There are various methods of space dyeing on different forms of yarn.
Hank or Skein printing: The ready to dye yarn in hank or skein form is mounted on a stand or laid on a suitable surface and then different colors are applied either by brush or by spraying at fixed places to achieve the desired multicolour effect. Depending on the type of substrate and the dyestuffs used the hanks are then processed for suitable dye-fixation followed by finishing. Though, this method imparts controlled yarn coloration at specified points and desired length, the process is cumbersome and time consuming and is mainly suitable for short length fabric.
Space dyeing in package form: Depending on the machinery available and the effect desired, the yarn printing in package form is done by two methods:
1. Manual operation: Colors are injected by hand at different places in the package using a syringe filled with the dye solution. The skill set developed by the technicians enable them to insert the needle in the package horizontally, vertically or at various angles and release the color while taking the needle out so that the required amount of dye is applied at the specified place in the package.
Another variant of this method is dip-stick process. In this case different places of the yarn package are dipped in different dye solution so that multiple colors get applied at various places and with varying intensity which after unwinding of yarn provides a unique fancy dyed effect.
2. Machine processing: The ready for dyeing yarn is pre-treated as per the standard application process for the specified substrate and dyed in a single package form in a machine which can dye up to 8 colors. Each color has a different feed tank as well as injector pump. The color is injected at a fixed place at high pressure and the excess color is collected through vacuum. This creates beautiful patterns of dyed patches on package with good sharpness. Subsequently the colored yarn package is given adequate dye fixation treatment followed by washing off of unfixed superficial dye and finishing with a yarn lubricant/softener.
Knit de knit process: This process involves first knitting the yarn on a circular or flat-bed knitting machine into a tubular fabric followed by printing using engraved rollers and then unraveling the knit to produce a space dyed yarn. As the printed color does not readily penetrate the areas of the yarn where it crosses itself, alternately dyed and undyed spaces appear. In another method, the pre-dyed knitted material is overprinted with different colors and subsequently de-knitted to produce contrast effect of overprinted and base dyed areas.
This imparts a unique 'micro-spaced' design, owing to the limited dye diffusion during the printing stage. The unraveled printed yarn is rewound onto cones and used for subsequent knitting or carpet weaving. Since this process achieves limited dye penetration into the yarn, as the pressure exerted by the printing rollers is insufficient to insure adequate dye diffusion, incomplete and non-uniform coloration may result. Also, there is a characteristic curl to the unraveled yarn due to pre-knitting which affects cut pile of carpets.
Continuous or warp yarn printing: In this process multiple strands of yarn are continuously printed at spaced intervals with different colors. These yarns usually have long spaces of each color spaced at about 3 to 7inches. The yarn is dyed as singles or piled form and the color is applied either by air jets or dye troughs. Given below are few methods of continuous yarn printing for achieving space dyeing effect based on the information gleaned from various patented processes.
One of the methods describes yarn dyeing at intervals along its length as it runs at very high speed through spaced dye baths. Another method specifies systems where yarns are taken from wound packages on a creel and color is applied, either by lick rollers or by a spinning disc applicator. Such warp printing imparts a 'long spacing' design which is generally preferred for manufacturing of tufted carpets.
One process indicates passing of yarns between a pair of cylinders around the surface of which are mounted rows of small dye applicator pads. The lower cylinder is dipped into a trough of dye liquor which gets picked up on the surface of the pads and when the opposing pairs are in the raised position the yarn passing between them gets printed.
Another method proposes space dyeing by running yarn through the nip of printing rollers which have patterned grooves on the outer periphery. In this apparatus, the printing rollers apply dye to the yarn only when the lands of the two rollers are aligned across the nip. Another process incorporates printing rollers with grooves about their peripheries to provide a gear-like appearance. Thus, when the yarn is deflected into the nip, that portion of the yarn which passes through the nip gets intermittently printed to achieve closely spaced marks or dots and thus further vary the dye pattern applied to the yarn.
The advantage of space dyeing process over conventional solid dyeing is not only in terms of the intended special effect but also in terms of reduced consumption of dyestuff and chemicals, avoidance of printing thickener and considerable reduction in effluent. However, the challenges associated with space dyeing process include process to avoid mixing or overlapping of colors along the length of yarn and on the adjacent yarns which otherwise tend to result in visible streaks on the face of the fabric affecting its appearance.
Another issue pertains to tendency of dye migration during the subsequent heat setting operation resulting in blurring of adjacent color bands affecting its appearance. Further, there is a chance of dye dripping or contact mark off between different yarn layers resulting in unwanted patches. Moreover, the dye overspray from the various colors being applied often mix together in a single collection system, which result in added costs for replacement of dye as well as for waste handling and disposal. This has necessitated further development of an in-line process for controlled, efficient and repeatable space-dyeing of yarn.
Space dyeing is a technique used to give yarn a unique, multi-colored effect. When woven or knitted together for apparel, home furnishing and carpet making, beautiful patterns can emerge depending on the length and variation of each color block. Adequate use of dyes and auxiliary chemical combined with specialized machines can create finished product as some of the best in the world. Presently the 'Space Dyeing' segment occupies a miniscule (less than 1%) share in the textile coloration space. However, considering its potential to offer unique and customized print design effects it has great potential to grow by many folds in the near future.
1. Warren S. Perkins, August 1991, A Review of Textile Dyeing Processes Vol. 23
2. Shangnan Shui and Alejandro Plastina; FAO/ICAC World Apparel Fibre Consumption Survey ICAC 2013
3. Google images