* Mechanical pre-treatment
* Chemical pre-treatment
Operations To Remove Impurities:
* Cleaning Operations:
* To remove applied impurity i.e.; sizing material. * Hydrolysis of sizing material (starch) using enzymes. * Starch (hydrophobic) is converted into glucose and fructose (hydrophilic). * Assessment by Tegewa or violet scale.
* To remove natural and artificial impurities i.e.; fats, waxes, oils, dust, rust etc. * Two phenomenon are involved, saponification and sequestering. * Assessment by capilliary rise test.
* To remove natural color impurity.
* Oxidative bleaching is used which produces bleaching ion in alkaline medium. * Soft water should be used.
* Value Addition Operations:
* Cold mercerization is done (at 15-18 °C).
* To increase the luster of fabric.
* Increase dye uptake.
* Shrinkage control.
* Increase of strength.
5. Optical Brightening (OB):
* Brightening agents convert UV light into visible light. * To make the surface more whiter.
* Burger whiteness increases up to 150.
* Where fabric has to use as a white.
* Colored substance.
* Affinity towards the substrate.
* Applied in an aqueous solution.
* Process by which physical or chemical changes are produced into the textile substrate. * Reflection of light appears colored.
* Can take place at various stages of textile production i.e.; on fibers, yarns, fabrics. Dyeing Processes:
1. Batch process (Exhaust process)
2. Semi continuous (Pad-batch process)
3. Continuous process
Classification Of Dye A/C To Fiber Type:
* Reactive dye onto cellulosic fiber:
* Natural and regenerated fiber.
* Cotton or cellulose.
* Acid dye onto animal fiber:
* Wool and silk
* Basic dye onto synthetic filament:
* Disperse dye onto synthetic filament:
* Direct dyes onto Cellulosic fiber:
* Cotton and cellulose
Water Soluble Colorants:
1. Direct Dye (Indosol)
2. Reactive Dye (Drimaren)
3. Acid Dye (Lanasyn/Optilan)
4. Cationic or basic Dye (Sandocryl)
Water Insoluble Colorants:
1. Disperse Dye (Foron)
* A localized form of dyeing i.e.; definite patterns or designs. * Color is bonded with the fiber, physically or chemically. Fiber Type Contribution in Printing:
* Cotton fiber48%
* Polyester/cotton or
polyester viscose blend fiber19%
* Viscose fiber15%
* Polyester fiber13%
* Othersup to 5%
Techniques/Styles of Textile Printing:
1. Direct Printing:
* By imprinting dye on the fabric in a paste form.
* Capable of application to almost every class of color known. 2. Discharge Printing:
* Applying a design to dyed fabric by printing a color-destroying agent, such as chlorine or hydrosulfite. * Dye the fabric.
* Print with a chemical that destroys the color in the designed areas. * Base color is removed and another color is printed in its place. 3. Resist Printing:
* Print the fabric with dye resist paste and then dyed. * Dye affects only those parts that are not covered by the resist paste. * Resist paste is removed after dyeing.
* Dyes with very high colorfastness can be used.
Methods of Textile Printing:
* Screen Printing
* Flat screen printing
* Rotary screen printing
Colorants for Printing:
Colorant Contribution in Printing:
Reactive dyes 27%