5/20/13

Direct dyes

Direct dyes are very conventional dyes. It is not used any more for industrial dyeing. Direct dye is one kind of anionic dye and having substantively for all types of cellulosic fibre like cotton, jute, hemp. They have strong affinity to the fibre which can be applied directly on the fibre surface and do not need any assistance.

Direct dye Also known as direct, substantive, benzidine or salt dyes. Group classification for dye which exhaust substantively on cellulosic fibres, cotton, viscose, cupro and high wet modulus fibres, especially in the presence of salt. Chemically they are polyazo or sulphonated disazo dye.It contains sulphonic acid group that’s why is has good solubility in water. The dye molecule contains a complex bond metal atom that’s why they have high light fastness properties. The color fastness is poor but it is easy to improve by dyeing after treatment with metal salts (Õ Aftercoppering dyes).

Benefit of Direct dye:

Direct dyes represent the main class of dyes for cellulosic fibres in terms of usage:
- Specially selected direct dyes are available for streaky dyeing viscose qualities.
- They are simple to apply.
- Economical or cost effective than any other dyes.
- It has generally good leveling properties
- A wide range of color variation and shade.
- Special types contain better wet fastness. It is possible to couple with readily soluble diazo compound by after treatment.
-Direct dyeing on cellulosic fibres exhibit considerable differences in colour fastness to light which ranges between 1 and 7–8.

Different direct dyes can therefore be used for articles which are only required to have low light fastness as well as goods with high light fastness. In general, direct dyes have poor wet fastness properties and dyeing must be after treated to improve their serviceability.

Properties of direct dye:
- Direct dye has sodium salt of sulphonic acid or carboxylic acid group. So it easily dissolve in water.
- Cheap comparative
- It has strong affinity to cellulose fibre. It is possible to dye protein fibre.
- Easily disperse in water and diffusible in to fibre.
- Wash fastness is not good. The range vary from 2 to 3
- It is possible to use in neutral and alkaline medium
- The dye is common in the practical point of view.
- The tin tropical power of this dye is very good.

Some trade and brand name of direct dyes
Benzo, Benzoform       - F.Bayer (Germany)
Coprantine                  - Ciba-geigy (Switzerland)
Solphenyl                    - Ciba-geigy (Switzerland)
Chlorazol Durazol        - Impartial Chemical Industry (ICI)
Solar                          - Sandoz A.G (Switzerland)

There are some related posts to get deep knowledge of direct dye:

# Classification of Direct dye
# How to dye with direct dyes
# Dyeing aftertreatment of direct dye
# Chemistry of dyeing related to direct dye
# Dyeing auxiliaries required for direct dye

Wish you good luck-------------------------------------------
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