Abstract: A water injection foaming devolatilizing method, and an apparatus for practicing the method according to the invention are designed as follows: A molten polymer material is kneaded in a water-injection dispersion zone (11) of an extruding machine having a pair of screws (6) each of which is turned in the same direction. Water is supplied to the molten polymer material, thus the water being dispersed therein while the molten polymer material is kneaded. In a devolatilizing zone (12) downstream of the water-injection dispersion zone, the volatile components in the molten polymer material are removed by being gasified together with the water. In this water injection foaming devolatilizing method, the molten polymer material is smoothly extruded from the filling zone (10) to the water-injection dispersion zone (11), and in the latter zone (11) water injection is performed with increased pressure due to the aid of a ring (15), thereby to achieve the devolatilizing of the molten polymer material.

Abstract: A water-injection foaming devolatilizing method includes the steps of: melting and kneading a polymer in a water-injection dispersing zone of an extruder having a screw; injecting water into a polymer melt so as to be dispersed into the polymer melt which is being kneaded; and vaporizing volatile components contained in the polymer melt together with water in a devolatilizing zone having a vent port and located on a downstream side of the water-injection dispersing zone, so that the volatile components are removed and discharged through the vent port. A pressure-reducing expansion zone is provided between the water-injection dispersing zone and the devolatilizing zone so as to be upstream of the vent port. The method further includes gradually reducing a pressure in the pressure-reducing expansion zone so that not only bubbles in the water which is dispersed into the polymer melt are made to grow up, but also the bubbles are broken down at a downstream end portion of the pressure-reducing expansion zone.