After Treatment Processes of Printed Fabrics
After printing, the fabrics are dried to retain the printed design. It is an essential step to avoid staining of unprinted areas. It prevents bleeding of print paste from the design areas. Drying is followed by steaming which transfer the pigment from print paste to the fabric.
In ageing or steaming process, the dyes and chemicals present superficially on the surface of the fabric is transferred into the fabric. The dried printed fabric has pigments or dyes, thickeners such as starch, gum etc. and printing auxiliaries on its surface. Steaming enhances the absorption of dyes or pigments on the fabric. In steaming or ageing, the dried printed fabric is exposed to steam at atmospheric or higher pressure for different time intervals. Steaming can be carried out continuously or batch-wise. When the printed fabric enters the steam chamber, steam condenses to form water molecules which are absorbed by the thickener present in the printed fabric. The water absorbed by the thickener dissolves the dyes or pigments and hence increases the rate of absorption of pigment from thickeners to the fabric. As soon as steaming is done the fabric has to be dried.
The printed fabric after undergoing steaming process contains exhausted thickeners and some printing auxiliaries. If the thickeners used are temporary thickeners, they are removed by washing. Washing is done using cold water. Fabrics are washed with neutral soaps to avoid bleed in water. Rinsing removes the print paste chemicals and unfixed dye molecules. For vat dyed printed fabric, oxidation is carried out first followed by soaping.
· Defines the print or design
· Prevents loss of colour
· Avoids spreading of colour beyond the design boundary
· Expensive process because it requires steam and floor space
· Chances of spoiling the printed fabric due to power cuts etc.