Sulfur Printing (Coating).

SUBJ-15:

Sulfur Printing (Coating).

Chemicals:

Sodium Sulfide or SSodium Hydrosulfite (Na2s2o4), Acetic Acid (Conc), hydrogen peroxide, Sodium Bicarbonate, Sodium Borate, Levling Agent(If Possible), Dispersing Agent (If Possible)Sodium Alginate, Soap (Polyglycolether, Nonionic).

Purpose:

Major use of Sulfur dyes as for as printing is concerned finds in coating application of Denim and heavy GSM twill fabrics. After coating with sulfur different washing outs are carried out like

Stonewash

 Enzyme Wash

 Hypochlorite Washings.

There are three classes of sulfur dyes, which are available commercially,
1.Conventional water insoluble dyes which have no substantively to cellulosic’s.
2.Solubilised sulfur dyes , which are water soluble and non substantive to cellulosic’s.
3.Pre-reduced sulfur dyes, in the stabilized leuco compound form , which are substantive to cellulosic’s.

These Washings gives very beautiful effects to denim fabric all because of Sulfur Dyes.

Sulfur Dyes:

Sulfur dyes are cheap with good washing fastness. Procedure is also quite simple. Stages Involved are.

1. Reduction of Dye
2. Printing
3. Oxidation of Dye

Reduction

This step is generally carried out in the presence of some reducing agent. Common reducing agent being utilized are Sodium Sulfite and King of reducing agents (HYDROS F) Sodium Hydrosulfite (Na2s2o4). Recipe of Sulfur Printing describes 3% amount of Reducing agent regarding to the concentration of dye is sufficient. Sulfur Molecules are complex and larger in Size So, insoluble in water and also have no substantivity towards the fabric. They are reduced to smaller size in the presence of some suitable reducer this makes the dyes to get solubilize and dye shows substantivity towards fabric too.

Some other parameter which are generally not being practiced while printing with sulfur dyes or coating are involved in reduction of dyes during dyeing are as follow

For Dyeing

Here it is worthy to mention that. During dyeing of sulfur. In addition to reducing agent. Caustic (NaoH) is also added. Ph is normally above 10. Temperature of the reduction bath is kept to 80C.

Recipe for Reduction:

Stock paste:

Sulfur Dye                              200g/Kg

Sodium Hydrosulfite              6-10g/Kg

Alginate Thickener                  35g/Kg

Water                                      Balance

Total                                       1 Kg

Note:

In addition to these basic chemicals some penetrating agents, stabilizers, dispersing and stabilizing agents  are also added into the recipe to get the better and leveled printing.

Printing

Process:

Print and dry at 130-150°C for 1Min.

Oxidation

Oxidation is the last step involve in printing of Sulfur Dyes. Oxidation phenomena actually brought back the dye to its original structure Big complex Molecular structure which is actually responsible for the good washing fastness of sulfur Dyes. Different Oxidation method which can be applied are

Oxidation through Air (atmospheric oxygen)

Oxidation through Chemicals

Acetic Acid

Hydrogen Peroxide

Commercially available Oxidizing agent like One of the famous in market Clariant product Diresul Oxidant BRI.

Sodium Bicarbonate

Sodium boromate

Recipe for Oxidation:

We can call this as our last stage mean washing stage and here we will carry out oxidation too.

1. Cold rinse
2. Hot Rinse
3. Hot Rinse With 5g/L Acetic Acid 80% Conc, Ph around (4.5)  (rinse it in acetic bath for One Min)

4. Hot Rinse With 5g/L Acetic Acid 80% Conc, Ph around (4.5), Oxidizing agent (Any of above five Mentioned approx 5g/L)  (rinse it in acetic bath for One Min)

5. Soap at 100^oC With Soap (For example a market famous soap Ladipur RSK Clariant Product)
6. Hot Rinse
7. Cold Rinse

         Oxidation with Acetic Acid.....Oxidation with Commercial Oxidizer

    No Oxidation, Direct Washing....Oxidation through Steamer and than washing

        Without  stabilizer, Oxidized with H2O2 ....With Stabilizer, Oxidized with H2O2

Again In addition to these Some other auxiliaries are added to enhance the oxidation of Printed Fabric.

Features of Sulfur Dyes:

1.Economical dyeing with excellent tinctorial value and good build up properties.

2.Good overall colorfastness properties such as wash fastness , light fastness , perspiration fastness etc. Moderate fastness to crocking and poor fastness to chlorines bleaching agents such as bleaching powder and sodium hypochlorite.

3.Limited shade range to produce only dull shades and there is no true red dye in the range.
4

These dyes can be applied by exhaust, semi continuous or continuous dyeing methods on garment , yarn , knits, fabric as well as loose stock etc.

5. Available in powder , granules and liquid forms.

6. Sulphur black 1 is the major black dye used world vide for dyeing of cellulosics.
7

.The conventional dyeing process is not environment friendly due to pollution problems of sodium sulphide as well as sod/pot. Dichromates.

8.When dyed by using non polluting reducing and oxidizing agents the process is

environment friendly.

Source for These Features.

http://dyeingworld1.blogspot.com

4-Different Oxidation Modes

Remarks:

We hope this post will entertain you. It will also help to understand the application of sulfur dyes in printing. as to the current  its utilization in dyeing is too big as compared to the printing or coating. Some Expert says black is never True Black until its Sulfur Black

If you are viewing this page on other forum, social networking site like Facebook, you are welcomed to visit http://appchemistry.blogspot.com and subscribe for daily updates.