Giving color decoration to fabric after it has been finished is known as dyeing. When the yarns are woven into the fabric the interesting and intricate design of weavers being to add beauty as well as service ability. The various finishing processes suggest additional means to enhance the appearance of newly from fabric. It remains for the dyeing and printing processes to provide beauty and delight to the eyes. Both these processes add color to the fabric. In the dyeing process fabric yarns or fabric is immersed in a solution of dyestuff and is then saturated with dye.
SELECTION OF DYE
To select the proper dye for a fiber it is necessary to know which dye have an affinity for the vegetable, animal, manmade synthetic fiber. In general the dye used for cotton and Lenin may be used for viscose and cupramanium rayon but it is necessary to produced a special class of dye for dictate.
DIRECT DYE – When a dye, color the fabric directly with one fabric operation of immulsion without using the acid of fixing agent, the dye is said to be direct dye. Direct dyes are the easiest to produce, simplest to apply and cheapest in their initial cost as well in application. They are not fast to washing and to light.
MORDANT – A dye that has an affirmity for one type of fiber may not suit to the other side of fabric containing a mixture of fabric by using a mordant in the dye bath. Salts of metal and tannic acids are typical examples of such chemical agents
NATURAL DYES – Primitive man obtained dyes from flower, nuts berries and other from of flowers and vegetable and animal sources. These sources have provided such natural dyes throughout civilization. They are no longer used in quantity by the dyeing industry. But they are still used in many parts of world for handicrafts.
ARTIFICIAL DYES – Although artificial dyes were first derived from coal tar in 1856, they were not developed in the US to any great extent until 1st world war. When the supply of imported synthetic dyes was cut off since then US have has built a dye industry in numerable dye compounds made from coal tar have now supplanted natural dyes. These artificial or synthetic dyes are constantly being improved as to beauty of color and color fastness. Lasting beauty of color is an important factor in consumers finished goods. Durability of colors depends upon.
Selection of important dye for the fabric to be dyed.
Selection of method of dyeing the fiber, yarn on fabric.
- CLASSIFICATIONS OF SYNTHETIC DYESThe synthetic dyes are classified as-
- Acid
- Basic
- Neutral or substantive
The acid dyes are used for wool and basic dyes are used for silk. The neutral dyes are a new class specially adapted for cotton, linen and rayon. For this reason, they are called direct cotton dyes.
ACID DYES – In the textile industry, acid dyes are known as commercial colors. They are used as direct dyes for wool and they are also used when delicate tins are required for silk. They can be applied with some difficulty to nylon.
SULPHUR DYES – They are used for cotton, linen and rayon. These dyes are fast to washing and light but have one weakness. Excessive chlorine bleaching will strip the color. They are more expensive than direct dyes because unusual care is required in extras operation. Sulphur is insoluble in water but it is made soluble with aid of sodium sulphite and soda ash. The dyeing is done at high temperature with a large quantity of salt, which helps to drive the color into the fabric. After immersion in the dye bath followed by rinsing the fabric is oxidized to the desired shape by exposure to the air or chemically by the use of potassium bicarbonate and acetic acid. The oxidizing process must be carefully controlled because penetration of the dye is retarded by premature oxidation. Also oxidization changes sulphur to sulphuric acid, which may be harmful to the fabric. Excess chemicals and excess dye must be removed through washing. Sulphur dye penetrates more thoroughly than any other dye of high temperature. They are excellent for khaki and heavy piece goods used in work clothes. Sulphur dyes produce dull colors such as navy, brown and black. They are used for blacks more than any other dye. If stored for a great length of time fabrics becomes tender.
VAT DYES – These are the fastest dyed for cotton, linen and rayon. They can also be applied to nylon, Dacron, orlon, nicara with the use of modern dyes. Vat dyes are not only resistant to dyes and to acids but they are equally resistant to the strong oxidizing bleach used in commercial laundries. In this respect vat dyes excel sulphur dyes, which are not fast to chlorine washing. In reds and pinks however absolute colorfastness is sacrificed for brilliancy of dye. Consequently, a label stating that a garment that is vat dye is not a guarantee that the fabric is absolutely fast to washing if it is of brilliant color. The name “ imdanthrene” on labels indicate that a special type of dye has been used that is particularly fast to dye and washing. This type was among the finest of the synthetic vat dyes.
SELECTION OF METHOD OF DYEING
Textile may be dyed at any stage of their development from fiber into fabric.
* Stock dyeing in the fiber stage
* Yarn dyeing after the fiber has been put into yarn.
* Piece dyeing after the yarn has been constructed into fabric.
* Cross-dyeing a combination of either stock dyeing or yarn dyeing with subsequent piece dyeing.
* Solution pigmenting or dyeing before the man made of synthetic fiber.
