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.
