EP0658221B1 - Process and device for producing cellulose fibres - Google Patents

Abstract

To prepare cellulose fibres, a solution of cellulose in a tertiary amine-oxide is shaped in hot condition to give filaments, the filaments are cooled and then introduced into a precipitation bath in order to precipitate the dissolved cellulose, whereby the shaped solution is exposed to an essentially laminar gas stream (FIG. 2a) for cooling before introduction into the precipitation bath.

Description

The invention relates to a process for producing cellulosic fibers by forming a solution of cellulose in a tertiary amine oxide in the warm state into filaments, cooling the filaments and then introducing them into a precipitation bath in order to precipitate the dissolved cellulose, and a device for carrying out the process .

From US Pat. No. 2,179,181 it is known that tertiary amine oxides can dissolve cellulose and that cellulosic fibers can be obtained from these solutions by precipitation. A method for producing such solutions is known for example from EP-A - 0 356 419. According to this publication, a suspension of cellulose in an aqueous tertiary amine oxide is first prepared. The amine oxide contains up to 40% by mass of water. The aqueous cellulose suspension is heated and water is drawn off under reduced pressure until the cellulose dissolves. The process is carried out in a specially developed, evacuable stirring device.

From DE-A-28 44 163 it is known to place an air gap or an air gap between the spinneret and the precipitation bath for the production of cellulose fibers in order to achieve a nozzle warpage. This warping of the nozzles is necessary because after the formed spinning solution comes into contact with the aqueous precipitation bath, it is very difficult to stretch the threads. The fiber structure set in the air gap is fixed in the precipitation bath.

A method of the type mentioned at the outset is known from DE-A-28 30 685, according to which a solution of cellulose in a tertiary amine oxide is formed into filaments in a warm state, the filaments are cooled with air and then introduced into a precipitation bath in order to dissolve them To cut down cellulose. The surface of the spun threads is further wetted with water to reduce their tendency to stick to adjacent threads.

It has been shown that all prior art processes are unsatisfactory in terms of filament formation and the textile properties of the fibers. Due to the short spinning gap between the spinneret and the precipitation bath, which is in the range of a few centimeters, and the associated, only short time in which the properties of the fiber can be adjusted, it is difficult for all filaments of the filament association and for those obtained after precipitation Fibers, for example to achieve an even titer, uniform strength and elongation.

This is where the invention comes in, which is therefore the task of improving the above-mentioned method in such a way that a dense thread structure can be spun using a spinneret with a high hole density, in which the textile properties of the spun threads can be better adjusted.

This object is achieved in such a way that in a process for the production of cellulosic fibers in which a solution of cellulose in a tertiary amine oxide is formed into filaments in the warm state, the filaments are cooled and then introduced into a precipitation bath in order to precipitate the dissolved cellulose , the shaped solution is exposed to a substantially laminar gas flow for cooling prior to introduction into the coagulation bath.

The invention is based on the knowledge that the textile properties of the fibers can be influenced by blowing with an inert gas, preferably air. The cooling process of the filament emerging from the spinneret affects not only the thread quality but also the stretching and elongation of the filaments. It has been shown according to the invention that fibers with uniform properties can be produced if the freshly extruded filaments are blown with a cooling gas stream which has as little turbulence as possible, that is to say is largely laminar. This leads to a decisive improvement in the spinning process.

A preferred variant of the method according to the invention is that the laminar gas flow is directed essentially perpendicular to the filaments.

It has proven to be advantageous to pass the warm, cellulosic solution through a spinneret with a plurality of spinning holes which are arranged in a ring, whereby an annular filament bandage is formed, the laminar gas flow being provided in the center of the ring formed by the spinning holes and is directed radially outwards.

The invention also relates to an apparatus for carrying out the method according to the invention, which comprises a supply for cooling gas and a spinneret with spinning holes, which are arranged essentially in a ring to form an annular filament array, and is characterized in that the supply for cooling gas in the center of the the arrangement of the spinning holes formed ring is provided and the feed is designed such that an essentially laminar gas flow hits the filaments and the filaments are cooled with a laminar gas flow.

An expedient embodiment of the device according to the invention is that the supply for cooling gas has a supply nozzle and an impact plate for deflecting the gas flow, the impact plate being designed so that the gas flow remains as laminar as possible during the deflection.

The invention further relates to the use of the device according to the invention for producing cellulosic fibers from a solution of cellulose in a tertiary amine oxide.

The process according to the invention is explained in more detail by way of example with reference to the drawing, in which FIG. 1 shows schematically the implementation of a dry / wet spinning process for producing cellulosic fibers according to the prior art, and FIG. 2a shows a preferred embodiment of the process according to the invention Show spinning device. FIG. 2b shows a section of FIG. 2a on an enlarged scale. 3 shows a device for comparison which does not have the features according to the invention.

In Figure 1, 1 denotes a heatable (heating not shown) spinneret, which via the feed line 2 with spinning mass 3, i.e. warm cellulose solution at a temperature of about 100 ° C, is charged. The pump 4 serves to meter the spinning mass and to set the pressure required for the extrusion. The thread structure extruded from the spinneret 1 via the spinning holes is designated by the reference number 5.

The thread assembly 5 reaches the precipitation bath 6 via an air gap, which is defined by the distance of the spinneret 1 from the surface of the precipitation bath 6, is collected and drawn off via a deflection roller 7. The extruded thread bandage 5 is cooled with air, which is shown schematically in the figure with an arrow. A delay is achieved by pulling the thread assembly 5 over the roller 7 at a higher speed than it leaves the spinneret 1.

Figure 2a shows in section an annular, heatable (heating not shown) spinneret 1 'and a blowing device consisting of a central, tubular feed 8 for cooling gas and a baffle plate 9 for deflecting the gas flow from the vertical to a substantially horizontal direction. The ring-shaped spinneret 1 'is fed at a point not shown in the drawing with spinning mass 3' which is spun into a dense, ring-shaped thread structure 5 'which is blown from the inside with cooling gas. The direction of blowing is indicated in the figure by means of a dashed arrow. The cooling air thus emerges from a circular slot nozzle, which is formed by the baffle plate 9 and the counterpart 10.

The gas flow strikes the plate-shaped baffle plate 9, is deflected horizontally, emerges as a laminar gas flow and hits the ring-shaped thread structure 5 'on its inside.

• α (Prallplatte): ≤ 12°, bevorzugt: 3 - 8°;
• β (oberes Leitblech): ≤ 10°, bevorzugt: 4 - 8°;
• δ (äußerer Wulst): ≤ 30°, bevorzugt: 15 - 25°;
• σ (α + β): ≤ 22°.

Ein abrupter Übergang zwischen der Zuführung 8 und dem Prallteller 9 führt zu einer Komprimierung des Luftstrahls mit Ausbildung einer hohen Turbulenz. Eine derartige Vorrichtung, die nicht erfindungsgemäß ist, ist in Fig. 3 dargestellt.The embodiment of the device according to the invention shown in FIG. 2a has a baffle plate for producing a laminar cooling gas flow, which deflects the vertical cooling gas flow into an essentially horizontal gas flow without an abrupt transition. FIG. 2b shows an enlarged view of that part of FIG. 2a that is provided for maintaining the laminar flow. The angles shown in FIG. 2b preferably have the following values:

• α (baffle plate): ≤ 12 °, preferably: 3 - 8 °;
• β (upper baffle): ≤ 10 °, preferably: 4 - 8 °;
• δ (outer bead): ≤ 30 °, preferably: 15-25 °;
• σ (α + β): ≤ 22 °.

An abrupt transition between the feed 8 and the baffle plate 9 leads to compression of the air jet with the formation of high turbulence. Such a device, which is not according to the invention, is shown in FIG. 3.

The blowing device shown in FIG. 2b can either form a structural unit together with the spinneret 1 'or represent a separate component on which the ring-shaped spinneret 1' rests. An insulation (not shown) is expediently provided between the blowing device and the spinneret in order to prevent heat transfer from the spinning mass to the cooling air.

It is also advantageous that the circular outlet slot opens at a total opening angle of 22 22 ° after the gas flow has been deflected. The steadily increasing cross-section minimizes the flow resistance for the cooling gas. The small total opening angle prevents the cooling gas flow from coming off and enables the filaments to flow without turbulence.

It has further been shown that the gas stream, after passing through the thread structure, returns to the thread structure, partly warmed due to eddy formation, which leads to inadequate and irregular cooling. The result is different warping properties of the filament assembly, which can lead to a filament bundle which is unevenly loaded by the warping force and in the foam to capillary cracks and to spinning disorders and sticking. In order to prevent this and to further optimize the spinning process, a preferred embodiment of the device according to the invention has an annular bead 11, which deflects the cooling gas stream that has passed through the thread structure slightly downward from the spinneret plane.

The invention is described in more detail with the following exemplary embodiments.

Example and comparative example

A cellulose solution prepared in accordance with the process described in EP-A-0 356 419 was filtered and spun in hot condition in accordance with the process shown in FIG. 1, the spinning device being that shown in FIG. 2a and in the comparative example that shown in section in section Device was used. Both devices had the same inner diameter of the tubular feed 8 for cooling gas (44 mm) and the same diameter of the baffle plate 9 (104 mm). In the example (device according to the invention), the angles α and β were each 5 °; the total opening angle σ was thus 10 °. The angle δ was 5 °.

The table shows the mass of cellulose solution spun per hour for the example and for the comparative example (kg / h), its composition (% by mass), its temperature (° C.) during spinning, the hole density (number of holes / mm) the spinneret, the diameter of the spinning holes (µ), the nozzle warpage, the supply of cooling air (m³ / h), its temperature (° C), the temperature (° C) the internal cooling air discharged, the fiber distortion, the NMMO content of the precipitation bath (mass% NMMO) and the final titer of the fibers produced (dtex). TABLE example Comparative example Cellulose solution (kg / h) 27.6 27.6 Cellulose content (% mass) 15 15 Temp. D cellulose solution. (° C) 117 117 Hole density (hole / mm) 1.59 1.59 Hole diameter (µm) 100 100 Nozzle warpage 14.5 12.4 Cooling air (m³ / h) 34.8 34.8 Temp. D. added Cooling air 21 21 Temp. D. dep. Cooling air 36 36 Precipitation bath (% NMMO) 20th 20th Temp. Precipitation bath 20th 20th Minimum thread titer (dtex) 1.18 1.38 It can thus be seen that the achievable thread fineness (= minimum thread titer in dtex) is shaped very decisively by the cooling gas flow through the blowing device, which is of favorable flow design. A nozzle draft ratio of 14.5: 1 could only be achieved with the blowing device according to the invention, the thread count being 1.18 dtex. In the comparative example, the achievable thread count was about 20% less favorable.

Claims (6)

1. Process for the preparation of cellulose fibres in which a solution of cellulose in a tertiary amine-oxide is moulded in a heated condition to give filaments, the filaments are cooled and are then introduced into a precipitation bath in order to precipitate the dissolved cellulose, characterised in that the moulded solution is cooled by exposure to an essentially laminar gas stream before it is introduced into the precipitation bath.
2. Process in accordance with Claim 1, characterised in that the laminar gas stream is directed substantially at right angles to the filaments.
3. Process in accordance with Claim 1 or 2 for the preparation of cellulose fibres, wherein the hot cellulose solution is led through a spinneret (1') having a multiplicity of spinning orifices which are arranged in an annular fashion, whereby an annular filament curtain (5') is formed, characterised in that the laminar gas stream is provided in the centre of the ring formed by the spinning orifices and is directed radially outwards.
4. Device for carrying out the process according to one of Claims 1 to 3, wherein the device includes an inlet for cooling gas and a spinneret (1') with spinning orifices which are arranged essentially in annular fashion to form an annular filament bundle (5'), characterised in that the inlet for cooling gas is provided in the centre of the ring formed by the arrangement of spinning orifices and the inlet is designed in such a way that an essentially laminar gas stream strikes the filaments and the filaments are cooled by a laminar gas stream.
5. Device in accordance with Claim 4, characterised in that the inlet for cooling gas has a pipe-shaped inlet (8) and a baffle plate (9) for deflecting the gas stream, whereby the baffle plate (9) is so arranged that the gas stream remains as laminar as possible during deflection.
6. Use of a device in accordance with one of Claims 4 or 5 for the preparation of cellulose fibres from a solution of cellulose in a tertiary amine-oxide.

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