The present invention relates to a method for pre-treating fabric incorporating fibres of keratin to impart shrink-resistance to the fabric. The term "fabric" is used herein to mean any assembly of fibres such as woven wool, top (aligned fibres), web or yarn.

It is well known that keratin fibres such as wool have a tendency to shrink during laundering. The shrinkage of wool during laundering is a result of the surface cuticular structure of the fibre. It is known to overcome this problem by treating the wool to reduce or eliminate the "directional frictional effect". Shrink resistance can be achieved by making use of three basic approaches:-

1. Scale masking or surface coating;

2. Chemical or enzymic modification of the fibre surface.

3. Formation of inter-fibre bonds in the fabric to restrict movement of the fibres during laundering.

Chemical modification has been achieved in the past using a variety of processes but the most popular process relies upon chlorination. In particular it is well known to pass a fabric through a fluid including chlorine and subsequently to apply to the chlorinated fabric a shrink proofing polymer. This approach is very effective and economic but as it is a "wet" finishing treatment some form of effluent processing is required. It is becoming highly undesirable to have to dispose of absorbable organohalogens into the water supply and thus the traditional chlorination route is becoming less and less acceptable.

Corona discharge is a well known and widely used alternative to chlorination tor achieving shrink resistance. This process involves the bombardment of the fabπc surface with high energy electrons which are of sufficient energy to break covalent bonds in the fibres. In addition, collision between electrons and components of the air results in the formation of ozone and nitrogen oxide. Subsequent reaction between tree valent species on the fibre surface and the corona atmosphere leads to the formation of a

polar surface encouraging wetting and adhesion of subsequently applied polymer surface treatments. Amino acid analysis of cuticular protein indicates the formation of cysteic acid. Corona treatment has been shown to improve shrink resistance, yarn tensile properties, spinnability and wettabilitv. and treated fabrics or yarns exhibit superior dyeing properties. Improvements in shrink resistance and spinnability have been attributed to an increase in fibre friction.

Thus electrical discharge does provide an alternative to conventional chlorination but unfortunately is economically unattractive as the process is relatively slow, reducing the maximum rate of production of treated fabric, and in addition cannot successfully treat fibres within bulky fabrics, e.g. wool top.

In 1946, Hudson and Alexander demonstrated that gaseous fluorination could be used to impart shrink resistance to wool. Subsequently a reference was made to their work in the general text book "RF Hudson and P Alexander, "Wool: Its Chemistry and Physics", Pub. Chapman and Hall, London, Sec. Ed., (1963)". The treatment times suggested by this work, however, indicated that a fabric to be treated had to be resident within a chamber containing fluorine gas for long periods, for example 20 minutes. Thus, fabric was treated in batches and continuous treatment of fabric was not possible. In addition, high concentrations of fluorine gas were required, for example 20% fluorine. Finally, it was stated that the wool had to be pre-dried before treatment. These requirements, particularly the required residence times and the required pre-drying, make it completely uneconomic to rely upon fluorination as described in the published documents.

It is an objective of the present invention to obviate or mitigate the problems outlined above

According to the present invention, there is provided a method for pre-treating a fabric incorporating fibres of keratin to impart shπnk-resistance to the fabric, wherein the fabric is passed continuous!) through an atmosphere containing fluorine gas

Thus, in contrast with the published fluorination method, fabric is passed continuousK through an atmosphere containing fluorine rather than being processed ^' batch-wise. This is made possible because of the realisation that good shrink resistance can be imparted by exposing a woollen fabπc to fluorine gas of relatively low

concentration for a relatively short period of time. For example the residence time of the fabric in the fluorine gas is preferably less than 60 seconds, for example less than 12 seconds. Good results have been achieved with residence times of less than 6 seconds, for example 4 seconds.

The atmosphere may contain 10% or less fluorine by volume, for example less than 5%. Good results have been achieved with an atmosphere containing 3% fluorine by volume.

The atmosphere may be a mixture of nitrogen and fluorine gases.

Preferably a polymer coating is applied to the fabric after fluorinisation to improve washability. The polymer is preferably an amino polysiloxane.

Embodiments of the present invention will now be described, by way of example, with reference to the following examples and the accompanying drawings in which:

Figures 1-3 are graphs of dye exhaustion against dyeing time for various dyes on wool fabric untreated and treated according to the present invention;

Figure 4 is a graph of total dye fixation efficiency against dyeing time for Lanasol Blue 3G dye on wool fabric untreated and treated according to the present invention; and

Figure 5 is a graph of dye exhaustion against dyeing time for Sandolan Milling Blue N-BL dye on wool fabric untreated and treated according to the present invention.

Tests were conducted using a 100% wool botany serge of 190 g/m\ Fabric shrinkage was assessed by taking fabric squares with a 20cm edge, marking the squares with reference points approximately 3cm from an edge, and then relaxing the fabric in water at a temperature below 40°C for 45 minutes. The wet distances between the points were measured and the resulting area calculated to give a measure of the initial area. Wash tests were carried out using a Wascator FOM 71 P machine with standard program 5 A and including 4g of detergent. Fabric shrinkage was determined after each wash cycle by measurement of the new fabric area and comparison of the new fabric area with the initial area.

The influence of the preparatory treatment on the mechanical properties of the fabric were assessed, both before and after an application ol polymer to be described

below using the Kawabata evaluation system for fabrics. The 20cm square samples were conditioned at 65% relative humidity and at 20°C prior to testing. Primary Hand Values (PHV) were calculated based on mens winter suiting. To provide comparative data, samples of fabric were not pretreated. Other samples were chlorinated in a conventional manner using the standard BASF method. In addition, corona treatments were carried out on ftirther samples at three levels of severity, that is 640 Wmin/m ² . 960 Wmin/m ^" and 1280 Wmin/m .

Samples of fabric were exposed to 3% fluorine in a nitrogen atmosphere. The level of fluorination was dependent on exposure time, that is the time taken for the sample to be pulled through a chamber filled with the 3% fluorine gas. At a sample speed of 1 metre per minute the sample was in contact with the fluorine environment for 60 seconds. This condition is referred to below as high fluorination level. At a fabric speed of 5 metres per minute, the contact time was 12 seconds (medium fluorination). At a fabric speed of 10 metres per minute, the contact time was 6 seconds (medium/low fluorination). At a fabric speed of 15 metres per minute the fabric was in contact with the fluorine for 4 seconds (low fluorination level).

The influence of all the above pre-treatments on the mechanical properties of the fabric are illustrated in Table 1 below. Both fluorination and corona pretreatments significantly increased shear and bending moments and overall fabric stiffness (P.HN. - oshi). This is consistent with previous research indicating an increase in fibre friction on exposure to corona discharge Increasing the severity of the corona treatment resulted in a concomitant deterioration in fabπc mechanical properties. However for the fluorine treated samples mechanical properties appeared independent of exposure time.

Table 2 below illustrates the effect of these pretreatments on shrinkage properties after 1. 3 and 5 5A wash cycles ( l x5A equivalent to 10 domestic wash cycles) Both corona and fiuoπnated treatments restricted fabπc shrinkage during washing In contrast to the corona treatment, where perhaps increased exposure improves wash performance, the behaviour of the fluoπnated samples appeared independent of treatment time. Whilst it is evident from Table 2 that all pretreatments reduce shrinkage, complete machine washability was not achieved. Samples were therefore treated with two commercial shπnkproofing polymers (of the type usualh

applied to chloπnated fabric) and their ensuing washing and mechanical properties assessed.

Table 3 below illustrates the effect of Basolan SW (a polyurethane) applied to the vaπous pretreated and control fabπcs on fabric shrinkage. Table 4 below indicates the implication of this treatment for fabric mechanical properties At the applied levels Basolan SW renders all pretreated fabπcs shπnk resistant. However, bending and shear properties and overall fabric stiffness increase severely.

The shrinkage results of Basolan MW (an ammo polysiloxane) applied at two concentrations are given in Table 5 below while Table 6 below indicates the implication of this treatment on fabric mechanical properties (at the higher application level). At the lower application levels, the fluoπnated fabπcs perform slightly better than equivalent corona pretreated fabrics. At higher application levels both corona and fluoπnated samples demonstrate excellent wash performance. Only the chlorinated fabric (and control) exhibit shrinkage. The mechanical properties of these samples were excellent.

Thus it can be concluded that:

Fluorination can be used as an alternative to both corona discharge and chlorination as a preparatory treatment for wool.

Fluorine treatment inhibits fabπc shrinkage during washing

Complete machine washabihty can be achieved by the application of a polymer (at low levels) with no impairment of fabπc handle

Given the short time for which fabric has to be resident in the fluoπne- containing gas. continuous treatment of a fabπc is possible in an economic manner

Investigations indicate that the descπbed procedures ιmpro\e the dyeabιht> pπntabihty and mechanical processing characteπstics of the fabπc

A test was conducted to establish the pπntabihty of fabπc treated in accordance with the present invention. Fluorination of wool fabπc results in improved wettabihn and therefore improved printing. Test showed that the of fluoπnated wool fabπc vastly improved with the reduction in wetting time from o\er 60 minutes for conventional chloπnated fabrics to 2 seconds for fabπc treated according to the present imention Wool fabπc was pπnted using a range of commercial d\ es following the manufacturer ^' s recommended procedures and the results are shown in Table 7 The

colour yield, K/S, for fluorinated wool is comparable to chlorinated wool and an obvious improvement on untreated wool.

Table 8 shows that fluorination improves whiteness of the fabric before and after steaming of the printed fabric in comparison to chlorinated wool. In pastel shades the brightness/whiteness of the uncoloured areas provides better colour contrast.

In dyeing tests it was established that modifying the surface of the wool fibre, through gaseous fluorination, improved the levelness of the final dyeing over the untreated wool. Figures 1.2 and 3 show the comparative rate of exhaustion for a range of dyes on untreated and fluorinated wool, the dyeing procedure as recommended by dye manufacturers. It will be seen that the rate of exhaustion is greatly improved.

Figure 4 shows that the level of dye fixation on fluorinated wool is greater than that on untreated wool. This has the advantages that the rate of fading of the fabric and the environmental damage caused by the washed off dye are both reduced.

Figure 5 shows the results of further tests performed to evaluate the effect of fluorination on lower temperature dyeings at 80-85 C. It was found again that the rate of exhaustion and levelness were much improved for the pretreated wool.

TABLE I the effect of fabric pretreatment on mechanical properties

TABLE 2 The effect of fabric pretreatment on fabπc shnnkage

TABLE 3 Influence of Basolan S W on Fabπc Shrinkage

SAMPLE % SHRINKAGE (no of wash cycles)

%owf I

Std non pretreated 1 3

Low Fluorination 0 0

Low Medium fluoπnarion 0

Medium Fluorination 0

High Fluoπnation 0 0

640 Wmιn/m ^: 0 1

960 Wmin'πr 0 0

1280 Wmin πr 0 0

Chlorinated 0

TABLE 4 Influence of Basolan SW on fabric mechanical propeπies

TABLE 5 Influence of Basolan MW on Fabric Shrinkage

TABLE 6 i nfluence of Basolan MW on fabπc mechanical propeπies

Table 7 Colour yields (K/S) of untreated and pretreated wool print _:

Dyes K/S u C

Milling

30g/kg Polar Red RLS (160%)

20 g/kg Polar Yellow 4G (160%)

20 g/kg Erionyl Red 3G

30g/kg Lanaset Blue 5G

Premetallised

1 ⁵ 9 g g Lanacron Red S-G 15.0 28.0 22.3

15 g/kg Irgalan Yellow 2GL KWL 15.8 24.7 24.7

15 g/kg Irgalan Navy Blue B KWL 15.7 29.3 22. ₁

Reactive

20 g/kg Lanasol Yellow 4G 8.3 20 9 17.8

20 g/kg Lanasol Red 6G 13.2 24 2 21.9

20 g/kg Lanasol Blue 3G 16.4 27 3 24.3

u Untreated wool c Chlorinated wool

Fluorinated wool

Table 8 Yellowness pretreated wool fabrics

B.P A.S .W

Untreated 22.8 25.3

Chlorinated 27.8 32.1

Fluorinated 25.6 27.2

B P Before printing

A S w After steaming and washing