GB2314568A - Fibre finishing treatment - Google Patents

Abstract

Lyocell fabric may be contacted with an aqueous solution of an acid, preferably a mineral acid, in a jet or similar dyeing machine, prior to dyeing in the same machine. This process permits the ready removal of undesirable primary fibrils, and the formation of desirable secondary fibrillation and a peachskin finish on the fabric.

Description

FABRIC FINISHING TREATMENT This invention relates to methods of dyeing and finishing lyocell fabrics, that is to say fabrics which comprise lyocell fibres, either alone or in blend with one or more other types of fibre.

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 fibres such as the viscose process, for example reduced environmental emissions.

Lyocell fibres are known to be prone to fibrillation.

Fibrillation is a phenomemon 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 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. Such fabrics dye uniformly, and the presence of the secondary fibrils confers an attractive visual appearance and handle, often called a peachskin finish, on the fabric.

It is known that fibrils can be removed from lyocell fabrics by conventional resin-finishing treatments, for example using an N-methylol resin such as dihydroxydimethylolethyleneurea (DHDMEU). Such treatments, however, serve to remove both primary and secondary fibrils and tend to suppress all subsequent fibrillation.

As described for example in the aforementioned paper by Breier, it is known that such a peachskin finish can be obtained by wet processing to induce primary fibrillation, 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. It is an object of the invention to provide an alternative and convenient way of creating a peachskin finish in lyocell fabric.

According to the present invention there is provided a method of finishing lyocell fabric, wherein the fabric is dyed under conventional conditions on a machine selected from the group consisting of a jet-dyeing machine, a garment drum dyeing machine, a garment drum washing machine and a wet-tumbling machine, characterised in that prior to the dyeing step the fabric is processed in the said machine in contact with an aqueous solution of an acid. The fabric is preferably a woven fabric but may be a knitted fabric. The fabric may be processed in rope or garment form.

Jet-dyeing machines are known and are the preferred type of machine for treatment of fabric in rope form according to the method of the invention. In such machines, a continuous loop of fabric is passed through a jet nozzle and a bath of treatment liquor. The fabric is impelled by a jet of liquid or air so that it circulates through (is processed in) the bath for a desired treatment time.

Garment drum washing and dyeing machines are known. In such machines the fabric (generally in garment form) is contained within a perforated drum adapted to rotate in a bath of treatment liquid. A commercial example of a wet tumbling machine is a Biancalani Airo 1000 (Trade Mark).

The acid is preferably a strong mineral acid, such as hydrochloric acid or particularly sulphuric acid. The concentration of acid in the solution is often in the range from 0.5 to 15, preferably from 1 to 5, grams per litre. The temperature of the acid solution may range from ambient to the boil; elevated temperatures in the range from 60 to 950C may be preferred. The circulation time through the acid solution is preferably in the range from 30 to 120 minutes.

The method of the invention preferably additionally includes the step of rinsing the fabric with water after the acid-treatment step and before the dyeing step.

The dyeing step is carried out in conventional manner.

The dyestuff may be any suitable dyestuff for cellulose, such as a direct or reactive dyestuff. After dyeing, the fabric may in conventional manner be washed free of excess dyestuff, treated with a softening agent such as a silicone softener, and dried.

The liquors used in the various steps of the method of the invention may contain known processing agents such as anti-creasing agents and lubricants.

The desired secondary fibrillation and peachskin finish may be induced during the rinsing, dyeing, washing or drying steps. Conventional commercial-scale jet-dyeing machines generally operate with sufficient vigour to induce fibrillation. Subsequent wet-processing, for example in a more vigorous jet-processing machine or by conventional laundering, of a fabric treated by the method of the invention may also serve to induce secondary fibrillation and a peachskin finish, particularly if the machine used in the method of the invention is gentle in its operation (as may be the case with small-scale machines). It has been observed that further primary fibrillation may take place during the first few laundering cycles, but that the primary fibrils thus formed are removed during subsequent cycles.

Accordingly, fabric treated by the method of the invention possesses the desirable secondary fibrils without undesirable primary fibrils. In a preferred embodiment of the invention, secondary fibrillation is induced by tumble drying and/or dry beating at the conclusion of the finishing process.

The invention is illustrated by the following Examples, in which parts and proportions are by weight unless otherwise specified: Example 1 A woven lyocell fabric (200 g/sq.m, twill) was prepared in open width in conventional manner. A length of this fabric (30 m) was loaded into a laboratory-scale jet dyeing machine (ROACHES laboratory jet, Trade Mark of Roaches Engineering). Its visual appearance was hairy but not fibrillated. During the following treatments the machine was charged with 300 1 of the relevant treatment liquor (liquor-to-goods ratio 10:1). The fabric was first circulated through the machine in aqueous sulphuric acid solution (5 g/l) containing the crease-resisting lubricant Perilan VF (4 g/l) (Trade Mark of Dr Petry GmbH) for 60 minutes at 800C. The solution was then discarded, and the fabric was rinsed with water. The visual appearance of the fabric remained unchanged. The fabric was then dyed by circulating it through the machine in an aqueous solution containing the reactive dyestuff Procion Blue HE-RD (3% by weight) (Trade Mark of ICI plc), Glaubers salt (55 g/l), soda ash (20 g/l) and Perilan VF (4 g/l) for 60 minutes at 800C. Excess reactive dyestuff was removed from the fabric by washing with water containing Perilan VF (4 g/l) in conventional manner.

The dyed fabric exhibited a low level of fibrillation.

Samples of fabric were laundered seven times using a conventional domestic washing machine and tumble dryer. Long primary fibrils were generated and subsequently removed by this process. Simultaneously, secondary fibrillation occurred, thereby providing the fabric with an attractive peachskin finish.

Example 2 A sample of the fabric as used in Example 1 was prepared as before. A length of this fabric (400 m) was loaded into a Gaston County Futura (Trade Mark) jet-dyeing machine (fully flooded type) containing water (1600 1) and Perilan VF (Trade Mark) (4 g/l). The fabric was circulated through the machine, sulphuric acid (1 g/l) was added, the temperature was raised to 950C, and this temperature was maintained for 60 minutes. The fabric was then rinsed, dyed in conventional manner with reactive dyes and rinsed again.

The fabric was then loaded into a Biancalani Airo 1000 (Trade Mark) (a high-speed tumbling machine adapted to both wet and dry treatments). The fabric was circulated through the machine in a solution of Sandoperm MEJ (Trade Mark) (3% by weight on fabric) (a softening agent for cellulosic fabrics) at 400C for 20 minutes. Excess solution was drained from the machine, after which the fabric was heated and tumbled at 1400C until dry, after which it was beaten at high speed (up to 1000 m/min) until primary fibrillation had been removed and secondary fibrillation induced, resulting in a desirable peachskin handle.

Claims (1)

1. CLAIM

   A method of finishing lyocell fabric, wherein the fabric is dyed under conventional conditions on a machine selected from the group consisting of a jet-dyeing machine, a garment drum dyeing machine, a garment drum washing machine and a wet-tumbling machine, characterised in that prior to the dyeing step the fabric is processed in the said machine in contact with an aqueous solution of an acid.