DETAILED DESCRIPTION OF INVENTION
According to this invention there is provided a process for continuous indigo dyeing of wool and wool blends characterized by continuous subjecting the wool and wool blends to a step of pretreatment, subjecting the pretreated wool and wool blend yarns to the step of indigo dyeing, the said step of dyeing includes a single step or a plurality of steps of impregnation of the pretreated wool and wool blends in indigo dye bath followed each time by the step of oxidation and post dyeing wash off.
The term wool used herein is intended to imply wool in loose tops, hanks, yarn packages etc. (e.g. Cones, Cheeses, Beams etc.) yarn ropes/sheets and fabrics. Further the present invention may be used as a continuous or batch, though distinct advantages are associated with a continuous process. Still further, the parameters described herein are with respect to a continuous process which are not intended to be implied in a restrictive manner with respect to a batch or continuous process.

One of the aspects of this invention resides in subjecting woolen and woolen blends to a shrink resist treatment prior to the step of dyeing. The shrink resist treatment may be effected in the spun yarn itself. However, the homogeneity is reduced on a spun yarn in comparison to effecting the shrink resist treatment to the fibre or wool top. The yarn is in a twisted form, and therefore the homogeneity is considerably reduced if such a shrink resist treatment is effected on the yarn. However, in effecting such a treatment prior to the step of spinning, the separated fibres are disposed along the longitudinal axis and spaced from each other, and whereby the absorbality is improved in comparison to a yarn. Such an absorbality provides a better dye uptake.
The shrink treatment composition and operating temperatures and time period are described hereinabelow. However, such operating temperatures and time period are only exemplary in nature and in no instance to be construed in a restrictive manner.
Treatment Procedure:
Set the bath at 15°C with a composition of
Acetic acid 0.3-0.5 gpl
Sodium Sulphate 1.5-3.0 gpl
Basolan DC (Sodium dichloro iso cynuric Dehydrate, 3.0-5.0 gpl
Shrink Resist Chemical)
pH 3.5 to 4.0 gpl
The temperature is raised to 50°C at 1°C per minute maintaining a pH of 3.50 to 4.0 and held 60 minutes.
Then sodium metabisulphite of 1.5-3.0 gpl is added. The bath is run for 35 minutes and drained. The tops are then washed twice cold, once hot (60°C) and finally cold.
The flow chart of the process for the present invention is shown hereinbelow with respect to wool being in the form of a rope and the process is continuous in nature. However, the flow chart does not show the pretreatment steps and the shrink resist treatment steps. The flow chart essentially shows certain of the operating parameters of the known machine for a continuous process, but having operating parameters for dyeing of wool in rope form. It is considered that the impregnation period and that of oxidation is inversely proportionate to the speed of the machine .
FLOW CHART 100% WOOL
BALL-WARPING LONG FORMING (M/c, Speed 75-100 mpm)
Creel Tension 25-30 gms)
↓
ROPE-DYEING INDIGO DYEING
REBEAMING (ON LCB M/C) (M/s. Speed 75-100 mpm)
Rope Tension 5-10 psi)
↓
SIZING
WEAVING
↓

FABRIC SETTING
↓
FINISHING
A typical dye bath is as follows:
Caustic soda - 1.5 to 3.0 gpl
Sodium hydrosulphite 1.8 to 3.0 gpl
Indigo - 0.5-5.0 j
An ionic Wetting agent
(Primasol NF-Salt of phosphoric acid ester) 0.05 to 0.5 gpl
An ionic Dispersing Agent (Setamol
WS-Condensation product of an aromatic 0.05 to 0.5 gpl
sulphonic acid)
Dye - bath temperature 25°C-3 5°C
pH 11.2-12.5
The flow chart for the slasher process for the dyeing of wool is as follows, but without showing the shrink resist treatment and ten pretreatment.

-10-SLASHER DYEING PROCESS FLOW
100% Wool Yarn
Direct Warping
↓

Indigo Dyeing cum sizing
↓
Weaving
↓

Finishing

A typical dye bath for the slasher process is
Caustic soda - 1 .5 to 3.0 gpl
Sodium hydrosulphite - 1.8 to 3.0 gpl
Indigo - 0.5-5.0 gpl
An ionic Wetting agent
(Primasol NF-Salt of phosphoric acid ester) 0.05 to 0.5 gpl
An ionic Dispersing Agent (Setamol
WS-Condensation product of an aromatic 0.05 to 0.5 gpl
sulphonic acid)
Dye - bath temperature 25°C-3 5°C
pH 11.2-12.5

The flow chart for hank indigo dyeing of woolen material is as follows.
TOP INDIGO DYEING AND HANK INDIGO DYEING OF WOOLEN MATERIAL:
SR Treatment of Woolen Tops
↓
Dyeing of Tops in Batch Reduced Form
↓
Oxidation
↓
Washing
↓
Drying A typical dye bath is as follows:
Caustic soda - 1 .5 to 3 .0 gpl
Sodium hydrosulphite - 1 . 8 to 3 . 0 gpl
Indigo - 0.5-5.0 gpl
An ionic Wetting agent
(Primasol NF-Salt of phosphoric acid ester) 0.05 to 0.5 gpl
An ionic Dispersing Agent (Setamol
WS-Condensation product of an aromatic 0.05 to 0.5 gpl
sulphonic acid)
Dye - bath temperature 25°C-3 5°C
pH 11.2-12.5
Reference is made hereinafter to process parameters for indigo dyeing of wool in the form of rope. However, the flow chart and the parameters are only illustrative. Further, the resist shrink treatment is not shown.
Reference is made hereinabove to the step of scouring. Though sodium hydroxide is the normal scouring agent for cotton, it has been found that sodium hydroxide cannot be used for wool, and that a preferable agent is a detergent and a wetting agent.
Further, subsequent to the step of dyeing, the hot washed dyed wool is washed with acetic acid as it helps in reversing any elongation loss.

WE CLAIM:
1. A process for continuous indigo dyeing of wool and wool blends characterized by continuous subjecting the wool and wool blends to a step of pre treatment, subjecting the pre treated wool and wool blend yarns to the step of indigo dyeing, the said step of dyeing includes a single step or a plurality of steps of impregnation of the pretreated wool and wool blends in indigo dye bath followed each time by the step of oxidation and post dyeing wash off.
2. A process as claimed in claim 1 wherein the wool and wool blend is in yarn (rope/sheet) or fabric form.
3. A process as claimed in claim 1 wherein the dye bath has a composition of 1.5 to 3.0 gpl caustic soda, 1.8 to 3.0 gpl sodium hydrosulphite, 0.5-5.0 gpl indigo, 0.05 - 0.5 gpl anionic wetting agent (Primasol NF-Salt of phosphonic acid ester), 0.05 - 0.5 gpl anionic dispersing agent (setamol WS-condensation product of an aromatic sulphonic acid) 25°C-35°C dye-bath temperature and 11.2-12.5 dye-bath pH.
4. A process for indigo dyeing of wool and wool blends substantially as herein described and illustrated.