Washing off dyed textile material

The present invention relates to the technical field of dyeing with reactive dyes.

Reactive dyes are widely used for dyeing cellulosic fibers, i.e., particularly cotton. In addition to the chromophore, they contain reactive groups, known as reactive anchors, which in the course of dyeing from an aqueous liquor under alkaline conditions combine with the hydroxyl groups of the cellulose to form covalent bonds. It is thus possible to obtain dyeings which have particularly good wetfastnesses. However, in dyeing, in addition to the desired reaction of the reactive group with the cellulose there is also a reaction taking place with water, causing the dye to become hydrolyzed. The hydrolyzed dye is no longer able to react with the cellulose and remains on the fiber in unattached form.

This hydrolyzed dye has to be removed as completely as possible after the dyeing step, since it would otherwise have an adverse effect on the wetfastnesses of the dyeing. For this purpose, the dyed textile material is treated in costly, inconvenient and time-intensive rinsing steps at temperatures of up to 95°C, in the course of which appreciable amounts of water and energy are consumed.

For example, circular knits exhaust-dyed in jet machines are generally washed off batchwise. In this art, the textile material, gathered into a rope on a lot- or piecewise basis, is propelled by a jet nozzle either with rinse liquor, with air/steam or with a combination of the two media and moves into a scray.

The washoff operation itself follows directly on from the dyeing step and always takes the form of initially discharging the dyeing liquor, then making good the lost liquor by replenishing with fresh water, heating if necessary, propelling the fabric rope in this treatment liquor for a defined period by means of the technique described above, discharging again, and repeating this operation until the rinse water is colorless and the fabric no longer releases hydrolyzed dye. Depending on the reactive group chemistry of the dyes used and the depth of shade, up to 6 rinse baths at various temperatures are generally needed, as the following schedule for washing off heterocyclic reactive anchor systems illustrates:

The individual treatment baths may optionally be additionally mixed with auxiliary chemicals for enhanced effects and efficiency.

Rinse operations are normally carried out in long liquor, i.e., a mass of water which is equal to 8-20 times the weight of fabric (liquor ratio = mass of water to weight of fabric). When computing total water consumption, it must be borne in mind that the fabric rope retains about 300% of its own weight of treatment liquor when the liquor is discharged from the machine. Hence a six-bath rinse operation in a liquor ratio of 10:1 requires about 42 I of water per/kg of dyed textile material.

EP 0 088 273 A2 for example discloses an aftertreatment process for reactive dyeings which consists of a sequence of alternating aqueous rinse and liquorless hot treatment operations. Rinse and liquorless hot treatment operations each need to be carried out 2 to 8 times to obtain an acceptable result. The process thus has appreciable water, energy and time requirements and does not meet present-day requirements in terms of ecology and economy.

A further process for aftertreating reactive dyeings on textile fiber materials wherein alkali metal silicates and metal aluminosilicates are used is known from EP 0 894 890 A1. It is thus clear that there is an urgent need for a rinsing process which is more economical, i.e., more particularly consumes less water and less energy, but does yield adequate fastness results.

It has now been found, surprisingly and contrary to a view very common among those skilled in the art, that two rinsing steps are sufficient provided a dwelling step is carried out in-between.

The present invention provides a process for washing off reactive-dyed textile material, which process consists of the sequence

(i) first rinsing step,

(ii) dwelling step, and

(ii) second rinsing step, which sequence is not repeated.

The process of the present invention generally immediately follows the dyeing step. Preferably, the first and second rinsing steps are carried out at a temperature of 70 to 95°C and each takes from 5 to 15 minutes, particularly advantageously 9 to 11 minutes. The first and second rinsing steps can be carried out in a single rinse bath or in two or more successive rinse baths. It is preferred to carry out the first rinsing step in two successive rinse baths and the second rinsing step in a single rinse bath.

During the dwelling step, the temperature is preferably maintained at 70 to 100 ⁰ C. When sheetlike textile material is treated, it is preferably agitated, for example with air or with steam, during the dwelling step. Apart from the optional maintenance of the temperature mentioned and the optional agitation of the textile material, no measures whatsoever are taken during the dwelling step. The dwelling step preferably takes from 10 to 15 minutes.

It is preferable for the process of the present invention to be carried out with sheetlike textile material or materials. In one preferred embodiment of the process according to the present invention, a textile fabric rope batch-dyed in a jet dyeing machine is rinsed by discharging the dyeing liquor and in the jet transportation apparatus rinsing once at 70 - 95°C for 9 to 11 minutes, then circulating the fabric at 70 - 100 ⁰ C and a liquor ratio of 150 - 300% via air/steam propulsion and then finally rinsing once more at 70 - 95°C for 9 to 11 minutes.

Particularly preferred assemblies in which this process can be carried out are for example the machines described in EP 0 310 013 A1 , EP 1 024 220 A2 and EP 1 526 205 A2, and also drum-type washing machines with tumbler function. In a further preferred embodiment of the process according to the present invention, a continuously dyed textile material is led after dyeing into a continuous washing assembly where the first rinsing step takes place, then into a suitable apparatus for the dwelling step and finally into a further continuous washing assembly where the second rinsing step takes place.

Suitable continuous washing assemblies are known to a person skilled in the art. Apparatuses suitable for the dwelling step are in particular steamers, particularly in the manner of the E-Control steamer, J-boxes, roller bed steamers, festoon loop steamers or tumblers. These apparatuses are known to a person skilled in the art and are customarily used in the textile industry.

The process of the present invention can be used to wash off in particular textile materials composed of natural or modified hydroxyl-containing or natural, modified or synthetic carboxamido-containing fiber materials. Cotton is a particularly preferred textile material. The textile material is preferably in the form of circular knits, in particular circular knits and wovens.

Compared with existing processes, the process of the present invention requires appreciably less water and energy and, what is more, takes significantly less time. It is thus distinctly superior both ecologically and economically. Example 1

A customary jet dyeing machine with air propulsion is used to dye a 180 g/m ² circular knit by an isothermal process in a liquor ratio of 8:1 with 1.5% of C.I. Reactive Red 198 based on the fabric weight for 60 min.

After dyeing, the dyeing liquor is discharged and the machine is refilled with fresh water to a liquor ratio of 8:1. After circulating at 80 ⁰ C for 10 min, the liquor is again discharged down to a fabric residual moisture content of about 250 - 300%.

During the discharging of the liquor, the fabric rope is further circulated for 15 min via purely air propulsion with air preheated to 70 ⁰ C and in the process further freed of excess rinsing liquor at a wipe-off device.

This is followed by refilling with water once more to a liquor ratio of 8:1 and circulating at 80°C for 10 min.

After discharging of the rinse liquor and drying, the material obtained corresponds in its fastness level to a material conventionally washed off with 7 baths.

Example 2

A conventional jet dyeing machine with air propulsion is used to dye a 140 g/m ² woven fabric by an isothermal process in a liquor ratio of 8:1 with 2% of C.I. Reactive Yellow 145 based on the fabric weight for 60 min.

After dyeing, the dyeing liquor is discharged and the machine is refilled with fresh water up to a liquor ratio of 8:1. The liquor is circulated at 80 ⁰ C for 10 min and then discharged again.

The fabric is removed from the machine, dewatered by passing it through a pad- mangle and presented to a festoon loop steamer for thermal treatment. Following a dwell time of 10 min at 80°C, the fabric additionally passes through two continuous washing compartments filled with water at 80°C. The fabric is subsequently squeezed off, plaited down and dried. The fastness level corresponds to that of a fabric continuously washed off by conventional methods.