Printing with Reactive dyes and Vat dyes

in steemiteducation •  5 months ago 

We have discussed about the basic methods of fabric printing that are widely applied in Textile sector.

If you missed that session, you may go through the following link: Basic Printing Methods

Today we will discuss about the Printing process using reactive dyes and vat dyes

Fabric printing with reactive dye

Thickener for printing with reactive dye

 Normal thickeners (British gum, guar gum, starch) are not suitable for printing with reactive dyes because terminal -OH group which readily reacts with reactive dyes.

 Na-alginate: Used for printing with reactive dyes. It shows improved flow properties and gives depth, sharpness & levelness in roller printing.

 Emulsion thickener: Used in screen printing, since Na-alginate doesn’t give sharp outline.

 Half emulsion (Mixture of Na-alginate emulsion): Suitable for reactive dye printing.

Printing process of cotton (Steaming process/single phase) with Reactive dye

 Recipe for printing:

Urea: 50-150 gm
Water: 420-245 g
Dye (Procion): 10-80 gm
Na-alginate (5%): 500 gm
Resist salt: 10 gm
Sodium bicarbonate: 10-15 gm
Temperature: 70ºC

 Printing paste preparation:

Paste-I: Urea + Dye + Boil water + Stirring

Paste-II: Paste-I + Na-alginate + Resist salt + stirring

Final Paste: Paste-II + Sodium bicarbonate

 Style & method of printing: Direct style in block or roller printing.

 Process sequence: Printing  drying (1400-1600 C for 4-6 min)  steaming (1000-1020c for 5-10 min)  washing off  dry.

Printing process of cotton (Flash ageing process/single phase) with Reactive dye

 Pretreatment: Brushing, singeing, desizing, scouring, bleaching & mercerizing.

 Recipe for printing:

1st phase-
Dye (Cibacron): 30-50 gm
Water: 450-470 ml
Na-alginate(5%)+CMC: 500 gm

2nd phase-
    Common salt: 150 gm

Potassium carbonate: 100 gm
Sodium hydroxide: 30 ml
Water: 720 ml

 1st phase: The printing paste is prepared with dye, Na-alginate & CMC, then water is added & stirring gently. The paste is used for direct style block or roller printing.

 2nd phase: After printing, fabric is padded with liquor containing common salt, potassium carbonate & sodium hydroxide.

 After padding, dye is fixed by steaming at 1200C for 30-60s, then soaped, washed & dried.

Advantage of single phase over two-phase method

 Urea is added for fixation of dye, but in two-phase method urea is not used.

 Printing paste is prepared at a time but in two-phase method double time required.

 Shorter washing-off time as alkali and Urea used.

Disadvantage of single phase method

 Complex to prepare printing paste

 Print is affected by irregular steaming.

Fabric printing with var dye

Thickener for printing with vat dye

 British gum: Best for printing with vat dye, easily soluble & help deeper penetration, but rapid oxidation of leuco vat dye may causes poor fixation.

 Starch: Prevent rapid oxidation & increased color yield, but bleeding at ageing & washing.

 Mixture of British gum & starch: Better thickener, good fixation & prevent bleeding.

Printing of cotton with vat dye

 Recipe for printing:

Starch-tragacanth: 500 gm
Water: 250 g
Vat dye: 100-200 gm
Glycerin: 50-75 gm
Dispersing agent: 30 gm
Potash: 80-120 gm
Reducing agent (Rongalite): 60-100 gm

 Style & method of printing: Direct style in block or roller printing.

 Process sequence: Printing  drying (low temp.)  steaming (1000-1020C for 3-5 min)  oxidation  washing off

After treatment:

 After printing, Fabric is dried & steamed for 3-5 min at 1000-1020C in air free steamer.

 The steamed fabric contains leuco vat dye which is converted to vat dye by oxidation. Oxidation may be air oxidation or chemical oxidation. Air oxidation takes long time.

 Chemical oxidation recipe:
Oxidizing agent: 2-4 gm/l
Acetic acid: 5 gm
Temperature: 600-700C

 Then the fabric is rinsed, soaped, washed & dried.

Fabric Printing with Direct Dye

Thickener for printing direct dye

 Gum Tragacanth, British gum, Starch Tragacanth, Starch etc.

Printing of cotton with direct dye

 Recipe for printing:

5-20 parts direct dye
385-310 parts Water
50 parts Urea
10-20 parts Trisodium Phosphate
500 parts Starch–Tragacanth (thickener)

 Printing paste preparation:

Paste-I: Direct dye + Urea + Water

Paste-II: Trisodium Phosphate + Water

Final Paste: Paste II + Paste III + Thickener

 Thickener preparation: 80 gm Starch-Tragacanth is mixed with water. Mixture is heated & stirred continuously until achieving required viscosity at 5-10 min.

After treatment

 After printing, Fabric is dried & steamed for about 1 hour in a cottage steamer followed by light soaping and then by washing.

 By increasing 10% Urea, the steaming time may be reduced from 1 hr to 5-10 min.

 The washing fastness may be improved with cationic dye fixing agents:

    Fixanol (Fixing agent): 1-3 gm/L
    Temperature: 750c

Time: 15 min.

 Then finally rinsing and dried.

This is Tariqul Islam , I am Lecturer of a recognised Textile Engineering College in Bangladesh. You may follow me to get posts about textiles, fashion and others..

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