DYEING WITH DYES

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DYEING

The color of a textile product may be its most important marketing attribute. It is the color of the dyed (or printed) fabric that first attracts and then draws consumers to particular items for sale. It is often the color of a product that sells the product. Dyeing is impregnating fiber, yarn, fabric or garment with a dyestuff. Dyes are colorants that are applied to, or formed in, a textile substrate in a molecularly dispersed form. they derive their color from the conjugated double bonds in their molecular structure.

The definition stresses that for use in textiles, dyes must be soluble or capable of being made soluble in the medium in which they are applied, or they must themselves be molecularly dispersible into the fibers. It is this property that distinguishes them from pigments. When a dye colors a fabric directly, without the aid of a fixing agent its called Direct Dye. In some other dyeing processes, a fixing agent is required to fix dye to fiber; the fixer is called mordent

Fastness of color is its ability to remain unchanged. Color fastness may be affected by such factors such as perspiration, dry cleaning, sunlight, salt water etc. Adding color to textiles, thus making fabrics marketable as fashion component, is a sophisticated and complex area where art and creativity meet with science and technology. Although the chemistry of dyes and dyeing are extremely complex, the development of electronic and computer science applied to the dyeing process has opened the world to rapid global trading and quick response systems. Matching shades of dyeing and the approval of colors may now be executed by phone and fax (without the necessity of seeing visual samples that must be sent by mail or courier) thus saving many weeks in international and domestic trade cycling. Details covering electronic and computer usage are included in this chapter as are explanations of the traditional processes of textile dyeing.

Although color is recognized as the most important element in textile sales and merchandising, it is also the source of most problems that consumers and the textile industry encounter in the production and use of fabrics. Fading, bleeding, color staining and color streaking are typical examples. Understanding the dyes and dyeing processes discussed in this chapter can aid in reducing or eliminating many of these problems.

Colorfastness of dyeing:

A fabric that retains its color during care and use is said to be dyeing colorfast. Fastness that is affected by the factors discussed above is an important concern of consumers. Small aggregates of dye molecules distributed evenly throughout the fiber make for a more satisfactory result than do surface applications of dyes. Fabrics may be more or less colorfast to a variety of different substances or conditions.

The importance of colorfastness of dyeing depends on the use of the fabric. Colorfastness to laundering is, of course, important in those garments and household textiles that must undergo frequent laundering. Some dyes are not fast to laundering but are fast to dry cleaning, or vice versa. Perspiration may cause some color change and/or color transfer, and some colors are may be lost or diminished by hear. Dyeinf colorfastness to sunlight may be important in evaluating the - usefulness of fabrics for curtains, draperies, carpets, and outdoor clothing in case of dyeing.

Light fastness of dyeing is usually a function of the dye structure rather than its retention within the fibers. The molecular structure that provides the color can be interrupted by light, particularly ultraviolet light. Additives or finishes are available to stabilize dyes from this type of action in case of dyeing.

Some dyes tend to crock, or rub off on fabrics or other materials with which they come in contact. Others will bleed into water during laundering and may be picked up by lighter-colored fabrics. Chlorine bleaches will remove color from most dyed fabrics, but some dyes are more sensitive than others to the action of chlorine bleaches of dyeing.

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