Indigo dye blue denim is popular than any items of apparel
because it maintains its brightness and hue on repeated washings.
Indigo belongs to a class of vat dyes and contain about 96%
indigotin, requiring only about 2% dye to produce the navy
blue. Dyeing method comprises of reduction of the dye (indigo)
with alkali (sodium hydroxide) in the presence of a reducing
agent (hydrosulphite) followed by treatment of the fabric
in the dye bath. Major disadvantages of this method are, variation
in concentration of reactants in the dye bath affecting the
quality of dyed fabric; frequent replenishment of reactants
and lesser affinity which require repeated dipping and nipping
techniques. In the case of cotton fabric it has other disadvantages
such as unstability of reducing agent, poor dye uptake, shade
depth fluctuation, poor and non uniform colour yield, no affinity
for dye, etc. From this point of view, particularly for dyeing
cotton fabric with indigo, a dyeing process with the use of
an alternative alkali has been developed. This process is
economical, time saving and consumes less amount of dye (Indigo).
The dyeing process developed is related
to the replacement of Sodium Hydroxide with organic alkalies
during the dyeing of cotton warp sheet with Indigo for the
manufacture of denim fabric. The method is based on the principle
that the Indigo yield is considerably higher if the dyeing
is carriedout in the pH range of 10.5 to 11.5. The use of
Sodium Hydroxide gives the pH range 12 - 13 at which Indigo
yield is much lower, whereas the organic alkalies give the
desired pH during dyeing. The process comprises of the following
steps : a) Reduction of dye (indigo) with organic alkali in
the presence of a reducing agent; b) Reaction of reduced indigo
with the cotton fabric; c) Squeezing of dyed cotton fabric;
d) Air oxidation of dyed cotton fabric; d) Air oxidation of
dyed cotton fabric; f) Drying of dyed fabric. The dye, organic
alkali and the reducing agent taken in the specified ratio
is mixed and allowed to react till the dye gets reduced to
monophenolate form. Reaction of the cotton fabric is carried
out at prescribed duration of interval. This is followed by
squeezing, air oxidation washing and drying of the fabric,
which are carried for a specified time and, at a specified
temperature.
Special Features:
The method of dyeing developed particularly
for cotton has the following advantages: Replacement of sodium
hydroxide alkali medium by organic alkali medium; Reduction
of dye in one go; Better dye uptake; Higher colour yield of
dye (Indigo); Higher colour yield of dye (Indigo)
Prospective Users:
All fabric manufacturers particularly cotton
denim
Keywords:
Fabric, Cotton, Dye
Type of Technology:Process
Status of IPR Protection:
Indian Patent Application No. 2931/DEL/98
dated 5.10.98 with title "Process for dyeing of cotton
with Indigo"
Major Equipment & Facilities required:
Existing facilities for the production of
blue denim cotton could be used. No additional equipment/facilities
are required Requirement of Raw Materials/Components:
Organic alkali replaces the use of Sodium
Hydroxide with the other raw materials remaining the same
for the preparation of blue indigo dye
Source:Managing Director
Foundation for Innovation and Technology Transfer (FITT)
Indian Institute of Technology, Delhi
Hauz Khas, New Delhi-110016, INDIA
Tel : 91-011-26597167, 26857762, 26581013, 26597153
Fax : 91-011-26851169
E-mail : drkdpn@gmail.com
