Dyeing
Dyeing is the process of adding color to textile products like fibers, yarns, and fabrics. Dyeing is normally done in a special solution containing dye sand particular chemical material. After dyeing, dye molecules have uncut Chemical bond with fiber molecules.
The Temperature, Time & Liquor Ratio controlling are three key factors in dyeing.
Dyeing Methods
Colour is applied to fabric by different methods of dyeing for different types of fiber and at different stages of the textile production process. Dyeing can be done during any stage in the textile manufacturing process. Textiles may be dyed as fibre, as yarn, as fabric, as garments, depending upon the type of the fabric or garment being produced.
These methods include
-
Direct Dyeing
-
Stock Dyeing
-
Top Dyeing
-
Yarn Dyeing
-
Piece Dyeing
-
Cross Dyeing
-
Union Dyeing
-
Tone on Tone Effect Dyeing
-
Solution Is Pigmenting or Dope Dyeing
-
Garment Dyeing
All of these direct dyeing and Yarn Dyeing methods are the most popular ones.
Direct Dyeing
When a dye is applied directly to the fabric without the aid of an affixing agent, it is called direct dyeing. In this method the dyestuff is either fermented (for natural dye) or chemically reduced (for synthetic vat and sulfur yes) before being applied. The direct dyes, which are largely used for dyeing cotton, are water soluble and can be applied directly to the fiber from an aqueous solution. Most other classes of synthetic dye, other than vat and sulfur dyes, are also applied in this way.
Stock Dyeing
Stock dyeing refers to the dyeing of the fibers, or stock, before it is spun in to yarn. It is done by putting loose, un-spun fibres in to large vats containing the dye bath, which is then heated to the appropriate temperature required for the dye application and dyeing process. Stock dyeing is usually suitable for woolen materials when heather like color effects are desired. Wool fibre dyed black, for example, might be blended and spun with un-dyed (white) wool fibre to produce soft heather like shade of grey yarn. Tweed fabrics with heather like color effects such as Harris Tweed are examples of stock dyed material. Other examples include heather like colours in covert and woolen cheviot.
Top Dyeing
Top dyeing is also the dyeing of the fibre before it is spun in to yarn and serves the same purpose as stock dyeing – that is, to produce soft, heather like color effects. The term top refers to the fibres of wool from which the short fibres have been removed. Top is thus selecting long fibres that are used to spin worsted yarn. The top in the form of sliver is dyed and then blended with other colors of dyed top to produce desired heather shades.
Yarn Dyeing
Yarn dyeing is the dyeing of the yarns before they have been woven or knitted into fabrics. Yarn dyeing is used to create interesting checks, stripes and plaids with different-colored yarns in the weaving process. In yarn dyeing, dyestuff penetrates the fibers in the core of the yarn. There are many forms of yarn dyeing- Skein (Hank) Dyeing, Package Dyeing, Warp-beam Dyeing, and Space Dyeing.
Skein (Hank) Dyeing: Skein dyeing consists of immersing large, loosely wound hanks (skeins) of yarn into dye vats that are especially designed for this purpose. Soft, lofty yarns, such as hand knitted yarns are usually skein dyed. Skein dyeing is the most costly yarn-dye method.
Package Dyeing: In package dyeing the yarn is wound on a small perforated spool or tube called a package. Many spools fit into the dyeing machine in which the flow of the dye bath alternates from the center to the outside, and then from the outside to the center of the package. Package dyed yarns do not retain the softness and loftiness that skein-dyed yarns do. They are however satisfactory and very widely used for most types of yarns that are found in knitted and woven fabrics.
Warp Beam Dyeing: Beam dyeing is the much larger version of package dyeing. An entire warp beam is wound on to a perforated cylinder, which is then placed in the beam dyeing machine, where the flow of the dye bath alternate as in the package dyeing. Beam dyeing is more economical than skein or package dyeing, but it is only used in the manufacture of woven fabrics where an entire warp beam is dyed. Knitted fabrics, which are mostly produced from the cones of the yarn, are not adaptable to beam dyeing.
Space Dyeing: In this method, the yarn is dyed at intervals along its length. For these two procedures- knit- deknit method and OPI Space-Dye Applicator- are adopted. In the first method, the yarn is knitted on either a circular or flat-bed knitting machine and the knitted cloth is then dyed and subsequently it is deknitted. Since the dye does not readily penetrate the areas of the yarn where it crosses itself, alternated dyed and undyed spaces appear. The OPI Space-Dye Applicator technique produces multi coloured space- dyed yarns. The yarns are dyed intermittently as they run at very high speeds through spaced dye baths. They are continuously subjected to shock waves produced by compressed air having supersonic velocities
Piece Dyeing
The dyeing of cloth after it is being woven or knitted is known as piece dyeing. It is the most common method of dyeing used. The various methods used for this type of dyeing include jet dyeing. Jig dyeing, pad dyeing and beam dyeing.
Cross Dyeing
Cross dyeing is a type of dyeing in which a yarn, a fabric, or even a garment made with two or more genetic fibres types having different dye affinities is dyed in a single bath containing two different class of dyes. Each class of dye colors only one type of the fibre. Two different colors can be dyed in one bath or either type of fibre may be dyed, leaving the other one white. If different fibres are blended in the same yarn, a stock-dyed effect can be obtained. If yarns of one kind of fibre and yarns of another kind of fibres are used in the warp direction, vertical stripes can be produced after dyeing. A plaid effect can be produced by weaving yarns of different kinds of fibre both in warp and filling directions and then dyeing the fabric in single bath with a mixture of two kinds of dyes. Whereas certain fibre combination allow for one bath process, other fibre combinations may require a two –step dyeing process to produce two colours. Cross dyeing is the more economical and quicker way to produce the same effects obtained by other methods. The effects achieved by expensive stock dyeing method can be replicated easily by this cross dyeing method.
Union Dyeing
Union dyeing is same as like cross dyeing, except that instead of multi color effects, one solid color is produced. The dyer accomplishes this by using two or more classes of dye, each of the same color. For example, a fabric composed of rayon and acetate can be dyed by a solid green color by using a direct dye for rayon and disperse dye for acetate.
Tone –on Tone Effects
Tone on tone effect is also possible by using one dye bath. They are light and dark shades of the same color in a fabric containing only one generic fibre – for example, deep red and light red colors on the same piece dyed polyester fabric. The effect can be produced by combining two different types of polyester in the same fabric. Both types are capable of combining with the same dye class, but one fibre has strong affinity for dye than the other. The fibre with the stronger affinity combines with greater quantity of dye, becoming deeper in shade, and second fibre remains a lighter shade of the same color. Tone on tone effects can only be achieved with the specific varieties of nylon, polyester and acrylic fibres. These special properties are imparted during the manufacture of the fibre, and the fibres are marketed to textile producers as deep –dye types. In addition nylon is produced in both deep-dye and ultra-deep-dye varieties, thus providing the possibility for three-tone effects of the same color. The tone on tone effects is widely used in the carpet industry for producing tweed-effect designs on piece dyed carpeting.
Solution in Pigmenting or Dope Dyeing:
This is a method applied for dyeing the synthetic fibers. Dye is added to the solution before it is extruded through the spinnerets for making synthetic filaments. This gives a colorfast fiber as the pigments are used which are the fastest known colors.
Garment Dyeing
Garment dyeing is the dyeing of the completed garments. The types of apparel that can be dyed are mostly non-tailored and simpler forms, such as sweaters, sweatshirts, T-shirts, hosiery, and pantyhose. The effect on sizing, thread, zippers, trims and snaps must be considered. Tailored items, such as suits or dresses, cannot be dyed as garments because the difference in shrinkage of the various components and linings disort and misshape the article. Garment dyeing is done by placing a suitable number of garments (usually about 24 sweaters or the equivalent, depending on the weight) into large nylon net bag. The garments are loosely packed. From 10 to 50 of the bags are placed in large tubs containing the dye bath and kept agitated by a motor– driven paddle in the dye tub. The machine is appropriately called a paddle dryer.