Chapter 8 TEXTILE SCIENCE

Spectrophotometer

A typical color-management system consists of a spectrophotometer (which is capable of analyzing the color of an input sample) and a computer (in whose memory are stored the color characteristics of the dyer's dyestuff inventory). The computer software enables the system to take the spectrophotometer reading of the sample, scan the computer memory, mathematically mix the dyes to reproduce the original sample shade, and output dye-color selections and percentages of each to be used for reproducing the color of the original sample.

Color Management Systems

Although the chemistry of dyes and dyeing is extremely complex, the development of electronics, sophisticated software, and information enabled communication services have made the use of color-management systems pervasive and necessary for large-scale dyeing production. Matching shades and the approval of colors are now executed over the internet, without the necessity of seeing visual samples that must be sent by mail or courier. Enable dyers to rapidly produce the original color formulations and are also capable of monitoring the dyeing cycle for samples and later large-scale production.

Crocking

At the completion of the dyeing cycle, the goods must be thoroughly scoured with soaps or detergents and then rinsed thoroughly to remove excess dye that has not reacted with the fiber. This is an important part of the dyeing procedure. Failure to remove the excess and unreacted dye results in poor initial washfastness and excessive rubbing off of color, called crocking, even after extensive wear.

Colorfastness

Colorfastness refers to the property of a dyed or printed textile to resist color loss or fading as a result of laundering, dry cleaning, sunlight, bleach, perspiration, environmental gases, swimming pool chlorine, and various other conditions of use.

Cross Dyeing

Cross dyeing is a type of dyeing in which a yarn, a fabric, or even a garment, made with two or more generic fiber types having different dye affinities, is dyed in a single bath containing two different classes of dyes. Each class of dye colors only one type fiber. Or one class of dye is put in, leaving other fibers white. Cross-dyeing can also be achieved with one generic fiber type. This can be done because some of the manufactured fibers are modified during their production to permit them to combine with other dye classes not compatible with the unmodified form of the same fiber.

Garment Dyeing

Garment dyeing is the dyeing of 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. A major advantage of garment dyeing is the ability to respond to quick changes in fashion and last-minute demands to quick changes in fashion and last-minute demands of retailers and customers. Cannot be used for tailored items because of shrinkage in linings and distortion.

Poor Penetration

In piece dyeing, when heavy or densely woven fabrics, or hightly twisted yarn fabrics, are piece dyed, sometimes the dye does not penetrate into the center of the yarn material. The condition, known simply as poor penetration, leaves the fibers in the center of the yarns, or at fabric interlacing, lightly colored or undyed.

Standard

Once a color is approved from lab dip, the color becomes the standard to which all future orders of the same colors must conform to in large-scale production. In actual practice, however, each new batch, or dye lot, is slightly different in shade from all other lots before or after.

Lab Dip

Once the dyer has a formula, a sample swatch of the dyeing known as a lab dip is made. Several lab dips, each with a formula adjustment, may be needed to exactly duplicate the desired color.

Dyes

One of two ways of imparting color to textiles. It is the most widely used method. The process involves the use of chemical dyes called dyestuffs and the treatment of the textile material in aqueous (water) solutions. First fabric is cleaned. Then water, dye, chemicals, and textile material are brought together for a period ranging from several minutes to several hours, depending on the dyes being used and the fibers being dyed. Then it must be thoroughly washed with detergents, failure to do so will lead to poor initial colorfastness.

Pigments

One of two ways of imparting color to textiles. Pigments are microscopic-sized, insoluble colored particles made to adhere to a fabric. Pigments, unlike dyes, are insoluble in water and do not unite or combine in any way with the textile fiber. Pigment particles are microscopic colored chips that may be held on the surface of a fiber by resin binding agents. Pigment color is usually mixed with a resin binder and applied as a resin/pigment mixture. In order for the pigment to adhere to the fabric, the resin must be heated in a process known as curing. This step, done after the pigment/resin mixture is applied to the fabric, involves heating the material for a specific time. Because pigments do not comibne or react with the textile fibers, they may be used with any fiber or combination of fibers. Crocking is an issue.

Solution Dyeing/Dope Dyeing

Solution dyeing is unlike either of the two categories (dye and pigment) described earlier in this chapter. Solution dyeing is part of the process of manufacturing fibers. In this method, the coloring agent is added to the liquid spinning solution of manufactured fiber before it is extruded from a spinnerette. The color becomes part of the fiber itself and is permanent. Fabrics made from solution-dyed yarns are thus well suited for draperies, automotive fabrics, and other applications where great sunlight exposure is anticipated. Solution-dyed materials are available in only a limited range of colors. Not widely used in apparel.

Stock Dyeing

Stock dyeing refers to the dyeing of fibers, or stock, before it is spun into yarn. It is done by putting loose, unspun fibers into large vats containing the dye bath, which is then heated to proper temperature. Stock dyeing is used mostly for woolen materials when heatherlike color effects are desired. Wool fiber dyed black might be blended and spun with undyed white wool fiber to produce a soft, heatherlike shade of gray yarn.

Depth of Shade

The darkness or lightness of color in dyeing, known as the depth of shade, is dependent on the quantity of dye used as a ratio with the fiber, yarn, fabric, or garment weight being dyed.

Piece Dyeing

The dyeing of cloth after it has been woven or knitted is known as piece dyeing. It is the most common method of dyeing used. Various methods used for this type of dyeing include jet dyeing, jig dyeing, pad dyeing, and beam dyeing.

Dye Classes

To make order out of what otherwise would be chaos in classifying which dye reacts with which fiber, all of the thousands of dyes are grouped into dye classes. Most dyes in each class possess similar (but by no means equal) colorfastness characteristics and are applied with similar techniques at similar temperatures.

Tone-on-tone Effects

Tone-on-tone effects are also possible by using one dye bath. They are light and dark shades of the same color on a fabric containing only one generic fiber. For example, deep red and light red colors on the same piece-dyed polyester fabric. This effect can be produced by combining two different types of polyester in the same fabric. Can be achieved with specific varieties of nylon, polyester, and acrylic fibers.

Top Dyeing

Top dyeing is also the dyeing of fiber before it is spun into yarn and serves the same purpose as stock dyeing--that is, to produce soft, heatherlike color effects. It is used in worsted materials. Top-dye fabrics include garbadine, worsted cheviot, and serge.

Union Dyeing

Union dyeing produces one solid color on a fabric containing two or more classes of fiber. The dyer accomplishes this by using two or more classes of dye, each of the same color.

Affinity

When a particular dye is capable of combining with a fiber and can impart color to it, the dye has affinity for that fiber.

Metamerism

When two colors match each other under one light condition--for example, daylight--but look different from each other in a different light--such as indoor light illumination--the condition is known as metamerism. May be caused when the dye components for the shade being matched are chemically different from the components that were used for the original. It is highly unlikely that metamerism would occur from dye lot to dye lot of the same color if all the dyeings were performed by the same dyer. Important in sportswear wear components must be same shade under all conditions

Yarn Dyeing

Yarn dyeing, as its name implies, is the dyeing of yarns before they have been woven or knitted into fabrics. Used mainly fr production of multicolored designs such as plaids, stripes, and checks. Typical yarn-dyed fabrics are multicolored gingham, madras, brocade, and multicolored weft knits.