CONTINUOUS METHOD FOR PRODUCING A THERMALLY STABILIZED MULTIFILAMENT THREAD, MULTIFILAMENT THREAD, AND FIBER

Abstract

The invention relates to a method for thermally stabilizing melt-spun PAN precursors. For this purpose, the invention provides a continuous method for producing a thermally stabilized multifilament thread made of a meltable copolymer of polyacrylonitrile (PAN), wherein a pre-stabilized multifilament thread is thermally stabilized and in the process at least temporarily stretched. The invention additionally relates to a thermally stabilized multifilament thread which can be obtained according to a corresponding method and to a carbon fiber which is made of the correspondingly thermally stabilized multifilament thread.

Claims

1-21. (canceled)

22. A continuous method for the production of a thermally stabilised multifilament yarn made of a meltable copolymer of polyacrylonitrile (PAN), in which a prestabilised multifilament yarn or a non-prestabilised multifilament yarn is fed continuously, in the case of a non-prestabilised multifilament yarn, a prestabilisation and subsequently a neutralisation are implemented, and subsequently the prestabilised multifilament yarn is thermally stabilised at a temperature greater than 0 C., and stretching of the multifilament yarn is implemented, at least at times, during, before and/or after the thermal stabilisation.

23. The method according to claim 22, wherein the strength of the thermally stabilised multifilament yarn standardised to the filament diameter is at least 50 MPa.

24. The method according to claim 22, wherein the multifilament yarn is stretched by 10 to 300%.

25. The method according to claim 22, wherein the thermal stabilisation is implemented, at least at times, at temperatures of 50 to 400 C.

26. The method according to claim 22, wherein the thermal stabilisation is effected by feeding the multifilament yarn through at least one oven or at least two ovens connected subsequently.

27. The method according to claim 22, wherein the thermal stabilisation is implemented in two stages, the multifilament yarn not being stretched or to a lower degree in the first stage than in the second stage and/or being stabilised, in the first stage, at lower temperatures on average than in the second stage.

28. The method according to claim 22, wherein the thermal stabilisation is implemented with rising or constant temperatures in the feeding direction of the multifilament yarn.

29. The method according to claim 22, wherein the thermal stabilisation is implemented such that a stabilisation degree (DOS) of the copolymer of polyacrylonitrile of 20 to 75% results.

30. The method according to claim 22, wherein the thermal stabilisation is implemented in an oxidising atmosphere.

31. The method according to claim 22, wherein the thermal stabilisation is implemented by feeding the multifilament yarn through at least two ovens which are connected subsequently, in at least a first oven, no stretching or stretching <10% and, in at least one further oven, stretching of at least 30%, is effected, and in at least a first oven, temperatures of 80 to 200 C. being set, and, in at least one further oven, temperatures of 130 to 270 C., being set.

32. The method according to claim 22, wherein the thermal stabilisation is effected with application of tensile stress to the multifilament.

33. The method according to claim 22, wherein the thermal stabilisation is implemented over a period of 10 to 180 min.

34. The method according to claim 22, wherein the copolymer of polyacrylonitrile (PAN) is produced by copolymerisation of 99.9 to 70% by mol of acrylonitrile with at least one comonomer selected from a) 0.1 to 20% by mol of at least one alkoxyalkylacrylate of the general formula I, ##STR00004## with R=C.sub.nH.sub.2n+1 and n=1-8 and m=1-8, b) 0 to 10% by mol of at least one alkylacrylate of the general formula II ##STR00005## with R=C.sub.nH.sub.2n+1 and n=1-18, and c) 0 to 10% by mol of at least one vinyl ester of the general formula III ##STR00006## with R=C.sub.nH.sub.2n+1 and n=1-18.

35. The method according to claim 22, wherein the multifilament yarn is produced by melting and extrusion of the copolymer of polyacrylonitrile through at least one spinning nozzle and spinning to form multifilaments.

36. The method according to claim 22, wherein the prestabilisation of the non-prestabilised multifilament yarn is implemented i) by treatment with a mixture comprising at least one solvent for polyacrylonitrile and an aqueous alkaline solution or consisting thereof, and subsequent neutralisation of the treated multifilament yarn, and/or ii) by electron beam crosslinking of the meltable copolymers of polyacrylonitrile (PAN), and/or iii) by removing any residual plasticiser contained in the meltable copolymer of polyacrylonitrile (PAN).

37. The method according to claim 36, wherein the prestabilisation is effected by guiding the non-prestabilised multifilament yarn through a modifying bath, comprising the mixture at a temperature of 20 to 80 C., within a dwell time of 5 s to 2 min, or the non-prestabilised multifilament yarn is sprayed with the mixture.

38. The method according to claim 36, wherein the aqueous alkaline solution comprises from 3 to 15 mol/l of at least one alkaline earth- or alkali salt.

39. The method according to claim 22, wherein the neutralisation is effected by guiding the prestabilised multifilament yarn through a neutralisation bath, comprising an aqueous acidic solution with a pH value of less than 3, and at a temperature of 5 to 95 C., within a dwell time of 5 s to 2 min.

40. The method according to claim 22, wherein a further temperature treatment under inert gas, at temperatures of 300 to 3,000 C., follows the thermal stabilisation, resulting in the production of a carbon fibre.

41. The multifilament yarn stabilised according to the method of claim 22.

42. The carbon fibre produced by the method of claim 40.

Description

EXAMPLES 1-9

[0057] The prestabilised PAN precursor is transported, by the method step according to the invention, corresponding to the below cited test arrangement, continuously through two pipe ovens (FIG. 2) which are scoured with ambient atmosphere. In the lower oven (3) by applying temperatures (T.sub.1-T.sub.3) in the range of 100 to 200 C. and exposure times at corresponding temperatures of 20 to 80 min, a stabilisation degree of >15% can be set in the fibre material. For example, a temperature gradient can be set in the lower oven (3) such that there applies, in the respectively separate zones of the oven: T.sub.1=100 C., T.sub.2=150 C. and T.sub.3=200 C. After passing through the lower oven (3), the fibre material arrives at the upper oven (8) and likewise passes through the latter. In this thermal method step (stretch-stabilisation), the fibre material is treated at temperatures (T.sub.4-T.sub.6) between 150 and 350 C. and exposure times at corresponding temperatures of 5 to 80 min. As a result of the speed ratio of the fibre transport devices (v.sub.3/v.sub.2), the fibres were stretched by 0%, 30% or 100% (Table 1). Only by stretching the fibres during the temperature exposure, can the entire process be conducted continuously and maintained according to FIG. 2. The result is a thermally stabilised fibre which is characterised by non-flammability, black colouration, fibre strengths of >50 MPa and fibre breaking elongations of >3% and also a stabilisation degree (DOS) of at least 30%.

[0058] Device with which a Thermally Stabilised Multifilament Yarn According to the Present Invention can be Produced

[0059] A prestabilised multifilament yarn is thereby wound off a roll (1) and introduced into a first oven (3) by means of a galette (2) running at a speed v.sub.1. The oven is thereby flowed through by air and is subdivided into three temperature zones (T.sub.1, T.sub.2, T.sub.3). In temperature zone T.sub.1, for example a temperature of approx. 100 C. can be set. The temperature in temperature zone T.sub.2 can be for example approx. 150 C., the temperature of temperature zone T.sub.3 for example approx. 200 C. The separate temperature-control in the individual zones of the oven (3) can thereby be effected by means of separate heating elements (4) provided in the respective zones. The wound-off thread is transported continuously through the oven. By means of a tension-measuring sensor (5), the tension applied to the multifilament yarn can be determined. The multifilament yarn exiting from the lower oven (3) is deflected by means of further galettes (6) and (7) and supplied to a second oven. In the case, illustrated in FIG. 2 by way of example, the speed at which the galettes (2) and (6) run can be the same so that there applies: v.sub.1=v.sub.2. By means of the galette (7), the multifilament yarn is supplied to the upper oven (8) which is likewise flowed through by air. Also this further oven (8) is subdivided into three temperature zones T.sub.4, T.sub.5 and T.sub.6, the temperatures of temperature zone T.sub.4 can be approx. 150 C., of temperature zone T.sub.5 approx. 200 C. and in temperature zone T.sub.6 approx. 250 C. Also in the oven (8), separate heating elements (4) are present which enable separate temperature-control of the zones. After exit of the now thermally stabilised multifilament yarn, a further tension measurement by means of the tension sensor (9) can be effected. The thermally stabilised multifilament yarn is thereby drawn off by means of the galette (10) which runs at a speed v.sub.3. The speed v.sub.3 is thereby greater than the speed v.sub.2 of the galette (7) so that stretching of the multifilament yarn is undertaken at least in the upper oven. The finally thermally stabilised multifilament yarn is finally wound onto a roll (11).

TABLE-US-00001 TABLE 1 Characteristics of the fibres thermally stabilised according to the method according to the invention. Fibres which were not stretched during the heat treatment (0%) cannot be transported continuously. Fibre transport Continuous speed fibre Temperature V.sub.2 in V.sub.3 in Stretching transport Strength DOS T.sub.4-T.sub.6 in [ C.] [m/h] [m/h] [%] possible [MPa] [%] 230 2.0 2.0 0 No 10 ~30 2.0 2.6 30 Yes 125 ~30 2.0 4.0 100 Yes 175 ~30 240 2.0 2.0 0 No 10 ~45 2.0 2.6 30 Yes 60 ~45 2.0 4.0 100 Yes 175 ~45 250 2.0 2.0 0 No 10 ~50 2.0 4.0 100 Yes 175 ~50 DOS: stabilisation degree