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Dyeing and Finishing-1
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Preconditioning Method of Reactive Dyeing:
This is a very simple and beneficial way of dyeing medium and dark shades of Vinylsulphones dyes. Although this process yields better results in the final production of shades by way of uniform and reproducible batches,
this dyeing method has still not been followed popularly.
For coarse variety of yarn, normal woven or knitted goods (
not very close and heavy fabrics like canvas or high GSM knits), this process is most economical and very useful.
The following few facts may be reason for avoid using this good method of dyeing.
- Since it is applied in cold condition, everybody has a fear that some part of the fabric or yarn may not be get dyed properly.
- The dyestuffs would not have reacted properly with the fiber due to cold conditions.
- The application of salt, soda and even a part of caustic alkali added even before adding the dyestuff, may have created an illusion that this type of dyeing may result in streaky (strikes) dyeing due the presence of
salt and alkali in the bath.
- The doubt on the fastness properties of cold dyed material
But please remember that this process does not work well if the preparation of the material is not good. (But it is true for all type bad preparations).
Steps in the Precondition method of Dyeing:
- Set the dye bath with the basic auxiliary chemicals that you may have been using it, like a sequestering agent, leveling agent, lubricant, de-foamer (in the case of Soft-flow machines).
- Load the RFD fabric in the machine.
- Run blank in the auxiliary bath for 20 minutes.
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A -
Add 1/2 the amount of Salt, 1/2 the amount of Soda and 1/4 amount caustic soda - Run 10 minutes.
B - Add 1/2 the amount of Salt, 1/2 the amount of Soda and 1/4 amount caustic soda - Run 10 minutes.
C - Add 1/2 the amount of pre-dissolved and filtered dye solution - Run for 10 minutes
D - Add 1/2 the amount of pre-dissolved and filtered dye solution - Run for 10 minutes
Raise the temperature to 40 to 45°C on the fabric.
Run for 30 minutes - check the shade and make additions if necessary.
E - Add 1/4 amount of balance caustic soda - Run 10 minutes
F - Add 1/4 amount of the final amount of caustic soda - Run 90 minutes at 45°C
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Drain --- Cold Running Wash – Neutralize – Hot wash – Hot Wash -Cold Wash – Soap at Boil – Fix
and do softening as required. (All hot washes should be done at min 60°C with good quality water).
This method is suitable for light to medium density fabrics and for medium to heavy depth of shades.
This method not only yields uniform shade but also gives around 20 to 30% more color yield, higher
rubbing and wash fastness results, which are mainly due to the full exhaustion and fixation of the dyestuffs.
The above method has been followed continuously in reputed dye houses in South India, for jigger
and winch dyeing.
The above recommendations are for un-mercerized cotton in the Material Liquor Ratio (MLR) 1:7 to 1:15.
PRECONDITIONING METHOD:
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