow-front of said molten thermoplastic resin passes said second feeding gate;(d) optionally, repeating steps (b) and (c) with additional portions of said thermoplastic resin and additional feeding gates, until all of said molten thermoplastic resin is fed, while maintaining said cavity clearance greater than said cavity clearance defining said final thickness of said molding;(e) closing said mold assembly until said cavity clearance becomes approximately equal to said cavity clearance defining said final thickness of said molding;(f) cooling said molten thermoplastic resin in said mold assembly with application of pressure to solidify said molten thermoplastic resin; and(g) opening said mold assembly and recovering said solidified thermoplastic resin from said mold assembly.