FACTS, FICTION…MY OPINION — COTTON SERIES…DYEING COTTON (The Fashion/Textile Industry)
FASHION TRENDING — : Fashion/Textile Industry (Dyeing Cotton)
Bruce Bisbey
Executive Producer / Partner Dumb Dog Productions — Media Arts International Film Corporation
Dyeing Cotton
Cotton is a soft, fluffy staple fiber. It is a natural and most popular fiber. Cotton is dyed with a range of dye types, including vat dyes, and modern synthetic reactive and direct dyes.
Dyeing is the application of dyes or pigments on textile materials such as fibers, yarns, and fabrics with the objective of achieving color with desired fastness. Dyeing is normally done in a special solution containing dyes and particular chemical material. Dye molecules are fixed to the fiber by absorption, diffusion, or bonding with temperature and time being key controlling factors. The bond between dye molecule and fiber may be strong or weak, depending on the dye used. Dyeing and printing are different applications; in printing color is applied to a localized area with desired patterns and in dyeing it is applied to the entire textile.
The primary source of dye, historically, has been nature, with the dyes being extracted from animals or plants. Since the mid-19th century, however, humans have produced artificial dyes to achieve a broader range of colors and to render the dyes more stable to washing and general use. Different classes of dyes are used for different types of fiber and at different stages of the textile production process, from loose fibers through yarn and cloth to complete garments.
Cotton is dyed with a range of dye types, including vat dyes, and modern synthetic reactive and direct dyes.
While both cotton and polyester are normally colored with synthetic dyes, dyeing cotton is a more water- and heat-intensive process.
While both cotton and polyester are normally colored with synthetic dyes, dyeing cotton is a more water- and heat-intensive process. The surface of cotton fibers is negatively charged and doesn’t readily react with negatively charged dye compounds.
Even with an assist from salts and alkali added to the dye solution, cotton takes up only about 75% of the dye. To ensure colorfastness, dyed fabric or yarn is washed over and over again in hot water, creating large amounts of wastewater.
The most commonly used processes for imparting color to cotton are piece dyeing and yarn dyeing. In piece dyeing, which is used primarily for fabrics that are to be a solid color, a continuous length of dry cloth is passed full-width through a trough of hot dye solution. The cloth then goes between padded rollers that squeeze in the color evenly and removes the excess liquid. In one variation of this basic method, the fabric, in a rope-like coil, is processed on a reel that passes in and out of a dye beck or vat.
Yarn dyeing, which occurs before the cloth is woven or knitted, is used to produce gingham checks, plaids, woven stripes and other special effects. Blue dyed warp yarns, for example, are combined with white filling yarns in denim construction.
One of the most commonly used yarn dyeing methods is package dyeing. In this system, yarn is wound on perforated cylinders or packages and placed on vertical spindles in a round dyeing machine.
Dye solution is forced alternately from the outside of the packages inward and from the inside out under pressure.
Computers are used increasingly in dyeing processes to formulate and match colors with greater speed and accuracy.
Printing
Printing colored designs on cotton cloth is similar to printing on paper. Long runs of the same fabric design are produced on a roller print machine Fabric Printing operating at speeds between 50 to 100 yards a minute. As many as of 10 different colors can be printed in one continuous operation.
A typical printing machine has a large padded drum or cylinder, which is surrounded by a series of copper rollers, each with its own dye trough and doctor blade that scrapes away excess dye. The number of rollers varies according to the fabric design, since each color in the design is etched on a separate roller. As the cloth moves between the rotating drum and rollers under great pressure, it picks up color from the engraved area of each roller in sequence. The printed cloth is dried immediately and conveyed to an oven that sets the dye.
Automatic screen-printing is another principal method for imparting colored designs to cotton fabrics. Although slower than roller printing, it has the advantage of producing much larger and more intricate designs, elaborate shadings and various handcrafted effects.
In flat bed screen-printing, the fabric design is reproduced on fine mesh screens, one for each color. On each screen, the areas in the design that are not to be penetrated by the dye are covered with lacquer or some other dye-resistant coating. The screens are coated with dye on the back and mounted in the proper sequence above a flat bed. As a belt carries the fabric along from screen to screen, a squeegee or roller presses the dye through the open area of the screen onto the fabric.
The new flatbed machines can have speeds of up to 1,200 yards per hour for a fabric with a 36-inch design repeat.
Faster by far are the recently developed rotary screen printing machines with production speeds of up to 3,500 yards an hour. The system combines roller and screen printing, utilizing perforated cylinders instead of flat screens. The color paste is fed inside the cylinders and a small metal roller forces the color through the pores of the cylinder onto the fabric which is moving continuously under the cylinders. As many as 16 colors can be printed on one fabric using this method. Use of this technique is increasing since the screens or cylinders can be produced less expensively than the engraved copper rollers used in roller printing.
Finishing
Finishing, as the term implies, is the final step in fabric production. Hundreds of finishes can be applied to textiles, and the methods of application are as varied as the finishes.
Cotton fabrics are probably finished in more different ways than any other type of fabrics. Some finishes change the look and feel of the cotton fabric, while others add special characteristics such as durable press, water repellency, flame resistance, shrinkage control and others. Several different finishes may be applied to a single fabric.
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 use 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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Sources, References & Credit: Google, Wikipedia, Wikihow, World Book Encyclopedia, Pinterest, Linked In, BBC, Wikimedia, The Free Dictionary By Farlex, Wikisource, New York Fashion Center Fabric, How Things are Made, The Guardian, Ickwhe, The Knot, Cotton Australia, Cottons Journey, National Cotton Council of America, Cotton.Org, Mulberry Cleaners, Stitch Fix, Shukr Clothing, Barnhardt Cotton, Cotton Spinning,
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Dyeing Cotton Fabric / Photo Credit: India Rajasthan — Getty Images
