Friday, 16 May 2008
Notes on Dyeing of sulphur black on Rope Dyeing Range
1. Process of dyeing of sulphur color:
1st Wash tank: mercerisation by taking 22% NaOH ie. 250 gpl
2nd Wash Tank: Hot Wash
3rd Wash Tank: Cold Wash
2. In 1st and 2nd dye bath take sulphur color 6-8% on the weight of the yarn sheet. Temperature 90 deg. cel. The solution contains the following:
1. solubalised sulphur color: 150 gpl
2. Na2S--> reducing agent: It is added to increase its reducing power
3. Caustinc Soda --> 10 gpl--> reducing agent
4. Wetting agent--> 2gpl
5. Antioxident Sulphide ( Glucose paste--> 5gpl). This is added to prevent the oxidation of of Sulphide solution. It will always remain in reduced form
( Alos if the shade is slightly greyish, one can add tiny tinge of sulpher blue--> 20gpl)
in III, IV and V dye bath--> cold wash
in 6th dye bath. We take H2O2(30%)+Acetic Acid(2:1 by weight). H2O2 acts as an oxidising agent. But as it acts on neutral pH (=7) and after cold bath the solution is slightly alkaline, to make it neutral wil add acetic acid. Acs in alkaline pH, oxidising action of H2O2 will be similar to the bleaching action, which may cause tendering in the fabric.
7th and 8th Dye Bath: Cold Wash
Wash Box Number 4: Here washing is done with detergent and soda ash at 60-70 deg.c
5th and 6th Wash Box: Hot Wash
7th wash Box: Here softner is added at 25 gpl. It is cationic softener with pH 4.5 to 6.5. As during oxidation of sulphur, strength is reduced by 10%. On a yarn sulphur is of two types :
1. Free Sulphur
2. Reacted Sulphur.
The free sulphur will react with moisture in the atmosphere to form:
H2O + S --> H2SO4
Which tenders the yarn. Now at acidic pH reaction is much faster. So we add only a small amount of softener (25 gpl) as against that in indigo which is 100gpl.
Over all during sulphur dyeing and storing, the yarn strength is reduced by 15% as compared to Indigo.
If ball formation takes place of sulphur dyed warp at loom shed, then we can taken in 4th dye bath little Na2S+Caustic to reduce the free sulphur.