Production of and drying of copolymer fibers

1. A process for reducing water in never-dried fiber comprising copolymer derived from the copolymerization of para-phenylenediamine, 5(6)-amino-2-(p-aminophenyl)benzimidazole, and terephthaloyl dichloride, the process having the following steps in a continuous process:

(a) a step of drying a never-dried fiber having at least 0.1 wt % sulfur at 150° C. or less until the moisture content of the fiber is less than 60 weight percent; and

(b) a step of further drying the fiber above 150° C. while the moisture content of the fiber is less than 60 weight percent;

the fiber being further heated to at least 350° C. in either an additional continuous or separate step.

2. The process of claim 1 where in step (a) the fiber is dried at 100° C. or less.

3. The process of claim 2 where in step (a) the fiber is dried at 50° C. or less.

4. The process of claim 1 where in step (a) the fiber is dried until the moisture content is less than 50%.

5. The process of claim 4 where in step (a) the fiber is dried until the moisture content is less than 40%.

6. The process of claim 2 wherein after step (a), the fiber is further dried at an additional step at less than 150° C. until moisture content is less than 50%, prior to step (b).

7. The process of claim 6 wherein after step (a) the fiber is further dried at an additional step at less than 150° C. until moisture content is less than 40%, prior to step (b).

8. The process of claim 1 , wherein the fiber is heated above 400° C. in the last step.

9. The process of claim 1 , wherein the fiber is heated in step (a) under a tension of at least 0.1 gpd.

10. The process of claim 1 , wherein the fiber is heated in the last step under a tension of less than 1 gpd.

11. The process of claim 1 , wherein the ratio of moles of 5(6)-amino-2-(p-aminophenyl)benzimidazole to the moles of para-phenylenediamine is 30/70 to 85/15.

12. The process of claim 11 wherein the ratio is 45/55 to 85/15.

13. The process of claim 1 , wherein the fiber is heated in an oven in step (a).

14. The process of claim 1 , wherein said fiber is heated by contacting said filaments with a hot surface.

15. A process for producing filaments comprising a copolymer derived from the copolymerization of para-phenylenediamine, 5(6)-amino-2-(p-aminophenyl)benzimidazole, and terephthaloyl dichloride, including the following steps in a continuous process:

(a) a step of spinning filaments into a coagulation bath from a sulfuric acid solution of the copolymer;

(b) a step of contacting the filaments with one or more of (i) wash and (ii) neutralization fluid;

(c) a step of drying the filaments having at least 0.1 wt % sulfur at 150° C. or less until the moisture content of the filaments is less than 60 weight percent;

(d) an optional step of further drying the filaments at a temperature higher than step (c);

(e) a step of further drying the filaments above 150° C. while the moisture content of the fiber is less than 60 weight percent;

the filaments being further heated to at least 350° C. in either an additional continuous or separate step.

16. The process of claim 15 wherein the filaments are heated above 400° C. in the last step.

17. The process of claim 15 wherein the filaments are heated in step (c) under a tension of at least 0.1 gpd.

18. The process of claim 15 wherein the filaments are heated in the last step under a tension of less than 1 gpd.

19. The process of claim 15 wherein said filaments are heated by contacting said filaments with a hot surface.