Kneading apparatus and method for producing thermoplastic resin molded product
A kneading apparatus includes a plasticizing cylinder in which a high pressure kneading zone and a pressure reduction zone are formed adjacently in this order from an upstream side so that a molten resin obtained by plasticizing a thermoplastic resin and a pressurized fluid are kneaded with each other in the high pressure kneading zone, and gasified pressurized fluid, which is gasified by reducing a resin internal pressure, is separated in the pressure reduction zone from the molten resin kneaded with the pressurized fluid, a screw which is arranged rotatably and movably back and forth in the plasticizing cylinder; and a downstream side seal mechanism which is provided between the high pressure kneading zone and the pressure reduction zone and which makes communication and disconnection between the high pressure kneading zone and the pressure reduction zone in accordance with a rotation state of the screw.
1. A kneading apparatus comprising:
a plasticizing cylinder in which a high pressure kneading zone and a pressure reduction zone are formed adjacently in this order from an upstream side so that a molten resin obtained by plasticizing a thermoplastic resin and a pressurized fluid are kneaded with each other in the high pressure kneading zone, and gasified pressurized fluid, which is gasified by reducing a resin internal pressure, is separated in the pressure reduction zone from the molten resin kneaded with the pressurized fluid,
a screw that rotates forwardly and reversely and that moves back and forth in the plasticizing cylinder; and
a downstream side seal mechanism that is provided between the high pressure kneading zone and the pressure reduction zone and that makes communication and disconnection of the pressurized fluid and the molten resin between the high pressure kneading zone and the pressure reduction zone in accordance with a rotation state of the screw, wherein
the downstream side seal mechanism is provided with a reduced diameter portion of the screw that is arranged between the high pressure kneading zone and the pressure reduction zone and that has a seal portion, and a seal ring that is externally fitted to the reduced diameter portion of the screw movably in an axial direction and that has a contact surface to abut against the seal portion; and
the high pressure kneading zone and pressure reduction zone are communicated with each other when the seal portion of the reduced diameter portion and the contact surface of the seal ring are separated from each other in one rotation state of the screw, while the high pressure kneading zone and the pressure reduction zone are disconnected from each other when the seal portion of the reduced diameter portion abuts against the contact surface of the seal ring in the other rotation state of the screw.
2. The kneading apparatus according to claim 1 , wherein the downstream side seal mechanism disconnects the high pressure kneading zone from the pressure reduction zone in accordance with reverse rotation of the screw.
3. The kneading apparatus according to claim 1 , wherein the downstream side seal mechanism makes communication between the high pressure kneading zone and the pressure reduction zone in accordance with any one of forward rotation of the screw, stop of rotation of the screw, and decrease in a number of revolutions of reverse rotation of the screw.
4. The kneading apparatus according to claim 1 , wherein:
the screw is provided with a fastening portion and the seal ring is provided with a fastening objective portion that is engageable and disengageable with respect to the fastening portion of the screw; and
the fastening portion of the screw and the fastening objective portion of the seal ring are engaged with each other when the screw is reversely rotated at a number of revolutions that is not less than a predetermined number of revolutions so that the screw and the seal ring corotate and thus an abutment state is maintained between the seal portion of the reduced diameter portion and the contact surface of the seal ring.
5. The kneading apparatus according to claim 1 , wherein:
a plasticizing zone, in which the thermoplastic resin is plasticized to provide the molten resin, is formed adjacently on an upstream side of the high pressure kneading zone in the plasticizing cylinder; and
the kneading apparatus further comprises an upstream side seal mechanism, which makes communication and disconnection between the plasticizing zone and the high pressure kneading zone in accordance with the rotation state of the screw, between the plasticizing zone and the high pressure kneading zone.
6. The kneading apparatus according to claim 1 , wherein the pressurized fluid contains high pressure carbon dioxide.
7. A method for producing a thermoplastic resin molded product by using the kneading apparatus as defined in claim 1 , the method comprising:
kneading the molten resin and the pressurized fluid with each other at a high pressure when disconnecting the high pressure kneading zone and the pressure reduction zone from each other by the downstream side seal mechanism; and
separating the gasified pressurized fluid from the molten resin kneaded with the pressurized fluid when making communication between the high pressure kneading zone and the pressure reduction zone by the downstream side seal mechanism to lower a resin internal pressure of the molten resin kneaded with the pressurized fluid.
8. The method for producing the thermoplastic resin molded product according to claim 7 , wherein the kneading and the separating are repeated a plurality of times in a state in which the molten resin is allowed to stay in the high pressure kneading zone.
9. The method for producing the thermoplastic resin molded product according to claim 7 , wherein the pressurized fluid contains a functional material.