Field of the invention

This invention relates to methods for finishing lyocell fabrics and in particular to the provision of lyocell fabrics which have a peachskin finish.

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 (NM O). 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 fibres such as the viscose process, for example reduced environmental emissions.

As used herein, "lyocell fabric" means a woven or knitted fabric which contains or consists of lyocell yarn or yarns. As used herein, "lyocell yarn" means a yarn which contains or consists of lyocell fibre.

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) , is uneven and often leads to pilling. This leads to an undesirable unsightly appearance, particularly in dyed fabric, because such fibrils generally dye to a paler shade than 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 and sufficiently short so as not to lead to pilling. Such fabrics dye uniformly, and the presence of the secondary fibrils confers an attractive visual appearance and handle, often aptly called a peachskin finish, on the fabric. Breier points out that fibrillation can be completely and permanently excluded only by reactive cross-linking. Breier describes the production of a peachskin finish by enzymatic defibrillation of lyocell fabric containing primary fibrils using a cellulase, followed by induction of secondary fibrillation by wet treatment in a jet-processing machine in conjunction with a silicone softener.

Background art

JP-A-6-146, 168 discloses that fibrillation of lyocell fibres can be prevented by finishing the fibre with a conventional N-methylol textile resin. The same disclosure was publicly made by J M Taylor at the Second Tencel Technical Conference, in the Industrial Technology Centre, Hammamatsu, Japan, on 16th July 1992.

B Dannhorn, in a paper entitled "Die Einfluss der Ausrϋstung it Vernetzern und Additiven bei Artikeln aus Lyocellfasern" in Lenzinger Berichte 9/94, pages 73-80, discloses the finishing of unfibrillated lyocell fabric with a mixture of a zero-formaldehyde textile resin such as butane-1 , 2 ,3,4-tetracarboxylic acid and a non-ionic silicone softener such as a polydi ethylsiloxane microeiriulsion. The finished fabric exhibited both a very low degree of fibrillation and a low tendency to fibrillate on laundering.

Disclosure of the invention

It is an object of the invention to provide a lyocell fabric with a peachskin finish which resists laundering.

According to the present invention a method of providing a lyocell fabric with a peachskin finish is characterised in that (a) a mixture of (i) a zero-formaldehyde textile resin and (ii) an emulsion of a silicone-based softener is applied to fibrillated lyocell fabric, and (b) the fabric is treated so as to cure the resin thereon.

The mixture of zero-formaldehyde textile resin and silicone softener is preferably water-based. The mixture is conveniently applied to the fabric by a conventional technique, such as by dipping in a bath or by padding.

The zero-formaldehyde textile resin may be any of those known as such in the art. One known class of such resins, which may be preferred, consists of N,N'-dialkylated cyclic ureas, for example and in particular N,N'-dimethyldihydroxy- ethyleneurea(4,5-dihydroxy-1,3-dimethylimidazolidin-2-one) . Examples of suitable commercial zero-formaldehyde textile resins of this kind include Arkofix NZF (Trade Mark of Hoechst AG) and Knittex FRF (Trade Mark of Ciba-Geigy AG) . Such resins are generally used in conjunction with an acid catalyst, usually a metal salt of the Lewis acid type such

as magnesium chloride, although other acid catalysts such as an amine salt or an organic acid such as citric acid may also be used. The concentration of catalyst depends on the particular catalyst but is generally such that the ratio by weight of the textile resin (cross-linking agent) to the catalyst is in the range from 4:1 to 20:1. Another known class of zero-formaldehyde textile resins consists of aliphatic polycarboxylic acids, for example butane-1,2,3,4-tetracarboxylic acid and citric acid. This latter class may generally be less preferred on environmental grounds, in that their satisfactory application generally requires the use of phosphate or hypophosphite catalysts. The concentration of the zero- formaldehyde textile resin in the application liquor may be in the range from 10 to 100 g/1, often 25 to 75 g/1.

Many silicone-based softeners are based on non-ionic polydialkylsiloxanes, for example polydimethylsiloxanes. They are supplied in the form of fine emulsions in water. The concentration of the silicone-based softener in the application liquor (calculated on the basis of the emulsion as supplied) may be in the range from 10 to 100 g/1, often 20 to 50 g/1. Examples of suitable commercial silicone-based softener emulsions include Cellusoft MEC (Trade Mark of Hoechst AG) and Sandoper MEJ (Trade Mark of Sandoz AG) . The silicone-based softener used in the method of the invention is preferably a microemulsion of a nonionic silicone, although other kinds may also be used.

The curing step may be carried out in any conventional manner. It may be preferred to effect curing by drying the fabric followed by heating at elevated temperature for a short time, for example at a temperature in the range from 150 to 200°C for a time in the range from 10 seconds to 5 minutes.

In one embodiment of the invention, the lyocell fabric subjected to the method of the invention contains primary

fibrils. This is a common consequence of using conventional wet-processing techniques, including dyeing, although care may need to be taken to ensure that primary fibrillation occurs throughout the whole of the fabric. Resin-finishing according to the method of the invention embrittles the primary fibrils, so that they can subsequently be removed by mechanical working under dry conditions, for example vigorous tumble-drying. It has surprisingly been found that secondary fibrils survive this treatment, or that primary fibrils break off so as to acquire the nature of secondary fibrils, when the method of the invention has been employed, so that the resultant fabric exhibits a desirable peachskin finish. Thus, according to this embodiment of the invention, a method for providing a lyocell fabric with a peachskin finish is characterised in that (a) a mixture of (i) a zero-formaldehyde textile resin and (ii) an emulsion of a silicone-based softener is applied to a fibrillated lyocell fabric containing primary fibrils, (b) the fabric is treated so as to cure the resin thereon, and (c) the fabric is subjected to mechanical working under dry conditions so that the primary fibrils are removed therefrom.

In another embodiment of the invention, the lyocell fabric subjected to the method of the invention contains few or no primary fibrils but does contain secondary fibrils, so that it already exhibits a peachskin finish. Primary fibrillation can be avoided by careful control of the preceding wet-processing steps, in particular by processing the fabric in open width. The desired secondary fibrillation can conveniently be induced prior to the resin-finishing step of the invention by inducing primary fibrillation by wet-processing, enzymatic removal of fibrils, and further wet processing (for example dyeing) to induce secondary fibrillation. It has surprisingly been found that the peachskin finish is retained through the resin-finishing step of the invention and further surprisingly through subsequent laundering. As pointed out by Breier in the above- mentioned paper, conventional resin finishing both

destroys existing fibrils and suppresses subsequent fibrillation (the fibrils are embrittled and easily removed) . Thus, according to this embodiment of the invention, a method for providing a lyocell fabric with a peachskin finish is characterised in that (a) a mixture of (i) a zero-formaldehyde textile resin and (ii) an emulsion of a silicone-based softener is applied to a fibrillated lyocell fabric containing secondary fibrils and essentially no primary fibrils, and (b) the fabric is treated so as to cure the resin thereon.

Fabric treated according to the method of the invention exhibits good washability, whereby the desirable peachskin finish is retained through conventional laundering cycles.

Experiments have shown that when a lyocell fabric is treated with a zero-formaldehyde resin alone, or an

N-methylol resin alone, the benefits of the invention are not obtained. All such treatments so embrittle both primary and secondary fibrils that they are thereafter readily removed from the fabric, for example during conventional laundering. In consequence, the desirable peachskin finish cannot be obtained, or it is lost if present before finishing, when such methods are employed. Treatment with low levels, for example 0.5 to 0.75% by weight on fabric, of the conventional low-formaldehyde N-methylol resin DHDMEU in conjunction with a silicone-based softener provides some retention of an existing peachskin effect, but at the expense of imparting a relatively harsh handle to the fabric.

Experiments have also shown that use of a silicone-based softener alone does not yield desirable results, in that pilling and crease marks are evident.

The invention is illustrated by the following Examples, in which parts and proportions are by weight unless otherwise specified:-

Example 1

Woven lyocell fabric (Tencel, Trade Mark of Courtaulds Fibres (Holdings) Limited), previously desized in open width form, was loaded into a Thies Rototumbler (Trade Mark) containing 2 g/1 Perilan VF (Trade Mark) at 60°C. Primary fibrillation was induced by adding 2 g/1 caustic soda (as solid) to this bath, raising the temperature to 115°C and running the fabric at 400 /min for 90 minutes. The fabric was subsequently enzyme-cleaned using 3 g/1 of the cellulase enzyme Primafast 100 (Trade Mark of Genencor) for 60 minutes at 55°C.

The fabric was then loaded onto a Thies Luftroto (Trade Mark) machine for dyeing using a Procion HEXL (Trade Mark) migration technique. The dyeing stage also serves to induce secondary fibrillation. The fabric was next dried, and then tumbled in a Thies Rototumbler for one hour. The resulting peachskin fabric pilled slightly after five domestic wash/tumble cycles and showed white line marks. The application of the following finishes immediately after the dyeing step gave results as follows:

(1) (Comparative) Silicone icroemulsion (38 g/1 Sandoperm MEJ - Trade Mark) ; padded, dried, dry tumbled - gave a pilled peachskin after five domestic wash/tumble cycles. (2) (Comparative) Zero-formaldehyde Resin (90 g/1 Arkofix NZF - Trade Mark) ; padded, dried, cured, dry tumbled - gave a smooth fabric with no peachskin after five domestic wash/tumble cycles, all the fibrils having been removed. (3) (According to the invention) Sandoperm MEJ (38 g/1) and Arkofix NZF (90 g/1); padded, dried, cured, and dry tumbled - gave a pristine perfect peachskin fabric free from white lines after five domestic wash/tumble cycles.

Example 2

Tencel fabric as in Example 1 was desized and dyed (with Procion HE dyes) using standard methods on a jig machine. The fabric was loaded onto a Thies Rototumbler (Trade Mark) machine containing 2 g/1 Perilan VF (Trade Mark) at 60°C. Primary fibrillation was induced by adding 2 g/1 caustic soda (as solid) to the bath, raising the temperature to 115°C and running the fabric at 400 m/min for 90 minutes.

The dyed and fibrillated fabric was stenter dried, and a mixture of silicone microemulsion (38 g/1) and zero- formaldehyde resin (90 g/1) as in Example 1 was padded on and cured. The fabric was then dried and then dry tumbled in a Biancalani Airo (Trade Mark) machine for 15 minutes at 400 m/min. The resulting fabric had a peachskin (aesthetic, secondary fibrillation) which was stable to domestic laundering and tumbling.

It is thought that a dye-resinate-tumble sequence will yield the same results if the dyeing is done on a jet-dyeing machine which is sufficiently aggressive to fibrillate the fabric fully during dyeing.