METHOD AND DEVICE FOR PRODUCING SPUNBONDED FABRIC

Abstract

A process for the production of spunbonded nonwoven (1) and a device for this purpose are shown, wherein a spinning mass (2) is extruded through a plurality of nozzle holes of at least one spinneret (3) to form filaments (4) and the filaments (4) are charged with a drawing air stream to be drawn in an extrusion direction, wherein the filaments (4) are deposited on a perforated conveying device (9) to form a spunbonded nonwoven (1) and wherein the spunbonded nonwoven (1) is subsequently subjected to at least one washing (10) and one drying (12) by means of hot air (15), with, in each case, one exhaust air stream (18, 19) being discharged during the drawing and washing (10). So as to be able to reduce the energy consumption in the process during the drying of the spunbonded nonwoven without decreasing the product quality, it is suggested that the hot air (15) for drying (12) is generated at least partially by preheating an air stream (16) by means of one of the exhaust air streams (18, 19) from the drawing and washing (10).

Claims

1. A process for producing a spunbonded nonwoven, comprising extruding a spinning mass through a plurality of nozzle holes of at least one spinneret to form filaments charging the filaments with a drawing air stream to be drawn in an extrusion direction, depositing the filaments on a perforated conveying device to form the spunbonded nonwoven and subsequently subjecting the spunbonded nonwoven to at least one washing and at least one drying by means of hot air, with, in each case, at least one exhaust air stream being discharged during drawing and the at least one washing, wherein the hot air for the at least one drying is generated at least partially by preheating an air stream by means of the at least one exhaust air stream from the drawing and the at least one washing.

2. The process according to claim 1, wherein fresh air is used as the air stream.

3. The process according to claim 1, wherein the spunbonded nonwoven is charged with the hot air during the at least one drying and the hot air enriched with water vapor is discharged from the at least one drying as an exhaust air stream.

4. The process according to claim 3, wherein the exhaust air stream from the at least one drying is used at least partially as the drawing air stream for drawing the extruded filaments in the extrusion direction.

5. The process according to claim 3, wherein the air stream for the at least one drying is preheated at least partially by the exhaust air stream from the at least one drying.

6. The process according to claim 1, wherein the air stream for the at least one drying is heated to a temperature of less than or equal to 150° C., optionally less than or equal to 140° C., or optionally less than or equal to 130° C.

7. The process according to claim 1, wherein between 500 and 1,500 kg/h, optionally between 600 and 1,400 kg/h, or optionally between 700 and 1,300 kg/h water per meter of a width spunbonded nonwoven is evaporated from the spunbonded nonwoven by charging the spunbonded nonwoven with the hot air during the at least one drying.

8. The process according to claim 1, wherein the spunbonded nonwoven is a cellulosic spunbonded nonwoven, and the spinning mass is a solution of cellulose in a direct solvent, optionally a tertiary amine oxide in an aqueous solution.

9. The process according to claim 1, wherein, upon extrusion from the at least one spinneret, the filaments are coagulated at least partly, optionally by being charged with a coagulation air stream comprising a coagulation liquid.

10. A device for producing a spunbonded nonwoven, comprising: at least one spinneret for extruding a spinning mass to form filaments; a drawing device for drawing the extruded filaments by means of a drawing air stream, the drawing device being allocated to the at least one spinneret, wherein the drawing device comprises a first suction for discharging a first exhaust air stream, a perforated conveying device for depositing the filaments and forming the spunbonded nonwoven; a washing device for washing the spunbonded nonwoven after the spunbonded nonwoven has been formed, wherein the washing device comprises a second suction for discharging a second exhaust air stream; a dryer for drying the spunbonded nonwoven by means of hot air downstream of the washing device, the dryer comprising at least one inlet for the hot air and an outlet for a third exhaust air stream; and a heat exchanger for heating an air stream to produce the hot air, wherein at least one of the first section of the drawing device and the second suction of the washing device are flow-connected to the heat exchanger.

11. The device according to claim 10, wherein the outlet of the dryer is flow-connected to the heat exchanger.

12. The device according to claim 10, wherein the outlet of the dryer is flow-connected to the drawing device for supplying the drawing air stream.

13. The device according to claim 10, wherein the first suction for discharging the first exhaust air stream from the drawing device is provided in an area of the perforated conveying device.

14. The device according to claim 10, wherein the device comprises a plurality of the at least one spinneret associated with a plurality of the drawing devices, wherein each of the first suction of the plurality of the drawing device being flow-connected to the heat exchanger.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In the following, the embodiment variants of the invention are illustrated on the basis of several figures.

[0040] FIG. 1 shows a schematic illustration of the process according to the invention and of the device according to a first embodiment variant, and

[0041] FIG. 2 shows a schematic illustration of the process according to the invention and of the device according to a second embodiment variant.

DETAILED DESCRIPTION OF THE INVENTION

[0042] In FIG. 1, a process 100 for the production of cellulosic spunbonded nonwoven 1 according to a first embodiment variant and, respectively, a device 200 for performing the process 100 are shown. In a first process step, a spinning mass 2 is produced from a cellulosic raw material and supplied to a spinneret 3 of the device 200. In this case, the cellulosic raw material for producing the spinning mass 2, which production is not shown in further detail in the figures, can be a conventional pulp made of wood or other plant-based starting materials. However, it is also conceivable that the cellulosic raw material consists at least partly of production waste from the production of spunbonded nonwoven or recycled textiles. In this case, the spinning mass 2 is a solution of cellulose in NMMO and water, with the cellulose content in the spinning mass ranging between 3% by weight and 17% by weight.

[0043] In a following step, the spinning mass 2 is then extruded through a plurality of nozzle holes in the spinneret 3 to form filaments 4. The extruded filaments 4 are then accelerated and drawn in the extrusion direction by being charged with a drawing air stream. For generating the drawing air stream, drawing air 5 is supplied to a drawing device 6 in the spinneret 3, with the drawing device 6 ensuring that the drawing air stream exits the spinneret 3 and the filaments 4 are accelerated after their extrusion.

[0044] In one embodiment variant, the drawing air stream can emerge between the nozzle holes of the spinneret 3. In a further embodiment variant, the drawing air stream may alternatively emerge around the nozzle holes. However, this is not illustrated in further detail in the figures. Such spinnerets 3 comprising drawing devices 6 for generating a drawing air stream are known from the prior art (U.S. Pat. Nos. 3,825,380 A, 4,380,570 A, WO 2019/068764 A1).

[0045] Moreover, the extruded and drawn filaments 4 are charged with a coagulation air stream 7, which is provided by a coagulation device 8. The coagulation air stream 7 usually comprises a coagulation liquid, for example, in the form of vapour, mist, etc. Due to the contact of the filaments 4 with the coagulation air stream 7 and the coagulation liquid contained therein, the filaments 4 are coagulated at least partly, which, in particular, reduces adhesions between the individual extruded filaments 4.

[0046] The drawn and at least partially coagulated filaments 4 are then deposited in a random orientation on the conveying device 9, forming the spunbonded nonwoven 1 there. After its formation, the spunbonded nonwoven 1 is subjected to washing 10 and hydroentanglement 11.

[0047] In a following step, the washed and hydroentangled spunbonded nonwoven 1 is then subjected to drying 12 in a dryer 13 in order to remove the remaining moisture and to obtain a finished spunbonded nonwoven 1. Finally, the process 200 is concluded by optionally winding 14 and/or packaging the finished spunbonded nonwoven 1.

[0048] During the drying 12 in the dryer 13, the spunbonded nonwoven 1 is charged with hot air 15. In doing so, the hot air 15 is formed by heating an air stream 16, in particular fresh air 16, by passing it through a plurality of heat exchangers 17. As shown in FIG. 1, the heat exchangers 17 are fed by the exhaust air stream 18 from the drawing, the exhaust air stream 19 from the washing 10, and the exhaust air stream 20 from the drying 12. In doing so, the residual heat in the exhaust air streams 18, 19, 20 in the heat exchangers 17 is transferred to the fresh air 16, which is thus heated.

[0049] Underneath the drawing, the device 100 therefore comprises a suction 21 for discharging the spent drawing air stream as an exhaust air stream 18. In this case, the suction 21 is advantageously arranged in the area of the perforated conveying device 9 on which the spunbonded nonwoven 1 is formed. The same applies to the washing 10, where a suction 22 is provided as an exhaust air stream 19 for discharging the air laden with moisture. In this case, the suction 20 and the suction 21 are each flow-connected to a heat exchanger 17. In a similar way, the outlet of the dryer 13 is flow-connected to the heat exchanger 17 for discharging the spent hot air laden with water vapour as an exhaust air stream 20.

[0050] In one embodiment variant, as shown in FIG. 1, the heat exchangers 17 can be designed as separate heat exchangers 17, and, thus, they can allow the air stream 16 or, respectively, the fresh air 16 to be gradually heated to produce the hot air 15. In a further embodiment variant, which is not illustrated in further detail in the figures, the heat exchanger 17 can alternatively be designed as a single unit, with all exhaust air streams 18, 19, 20 running through the single heat exchanger 17.

[0051] The exhaust air streams 18, 19, 20 from the drawing, the washing 10 and the drying 12 are then discharged after they have been passed through the heat exchangers 17. For example, in a further embodiment, which is not illustrated in further detail in the figures, the exhaust air streams 18, 19, 20 can thus be treated further for the recovery of water and/or solvent.

[0052] Due to the multi-stage heating of the fresh air 16 in the heat exchangers 17 by various exhaust air streams 18, 19, 20 accumulating in the course of the process 100 for the production of the cellulosic spunbonded nonwoven 1, a process with a holistic energy use can be created, which minimizes energy losses and, in particular, allows a reliable and fast drying 13 of the spunbonded nonwoven 1.

[0053] FIG. 2 shows a process 101 according to the invention for the production of cellulosic spunbonded nonwoven 1 according to a second embodiment variant and, respectively, a device 201 for this purpose. The process 101 differs from the process 100 illustrated in FIG. 1 in that the hot air enriched with water vapour is discharged from the drying 12 as an exhaust air stream 20 through the heat exchanger 17 and, after having passed through the heat exchanger 17, is supplied further to the drawing device 6 as drawing air 5, for which purpose the outlet of the dryer 13 for the exhaust air stream 20 is flow-connected to the drawing device 6. A particularly efficient energy use for the entire device 101 or, respectively, the entire process 201 can thus be achieved. With regard to further features, reference is made to the above explanations concerning FIG. 1.

Example

[0054] The invention is demonstrated below using an example. In the course of the process according to the invention, both the exhaust air stream from the drawing and the exhaust air stream from the washing were supplied to a heat exchanger in order to heat fresh air.

[0055] In doing so, the cellulose throughput was 200 kg/h with a spunbonded nonwoven width of 1 m, and the spunbonded nonwoven that was produced had a basis weight of 45 g/m2. In this case, the moisture content of the spunbonded nonwoven on entry into the dryer amounted to about 3 kg of water per kg of cellulose. After drying, the finished spunbonded nonwoven had a relative moisture content of below 10%.

[0056] In this case, it has been shown that, depending on the negative pressure in the deposit surface, the temperature and the relative moisture content of the exhaust air stream from the spunbonded nonwoven deposition vary, namely between about 40° C. and 70% at 80 mbar negative pressure in the spunbonded nonwoven deposit surface and about 60° C. and 30% at 140 mbar negative pressure in the spunbonded nonwoven deposit surface.

[0057] The temperature and the relative moisture content of the exhaust air stream from the washing, in turn, varied between 40° C. and 80% at 150 mbar negative pressure and 90° C. and 30% at 250 mbar negative pressure, depending on the negative pressure in the suction pipes of the washing.

[0058] Furthermore, it has been shown that the volume flows of the two exhaust air streams are many times greater than the volume flow of fresh air, which is supplied to the dryer. For example, the exhaust air stream from the spunbonded nonwoven deposition ranged between 15,000 Nm3 (standard cubic metres) and 30,000 Nm3 per hour, and the exhaust air stream from the washing ranged between 10,000 Nm3 and 20,000 Nm.sup.3 per hour, while only between 8,000 Nm3 and 16,000 Nm.sup.3 of fresh air was supplied to the dryer. Without the heat recovery according to the invention from the exhaust air streams, a lot of energy would be lost, on the one hand, and a lot of energy would be required for heating the fresh air, on the other hand, so as to heat it from, e.g., 15° C. to, e.g., 140° C.

[0059] As a result of the heat recovery according to the invention by supplying the exhaust air streams from the drawing and the washing, the energy costs for drying could be reduced by up to 70%, since the fresh air could be tempered to 70° C. already after it had been passed through the heat exchangers.

[0060] Furthermore, the exhaust air stream from drying was introduced as drawing air for drawing the filaments, wherein it had a temperature of between 80° C. and 160° C. with a moisture content of between 5 g/kg and 500 g/kg. By using the exhaust air stream from drying as drawing air, the properties of the spunbonded nonwoven could be positively influenced. For example, the fibre diameter could thus be reduced by up to 50%, while maintaining the same drawing air pressure and spinning mass throughput.

[0061] Compared to the prior art, in which the adjustment of the moisture content in the drawing air is effected, for example, via vapour injection and is very cost-intensive due to the large amounts of air that are required, the costs for humidifying and heating the drawing air could be reduced by up to 70%, using the already very humid exhaust air stream from drying.