Steps in Printing Process
- Preparation of the print paste
- Printing of fabric
- Drying
- Fixation of dyestuff
- Washing – off
Preparation Of Printing Paste
The type of specific formulation used depends on the fiber, the colorant system used, and to some extent the type of printing machine.
Typical ingredients used include:
- Dyes or pigments
- Thickeners
- Binders, cross-linking agents
- Sequestering agents
- Dispersing agents
- Water retaining agents
- Adhesion promoters
- Defoamers
- Catalysts
- Hand modifiers
Dyestuff or pigments
Depending on the nature of the fiber on which the printing is done, suitable dyes or pigments are selected. Pigment color can be used for printing on all types of fibers. Reactive, vat, or azoic colors are used for cotton; disperse dyes for polyester and acid dyes and basic dyes for wool and silk.
Thickener
To make a viscous paste of dyes in water, a thickener is used. For example emulsion thickener, sodium alginate, starch, etc. the thickener will be dependent on the class of dyes to be printed and the style of printing.
Wetting agent
It helps in obtaining a smooth paste of dyes without any lumps, for example, TRO and ethylene oxide condensation.
Defoaming agent
Formation of foam during print paste preparation and application is quite common but should be avoided. The foam may produce specky dyeing. The antifoaming agents help in foam generation.
Acid or alkali
Depending on the types of dyes used in printing, acid or alkali is used in the print paste. An acid liberating salt is commonly used, for example, ammonium chloride and diammonium hydrogen phosphate. For reactive printing on cotton, sodium carbonate or sodium bicarbonate are used.
The oxidizing or reducing agent
They are used in printing with solubilized vat colors and also in discharge and resist printing. Discharging agents such as Sodium sulphoxylate formaldehyde (Rongalite) are used in the discharge printing.
Hygroscopic agents
The function of hygroscopic agents is to take up a sufficient amount of water (moisture) during steaming to give mobility to the dyes to move into the fiber. Eg. Urea and Glycerin.
Dispersing Agent
Dispersing agents are necessary for the print paste to prevent aggregation of the dyestuff in the highly concentrated pastes. E.g. Diethylene glycol
Preservatives
Preservatives are used to prevent the action of bacteria and fungus to make it dilute. Eg. Salicylic acid.
Binders
Binders are used in pigment printing as a thin film-forming polymer. Eg. Melamine formaldehyde resin.
Fixation methods
Atmospheric steam
- treatment at 212 degrees f with saturated steam
- used with
- Direct dyes
- Vat dyes
- Naphthol dyes
- Acid dyes
- Cationic dyes
- Reactive dyes
- festoon steamer most common equipment
- Acid agar for acid dyes
Pressure steam
- treatment at 230 degrees f under pressure
- used with disperse dyes
- Turbo-autoclave most common equipment.
High-temperature steam
- treatment with superheated steam at temperature up to 420 degrees f
- used with disperse dyes and pigments
- can also be used as an atmospheric steamer
Dry heat
- treatment with dry heat at temperatures up to 420 degrees
- used with dispersed dyes and reactive dyes.
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