Vat Dye (Full PDF)

1. Vat Dye
The word vat means, ‘Vessel’. The dyes take their
name from vatting. The vat dyes are naturally
coloring matter and kept in wooden vat and make
solubilise vat dyes by the process of farmantation –
so it is called vat dyes. They are applied in a special
kind of a dyebath in which the dye is reduced to a
soluble form by means of a strong reducing agent,
such as hydrosulphite.

2. Classification of Vat Dyes
(a) Indigo, including both natural and Synthetic
(b) Thio-indigo dyes
(c) Indigo derivatives
(d) Anthraquinone derivatives
(e) Carbazol derivatives

3. Application of Vat Dye
Stages in Dying :
(i) Vatting
(ii) Dying
(iii) Oxidation

4. Properties of vat dye :
• Vat dye is water insoluble and can’t be applied directly
on textile material.
• Mainly use for cellulose fibre dyeing but in protein fibre
dyeing ph should be controlled.
• Rubbing fastness is not good.
• Various shade is found.
• Dyeing process is difficult.
• Costly.
• washing fastness of vat dye is very good with rating 4-5.

5. Principle of vat dye
Vatting : In this step insoluble dyes gone into a substantative from of
dyes i.e. Na salt of leuco form.
Dyeing : The absorption and diffusion of vat dyes in the fibre are obtain here
when NaHSO4 , NaOH and temperature are property maintained in time
of dyeing. Na salt at adequate rate of electrolyte is added to increase the
exhaustion.
Re-Oxidation of vat dyes : In which the soluble form dye is reconverted into
insoluble form by airing or by chemical oxidation of at a temperature 50-
70 degree.
• After treatment : Dyed material is subjected to boiling soap to get proper
tone by aggregation of dyes and also improve rubbing fastness by
removing surface deposited dye particles.

6. Solubilized vat dyes
• Solubilized vat dye is a disulphonic ester of leuco
compound by causing it in pyridine. It is done by reacting
in souble dyes with chlorosulphonic acid.
• This leuco compound is converted into Na salt of ester by
reacting with NaOH.
• This proved to be stable, soluble in water, substantative
to cellulose and capable of being oxidized in fibre.

7. Theory of Vat Dyeing
The insoluble vat dye has been uniformly applied to the fabric
surface, usually with the aid of special dispersing agents
(detergents), it can be solubilized by reaction with a reducing
agent, e.g., sodium hydrosulfite ("hydros", Na2S2O4) in dilute
NaOH. Once it has been converted to its soluble (LEUCO)
form, the vat dye can penetrate into the cotton fibers. After
adequate time for penetration to occur, the fabric is
withdrawn from the bath and oxidized by air or an oxidizing
agent such as sodium perborate or hydrogen peroxide.