NO314026B1 - Use and method of producing cylindrical cellulose film - Google Patents

Description

Method for the production of cylindrical cellulose foil and use of a device for carrying out the method.

The present invention relates to a method for the production of cylindrical cellulose foil by extruding a solution of cellulose in an aqueous tertiary amine oxide into a precipitant, a solution of cellulose in an aqueous tertiary amine oxide being extruded through a die with a mainly annular extrusion gap. so that the reading takes the form of a cylinder, which is then transported down into a precipitation bath where both its outside and inside are brought into contact with a precipitation agent so that the cellulose is precipitated and the cylinder foil is formed. The present invention also relates to the use of a device for carrying out the method.

From US patent no. 2,179,181 it is known that tertiary amine oxides are able to dissolve cellulose and that cellulose-containing shaped bodies, such as fibres, can be formed from such solutions by precipitation.

A method for producing such readings is known, for example, from EP-A 0 356 419. According to this publication, a suspension of cellulose is then prepared in an aqueous tertiary amine oxide. The amine oxide contains up to 40% by weight of water. The aqueous cellulose suspension is heated and, while reducing the pressure, water is removed until the cellulose dissolves.

From DE-A 28 44 163 it is known when producing cellulose fibers between the spinning nozzle and the precipitation bath to lay an air section or an air gap to achieve a nozzle delay (Diisenverzug). This nozzle delay is necessary because after contact of the formed spinning solution with the aqueous precipitation bath it becomes very difficult to get a "Reckung" of the threads. \

. in the precipitation bath, the fiber structure set in the air gap is fixed.

A method for producing cellulose threads is further known from DE-A-28 30 685, after which a solution of cellulose in a tertiary amine oxide in a hot state is formed into filaments, the filaments. is cooled with air and then transferred to a precipitation bath to precipitate the dissolved cellulose. The surface of the spun threads is further moistened with water to reduce their tendency to! to stick to adjacent threads.

A device for producing som-free cylindrical foils is also known from WO 93/13670. According to this known method, by being fed through an annular extrusion slit, the cellulose solution is formed into a cylinder which is pulled over a cylindrical mandrel and brought into a precipitation bath. So that the extruded cylinder foil does not adhere to the mandrel surface. its surface is covered with a film of water so that the inside of the foil coagulates and slides over the cylindrical mandrel. However, this has the disadvantage that water introduced to wet the mandrel surface. can rise ten! the extrusion gap and moisten the die from the piece so that it not only works for the desired coagulation, but also cools the extrusion die itself. This is undesirable for the reason that the cooled nozzle cools the solution to be extruded, and the viscosity of this increases so that a perfect foil extrusion with uniform thickness is no longer possible. In addition, this known device is complicated to rebuild if, for example, foils of different thicknesses are to be produced.

From EP-A 0 042 517, a method is known for producing a dialysis membrane of cellulose, which membrane is produced from flat foil or cylindrical foil or from hollow wire using corresponding nozzles.

From WO 95/35340, a blowing method is known for the production of oriented cellulose foils by spinning a cellulose solution in a precipitation bath. where the solution is extruded over a film blowing nozzle and an outer air gap into the precipitation bath. The degree of orientation can be increased in both longitudinal and transverse directions.

From DE-A 195 15 137 it is known that there is a method for producing cylinder-shaped foil, where the cellulose solution is first extruded into a cylinder which, on the way between the outlet of the annular nozzle and the precipitation medium, is stretched and, with the help of a gas overpressure inside the cylinder, expanded in a ratio in the range between 1:1 and 1:10. Through this stretching, the cylinder foil is stretched both transversely and along the extrusion direction.

A device of the type described at the outset, i.e. for the production of cylindrical cellulose foil By extruding a cellulose solution in a tertiary amine oxide into a precipitating agent located below the device, which device comprises an extrusion die with a mainly cylindrical extrusion gap, where to the inside of the ring which the extrusion gap forms is quickly a supply line for precipitant and a drain line for consumed precipitant. found in WO 95/07811. With this device, a spacer disc can be placed under the drain line to prevent possible collapse of the cylinder foil in the precipitation bath.

The devices according to the state of the art for the production of cylindrical foil have a complex structure. It is therefore an aim of the present invention to provide a method for the production of cylindrical foil which can make use of a device which is simple in its

structure.

The invention consists of a method as stated in patent claim 1 and an application of a device as stated in patent claim 8.

Preferred embodiments of method and application appear from the non-independent patent claims.

The method according to the invention for the production of cylindrical cellulose foil by extruding a solution of cellulose in a tertiary amine oxide into a precipitating agent, makes use of a device comprising an extrusion nozzle with a mainly annular extrusion gap, where to the inside of the ring that the extrusion gap forms is often a supply line for the precipitating agent and a drain line for used precipitating agent, and where the supply line for the precipitating agent ends lower than the drain line for the used precipitating agent.

It has been shown that with the method according to the invention, the liquid mirror in the interior of the cylinder can be set in a simple way and, above all, kept constant. Furthermore, with the precipitation method, it has proven to be an advantage that the precipitation agent flows in the opposite direction to the direction of extrusion, that is to say the direction of transport in the precipitation bath. Also in this respect, the present invention differs from the state of the art, where - as described below - fresh precipitating agent continuously comes into contact with the foil area, also where the cellulose is already largely present in a precipitated state. Most of the amine oxide-enriched precipitant, however, comes into contact with the foil area where the cellulose is still to a lesser extent precipitated.

A preferred design of the device that is used in the application according to the invention has a spacer placed below the extrusion gap, which spacer is preferably made so that it has an essentially circular surface.

The cross-sectional area of the spacer may be larger than the area formed by the ring of the extrusion gap. In this way, a stretching of the cylindrical extruded discharge across the direction of extrusion is possible.

However, the cross-sectional area of the spacer can also be smaller than the area formed by the ring of the extrusion gap.

The spacer is preferably designed in such a way that the size of the cross-sectional area can be changed. This is possible, for example, with a disc or a ring with displaceable bodies, analogous to a light mixer, which can slide in or out at the displaceable parts, so that the outer diameter changes.

Furthermore, a change in the size of the cross-sectional area can also be achieved by the spacer consisting of an elastic ring, for example of rubber, which can be expanded with air, water or the like. With the help of the medium inside the elastic ring, its diameter can be adjusted. A variant of this embodiment is that a whole ring is not used, but that the inside consists of a fixed part, for example of steel or plastic, and to this an elastic part is attached. An alternative embodiment consists of a split ring or disc, possibly consisting of segments whose fixing points are displaceable, so that the outer diameter can be changed through this (umbrella principle).

In the method according to the invention, the cylindrical discharge can be stretched in the direction of transport and/or across the direction of transport.

The stretching of the cylindrical solution across the transport direction can be carried out by means of hydrostatic pressure or with gas pressure or by means of a spacer.

The cylinder foil formed by precipitation of cellulose is dried after being passed through the precipitation bath, whereby the cylinder foil is preferably kept stretched to prevent shrinkage.

The method according to the invention is particularly suitable for processing readings of cellulose in aqueous N-Methylmorpholine-N-oxide (NMMO).

With the help of the attached drawing, a preferred embodiment of the method according to the invention, and the device used thereby, will be described in more detail.

Figure 1 schematically shows a cross-section of the lower part of an extrusion device which essentially shows an annular nozzle 1 with an annular extrusion slit 2, a supply line 3 for new • precipitant (water or amine oxide/water mixture) and a drain line 4 for used precipitant.

The cellulose solution is pressed from the annular space for the spinning mass through the extrusion gap 2, whereby the cellulose solution is extruded into a cylindrical shape in the air space between the precipitation bath surface 7 and the underside 12 of the ring die 1.

The cylindrical extruded solution 6 is drawn down into the precipitation bath 7 where it comes into contact with a precipitating agent on the outside, whereby the dissolved cellulose coagulates and the amine oxide is released into the precipitation bath. There is also a precipitant inside the cylinder 6. so that the cellulose also coagulates on the inside. Here too, amine oxide is released.

In the figure, level 8 of precipitating agent inside the cylinder 6 is at the same level as the precipitating bath 7. Through supply line 3, precipitating agent can be supplied to the interior of the cylinder and via drain line 4, precipitating agent can be removed. In this way, the level 8 of precipitant inside the cylinder 6 can be adjusted.

With the method according to the invention, the level 8 of precipitating agent inside the cylinder 6 can also be set higher or lower than the level 7 in the precipitating bath. The composition of precipitating agent inside the cylinder 6 can be different for each precipitating bath.

The cylinder foil 6 is pulled at an angle over a turning device 10 and thereby stretched in the transport direction, that is to say in the direction from the nozzle towards the precipitation bath.

The cylinder foil is pulled over a spacer 9. This spacer 9 has the shape of a circular disk which is firmly connected to the nozzle 1 through the rods 11. The spacer 9 has through holes 9a for circulation of medium. The supply line 3 is led through the spacer 9. Instead of a disc, a ring can also be used as a spacer.

With the spacer 9, the cylinder 6 is expanded, corresponding to a stretch across the transport direction. It is clear that this stretching across the transport direction increases with increasing size of the circular spacer.

When supplying new precipitating agent via supply line 3 and removing used, i.e., amine oxide-containing precipitation bath via drain line 4, which ends higher than supply line 3, the amine oxide concentration increases in the direction of level 8, i.e. it decreases in the direction of transport for the cylinder foil 6 .

At the end of supply line 3, directional control equipment (not shown) can possibly be placed to control the liquid flow from supply line 3 upwards in the direction of level 8.

A stretch across the transport direction can also be achieved with hydrostatic pressure instead of using spacers. To achieve this, the level 8 of precipitant inside the cylinder 8 is simply set at a level higher than the precipitation bath 7. The pressure of the parts of the precipitant inside the cylinder which are above the level 7 contributes to this stretching.

the drawing can also be done with gas pressure, whereby naturally a gas supply (not shown) must be provided at the nozzle 1, with which the cylinder foil 6 in the space between the underside of 12 of the nozzle and the precipitation bath 7 is inflated. With this, the gas can also be replaced, i.e. the work is done with a gas surplus. In this case, it is natural to place a gas outlet (not shown) at the nozzle.

Claims (12)

1. Process for the production of cylindrical cellulose foil, whereby a solution of cellulose in an aqueous solution of amine oxide is extruded through a nozzle with a mainly annular extrusion gap so that the entire solution takes the form of a cylinder, which solution is transported to a precipitation bath and thereby with both its inside and outside are brought into contact with a precipitating agent so that the cellulose is precipitated and the cylinder foil is formed, characterized in that the precipitant which is brought into contact with the inside of the cylindrical solution contains a dissolved tertiary amine oxide whose concentration decreases in the direction of transport of the cylindrical solution. 2. Method according to claim 1. characterized by all the cylindrical solution being stretched in the transport direction. 3. Method according to one of claims 1 or 2, characterized in that the cylindrical discharge is stretched across the direction of transport. 4. Procedure according to claim 3. characterized in that the cylindrical solution is stretched across the direction of transport by means of hydrostatic pressure or gas pressure. 5. Procedure according to claim 3, characterized in that the cylindrical solution is stretched across the direction of transport by means of a spacer (9). 6. Method according to one of claims 1 to 5, characterized in that the cylinder foil (6) which is formed by precipitation of cellulose after transport through the precipitation bath is dried, whereby the cylinder foil (6) is kept taut to prevent shrinkage. 7. Method according to one or more of claims 1 to 6, characterized in that N-Methylmorpholine-N-oxide is used as tertiary amine oxide. 8. Application of a device comprising an extrusion nozzle with a mainly annular extrusion slot as well as a supply line (3) for precipitant and a drain line (4) for spent precipitant provided on the inside of the ring formed by the extrusion slot, which supply line (3) ends lower than the drain line ( 4), for the production of cylindrical cellulose foil by extruding a solution of cellulose in an aqueous tertiary amine oxide into a precipitant below the device. 9. Application as stated in claim 8, in that a spacer (9) is arranged below the extrusion gap (2). 10. Application as stated in claim 9, in that the spacer (9) is so shaped that its outer edge is mainly circular. ,. 11. Application as stated in claim 9 or 10, the cross-sectional area of the spacer (9) being larger than the area defined by the ring of the extrusion gap (2). 12. Application as stated in one of claims 8 to 11, in that the spacer (9) is constructed in such a way that its cross-sectional surface can be changed.