TEXTILE CHEMISTRY

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Thursday 25 April 2019

Printing of Polyester by Discharge Style


Principle     
·         Polyester fabric is dyed with dischargeable disperse dye and then printed with paste containing reducing agent for white discharge and non-dischargeable dyes for colour discharge.
·         Discharge printing of polyester is very difficult, because the dye is dissolves in polyester fabric.
·         If the fabric is dyed with HTHP method, then it is very difficult to discharge the ground.
·         But if the ground shade is obtained by carrier dyeing, then it is easy to discharge ground shade.
Dyeing
·         The cloth is first padded with a dispersion of the dischargeable dye and dried at low temperature so that colour does not get fixed at this stage, also the bath contains 2 g/l sodium alginate made acidic with tartaric acid (pH 5 – 6), then dry the fabric at 60°C and printed with a paste.
Procedure
For White Discharge
·         The printing paste is prepared as follows:-

     200 parts    Safolin
                               70 parts    Water
                             650 parts    Loust bean gum (10 %) or Meyprogum (8 %)
                               30 parts    Citric acid or (1 – 2 parts Tartaric acid)
                               50 parts    Thiodiethylene Glycol
1000parts

For Colour Discharge
·         The printing paste is prepared as follows:-

       50 parts    Disperse Dye (non-dischargeable)
     200 parts    Stannous Chloride
                               70 parts    Water
                             600 parts    Loust bean gum (10 %) or Meyprogum (8 %)
                               30 parts    Citric acid or (1 – 2 parts Tartaric acid)
50    parts   Sodium Thoicynate
1000 parts

After printing, fabric is dried and steamed for 30 minutes at 128ºC (30 psi pressure). This system produces full colour yield and bright prints.
After fixation, fabric is rinsed with cold water and hot water, reduction cleared (at 40 – 50ºC for 15minutes) in following bath:-

20 parts           Sodium hydrosulphite
30 parts           Sodium hydroxide
                                            1000 parts
·         Finally, the cloth is rinsed, soaped at the boil, washed and dried.

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