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Dyeing
By :   Dg Ladha 
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"The process of applying color to fiber stock, yarn or fabric is called dyeing." There may or may not be thorough penetration of the colorant into the fibers or yarns.


Dyes can be used on vegetable, animal or man made fibers only if they have affinity to them. Textile dyes include acid dyes, used mainly for dyeing wool, silk and nylon and direct or substantive dyes, which have a strong affinity for cellulose fibers. Mordant dyes require the addition of chemical substances, such as salts to give them an affinity for the material being dyed. They are applied to cellulose fibers, wool or silk after such materials have been treated with metal salts. Sulfur dyes, used to dye cellulose, are inexpensive, but produce colors lacking brilliance. Azoic dyes are insoluble pigments formed within the fiber by padding, first with a soluble coupling compound and then with a diazotized base. Vat dyes, insoluble in water, are converted into soluble colorless compounds by means of alkaline sodium hydrosulfite. These colorless compounds are absorbed by the cellulose, which are subsequently oxidized to an insoluble pigment. Such dyes are colorfast. Disperse dyes are suspensions of finely divided insoluble, organic pigments used to dye such hydrophobic fibers as polyesters, nylon and cellulose acetates.

Reactive dyes combine directly with the fiber, resulting in excellent colorfastness. The first ranges of reactive dyes for cellulose fibers were introduced in the mid-1950. Today, a wide variety is available.


Methods of Dyeing:


1) 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.


2) 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 mlange, mottled or streaked effect, imitated in machine printing.


3) Beam Dyeing: In this method the warp is dyed prior to weaving. It is wound onto a perforated beam and the dye is forced through the perforations thereby saturating the yarn with color.


4) Burl or speck Dyeing: This is done mostly on woolens 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.


5) 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.


6) Cross Dyeing: This is a very popular method in which varied color effects are obtained in the one dye bath 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.


7) Jig Dyeing: This is done in a jig, kier, vat, beck or vessel in an open formation of the goods. The fabric goes from one roller to another through a deep dye bath until the desired shade is achieved.


8) Piece Dyeing: The dyeing of fabrics in the cut, bolt or piece form is called piece dyeing. It follows the weaving of the goods and provides a single color for the material, such as blue serge, a green organdy.


9) 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 onto 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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Published On Saturday, January 17, 2009
 
 
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