undercurrent washing

The present invention relates to a method for washing filaments.

State of the art

Filaments, in particular based on cellulose are produced on a large scale and used in many areas, such as the textile industry but also in technical areas. An example of such filaments are filaments made by the Lyocell process from a composition of cellulose in a solvent, usually a mixture of water and N-methylmorpholine-N-oxide (NMNO). The spinning solution produced therefrom is spun through nozzles to produce filaments, which are regenerated in an aqueous precipitation bath. The Lyocell filaments obtained in this way are so-called regenerated cellulose fibers, which are characterized by a special combination of product properties (such as high dry and wet strength with a simultaneously soft feel and good moisture absorbency).

The fact that the individual components of the spinning solution and the precipitation bath solution used in the production of Lyocell filaments can be conducted in closed material cycles so that a high degree of reuse of the materials used is achieved is the manufacturing process the lyocell filaments are more environmentally friendly, especially in comparison to other regenerated cellulose fibers such as viscose. In addition, the solvents used in the process (water and NMNO) as such are significantly more environmentally friendly than, for example, the components used in the viscose process.

After the precipitation/regeneration of the lyocell filaments, the filaments obtained are fed to further treatment stages. An essential treatment stage is the washing of the filaments obtained, which removes in particular any solvent (NMNO) still adhering, but also other components of the spinning solution and/or the precipitation bath.

For such washes, there are a number of approaches, such as the classic bath wash (the filament is passed through a bath with washing liquid), the directed bath wash cal (an embodiment similar to the classic bath wash), a wash by the application of washing liquid on the filaments through nozzles or emitters, or also

Processes that are more complex in terms of apparatus, such as alternating roller washers (in which the filament is again guided through a bath with washing liquid, with the filament being guided over a deflection roller outside the washing liquid between individual washing steps so that, for example, excess liquid can drip off), perforated drum washers or pressure chamber scrubber.

All of these approaches to washing have in common that the filament is either surrounded by a very large amount of washing water or is subjected to a very large amount of water. However, only a small part of the water comes into direct contact with the filament. At the same time, accumulation of the washed-out solvent, for example, results in an enrichment of these components in the washing bath, so that the quality of the laundry decreases as long as no countermeasures are taken. Suitable countermeasures, such as replacing the water, again lead to an increase in the amount of water used and thus to less environmental friendliness and higher costs.

Although there is also the approach in such washing methods that the water is collected and circulated and used several times at the same place for washing, this also leads to a reduction in washing performance after a certain time. Again, this can only be compensated for by supplying new fresh water.

[0006] Washing processes and systems of this type are described, for example, in US Pat. No. 4,549,415. Although a cascade of washing areas is already used here, these are interconnected and the washing is carried out by passing the fibers through the washing bath, which again requires a large amount of washing liquid. WO 00/18991 A1 discloses a method in which a fleece formed from staple fibers is washed. US 2019/264356 A1 also discloses a method in which a nonwoven fabric is washed. In both of the documents mentioned above, a large excess of washing liquid is used, since otherwise an adequate effect is not achieved on the nonwovens to be treated.

Since in all of these approaches only a comparatively small part of the wash water comes into contact with the filament, but in particular the washed out solvent mixes again with the water that is not, or only slightly, contaminated, the efficiency of the wash decreases. This is particularly problematic in view of the ever-increasing demands with regard to the careful use of resources. At the same timen especially in the textile sector, even if small residual amounts of solvents or similar on the filament are neither harmful to health nor problematic in terms of wearing comfort, etc., ever increasing demands are being placed on "free from chemicals".

There is therefore a need for processes for the treatment of filaments which, on the one hand, enable a highly efficient and as complete as possible removal of solvents and process chemicals. With regard to the washing of lyocell filaments, this means in particular a removal of the solvent NMNO from manufactured lyocell filaments. At the same time, the amount of washing liquid used, i.e. water in the case of Lyocell filaments, should be as small as possible.

Brief description of the invention

[0009] This object is achieved by the method according to claim 1. Preferred embodiments are given in the dependent claims and also in the following description. Furthermore, this object is achieved by a system according to claim 9, wherein he newly preferred embodiments are specified in the subclaims and the following description.

Brief description of the character

The figure shows schematically the course of a countercurrent washing or a system for countercurrent washing in accordance with the present invention using two washing stages.

Detailed description of the invention

The present invention will first be described in terms of the method. However, it is clear to the person skilled in the art that the statements made in this context also apply analogously to the claimed system. The method of the present invention is applicable to a variety of different filaments. Even if the following description, especially in the preferred embodiments, is aimed at washing Lyocell filaments with the washing liquid water, to remove the residual amounts of the solvent NMNO still adhering to the filaments, it is obvious to the person skilled in the art that this method can also be used with other types of filaments, using other washing liquids and to remove other components adhering to the filaments.

The method according to the invention is characterized on the one hand by the fact that the filament to be washed and the washing liquid are conducted in countercurrent. In the figure, this is indicated by the opposite arrow directions for fresh water (washing liquid) and product stream (filament). This means that unloaded washing liquid is fed to the last washing stage, while the filament to be treated is fed to the first washing stage. In the figure, a method with two washing stages is shown as an example; however, methods with a significantly higher number of washing stages are preferred according to the invention. Processes with preferably 2 to 60, in particular 10 to 50 and more preferably 20 to 40 washing stages have proven to be suitable. The number of washing stages can vary depending on the result to be achieved (e.g. residual proportion of defined substances on the fiber, such as NMNO) and product properties, such as the thread size of the filament/filament bundle (larger thread size (i.e. basically higher values ​​for the diameter of the filament or filament bundle) often require a higher number of washing stages) and/or the production speed (higher speeds also frequently require a larger number of washing stages).

This procedure ensures that fresh washing liquid is used in the last washing stage, in which the filaments to be treated have only the smallest amount of components to be removed, so that an excellent effect is achieved.

At the same time, the method according to the invention is characterized in that the filament neither has to be passed through a bath of washing liquid nor sprayed with a large amount of washing liquid. In order to minimize the amount of washing liquid used in the process according to the invention, the filaments to be washed are exposed to the washing liquid in each washing stage by a washing element (W1, W2) in such a way that only as much liquid is transferred to the filaments as the filaments absorb and can bind. This is completely sufficient for an efficient washing effect, since the relevant mass transfer processes during washing/washing out only take place in very thin areas directly on the surface of the filaments (e.g. in the case of lyocell filaments the transfer of the adhering residual amounts of NMNO from the filament into the washing liquid. It has been shown that the targeted use of minimized but optimized amounts of washing liquid is completely sufficient for efficient treatment - with significantly larger amounts of washing liquid used, only the amount of washing liquid used is increasedbut does not increase the effectiveness of the wash.

Such a targeted and minimal loading of the filaments with washing liquid can be achieved, for example, by the washing element (W1, W2) providing a thin, falling film of washing liquid (in particular water) which the filaments to be washed are guided past in this way so that they can just be wetted by the surface of the washing liquid. This allows a small but sufficient amount of washing liquid to be transferred. Other configurations of the washing element are, for example, rollers or rollers wetted with washing liquid, in particular slow-running contact rollers, which are known to those skilled in the art, but are used according to the invention in a new and inventive way (possibly with suitable surface structuring; such as grooves and grooves running all around or are provided in the axial direction). These cylinders and/or rollers can be exposed to washing liquid by means of spray elements, small immersion baths or similar devices. Another way of applying the desired small amount of washing liquid to the filament/filament bundle is to use a preparation thread guide. Such devices, which are known to those skilled in the art, are designed in such a way that the washing liquid is applied from one side, so that a liquid film is generated on the other side, on which the filament/filament bundle is guided past in such a way that the desired wetting with washing liquid is reached. Yarn guides in combination with a ram jet washer are also suitable. The filament/filament bundle is wetted with washing liquid through a nozzle, which is preferably provided transversely to the transport direction of the filament/filament bundle.

As already described above, the filaments/filament bundles to be washed are guided past the liquid films provided by the different elements in such a way that the desired wetting with washing liquid is achieved while at the same time minimizing the amount of washing liquid used. The filaments/filament bundles can be guided in any orientation, from vertical, as shown in the figure, to horizontal, as with rollers/rollers.

[0016] This ensures that only the absolutely necessary amount of washing liquid is used in a washing stage. The washing liquid used in a given washing stage but not used up can be reused in the same washing stage, for example by suitable recycling of the washing liquid. Each washing stage or at least one group of washing stages is separated from the others, for example by a housing Washing stages or groups of washing stages separately, so that in particular there is no mixing of the washing liquid quantities that were actually used to wash the filaments and therefore have an increased proportion of washed-out components after separation from the filaments. This used washing liquid is removed again from the filaments/filament bundles in a suitable manner by centrifuging, the use of scrapers, etc. This ensures that in particular no unwanted mixing of the amounts of contaminated washing liquid occurring in a washing stage occurs.

We claim:

Expectations

1. Method for washing filaments, characterized in that the filament to be washed and the washing liquid are conducted in countercurrent, the method comprising at least two washing stages and in each washing stage the filament is washed with fresh washing liquid by means of a washing element (W1, W2) is brought into contact in such a way that only the amount of washing liquid that sticks to the filament itself, for example by adhesion, is transferred to the filament, in each washing stage the washing liquid is then separated from the filaments again and the separated washing liquid (S2) is collected in such a way that it is not mixed with the separated washing liquid from other washing stages of the process, but is used as fresh washing liquid in the washing element (W2) of the preceding washing stage.

2. The method according to claim 1, comprising at least 5 washing stages.

3. The method according to claim 1 or 2, wherein the washing liquid is separated from the filaments in each washing stage by stripping, squeezing or centrifugal elements.

4. The method according to any one of claims 1 to 3, wherein the washing element produces a falling film of washing liquid.

5. The method according to any one of claims 1 to 4, wherein the filaments are lyocell filaments and the washing liquid is water.

6. The method according to any one of claims 1 to 5, wherein the individual washing stages are separated by housing from the other washing stages.

7. The method according to any one of claims 1 to 6, wherein the filaments are guided past the washing element essentially perpendicularly.

8. The method as claimed in one of claims 1 to 7, in which the used washing liquid separated from the method is either purified so that fresh washing liquid is obtained for the last washing stage or is used as a process liquid in filament production.

9. System for washing filaments, the method comprising at least two washing stages and in each washing stage the filament is brought into contact with fresh washing liquid by means of a washing element (W1, W2) in such a way that only the amount of washing liquid is transferred to the filament which sticks to the filament itself, for example by adhesion, the washing liquid is then separated from the filaments again in each washing stage and the separated washing liquid (S2) is collected in such a way that it does not mix with the separated washing liquid speed of other washing stages of the process but is used as fresh washing liquid in the washing element (W2) of the preceding washing stage.

10. System according to claim 9, wherein the washing element is selected from elements for providing a falling film of washing liquid, rollers and/or rollers, which can have a surface structure, preparation thread guides and a combination of ram jet washers and thread guides.

11. System according to claim 9 or 10, wherein the individual washing stages or groups of washing stages are separated from one another by housings.

12. System according to at least one of claims 9 to 11, wherein the washing liquid is separated from the filaments by scrapers, squeezing mechanisms and/or centrifugal goods.

13. System according to at least one of claims 9 to 12, wherein the supply of the washing liquid to the washing elements takes place by pumps.

14. System according to at least one of claims 9 to 13, wherein the washing liquid is provided for each washing stage in storage chambers.

15. System according to at least one of claims 11 to 14, wherein each housing has an outlet for the washing liquid used in the respective washing stage.