The document discusses vat dyes, which are water-insoluble dyes that must be chemically modified before use. It provides details on: - The history and development of vat dyes, with the original being indigo obtained from plants. - The chemical process of reducing vat dyes with sodium dithionite to create water-soluble leuco compounds that can be applied to fabrics. - The dyeing process, which involves vatting, dyeing the fabric in alkaline conditions, oxidizing the dye, and soaping to improve fastness. - Examples of common vat dyes like indanthrones and flavanthrones and their properties. - The excellent fastness to light

1. Tonmoy
Textile 36 Batch
University of south asia

2. The vat dye is one of the most significant textile dye which was
invented in the 20th century. Vat dyes are water insoluble colored
compound and they can’t be applied on cotton or other fibers without
modification. Vat dyes are processed with reducing agent to convert it
into leuco compound which soluble in water in the presence of alkali.
In ancient time one kind of container vessel named vat was used for
the reduction of vat dyes, for this vat is so called.
The original vat dye is indigo, once obtained from plants but now
produced synthetically.
VAT DYE

3. Typical Examples of vat dyes.
Indanthrones:
Blue in color.
Possibility to over
reduction
and oxidation.
Excellent fastness.
Moderate cost.
Flavanthrones:
Yellow in color.
Good light fastness.
Slow oxidation.
Tendency to photochromism.

4. Pyranthrones:
Orange in color.
Good leveling
property.
High color strength.
Moderate cost.
Inferior light fastness.
Isodibenzanthrones:
Violet in color.
High color strength.
Good fastness to
bleaching.

5.  The vat dyes are water insoluble colored compounds.
 They can not be used for dyeing without modification.
 Vat dyes are mainly used for dyeing cellulosic fibers.
 Applied in alkaline medium.
 Dyeing process is difficult.
 Various shades are found.
 Washing fastness is excellent.
 All dyes contain two or more keto (C=O) group.
 Light fastness is very good.
 Relatively dull shade is found after soaping.
 Vat dye is very expensive compared with other dyes.

6. Because of the use of caustic soda, and the very high pH
of the dye bath in the dyeing process, wool cannot be
dyed using vat dyestuffs. Wool is soluble in caustic
soda solutions. It is possible to dye wool at room
temperatures with indigo (vat blue 1) and other low
substantive vat dyes using soda ash as the alkali source
with very little strength loss.

7. Chemical reactions such
as oxidation, reduction, pH control are often necessary;
even the dissolution process necessitates measuring out
appropriate quantities of caustic soda and sodium
hydrosulphite in order to achieve reduction. The dye is
soluble only in its reduced (oxygen -free) form. The
fiber is immersed repeatedly in this oxygen-free dye
bath, then exposed to the air, whereupon the water-
soluble reduced form changes color as oxygen turns it
to the water-insoluble form. For these reasons, vat dyes
are less suitable than fiber-reactive dyes for amateur
use.

8. Trade Name Manufacturer Country
Algosol General dye stuff corporation. U.S.A.
Anthrasol Hoechst Germany
Indigosol Sandoz Switzerland
Indanthrene National Chemical Ind. India
Anthraquinone ICI UK
Cibanone Ciba Switzerland

9. Vat dyes may be classified based on their chemical
constitution or based on their method of application.
According to chemical structure vat dyes are of two
types.
(a) Indigoid (b) Anthraquinoniod

10. and –NH−,−S− groups as the auxochromoes.
In the Anthraquinonoid vat dyes one or more quinone (>C=O) groups act as chromophores and
groups such as amino(−NH2), hydroxy (−OH), alkylamino (−NHR or −NR2), alkoxy (−OR) etc.
are the auxochromes. The Anthraquinonoids give colored leuco compounds which are soluble
only in strong alkalis.

11. 1. Indanthrane Kalt (IK):
Low alkali concentration is required.
Low vatting temperature is required; i.e. 400C.
Low dyeing temperature is required; i.e. 200C.
Sufficient salt is required.
2. Indanthrane Worm (IW):
Moderate alkali concentration is required.
Moderate vatting temperature is required; i.e. 500C.
Moderate dyeing temperature is required; i.e. 500C.
A small amount of salt required for complete exhaustion.
3. Indanthrane Normal:
 By using no electrolyte well exhaustion can be achieved.
High alkali concentration is required.
High vatting temperature is required (50-600C).
High dyeing temperature is required
(dyeing starts at 300C occurs at 600C).
Retarding agent is required.

12. Dyeing with vat dye involves four steps:
 Vatting.
Dyeing.
Oxidation.
Soaping.

13. The process by which insoluble vat dye is converted into soluble
leuco compound is called vatting.
Vat dyes characteristically require a reducing agent to solubilize
them.
The most common reducing agent is sodium dithionite (Na2S2O4),
which converts the dye to its "leuco" form that is soluble.

14. (1) Vatting proceeds almost twice as rapidly with an increase in
temperature of 10°C.
(2) Above pH 12 the rate of vatting is not dependent on the hydroxide
ion concentration.
(3) The higher the concentration of reducing agent and dye, the more
rapidly reduction takes place.
(4) The rate of vatting is dependent on the crystalline form and particle
size of the dye.

15. Dyeing :
The soluble Sodium salt of the leuco vat is absorbed by the textile material
from an alkaline reducing medium.
Oxidation :
The soluble Sodium salt of the leuco vat absorbed by the fiber is
reconverted into the original insoluble dye by atmospheric oxygen or by a
chemical oxidizing treatment. Chemical oxidation is carried out by
hydrogen peroxide, sodium perborate or sodium m-nitrobenzenesulphonate.
Soaping :
After oxidation the dyed materials are treated at the boil in an aqueous
solution of a surfactant, an operation generally referred to as ‘soaping’. This
process is very important in vat dyeing. Loose dye absorbed by fiber is
removed and the properties of the dyeing are changed significantly, e.g. the
fastness to light and washing may be improved and there may be a change
in color.

16. Vat dyes provide outstanding color & washing fastness.
It has excellent fastness to mercerizing, soda boiling, chlorite &
hypochlorite bleaching.
Light fastness is good. Certain combination of yellow with blue or
green dyes there can be adverse action on exposure to light, resulting
in the blue or green component fading more rapidly than anticipated.
This effect is commonly referred to as catalytic fading.
Long time exposure to light, degradation of the cellulosic fiber can
occur more rapidly, leading to the formation of oxycellulose.

17. Reducing agent:
Sodium dithionite, generally referred to as hydrosulphite or
hydros reacts with insoluble vat dye and converts it into
insoluble acidic leuco compound.
Sodium hydroxide:
It is used to form soluble sodium salt of leuco vat by
neutralizing the acidic leuco compound.

18. Dispersing agent:
The addition of supplementary dispersing agents prevents the
aggregation of undissolved particles of vat dye. For little dye
particle size the vatting will be faster. So it is cleverer to keep
the dye particles small in size by using dispersing agent.
Salt :
Salts, e.g. sodium sulphate or chloride, can increase the
substantivity of the leuco dye for the fibre.
Soap:
Soap or detergent removes the loose dye particles absorbed by
dyed goods & enhance the fastness properties (e.g. washing
fastness, light fastness) of the dyed goods.

19. 1. Effect of atmospheric oxygen:-
Oxidation of hydrosulphite by the atmospheric oxygen leads to the production of acidic products which
partially neutralize the alkali.
2. Effect of pH:
If the alkali contents falls below certain level the leuco vat dye separates as a precipitate. Excess use of
sodium hydroxide in vatting bath it is necessary to ensure the stability of the vatted solution.
3. Over oxidation:
Over Oxidation must be avoided, because it may attack the developed dye.
4. Stability of Alkaline solution:
The stability of alkaline solution of reducing agents may decrease for the following reasons:
 Due to the increased temperature.
 Longer time exposure to air.
 Greater agitation.
 Lower concentration of reducing agent.

20. Stripping of vat dye:
Dyed material is treated with
sodium hydroxide and hydros resulting the dyed material
colorless. This process is referred to as re-vatting.
Question:-Explain the dyeing procedure of cotton fabric with vat dye with
proper recipe and cycle diagram.

21. Light-oxidized vat dyes:-
Inkodye is a type of vat dye that uses light rather than oxygen to
"fix" the dye, with a wide variety of possible effects. These dyes,
which are chemically similar to vat dyes, are developed by light
instead of being applied in an oxygen-free bath and being
developed in the fabric by exposure to oxygen. Inkodyes are true
dyes, not fabric paints. A dye itself attaches to the fabric; fabric
paint includes a glue-like binder, which imparts a stiffer feeling to
the fabric.

22. Thank You