Method for producing foamed molded product

1. A method for producing a foamed molded product, the method comprising:

using a molding apparatus including a plasticizing cylinder having a high pressure kneading zone in which a molten resin, obtained by plasticizing a thermoplastic resin, is brought in contact and kneaded with a physical foaming agent, and a pressure reduction zone in which the gasified physical foaming agent is discharged from the molten resin brought in contact and kneaded with the physical foaming agent; and a screw arranged rotatably and movably back and forth in the plasticizing cylinder;

plasticizing the thermoplastic resin to provide the molten resin;

shutting off communication between the high pressure kneading zone and the pressure reduction zone;

bringing in contact and kneading the molten resin with the physical foaming agent in a state that the communication between the high pressure kneading zone and the pressure reduction zone is shut off;

controlling a pressure of the pressure reduction zone to be a first pressure in a state that the communication between the high pressure kneading zone and the pressure reduction zone is shut off, the first pressure being not less than an atmospheric pressure and not more than a maximum pressure of the high pressure kneading zone which is reached in a case that the molten resin is brought in contact and kneaded with the physical foaming agent;

communicating the high pressure kneading zone and the pressure reduction zone;

lowering a pressure of the molten resin brought in contact and kneaded with the physical foaming agent so as to separate the gasified physical foaming agent from the molten resin;

controlling a back pressure of the screw to be a second pressure which is not less than the first pressure;

measuring a predetermined amount of the molten resin from which the gasified physical foaming agent has been separated; and

foaming and molding the measured molten resin into a desired shape.

2. The method for producing the foamed molded product according to claim 1 , wherein the second pressure is greater than the first pressure by a value in a range of 0.5 MPa to 5 MPa.

3. The method for producing the foamed molded product according to claim 1 , wherein the second pressure is not more than 10 MPa.

4. The method for producing the foamed molded product according to claim 1 , wherein the controlling of the pressure of the pressure reduction zone includes controlling a pressure of a gas in the pressure reduction zone.

5. The method for producing the foamed molded product according to claim 1 , wherein the controlling of the pressure of the pressure reduction zone includes introducing an inert gas into the pressure reduction zone so as to pressurize the pressure reduction zone and/or discharging the gasified physical foaming agent from the pressure reduction zone by using a back pressure valve.

6. The method for producing the foamed molded product according to claim 1 , wherein in a case that the gasified physical foaming agent is separated from the molten resin, a temperature of the pressure reduction zone is controlled to be lower than a temperature of the high pressure kneading zone.

7. The method for producing the foamed molded product according to claim 6 , wherein in a case that the gasified physical foaming agent is separated from the molten resin, the pressure reduction zone is cooled.

8. The method for producing the foamed molded product according to claim 1 , wherein a process, in which the molten resin and the physical foaming agent are brought in contact and kneaded with each other and the gasified physical foaming agent is separated from the molten resin, is repeated a plurality of times in a state that the molten resin is allowed to stay in the high pressure kneading zone.

9. The method for producing the foamed molded product according to claim 8 , wherein a process, in which the high pressure kneading zone and the pressure reduction zone are communicated with each other and shut off from each other, is repeated a plurality of times.

10. The method for producing the foamed molded product according to claim 1 , wherein the physical foaming agent, which is to be brought in contact and kneaded with the molten resin, is supplied to the high pressure kneading zone without controlling a supply amount of the physical foaming agent.

11. The method for producing the foamed molded product according to claim 1 , wherein the physical foaming agent is pressurized nitrogen or pressurized carbon dioxide.

12. The method for producing the foamed molded product according to claim 1 , wherein the physical foaming agent is pressurized carbon dioxide and further contains a functional material.

13. The method for producing the foamed molded product according to claim 12 , wherein the functional material is a metal complex.

14. The method for producing the foamed molded product according to claim 1 , wherein a concentration of the physical foaming agent in the molten resin is allowed to approach a saturated solubility by separating the gasified physical foaming agent from the molten resin.

15. The method for producing the foamed molded product according to claim 1 , wherein the communication between the high pressure kneading zone and the pressure reduction zone is shut off in accordance with a rotation state of the screw.

16. The method for producing the foamed molded product according to claim 15 , wherein the communication between the high pressure kneading zone and the pressure reduction zone is shut off by reverse rotation of the screw.

17. The method for producing the foamed molded product according to claim 15 , wherein the high pressure kneading zone and the pressure reduction zone are communicated with each other by any one of forward rotation of the screw, stop of rotation of the screw, and decrease in a number of reverse rotation of the screw.