Sulphur Dyes produce full colour range, offertechnical advantage in dyeing are available at moderate rate & relatively good colour fastness. Sulphur dyes are mainly employed for dyeing of cotton, linen, viscos rayon & celulosic component of polyester celulosic blends. To produce optimum results as are brightness, depth & fastness. It is essential that proper prcautions are taken while dyeing as :

Dyeing Temperature

Sulphur liquids are found highly substantive and dye best at room temperature. Temperature of 50 - 60 degrees may be employed when dyeing liquids by pad-jig or pad-steam when faced with the problem of tailing.

Water

The use of soft water or purified water is preferred but in cases where hard water is only available, a sequestering agent based on sodium hexa-meta-phosphate, ethylene amine tetra acetic acid or ethylene di-armine tetra carbonic acid should be used.

Oxidation

Chemical oxidation after treatments are used after dyeing and rinsing to convert the reduced sulphur dyes back to their original insoluble form on the material to give a stable shade and improved fastness properties compared with simple air oxidation.

Wetting Agents

Wetting agents compatible with sulphur dyes must be used. The recommended wetting agents are Sulfaid Penetrant IX, which is stable in alkaline leuco baths and padding liquors.

Soaping

Soaping removes loose dyes from the surface of the material and more importantly develops the full shade and fastness properties of the dyeing by increasing the crystallization of the dye in the fibre.

Resin Finishes

Sulphur dyes fabric may show some change in shade when finished with cease resisiting durable press resins. This shade change is often due to acidity or metal salt of the catalyst.

Dark Selvedges

An uneven jig roll is primarily the cause of this trouble. Addition of sequestering agent to the dyebath is desirable.

Washing

A complete and thorough washing before oxidation is of utmost importance in sulphur dyeing.

Pad Box Level

Pad box level in continous dyeing is very critical. If dyebath level varies so will the shades.

Tensile Strength

Through washing before and after oxidation and keeping the pH of the finished cloth or yarn slightly alkaline will prevent any loss in tensile strength.

Fabric preparation

sulphur dyes can also be applied on grey fabric provided polyvinyl alchol is not used in sizing.

Mercerizing

Mercerizing improves color yield of sulphur dyes by 30-40% over un-mercerized goods.

Polysulfides

Polysulfides, rising and soaping can contribute to achieving dyeing free from bronziness.

Chelating Agents

If water has too high levels of calcium or magnesium, hardness, suitable sequestering agents must be used to lower the hardness.

Electrolyte

It is a standard practice to add electrolyte to the dyebath usually sodium chloride or sulphate to promote dye uptake.