Printing:- Explained in brief
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Printing:-
Textile printing is avery important area of application for reactive dyes. There is no difference in the fundamental principles associated with reactive dye applicatiion by dyeing versus printing. During printing, a reactive dye is applied from a print-paste containing a thickening agent and auxiliaries such as urea and alkali, instead of being applied from an aqueous solution. Two main methods for the fixation of reactive dye prints are atmospheric steaming using saturated steam and dry-heat fixation. To be suitable for thsi application, the reactive dyes must possess good water solubility. However, the preferred dyes have less substantivity for cellulose than have those intended for dyeing. The reactivity of these dyes should be such that the print may be fixed using the temperature and processing times normally employed. At the same time, alkali-containing print pastes must remain stable for long time periods. Washing out hydrolyzed dyes should also be easy.
Ease of was off minimizes staining of adjacent white areas, making the lower substantive dyes preferred. The fixation of reactive dyes on the cotton after printing is not high. While a degree of fixation exceeding 90% can be achieved in dying processes, the reactive dyes used in printing often have a fixation level of only 60%
