Color Discharge on Reactive Printed/Dyed fabric through Sulfur Dyes.

SUBJ-19:

Color Discharge on Reactive Printed/Dyed fabric through Sulfur Dyes.

Chemicals:

Urea, Sodium Bicrarbonater, Sulfur Dyes, Reactive Dyes, Rangolit C (Sodium formaldehyde Sulfoxylate HOCH2SO2Na). Sodium perborate, Textile Washing off agent.

Discharge:

Discharge is not a new term for a textile Person. Discharge is classified into white and Color Discharge. Term Discharge may be mixed up or used instead of stripping which is not right as stripping is to lower the depth of shade (usual dyers term) where as during discharge screens are used to create patterns by removing partial or full color of the fabric (Textile Printers term).

Printing is now done on variety of fabrics consequently with variety of dyes. In this post we are just focusing on discharging cotton fabric printed/Dyed with Reactive dyes. Suitable discharging agent for reactive dyes or printed fabric is Rangolit C (Sodium formaldehyde Sulfoxylate HOCH2SO2Na). It is prepared by chemically reacting dilute solution of formaldehyde with Sodium Hydrosulfite. So, like Hydrosulfite it is also strong reducing agents. That why no dye can stand with Rangolit and get reduced consequently ending up by losing their colors. Therefore discharging reactive with reactive is not frequently heard process.

Black Ground Discharged with Yellow Sulfur Dye.

As, discussed Earlier discharge can be of two types White or color Discharge. White is done with rangolic C and later one is majorly carried out with Pigment and Binder system, Such binders are considered which are stable with rangolit C. so Rangolit C (Sodium formaldehyde Sulfoxylate HOCH2SO2Na) discharges ground dyed/Printed Fabric and resultantly pigment take over the white ground produced by rangolit C. The only drawback in this process is that pigment printed fabrics have very poor rubbing and washing fastnesses. So, One has to compromise at this end. So, why not to propose some other method rather than a typical pigment binder color discharge.

Purpose:

Purpose is to propose an other method else than pigment binder for color discharge on reactive Printed/Dyed Fabric.

Sulfur Dye Suitability:

Sulfur dyes are reduced before dyeing or Printing.Normally this is done with reducing agent like Sodium Hydrosulfite Na2S2O4. As, we have discussed earlier  Rangolit C (Sodium formaldehyde Sulfoxylate HOCH2SO2Na) is a reducing agent which can replace Hydro sulfite but, Here need of Rangolit will be much greater as it has to perform two tasks one, Iit has to reduce the dye and secondly it has to discharge the ground color.

Recipe:

Ground Print (Full Bloch)

Reactive Black (Preferably VS Dye)  30 to 50g/kg

Over Print (Design Screen, containing sulfur dye and discharging agent):

 Alginate Thickener                              30   g/Kg

Sulfur Dye (Preferably Yellow)             200g/Kg

Caustic 48Be                                       30  g/Kg

Rangolit C                                           150 g/Kg

Sequessting Agent                                20  g/Kg

Total                                                    1     Kg

Process:

Print, Dry at 150C for 1.5Min

Saturated Steam at 102C for 8Min

Oxidation:

First Bath:

Acetic acid 2g/l for 1Min.

Second Bath:

Acetic acid 2g/l, Sodium per borate 3g/L for 5Min

Washing:

§     Cold rinse

§     Soap at 60^oC With:

                        1-2 ml/l of Ladipur RSK liq.

§     Hot Rinse

§     Cold Rinse

A Bit More About Sulfur Dyes:

Warning! The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Sulfur Dye 

any of the organic dyes that are high-molecular-weight compounds containing the heterocycles

and the groups SH and S_n, where n ≥ 2 (the precise chemical structure has not been established). Sulfur dyes are amorphous substances, insoluble in water and most organic solvents; when acted upon by Na₂ S, they form water-soluble leuco compounds according to the scheme

After imparting color, these compounds are oxidized by oxygen in the air and are reconverted on the fiber to insoluble sulfur dyes.
Sulfur dyes are obtained by a prolonged heating of such organic compounds as aromatic amino, nitro, amino-hydroxy, and nitro-hydroxy compounds and heterocyclic azines with sulfur or a polysulfide of sodium (Na₂ S_n’n = 2–9).
Sulfur dyes are usually pale. The black, blue, brown, and green dyes have the greatest importance; the yellow and orange dyes have only limited use. Red sulfur dyes are unknown. While the black dyes are fast, the other sulfur dyes impart colors of lesser permanence. Sulfur dyes are inexpensive and convenient. They are widely used for dyeing cotton fabric; in the textile industry, however, they have been partially replaced by vat dyes and reaction dyes, which offer brighter and more permanent colors.

Source:
http://encyclopedia2.thefreedictionary.com/Sulphur+dye


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