Methods of Space Dye Yarn
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.
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.
Yarns suitable for segment dyeing include: cotton, polyester cotton, acrylic cotton, viscose staple filament, acrylic, rayon, polyester yarn, pure plush yarn, nylon yarn, nylon staple filament and various blended yarns , The dyes that can be used for segment dyeing are: reactive dyes, acid dyes, disperse dyes, coatings, etc.
Dope dyeing of cotton yarn
The paint section has complete dyeing spectrum, convenient color matching, stable color and light, not easy to permeate, clear outline, simple process, and the disadvantage is that it feels hard.
Technological process: After scouring, the scouring and printing section of the yarn is dyed and sizing and then steamed (100-102℃, 5-10min)—washing—drying—sizing
Process points: Adhesives: Use cross-linking adhesives, such as screen printing adhesives, with good film-forming feel, high brushing fastness, and no yellowing at high temperature. The dosage should be determined according to the concentration of the paint in the color paste. High, if the dosage is too small, the fastness is poor;
Reactive dyestuffs of cotton yarns
The reactive dyes have complete chromatogram and excellent dyeing fastness. The dyeing of pure cotton yarn mainly uses KE reactive dyes. However, it is found in production that if KE is used for segment dyeing, the washed dyes are easily contaminated, resulting in fast dyeing. This may be because the KE type is a dual reactive base type, and the reactivity is higher than that of the K type. Unreacted dyes and hydrolyzed dyes are easily stained when washed with water. For this reason, K type dyes for printing are used, which are reasonably priced and easy to use. Satisfactory fastness can be obtained.
Process flow
The scouring yarn is dyed and sizing in the jet printing section and then steamed (100-102℃, 5-10min)-washing-drying-sizing.
The main points of the process are as follows
When steaming, wrap the yarn with dry cloth to prevent seepage; choose medium-viscosity seaweed pulp, which is conducive to the color paste sprayed from the nozzle and penetrated into the lower layer of yarn, and 0.25%-0.5% of Sodium hexametaphosphate to prevent the influence of calcium ions, at the same time adjust pH=7-8 with soda ash, the whole paste requires no agglomeration; urea plays the role of wetting and solubilization, because the yarn is directly sprayed on the dyed size without drying. For steaming, when the amount of urea is large, it will cause serious infiltration. When it is dark, it can be added appropriately, and it can be omitted for medium and light colors. Baking soda is used as an alkali release agent, and the temperature of the paste should be lowered to room temperature before adding it. Otherwise, a large number of air bubbles will be generated in the color paste, and the stability of the color paste will decrease, which will affect the color supply and color fastness; the dye dissolution temperature does not exceed 90 °C, and the dye fastness of the reactive dye section is good and the hand feel is also good. Dye is used more.
Specific examples of segment dyeing process
Type B reactive dyes direct segment dyeing process. The orange segment dyeing process draws on the fabric printing method. In order to make the segment dyed part impermeable, the dye is formulated into a color paste, printed on the skein by the method of pad printing, and then the dye is fixed by appropriate post-treatment.
