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Yarn Printing or Space Dyeing | Process of Yarn Printing

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Yarn Printing (Space Dyeing):
Yarn printing is also known as “Space Dyeing”. Although the printing of yarns for true patterned effects proved very difficult tom control, the random space-dyed effects that can be more readily attained by a variety of yarn-printing methods have continued to be popular. The patent literature abounds with systems for producing colored flecked effects on yarns but the two most successful methods entail either warp printing or color application to a tubular knitted ‘sock’. The essential process sequence begins with dye liquor application, followed by steam fixation, washing-off and drying . 
 
space dyeing
Various warp-printing methods have been used over the years. In most present-day systems several ends of carpet yarn are taken from wound packages on a creel and colour is applied, either by lick rollers or by some form of spray or spinning disc applicator, to the yarns. The yarns are carried past the print heads in warp form or lying on a brattice on which they have been laid down in a continuous circular or elliptical coil. Warp printing tends to give the so-called ‘long spacing’ designs in the tufted carpet produced from them.

Knit–deknit applications, on the other hand, tend to give characteristically speckled ‘microspaced’ designs, because of the limited degree of penetration of dye liquor achieved by the duplex printing rollers into the yarn sock. 
 
yarn printing
Although the end-effects produced by the two methods are basically different, the processes can be modified so that their results are more closely comparable. Thus the long spacing effects of warp printing can be imitated by overall application of a ground colour followed by colour spotting with segmented lick rollers or oscillating jets of dye liquor. Similarly oscillating jets of liquor can be applied to knitted sock and excess liquor squeezed out before steaming. This leaves large coloured areas with good liquor penetration and, when tufted, the long spacing effect is achieved. Some examples of machines used for space dyeing are listed in Table 4.2.

Table: Space dyeing systems
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Yarn application Knit–deknit application
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Martin Processing Fleissner
Callebaut de Blicquy Ilma
Superbaa Whitaker
Hoeraufa Murphy
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In these machines dye fixation and heat setting of the yarns is achieved simultaneously

In contrast, the Crawford Pickering warp-printing system was designed to produce fully patterned tufted carpets with up to eight colors. The warp of yarns was passed between a pair of cylinders, around the surface of which were mounted rows of small dye applicator pads (about 20 mm square). The lower cylinder dipped into a trough of dye liquor and dye was thus picked up on the surface of the pads. These pads could be actuated mechanically so that when opposing pairs were in the raised position the yarn passing between them was printed. With a typical 5 mm pile height carpet, a 20 mm printed length of yarn was equivalent to two tufts of the final carpet. With longer pile carpets of the Saxony or shag pile type single tuft definition was possible, and it was on such carpet constructions that the best results were ultimately obtained. In the original machine the pattern control mechanism was a movable notched bar, the positions of the notches determining the raising or lowering of the print pads. Preparation of pattern bars was therefore rather tedious; later, one company introduced electro pneumatic actuation of the individual print pads with pattern data provided from a microprocessor. Ultimately, however, the full patterning potential of this machine was not realized, mainly because of the problem of keeping a warp of printed yarns in register. There is now only one machine left in operation.


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