Lyocell fibres are known, and their manufacture is described for example in US-A-4,416,698, the contents of which are incorporated herein by way of reference. Cellulose is dissolved in a solvent containing a tertiary amine N- oxide (which may also be called for brevity an amine oxide), for example N-methylmorpholine N-oxide (NMMO). The solvent generally also contains a proportion of a non-solvent for cellulose, for example water. The resulting solution is extruded through a suitable die to produce fibres, which are coagulated, washed in water to remove the solvent, and dried. This process of extrusion and coagulation is referred to as"solvent-spinning", and the cellulose fibre produced thereby is referred to as"solvent-spun"cellulose fibre or under the generic name lyocell fibre. It is also known that cellulose fibres can be made by extrusion of a solution of a cellulose derivative into a coagulating and regenerating bath. One example of such a process is the viscose process, in which the cellulose derivative is cellulose xanthate.

Solvent-spinning has a number of advantages over other known processes for the manufacture of cellulosic fibre such as the viscose process, for example reduced environmental emissions.

Lyocell fibres are known to be prone to fibrillation.

Fibrillation is a phenomenon which in the main occurs when lyocell fibres are subjected to mechanical forces during wet-processing, and it results in the partial detachment of

fine longitudinal fibrils from the fibres. Two types of fibrillation are recognised in lyocell fabrics, under the names primary fibrillation and secondary fibrillation, as described by R Breier in a paper entitled"Die Veredlung von Lyocellfasern-Ein Ehrfahrungsbericht"in Lenzinger Berichte 9/94 at pages 99-101. Primary fibrillation results in the formation of relatively long fibrils (often 1 mm or longer) and is uneven. This leads to an undesirable unsightly appearance, particularly in dyed fabric, because primary fibrils are often found to dye to a different shade from the bulk of the fibre. In contrast, secondary fibrillation results in the formation of relatively short fibrils, typically a fraction of a millimetre long, evenly distributed over the fabric. The resulting fabrics dye uniformly, and the presence of the secondary fibrils confers an attractive visual appearance and handle, often called a peach-skin finish, on the fabric.

Background Art Various processes have been suggested for reducing the degree of fibrillation and/or the tendency to fibrillate of a lyocell fabric. For example, WO-A-95/30043 describes contacting the fabric with an aqueous liquor containing an acid catalyst and optionally a crosslinking agent. WO-A- 94/09191 describes contacting the fabric with a chemical reagent having at least two functional groups which are reactive with cellulose, for example vinyl sulphone groups or electrophilic three-membered heterocyclic rings. WO-A- 94/09191 describes contacting lyocell at elevated temperature with a solution of a reagent having acrylamido groups. EP-A-538977 describes contacting lyocell with a chemical reagent having 2 to 6 groups reactive with cellulose such as a colourless dye.

All the above processes require wet processing of the lyocell fabric to reduce fibrillation. Extended wet processing is costly and can lead to breakdown of the fabric structure, particularly for example on collars and cuffs of

garments if the fabric is treated in garment form.

As described for example in the aforementioned paper by Breier, it is known that such a peach-skin finish can be obtained by wet processing to induce primary fibrillation, and removing the primary fibrils by enzymatic treatment with a cellulase, followed by further wet processing to induce secondary fibrillation. This is a lengthy and expensive process, and disposal of enzyme-containing liquors may pose environmental problems. Enzymatic treatment can lead to the premature breakdown by abrasion of threads in the fabric at cuffs and collars during wet processing. It is an object of the invention to provide an alternative and convenient way of creating a peach-skin finish in lyocell fabric.

Disclosure of the Invention According to the present invention, a process for reducing the degree of primary fibrillation of a fibrillated lyocell fabric is characterised in that the fabric is tumbled in a drying gas in a tumble dryer for at least 5 minutes after the fabric has reached a normal level of dryness, that is after it has reached a moisture content of about 8% by weight.

The invention also provides a process for producing a garment having a peach-skin effect from a fabric comprising lyocell fibres, characterised in that the fabric is subjected to wet processing such that it develops primary fibrillation, and the fabric in garment form is subsequently tumbled in a drying gas in a tumble dryer to remove primary fibrillation and to induce secondary fibrillation, giving the peach-skin effect.

The invention is particularly suitable for treating garments. The wet processing step can be carried out on lyocell fabric before or after it has been made into garments. The tumble drying step is preferably carried out

with the fabric in garment form, although pieces of fabric can be treated. Garments are more easily treated in a tumble dryer than lengths of flat fabric. A variety of fabrics can be treated, including woven, knitted and non-woven fabrics.

The process is particularly effective for woven fabrics. The fabric can be formed wholly or partly of lyocell fibres; usually the lyocell fibres form at least 50% by weight of the fibres in the fabric.

The tumble dryer can be any tumble dryer as sold commercially, for example a Huebsch, Milnor, Ajax or ATP dryer. In general, the fabrics or garments to be treated are placed within a perforated drum which is rotated about a substantially horizontal axis while a drying gas is introduced. The speed of rotation of the dryer is preferably sufficiently slow, for example 40 rpm, that the fabrics or garments are not carried around by the drum but fall off as they approach the top of the dryer and drop through the drying gas, but it should be greater than 20 rpm, for example about 30 rpm, to achieve defibrillation in a commercially practical time. The drying gas is usually hot air, for example at a temperature of 50 to 120°C. The loading of the dryer is preferably in the range 10 to 40 kg per cubic metre of dryer volume, for example 25 to 33 kg per cubic metre, which is less than the recommended loading of 50 kg for a 1 cubic metre commercial tumble dryer.

In normal practice when the tumble dryer is used for drying, drying is not continued beyond a moisture content of the garments of about 8 to 10% by weight. We have found according to the invention that extending the tumble drying beyond this point removes primary fibrillation from the lyocell fabric and induces the secondary fibrillation which gives a peach-skin effect. Tumbling of the fabric in the drying gas is generally continued for at least 5 and preferably at least 10 minutes, for example for up to 20 or 30 minutes, after this moisture content has been reached.

Preferably the garment is tumbled in the drying gas for at

least 150% of the time required to reach a normal level of dryness.

The fabric or garment can be introduced into the tumble dryer in a normally dry state, that is having a moisture content of about 8 to 10% by weight, and tumbled in the drying gas for at least 5 minutes. Alternatively, the defibrillation process of the invention can follow on from a drying step if the fabric is damp or wet from a previous wet processing step. In this case the fabric or garment is introduced into the tumble dryer in its-damp or wet state, usually having a moisture content of above 15% by weight, and is tumble dried to a moisture content of 8% by weight and for at least 5 minutes after it has reached this moisture content.

The wet processing step which induces primary fibrillation can for example be a dyeing step, which can be a fabric or garment dyeing and may for example be dyeing in a jet dyeing machine or a garment rotary drum dyeing machine, for example a Dytex or Milnor dyeing machine.

Garment dyeing for example generally involves wet processing for a period of 1 to 6 hours. The wet processing step can alternatively be washing, for example garment washing in a garment rotary drum washing machine or indigo washing.

Indigo dyeing may be carried out on yarn which is then woven into fabric, or on open width fabric, before the fabric is made up into garments. The garments are washed to create the abrasion required for the fashion end use, for example in denim fabrics.

There is no universally accepted standard for assessment of primary fibrillation, and the following method was used to assess Fibrillation Index (F. I.). Samples of fibre were arranged into a series showing increasing degrees of primary fibrillation. A standard length of fibre from each sample was then measured and the number of primary fibrils (fine hairy spurs extending from the main body of

the fibre) along the standard length was counted. The length of each fibril was measured, and an arbitrary number, being the number of fibrils multiplied by the average length of each fibril, was determined for each fibre. The fibre exhibiting the highest value of this arbitrary number was identified as being the most fibrillated fibre and was assigned an arbitrary Fibrillation Index of 10. A wholly unfibrillated fibre was assigned a Fibrillation Index of zero, and the remaining fibres were graded from 0 to 10 based on the microscopically measured arbitrary numbers.

The measured fibres were then used to form a standard graded scale. To determine the Fibrillation Index for any other sample of fibre, five or ten fibres were visually compared under the microscope with the standard graded fibres. The visually determined numbers for each fibre were then averaged to give a Fibrillation Index for the sample under test. It will be appreciated that visual determination and averaging is many times quicker than measurement, and it has been found that skilled fibre technologists are consistent in their rating of fibres.

The Fibrillation Index of fabrics can be assessed on fibres drawn from the surface of the fabric. Woven and knitted fabrics having an F. I. of more than about 2.0 to 2.5 exhibit an unsightly appearance.

The fabrics or garments used in the present invention generally have a Fibrillation Index of at least 4 after the wet processing step, for example a Fibrillation Index of 6 to 7 for a heavyweight (above about 250 g/sq. metre) fabric or a Fibrillation Index of 5 to 6 for a lightweight (below about 250 g/sq. metre) fabric. After the tumble drying step according to the invention the fabrics generally have a Fibrillation Index of below 2, for example a Fibrillation Index of about 0.5 to 1.0, which is typical of a"peach- skin"fabric.

In general, a valuable reduction of fibrillation can be achieved by tumbling the lyocell fabric in the drying gas as described above without adding anything else to the tumble dryer. The removal of primary fibrils can be accelerated by adding one or more abrasive articles (preferably a textile article) to the tumble dryer so that the lyocell fabric is tumbled with the abrasive article. The abrasive article can for example be a fabric formed of knotted high strength yarn such as polyester yarn, for example a bag made of such a fabric.

Following the treatment in the tumble dryer, the fabric or garment is generally remoistened so that it has its equilibrium moisture content when normally dry in an atmosphere of relative humidity about 50-70% at 20°C, that is to say a moisture content of about 8-10% by weight. The fabric or garment can for example be remoistened by moist air or by steam. In general it will be preferred to remoisten a garment in this way if it is to be ironed or pressed after tumbling in the dryer. Alternatively, the fabric or garment can be allowed to regain moisture by contact with ambient air.

The invention is illustrated by the following Examples.

In all cases, the lyocell fabrics used consisted solely of lyocell fibres. Lyocell fibre is available from Courtaulds Fibres (Holdings) Limited under the Trade Mark TENCEL.

Example 1 Tencel lyocell fibre was spun into yarns having nominal Nm counts of 50 and 34. These yarns were woven into a fabric having a 3: 1 twill construction with a warp of 45 ends/cm of 50 Nm yarn and a weft of 23 picks/cm of 34 Nm yarn. The finished fabric had a weight of 170 g/m2.

The fabric was prepared by desizing and scouring on a Benninger open-width preparation machine before being made

into shirts. The shirts were dyed in garment form by a direct dye process as follows: Set the bath with water at 40°C and wetting agent, add garments, run 3 minutes to allow garments to wet. Add direct dyestuff, run 5 minutes to equalise, raise to 90°C, maintain for 30 minutes. Add salt to exhaust the dye, run for 30 minutes. Cool to 40°C, rinse for 5 minutes in cold water. Set bath at 40°C, add softener, run 10 minutes. Drain and hydro-extract at 700 rpm for 5 minutes.

After the dyeing treatment, the fabric had a Fibrillation Index of 5.5.

30 kg shirts still in a damp condition from dyeing (moisture content about 60% by weight) were loaded into a Huebsch tumble dryer of volume 1 cubic metre and nominal capacity 50 kg. The tumble dryer was operated at 30 rpm using an inlet temperature of 100°C for 28 minutes. The fabric after tumble drying was substantially free of primary fibrillation (Fibrillation Index about 0.5) and had an attractive peach-skin texture.

The time required to tumble dry this load to normal dryness (about 8% moisture content) under the same conditions is about 14 minutes.

Example 2 Yarns of Tencel fibre were woven into a twill fabric of weight 350 g/sq. metre, and pairs of trousers were made from the fabric. The trousers were dyed by reactive dyes at 80°C for 60 minutes in a Dytex rotary drum garment dyeing machine. After the dyeing treatment, the fabric had a Fibrillation Index of 6.6 (heavy primary fibrillation).

30 kg trousers still in a damp condition from dyeing (moisture-content about 65% by weight) were loaded into the dryer used in Example 1 and were dried for 30 minutes under

the same conditions as used in Example 1. The fabric after tumble drying was substantially free of primary fibrillation (Fibrillation Index about 0.5) and had an attractive peach- skin texture.

The time required to tumble dry this load to normal dryness (about 8% by weight moisture) under the same conditions is about 15 minutes.