Devolatilization section of the kneading screw
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 kneading screw 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.
In other words, according to the present invention, 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 the devolatilization segment section 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.
In the sheet production extruder described above, L/D is preferably equal to 2 or more, D indicating indicating a diameter of the kneading chamber and L indicating a length of the devolatilization segment section in a rotational-axis direction of the kneading screw. Consequently, this contributes to further improvement in the efficiency of the devolatilization operation. Accordingly, due to the fact that the devolatilization operation is performed in the devolatilization segment section having a kneading function and occupying a relatively large proportion of the kneading screw, the devolatilization operation can be performed efficiently.