JPS6357216B

PURPOSE:To contrive protection of each element and early stabilization of a process, by a method wherein at least two or more of bleed valves are provided on upstream side of a gear pump, a filter and a metallic cap, and a foreign matter and modified resin are discharged out of series by opening the valves in order from the upstream side at the starting time of extrusion. CONSTITUTION:An extruder 1 is driven by opening a bleed valve 17 at the starting time of extrusion. Modified resin and a foreign matter in piping 6 are extruded out of series through the valve 17. When a discharged molten resin is turned into a normal state, the valve 17 is closed and a downstream side bleed valve 18 is opened. In this instance, although the molten resin passes through the inside of a gear pump 8, damage of the gear 8 and a gear case 9 is prevented. As for the valve 18, as the molten resin which has been retained within a gear pump 7 and piping 10 is discharged the modified resin and a foreign matter do not enter into a filter 11 side. After completion of discharge the valve 18 is closed and a bleed valve 19 is opened. Then the modified resin and the foreign matter in the filter 11 and piping 14 and a foreign matter to be mixed from the outside at the time of exchange of either filter 11 or a mouthpiece 15 are discharged along with the molten resin.