Blowing agent introduction systems and methods
The present invention provides blowing agent introduction systems and methods for introducing blowing agent into polymeric foam processing systems. The methods may involve introducing one or more doses of blowing agent into polymeric material in an extruder during a plastication period of a molding cycle. Prior to introduction, a dose is confined in an accumulator which, for example, has a volume defined between an inlet valve and an outlet valve. A control system may receive inputs related to system parameters (e.g., pressure of polymeric material in extruder, axial position of screw in barrel, whether screw is rotating, and the like) and based on the inputs coordinates operation of the valves to confine and introduce the blowing agent dose(s). The introduction systems may be used in discontinuous plasticating processes, such as injection molding and blow molding, and can be particularly useful in processes that use precise quantities of blowing agent.
1. A method of introducing blowing agent into polymeric material comprising:
accumulating a first dose of blowing agent in an accumulator;
controlling pressure of the first dose of blowing agent in the accumulator to a value between about 50 psi and about 1000 psi greater than pressure of polymeric material in the vicinity of a blowing agent port of a polymer processing apparatus;
introducing a first dose of blowing agent from the accumulator through the blowing-agent port into the polymeric material in the polymer processing apparatus;
accumulating a second dose of blowing agent in an accumulator;
controlling pressure of the second dose of blowing agent in the accumulator to a value between about 50 psi and about 1000 psi greater than pressure of polymeric material in the vicinity of a blowing agent port of a polymer processing apparatus; and
introducing the second dose of blowing agent from the accumulator through the blowing agent port into the polymeric material in the polymer processing apparatus.
2. The method of claim 1 , wherein the first dose is about the same mass as the second dose.
3. The method of claim 1 , wherein there is a period of time of at least about 1.0 second between the introduction of the first dose and the introduction of the second dose.
4. The method of claim 1 , wherein the first dose and the second dose are less than 0.1 g.
5. The method of claim 1 , wherein the first dose and the second dose are less than 0.01 g.
6. The method of claim 1 , further comprising accumulating and introducing additional doses of blowing agent into the polymeric material.
7. The method of claim 1 , further comprising mixing the first dose and the second dose with the polymeric material to form a mixture.
8. The method of claim 7 , wherein the mixture is a single-phase solution.
9. The method of claim 7 , further comprising processing the mixture to form a microcellular article.
10. The method of claim 7 , further comprising processing the mixture to form a microcellular article.
11. The method of claim 7 , further comprising accumulating the mixture and injecting the mixture into a mold to form an injection molded article.
12. The method of claim 7 , wherein the mixture has a controlled ratio of blowing agent to polymeric material.
13. The method of claim 1 , comprising respectively controlling pressure of the first dose and the second dose of blowing agent in an accumulator to a value between about 50 psi and about 500 psi greater than the pressure of polymeric material in the vicinity of the blowing agent port of the polymer processing apparatus.
14. The method of claim 1 , wherein a control system sends a signal to introduce the first dose of blowing agent into the polymeric material when the first dose has been pressurized to a pressure between about 50 psi and about 1000 psi greater than the pressure of polymeric material in the extruder in the vicinity of the blowing agent port.
15. The method of claim 1 , further comprising determining the mass of the first dose prior to introducing the first dose and determining the mass of the second dose prior to introducing the second dose.
16. The method of claim 15 , comprising determining the mass of the first dose, at least in part, from the pressure of the first dose and determining the mass of the second dose, at least in part, from the pressure of the second dose.
17. The method of claim 16 , comprising determining the mass of the first dose, at least in part, from the temperature and volume of the first dose and determining the mass of the second dose, at least in part, from the temperature and volume of the second dose.
18. The method of claim 1 , wherein the first dose and the second dose are introduced into the polymeric material in a first plastication period of a molding cycle.
19. The method of claim 1 , wherein the first dose is introduced into the polymeric material as a result of the pressure of the first dose being greater than the pressure of the polymeric material in the vicinity of the blowing agent port.
20. The method of claim 1 , wherein the polymer processing apparatus is an extruder.