Process for the production of a cellulosic fiber from a solution of cellulose in a tertiary amine-oxide and device for carrying out said process

The current invention relates to a process for the production of a cellulosic fiber from a solution of cellulose in a tertiary amine-oxide according to claim 1 and a device to carry out such a process according to claim 12.

In recent years, processes have been established which produce cellulose fibers in a mixture of an organic solvent and water. Cellulosic fibers produced from such a solution are called Lyocell fibers. The only profitable process to obtain Lyocell fibers up to now is the production from a tertiary amine oxide solvent, especially from N-methylmorpholine-N-oxide (NMMO). The process yields fibers which are characterized by high strength, a high wet module and improved loop strength, and is commonly known as "amine-oxide process".

From US 4,246,221 a solution containing cellulose dissolved in a tertiary amine N-oxide solvent containing a nonsolvent for cellulose such as water shaped by extrusion or another shaping process to form a shaped cellulose fiber, rod, plate, tubing or film is known. The extruded shaped article is stretched in air while still a solution to impart improved physical properties thereto and the cellulose is precipitated from the shaped solution to set the properties without additional drawing. The shaped article may be prepared by dissolving cellulose in the tertiary amine N-oxide solvent in the barrel of an extrusion apparatus, extruding the solution, orienting by stretching the resulting product in air while still a solution and then precipitating the cellulose from the shaped article before significant degradation of the cellulose. The cellulose and tertiary amine N-oxide may be ground to substantially the same particle size before charging the extruder barrel. The tertiary amine N-oxide is recovered and recycled to avoid environmental pollution problems. The resulting cellulose fibers or films can be used to make fabrics, wrappings or packaging materials or nonwoven products.

Lyocell fibers nowadays are produced using basically two different techniques. According to a first method a spinning funnel is used which has an outlet in the bottom from which the filaments are drawn off by a drawing force. EP 0 574 870 discloses embodiments of this technique. Side streams threatening the fibers to stick together can be avoided by guide plates. A second method implies the drawing force to the fibers by mechanical means out of a precipitation bath. The drawing-off device is arranged outside the precipitation bath container, such as e.g. shown in US 4,246,221 or WO 93/19230.

A method and a device for extruding continuous molded bodies is known from WO 02/12599 Al . An extrusion solution, especially an extrusion solution containing water, cellulose and a tertiary amine oxide, is extruded through an extrusion opening in order to obtain a continuous moulded body and then deviated by means of a deviating device. The extrusion openings are arranged in a row in such a way that the individual continuous moulded bodies exit the extrusion head in the form of a curtain in order to enhance the quality of the product. This curtain is then deviated by the deviating device.

The devices and processes known from the state of the art are restricted concerning the width of the air gap between the spinneret and the precipitation bath, the depth of the precipitation bath and the drawing-off angle of the extruded filaments. The latter is an essential factor to the yield and the quality of the fibers. It is defined by the angle between the fibers leaving the spinneret and a horizontal axis. The more openings in the spinneret, the larger the angle will become, the filaments thus tending to stick together or being torn off. On the other hand, a smaller number of openings reduces the yield of the device, thus increasing the production cost of the fibers.

According to the state of the art it is not possible to start the spinning process after maintenance or suspension of the device automatically without manual intervention.

It is therefore an object of the present invention to provide a process and a device for the production of a cellulosic fiber from a solution of cellulose which avoid the drawbacks of the devices and processes known from the state of the art.

Especially it is an object of the invention to allow a free choice of the parameters defining the width of the air gap, the depth of the precipitation bath and the drawing-off angle of the filaments from the spinneret.

It is yet another object of the invention to provide a device by means of which the spinning process can be started automatically after a shutdown.

These objects are obtained by a process for the production of a cellulosic fiber from a solution of cellulose according to claim 1 and by a device for carrying out said process according to claim 12.

The process for the production of a cellulosic fiber from a solution of cellulose in a tertiary amine-oxide via a jet-wet process according to the present invention comprises the steps of pressing the solution of cellulose through a spinneret, thereby obtaining filaments, conducting the filaments through an air gap into a container containing a precipitation bath, drawing the

filaments in the air gap, transporting the filaments out of the precipitation bath, further processing of the filaments, wherein drawing of the filaments is performed via a mechanically driven drawing-off device exerting a drawing force and at least part of the drawing force is transmitted onto the filaments by contacting the filaments with the drawing-off device at a location within the precipitation bath.

Further processing steps include all steps performed on the filaments including the transport of the filaments after passing the precipitation bath. Major steps of processing are cutting and washing of the filaments.

The device for carrying out a process according to the present invention comprises a spinneret for extruding the solution of cellulose to form cellulose filaments, a container for a precipitation bath located beneath the spinneret and located at a distance from the spinneret such that when the container is filled with the precipitation bath, an air gap between the surface of the precipitation liquid and the surface of the spinneret is formed, a mechanically driven drawing-off device for drawing the filaments in the air gap by means of a drawing force exerted by said drawing-off device wherein the drawing-off device having a contact point at which the filaments are contacted with the device and at which at least part of the drawing force is transmitted onto the filaments. The contact point is located within the container for the precipitation bath.

In contrast to prior art methods the inventive device and process are characterized by a mechanical drawing-off device which is arranged in the precipitation bath and applies the drawing force to the fiber there. Prior art documents show a drawing-off device arranged outside the bath thereby restricting the flexibility for the geometric design of the apparatus. The fiber leaves the bath smooth and drawn to its final length and is immediately ready for further processing without further drawing.

Further advantages and embodiments of the present invention are apparent from the dependent claims.

According to a preferred embodiment of the invention essentially the entire drawing force is transmitted onto the filaments at said location within the precipitation bath. Since the whole device exerting the drawing force on the filaments is located in the precipitation bath, it is advantageous to restrict drawing to the same area.

According to another preferred embodiment of the invention the tensile load in longitudinal direction the filaments are exposed to is less than 5,5 cN/tex. As known from WO 97/33020 it

is advantageous not to exert tension on the filaments after they have been drawn. The filaments thereby produced have less tendency of fibrillation.

According to another preferred embodiment of the invention said drawing-off device is a device selected from the group consisting of rolls, belts, and systems comprising both rolls and belts.

According to yet another preferred embodiment of the invention the rolls and belts are equipped with a filament-contacting surface designed to allow the transmission of at least part of the drawing force by way of adhesion between the filaments and the surface.

According to another preferred embodiment of the invention the design of the surface is selected from the group consisting of micro-structured, corrugated, permeable, ribbed and/or expandable design.

Yet another preferred embodiment of the invention shows the removal of the filaments from the drawing-off device by means of a step selected from the group consisting of flushing with water, shaking, chafing, brushing, sucking and blowing.

Furthermore it is advantageous that the filaments are deflected in the precipitation bath and transported out of the precipitation bath at a side wall of the precipitation bath container or via the surface of the precipitation bath. Alternatively, the filaments are transported out of the precipitation bath in a downward direction at the bottom of the precipitation bath container. In the case of the fibers leaving the bath container through the bottom or the side wall of the container, the drawing-off device is designed such as to essentially prevent leakage of the precipitation bath out of the precipitation bath container.

It is also advantageous that the filaments are drawn and transported out of the precipitation bath in the form of a curtain whereby the drawing-off angle is reduced considerably.

According to another preferred embodiment of the invention, the drawing-off device is a device selected from the group consisting of rolls, belts, and systems comprising both rolls and belts.

According to yet another preferred embodiment of the invention the filament-contacting surface of the rolls or belts, respectively, is designed such as to allow the transmission of at least part of the drawing force by way of adhesion between the filaments and the surface, said surface being of a design selected from the group consisting of micro-structured, corrugated, permeable, ribbed and/or expandable design.

According to another advantageous embodiment of the invention the drawing-off device comprises means for removing the filaments from the drawing-off device, a deflecting means for deflecting the filaments in the precipitation bath, means for transporting the filaments out of the precipitation bath via the surface of the precipitation bath.

Preferably the drawing-off device is located at the bottom of the precipitation bath container and comprises means for transporting the filaments out of the precipitation bath in a downward direction, comprising two rolls located at the bottom of the precipitation bath container or at a side wall of the precipitation bath container, said rolls defining a gap through which the filaments pass when being drawn-off, said gap being defined such as to essentially prevent leakage of the precipitation bath from the container.

Preferably the rolls at the bottom of the container of precipitation bath are arranged to be movable against each other in order to adjust the size of the gap between the rolls.

As already mentioned, the present invention provides a very high degree of flexibility in adapting the geometrical design of the precipitation bath, especially its depth. It is possible to have very low precipitation bath depths. Therefore, in one further aspect of the invention said precipitation bath has a depth, the minimum depth of the container being defined as approximately equal to the radius of the rolls.

Furthermore, the spinneret preferably is a rectangular spinneret for spinning the filaments in the form of a curtain, wherein the drawing-off device is designed such as to draw and transport the filaments out of the precipitation bath container in the form of a curtain.

Preferred embodiments of the present invention are depicted in the drawings and are explained in more detail in the following description.

In the drawings:

Fig. IA is a schematic side view of a preferred embodiment of the device according to the present invention,

Fig. IB is a schematic side view of a second embodiment of the device according to the present invention,

Fig. 2 is a schematic view of a curtain of filaments,

Fig. 3A-B are schematic views of a third and a fourth embodiment of the device according to the present invention,

Fig. 3C is a schematic view of a fifth embodiment of the device according to the present invention, and

Fig. 4 is a schematic view of a sixth embodiment of the device according to the present invention.

Same reference numerals refer to same or similar elements in the drawings.

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown.

The process for the production of a cellulosic fiber from a solution of cellulose in a tertiary amine-oxide via a jet- wet process generally comprises several steps which have significant impact on the structure and texture of the filaments. A first embodiment of a device 1 suitable for the carrying out of said process is shown in Fig. IA. First, the solution of cellulose is pressed through a spinneret (not shown), which can include one or more openings arranged in different configurations like one or more circles etc. Alternatively, the spinneret is a rectangular spinneret for spinning the filaments in the form of a curtain.

The filaments 2 obtained thereby are conducted through an air gap 3 between the spinneret and a container 4 containing a precipitation bath. While passing the air gap 3, the filaments 2 are drawn to impart improved physical properties like advanced wet moduli thereto.

According to the prior art, the drawing-off angle of the filaments 2 leaving the spinneret is limited for example by the width of the air gap 3. Since the drawing-off angle defined by the angle between the filaments 2 leaving the spinneret and a horizontal axis is an essential factor for the yield and the quality of the fibers it is desireable to keep it as small as possible. The more openings in the spinneret, the larger the angle will become, the filaments thus tending to stick together or being torn off when the air gap 3 is too narrow. On the other hand, a smaller number of openings reduces the yield of the device, thus increasing the production costs of the fibers. The invention thus allows to use spinnerets with more outlet openings since the air gap 3 or the depth of the precipitation bath can be wider or deeper respectively compared to the devices of the prior art.

The drawing of the filaments 2 is performed via a mechanically driven drawing-off device 5 exerting a drawing force on the filaments 2. This means that the device 5 exerting the drawing

force is driven mechanically, in contrast to funnel -spinning where the drawing force is exerted by the co-current stream of precipitation liquid. Afterwards the filaments 2 are transported out of the precipitation bath container 4 and further processed.

According to the invention at least part of the drawing force is transmitted onto the filaments 2 by contacting the filaments 2 with the drawing-off device 5 at a location within the container 4 containing the precipitation bath. More specific, a contact point C of the filaments 2 with the drawing-off device 5 is located within the precipitation bath or rather under the surface of the precipitation bath solution. Preferably the entire drawing force can be exerted onto the filaments 2 at said contact point C within the precipitation bath.

The tensile load in longitudinal direction the filaments 2 are exposed to is in preferably less than 5,5 cN/tex during further processing, i.e. after having been drawn. Thus the filaments have less tendency for fibrillation during further processing.

Further processing steps include all steps performed on the filaments 2 including the transport of the filaments 2 after passing the first contact point C. Major steps of processing are cutting and washing of the filaments 2.

The drawing-off device 5 is a device selected from the group consisting of rolls 6 and belts 7 as well as systems comprising both rolls 6 and belts 7. The embodiment according Fig. IA comprises two rolls 6 and a belt 7 connecting the rolls 6, while a second embodiment according to Fig. IB comprises seven rolls 6 arranged in two groups by two belts 7. By means of this the stretching force exerted on the filaments 2 can be controlled. This is especially enabled by movably mounted rolls 6 as indicated in Fig. I B. In the embodiment of Fig. IB the contact point C is located on a roll 6 located near the bottom of the precipitation bath container 4, but alternatively the contact point C can be located at the topmost pair of rolls 6". This enables an exertion of the drawing force in the upper part of the precipitation bath container 4 and a subsequent passage of the filaments 2 through the precipitation bath without further stretching.

In case the spinneret is designed in a rectangular form the drawing-off device 5 is designed such as to draw and transport the filaments 2 out of the precipitation bath container 4 in the form of a curtain. It is also possible to use a plurality of rectangular spinnerets producing a plurality of parallel curtains of filaments 2. The curtains are guided through the precipitation bath similar to a single curtain of filaments 2.

Rolls 6 and/or belts 7 are equipped with a surface 8 contacting the filaments 2. The surface 8 of the rolls 6 and/or belts 7 is designed to allow the transmission of a part of the drawing force

or the entire drawing-force by way of adhesion between the filaments 2 and the surface 8, the design of the surface 8 being micro-structured, corrugated, permeable, ribbed and/or expandable. Fig. 2 shows a very schematic view from above on a group of filaments 2 deviated by a roll 6 and transported by a belt 7. The filaments 2 stick to the belt 7 until they are removed. Especially a ribbed surface can be designed in different ways; on the one hand, tops of the ribbed structure of one roll surface can meet corresponding depressions of the opposite roll surface, on the other hand, the tops of the corresponding surface structures can come in contact during rotation of the rolls 6.

To remove the filaments 2 from the surface 8 of the rolls 6 and/or belts 7 of the drawing-off device 5 means for removal are necessary. Said means can for example flush the filaments 2 off the surface 8 by water, the beam of water assuming various shapes. Other possibilities can be of mechanical nature like shaking, reloading, sucking or blowing or removal by auxiliary means like chafers or brushes.

Further embodiments of devices 1 for the processing of the filaments 2 in the container 4 of the precipitation bath transporting the filaments 2 out of the precipitation bath in a downward direction at the bottom of the precipitation bath container 4 are shown in Figs. 3 A through 3C, where the drawing-off device 5 is arranged at the bottom of the container 4 and is designed such as to essentially prevent leakage of the precipitation bath out of the precipitation bath container 4.

When the drawing-off device 5 is located at the bottom of the precipitation bath container 4, it comprises means for transporting the filaments out of the precipitation bath in a downward direction. Those means are represented by two rolls 12 located at the bottom of the precipitation bath container 4 or at a side wall of the precipitation bath container 4, said rolls 12 defining a gap 11 between them through which the filaments 2 pass when being drawn-off. Said gap 1 1 is adequately dimensioned to essentially prevent leakage of the precipitation bath from the container 4. Moreover, said rolls 12 are arranged movably against each other in order to adjust the size of the gap 1 1 between the rolls 12 according to the thickness of the filaments 2 or curtain of filaments 2.

The embodiments shown in Figs. 3 A through 3C illustrate various possibilities of design regarding the number of rolls 6 and belts 7 ranging from the simple embodiment according to Fig. 3 A containing only the two rolls 12, over an embodiment according to Fig. 3B containing two rolls 6 for deflection connected to the two rolls 12 by two belts 7, to an arrangement according to Fig. 3C showing an elongated design to allow further processing of the filaments 2 leaving the container 4, for example by applying a treatment fluid.

Alternatively, the filaments 2 deflected in the precipitation bath by means of deflection 10 can be transported out of the precipitation bath container 4 through a side wall 9 of the precipitation bath container 4 according to Fig. 4 or via the surface of the precipitation bath. The latter alternative is shown in Figs. IA and IB, the means of deflection 10 there being represented by the rolls 6, especially by a bottommost roll 6'. Said bottommost roll 6' is preferably the roll by which the contact point C of the filaments 2 with the drawing-off device 5 is marked.

When deflected through the side wall 9 of the precipitation bath container 4 the rolls 12 are arranged on the side wall 9 too. For the rest the arrangement according to Figs. 3A through 3C can be applied accordingly.

The minimum depth of the precipitation bath container 4 of all embodiments described above is only limited by a radius R of the rolls 6. The minimum depth of the container 4 is approximately equal to the radius R of the rolls 6 at which the contact point C is located. A typical value for the radius R and the respective minimum depth of the container 4 may be approximately 6 cm. The device 1 can be significantly reduced in size by this, requiring less space.

The invention is not restricted to the embodiments described above.