This invention relates to methods of manufacturing lyocell elongate members, including fibres and films, of modified shape.

Background Art

It is known that cellulose fibre can be made by extrusion of a solution of cellulose in a suitable solvent into a coagulating bath. This process is referred to as "solvent-spinning", and the cellulose fibre produced thereby is referred to as "solvent-spun" cellulose fibre or as lyocell fibre. Lyocell fibre is to be distinguished from cellulose fibre made by other known processes, which rely on the formation of a soluble chemical derivative of cellulose and its subsequent decomposition to regenerate the cellulose, for example the viscose process. Lyocell fibres are known for their impressive textile-physical properties such as tenacity in comparison with fibres such as viscose rayon fibres. One example of a solvent-spinning process is described in US-A-4,246,221, the contents of which are incorporated herein by way of reference. Cellulose is dissolved in a solvent such as an aqueous tertiary amine N-oxide (commonly called an amine oxide), for example N-methylmorpholine N-oxide. The resulting solution is then extruded through a die into an aqueous bath to produce an assembly of filaments, which is washed with water to remove the solvent and is subsequently dried. Lyocell films can be manufactured by analogous procedures.

The cross-section of lyocell filaments extruded through circular spinnerette holes is generally circular or slightly elliptical. Lyocell filaments generally exhibit no or very low levels of crimp. Lyocell filaments and fibres consist of cellulose and are accordingly not thermoplastic.

Disclosure of Invention

According to the invention there is provided a method for modifying the shape of a lyocell elongate member, characterised in that a transverse deforming force is applied to the lyocell elongate member in plasticised never-dried state.

According to the invention there is further provided a method for manufacturing a lyocell elongate member, including the steps in sequential order of: (1) dissolving cellulose in an aqueous tertiary amine N-oxide solvent to form a solution; (2) extruding the solution through a die by way of a gaseous gap into an aqueous coagulating bath to form a coagulated elongate member; (3) washing the coagulated elongate member to remove residual solvent therefrom, thereby producing a never-dried lyocell elongate member; and (4) drying the never-dried lyocell elongate member, characterised in that a transverse deforming force is applied to the coagulated elongate member in plasticised state, thereby modifying the shape of the coagulated elongate member and consequently of the lyocell elongate member. The gas in the gaseous gap is commonly air, although other inert gases such as nitrogen may also be used. The length of the gaseous gap is preferably in the range from 10 to 100 mm, more preferably from 20 to 50 mm. The tertiary amine N-oxide is preferably based on a cyclic amine and is further preferably N-methylmorpholine N-oxide (NMMO) .

The elongate member may take the form of a film or (which may be preferred) of a fibre, including fibre in the form of continuous filaments, tow or staple fibre.

The deforming force may be entirely transverse or may possess transverse and longitudinal components. The deforming force may for example be applied by passing the coagulated elongate member through a constriction, for

example a nip between a roller pair. Alternatively, the deforming force may be applied by passing the coagulated elongate member under tension through an angle over an edge or over a gear wheel or between inter eshing gear wheels. Further alternatively, the deforming force may be applied by impacting a fluid stream, for example a water jet, against the coagulated elongate member.

The elongate member to which the deforming force is applied comprises cellulose, water and plasticiser. The plasticiser is preferably soluble in water. Examples of suitable plasticisers include cellulose solvents such as tertiary amine N-oxides. Other examples of suitable plasticisers include alkalis, in particular strong inorganic alkalis such as sodium hydroxide. Mixtures of plasticisers may be employed. Conveniently, the elongate member may be passed through a bath containing the plasticiser in aqueous solution immediately before application of the deforming force. It will be appreciated that the concentration of plasticiser in the bath should preferably not be so high that significant dissolution of the cellulose occurs. It will further be appreciated that the concentration of plasticiser in the elongate member should preferably not be so high that the plasticised member tends to stick to surfaces including other plasticised members when subjected to the deforming force. Suitable plasticiser concentrations can readily be determined by trial and error in any particular case. For example, a suitable concentration for sodium hydroxide in an aqueous plasticising bath may be in the range from 2 to 10 percent by weight (based on the weight of the bath) .

Alternatively, the elongate member may be plasticised by the presence of residual amine oxide from the spinning solution therein or by passage through a bath of aqueous amine oxide solution.

In one embodiment of the invention, the deforming force

serves to modify the cross-sectional shape of the elongate member. A bundle of parallelised circular lyocell filaments may be subjected to lateral compression, whereby the close-packed filaments are deformed so that their cross-sectional shapes tend towards the polygonal, especially the hexagonal. Such filaments may exhibit increased bulkiness. Alternatively, a thin web of lyocell filaments may be subjected to transverse compression to provide filaments of flattened cross-section. Such deformation in cross-section is permanent. The deformation may be more or less uniform over the fibre bundle, as desired.

In another embodiment of the invention, the deforming force serves to impart crimp to lyocell fibres and filaments. In this embodiment, the plasticised fibres or filaments may be compressed between patterned rollers. Alternatively, one or more fluid streams, for example high-pressure water jets, may be directed against fibres or filaments in contact with a patterned surface, for example a woven mesh belt. In another alternative, a tow of plasticised never-dried lyocell fibre may be overfed onto a conveyor and subjected to a transverse compressive force to induce crimp in the fibre. Although crimp produced in this manner may have a degree of permanence, it will be appreciated that fibre crimp level is often reduced when the fibre is subjected to the tensile forces to which it is exposed in yarn spinning operations.

In a further embodiment of the invention, the deforming force serves to create a three-dimensional pattern in a lyocell film, for example by compressing the plasticised film between patterned rollers or by impacting a fluid stream against the film whilst in contact with a patterned surface.

After the deformation step, the elongate member may be washed free of plasticiser and subsequently dried in

conventional manner.

Brief description of drawings

The invention will now be more particularly described with respect to the accompanying Figures, in which:-

Figure 1 is a schematic drawing of laboratory apparatus for spinning lyocell fibre; and

Figure 2 is a schematic detail of the nip roller assembly in the apparatus of Figure 1.

Referring to Figure 1, a laboratory apparatus for spinning lyocell fibre comprises an extrusion head 11, a spinbath unit 12, a nip roller assembly 13 and a fibre take- up reel 14. The extrusion head 11 comprises a stainless steel tube 15 (22 mm ID) equipped with a supply line 16 for pressurised nitrogen, a thermostatic jacket 17, an extrusion die 18 having a single extrusion hole (100 micrometre diameter), and a vent line 19 incorporating a bursting disc which serves as an excess pressure relief assembly. The spinbath unit 12 comprises a tank 20, a guide roller 21 and a thermostatic heater/circulating pump (not shown). The take-up reel 14 comprises a plastic reel (51 mm diameter) drivable by a variable-speed motor (not shown) at a surface speed (take-up speed) of up to 320 m/min.

Referring to Figure 2, the nip roller assembly 13 comprises an arm 30 adjustably and removably mounted with respect to the tank 20. The arm 30 carries a driven roller 31 and a pivotally-mounted lever 32. The driven roller 31 is drivable by a variable-speed motor (not shown) connected thereto by means of an axially-connected flexible drive shaft (not shown) . The lever 32 carries at the one end an undriven roller 33 and at the other end an assemblage of springs and weights which serves to urge the undriven roller 33 under defined adjustable conditions against the driven roller 31 in the manner generally indicated by the arrow 34,

thus forming a nip between the rollers 31, 33. The rollers 31, 33 each comprise a stainless steel rod carrying an elastomeric sleeve 3 mm thick (OD 25.4 mm).

In use, the tube 15 equipped with the die 18 is charged with chipped solid lyocell dope (nominally 15% cellulose, 75% NMMO, 10% water, by weight) (ca. 20 g) . A plastic disc (a few mm thick) (not shown) is placed on top of the chips to minimise the risk of channelling during the extrusion step. The tube 15 is placed inside the thermostatic jacket 17 and the remaining parts of the extrusion head are assembled. The dope is stored at 90°C for 45 minutes to cause it to melt. The temperature is then raised to 105°C (nominal) in preparation for spinning, and the apparatus is allowed to equilibrate for 15 minutes.

Pressurised nitrogen is supplied through line 16 so as to urge the liquefied dope downwardly through the die 18 by way of an air gap (20 mm long) into spinbath liquor (water, maintained at 22°C by the thermostatic controller) contained in tank 20. The thusly-formed lyocell filament passes downwardly through the liquor, between the submerged rollers 31, 33, and around the submerged guide roller 21 from which it passes at an upward angle to the take-up reel 14 where it is collected. At start-up, it has generally been found preferable to establish stable spinning before engaging the nip rollers on the extruded filament. The collected filament is washed with water until free of NMMO and dried. Referring to Figure 1, the spinbath liquor level is indicated by the dotted line 22, and the path of filament travel is indicated by the solid line 23, 23'. The depth of the nip below the surface of the spinbath liquor is preferably in the range from 10 to 150 mm, more preferably from 20 to 100 mm. Dope flow is measured by collecting and weighing the dope extruded through the die in a known time (ca. 1 min) before and after each series of experiments.

The invention is illustrated by the following Examples,

in which parts and proportions are by weight unless otherwise specified:-

Example 1

The apparatus described hereinabove was employed. Dope extrusion rate was 111 mg/min. The nip was located either 13 or 41 mm below the surface of the spinbath liquor. The force between the nip rollers was adjusted to either 0 (rollers disengaged, comparative experiment), 10.7 or 41.5 N. Take-up speed was either 10 or 20 m/min. The surface speed of the nip rollers was the same as that of the take-up reel. Filament titre was 16-17.5 dtex at 10 m/min and 9-10.5 dtex at 20 m/min take-up speed. Use of the nip rollers had no apparent effect on the tensile properties of the filaments. The filaments were found to possess cross-sections of the kind indicated in Table 1:

Table 1

Nip force N Cross-section

0 Circular

10.7 Oval 41.5 Lemon-shaped

It is thought that the lemon-shaped cross-sections may have resulted from excessive deformation of the rubber sleeves on the rollers.

The aspect ratio (ratio of major diameter to minor diameter) of the filaments was measured, with the results shown in Table 2 :

Table 2

Nip force N Nip in Take-up speed Aspect ratio m/min

0 - 10 1.03 o - 20 1.00

41. 5 13 10 1.26

41.5 13 20 1.12

41. 5 41 10 1. 38

41. 5 41 20 1.29 Aspect ratio was observed to decrease as spinning speed was increased and (unexpectedly) to increase as the submersion depth of the nip rollers was increased.

Example 2

Example 1 was repeated, with the variations detailed below. The elastomeric sleeve on the driven roller 31 was replaced by a PTFE sleeve (OD 28 mm) . The OD of the undriven roller 33 (elastomeric sleeve) was 24 mm. A miniature spinning apparatus equipped with a spinerette having 10 holes of 100 micrometre diameter was employed. Spinbath temperature was 25°C. Filament titre was 1.7 dtex. The following results were obtained:

Table 3

Ref. Dope flow Air gap Nip immersion Nip force Cross-section mg/min mm mm N

A 169 20 0 29 .2 Slightly oval B 169 100 0 29.2 Lemon-shaped X 306 20 80 29.2 Tending to polygonal

Y 306 100 80 29.2 Aε X

306 100 80 55. 7 As X, some lemon shapes