METHOD AND DEVICE FOR PRODUCING TUBULAR CELLULOSIC SPUN-BONDED NONWOVEN FABRICS

Abstract

A device for producing a seamless tubular cellulosic spunbonded nonwoven fabric, comprising a spinning dope production (8), a spinning system (2), a coagulation system (4), a deposition section (3) for depositing and dewatering the spunbonded nonwoven, a transport device (13, 22) for carrying off the spunbonded nonwoven in the transport direction, a washing system (5) and a drying system (6), wherein the deposition section (3) is designed so as to be rotatable, with the axis of rotation of the deposition section (3) lying along the transport direction.

Claims

1. A device for producing a seamless tubular cellulosic spunbonded nonwoven fabric, comprising: a spinning dope production, a spinning system, a coagulation system, a deposition section for depositing and dewatering the spunbonded nonwoven, a transport device for carrying off the spunbonded nonwoven in a transport direction, a washing system and a drying system, wherein the deposition section is designed so as to be rotatable, with an axis of rotation of the deposition section lying along the transport direction.

2. The device according to claim 1, further comprising at least one suction device associated with the deposition section.

3. The device according to claim 2, wherein the at least one suction device is inclined at least in sections.

4. The device according to claim 1, further comprising a cutting unit.

5. A method of producing a seamless multi-layered tubular cellulosic spunbonded nonwoven fabric, comprising: processing cellulose into a spinning dope and, subsequently, extruding the spinning dope with a spinning system to form drawn filaments by using hot air, and moistening the drawn filaments, before a deposition, with a coagulation liquid in such a way that adhesions will form at least between the drawn filaments or across several layers during the deposition, wherein the drawn filaments are deposited on a rotating tray, dewatered, washed and dried.

6. The method according to claim 5, further comprising washing a solvent out of the spunbonded nonwoven and supplying it to a solvent recovery.

7. The method according to claim 6, further comprising extracting process air and supplying it to the solvent recovery.

8. A seamless tube comprising several layers of drawn cellulose filaments, wherein the cellulose filaments adhere to each other in each layer section wise, and wherein the individual layers adhere to each other section wise, with the tube being essentially free from binders.

9. A filter comprising a tube according to claim 8.

10. The filter according to claim 9, wherein the filter is used for at least one of: adsorption, chemical bonding or absorption of substances from gases, liquids and emulsions, separation of emulsions, dedusting of waste gases, as a droplet separator, decolorization of liquids, disinfection of gases and liquids, drinking water treatment, water softening, separating oil from gases, separating emulsions, deodorization in the food industry.

11. A method according to claim 5, wherein the drawn filaments adhere to each other section wise.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0034] For a better illustration of the invention, the essential features are depicted in the following figures, based on preferred embodiments of the device according to the invention:

[0035] FIG. 1 shows a block diagram of the method according to the invention.

[0036] FIG. 2 schematically shows a device according to the invention for the production of filter cartridges in a side view.

[0037] FIG. 3 schematically shows a device according to the invention for the production of filtering tubes in a side view.

[0038] FIGS. 4a, 4b schematically show the rotating deposition section in a perspective illustration and in a front view.

[0039] FIG. 5 shows a device according to the invention in a side view, for the continuous production of a cellulosic spunbonded nonwoven tube without a winding core.

[0040] FIG. 6 shows a device according to the invention in a side view, for the continuous production of a cellulosic spunbonded nonwoven tube with a winding core.

[0041] FIG. 7 shows a device according to the invention in a side view, for the batchwise production of a cellulosic spunbonded nonwoven tube with a winding core.

[0042] FIG. 8 schematically shows a piece of a spunbonded nonwoven tube and, respectively, a filter cartridge.

[0043] FIG. 9 shows a spunbonded nonwoven layer with many surfaces stuck together and the open pores therebetween.

[0044] FIG. 10 shows a spunbonded nonwoven layer with a small number of adhesions.

[0045] FIG. 1 shows a block diagram of the method according to the invention in which a cellulosic spinning dope is extruded through a meltblown nozzle to form fine filaments and is drawn by means of hot air. According to the invention, even before they are deposited on a rotating cylinder, the drawn filaments are moistened with coagulation liquid only to the extent that adhesions will form between the individual filaments and the individual layers of the spunbonded nonwoven tube that is produced. It has been shown that those adhesions impart sufficient stability to the spunbonded nonwoven tube after washing and drying so that, finally, it can be wound up or cut into individual tube pieces. The addition of binders was therefore not necessary, since the adhesions of individual filaments between several layers and the pronounced hydrogen bonds of the cellulose after drying impart sufficient stability and cohesion to the produced spunbonded nonwoven tube across layers so that it can be used, for example, in different areas of filtration.

[0046] For performing the method according to the invention and the production of filter cartridges, the device 1 according to the invention as described in FIG. 2 can be used. The device 1 according to the invention comprises a spinning dope production 8, a spinning system 2, and a deposition section 3 for depositing the spunbonded nonwoven, a coagulation system 4, a washing system 5 (or, respectively, aftertreatment), a drying system 6 (optionally for carbonization and activation) 6, a cutting unit 7 and a hot air supply 9. By means of the device 1 according to the invention, the filaments 10 can be extruded, drawn, coagulated and formed into a spunbonded nonwoven tube 11 on the rotating deposition section 3 for depositing the spunbonded nonwoven. Downstream of the washing system 5 and the drying system 6, the continuously produced spunbonded nonwoven tube can be wound either into filter cartridges 12 or, as shown in FIG. 3, into filtering tubes 18. The device according to FIG. 3 has essentially the same structure as the device of FIG. 2 with the difference in winding.

[0047] The continuous production of the product according to the invention without a core can be enabled by means of driven take-off rollers 13, as illustrated in FIG. 5. If the rotating deposition section 3 is a brightly polished shaft, the filtering tube is drawn from the shaft by the take-off rollers 13, and the linear movement of the rotating tube underneath the nozzle is enabled. The rotating deposition section 3 may also have at least one helical thread on the surface from front to back. Due to the friction of the spunbonded nonwoven tube shown in FIG. 3 on the external surface with the suction unit 17 and the friction with the rotating helical thread in the interior of the tube, the tube is conveyed uniformly in the direction of the washing system 5 (similar to the delivery principle of a screw conveyor or an extruder). Alternatively, however, as shown in FIG. 6, cores 23 may also be used for the deposition of the spunbonded nonwoven in order to produce filter cartridges. In this case, perforated winding cores 23 are supplied piece by piece, connected and transported further continuously via drive rollers 22. Another variant is also the batchwise production with a winding core 23, which is depicted in FIG. 7. In this case, the filaments are sprayed alternately onto two rotating deposition sections 3 for depositing the spunbonded nonwoven. While the deposition section 3 for depositing the spunbonded nonwoven is sprayed underneath the nozzle of the spinning system 2, the spunbonded nonwoven tube 11, including the core 23, is withdrawn from a second deposition section 3 for depositing the spunbonded nonwoven and is fitted with an empty core 23. The spunbonded nonwoven tube is then washed (optionally aftertreated with chemicals), dried (optionally carbonized and activated) and processed or, respectively, cut, for example, into filter cartridges 12. It has been shown that, with the present device and variations in the preferred design, seamless, multi-layered, cellulosic filtering tubes and, respectively, filter cartridges with and without a core can be produced.

[0048] FIG. 8 schematically shows a filter cartridge with the hollow space in the middle and the surrounding spunbonded nonwoven layers. Since the spunbonded nonwoven 11 is moved with the filaments 10 during spraying, the layers are gradually built up under the spinning system 2 along the movement. In this case, one spinning system 2 can be used, or several spinning systems 2 can be used, with equal or different filament diameters. It has been shown that the adhesions can be varied depending on the spinning system and, as a result, filter materials with different layers, filament diameters, pore sizes and thus a wide variety of filtration properties can be produced. FIG. 9 shows a spunbonded nonwoven layer with many adhesions, while the spunbonded nonwoven in FIG. 10 has many individual filaments. It is also possible to use additional spinning systems 2 with a non-cellulosic spinning dope, for example, thermoplastic melts, in order to produce tubular products with cellulosic and non-cellulosic layers, thereby influencing the properties of the tubular product.

[0049] The product according to the invention comprises, among other things, a seamless, multi-layered filtering tube made of cellulose, which can be processed, for example, into filter cartridges and filtering tubes. The product according to the invention may also contain non-cellulosic layers, may be chemically aftertreated or, respectively, functionalized, may contain additives for increasing the filtration performance, enhancing flame resistance, allowing ion exchange and increasing the chemical resistance against the filtration medium. In addition, the filtering tube can be carbonized and/or activated partially or completely in order to increase surface activity and adsorption properties. The product according to the invention can be used, for example, for filtration, separation, ion exchange, disinfection of liquids and gases, separation of emulsions, oil separation and other applications for filtering tubes and filter cartridges which are known to a person skilled in the art.

[0050] For the method according to the invention, a wide variety of pulps, solvents and cellulosic spinning dopes produced therefrom can be used. A spinning dope is understood to be a multi-substance system in which cellulose is solubilized by a suitable solvent, for example, ionic liquids, preferably tertiary amine oxides, more preferably an NMMO/water mixture, and, thus, becomes extrudable and spinnable. The pulp content in case of a lyocell spinning dope may be between 4 and 15%, preferably between 6% and 14%, more preferably between 7% and 13%. In case of the lyocell spinning dope, the temperature may be between 80° C. and 160° C., preferably between 90° C. and 150° C., more preferably between 100° C. and 140° C.

[0051] It has been shown that the spinning dope can be extruded and drawn by both single-row and multi-row meltblown nozzles (spinning system 2). Several sequentially arranged spinning systems 2 can be used for producing layers of different filament diameters. If only one spinning system 2 is used, the extrusion hole geometry can vary from one side of the nozzle to the other side of the nozzle both in size and in geometry (e.g., becoming larger along the nozzle, holes are circular at the beginning and Y-shaped at the end) to produce fine filaments in the inner layers and coarse filaments in the outer layers, or circular filaments inside and hollow fibres outside. Further combinations of size, gradient and geometry are possible depending on the desired product properties. In this case, the hot process air emerges from a gap or from a hole next to or around the extrusion openings and entrains the spinning dope filaments, depending on the nozzle design. The filament is accelerated, and the diameter is reduced. Subsequently, the filaments are swirled by the turbulence of the process air and can be deposited as a spunbonded nonwoven on a rotating surface. The nozzle length may be between 50 mm and 2000 mm, preferably between 100 mm and 1000 mm, more preferably between 200 mm and 500 mm. The cellulose throughput may be between 1 kg/h/m and 500 kg/h/m nozzle length, preferably between 15 kg/h/m and 250 kg/h/m, more preferably between 20 kg/h/m and 100 kg/h/m. The extrusion holes of the nozzle may be between 0.05 mm and 3 mm, preferably between 0.2 mm and 1 mm, more preferably between 0.3 mm and 0.6 mm. The pulp throughput per extrusion hole may be between 0.001 g/hole/min and 30 g/hole/min, preferably between 0.1 g/hole/min and 20 g/hole/min, more preferably between 1 g/hole/min and 10 g/hole/min. In case of single-row slot nozzles, the air gap width may be between 0.5 mm and 5 mm, preferably between 1 mm and 3 mm, more preferably between 1.5 mm and 2 mm. In case of multi-row nozzles, the air outlet diameter may be between 0.5 mm and 5 mm, preferably between 1 mm and 3 mm, more preferably between 1.5 mm and 2 mm. The process air overpressures that are used may be between 0.1 bar and 10 bar, preferably between 0.3 bar and 5 bar, more preferably between 0.5 bar and 2 bar. This results in air outlet speeds at a nozzle distance of 20 mm of 50 m/s to 300 m/s, preferably 70 m/s to 250 m/s, more preferably 100 m/s to 200 m/s. At a distance between the nozzle and the rotating tray of 50 mm to 1000 mm, preferably 200 mm to 800 mm, more preferably 300 mm to 600 mm, there will be diameters of individual fibres of 0.1 μm to 100 μm, preferably 0.5 μm to 50 μm, more preferably between 1 μm and 30 μm.

[0052] It has been shown that the degree of adhesion can be specifically influenced by the coagulation, i.e., the regeneration of the cellulose. In this connection, the fusion of several individual filaments at their points of contact is referred to as an adhesion. Before they impinge on the tray, the filaments are moistened with the coagulation liquid only to the extent that they remain partly liquid and fuse together upon contact, whereby an adhesion is created. According to the invention, no coagulation liquid is applied in extreme cases, and a maximum of adhesions is thereby produced. In this case, the adhesions can be spherical, for example, or else flat and can have a diameter of 10 μm to 500 μm, preferably 30 μm to 300 μm, more preferably 50 to 200 μm. The coagulation liquid can either be injected directly into the process air or sprayed onto the filament curtain via a wide variety of spraying and nebulization systems. Water and various solvent mixtures such as, e.g., an NMMO/water mixture can be used as the coagulation liquid. The concentration of NMMO in the coagulation liquid may be between 0-45%, preferably from 10 to 40%, more preferably between 20 and 30%. The temperature of the coagulation liquid may be between 5° C. and 90° C., preferably between 10° C. and 70° C., more preferably between 20° C. and 60° C.

[0053] After coagulation, the filaments are deposited on a rotating deposition section 3 for depositing the spunbonded nonwoven. The rotating deposition section 3 for depositing the spunbonded nonwoven may be like a driven shaft or, respectively, a mandrel made of metal. The diameter of the rotating tray may be between 1 cm and 100 cm, preferably between 1.5 cm and 50 cm, more preferably between 2 cm and 30 cm. Depending on the nozzle length, the rotating tray may have a length of 25 to 500 cm, preferably 50 to 400 cm, more preferably 100 to 300 cm, for a continuous production without a core (FIG. 5). In a continuous core production involving a core as shown in FIG. 6, the winding cores are used as a rotating tray. In both cases, drive rollers 22 and take-off rollers 13 can be used for the continuous production to permit the linear movement of the spunbonded nonwoven tube along the nozzle length. In the batch production as shown in FIG. 7, the entire rotating tray is moved under the spinning system in order to load the core with layers of spunbonded nonwoven. When a core is coated, it is pulled away from the nozzle and replaced with a new core. The latter is then again shifted linearly along the nozzle until a spunbonded nonwoven tube is formed. In all three cases, the linear movement of the rotating tray 3 under the spinning system 2 is responsible for the fact that the spunbonded nonwoven tube is built up from the inside to the outside. Therefore, a variation in the filament fineness along the spinneret has the effect that the porosity and, respectively, the air permeability of the different layers can be varied. This type of product variation is especially desirable for filtration applications. The filtering tube consists of at least one layer. It has been shown that the number of layers and thus the thickness of the produced filtering tube can be varied depending on the application by adjusting either the throughput through the nozzle, the rotational speed of the rotating tray 3 or the take-off speed of the drive and take-off rollers, respectively.

[0054] According to the invention, the deposition can also be influenced by using a perforated pipe placed under vacuum 24 as the rotating tray. In doing so, the filaments are specifically aspirated and simultaneously dewatered. Excess coagulation liquid either can, as shown in FIG. 2, be drained off and collected with drain trays, or can be removed actively via the suction unit shown in FIG. 4a. The rotatable deposition section 13 shown in FIG. 4a has a suction unit which can be used for removing the coagulation liquid, the process air and the washing liquid in the washing. In this case, the spunbonded nonwoven tube is supported by pulleys 19 and/or, as illustrated in FIG. 4a, by a conveyor belt 20. The pulleys 19 and, respectively, the conveyor belt 20 thereby rotate at the same speed as the rotating tray 3 or, respectively, the spunbonded nonwoven tube 11. Between the pulleys 19 and under the conveyor belt 20, there is a suction unit 21. The spunbonded nonwoven tube is dewatered by means of the suction unit. As shown in FIG. 4b, the dewatering effect can be enhanced by the take-off rollers 13, which, in this case, serve as pressure rollers. The moisture content can be reduced down to 30% by the dewatering unit. As illustrated in FIG. 3, the liquids from the dewatering boxes reach either the coagulation container 15 or the washing-system container 14. The liquid from the coagulation container 15 is supplied to the solvent recovery, while the liquid from the washing-system container can be used for the coagulation system 4.

[0055] After the formation of the nonwoven, the spunbonded nonwoven tube gets into the washing. The remaining solvent is thereby removed from the spunbonded nonwoven tube. The spunbonded nonwoven tube either can be guided through a basin or bath, under spray nozzles or other sprinklings in which water is supplied in counterflow and solvent is discharged, or through several consecutive stages in which, for example, water is sprayed onto the spunbonded nonwoven tube in counterflow and either drips off or is removed by the suction unit 17. The washing can consist of several washing stages in which the counterflow extraction is repeated until the desired purity is obtained. The temperature of the washing liquid may be between 20 and 90° C., preferably between 30 and 85° C., more preferably between 40 and 80° C. The temperature can also be varied for the different washing stages. For example, the first washing stage may be warmer than the last one. Based on the counterflow principle of the washing, the concentration of the solvent in the spunbonded nonwoven tube decreases, while the wash water is concentrated. The concentrated wash water can then be used for the coagulation. In the washing, the properties of the spunbonded nonwoven tube can be influenced by the addition of chemicals, for example, in order to increase the temperature resistance, chemical resistance, dimensional stability and filtration performance by functional groups. Furthermore, disinfectants and flame retardant impregnating agents may also be added (chemical aftertreatment).

[0056] After washing, the spunbonded nonwoven tube 11 still has to be dried. In doing so, flow dryers (convection dryers), radiation dryers (IR, UV, microwave) as well as contact dryers with heated rollers can be used. In this case, the moisture content is reduced to 2 to 14%, preferably 4 to 12%, more preferably 6 to 10%. It has been shown that the spunbonded nonwoven tubes can also be carbonized and/or activated partially or completely upon appropriate impregnation in the washing. As a result, the specific surface area of the product, the absorption and adsorption properties are significantly increased.

[0057] In a continuous production, the spunbonded nonwoven tube can either be cut into smaller units (FIG. 2) or wound up as a tubular roll (FIG. 3).

[0058] The washing (chemical aftertreatment) and drying (or, respectively, carbonization) as described is performed batchwise in a batch production.

[0059] The manufactured product can be used as a pure cellulose spunbonded nonwoven tube, as a cellulose/thermoplastic spunbonded nonwoven tube, as a carbonized spunbonded nonwoven tube, as an activated spunbonded nonwoven tube, chemically aftertreated in order to increase flame resistance and temperature stability and to improve the adsorption, the chemical binding and the absorption of substances from gases, liquids and emulsions, for example, as a filter cloth, filter cartridge, filtering tube, bag filter, for separating solids from gases and liquids, for separating liquids from gases, for separating emulsions, for the dedusting of waste gases, as a droplet separator, for the decolorization of liquids, for the disinfection of gases and liquids, for drinking water treatment, water softening, the separation of oil from gases, the separation of emulsions, for deodorization in the food industry, in the chemical industry, in the pharmaceutical industry, in the automotive industry, in the electrical industry, in the oil industry, in the petrochemical industry, in the cosmetics industry and in the private sector.

[0060] Furthermore, the product according to the invention can be used for extraction sleeves in the laboratory and as a filter for instrumental analysis. The filtering tube can also be processed, for example, into tea bags and coffee filters.

[0061] In the cosmetics sector, the filtering tube can be used, for example, as a finger tube for applying and, respectively, removing cosmetics (cream, powder, . . . ). Cellulosic filtering tubes can be used commercially as a biodegradable packaging material for fruits and vegetables. Due to the water absorption of the cellulose, the product according to the invention is also suitable for packaging and as a corrosion protection of metal parts for transport and storage. In the agricultural sector, the product of the invention can be used for protecting plants from mechanical attack, desiccation, insects and animals or for supplying nutrients to the plant.

[0062] The spunbonded nonwoven tube can also be used as a bandage in the therapeutic or medical field for supporting the musculature, as a wound dressing, as a support bandage, for moisture regulation and for the promotion of wound healing.