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Textile Printing

Printing has often been described as dyeing in a localized, patterned design. Textile printing utilizes the same dyes or pigments applied to produce a dyed fabric.The same principles of specific dye classes having select fibre affinities and the general fastness characteristics apply equally to printing as to dyeing.

Dyes or pigments used in dyeing are usually in a water bath solution. When the same dyes or pigments are used for printing, they must be thickened with gums or starches to prevent the wicking or flowing of the print design.The thickened solution, about the consistency of heavy buttermilk, is called the print paste.

Many dyes cannot be used in printing pastes. Some of the reasons include insufficient solubility, Low colour yield and poor print paste stability.

METHODS OF PRINTING

There are several methods for printing of textiles. Two are of significant commercial importance: the roller print method and the screen print method. A third method, heat transfer printing, is of less significance. Other printing methods, not widely used in commercial production of textiles, are block and batik printing.

In roller printing, the design is put into fabric by copper engraved rollers (sometimes called copper engraved cylinders). The roller engravings match exactly the artist-designer's creative sketch. A separate engraved cylinder is required for each colour in the print. The size of the engraved cylinders is governed by the printing machine and the design.

HOW ROLLER PRINTS ARE MADE

1. The Engraved Copper Roller A in rotation makes contact with Colour Furnisher B (whose surface is much like that of a paint roller used in house painting). The entire surface of Roller A becomes covered with print paste.

2. Colour Furnisher B, also in rotation, picks up a constantly fresh supply of print paste from Colour Box E.

3. Meanwhile, Engraved Copper Roller A in rotation comes in contact with Doctor Blade C. This is a steel blade which functions somewhat like a squeegee. It scrapes off all the print paste on the surface of Roller A, but cannot clean off the print paste from the engraved portion, and thus leaves behind the print paste inside the etched copper.

4. The cloth to be printed is drawn and guided between the Cylinder Roller and Engraved Copper Roller A. The pressure created at the point of contact causes the print paste to be transferred from inside the etched copper to the cloth. The pattern is now on the cloth.

5. Engraved Copper Roller A continues in rotation and comes in contact with Lint Doctor D, a steel blade which comes in contact with Roller A and removes any lint picked up from the fabric being printed.

6. The cloth being printed continues its path around the Cylinder Roller. If a 2nd, 3rd or 4th colour is to be printed on the same fabric, then Steps 1 through 5 will be repeated for the respective 2nd, 3rd or 4th sets of Engraved Copper Roller, Doctor Blades, Colour Box and so forth. The fabric makes only one pass through the roller printing machine. Successive colours do not become smudged because the pressure of the engraved roller on the fabric being printed literally squeezes the print paste into the fabric and the surface colour dries instantly.

7. The printed cloth on leaving the machine is immediately dried so that the fabric can be touched without smudging the print. Afterwards, the fabric is transferred to a steam chamber where moisture and heat will set the dyes. If pigments rather than dyes are used, the fabric is entered into a dry heat curing oven at temperatures up to 400°F.

8. 'The Back Grey is a fabric that moves through the print machine along-with and in back of the fabric being printed. Its function is to absorb the excess print paste which may strike through and stain the Cylinder Roller cover. The Back Grey is later washed out and used over and again. It eventually takes on a dingy grey colour, hence its name.