Process for injection molding information recording disks

A process for injection molding rigid, transparent plastic objects comprising the steps of:

• providing an unpelletized, unextruded, granular resin feedstock wherein said resin feedstock has not been subjected to predrying;
• inserting said resin feedstock into a feed port of an injection machine having a vent port;
• rotating a threaded plasticating screw in a plasticating cylinder fed by said feed port, said plasticating cylinder having the threaded plasticating screw inserted therein, wherein a check valve comprising a mushroom-shaped valve body having a cone-shaped tip is attached to the front end of said screw;
• drawing said resin feedstock through said feed port into said plasticating cylinder of said injection machine;
• heating said plasticating cylinder;
• melting and kneading said resin feedstock through said heating and said rotating to produce molten resin, wherein an inert gas for preventing said resin feedstock from oxidizing during said melting and kneading is provided within said plasticating cylinder;
• forcing said molten resin along said plasticating cylinder by said rotating;
• vaporizing volatile components and impurities contained within said resin feedstock by said heating;
• exhausting said volatile components and impurities out of said plasticating cylinder;
• metering said molten resin by forcing a predetermined quantity of said molten resin from said plasticating cylinder into a front portion of an injection cylinder having a plunger for metering and injecting, wherein the check valve is closed by the backward movement of the screw to prevent the molten resin from flowing back to the plasticating cylinder side;
• and
• injecting said molten resin into a mold having at least one cavity for producing said molded plastic objects.