Method for crystallizing crystallizable polymers having a high tendency to agglomerate
The invention relates to a method for producing a semicrystalline polymer, said method comprising the following steps: producing a polymer melt from a crystallizable polymer; shaping particles and solidifying the polymer melt, the step of shaping the particles being carried out before or after solidification; cooling the particles; treating the particles to reduce their tendency to agglomerate; crystallizing the particles. The invention is characterized in that the treatment is carried out by shaking at a temperature T1 which is below the glass transition temperature of the polymer plus 10° C., i.e. T1<Tg+10° C.
1. A method for the preparing a semicrystalline polymer, comprising steps of:
a) preparing a polymer melt from a crystallizable polymer;
b) forming and solidifying particles of the polymer melt, wherein formation of the particles may be effected before or after solidification;
c) cooling the particles;
d) treating the particles for reducing their tendency to agglomerate;
e) crystallizing the particles;
wherein the treating step is effected between the cooling of the particles and the crystallizing the particles by shaking for one minute to thirty minutes at a temperature T1 which is below the glass transition temperature Tg of the polymer plus 10° C., i.e. T1<Tg+10° C., wherein a multiplicity of impacts is transmitted to the particles by the shaking, wherein the average number of impacts on the particles is more than 150 and a specific kinetic energy input per impact of more than 0.1 J/kg is effected, and wherein the crystallizing is effected in a thermal manner under supply of heat.
2. The method according to claim 1 , wherein T1 is greater than or equal to Tg−60° C.
3. The method according to claim 2 , wherein the cooling of the particles is effected to a temperature T2 in the range from Tg-60° C. to Tg+10° C.
4. The method according to claim 2 , wherein the cooling of the particles is effected to a temperature T2 below Tg-60° C. and wherein a further step of heating to the temperature T1 is effected before the crystallizing step.
5. The method according to claim 1 , wherein the treating step comprises shaking at the temperature T1 in the range from Tg-40° C. to Tg+5° C.
6. The method according to claim 5 , wherein the cooling of the particles is effected to a temperature T2 in the range from Tg-40° C. to Tg+5° C.
7. The method according to claim 5 , wherein the cooling of the particles is effected to a temperature T2 below Tg-40° C. and wherein a further step of heating to the temperature T1 is effected before the crystallizing step.
8. The method according to claim 1 , wherein the cooling of the particles is effected in a cooling fluid and wherein a separation of the particles from the cooling fluid is effected before treating the particles for reducing their tendency to agglomerate.
9. The method according to claim 1 , wherein the intensity and duration of the shaking are chosen such that the tendency of the particles to agglomerate in the crystallizing step decreases by at least a factor of 2.
10. The method according to claim 1 , wherein the intensity and duration of the shaking is chosen such that the Tg discontinuity in the DSC increases by at least a factor of 1.2.
11. The method according to claim 1 , wherein the intensity and duration of the shaking is chosen such that the Tg discontinuity in the DSC increases by at least a factor of 1.3.
12. The method according to claim 1 , wherein the shaking is effected by a fluidization with the aid of a process gas.
13. The method according to claim 1 , wherein the shaking is effected by mechanical movement.
14. The method according to claim 1 , wherein a step for separating off undesirably large particles, or undesirably small particles, or both, is effected between the step for cooling the particles and the crystallizing step.
15. The method according to claim 1 , wherein a multiplicity of impacts is transmitted to the particles by the shaking, wherein the average number of impacts on the particles is more than 300.
16. The method according to claim 1 , wherein a multiplicity of impacts is transmitted to the particles by the shaking, wherein the average number of impacts on the particles is more than 500.
17. The method according to claim 1 , wherein a multiplicity of impacts is transmitted to the particles by the shaking, wherein a specific kinetic energy input per impact of more than 0.5 J/kg is effected.
18. The method according to claim 1 , wherein a multiplicity of impacts is transmitted to the particles by the shaking, wherein a specific kinetic energy input per impact of more than 1 J/kg is effected.
19. The method according to claim 1 , wherein a multiplicity of impacts is transmitted to the particles by the shaking, wherein altogether a specific kinetic energy input of more than 200 J/kg is effected.
20. The method according to claim 1 , wherein a multiplicity of impacts is transmitted to the particles by the shaking, wherein altogether a specific kinetic energy input of more than 400 J/kg is effected.
21. The method according to claim 1 , wherein a multiplicity of impacts is transmitted to the particles by the shaking, wherein altogether a specific kinetic energy input of more than 800 J/kg is effected.
22. The method according to claim 1 , wherein the polymers are polycondensates.
23. The method according to claim 22 , wherein the polycondensates are selected from the group consisting of polyamides, polyesters, polycarbonate, polyhydroxyalkanoates, polylactides, and copolymers thereof.
24. The method according to claim 23 , wherein the polyester is a polyethylene terephthalate or one of its copolymers.
25. The method according to claim 23 , wherein the shaking is effected at a temperature in the range from 30° C. to 85° C.
26. The method according to claim 23 , wherein the shaking is effected at a temperature in the range from 50° C. to 80° C.