Dye | Classification of Dye According to Application

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Dye:
By definition dyes can be said to be coloured, ionizing and aromatic organic compounds which shows an affinity towards the substrate to which it is being applied. It is generally applied in a solution that is aqueous. Dyes may also require a mordant to better the fastness of the dye on the material on which it is applied. The dyes were obtained from animal, vegetable or mineral origin with no or very little processing. By far the greatest source of dyes has been from the plant kingdom, notably roots, berries, bark, leaves and wood, but only a few have ever been used on a commercial scale.
Different dyes
Different dyes
Classification of Dye According to Application
  1. Reactive Dyes
  2. Acid Dyes
  3. Premetallized Dyes
  4. Direct Dyes
  5. Azoic (Napthol) Dyes
  6. Disperse Dyes
  7. Vat Dyes
  8. Sulfur Dyes
  9. Basic Dyes
1. REACTIVE DYES
Reactive dyes are the most recent of dyes. These are the most popular in the world among fibre and fabric artists, used at first only by surface designers, but recently by weavers as well. There are now reactive dyes for a wide range of fibres, e.g. cotton (PROCION), silk and wool (PROCILAN). The dye actually reacts with the fibre molecules to form colour and is, as a result, extremely fast to both light and washing. There are hot and cold water reactive dyes, in fact there is a dye for almost every need. They can be most successfully used for silk painting, with a much better colour fastness than the traditional basic dyes, and are already used by batik artists. we can identify a reactive dye by the alkali used to set off the fixation process, which requires time to take place (silk and wool reactives uses acetic acid). Assistants used are salt, soda ash and resist salt, and sometimes bicarbonate of soda and urea. Reactive dyes are equally suited to screen printing polychromatic printing, fabric painting yarn and piece dyeing.

2. ACID DYES
These are acidified basic dyes, intended for use on protein fibres but can be used on nylon and acrylics. They have a fair light fastness but poor wash fastness

3. PREMETALLIZED DYES
These are an acid dyes with the addition of one or two molecules of chromium. The dyesgive mutetonings, not unlike those of natural dyes. They are the synthetic dyes mostly used by weavers who dye their own yarns.

4. DIRECT DYES
These substantive dyes colour cellulose fibres directly in a hot dyebath without a mordant, to give bright colours. They are not very fast to light or to washing. Direct dyes are generally any dyes which use salt as their only fixative, e.g. Dylon dyes (not to be confused with reactive dyes, which use salt plus other chemicals).

5. AZOIC (NAPHTHOL) DYES

These are another sort of direct dye, but ones that are extremely fast to washing, bleach and light. They are intended for cellulose fibres and can be used successfully on protein fibres, although the colours are different. These dyes are widely used all over Asia and Australia for batik and direct application. They can be used to give interesting texture colour effects on fabric, thread or paper. Their use for straight silk painting is minimal because of the difficulty in achieving evenness of painted colour.

6. DISPERSE DYES

Originally developed for acetate fibres, these are now the major dyes for synthetics. They are not soluble in water, but in the actual fibres themselves. They require a carrier to swell the fibres so that the finely ground particles can penetrate. They are dyed hot, like direct dyes, but do not use salt. Disperse dyes are widely used for heat transfer printing (Polysol). Dye is printed or painted onto paper and heat pressed onto fabric. Prints have excellent light and wash fastness and strong bright colours. Their major disadvantage is that only synthetic fabrics can be used.

7. VAT DYES
Vat dyes are the fastest for cellulose fibres. The dye is made soluble with alkali, put in a 'vat' with a reducing agent, usually sodium hydrosulphite, which removes all oxygen from the liquid, and the fabric is dyed, then oxidized in the air to achieve the true colour. Synthetic indigo is a characteristic vat dye, but there are many colours available  
 
8. BASIC DYES
The colours are very bright, but not very fast to light, washing, perspiration. Fastness is improved if they are given an after-treatment or steaming, e.g. French Silk dyes are basic dyes and should be steamed to fix.

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