PROCESS FOR LIQUID REMOVAL FROM CELLULOSE FILAMENTS YARNS OR FIBERS

Abstract

The present invention provides a process for the viable removal of liquid from lyocell cellulose continuous filament yarns at very high production speeds.

Claims

1. A process for the removal of liquid from lyocell type cellulose filament bundles or yarns from a lyocell spinning solution of cellulose in an aqueous tertiary amine oxide, wherein the lyocell type cellulose filament bundles or yarns are guided around a roller under conditions so that equation (1) is fulfilled, with the proviso that a_sp is at least 296 m/s.sup.2:
a_sp=r×φ.sup.2×titer/40  (1) with r being the radius of the roller (m), φ being the angular speed (1/s), and titer (dtex) being the bundle/yarn titer, with the proviso that same is at least 20.

2. The process according to claim 1, wherein r is from 0.010 to 0.200 m.

3. The process according to claim 1, wherein the titer is from 20 to 400 dtex.

4. The process according to claim 1, wherein the roller is a driven roller.

5. The process according to claim 1, wherein the roller is driven by the filament movement.

6. The process according to claim 1, wherein the lyocell type cellulose filament bundles or yarns are in contact with at least 12.5% of the circumferential surface of the roller (45°).

7. The process according to claim 1, wherein two or more rollers for liquid removal are provided without intermittent steps of contacting the lyocell type cellulose filament bundles or yarns with fresh washing liquid.

8. The process according to claim 1, wherein two or more rollers for liquid removal are provided with intermittent steps of contacting the lyocell type cellulose filament bundles or yarns with fresh washing liquid.

9. The process according to claim 1, wherein the filament tension during the removal of liquid is 2 cN per filament or more.

10. The process according to claim 1, wherein the filament tension during the removal of liquid is 0.4 cN/dtex or less.

11. The process according to claim 2, wherein r is from 0.0125 to 0.150 m.

12. The process according to claim 6, wherein the lyocell type cellulose filament bundles or yarns are in contact with at least 25% of the circumferential surface of the roller (90°).

Description

BRIEF DESCRIPTION OF THE FIGURE

[0024] FIG. 1 shows a schematic representation of the process step disclosed herein.

DETAILED DESCRIPTION OF THE INVENTION

[0025] The limitations of the state of the art have been overcome by the invention disclosed herein. Namely the present invention provides a process for liquid removal from lyocell filaments and lyocell multifilament yarns as defined in claim 1. The present invention will be described in detail referring to the required process control in relation to the relevant process steps and parameters to be employed. It is to be understood, that these process steps and their respective preferred embodiments can be combined as appropriate and that the present application covers these combinations and discloses same, even if not explicitly described herein.

[0026] The inventors have determined, that for productions velocities of 400 m/min or more a desired process control, enabling a good liquid removal from a filament bundle or multifilament yarn can be achieved, without requiring the use of wiping, squeezing or stripping devices, if the filament bundle or multifilament yarn is guided around a roller under specific conditions. These conditions ensure that a vast amount of liquid is removed from the bundle/yarn, even if entrapped in between different filaments within the bundle/yarn or within the filament itself. This is important, as the efficacy of any washing process requires that not only undesired materials are removed from the surface of the filaments but also from within the filament. This requires a good removal of as much liquid as possible, for the initial removal of coagulation bath liquid to any subsequent removal of washing liquid (typically water). Only if a very high proportion of the washing liquid remaining with the filament bundle/yarn, after contact with the washing liquid, is removed, can subsequent washing steps achieve the required further purification of the product. Accordingly it is essential that the liquid removal is as efficient as possible, while not affecting the filaments formed.

[0027] Namely, for the high production velocities required (400 m/min or more) the present invention provides a means for efficient liquid removal for filament bundles/yarns of at least 40 dtex, by adjusting the specific acceleration (a_sp) of the filaments being guided around a roller to at least 296 m/s.sup.2 per 40 dtex. This specific acceleration can be described by the following equation (1):

a_sp=r×ω.sup.2×titer/40  (1)

with r being the radius of the roller (m), ω being the angular speed (1/s), and titer (dtex) being the bundle/yarn titer, with the proviso that same is at least 20. Accordingly, suitable process conditions for any given titer and production speed (which relates to the angular speed) can be determined by appropriately selecting the variables so that the liquid removal process is carried out under conditions satisfying the equation above.

[0028] It has been found unexpectedly that by adjusting the process parameters as indicated above, a highly efficient liquid removal can be ensured. In this regard it has been found that the process as described herein is applicable at production speeds of 400 m/min or more, in particular for production speeds of from 400 to 2000 m/min. Even at such high production speeds, which require high speed transfer of the filament bundles/yarns around the roller for liquid removal, no detrimental effect is asserted on the produced filaments. However, the desired efficient removal of liquid is obtained, as long as the equation above is satisfied.

[0029] In accordance with the present invention it is preferred that the radius of the roller around which the filament bundles/yarns are guided is in the range of from 10 to 200 mm, preferably 12.5 to 150 mm. The titer of the filament bundle/yarn is preferably in the range of from 20 (the required minimum titer) to 500 dtex, more preferably in the range of from 40 to 400 dtex.

[0030] In addition, it has been determined, that it is advantageous of the filament bundle/yarn is in contact with at least 12.5% of the roller circumference (45°), more preferably with at least 25% (90°). This ensures that the filament bundle/yarn is in contact with the roller surface for a time long enough so that a high amount of liquid moves from the inside of the filaments or the filament bundle/yarn to the outside thereof, so that it is then spun away (catapulted/centrifuged away).

[0031] Accordingly, the present invention provides an efficient way to remove liquid from filament bundles/yarns even at high production speeds, by providing a correlation between production speed, bundle/yarn titer and roller radius to enable efficient and simple liquid removal.

[0032] The teaching of the present invention may be employed for the initial removal of coagulation bath liquid and/or for any subsequent removal of washing liquid. In accordance with the present invention one or more rollers for liquid removal as described herein may be present in a process for the production of lyocell multifilament yarns, with or without additional washing steps (i.e. new contact with washing liquid) between two rollers for liquid removal.

[0033] The type of roller is not critical, including surface material etc., as long as the rollers enable the guidance of the filament bundles/yarns around the roller at the given production speed as explained above. Usual rollers employed in the lyocell process may be used. The roller speed is typically about the same as the speed of the filament bundle/yarn and the rollers may comprise means for generation of roller movement (driven roller) or the filament movement generates the roller movement. The term that the roller speed and the filament speed are substantially the same in accordance with the present invention means that the speeds are within ±10% of each other, more preferably within ±5%. As regards filament tension it has been found advantageous if same is 2 cN or more. The following examples illustrate the present invention further:

[0034] Multifilament yarns from a lyocell filament spinning process were subjected to a liquid removal step after contact with washing water in accordance with the present invention. The following table summarizes the relevant process parameters (v being the production speed). The entry “A” designates that no problems/defects were detected after the liquid removal and that in addition a high proportion of liquid in fact was removed from the filament bundle/yarn.

TABLE-US-00001 Titer (dtex) 40 80 300 V (m/min) r (m) ω (1/s) evaluation evaluation evaluation 400 0.0125 533 A A A 700 0.0125 933 A A A 1000 0.0125 1333 A A A 400 0.074 90 A A A 700 0.074 158 A A A 1000 0.074 225 A A A 400 0.15 44 A A A 700 0.15 78 A A A 1000 0.15 111 A A A