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1. DESCRIPTION OF TECHNIQUES, METHODS AND EQUIPMENT


To achieve the best results, an appropriate pretreatment for all dye-classes is indispensable. The following stages are necessary:


1.) Cleaning of the fibre-material
  • singeing
  • shearing
  • pre-washing


2.) Stabilising, pre-fixation of the fabric
  • crabbing
  • baking


3.) increase of dye-affinity
  • Chlorination
  • bleaching
  • optical illumination


The most important process step is Chlorination, which has to be conducted very carefully. Thus arise the following advantages:

- higher dye-affinity: makeup and brilliance

- better printing properties

- better dimension stability: prevention of felting and shrinking

Chlorination will have to be replaced by print-pretreatment in the future, which does not pollute the wastewater with AOX.

Subsequently, the differences concerning process engineering, between the use of vinyl-sulfone-dyes and of acid and metal complex dyes shall be discussed. Vinyl-sulfone dyes do not pollute the waste water of print-washing with AOX, contrary to Chlorine-triazine reactive dyes. Both dye classes only differ in fixation time and an additional cationic after-treatment in the case of acid- and metal complex dyes. Even though the costs of wool printing are quite high altogether due to these complex processes, the main part of the costs remains with the actual printing procedure: pretreatment 15%; pattern preparation and stencil production 15%; colouration and production of the paste 20%; machine preparation, printing and drying 30%; fixation, washing and drying 10%; finishing 10%.

Standard printing pastes have the following composition:

Acid dye:

1.) colour solvent (thiodiglycole)

2.) urea (solution agent, moisture regulator, fibre moisture expansion)

3.) swelling (kern flour, Guar)

4.) acid donor (sal ammoniac, organic acid)

During solution of acid- and metal complex dyes it is often necessary to use so-called “colour solvents” such as thiodiglycole, because some dyes are not easily soluble. Furthermore, it is necessary to use hot water for solution. Vinyl-sulfone dyes have many advantages in this field, because they do not need certain dye solvents or hot water, due to their high solubility as powder granules. Urea (hydrophobic) serves as a solution agent for both acid- and metal-complex- and vinyl-sulfone-dyes in the printing paste. In addition, it promotes water absorption and works as a fibre moisture expansion agent during steaming. With acid- and metal-complex dyes, acid resistant swelling agents are applied. These are for example kern flour or Guar-derivates. When working with vinyl-sulfone dyes, alginate swelling agents can be used as well, because there is no addition of acid to the paste. The fixation of acid- and metal complex dyes is carried out in acid medium. Either acid donors such as ammonium sulphate or organic acids such as citric acid are added to the printing paste. Vinyl-sulfone dyes are fixed using sodium-acetate as alkali donor. When using sodium-acetate, one can achieve good paste durability. In order to protect the reactive dye against reductive influences, sodium-m-nitrobenzenesulfate is added to the paste. For both, acid- and metal complex dyes and vinyl-sulfone dyes, saturated steam is needed for fixation. The print should not proceed to steaming in an over-dryed state; as an alternative, it can be moisturised by spraying before entering the steamer. Concerning the necessary fixation times, vinyl-sulfone dyes can offer some advantages compared to acid- and metal-complex dyes. Depending on the quality of the saturated steam, the fixation is carried out within 10-20 min, whereas acid- and metal complex dyes are steamed for 45-60 min. With vinyl-sulfone continuous steaming is possible. Furthermore the following advantages result:

- reduction of steam consumption

- higher level of utilisation of the continuous steamer

When using acid- and metal complex dyes, the maximum temperature during print-after-washing is 40°C, because on the one hand, there is the risk that an increasing amount of ionic adhered dyestuff dissolutes, which can lead to un-welcome colour illumination, and on the other hand there is an increasing danger of stock-fouling due to the dissoluted dyestuff. When using vinyl-sulfone dyestuff, the temperature is increased up to 70-80°C after the first warm- and cold-flushing, in order to remove the small amount of non-reactively fixed vinyl-sulfone dye from the fibre and to ensure high resistances. Acid- and metal complex dyes require certain auxiliaries to protect the white-stock during the first flushing. In order to increase the resistances, usually a cationic after-treatment follows. Thus an increase of resistance properties of about one degree is achieved. A disadvantage is the fact that cation-active after-treatment agents can decrease the resistance against light (especially with light tones). The cationic fibre surface is highly affine to dissolved dyestuff, which is left in the liquid (etching-effect). In addition, the cationic after-treatment does not achieve lasting results: the complex gets more and more instable with every wash. When cationic after-treatment is applied together with a diluent, the products have to be adjusted. Vinyl-sulfone dyes only need 1-2 g/l ammonia conc. to inactivate the non-fixed reactive dyestuff and to protect the white-stock to achieve the required resistances.


Stages of direct printing on wool.jpg

Source: “Lexikon der Textilveredlung” 1995


2. NEW TECHNOLOGIES


a) Changes in the process

No information is available.

b) Changes in the heat supply system

No information is available.

c) Changes in the energy distribution system

No information is available.


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