HRP950069A2 - Process and device for producing cellulose films - Google Patents

Description

This invention relates to a device and process for the production of cellulose films by extruding a hot solution of cellulose in tertiary amine oxide through an air gap into a coagulation bath. This invention particularly relates to a device and a process for the production of cellulose intestinal foils. In the spirit of the subsequent description and patent claims, the designation "foil" should be understood as including other flat shaped bodies such as films.

It is known from US-PS 2,179,181 that tertiary amine oxides can dissolve cellulose and that cellulose bodies can be obtained as fibers from these solutions by precipitation. One procedure for the production of solutions of this type is known, for example, from EP-A-0 356 419. According to that published work, a suspension of cellulose in aqueous tertiary amine oxide is first prepared. Aminoxide contains up to 40% water by mass. The water suspension of the cellulose is heated and under reduced pressure the water is extracted for a long time, while the cellulose spins into the solution.

From DE-A - 28 44 163 it is known, for the production of cellulose fibers, to leave an air gap or an air gap between the spinning nozzle and the settling bath, in order to achieve nozzle lag. This lagging of the nozzle is necessary, since after the contact of the formed spinning solution with the aqueous precipitation bath, it is very difficult to tighten the threads. In the deposition bath, the fiber structure arranged in the air gap is fixed.

One process for the production of cellulose threads is further known from DE-A - 28 30 685, according to which a solution of cellulose in a tertiary amine oxide in a warm state is transformed into threads, the threads are cooled with air and finally introduced into a precipitation bath, in order to precipitate dissolved cellulose. The surface of the twisted strands is further soaked with water to prevent adjacent strands from sticking together.

The device and process of the type mentioned in the introduction for the production of seamless intestinal foils are known from WO 93/13670. According to this known process, the cellulose solution is formed through an extrusion nozzle with an annular extrusion gap into a hose, which is pulled over a cylindrical mandrel and introduced into the deposition bath. To prevent the extruded hose from sticking to the surface of the mandrel, its surface is coated with a water film, so that the inner side of the hose coagulates and slides over the cylindrical mandrel. However, this has one drawback, that the water supplied to wet the surface of the mandrel can rise to the extrusion gap and wet the nozzle lips, which not only causes unwanted coagulation during the extrusion process itself, but also cools the extrusion nozzle. This is undesirable because of this, because the cooled nozzle cools the solution being extruded, the viscosity of which decreases so much that flawless extrusion into a film of uniform thickness is no longer possible. Added to this is the fact that the previously known device can only be built at high costs, when, for example, foils of different thicknesses are to be produced.

A further disadvantage of the device described in WO 93/13670 is that it does not provide a high power output. This is because the cooling of the extrudate is not effective enough, since the heat of the heated extruded film cannot be dissipated quickly enough.

Cellulose solutions for extruding, among other things, due to their extremely high viscosity, must be heated to temperatures above 110°C, in order to be processed at all. After exiting the extrudate from the nozzle, the extruded solution must be cooled to a certain extent and solidified, so that it can be stretched before being introduced into the deposition bath, i.e. before coagulation. If the cooling is not effective, then the time the extruded solution remains in the air gap must be sufficiently long, which can only be achieved by increasing the extraction speed. On the other hand, if it is extruded at a lower temperature, then there are difficulties in mass distribution in the extrusion device.

The task of this invention is to provide a device and a process for the production of cellulose films by extruding a hot solution of cellulose in tertiary amine oxide, which does not show the above-mentioned disadvantages, and especially has a high production efficiency.

The device according to the invention of the type mentioned in the introduction for the production of cellulose films includes an extrusion nozzle with an extrusion gap and is characterized by the fact that a cooling gas inlet is provided for cooling the extruded film directly below the extrusion gap. Cooled air with a temperature of, for example, -10°C to +5°C is suitable as a cooling gas. But air at room temperature can also be used to cool the hot extrudate. It is completely clear that by cooling according to the invention with gas via the temperature parameter and the obtained quantity, the cooling effect can be adapted to the relevant process conditions in the simplest way, which significantly increases productivity. The purposeful design of the device according to the invention consists in the fact that on both sides of the extrusion gap, cooling air supply is provided.

The primary construction of the device according to the invention serves for the production of cellulose intestinal films and is characterized by the fact that the extrusion gap of the extruding nozzle is made mainly ring-shaped and that the supply of cooling air is provided outside the ring created by the extrusion gap. This construction of the device according to the invention is very suitable for the production of intestinal foils with a relatively small diameter of, for example, less than 70 mm.

The second primary construction of the device according to the invention with the annular shape of the extrusion gap serves for the production of cellulose hose films of large diameter and is characterized by the fact that the inlet for the cooling gas is provided inside the ring created by the extrusion gap. In this case, a drain for the used cooling gas must also be provided inside the extrusion gap, since the used cooling gas cannot escape through the closed hose. The supply for the cooling gas is best done in such a way that the cooling gas is directed to the exit edges of the extrusion gap.

For particularly improved cooling, this design of the device according to the invention has a further supply of cooling gas, which is provided outside the ring created by the extrusion gap. The device proved to be particularly reliable, which additionally has an inlet for the cellulose deposition agent in the center of the ring created by the extrusion gap and a drain for the liquid from the deposition bath.

Furthermore, it proved to be expedient when the device according to the invention has at least one spacer plate under the drain for the liquid from the sedimentation bath. This feature can effectively prevent the extruded film from collapsing into the deposition bath.

The invention further relates to a process for the production of cellulose films, according to which a solution of cellulose in a tertiary amide is extruded in a hot state through an extrusion nozzle with an extrusion gap and the hot, extruded solution is fed into a precipitation bath, in order to precipitate the dissolved cellulose, which is characterized by the fact that the hot, extruded solution is cooled before being introduced into the deposition bath, whereby the hot solution is exposed to a gas stream immediately after extrusion. It is particularly reliable when the gas flow is mostly at right angles to the direction of extrusion.

Improved cooling is provided when the hot extruded solution is exposed to two gas streams, and this occurs best in such a way that the hot, extruded solution meets on its opposite sides. The process according to the invention can be applied to produce cellulosic hose films of relatively small diameter (e.g. less than 70 mm), when the hot cellulose solution is extruded through an extrusion nozzle with a comb-shaped extrusion gap, whereby the hot, extruded hose-shaped solution is exposed to a gas stream on its outside. For the production of intestinal films with a larger diameter, it is best when the extruded solution is cooled from the inside. Also, with this form of the process according to the invention, a particularly improved cooling is achieved, when the hot, extruded, tubular solution is exposed to the gas flow on its inner side, as well as on its outer side.

It has been shown to be expedient to bring the hot, extruded solution of the intestinal form into contact with the cellulose precipitating agent on its inner side after cooling and before being led into the deposition bath.

The device according to the invention and the process according to the invention are particularly well suited for the processing of aqueous solutions of cellulose in N-methylmorpholine-N-oxide (NMMO).

The primary forms of the invention will be explained in more detail with the help of the attached drawings, where Figure 1 schematically shows a device for the production of cellulosic films, and Figure 2 shows a device for the production of cellulose intestinal films. Figure 1 shows a longitudinal section of the extrusion device, which mainly consists of an extrusion nozzle 1a and two inlets 2a and 2b for cooling gas, with which the extruded solution 3a in the form of a foil is cooled on both sides. The introduction of cooling air into inlets 2a and 2b is indicated by downward sloping arrows. The cooled extrudate is drawn across the air gap, which is defined by the distance from the bottom of the nozzle to the surface of the deposition bath. In the precipitation bath, the cellulose coagulates and the tertiary amine oxide is transferred to the precipitation bath. The surface of the sedimentation bath is indicated with a dashed line, and 4a and 4b indicate the two leading slats. In the deposition bath, the foil is rotated over a roller (not shown) and pulled out of the deposition bath.

As can be seen in Figure 1, the presented extrusion nozzle 1a consists of several parts, which can be connected to each other with screws or slots. The construction of this nozzle is in accordance with the construction of any nozzle used to extrude melts of polymeric, high-viscosity substances in the usual way. For example, it is advantageous to provide devices in the nozzle for uniform distribution of the extruded mass (not shown).

The NMMD-cellulose solution is supplied from above above the extrusion nozzle la under pressure (indicated by the vertical arrow) and is pushed through the filter plate, which is shown in the figure as a black drawn line. This filter plate is supported by a support plate located below it. After that, the filtered extrudate enters the actual nozzle body, which is composed of parts 9a and 9b. The NMMO-cellulose solution is extruded through the extrusion gap 5. The extrusion gap 5 has a cross-sectional extension, which acts as a decompression zone. The extrusion nozzle 1a is heated indirectly by means of a heat transfer agent, which is guided through the channel 6 in the form of a slot. A thermal insulation (not shown) can be provided between the extrusion nozzle 1a and the cooling air inlets 2a and 2b, to prevent heat transfer from the nozzle 1a to the inlets 2a and 2b.

Adjusting the nozzle section can be carried out relatively simply by changing both parts 9a and 9b, whereby the dimensions of the remaining parts of the device do not have to be changed, which represents a decisive advantage of the device according to the invention.

Figure 1 shows a device where the extrudate is blown with cooling gas on two sides, the blowing direction being mostly perpendicular to the extrusion direction.

Figure 2 shows a section of the device according to the invention for the production of intestinal film. The device mainly consists of an annular extrusion nozzle Ib, which consists of several parts, which can be connected to each other with screws or slots.

The supply of the cellulose solution is carried out eccentrically from above, as shown by the vertical arrow in Figure 2. The cellulose solution for extruding enters an annular space for distribution 1, which is heated from the outside. From the annular space for distribution 7, the solution is pushed through the annular filter plate, which is shown in the picture as a drawn black line, and is carried by the support plate located below it. Finally, the filtered solution enters the split body of the nozzle, which is formed by two annular halves 8a and 8b. Also, in the construction of the device according to the invention, an expansion for decompression is provided in the extrusion gap 5. From the nozzle lips of the extrusion gap 5, the cellulose extruding solution is pushed into the air gap as a thick, hot extrudate.

Analogously to the one shown in Figure 1, here too, the adjustment of the nozzle section can be made relatively simply by changing both parts 8a and 8b. In the annular cavity created by both parts 8a and 8b, an annular body is inserted, which on its inner side has a flow in the form of thread lines through which the filtered solution is forced into the extrusion gap. In the center of the annular nozzle 1b, in the form of concentric pipes, inlets and outlets for cooling air, or used air and water, or liquid for the sedimentation bath are provided. With the corresponding number 11a, the supply of cooling air is marked, which comes to the current-favorably shaped deflector tray 13, there it rotates horizontally and the hose-like extruded solution 3b comes to the inner side of the hose. The guide sheet 14 ensures that a part of the cooling air comes directly to the outlet edge of the extrusion gap 5. The used cooling air exits further via outlet 11b.

To improve the cooling outside the ring created by the extrusion gap 5, one inlet 2c for cooling air is provided. The intake of this second cooling air - as in Figure 1 - is indicated by two slanting arrows pointing downwards.

A plate-shaped plate 15 is provided under the baffle plate 13, over which the hose 3b is moistened with a settling agent (water). The inlet for that precipitating agent is marked with the respective number 12a.

In order to be able to guide the foil relatively long cylindrically, immediately below the surface of the deposition bath, there are provided (indicated in dashed lines) baffle plates 16, the outer edge of which is rounded, so that the coagulated, but still sensitive foil is not damaged when sliding over it. Therefore, it is expedient to take care that the entrance surface, which represents the friction surface between the spacer plate 16 and the foil 3b, is kept small. The spacer plate 16 is immersed in the sedimentation bath and also serves to stabilize the strip. In addition, holes are provided through which the substance can be changed. Guiding the intestinal film into the sedimentation bath can be carried out via several spacer plates 16, before it is rotated via the guide rollers provided in the sedimentation bath (not shown).

In the device shown in Figure 2, a dip tube 17 is also provided, through which the used precipitating agent, which was supplied via 12a, can be sucked off again. The suction pipes 18, which are provided just above the surface of the sedimentation bath, are also poured into this immersion pipe. The function of this immersion tube is now as follows: As long as the suction tube 18 is not immersed in the surface of the sedimentation bath, it is not the liquid that is sucked out, but the air. When the level of the sedimentation bath rises and both suction pipes are immersed, the liquid of the sedimentation bath is sucked out immediately via the suction pipe 18 as well as via the immersion pipe 17, until both suction pipes exit the sedimentation bath again. This measure also prevents the accumulation of NMMO in the lower part of the intestine, which is standing in the settling bath.

In a purposeful way, the baffle trays 13 and plate-like plates 15 on the immersion tube 17 are placed so that they can slide, so that cooling and internal humidification can be regulated. The cooling according to the invention is improved in such a way that the films can be extruded at a higher mass throughput than is possible with the proposed extrusion devices for cellulose solutions according to the current state of the art.

Claims (17)

1. A device for the production of cellulose films by extruding a hot solution of cellulose in a tertiary amine oxide, which device includes an extrusion nozzle (la; Ib) with an extrusion gap (5), indicated by the fact that an inlet is provided directly below the extrusion gap (5) 2a; 2b; 2c; lla) for cooling gas for cooling the extruded film (3a; 3b). 2. Device according to claim 1, characterized by the fact that on both sides of the extrusion gap (5) an inlet (2a; 2b; 2c; 11a) for cooling gas is provided. 3. The device according to claim 1 for the production of cellulose intestinal film, characterized in that the extrusion gap (5) of the extrusion nozzle (1a; 1b) is mainly made annular and that the supply (2c) for the cooling gas outside the ring is provided. 4. The device according to claim 1 for the production of cellulose intestinal film, indicated by the fact that the extrusion gap (5) of the extrusion nozzle (la; Ib) is mainly made annular and that an inlet (lla) for cooling gas and a drain (11b) for used cooling gas in the center of the ring created by the extrusion gap. 5. Device according to claim 4, indicated by the fact that the supply (11a) is made for cooling gas of this type, that the cooling gas is directed to the exit edges of the extrusion gap (59. 6. Device according to claim 4 or 5, characterized in that a further supply (2c) is provided for the cooling gas, which is provided outside the ring created by the extrusion gap (5). 7. A device according to one of claims 4 to 6, characterized in that in the center of the ring created by the extrusion gap (5) there is provided an inlet (12a) for a precipitating agent for cellulose and an outlet (12b) for a precipitating liquid. 8. Device according to one of claims 4 to 7, characterized in that at least one spacer plate (16) is provided under the drain (18) for the settling liquid, to prevent the extruded film (3b) from overlapping in the settling cup. 9. Process for the production of cellulose film, indicated by the fact that the solution of cellulose in a tertiary amine oxide is extruded in a hot state through an extrusion nozzle (1a; 1b) with an extrusion gap and the hot, extruded solution is led into a precipitation bath, in order to precipitate the dissolved cellulose, that the hot, extruded solution is cooled before being introduced into the deposition bath, whereby the hot solution is exposed to a gas stream immediately after extrusion. 10. The method according to claim 9, characterized in that the extrusion direction is mainly perpendicular to the gas flow. 11. The method according to claims 9 or 10, characterized in that the hot, extruded solution is exposed to two gas streams. 12. The method according to claim 11, characterized in that the hot, shaped solution is exposed to two gas streams in such a way that they meet the hot, extruded solution on its opposite sides. 13. The method according to claim 9 for the production of cellulose intestinal foils, according to which the hot cellulose solution is extruded through an extrusion nozzle with an annular extrusion gap of an intestinal shape, indicated by the fact that the hot extruded solvent of an intestinal shape is exposed to the gas stream on its outer side. 14. The method according to claim 9 for the production of cellulose intestinal films, according to which the hot cellulose solution is extruded through an extrusion nozzle (1a; 1b) with an annular extrusion gap (5), indicated by the fact that the hot, extruded, intestinal-shaped solution is exposed to a gas stream at to its inner side. 15. The method according to claim 14, indicated by the fact that the hot, extruded solution in the form of a tube is exposed to the gas flow both on its inner side and also on its outer side. 16. The method according to claim 14 or 15, characterized in that the hot, extruded solution in the form of an intestine is brought into contact with a means for cellulose deposition on its inner side after cooling and before being introduced into the deposition bath. 17. Process: according to one or more claims 9 to 16, characterized in that N-methylmorpholine-N-oxide is used as the tertiary amine oxide.