Kneading apparatus and method for producing thermoplastic resin molded product

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.