DYEING METHOD:-
Dyeing Methods:-
Coloration may be carried out at any stage in the manufacture of textile goods, and dyeing machines are available for dyeing textiles in the form of loose stock, tow, slubbing, sliver, yarn or fabric. Fabric may be dyed in all its forms, such as woven, non‐woven and knitted fabrics or as hosiery or garments, so there is a wide variety of dyeing machines available.
top dyeing
Color is applied to fiber, yarn, fabric or garment 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 fiber, as yarn, as fabric, as garments, depending upon the type of the fabric or garment being produced. Dyeing machineries can be classified accordingly.
Types of textile material to be processed:-
1) Loose-stock dyeing machine for fibers.
Hank/package/rope dyeing machines for yarns.
2) Jigger/winch/jet/beam/padding mangle dyeing machines for fabrics.
3) Rotary drum/side paddle for dyeing garments.
Processing methods:-
1) Discontinuous method; batchwise in rope form (winch, jet) or in open width (jigger).
2) Semi-continuous systems.
3) Continuous systems for high production.
Operating Principle s:
1) Dyebath circulation systems
2) Textile material moving systems
3) Both dyebath circulation and textile material moving systems.
Process Conditions:-
1) Closed (high pressure/high temperature) or open systems according to the type of material and the process to be carried out.
Classification of Dyeing Methods / Dyeing Techniques/ Dyeing Process:-
Dyeing methods can be classified into two main types: exhaust dyeing and pad dyeing.
A) Exhaust Dyeing:-
In exhaust dyeing, a finite amount of textile materials (in the form of fibers, yarn or fabric) is placed in the dye liquor and remains in its contact throughout the dyeing time, during which the dye molecules gradually move (or exhaust) from the liquor toward the fabric, for absorption and fixation in the textile material. The rate of dye exhaustion, absorption and fixation are controlled with the help of dyeing temperature, liquor agitation, pH or auxiliaries such as electrolytes, alkalis, leveling agents or retarding agents, etc. the liquor to material ratio (L:R) is also an important factor in exhaust dyeing i. e. the ratio between the amount of liquor and the weight of textile material dyed in that liquor in a batch. Total dyeing time required in exhaust dyeing depends on several factors including: depth of shade, type of dyestuff, nature of textile material and type of dyeing machine. The general phases in exhaust dyeing include the following:
1) Disaggregation of dye particles in aqueous solution or dispersion
2) Exhaustion or movement of the dye molecules from the solution / dispersion towards the textile substrate.
3)Adsorption of the dye molecules on the surface of the textile substrate
4)Absorption, penetration or diffusion of the dye molecules into the fibers of the textile substrate
5)Fixation of the diffused dye in the fibers through chemical bonding or by some other mechanism.
B) Pad Dyeing:-
In pad dyeing method, a continuous batch of fabric in open width, passes through an impregnator (or padding trough) containing dye liquor, followed by a passage between a pair of squeeze rollers. The pressure of the squeeze rollers can be adjusted to obtain a desired wet pick-up. For example, a wet pick-up of 100 % would result in fabric twice its original dry weight, after the impregnation and squeezing. The concentration of the dye in the padding tough and the wet pick influence the final depth of color obtained on the fabric. After passing through the squeeze rollers, the fixation of the dye on the fabric may be accomplished by variety of means including: making a batch of fabric and keep rolling the batch for a specific period (pad-batch dyeing method); passing the fabric through a drying and fixation unit (pad-dry-fix dyeing methods); passing the fabric through a drying and steaming unit (pad-drysteam dyeing method); passing the fabric through a steaming unit (pad-steam dyeing methods). After both the exhaust and pad dyeing methods, the dyed fabric is usually subjected to a washing / rinsing step to remove any unfixed dye from the fabric. Selection of a particular dyeing method depends on several factors including the form of textile material (fiber, yarn, knitted or woven fabric), availability of suitable equipment in the mill and batch size of the textile material.
Coloration of a textile material is achieved in a number of different ways. These coloration or dyeing methods include:
1) Direct dyeing;
2) Stock dyeing;
3) Top dyeing;
4) Yarn dyeing;
5) Piece dyeing;
6) Beck dyeing;
7) Cross dyeing;
8) Garment dyeing;
9) Solution pigmenting or dope dyeing;
10) Bale dyeing;
11)Batik dyeing;
12) Beam dyeing;
13) Burl or Speck dyeing;
14) Chain dyeing;
15) Blends dyeing etc.
Of these Direct dyeing and Yarn Dyeing methods are the most popular ones.
1) Direct Dyyeing
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 dyes) 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 sulphur dyes, are also applied in this way.
2) 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, unspun fibers 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 fiber dyed black, for example, might be blended and spun with un-dyed (white) wool fiber 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 colors in covert and woolen cheviot.
3) Top Dyeing:-
Top dyeing is also the dyeing of the fiber 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 fibers of wool from which the short fibers have been removed. Top is thus selecting long fibers that are used to spin worsted yarn. A top is made from a sliver, a thick band of carded and combed but untwisted fibers that lie parallel to each other, by cross‐winding it into a ball about 40 cm in diameter, securing it with strings and then flattening it somewhat into a more cylindrical shape.
Fig: Nine cages, each containing five bump tops, ready to be hoist into the dyeing machine
4) 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-
1) Skein (Hank) Dyeing,
2) Package Dyeing,
3) Warp-beam Dyeing, and
4) Space Dyeing.
a) Skein (Hank) Dyeing:-
Skein or Hank 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.
b): Package Dyeing:-
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. 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.
package dyeing
Fig: Cheese packages on rigid plastic formers, after dyeing.
c) 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. 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.
d) Space Dyeing:
In this method, the yarn is dyed at intervals along its length. For these, two procedures such as knit–deknit method and OPI space–dye applicator are adopted. In the first method, the yarn is knitted on either a circular or a flatbed 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 multicolored space-dyed yarns. The yarns are dyed intermittently as they run at very high speeds through spaced dyebaths. They are continuously subjected to shock waves produced by compressed air having supersonic velocities.
e) Piece Dyeing:-
The dyeing of cloth after it is being woven or knitted is known as piece dyeing. It is the most common methods of dyeing used. The various methods used for this type of dyeing include jet dyeing, Jig dyeing, pad dyeing and beam dyeing.
f) Beck Dyeing:-
It is used for dyeing long yards of fabric. The fabric is passed in rope form through the dyebath. This rope of the fabric moves over a rail on to a reel which immerses it into the dye and then draws the fabric up and forward and brings it to the front of the machine. This process is repeated many times until the desired color intensity is obtained.
g) Cross Dyeing:-
This is a very popular method in which varied color effects are obtained in the one dyebath for a cloth which contains fibers with varying affinities for the dye used. For example, a blue dyestuff might give nylon 6 a dark blue shade, nylon 6,6 a light blue shade, and have no affinity for polyester area unscathed or white.
h) 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.
9) Solution 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.
10) Bale Dyeing:-
This is a low cost method to dye cotton cloth. The material is sent without scouring or singeing, through a cold water bath where the sized warp has affinity for the dye. Imitation chambray and comparable fabrics are often dyed this way.
11) Batik Dyeing:-
This is one of the oldest forms known to man. It originated in Java. Portions of the fabric are coated with wax so that only un-waxed areas will take on the dye matter. The operation may be repeated several times and several colors may used for the bizarre effects. Motifs show a mélange, mottled or streaked effect, imitated in machine printing.
12) Beam Dyeing ;-
In this method the warp is dyed prior to weaving. It is wound on to a perforated beam and the dye is forced through the perforations thereby saturating the yarn with color.
13) Burl or Speck Dyeing:-
This is done mostly on woollens or worsteds, colored specks and blemishes are covered by the use of special colored links which come in many colors and shades. It is a hand operation.
14) Chain Dyeing:
This is used when yarns and cloth are low in tensile strength. Several cuts or pieces of cloth are tacked end-to-end and run through in a continuous chain in the dye color. This method affords high production.
15) Blend Dyeing:-
Textile fabrics comprising blend of more than one type of fibers can be dyed with suitable dyes to achieve different dyeing effect. In “union dyeing” both the fibers in a two-fiber blend (e. g. polyester / cotton) are dyed to have the same shade. In “cross dyeing”, each fiber component in a blend is dyed in different shade. In “tone-on-tone dyeing” two fibers in a blend (e. g. cotton / viscose rayon) are dyed with the same class of dye but the two types of fibers have different depth of shade.
16) Random Dyeing;-
Coloring only certain designated portions of the yarn. There are three ways of doing this type of coloring. Skeins may be tightly dyed in two or more places and dyed at one side of the dye with one color and at the other side with another one. color may be printed on to the skeins which are spread out on the blanket fabric of the printing machine.
Cones or packages of yarn on hollow spindles may be arranged to form channels through which the yarn, by means of air-operated punch, and the dyestuff are drawn through these holes by suction. The yarn in the immediate area of the punch absorbs the dye and the random effects are thereby attained.
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