EP1327013B1

EP1327013B1 - Crimped fibre and its production

Info

Publication number: EP1327013B1
Application number: EP01986728A
Authority: EP
Inventors: Gregory James Askew; Malcom John Hayhurst; Andrew Peter Slater
Original assignee: Lenzing AG; Chemiefaser Lenzing AG
Current assignee: Lenzing AG
Priority date: 2000-10-12
Filing date: 2001-10-12
Publication date: 2007-01-10
Anticipated expiration: 2021-10-12
Also published as: DE60125964D1; CN1469943A; GB2368342A; EP1327013A1; KR100808724B1; AU2001294030A1; DE60125964T2; GB0025080D0; KR20030061374A; CN1214136C; WO2002031236A1

Description

This invention relates to modified lyocell fibre and to a process for the preparation of modified lyocell fibre. "Fibre" is used in this specification to include continuous filament yarns, tows of yarn for cutting into staple fibre and also staple fibre formed from such a tow.
Lyocell fibre is produced by dissolving cellulose in a suitable solvent, for example a tertiary amine N-oxide such as N-methyl morpholine oxide mixed with water. A suitable method of manufacture is described in US-A-4,416,698. The solution of cellulose in the amine oxide solvent, which is solid at ambient temperature, is extruded at a temperature of 95-125°C from a spinneret through an air gap into a precipitation bath of water or dilute aqueous amine oxide, and the amine oxide solvent leaches into the bath, producing cellulose fibre.
JP-A-8-170224 discloses a disperse dyeable biconstituent fibre of the islands-in-the-sea type in which the continuous "sea" component is a cellulose polymer spun from an organic solvent system and the "islands" are composed of a polymer dyeable by a disperse dye and are 0.01-3 m in size and form 2-45% by weight of the fibre.
GB-A-2121069 discloses viscose rayon fibres for the production of non-wovens containing as mineral fillers barium sulphate, talcum, muskovite, or a mixture thereof, in an amount of from 15 to 60%, preferably 40 to 50%, of the total fibre mass, and, if desired, additionally hydrophobic, polymer or oligomer substances, such as polyethylene, polypropylene, polystyrene, polyacrylic acid ester, polyester, polytetrafluoroethylene or waxes, in an amount of from 1 to 60%, preferably 25 to 50%, of the total fibre mass. GB-A-2008126 discloses the use of polystyrene as a delustrant for viscose rayon fibres.
WO-A-98/46814 discloses lyocell fibre containing elongated domains of polyester, polyamide or an olefin copolymer, the domains having an aspect ratio of at least 1.5 and being aligned substantially parallel to the axis of the fibre. The domains are 70-1000 nm in length and 30-400 nm in diameter. It has however been found that it is difficult to control domain dimensions within these limits during commercial scale production. In this reference it is also taught that the fibre can be carded without the use of a lubricant. In contrast, lyocell fibre which does not contain low-melting thermoplastic polymer requires a lubricant for carding, and the conventional stage to apply the lubricant is to the wet fibre, before it is dried during the production process.
Example 1 of WO-A-98/46814 forms spun fibre by extruding a solidified dope prepared from a cooled solution of cellulose in N-methylmorpholine oxide and dispersed polyester (Mpt 90°C; 2 wt% based on cellulose) to form filaments which cross an air gap into an aqueous spin bath. It then collects a tow of the filaments, dries the tow and crimps it in a stuffer-box before cutting it into 38mm staple fibre.
Lyocell fibre is naturally uncrimped. However, crimp is desirable, particularly in staple fibre. Crimp can be generated in lyocell fibre by compression of wet fibre in accordance with the disclosure of EP-A- 0,797,696 or by stuffer-box crimping with the aid of dry steam, as disclosed in EP-A-0,703,997. Experience has shown that such a dry steam process, although less damaging to the fibre, is unable to generate more than about 2.3 crimps/cm without damage in conventional lyocell fibre. By the term "conventional lyocell fibre" as used herein, is meant lyocell fibre which does not contain low-melting thermoplastic polymer. Only conventional lyocell fibre is and ever has been commercially available. WO-A-96/46814 is silent as to the number of crimps/cm generated and does not suggest a level of crimping above 2.3 crimps/cm.
It has also been found that high-speed carding of lyocell fibre may result in problems such as the formation of excessive fly and of rolling laps of fibre. High-speed carding is desirable for high productivity in the manufacture of spun yarn and especially of non-wovens.
It is an object of the present invention to reduce or substantially to overcome these disadvantages.
According to the invention there is provided a method for the manufacture of lyocell fibre including the steps of:

(i) forming a solution of cellulose in an aqueous tertiary amine N-oxide solvent at a temperature above ambient, the solution having dispersed therein from 0.01 to 30 percent, more preferably from 0.01 to 20 percent, most preferably from 0.1 to 10 percent, by weight, based on the weight of cellulose, of particles of a thermoplastic polymer having a glass transition temperature below the temperature at which the solution is formed;
(ii) extruding the solution by way of a die into an aqueous coagulating bath, thereby forming lyocell fibre;
(iii) washing the fibre to remove residual amine N-oxide therefrom, and drying the fibre; and
(iv) crimping the fibre;

The quantity of thermoplastic polymer used is sufficient to show a change in colour on dyeing with a disperse dye of the fibre containing the thermoplastic polymer.
The glass transition temperature (Tg) indicates the temperature region in which the polymer characteristically changes from a hard, more or less brittle glass to a rubbery or viscous polymer within which motions of portions of the chains, usually called segments, are comparatively unhampered by the interactions of neighbouring chains (Principles of Polymer Chemistry, Paul J Flory, Cornell University Press, 15^th printing 1992, ISBN 0-8014-0134-8, page 56).
In a preferred embodiment of the method according to the invention, the thermoplastic polymer has a melting point greater than 50°C, preferably of not more than 150°C, more preferably of between 80°C and 130°C, as measured by differential thermal analysis.
The glass transition temperature (Tg) of the polymer is preferably between -20°C and 130°C, more preferably between 30°C and 130°C.
The thermoplastic polymer is preferably a thermoplastic polymer selected from the group consisting of polyesters, polyamides and olefin polymers.
The thermoplastic polymer is preferably dispersed throughout the lyocell in domains, and the maximum dimension of substantially all of the domains is preferably no more than 50 nanometres (nm).
The fibre is preferably crimped so as to induce from 3.5 to 8 crimps/cm in the fibre.
The solution may have a matting agent such as titanium dioxide particles dispersed therein, whereby the resulting fibre contains dispersed therein from 0.1 to 5 percent by weight, preferably from 0.1 to 2 percent by weight, more preferably from 0.2 to 1 percent by weight, of titanium dioxide particles based on the weight of cellulose.
In a preferred embodiment of the method according to the invention, soft finish (lubricant) is applied to the fibre prior to crimping.
The amount of soft finish applied is preferably in the range from 0.01 to 2 percent by weight, more preferably from 0.1 to 0.5 percent by weight, most preferably from 0.15 to 0.4 percent by weight, based on the weight of the fibre. The achievable crimp level may be found to vary directly with the amount of soft finish applied, at least within the lower regions of these ranges.
Crimp may be induced in the fibre by the method disclosed in EP-A-0 703 997. The resulting fibre preferably has a titre in the range from 0.5 to 5 decitex, more preferably from 1 to 3.5 decitex.
The method of the invention may further include the step of cutting the fibre to a staple length in the range from 3 to 100 mm, more preferably from 20 to 75mm.
In a preferred embodiment of the method according to the invention, the fibre has applied to it after washing and before drying a reagent having from two to six functional groups reactive with cellulose, which is reacted onto the fibre, either before or during drying.
According to the invention, there is further provided lyocell fibre having dispersed therein from 0.01 to 30 percent by weight, more preferably from 0.01 to 10 percent by weight, most preferably from 0.1 to 10 percent by weight, based on the weight of cellulose, of particles of a thermoplastic polymer having a melting point of from greater than 50°C to 150°C, the fibre being characterised by having from 2.5 to 8 crimps/cm.
The low-melting thermoplastic polymer is preferably a low-melting thermoplastic polymer selected from the group consisting of polyesters, polyamides and olefin polymers.
It has surprisingly been found that fibre made by the method of the invention and fibre of the invention can be carded satisfactorily at remarkably high speeds, in some cases even at about twice the speed which can satisfactorily be used on conventional lyocell fibre. Carding speed is a very significant rate-limiting factor in the production of non-wovens. Non-wovens frequently use a dull or matt fibre and the presence of titanium dioxide as dulling or matting agent does not adversely affect the process of the invention or the properties of the fibre of the invention, including its high speed carding properties.
The lyocell fibre according to the invention may be in the form of a staple fibre of length preferably in the range from 3 to 100 mm, more preferably from 20 to 75 mm.
The lyocell fibre according to the invention has preferably had applied thereto from 0.01 to 2 percent by weight, more preferably from 0.1 to 0.5 percent by weight, most preferably from 0.15 to 0.4 percent by weight, of a soft finish, based on the weight of the fibre.
Preferred lyocell fibre according to the invention includes domains of the low-melting thermoplastic polymer, which is selected from the group consisting of polyesters, polyamides and olefin polymers, and it contains from 0.1 to 30 percent by weight, preferably from 0.5 to 10 percent by weight, most preferably from 1 to 5 percent by weight, based on the weight of cellulose, of the low-melting thermoplastic polymer, and substantially all of the domains are not visible when viewed by electron microscopy at x9000 enlargement The maximum dimension of substantially all of the domains is no more than 50 nm. The domains may be visible at higher magnifications, for example x55000 enlargement.
The fibre of the invention can be made from a solution of cellulose in an aqueous tertiary amine N-oxide ("amine oxide"), e.g. N-methylinorpholine N-oxide, which solution contains a suitable thermoplastic low-melting polymer in molten form. The solution is extruded through a spinneret via an air-gap into an aqueous coagulating bath. The extrusion temperature is typically in the range from 90 to 125°C. The thusly-extruded fibre is then washed and dried.
The thermoplastic low-melting polymer should generally be sufficiently compatible with the cellulose solution that the polymer when molten does not agglomerate as a separate phase from the cellulose solution, but it is preferably not soluble either in amine oxide at the dilution at which it is used in the coagulating bath or in water. A polymer should be chosen which is essentially all retained in the fibre during the extrusion (spinning), washing and drying processes. One type of preferred low-melting polymer is a polyester, carboxy-functional polyesters being particularly preferred.
In general, we have found that the presence of carboxylic acid groups in the low-melting polymer increases its compatibility with the cellulose solution, giving more thorough mixing of the cellulose and the low-melting polymer. For most uses, the polymer preferably has an acid value of at least 10, up to for example 50 or 100 or even 150. We also believe that a branched polymer structure may be advantageous.
Examples of polyesters of this type having the required low melting point are formed from a mixture of aromatic dicarboxylic acids selected from isophthalic acid, terephthalic acid and phthalic acid or anhydride, optionally with an aliphatic dicarboxylic acid such as adipic, succinic or sebacic acid, and one or more aliphatic diols such as neopentyl glycol, ethylene glycol, propylene glycol, propane-1,3-diol, butane-1,4-diol, butylene glycol or diethylene glycol. Branching can be introduced by a trifunctional reagent, for example trimellitic acid or anhydride or trimethylolpropane, glycerol or pentaerythritol. The required acid value can be obtained by using an appropriate excess of carboxylic acid-functional reagent. Such polyesters are sold for use in thermosetting powder coatings, for example under the Trade Marks "Alftalat","Uralac" or "Grilesta".
Alternative thermoplastic low-melting polymers include polyamides, for example polyamides formed from fatty acid dimers and aliphatic diamines or the copolyamide sold under the Trade Mark "Griltex", or olefin copolymers, for example ethylene/vinyl acetate or ethylene/butylene/butyl acrylate copolymers, preferably containing a small amount of acrylic acid comonomer to give the preferred acid value. A further alternative low-melting thermoplastic polymer is an olefinic polymer such as poly(vinyl alcohol).
The concentration of cellulose in the solution to be extruded (otherwise known as the spinning solution) is generally 10 to 20% by weight, preferably at least 13 or 15% up to 17 or 18% by weight. The spinning solution preferably contains water, usually in the range 5-15% by weight, with the remainder, generally 65-83% by weight, being amine oxide. The extrusion temperature is generally 95 to 125°C.
The low-melting polymer can be added to the cellulose solution at any of various points during its preparation. The polymer can for example be premixed with cellulose pulp, the pulp then being mixed with amine oxide and water to form the spinning solution. The polymer can alternatively be added, preferably in molten form, to a preformed cellulose solution. In a further alternative, a relatively high proportion of low-melting polymer is premixed with a preformed cellulose solution, for example forming 10 to 50% by weight of the mixture. The premixture can then be used as a masterbatch to add the low-melting polymer to cellulose solution at the required level. In a still further alternative, the polymer is added to the amine oxide solvent and the resulting mixture is used to dissolve the cellulose.
The cellulose solution containing a low-melting polymer can be extruded to form fibres using the same spinneret at the same temperature as is conventionally used for forming lyocell fibre.
The domains of low-melting polymer are believed to be distributed uniformly throughout the fibre as a separate phase.
The level of low-melting polymer present in the fibre is from 0.01 to 30 percent by weight, based on cellulose. The presence of the domains of low-melting polymer gives rise to various effects depending on the concentration of low-melting polymer and on the type of low-melting polymer used. More specifically, an amount of up to 15 percent by weight, preferably from 0.01 to 5 percent by weight, may be preferred if only crimp effects (explained hereinafter) are desired, whereas an amount from 1 to 20 percent by weight, preferably from 5 to 15 percent by weight, may be preferred if textile effects (explained hereinafter) are desired.
The desired small domains of the thermoplastic polymer can be obtained in various ways. For example, the polymer may be synthesised as small particles. Alternatively, large particles can be comminuted, for example by milling or grinding or, preferably, by subjecting the spinning solution to high-shear conditions.
In contrast to conventional lyocell fibre, surprisingly, we have found the process disclosed in EP-A-0 703 997 can generate up to about 8 crimps/ cm in fibre of the invention. Furthermore, we have also surprisingly found that variation of crimper settings and temperature and of soft finish level on fibre has considerably more effect on fibre of the invention than it does on conventional lyocell fibre. We have also found that crimped fibre of the invention may have a higher crimp intensity with a lower crimp amplitude, and that it may be less susceptible to mechanical damage during crimping, than conventional lyocell fibre.
We have also surprisingly found that fibre of the invention is considerably easier to dry than conventional lyocell fibre. This permits useful energy savings.
It is known that lyocell can be reacted with polyfunctional reagents in order to reduce its fibrillation tendency. See, for example, EP 0 538 977, EP 0 665 904 and EP 0 755 467, the contents of all of which are incorporated herein by this reference. Such reactions can be performed either on never-dried or on previously-dried fibre. Similar reactions can be performed on fibre of the invention.
We have found that fibre of the invention containing more than 6 percent by weight of low melting thermoplastic polyester may react less readily with such polyfunctional reagents than does conventional fibre. This can be counteracted by using more forcing conditions, for example a higher reagent concentration.
We have surprisingly found that yarn spun from fibre of the invention advantageously has improved textile effects including higher tenacity and extensibility and contains fewer irregularities (thick and thin spots and neps) and is less hairy than yarn spun from conventional fibre. The differences are especially marked if the fibres being compared were reacted in never-dried state.
Yarn spun from crimped fibre of the invention, and fabric formed therefrom, may be more bulky than yarn and fabric of conventional crimped lyocell fibre. This means that fabrics having acceptable porosity to light can be produced from finer yarns, i.e. yarns having a lower tex. The fabric produced from these finer yarns is more uniform and drapes more fluidly.
Fibre of the invention may be continuous filament or staple fibre.
Fibre of the invention can be formed into woven, knitted or nonwoven (e.g. hydroentangled, needlepunched or meltbonded) fabrics. Such fabrics can be subjected to conventional processing treatments, such as being given a crease-resistant finishing resinated treatment. We have found that such resinated fabric may exhibit a cleaner appearance after repeated laundering than resinated fabric of conventional lyocell fibre. We have found that care should be taken if fibre of the invention containing polyester is to be hot causticised at temperatures above about 50°C, because sodium hydroxide tends to hydrolyse the ester linkages.
Fibre of the invention may be dyed with conventional dyes for cellulose, for example direct and reactive dyes. The fibre of the invention generally has a lower water imbibition than conventional fibre. This means that the fibre is less inclined to swell and this enhances the uniformity of dyeing in some applications.
One known finishing treatment for lyocell fabric involves deliberate induction of fibrillation, for example by harsh wet processing; defibrillation, for example by enzymatic treatment with a cellulase and dyeing. We have found that fabric formed from fibre of the invention is preferably treated with less aggressive cellulases than is fabric formed from conventional fibre. We have further found that fabric finished in this way may be more absorbent and exhibit better wicking properties than conventional fabric finished in this way, even though the fibre from which it is formed had lower absorbency.
The low-melting polymer is generally a hydrophobic polymer, and thus susceptible to dyeing with disperse dyes. We have however found that fibre of the invention dyed with a disperse dye may suffer from cross-staining on laundering. Accordingly, the dyeing of fibre of the invention with disperse dyes is in general not recommended.
Crimp in lyocell fibre can be assessed as follows. A sample of titre about 200 tex is taken from a dry tow and placed under sufficient tension to pull out the crimp. Marks are made on the sample 10 cm apart, and the tension removed. The number of crimps between the marks is then counted. The ratio of tensioned to untensioned length gives the crimp intensity or crimp ratio.
The invention is illustrated by the following Examples in which parts, percentages and ratios are by weight.

Example 1

A carboxy-functional saturated polyester resin of the kind used in powder coatings, having acid value about 40, melting within the range 95°C to 130°C, and having a branched structure was mixed with 77/23 N-methylmorpholine N-oxide (NMMO)/water in a ploughshare mixer at about 70°C. After about 2 minutes, shredded woodpulp was added, after which mixing was continued for a further 10 minutes. The ratio of woodpulp to resin was 92.8:7.2.
The mixture was passed through a Buss 5.5m² Filmtruder (Trade Mark) Unit HS0055 to remove excess water and thereby form the spinning solution. Within the Filmtruder, the mixture was heated by a water jacket at a temperature of 130°C under a vacuum of 200 mm of mercury. However, temperatures of between 80°C and 150°C could be used and higher or lower vacuums could be used. During passage through the Filmtruder, the mixture was subjected to high-shear conditions in a layer about 2-2.5 mm thick with blade speed about 5 m/sec for about 10 minutes. The spinning solution contained 13.5% cellulose, 1.1% polyester, 75.4% NMMO and the balance water.
The solution was extruded at 105°C through a spinnerette by way of an airgap into an aqueous coagulating bath to form a fibre tow in conventional manner. The fibre was then dried as a tow and crimped in the general manner described in EP - A - 0 703 997. The dried fibre was of titre 1.7 dtex, contained about 8.1% polyester on cellulose, and had 8% moisture content. A fibre having a diameter of approximately 10 x 10^-6m was produced. A cross section of the fibre produced, photographed using transmission electron microscopy at x9000 enlargement, is shown in Figure 1 of the accompanying Figures. The large black cracks are a result of the sample preparation and do not indicate the presence of another material other than cellulose. Traces of polyester domains were visible in the fibre at x9000 enlargement (believed to correspond to a resolution of about 50 nm) but substantially all of the polyester domains are not visible. Optical enlargement of the picture shown in Figure 1 does not reveal any additional traces of the polyester domains.
A cross section of the same fibre photographed using transmission electron microscopy at x55000 enlargement is shown in Figure 2 of the accompanying Figures and a longitudinal section at the same enlargement is shown in Figure 3 of the accompanying Figures.
Polyester domains show as white areas in these Figures. From Figures 2 and 3, it can be seen that the visible polyester domains, compared to the scale at the bottom of the Figures, have a maximum dimension of about 20 nm.
The fibre had 2.6 crimps/cm and crimp intensity 1.3. In comparison, conventional lyocell fibre crimped under the same conditions had 2.3 crimps/cm and crimp intensity 1.23.
The fibre was cut to 38 mm staple and ring-spun to make 20 tex yarn. The results obtained are shown in the following table, in which:

Control = conventional lyocell fibre
C.V.% = Coefficient of Variance of yarn mass, expressed as a percentage
Irregularity Index = Actual C.V.% divided by the Limiting C.V.%, where Limiting C.V.% = 100/√n, where n is the number of fibres in cross section (yarn tex divided by fibre tex). An Irregularity Index of 1 is a perfect yarn.
Thins (-40%) = in a kilometre of yarn, the number of places at which the thickness of the yarn is less than 40% of the nominal thickness, as determined by the Uster Tester 3 test
Thicks (+50%) = in a kilometre of yarn, the number of places at which the thickness of the yarn is greater than 50% of the nominal thickness, as determined by the Uster Tester 3 test
Neps (+200%) = in a kilometre of yarn, the number of places at which the thickness of the yarn is greater than 200% of the nominal thickness, as determined by the Uster Tester 3 test
Hairs = indirect measure for the number and cumulative length of all fibres protruding from the yarn surface, as determined by the Uster Tester 3 test

Yarn	Tenacity cN/tex	Extension %	Regularity C.V. %	Irregularity Index	Thins (-40%)	Thicks (+50%)	Neps (+200%)	Hairs
Control
	25	7.3	13.3	1.44	87	10	15	5.85
Example 1	27	8.5	12.3	1.34	41	7	7	5.52

Example 2

Example 1 was repeated, except that crimper conditions and fibre soft finish levels were varied. Conventional fibre can be crimped as set out in EP-A-0,703,997 using a stuffer box pressure of about 8psig (55 kPa) and steam pressure of about 20 psig (138 kPa). Higher pressures lead to uneven crimp, tow damage, and stuffer box blockage. In contrast to conventional lyocell fibre, fibre of the invention is capable of withstanding more forcing crimping conditions (higher stuffer box pressure, higher steam pressure and higher nip roller pressure) which would irrevocably damage conventional lyocell fibre. These more forcing conditions result in a greater number of crimps per centimetre. It is known that the carding lubricant applied to conventional lyocell fibre has no significant effect on crimping parameters. It is taught in W0-A-98/46814 that lyocell containing polyester is able to be carded without the addition of lubricant. Unexpectedly, it has been found that the addition of a soft finish or lubricant can have a very significant beneficial effect on the crimping parameters of the fibre of the invention. The graph of Figure 4 shows the benefit of increasing lubricant levels on the maximum achievable crimp level. It can be seen that increasing the applied soft finish level from 0.17% to 0.35% increases the maximum number of crimps from 3.5 per cm to 5 per cm. The graph also shows that the maximum stuffer box pressure can also be doubled compared to conventional lyocell. Further; the graph shows that the increase in maximum crimp is directly related to increasing the soft finish level. Lower pressures yielded fibre with a similar number of crimps per centimetre to crimped conventional fibre, but with reduced crimp intensity due to reduced crimp amplitude.

Example 3

Example 1 was repeated, except that the fibre was reacted in never-dried state with 1,3,5-triacryloylhexahydro-1,3,5-hexahydrotriazine (TAHT) as described in EP-A-0,755,467 at an application level of 0.7% by weight on the fibre as an anti-fibrillation treatment. In the following table, control refers to fibre manufactured from conventional lyocell which incorporates 0.7% TAHT. The following results were obtained on yarns spun from treated fibres:

Yarn	Crimps per 10 cm	Tenacity cN/tex	Extension %	Irregularity Index	Thins (-30%)	Thins (-40%)	Thicks (+50%)	Neps (+200%)	Hairs
Control	24	24	7.9	1.48	1049	72	62	48	6.37
Example 3	24	25	8.2	1.32	595	29	23	31	5.30
Example 3	30	26	8.5	1.32	590	25	12	19	5.05
Example 3	40	26	8.8	1.27	443	14	13	13	5.09

Dyed single-jersey knitted fabrics made from yarns spun from treated fibre of the invention showed no signs of fibrillation after 10 domestic wash/tumble cycles at 40°C.

Example 4

1.7 dtex lyocell fibre was spun from a solution of cellulose in aqueous NMM0 in conventional manner, the solution containing 4% dispersed thermoplastic carboxy-functional saturated polyester resin of the kind used in powder coatings, having acid value about 40, melting within the range 95°C to 130°C, and having a branched structure and 0.5% titanium dioxide as a matting or dulling agent, both based on the weight of cellulose. The fibre was washed and 0.25% soft finish based on the weight of fibre applied to it. The fibre was then dried, and compressed in a stuffer box in the presence of dry steam so as to induce crimp in the fibre. The conditions under which the fibre was crimped are shown in the following table and illustrated in the graph of Figure 5.

Stuffer box pressure (psig) Relative stuffer box pressure Mean crimp level (crimps per extended 10 cm)

8 1 25

20 2.5 35

26 3.3 40

The fibre was then cut to 38 mm staple length.

The fibre was carded on a Thibeau CA 11 card, 2.5 m wide and equipped with double doffing rollers. The target basis weight for the carded web was 30 gsm. The following results were obtained for fibre of the invention and for comparative fibre.

	Max carding speed, m/min
Fibre of Example 4, 2.5 crimps/cm	ca. 140
Fibre of Example 4, 3.5 crimps/cm	200-220
Fibre of Example 4, 4.0 crimps/cm	250-270
Conventional lyocell, 2.3 crimps/cm	100
Viscose	ca 150
Polyester	200+
Polypropylene	ca 250

Higher levels of crimp could not be achieved in the conventional lyocell fibre because of instability in the crimping process. In contrast, the fibre of the invention could be stably crimped under higher pressures than the conventional fibre; and the level of crimp induced by a given pressure was higher for the fibre of the invention than for the conventional fibre.

Claims

A method for the manufacture of lyocell fibre, including the steps of:
(i) forming a solution of cellulose in an aqueous tertiary amine N-oxide solvent at a temperature above ambient temperature, the solution having dispersed therein from 0.01 to 30 percent by weight, based on the weight of cellulose, of particles of a thermoplastic polymer having a glass transition temperature below the temperature at which the solution is formed;

(ii) extruding the solution by way of a die into an aqueous coagulating bath, thereby forming lyocell fibre;

(iii) washing the fibre to remove residual amine N-oxide therefrom, and drying the fibre; and

(iv) crimping the fibre
characterised in that the fibre is crimped so as to induce from 2.5 to 8 crimps/cm in the fibre.
A method as claimed in claim 1, in which the cellulose solution has from 0.01 to 20, preferably from 0.1 to 10, percent by weight of particles of the thermoplastic polymer.
A method as claimed in claim 1 or 2, in which the thermoplastic polymer has a melting point greater than 50°C, preferably not more than 150°C, more preferably between 80 and 130°C.
A method as claimed in any of claims 1 to 3, in which the thermoplastic polymer has a glass transition temperature between -20 and +130°C, preferably between 30 and 130°C.
A method as claimed in any of claims 1 to 4, in which the thermoplastic polymer is selected from the group consisting of polyesters, polyamides and olefin polymers.
A method as claimed in any of claims 1 to 5, in which the thermoplastic polymer is dispersed throughout the lyocell in domains, and the maximum dimension of substantially all of the domains is no more than 50 nanometres (nm).
A method as claimed in any of claims 1 to 6, in which the washed fibre has a soft finish applied to it prior to crimping, desirably at a level of from 0.01 to 2, preferably from 0.1 to 0.5, more preferably from 0.15 to 0.4, percent by weight, based on the weight of the fibre.
A method as claimed in any of claims 1 to 7, in which the fibre is crimped so as to induce from 3.5 to 8 crimps/cm in the fibre.
A method as claimed in any of claims 1 to 8, in which the solution includes a matting agent so as to incorporate the matting agent in the fibre.
A method as claimed in any of claims 1 to 9, in which the fibre has applied to it after washing and before drying a reagent having from two to six functional groups reactive with cellulose, which is reacted onto the fibre either before or during drying.
A method as claimed in any of claims 1 to 10, in which the resulting fibre has a titre in the range from 0.5 to 5 decitex, preferably from 1 to 3.5 decitex.
A method as claimed in any of claims 1 to 11, which method further includes the step of cutting the fibre to a staple length in the range from 3 to 100 mm, preferably from 20 to 75mm.
A method as claimed in claim 12, followed by processing the fibre into a card, preferably a card having a weight of 30 gsm, preferably by a method which comprises carding the fibre at a web speed in the range of 150 to 275 metres per minute on a Thibeau CA 11 carding machine or at a functionally equivalent speed on a functionally equivalent machine.
Lyocell fibre having dispersed therein from 0.01 to 30 percent by weight, based on the weight of cellulose, of particles of a thermoplastic polymer having a melting point of from greater than 50°C to 150°, the fibre being characterised by having from 2.5 to 8 crimps/cm.
Lyocell fibre as claimed in claim 14 having dispersed therein from 0.01 to 20, more preferably from 0.1 to 10, percent by weight of particles of the thermoplastic polymer.
Lyocell fibre as claimed in claim 14 or 15, in which the thermoplastic polymer is selected from the group consisting of polyesters, polyamides and olefin polymers.
Lyocell fibre as claimed in any of claims 14 to 16, in which the fibre has thereon a reagent having from two to six functional groups reactive with cellulose, which has been applied onto never-dried fibre and has been reacted thereon either before or during drying.
Lyocell fibre as claimed in any of claims 14 to 17, in which the thermoplastic polymer is dispersed throughout the lyocell in domains in which the maximum dimension of substantially all of the domains is no more than 50 nm.
Lyocell fibre as claimed in any of claims 14 to 18, having dispersed therein from 0.1 to 5, preferably from 0.1 to 2, more preferably from 0.2 to 1, percent by weight of titanium dioxide particles based on the weight of cellulose.
Lyocell fibre as claimed in any of claims 14 to 19, which has had applied thereto from 0.01 to 2, preferably from 0.1 to 0.5, more preferably from 0.15 to 0.4, percent by weight of a soft finish based on the weight of the fibre.
Lyocell fibre as claimed in any of claims 15 to 20 which contains from 0.1 to 30 percent by weight, based on the weight of cellulose, of the thermoplastic polymer which is selected from the group consisting of polyesters, polyamides and olefin polymers and which is located in domains substantially all of which are not visible when viewed by electron microscopy at x9000 enlargement.
Lyocell fibre as claimed in any of claims 15 to 20 which contains from 0.1 to 30 percent by weight, based on the weight of cellulose, of the thermoplastic polymer which is selected from the group consisting of polyesters, polyamides and olefin polymers and which is located in domains, the maximum dimension of substantially all of the domains being no more than 50 nm.
Lyocell fibre as claimed in claim 21 or claim 22, in which the fibre contains from 0.5 to 10, preferably from 1 to 5, percent by weight of the thermoplastic polymer.