MXPA00011863A - Methods of manufacture of nonwoven fabric - Google Patents

Abstract

A method of manufacture of a nonwoven cellulose fabric involves the fibres being formed by extruding a solution of cellulose through at least one spinning jet and subjecting the extrudate fibre to a high velocity gas flow. The fibre passes through a vapour mist which at least partially coagulates the fibre prior to collection as a fibre web. By use of such method, a fabric having a high loft and a relatively low density may be obtained.

Description

METHODS OF MANUFACTURE OF NON-WOVEN FABRIC This invention relates to a method of manufacturing a nonwoven fabric of cellulose ax and in particular of a cellulose solution. Cellulose fibers and filaments can be produced by winding a solution of cellulose in a solvent of amino oxides that are filtered in water or in a dilute solution of aqueous amino oxide, to produce cellulose filaments which can be cut into stapled fibers . This extrusion and coagulation process is referred to as a solvent flutter, and the solvent-developed cellulose fibers produced are known under the generic name of lyocell. It is possible to produce small decitex fibers below 1.0 dtex by disintegrating the stapled fibers, however, this is expensive and requires a high energy consumption. The present applicant's international patent application PCT / GB97 / 03391 discloses a method of manufacturing a cellulose fiber made from fibers formed by extruding a cellulose solution through at least one winding jet and holding the fiber extruded to a high velocity gas flow, where the fibers are collected on a surface in which the fiber coagulates subsequently. The fibers tend to bind together prior to coagulation forming a relatively dense, non-woven fabric that is highly agglutinated. In some applications a highly bonded web with high density is not desirable, for example for filtration materials or for materials that require a high water retention capacity. The present invention provides a method of manufacturing a non-woven cellulose fabric having a high storage and a relatively low density. According to the present invention there is provided a method for manufacturing a non-woven cellulose fabric in which the extruded fiber produced from a spinning jet is subject to a high velocity gas flow, and the fiber is passed through. through a vapor mist that coagulates the fiber at least partially before its collection as a fiber network. The extruded fiber is attenuated by the gas flow and can be divided into indefinite lengths. Steam mist can be formed from any suitable coagulant. The mist is preferably an aqueous mist, although diminished alkyl alcohols, for example, may also be used. Conveniently, the atomized water can be sprayed from a nozzle located under the winding jet. The cellulose solution is preferably a solution of cellulose in a solvent of amino oxides, typically a tertiary N-amino oxide and in particular N-oxide-N-methylmorpholene- (NMMO). The cellulose solution may contain 4-22% by weight of cellulose, preferably 10-15%, with a degree of polymerization of 200-5,000, and more typically of 400-1,000. In one embodiment the solution is preferably of cellulose comprises 14% by weight of cellulose, 12% by weight of water and 74% by weight of NMMO, cellulose has a degree of polymerization in the order of 600. Microfibers that form attenuated fiber or fibrils are collected and then coagulated (alternatively referred to as they are "regenerated") through water elements, or a dilute aqueous solution of amino oxides containing up to 205 amino oxides in water. The fibrils can be collected directly in a coagulation bath, or they can be collected on a surface and then coagulated. The gas, preferably air or dry steam, is blown on the extruded fibers at a rate between 200.s-1 (meters per second) and 500 ms "1 and has a temperature of between 100 ° C and 155 ° C, preferably around 145 ° C for a concentration of 14-15% The lower the cellulose acetate content of this cellulose acetate, the lower the air temperature that can be used.The gas velocity should be at least 50 times higher than the speed of the extruded fiber that emerges from the spinning stream, and preferably between 15 ° and 45 ° with respect to the longitudinal axis of the extrudate, and more preferably around 30 °. The air jets can also be biased at a second angle of bias relative to the winding jet so that the air jet shafts and the fiber shafts do not intersect, the air jets tangential to the surface of the extruded fiber. The fiber collection surface can be flexible or resistant. Preferably the fiber collection can be carried out in a foam bed which is preferably sunk in water or an aqueous solution of NMMO. The invention also provides a non-woven lyocell fabric in which the fibers are bonded or entangled together without the use of a binder, the fabric has a density that is not greater than 175 g.dpT3, and / or a stretched tensile extension of at least 7%. The invention will now be described in greater detail by way of example only, with reference to the accompanying drawings in which: Figure 1 is a schematic drawing of an embodiment of the apparatus for the production of a fabric nonwoven according to the present invention; Figure 2 is a plan view of a spinning jet nozzle used in the apparatus of Figure 1; Figure 3 is a side elevation of a nozzle shown in Figure 2, with internal passage in spec; and Figure 4 is an axial cross section through the nozzle shown in Figure 2 and Figure 3. With reference to Figure 1, where an extruder 10 having a nozzle 11 fixed thereto is shown. The extruder is fed with a solution comprising 14% by weight of cellulose, 12% by weight of water and 74% by weight of N-oxide-N-methylmorpholene (NMMO). The cellulose has an average degree of polymerization of about 600. The cellulose solution can be manufactured as described in WO 94/28217. The cellulose solution in the extruder is maintained at a temperature between 95 and 100 ° C, preferably 105 ° C, and forced through the nozzle to extrude as a continuous filament of cellulose acetate. The nozzle 11 shown in Figures 2 and 3 and can be secured directly to the extruder 10, or can be secured to an adapter (not shown) which in turn is secured to the extruder 10. The nozzle 11 has a hollow screw threaded rod 13. on its rear face 12 and a central passage 14 ending in a jet opening 15. The jet has a diameter of the order of 0.2 and 0.3 mm, and preferably of about 0.27 mm. The cellulose acetate is forced into passage 14 under pressure and extruded through jet 15. Nozzle 11 also has a plurality of outlet passages 16, preferably three, spaced around central passage 14. Each of the passages of The gas 16 is inclined with respect to the jet axis, and they are equally circumferentially spaced around the jet 15 so that each of the gas flows leaving its respective passage 15 has the same effect on the extruded filament. The gas passage 16 makes a polarization or angle of convergence with the longitudinal axis of the jet between 156 ° and 45 ° and more preferably 30 °. The passages 16 are also skewed so that the axes of the passages 16 do not converge to themselves. The gas passages are around 2.0 mm in diameter. The rear face 12 of the nozzle has an annular groove 17 there interconnects the ends of the three passages 16. When the nozzle is secured to the extruder, the central passage 14 is connected to the cellulose acetate feed and the annular passage 17 is connects to a gas supply, preferably compressed gas. With reference to Figure 1, the compressed air is fed from a source (not shown) through a flow regulating valve 21, a flow meter 22, a heater 23 and a temperature sensor 24 can be connected to the air heater 24 for control of air temperature. The extruded filaments emerging from the nozzle 11 are subject to attenuation by high velocity airflows 25 emerging from the outlet passages 16, and the filament is pulled out and can fracture either directly blown into a coagulation bath 27 or, preferably, blown on a support surface 26 located about 30 cm from the nozzle 11. The flow rate of the cellulose acetate is preferably about 0.2 g.min "1. In the illustrated embodiment the supporting surface 26 it is formed through the peripheral outer surface of a rotary drum 28, which rotates at about 10 revolutions per minute (rpm) to build a non-woven fabric layer in the drum.The extruded filaments pass through a fine mist 30. of water vapor, generated by water sprayed from a nozzle that atomizes air 32 located about 10 cm below the nozzle 11. The surface of the drum can be covered with handy material com or a foam layer, preferably a 2 mm thick layer of polyurethane foam having an average cell size of 50 μm. The foam can sink into water or an aqueous solution of NMMO. Subsequent to the formation of a layer of non-woven fabric in the drum 28, the drum 28 is immersed in a coagulating bath 27 containing a suitable coagulant such as water or a dilute solution of amino oxide in water, to coagulate the nonwoven cellulose fabric in the drum. The cloth layer is dried in the drum after washing to remove the solvent. Table 1 below summarizes the various conditions used in the formation of extruded filament. TABLE 1 The air flow rate of 2.4 l.s "1 (liters / second) corresponds approximately to the air velocity of 250 m.s "1.

Samples 3 and 4 were made in accordance with the present inventions. Table 2 below summarizes the storage of the network by means of the thickness measurements, carried out using a Mitutoyo Quadrant Thickness Gauge, fitted with film / network measuring plates. Because the base weights are different, the thickness is normalized to a basis weight of g.m "Table 2 For examples 2,3 and 4, where the surface of the drum is partially submerged in the coagulation bath so that the surface of the drum becomes wet, an additional coagulation is carried out in contact with the wet drum or the previously laid fibers. For example 1, the surface of the drum is dry and the factory regenerates after accumulating in the drum.

Samples 3 and 4, collected in the drum after passing through the vapor mist, clearly have a lower tensile force but a larger rupture extension while still maintaining some integrity after the point of rupture. This high-storage material is suitable for use as filters and high-absorbency materials. Although the invention is described for the attenuation of cellulose acetate containing 14% cellulose, it can be applied to other acetates as described in PCT / GB97 / 03391, content of which is incorporated herein by reference.

Claims (17)

1. Claims 1. A method of manufacturing a non-woven cellulose fabric made of fibers formed by extruding a cellulose solution through at least one flash stream and holding the extruded fiber to a high speed gas flow, where the fiber passes through a vapor mist which coagulates the fiber at least partially before harvesting as a fiber network.
2. 2. A method as described in Claim 1, wherein the cellulose solution is a solution of an amino oxide solvent and the vapor mist is an aqueous mist.
3. 3. A method as described in Claim 1 and Claim 2, wherein the gas flow rate is at least 200 meters per second.
4. 4. A method as described in Claim 3, wherein the gas flow is at least 50 times faster than the flow rate of the extrudate.
5. A method as described in any of Claims 1 to 4, wherein the gas in the gas flow has a temperature of at least 100 ° C.
6. 6. A method as described in one of claims 1 to 5, wherein the mist is formed through an atomizer nozzle that is spaced from and below the winding jet.
7. A method as described in any one of Claims 1 to 6, wherein the cellulose solution contains 4-22% by weight of cellulose, preferably about 10 to 15% by weight of cellulose.
8. 8. A method as described in any of Claims 1 to 7, wherein the cellulose has an average polymerization degree of about 600.
9. 9. A method as described in any one of Claims 1 to 8, wherein the gas flow comprises compressed air which is directed over the fibers at a polarized angle of about 30 ° C to the axis of the extruded fiber.
10. A method as described in any one of Claims 1 to 9, wherein the fiber network is collected on a dry surface and the network is further treated in a subsequent manner with a coagulant.
11. 11. A method as described in any one of claims 1 to 9, wherein the fiber network is collected on a surface that is wet or the coagulant.
12. 12. A method as described in any of Claims 1 to 11, wherein the fiber network is collected on a manageable surface.
13. 13. A method as described in Claim 12, wherein the operable surface is provided by a layer of foam about 2 mm thick.
14. 14. A non-woven lyocell fabric made through a method as described in any one of Claims 1 to 13.
15. 15. A network of non-woven lyocell fabric in which the fibers are bonded together without the use of a binder, where the web network has a density of less than 175 g.dm "" 3.
16. 16. A non-woven fabric as described in Claim 14, wherein the fabric has an elongation at break of at least 7%.
17. 17. A network of. non-woven lyocell fabric in which the fibers are bonded together without the use of a binder, where the web of the fabric has an elongation at break of at least 7%.