Controlling the crystallization of polyesters by means of their water content
View Patent ↗Methods are disclosed herein to reduce and/or eliminate agglomerations and deformations of pellets comprised of crystallizable thermoplastic polymer material during a crystallization or crystallization of the pellets. As described herein, polymer material is subjected to one or more conditioning steps prior to crystallization, in which a controlled moisture content and/or controlled moisture profile is set in the material, or in which the polymer material was obtained via solidification from a polymer melt in such a way that the polymer material has a defined initial moisture profile before the crystallization step
1. A method for crystallizing an at least partially amorphous, thermoplastic polymer material obtained by solidification from a polymer melt in the form of a granulate, strands or strips, comprising:
conditioning a polymer material at a temperature below a crystallization point of the polymer material immediately after solidification to set a controlled moisture content and/or a controlled moisture profile in the polymer material prior to crystallization; and
crystallizing the polymer material using said controlled moisture content and/or controlled moisture profile in the material.
2. The method according to claim 1 , wherein the polymer material is a polycondensate.
3. The method according to claim 2 , wherein the polymer material is a polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate or copolymers thereof, wherein the latter was obtained from new material and/or recycled material.
4. The method according to claim 1 , wherein each conditioning step takes place in a medium with a specific water content at a specific temperature over a specific period of time.
5. The method according to claim 1 , wherein the polymer material is introduced in a medium for conditioning immediately after solidification.
6. The method according to claim 1 , wherein the polymer material has a non-defined moisture content and/or a non-defined moisture profile before conditioning.
7. The method according to claim 1 , wherein the conditioning step includes a step for moistening the polymer material.
8. The method according to claim 7 , wherein the conditioning step involves preliminary drying.
9. The method according to claim 8 , wherein the moistening step takes place for 0.5 mm to 4 h, under water in water vapor under constant conditions in terms of temperature and pressure.
10. The method according to claim 6 , wherein the conditioning step includes drying the polymer material.
11. The method according to claim 10 , wherein the preliminary drying step takes place for 1 mm to 72 h, in a dry gas stream under constant conditions relative to temperature and residual moisture quantity.
12. The method according to claim 1 , wherein the polymer material is converted into a granulate, strand or strip.
13. The method according to claim 12 , wherein the polymer material is converted into a granulate after being solidified.
14. The method according to claim 12 , wherein the polymer material is converted from a still liquid state into a granulate form and then solidified.
15. A method for crystallizing a partially amorphous, thermoplastic polymer material comprising:
solidifying a polymer melt into a polymer material in the form of a granulate, strands or strips;
conditioning the polymer material at a temperature below a crystallization point of the polymer material immediately after the solidifying to have a defined initial moisture profile before crystallizing the polymer material; and
crystallizing the polymer material.
16. The method according to claim 15 , wherein a surface of the polymer material has a lower water content, and a center has a higher water content before the polymer material is crystallized.
17. The method according to claim 15 , wherein the polymer material has a constant moisture profile from a surface to a center thereof before the polymer material is crystallized.
18. The method according to claim 15 , wherein a surface of the polymer material has a higher water content, and a center of the polymer material has a lower water content before the polymer material is crystallized.
19. The method according to claim 18 , wherein the lower water content in the center is locally constant.
20. The method according to claim 19 , wherein the surface with the higher water content extends by a maximum of 20% of a path from the surface to the center into the polymer material.
21. The method according to claim 15 , wherein the polymer material is crystallized in a hot gas stream.
22. The method according to claim 1 , wherein the conditioning steps take place continuously.
23. The method according to claim 1 wherein the crystallization step is followed by a solid-phase post-condensation or solid-phase polyaddition step.
24. Method according to claim 1 , wherein the polymer material is a polyester or a polyamide.
25. The method according to claim 8 , wherein the moistening step takes place for 2 mm to 30 mm, under water in water vapor under constant conditions in terms of temperature and pressure.
26. The method according to claim 8 , wherein the moistening step takes place for 15 mm to 72 h, in a moist gas under constant conditions relative to temperature and moisture quantity.
27. The method according to claim 8 , wherein the moistening step takes place for 4 h to 24 h, under water in water vapor under constant conditions in terms of temperature and pressure.
28. The method according to claim 10 , wherein the drying takes place for 30 mm to 24 h, in a dry gas stream under constant conditions relative to temperature and residual moisture quantity.
29. The method according to claim 10 , wherein the drying takes place under a vacuum under constant conditions relative to temperature and pressure.