Devolatilization segment section of the kneading screw
Specifically, sheet production extruder includes a barrel having a kneading chamber therein; a kneading screw comprising plural segments, said kneading screw extending through said kneading chamber in a rotatable fashion, said kneading screw being rotated so as to knead a material and to transfer the material from an upstream side of the extruder towards a downstream side of the extruder; a devolatilization segment section in said kneading screw, said devolatilization segment section being provided with a kneading flight twisted around said devolatilization segment section so as to transfer the material downstream, said kneading flight kneading the material while transferring the material downstream and separating a volatile component from the material; a feeding section disposed adjacent to a downstream side of said devolatilization segment section, said feeding section including a screw segment; a vacuum suction hole at a position corresponding to a position of said barrel where the feeding section is disposed, said vacuum suction hole communicating with a portion of said kneading chamber through which said devolatilization segment section extends; and impregnation sections disposed adjacent to an upstream side of said devolatilization segment section and to a downstream side of said feeding section, said impregnation sections being provided for impregnating said kneading chamber with the material. Accordingly, since the devolatilization segment section kneads the material while devolatilizing the material, the devolatilization operation can be performed efficiently.
Furthermore, since the devolatilization segment section of the twin screw extruder is pressure-sealed by the impregnation sections disposed adjacent to the upstream side of the devolatilization section and to the downstream side of the devolatilization segment section, the negative-pressure state for the devolatilization section can be properly maintained. Therefore, the volatile component evaporating from the material is properly released outward through the vacuum suction hole communicating with the devolatilization segment section. Accordingly, this further improves the efficiency of the devolatilization operation of the material.
A portion of the kneading chamber in which the air-tightness is maintained by the impregnation sections contains the devolatilization segment section, and the devolatilization segment section is provided with a kneading flight twisted around the devolatilization section in a direction for transferring the material downstream. Thus, the kneading flight of the devolatilization segment section kneads the material while transferring the material downstream and also performs a surface-renewal operation of the material. As a result of this surface renewal operation, the separation of the volatile component is enhanced.
Moreover, due to the fact that single screw extruder is not provided with a flight that is twisted in the reverse direction, the devolatilization segment section itself does not have an impregnation section of the material. Thus, a negative-pressure state can extend over a wide range (long range) of the kneading chamber. Consequently, the region to be used for the devolatilization of the material by the surface-renewal operation can be used to the maximum extent as a negative-pressure region for vacuum suction, whereby an efficient devolatilization operation can be achieved.