Title of Invention

"PROCESS FOR THE PREPARATION OF CELLULOSIC SHAPED BODIES"

Abstract

A process is provided for producing cellulosic shaped objects, wherein a solution of cellulose in a tertiary amine-N-oxide and water if required is shaped in the warm state and the shaped solution, before being introduced into a coagulation bath, is passed through a gaseous medium for cooling, wherein the gaseous medium permeates the shaped solution from the gas inlet side to the gas outlet side, characterised in that the gaseous medium is removed by suction at an angle of 0° to 180° relative to the direction of motion of the shaped solution, the angle of 0° corresponding to the direction opposite the direction of motion of the shaped solution.

Full Text

Description: The present invention relates to a process for producing cellulosic shaped objects, in which a solution of cellulose in a tertiary amine-N-oxide, with water if required, is shaped in the warm state and in which the shaped solution is passed through a gaseous medium for cooling, before the solution is introduced to a coagulation bath, wherein the gaseous medium permeates the shaped solution from the gas inlet side to the gas outlet side. A process for cooling cellulosic shaped objects with a gaseous medium is described, for example, in WO 93/19230, wherein cooling takes place immediately after shaping. This process is intended to reduce the tackiness of the freshly extruded shaped objects, so that a spinneret with a higher density of holes can be used in producing cellulosic fibres. The preferred means of cooling the shaped solution is to use a gas stream. Cooling of the warm shaped solution already occurs when the shaped solution leaves the shaping element, such as a spinneret, in which the temperatures are typically above 70°C, and passes into the so-called air gap. The "air gap" means the area between the shaping element and the coagulation bath, in which the cellulose is precipitated. The temperature in the air gap is lower than in the spinneret but is significantly higher than the ambient temperature, as a result of thermal radiation from the spinneret and warming of the air, resulting from the enthalpy stream from the shaped objects. As a result of the continuous evaporation of water, which is usually used in the coagulation bath together with the tertiary amine-N-oxide, the air gap is warm and moist. The step suggested in WO 93/19230, i.e. to cool the shaped solution immediately after shaping, results a more rapid cooling, so that the tackiness of the shaped solution then decreases more rapidly. WO 96/17118 discloses a method for producing cellulosic shaped objects by shalping a solution of cellulose in a tertiary amine-N-oxide, with water if required, in the warm state and cooling the resulting shaped solution with air, before it is introduced into a coagulation bath. In accordance with this specification, conditioned air is used, with a water content of 0.1 g to 7 g water vapour per kg of dry air and a relative humidity of less than 85%. Advantageously the conditioned air is sucked through a bundle of freshly spun fibres or filaments by a combination of blowing and suction. The air stream should be at an angle of 0° to 120°, preferably 90°, relative to the direction of movement of the shaped solution. The process disclosed in WO 96/17118 is intended to lead to more effective cooling of the freshly extruded shaped objects with less conglutination, yielding filaments having a cross-sectional area with a low coefficient of variation. Although the cooling process described in WO 96/17118 is well suited in itself, there is still room for improvement. For example, when the blowing stream is transverse to the direction of movement of the shaped solution, the side opposite the blowing side is often not accessible adequately or rapidly enough by the conditioned air. This is particularly the case when the process is performed with relatively low rates of air blowing and/or, for example, when a large number of filaments are extruded. If, for example, cellulosic multifilaments are extruded, relatively pronounced conglutination can develop between the filaments on the side opposite the blowing side, in spite of intensive blowing, leading to impairment of process stability since permeation is not guaranteed, owing to of the density of the filaments. It is of course in principle possible to increase the intensity of the cooling by increasing the blowing volume and/or the length of the air gap. Such measures however also Imply the risk of greater turbulence of the shaped solution, e.g. the filaments, and are therefore often undesirable. The object of the present Invention is therefore to at least reduce the disadvantages of the prior-art processes. This object is achieved by a process for producing cellulosic shaped objects as described in the introductory paragraph, characterized in that the gaseous medium is removed by suction on the gas outlet side at an angle of 0° to 180° relative to the direction of motion of the shaped solution, wherein an angle of 0° means the direction opposite the direction of motion of the shaped solution. Preferably according to the invention, the angle of the permeating gaseous (cooling) medium relative to the blowing angle on to the shaped solution is altered by the suction. This change in direction results in better permeation of the side of the shaped solution that lies opposite to the blowing side. Removal by suction on the gas outlet side preferably occurs immediately after permeation of the shaped solution at an angle of 0°, i.e. opposite to the direction of motion of the shaped solution. As will be described in more detail below, the suction is performed vertically upward, for example through a perforated plate immediately following the spinneret. According to the present invention, it is particularly preferred if the gaseous medium on the gas inlet side has an angle of incidence relative to the direction of motion of the shaped solution of between about 45° and about 135°, with about 90° being even more preferred. If the angle of incidence is about 90° and the removal by suction on the gas outlet side occurs at an angle of 0° relative to the direction of motion of the shaped solution, removal by suction will then occur at an angle of about 90° to the blowing stream, which leads to excellent permeation of all areas of the shaped solution. The permeation of the shaped solution by the gaseous medium can of course in principle be effected by convection, such as air movement, or by the effect of the suction of the shaped solution (so-called "self-suction") on the gaseous medium. As a result of self-suction, the shaped solution is, for example, first permeated at an angle of 180°, i.e. in the direction of motion. If in such a case suction is then applied at an angle of 0°, the upward suction of the gaseous medium will then be opposed to the downward suction resulting from the extrusion. It is however preferred for the permeation of the shaped solution by the gaseous medium to be accomplished by blowing on the gas inlet side. This makes it possible to adjust various parameters of the gaseous medium, such as the blowing angle, velocity, temperature and, if required, also the moisture content, e.g. by conditioning the biowing gaseous medium. Blowing is normally earned out over the entire length of the air gap, i.e. between the shaping element, such as the spinneret, and the coagulation bath. It is of course also possible to blow onto the shaped solution for only a part of this distance. For example, the gaseous medium can be applied only in the first section, i.e. the section of the air gap immediately after the shaping element For the most effective design of the process in accordance with the invention, it is desirable if a larger volume of gaseous medium is removed by suction on the gas outlet side than is produced by blowing. This step guarantees quantitative flow of the gaseous medium in the direction of suction, since a greater volume is removed than is produced by blowing. Particularly advantageously, the volume of gaseous medium removed by suction at the gas outlet side is at least twice, preferably three times, the volume produced by blowing. As already mentioned, the process in accordance with the present invention is well suited for those processes in which the velocities of the gaseous medium are relatively low. Preferably therefore, the shaped solution is permeated at velocities of the gaseous medium between 0.5 and 2 m/s. This has the advantage that undesired turbulence can be largely avoided. As already mentioned, the freshly extruded shaped objects are cooled in the air gap to rapidly reduce their tackiness. For cooling to be possible at all, the stream of gas must of course be at a lower temperature than the shaped solution. In the process according to the invention, good results have been obtained by permeation with the gaseous medium at temperatures between 0° and 40°C, preferably 20° to 30°C. All conventional and well known gaseous media can in principle be used for cooling, e.g. inert gases such as nitrogen, carbon dioxide, or argon. It is however normally preferred for the gaseous medium to be air. Since it is well known that not only the temperature itself, but also the water content of the gaseous medium and its relative humidity can have a substantial influence on the properties of the cellulosic shaped objects, it is preferred to condition the gaseous medium before it is used, i.e. it Is adjusted to a defined moisture content. If the gaseous medium is air, preferably the air is adjusted to a relative humidity of 5% to 30%. How the air is conditioned, i.e. the adjustment of the water content and the relative humidity at a given temperature, is known to one skilled in the art and can, for example, be gathered from WO 96/17118. It is important to ensure that conditioning is performed as uniformly as possible. The process in accordance with the invention allows the advantageous production of fibres, particularly filaments, so-called continuous fibres, staple fibres, films, hollow fibres and membranes, for example for use in dialysis, oxygenation, or filtration. The shaping of the solution into a desired cellufosic shaped object can be performed with I known spinnerets for producing fibres, slit dies, or hollow-fibre spinnerets. The shaped solution can then be drawn following shaping, i.e. before it is introduced into the coagulation bath. The invention will be explained in more detail on the basis of the following drawing. The drawing is a schematic representation of the construction of the apparatus for working the invention. In the diagram, a spinneret 1 is shown with several spinning locations, from each of which the shaped solution 2 is spun into a gas such as the ambient air. The shaped solution is then immersed in a coagulation liquid in a reservoir 3. The shaped solution 2 is blown through an insulated tube 4 on the gas inlet side, introduced from an air-conditioning system. The arrows in the figure diagrammatically show the direction of the blowing stream. Blowing is performed roughly perpendicular to the direction of motion of the shaped solution 2 and over the complete length of the spinneret 1. The removal by suction on the gas outlet side of the gaseous medium produced by blowing is carried out vertically upward at the edge of the spinneret 1, at 90° to the direction of blowing. The gaseous medium is removed by suction via a perforated plate 5 which is installed immediately behind the spinneret 1. The removal by suction is also performed over the entire length of the spinneret. The perforated plate 5 used for removal by suction is flush with the spinneret 1, with which it thus forms a single plane. As a result of the upward removal by suction and the flush arrangement of the suction system and the spinneret 1, the spinneret 1 and the individual spinning locations are readily accessible from every side, in particular from the longitudinal side of the spinneret 1. This greatly facilitates handling of the apparatus, e.g. in starting the spinning operation, isolating the filaments, or servicing the spinneret 1. WO 96/17118 and its US counterpart, US-A-5,902,532 discloses a method for the preparation of cellulosic shaped bodies by shaping a solution of cellulose in a tertiary amine N-oxide and, optionally, water in the hot state and cooling the thus shaped solution with air before it is introduced into a coagualtion bath. According to that disclosure use is made of conditined air with a water content of from 0.1 to 7 g water vapour per kg of dry air and a relative humidity of less than 85%. Advantageously, the conditioned air is forced through a bundle of freshly spun fibres or filaments by a combination of blowing in and removal by suction. In this process the air flows at an angle of 0 to 120°, preferably 90°, relative to the direction of movement of the shaped solution, the angle of 0° corresponding to a flow opposite to the running direction of the formed solution. The process disclosed in WO 96/17118 produces a more effective cooling of the freshly extruded shaped bodies with less conglutination, and the filaments obtained have cross-sectional areas with a low coefficient of variation. Although the cooling process described in WO 96/17118 is a good process as such, there is still room for improvements. Thus, with an incident flow of conditoned air perpendicular (transverse) to the direction of movement of the shaped solution the side of the shaped solution opposite to the incident air flow side is often not reached adequately, or not reached quickly enough, by the conditioned air. This is especially the case when the process is carried out with a comparatively low flow velocity of the conditioned air and/or when, for example, a large number of filaments is extruded. When cellulosic multifilaments are extruded, for example, despite intensive incident flow (blowing) of the conditioned air, more or less extensive conglutination can occur in the case of the filaments on the side opposite to the incident air flow side, leading to an impairment of the stability of the process, because permeation of the air through the solution is not guranteed. In principle, the intesnity of the cooling could of course be increased by increasing the incident flow volume of the conditioned air/or by increasing the length of the air gap. Such measures, however, at the same time entail a risk of greater intermingling of the shaped solution, and thus of the filaments for example, and for that reason they are often undesirable. Disclosure of the invention The present invention therefore seeks at least to reduce the drawbacks of the prior art processes. According to the invention there is provided a process for the preparation of cellulosic shaped bodies such as described in the opening paragraph, which is characterised in that the gaseous medium on the gas outlet side is removed by suction at the gas outlet side in a direction substantially parallel to the direction of movement of the shaped solution. The direction may be 0° relative to the direction of movement of the shaped solution, that is to say parallel to and in the same direction as the movement of the shaped solution, or it may differ from 0° by a small angle, for example of up to 5° or 10° or more, but less than 45°. In the process according to the invention it is moreover preferred if the angle of flow of the gaseous (cooling) medium flowing out of the shaped solution (suction side) changes relative to the angle of the air flowing into the shaped solution because of the removal by suction. This change of direction results in a better flow of the gaseous medium at the side of the shaped solution situated opposite to the gaseous medium inflow (blowing) side. As will be explained in greater detail below, in such a process there is preferably removal by suction, for example through a perforated plate immediately following the spinneret. Within the framework of the present invention it is especially preferred when the gaseous medium on the gas inlet (blowing) side meets the shaped solution at an angle from about 45° to about 135°, more preferably at about 90°, relative to the direction of movement of the shaped solution. At an incident flow angle of gaseous medium of about 90° and a removal by suction of gaseous medium on the gas outlet side of 0° relative to the direction of travel of the formed solution, the removal by suction therefore takes place turned by about 90° relative to the blowing in, which leads to excellent flow of the gaseous medium through all regions of the shaped solution. In principle, of course, the flow of gaseous medium through the shaped solution can be triggered by convection, e.g. by movement of air, or else by suction of the shaped solution (so-called "self-suction") on the gaseous medium. By self-suction the shaped solution for instance is first permeated at an angle of 0°, i.e. in its direction of movement. However, it is preferred that the flow of the gaseous medium through the shaped solution is achieved by blowing in of the gaseous medium at the gas inlet side. This makes it possible to adjust various parameters of the gaseous medium, for example the blowing angle, the speed, the temperature, and, optionally, also the water content, by conditioning the gaseous medium blown in. Generally, the blowing in takes place along the entire length of the air gap, i.e. between the shaping device, for example the spinneret, and the coagulation bath. Of course, it is also possible to expose the shaped solution to the blowing in over only part of this length. Thus, for example, the gasesous medium can be blown in only in the first section of the air gap, i.e. the section which immediately adjoins the shaping device. In order to carry out the process according to the invention as efficiently as possible, it is desirable to have a larger volume of gaseous medium removed by suction on the gas outlet side than is blown in. This guarantees a quantitative flow of the gaseous medium in the direction of removal by suction, since a larger volume flow is removed by suction than is blown in. It has proved especially advantageous in this process for the volume of gaseous medium removed by suction on the gas outlet side to be at least twice, preferably three times, as large as is blown in. As mentioned earlier, the present invention proves well suited to those processes which may be drawn. Description of the drawing The invention is explained in greater detail with reference to the accompanying drawing, which schematically shows the construction of an apparatus for carrying out a process in the opposite direction to that according to the invention. In the drawing a spinneret 1 is constructed with several spinning positions, from each of which a shaped solution 2 is spun into a gas, for instance ambient air. The shaped solution is then immersed in a coagualtion liquid, present in coagualtion bath 3. The blowing in of the gaseous medium into the shaped solution 2 takes place via an insulated pipe 4 on the gas inlet side, which is brought up from an air-conditioning plant. The arrows drawn in the figure schematically indicate the direction of the blowing in. The blowing in takes place approximately perpendicular to the direction of movement of the shaped solution 2 and over the entire length of the spinneret 1. The removal by suction of the gaseous medium blown in takes place on the gas outlet side turned by about 90° towards the blowing in direction, vertially upwards at the edge of spinneret 1 and thus in the opposite direction to the direction of movement of the shaped solution as shown in the drawing. In this process the gaseous medium is removed by suction via a perforated sheet 5, which is mounted immediately following the spinneret 1. The removal by suction likewise takes place over the entire length of the spinneret. The perforated sheet 5 used for the removal by suction joins flush with the spinneret 1, i.e. forms a plane with it. Through the removal by suction and the flush arrangement of the extraction and the spinneret 1 good accessibility of the spinneret 1 and the individual spinning positions is provided from each side, but especially from the longitudinal side of the spinneret 1. As a result, the handling of the equipment, e.g. when stringing up, separating filaments and servicing spinneret 1, is clearly made easier. WE CLAIM: 1. A process for the prepartion of cellulosic shaped bodies wherein a solution of cellulose in a tertiary amine N-oxide and, optionally, water is shaped in the hot state and the shaped solution is cooled with a gaseous medium prior to being introduced into a coagulation bath, the gaseous medium flowing through the shaped solution from a gas inlet side to a gas outlet side, characterised in that the gaseous medium is removed by suction at the gas outlet side in a direction parellel to or at an angle of less than 45° to the direction of movement of the shaped solution. 2. A process as claimed in claim 1, wherein the gaseous medium flows into the shaped solution at an angle from 45° to 135°, preferably 90°, relative to the direction of movement of the shaped solution. 3. A process as claimed in claim 1 or 2, wherein the flow of the gaseous medium into the shaped solution is achieved by blowing in. 4. A process as claimed in claim 3, wherein a greater volume of gaseous medium is removed by suction than is blown in. 5. A proces as claimed in claim 4, wherein the volume of gaseous medium removed by suction is at least twice, preferably three times, as great as the volume blown in. 6. A process as claimed in claims 1 to 5, wherein the incident gaseous medium has a velocity in the range from 0.5 to 2 m/s. 7. A process as claimed in any of claims 1 to 6, wherein the incident temperature of the gaseous medium is from 0 to 40° C, preferably from 20 to 30°C. 8. A process as claimed in any of claims 1 to 7, wherein the gaseous medium is air. 9. A process as claimed in claim 8, wherein the air has a relative humidity of 5 to 30%. 10. A process as claimed in any of claims 1 to 9, wherein the shaped bodies produced are fibres, more particularly filaments, films, hollow fibres, or membranes.

Documents:

208-DELNP-2004-Abstract-(02-02-2009).pdf

208-DELNP-2004-Abstract-(18-12-2008).pdf

208-delnp-2004-abstract.pdf

208-DELNP-2004-Claims-(02-02-2009).pdf

208-DELNP-2004-Claims-(06-02-2009).pdf

208-DELNP-2004-Claims-(18-12-2008).pdf

208-delnp-2004-claims.pdf

208-DELNP-2004-Correspondence-Others-(02-02-2009).pdf

208-DELNP-2004-Correspondence-Others-(06-02-2009).pdf

208-DELNP-2004-Correspondence-Others-(09-02-2009).pdf

208-DELNP-2004-Correspondence-Others-(11-08-2008).pdf

208-DELNP-2004-Correspondence-Others-(18-12-2008).pdf

208-delnp-2004-correspondence-others.pdf

208-DELNP-2004-Description (Complete)-(02-02-2009).pdf

208-DELNP-2004-Description (Complete)-(18-12-2008).pdf

208-delnp-2004-description (complete).pdf

208-DELNP-2004-Drawings-(18-12-2008).pdf

208-delnp-2004-drawings.pdf

208-DELNP-2004-Form-1-(06-02-2009).pdf

208-delnp-2004-form-1.pdf

208-delnp-2004-form-13.pdf

208-delnp-2004-form-18.pdf

208-DELNP-2004-Form-2-(18-12-2008).pdf

208-delnp-2004-form-2.pdf

208-DELNP-2004-Form-3-(18-12-2008).pdf

208-delnp-2004-form-3.pdf

208-delnp-2004-form-5.pdf

208-DELNP-2004-GPA-(06-02-2009).pdf

208-DELNP-2004-Others-Document-(02-02-2009).pdf

208-DELNP-2004-Others-Document-(11-08-2008).pdf

208-delnp-2004-pct-210.pdf

208-delnp-2004-pct-306.pdf

208-delnp-2004-pct-409.pdf

208-DELNP-2004-Petition-137-(02-02-2009).pdf