Cross-flow washing

Abstract

The present invention relates to a method for cleaning a filament.

Description

Technical Field

[0001] The present invention relates to a process for cleaning filaments.

Background Art

[0002] Filaments are produced on a large scale, especially based on cellulose, and are used in many fields such as the fiber industry, but also in the industrial field. An example of such a filament is a filament produced by the lyocell process from a composition of cellulose in a solvent, usually a mixture of water and N-methylmorpholine N-oxide. The resulting spinning solution is spun through a nozzle to produce filaments and regenerated in an aqueous precipitation bath. The resulting lyocell filaments are so-called regenerated cellulose fibers, characterized by a special combination of product properties (e.g., high dry and wet strength combined with a soft touch and good hygroscopicity).

[0003] The individual components of the spinning solution and precipitation bath solution used in the production of lyocell filaments can be carried out in a closed material cycle, and a high degree of reuse of the materials used is achieved. Therefore, the production process of lyocell filaments is more environmentally friendly, especially compared to other regenerated cellulose fibers such as viscose. Furthermore, the solvents used in the process (water and NMNO) are much more environmentally friendly than the components used in the viscose process, for example.

[0004] After precipitation / regeneration of the lyocell filaments, the resulting filaments are fed to a further processing step. An essential processing step is the cleaning of the resulting filaments, thereby removing not only the still adhering solvent (NMNO), but also other components of the spinning solution and / or precipitation bath.

[0005] Such cleaning includes classical bath cleaning (where the filament is passed through a bath containing the cleaning liquid), controlled bath cleaning (a design similar to classical bath cleaning), cleaning by applying the cleaning liquid to the filament through nozzles or jets, or more complex processes such as an alternating roller cleaning device (where the filament is passed through a bath of cleaning liquid again and during individual cleaning steps the filament is passed over deflector rollers outside the cleaning liquid, for example so that excess liquid drips off), and there are many approaches such as a perforated drum cleaning device or a pressure chamber cleaning device.

[0006] All of these cleaning methods are common in that the filament is surrounded by or exposed to a very large amount of cleaning water. However, only a very small part of the water directly contacts the filament. At the same time, for example, if the washed-off solvents accumulate, these components accumulate in the cleaning tank and, unless countermeasures are taken, the quality of the laundry deteriorates. Taking appropriate countermeasures such as exchanging the water leads to an increase in water usage, and thus to a reduction in environmental impact and an increase in costs.

[0007] In such cleaning processes, there is also an approach of collecting and circulating the water and using it several times in the same place, but this leads to a decrease in cleaning performance after a certain period of time. Also, this can only be compensated by adding fresh water.

[0008] Such cleaning processes and plants are described, for example, in U.S. Patent No. 4,549,415. Here, cascades in the cleaning area are already used, but they are connected to each other and the cleaning is done by guiding the fibers through a cleaning bath, which also requires a large amount of cleaning liquid. International Publication No. 00 / 18991 A1 shows a process for cleaning a fleece formed from short fibers. U.S. Patent Application Publication No. 2019 / 264356 A1 also shows a process for cleaning a fiber fleece. Otherwise, since sufficient effects cannot be obtained in the fleece to be treated, a large amount of cleaning liquid is used in any of the methods in the above-mentioned documents.

[0009] In all of these approaches, only a very small portion of the washing water comes into contact with the filaments. In particular, the solvent that has been washed off is remixed with the uncontaminated or slightly contaminated water again, so the efficiency of the washing decreases. This is particularly problematic considering the growing demand for careful use of resources. At the same time, especially in the fiber field, even if a small amount of solvent or the like remains on the filaments, it does not have an adverse effect on health, and even if there is no problem in terms of comfort, etc., the demand for "release from chemical substances" is increasing more and more.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0011] Therefore, on the one hand, a filament treatment process that enables efficient and complete removal as much as possible, and on the other hand, that can handle solvents and chemical substances is required. Regarding the washing of lyocell filaments, this particularly means removing the solvent NMNO from the produced lyocell filaments. At the same time, the amount of the washing liquid (water in the case of lyocell filaments) should be minimized.

Means for Solving the Problems

[0012] This problem is solved by the process according to claim 1. Preferred embodiments are described in the dependent claims and also in the following description. Furthermore, this problem is solved by the system according to claim 9, whereby again preferred embodiments are shown in the dependent claims and the following description.

Brief Description of the Drawings

[0013] The figure schematically shows a countercurrent washing process or a system for countercurrent washing according to the invention using two washing stages.

Mode for Carrying Out the Invention

[0014] The present invention will first be described with respect to its process. However, it will be apparent to those skilled in the art that the explanations made in this context are equally applicable to the system described in the claims. The process of the present invention is applicable to a number of different filaments. Even if the following description is directed at a particularly preferred design for washing lyocell filaments with water as the washing liquid and for removing the remaining amount of the solvent NMNO still adhering to the filaments, it will be apparent to those skilled in the art that this method can also be used to remove other components adhering to the filaments using other washing liquids, together with other types of filaments.

[0015] The process of the present invention is characterized by the fact that the filament to be cleaned and the cleaning liquid are led in countercurrent on the one hand. In the figure, the fresh water (cleaning liquid) and the product flow (filament) are indicated by arrows in opposite directions. This means that the uncontaminated cleaning liquid is supplied to the final cleaning stage and the filament to be treated is supplied to the first cleaning stage. The figure shows an example of a process with two cleaning stages, but according to the present invention, a process with a significantly larger number of cleaning stages is preferred. It has been proven that a process having preferably 2 to 60, particularly 10 to 50, preferably 20 to 40 cleaning stages is appropriate. The number of cleaning stages can be selected according to product characteristics such as the result to be achieved (for example, the remaining amount of a specified substance such as NMNO on the fiber) and the yarn thickness of the filament / filament bundle (the larger value of the diameter of the filament or filament bundle), and / or according to the production speed (higher speeds often require more cleaning stages).

[0016] By this process, fresh cleaning liquid is used in the final cleaning stage, and the filament to be treated has a minimum amount of components to be removed, so an excellent effect is obtained.

[0017] At the same time, the method of the present invention is characterized in that it is not necessary to pass the filament through a bath of the cleaning liquid and it is not necessary to spray a large amount of the cleaning liquid. In order to minimize the amount of the cleaning liquid used in the method of the present invention, the filament to be cleaned is cleaned by the cleaning elements (W1, W2) at each cleaning stage so that only as much liquid as the filament can absorb and bind transfers to the filament. Since the associated mass transfer process during cleaning, i.e., the cleaning process, occurs directly in a very thin region on the surface of the filament (for example, in the case of lyocell filaments, the attached residual amount of NMNO moves from the filament to the cleaning liquid), this is completely sufficient for an efficient cleaning effect. The targeted use of an optimized amount of the cleaning liquid while minimizing it has been shown to be completely sufficient for efficient processing, and with a considerably large amount of the cleaning liquid, only the amount of the cleaning liquid used increases, but the cleaning effectiveness does not increase.

[0018] The minimum exposure of such filaments to the cleaning liquid can be achieved, for example, by cleaning elements (W1, W2) that provide a thin falling film of the cleaning liquid (especially water), and the filaments to be cleaned are guided through the film so as to be wetted by the cleaning liquid on the surface. Thereby, a sufficient amount of the cleaning liquid, although in a small quantity, can be transferred. Other designs of the cleaning elements are, for example, rolls or rollers wetted with the cleaning liquid, which are known to experts but used in a novel and inventive way according to the present invention (possibly with a suitable surface structure, such as grooves and channels provided in the circumferential or axial direction). These rolls and / or rollers can be supplied with the cleaning liquid by spray elements, small immersion baths or similar devices. Another possibility of applying a desired small amount of the cleaning liquid to the filament / filament bundle is the use of a preparation yarn guide. Such a device is known to experts and is designed to apply the cleaning liquid from one side to form a liquid film on the other side and guide it through the filament / filament bundle so that the desired wetting by the cleaning liquid is achieved. A screw guide combined with a ramjet cleaning device is also suitable. Here, the filament / filament bundle is preferably wetted with the cleaning liquid through a nozzle provided transversely to the transport direction of the filament / filament bundle. The filament / filament bundle to be cleaned is guided through the liquid film provided by different elements as described above, achieving the desired wetting by the cleaning liquid while minimizing the amount of the cleaning liquid used. The filament / filament bundle can be guided in any direction, from vertical to horizontal as shown, as in the case of rolls / rollers.

[0019] Thereby, only the absolutely necessary amount of the cleaning liquid is used in each cleaning stage. The cleaning liquid used but not consumed in a given cleaning stage can be reused in the same cleaning stage, for example, by appropriate recycling of the cleaning liquid.

[0020] Each washing stage or at least a group of washing stages is separated from other washing stages or groups of washing stages, for example by an enclosure, so that, in particular, the amount of cleaning liquid actually used to clean the filaments is not mixed, and thus the proportion of components washed off after separation from the filaments is increased. This used cleaning liquid is removed from the filaments / filament bundles in a suitable manner, for example by centrifugation, use of a scraper, etc. This ensures that, in particular, no unwanted mixing of the contaminated cleaning liquid occurring in the washing stages takes place. The method according to the invention is designed such that the amount of contamination of the cleaning liquid generated in one washing stage is supplied as cleaning liquid to the previous washing stage in order to enable maximum utilization of the cleaning liquid. If each washing stage is not separated individually from the other washing stages, but only groups of washing stages are separated from each other, and there are at least two different groups of washing stages, preferably more than two groups of washing stages significantly exceeding the above-mentioned number, this is sufficient according to the invention.

[0021] Referring to the figure, it can be described as follows. In the final washing stage (the washing stage on the right side of the washing element W1), pure water is used as the cleaning liquid. This is led from the storage tank S1 to the washing element W1. The filaments guided along the washing element W1 have, for example, an amount of the cleaning liquid taken in by a deflection roller (however, here other methods of removing the cleaning liquid, such as wiping or squeezing, can also be used) and are removed from the filaments within the washing stage. In this way, the contained NMNO removed by the cleaning liquid at this stage is separated (when the lyocell filaments are washed with water). This cleaning liquid, although slightly contaminated with NMNO, cannot be used in the final washing stage, but the NMNO content is still low and can be used as the cleaning liquid for the pre-washing stage by the washing element W2.

[0022] For this purpose, the amount of used cleaning liquid from the last stage is supplied to the storage tank S2, from where this cleaning liquid is supplied to the cleaning element W2. This countercurrent guidance of the filament and the cleaning liquid can be applied to more cleaning stages than the example having two cleaning stages shown here. In any case, the used cleaning liquid of a certain stage is supplied as "fresh" cleaning liquid to the stage before it. This increases the proportion of the components to be cleaned, such as NMNO in the cleaning liquid, but the fact that the proportion of these components on the filament in the previous cleaning stage is higher means that a good cleaning effect is still achieved in each cleaning stage.

[0023] As already mentioned, in each cleaning stage, not only is the filament wetted with the cleaning liquid, but this cleaning liquid is also separated from the filament (the undesirable mixing of the individual cleaning liquids is prevented by the separation between the individual cleaning stages). This can be done by simple dripping, or by using other means such as guiding around a roller for centrifuging the cleaning liquid, a scraper or a squeezing device. This separated used cleaning liquid is used as the cleaning liquid in the cleaning stage before it.

[0024] Considering the last washing stage of the lyocell filament washing process, this means that the slightly contaminated used washing water obtained in this washing stage is fed to a previous washing stage where the lyocell filament still has a slightly higher proportion of, for example, solvent. The water used in this washing stage also contains a certain amount of solvent (for the final washing stage), but since this washing liquid is still sufficiently clean, the filaments are also well washed in the previous washing stages. For this purpose, the washing water is reintroduced into the washing elements of the previous washing stage, and by properly guiding the filaments in said washing elements, it is ensured that only the necessary amount of water comes into contact with the filaments. This washing stage is separated from the adjacent washing stages by its own enclosure, the washing water is removed from the filaments again by suitable means (rollers, wipers, squeezing units), the used washing water accumulates again in this washing stage, and the proportion of NMNO in this washing water further increases. Then, this washing water can be returned to a previous washing stage, thereby enabling the washing water containing an even higher proportion of NMNO to come into contact again with filaments having a higher proportion of NMNO.

[0025] The above-described storage tanks for the washing liquids of different washing stages can be provided in a suitable form. The figure shows a schematic diagram of a storage tank having separate areas for different washing liquids (S1, S2, which differ essentially only in the proportion of the components washed off from the filaments, whereby the content of these washed-off components increases slowly, i.e., S2 is higher than S1), where these areas are separated by simple partitions. Thus, for example, unwanted mixing can be prevented by simply checking the levels of the individual segments (S1, S2).

[0026] This process design enables the filaments to be successively contacted countercurrently with the cleaning liquid, so that fresh cleaning liquid contacts filaments that are only lightly loaded with solvent, while at the same time, used cleaning liquid from a previous cleaning stage is removed from the filaments by countercurrent flow of the used cleaning liquid, despite the fact that the components washed off (such as NMNO) in the cleaning liquid gradually increase. (Although the filaments are still exposed to a larger amount of NMNO in each individual cleaning stage, effective cleaning is provided by the cleaning water contaminated with NMNO), and still good results are achieved.

[0027] Particularly in comparison with conventional tank cleaning, such a process can significantly reduce the consumption of the cleaning liquid during the laundry. At the same time, the cleaning efficiency is good, and more filaments can be overall cleaned with a small amount of cleaning liquid. It is also shown that the number of cleaning stages can be overall reduced by the process management of the present invention. By using the cleaning liquid as needed and not using an unnecessarily large amount of cleaning liquid, the efficiency can be improved significantly beyond expectation.

[0028] According to the present invention, the washing of the lyocell filaments can be carried out by feeding the filaments coming out of the manufacturing process, after removing the adhering liquid if necessary, from the precipitation bath to the individual washing stages. Thus, as shown in the figure, the filaments are fed to the first washing stage, where the filaments are basically guided vertically through the washing element W2 by means of deflection rollers or the like. The filaments are brought into sufficient contact with the washing liquid and are guided to absorb the washing liquid. The washing element W2 is designed, by means of a suitable holding and circulation design, so that the unused washing liquid can be reused in the washing stage. The washing liquid S2 used in this stage is the used washing liquid recovered from a later washing stage. The filaments are passed around a further roll which serves to remove the washing liquid from the filaments in the process shown in the figure. Thus separated from the filaments, the washing liquid used in this washing stage is recovered in a suitable manner and then discharged through the line shown at the bottom of the washing stage and is used for discharge from the system or as fresh washing liquid in a previous washing stage (not shown in the figure). When discharging the used washing water from the washing system, it is purified (for example, so that fresh water for the final washing stage can be obtained again in addition to a small amount of washed-off washing components), or this mixture containing essentially only water and NMNO can be used at other locations in the filament manufacturing process (for example, in the preparation of the spinning solution or in the precipitation bath). In this way, an overall balance with extremely resource-saving washing liquid input can be achieved again. The filaments are transferred to the next washing stage, where the washing element W1 applies the washing liquid to the filaments again. Then the washing liquid is separated from the filaments again. The used washing liquid recovered and discharged at this stage is used as the fresh washing liquid S2 for the washing element W2. In the washing element W1, the supplied fresh water is used as the washing liquid S1.

[0029] Tests using lyocell filaments have shown that the use of the countercurrent washing system according to the invention reduces the residual NMNO content on the filaments by more than 80% with the same number of washing stages compared to a washing stage without separation and countercurrent induction. At the same time, the countercurrent washing system described herein has excellent stability and effectiveness even at very high filament / filament bundle speeds (e.g., 1200 m / min or more) without being hindered in production. Furthermore, high production capacity can be ensured by possible continuous process control.

[0030] As described above, the present invention also provides a system (apparatus) for washing filaments that can be easily combined with existing filament production plants. This system includes washing elements (W1, W2) that bring the filaments into contact with fresh washing liquid such that only the amount of washing liquid adhering to the filaments themselves by adhesion is transferred to the filaments, and then a separation element that re-separates the washing liquid from the filaments. The separated washing liquid (S2) is designed to be recovered so that it is not mixed with the separated washing liquid of other washing stages of the process and can be used as fresh washing liquid for the washing element (W2) of the previous washing stage. It comprises at least two washing stages. Each washing stage includes a recovery tank for the separated washing liquid, and this is achieved by designing the recovery tank such that the separated and recovered washing liquid is supplied to the washing element of the stage before it, for example, by piping, pumps, etc. These recovery tanks and the other devices (piping, pumps, etc.) described above can be designed in an appropriate manner. The required devices / elements are familiar to experts.

[0031] For this purpose, the system also includes the piping necessary for the supply and discharge of the cleaning liquid, as well as suitable devices such as pumps for maintaining the supply and discharge of the cleaning liquid. The cleaning liquid for each cleaning stage can be stored in a storage chamber, and thus these storage chambers can be designed, for example, as sections arranged adjacent to a large storage tank. In this design, different storage chambers are separated from each other, for example, by partition walls. By appropriately using partition walls of different heights, a storage tank having a number of chambers can be provided in a simple manner, thereby preventing undesirable backmixing between a more highly loaded washing liquid and a less loaded washing liquid.

[0032] The cleaning element can be selected in particular from elements providing a falling film of the cleaning liquid, rollers and / or rolls which may have a surface texture, a preparatory yarn guide, and combinations of a ram jet cleaning device and a yarn guide.

[0033] The element for removing the cleaning liquid from the filament can be selected in particular from centrifugal elements, squeezing devices and / or scrapers.

[0034] The preferred enclosure provided by the present invention separates individual cleaning stages or groups of cleaning stages from each other. Such an enclosure can be easily manufactured from a suitable material such as a steel plate. The housing is usually designed such that the used cleaning liquid (i.e., the cleaning liquid removed from the filament) collects at the bottom, thereby enabling simple and safe discharge into the storage chamber for the previous cleaning stage.

[0035] The system also includes the rolls and / or rollers necessary to guide the filament so that the filament passes through the cleaning system.

Claims

1. A process for cleaning a filament, wherein the filament to be cleaned and the cleaning liquid are passed in countercurrent, including at least two cleaning stages. In each cleaning stage, the cleaning element (W1, W2) brings the filament into contact with fresh cleaning liquid such that only the amount of cleaning liquid adhering to the filament itself, for example by adhesion, transfers to the filament. Then, in each cleaning stage, the cleaning liquid is separated from the filament again, and the separated cleaning liquid (S2) is recovered in such a way that it is not mixed with the separated cleaning liquid from other cleaning stages of the process and is used as fresh cleaning liquid in the cleaning element (W2) of the previous cleaning stage. Process.

2. The process according to claim 1, including at least five cleaning steps.

3. The process according to claim 1 or 2, wherein the separation of the cleaning liquid from the filament in each cleaning stage is performed by a stripping element, a squeezing element, or a centrifugal separation element.

4. The process according to any one of claims 1 to 3, wherein the cleaning element forms a downward flowing film of the cleaning liquid.

5. The process according to any one of claims 1 to 4, wherein the filament is a lyocell filament and the cleaning liquid is water.

6. The process according to any one of claims 1 to 5, wherein the individual cleaning stages are separated from other cleaning stages by enclosures.

7. The process according to any one of claims 1 to 6, wherein the filament passes substantially vertically through the cleaning element.

8. Purifying the used cleaning liquid separated from the process to obtain a fresh cleaning liquid for the final cleaning stage or using it as a process liquid for filament production, the process according to any one of claims 1 to 7.

9. A system for cleaning filaments, comprising at least two cleaning stages, in each cleaning stage, the filaments are brought into contact with fresh cleaning liquid by cleaning elements (W1, W2) such that, for example, the amount of cleaning liquid adhering to the filaments themselves by adhesion migrates to the filaments, in each cleaning stage, the cleaning liquid is separated from the filaments again, and the separated cleaning liquid (S2) is not mixed with the cleaning liquid separated from other cleaning stages of the process and is recovered to be used as fresh cleaning liquid in the cleaning element (W2) of the previous cleaning stage.

10. The cleaning element is selected from an element providing a flowing-down film of the cleaning liquid, a roller and / or roll which may have a surface texture, a preparatory yarn guide, and a combination of a ram jet cleaning device and a yarn guide, the system according to claim 9.

11. The individual cleaning stages or groups of cleaning stages are separated from each other by enclosures, the system according to claim 9 or 10.

12. The separation of the cleaning liquid from the filaments is performed by a scraper, a squeezer and / or a centrifugal roll, the system according to any one of claims 9 to 11.

13. The supply of the cleaning liquid to the cleaning element is performed by pumping, the system according to any one of claims 9 to 12.

14. The cleaning liquid for each cleaning stage is supplied from a storage chamber, the system according to any one of claims 9 to 13.

15. The enclosure has an outlet for the cleaning liquid used in each cleaning stage, the system according to claim 11.

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