White discharge on 100% Polyester Knit Fabric dyed with disperse dyes in exhaust process.

Object:
White discharge on 100% Polyester Knit Fabric dyed with disperse dyes in exhaust process.

Chemicals:
Leveling agent, Swelling agent, Caustic solid Pellets, Special Thickener modified (to sustain high alkaline ph), Sodium Hydro sulfite.

Detail:
Discharging, disperse dyed fabric is more difficult as compared to reactive dyed cotton  fabric and knit fabric adds more complexity. For discharging polyester common in use chemicals are Rangolit C and Tin chloride (Later one is  strong reducing agent and expensive too). Results with these two are satisfactory when fabric is woven and just have undergone through padding and not fixed, in other words these reducing agents work well at pre fixation stage but if disperse dye is fixed its quite hard to remove or cut dye from selected area. In case of knit as dyeing is done in exhaust phase, at temperature 130°C so discharging reaches near to impossible. So, here what we have selected is, Two very cheap chemicals, Which will play their part in changing the chemistry of disperse dyes to obtain our result. These two legends are Caustic (NaOH) and Sodium Hydrosulfite (Na2SO4). Principle of discharge is simple and that is” no disperse dye can with stand high alkaline medium generated by 100%  Caustic, Although we do listen some dyes are stable to alkaline medium but believe no dye have a chance to with stand such high alkaline medium.” So, basing on this principle we can utilize these chemicals, One can ask why not than choose only one chemicals between  Sodium hydro sulfite and caustic? Answer to this question is very simple. Sodium hydrosulfite works well until its critical concentration reaches and above this it will not work efficiently, we can call this a saturation limit, in addition it has very pungent order. On the other hand concentration of caustic above 10% start to causing tear and weakens the fabrics too much. So our typical recipe will be as follow.



Recipe:
Thickener Special modified        =  80g/kg
Sodium Hydrosulfite                  = 50g/kg
Caustic solid Pellets                   = 100g/kg
Leveling agent                           = 20g/kg
Swelling Agent for polyester      = 20g/kg
Total                                        = 1kg

Process:
Print, Dry at 120°C for 2Min,

Fixation:
Pressure steamer 2Bar at 135°C for 30Min
Or
Thermo fixation at 210°C for 1.5Min.



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