Stages of Dyeing in Textile:
Dyeing can be done during various stages in textile, from the raw fiber right through to the finished garment. Earlier the stage of dyeing, the better is the penetration, resulting in better fastness properties of dyes. The later the stage of color application, lower is the cost and quicker is the response to the fashion trends but comparatively poor fastness properties. The following are the four stages at which dyeing can be carried out in textile:
- Fiber dyeing (also called stock dyeing)
- Yarn dyeing
- Fabric dyeing (also piece dyeing)
- Garment dyeing
The considerations that govern the choice of the dyeing stage are mainly technical and economical. Dyeing at the fiber stage is much more expensive than at other stages, but it will normally give the best fastness result as well as enabling production of a fancy color effect such as mottle, heather, etc., after a fiber blending process. Yarn dyeing is mainly used to produce a checks or stripe effect with different colored yarns. The details of these dyeing stages in textile industry are discussed in the following subsections.
A. Dyeing in Fiber Stage:
The process of dyeing at fiber stage is called as fiber dyeing. It includes stock dyeing, top dyeing and dope dyeing. Fiber dyeing is carried out on loose stock before the fiber is spun into yarn. It is done by putting packed loose fibers into the container of the loose-stock dyeing machine in which the dyeing will take place. The process is mostly used in the production of woolen materials, especially when mottled and heather-like color effects are desired. Fiber dyeing usually results in even dyeing and excellent penetration of dyes into the fibers, and hence good fastness properties. However, it is the most costly method for dyeing because the production rate is relatively low and there is 10%–15% waste due to loss of fibers during the process.
B. Dyeing in Yarn Stage:
Yarn dyeing is carried out after fiber has been spun into yarn. Yarn is dyed either as hanks or wound on to compact reels known as packages, mounted on hollow spindles. The process is mainly used to produce various effects of stripes, checks, plaids or other multicolor designs with different colored yarns in the weaving and knitting process. Moreover, threads for sewing and embroidery purposes are all dyed at the yarn stage. Yarns may be dyed in different forms:
1. Hank dyeing (Skein dyeing): Hank dyeing machines are relatively simple in their construction, though a number of different designs are available, including:
- Hussong type
- Cabinet style
- Hank spray type
- Space dyeing
Hank dyeing is much less common than package dyeing but is still used for dyeing lofty yarns such as wool and high‐bulk acrylic yarns for knitting and carpet manufacture.
2. Package dyeing (cone dyeing): In package dyeing, the pump forces the dye liquor up the hollow spindles and through the packages. The flow is reversed from time to time. The frame holding the spindles and the packages is contained in a cylindrical vessel with a dome‐shaped lid. Packages can take a variety of forms, with names such as cheeses, cones or cakes. The most commonly used type is the cheese, which is parallel sided and formed by winding the yarn on to cylindrically shaped formers.
3. Slasher dyeing / Warp beam dyeing: Beam dyeing machines are very similar to package dyeing machines but are used to dye yarn that is wound on to a beam ready for its use on the weaving loom as the warp. The yarn is wound carefully onto a specially perforated hollow beam. The dye liquor is forced through the perforated beam and through the yarn. As in the package machine the flow of liquor can be either in or out or changed between the two to even out the different pressures. The arrangement is similar to the horizontal package machine in that the beam is loaded horizontally into a vessel.
4. Rope dyeing: Rope dyeing is a method of dyeing yarns in bundles (ropes) of a certain number of threads. It is considered a superior dyeing technology where the dyeing uniformity achieved is better than any other indigo dyeing technologies like slasher dyeing. Rope dyeing machinery installation cost is higher than slasher dyeing.
C. Dyeing in Fabric Stage:
Fabric dyeing, also called piece dyeing, is the most popular production method for solid color, as it gives the greatest flexibility to the manufacturer in terms of inventory as well as production capacity. Large orders of woven fabric can be dyed in a continuous process, i.e., pad dyeing, while the batchwise jig dyeing is suitable for small batch production. For tension-sensitive materials, such as knitted fabrics or some thin woven fabrics, the batchwise process of winch dyeing and jet dyeing are the most appropriate dyeing methods.
The description of each dyeing method is discussed in the following list:
- Pad dyeing is a continuous process used to dye fabric in open-width form. The fabric is passed through a trough of dye liquid and then squeezed evenly by a pair of pad mangles to impregnate dye deep into the fibers. After padding, a series of operations like intermediate drying, chemical fixing of the dye, steaming, successive washing off and final drying will be followed.
- Jig dyeing is commonly used in the production of tightly woven fabric of medium to heavy weight, e.g., corduroy, canvas, etc. In the jigger dyeing machine (also called jigger), the fabric is held on rollers in open-width form and transferred repeatedly from one roller to another through a trough of dye liquor.
- Winch dyeing is the traditional dyeing method in the production of knitted fabrics. Pieces of fabric (to make up appropriate weight) sewn in rope form are loaded into the winch which essentially consists of a dye vessel fitted with a motor-driven wheel (also named winch). During operation, the winch will rotate and initiate an endless fabric movement with minimized tension through the dye liquid. The operation of winch dyeing is among the simplest, and the dyed materials retain much of their original fullness and softness.
- Jet dyeing is somewhat similar to winch dyeing in the sense that fabric in rope form is circulated through a dye liquid bath. However, in a jet-dyeing machine fabric movement is generated by a jet flow of dye solution instead of mechanical pull as in winch dyeing. As such, the dyed fabrics are almost free from creases and rope marks. Pressurized dyeing up to 130°C is also possible for synthetic fibers. Recent developments in jet-dyeing machines are moving towards process automation and cost reduction.
D. Dyeing in Product Stage (Garment Dyeing):
This is the last stage of dyeing in textile. When the finished product such as garment is dyed, it is called as product dyeing or garment dyeing. Garment dyeing is the dyeing of completed garments. Fully fashioned garments and body blanks for the cut-and-sew industry are increasingly dyed in garment form, as this allows the supplier to delay the choice of shade until the latest possible time before the garments appear on retail counters. Garment dyeing is primarily an economical method used for non-tailored garments such as sweaters, hosiery and pantyhose, etc. Nowadays fashion trends also require some cotton jeans and shirts to be dyed in completed garment form. During processing, an appropriate number of garments are loaded into the specific dyeing machine, either a paddle type or a rotating-drum type, which is more or less similar to that of a domestic washing machine, and the garments are agitated in the dye bath during color buildup.
References:
- A Novel Green Treatment for Textiles: Plasma Treatment as a Sustainable Technology by Chi-wai Kan
- An Introduction to Textile Coloration: Principles and Practice By Roger H. Wardman
- The Coloration of Wool and other Keratin Fibres Edited by David M. Lewis and John A. Rippon
