Dyeing

(chemical engineering) The application of color-producing agents to material, usually fibrous or film, in order to impart a degree of color permanence demanded by the projected end use.

The application of color-producing agents to material, usually fibrous or film, in order to impart a degree of color permanence demanded by the projected end use. True dyeing covers mechanisms in which molecules of material to be dyed become involved by various means with the molecules of the coloring matter, or small aggregates thereof. There is some overlapping between true dyeing and other methods of coloring, which are called dyeing in the industry. Products which are commonly dyed include textile fibers, plastic films, anodized aluminum, fur, wood, paper, leather, and some foodstuffs. See also Dye.

Dyeing is accomplished by dissolving or dispersing the colorant in a suitable vehicle (usually water) and bringing this system into contact with the material to be dyed. Although many dye molecules or aggregates may adhere to the material surface when they meet, dyeing does not occur until the adhering dye particles migrate within the fibers or films. All dyeing processes are designed to accomplish ultimately penetration of the undyed substance by the colorant.

Assistants are materials which do not impart color to the product to be dyed but promote or retard dyeing. Usually, they affect the dye molecule.

Swelling agents are assistants which open up the structure of the fiber temporarily so that dye molecules or aggegates may enter more freely and reach otherwise inaccessible dye sites.

Carriers are agents (often solvents of low water solubility) which accelerate dyeing by breaking up or dissolving dye aggregates and bringing them to the fiber-water interface in a size small enough to be absorbed by the material.

Dye retarders are a class of dyeing assistants, usually inorganic or organic salts, which slow up the dyeing process by forming evanescent compounds with the dye, by buffering or depressing the ionization of an acid assistant, or by temporarily occupying the more active or more accessible dye sites on the fiber, later to be dislodged therefrom by the dye.

Aftertreating agents are salts, resins, or other products (more frequently applied to cellulosic fibers) to render the colored fabric more resistant to the effects of washing, perspiration, or fading by ozone or combustion gases. More often than not, their application causes a loss in light fastness of the dyed material.

Textiles

Cellulose fibers, such as cotton and rayon, are most commonly dyed by immersion of the fibers in a solution of direct dyes using an electrolyte such as common salt as assistant and then boiling this dyebath. Such dyeings usually exhibit only commercial (minimum) resistance to washing. Treatment of the properly dyed fibers with resins and copper, for example, increases the resistance to washing with minimum loss of light resistance.

Synthetic fibers, such as cellulose acetates and triacetate (Arnel), are dyed in a supension of solvent-soluble dyes by immersion. Polyamide synthetic fibers are dyed like wool with acid, metallized acid, neutral metallized, or fiber-reactive mordant dyes, azoics, and selected direct dyes from an acid bath. Special processes have also been developed for acrylic, polyester, and propylene fibers.

Nontextile materials

Anodized aluminum is readily dyed by many textile dyes. Light and weather resistance undreamed of in textile applications of some of these same dyes is achieved.

Paper pulp is usually dyed in the paper beater by dyes normally employed for cotton; on occasion, it is tinted by wool dyes, and it is frequently tinted by addition of pigments to the beater. Finished paper is also colored by passing it over rollers which supply dye or colored coatings to its surface (calender staining).

Leather is dyed at low temperatures with the classes of dyes normally used for wool and cotton. Formic acid is normally used to exhaust the dye. For dress gloves, leather is usually colored by applying the dye on the grain surface, leaving the flesh side undyed. Leather is also dyed with natural dyes such as logwood, fustic, and quercitron. Leather fresh from tanning and containing considerable moisture is dyed in Europe by tumbling with dry water-soluble dye.

Most food products which are artificially colored are not actually dyed. Maraschino cherries, however, are dyed for several hours with food dyes, then washed and placed in flavored syrup.

Many plastic materials may be dyed by processes similar to those employed for textiles. Nylon, cellulose acetate, polyethylene, polypropylene, and polyester resins are dyeable with dyes which color these materials in yarn form. See also Manufactured fiber; Natural fiber.

Tutor's tip: The factory workers feared they were "dying" (present participle of die) young because of the "dyeing" (coloring fabrics) processes in their work.

Pigments for sale at a market in Goa, India.

Cotton being dyed manually in contemporary India.

Dyeing is the process of imparting colours to a textile material in loose fibre, yarn, cloth or garment form by treatment with a dye.

Contents 1 Dye types 2 Methods 2.1 Direct application 2.2 Yarn dyeing 3 Removal of dyes 4 History 5 See also 6 References 7 External links

Dye types

Main article: Dye

For most of the thousands of years in which dyeing has been used by humans to decorate clothing, or fabrics for other uses, the primary source of dye has been nature, with the dyes being extracted from animals or plants. In the last 150 years, man has produced artificial dyes to achieve a broader range of colors, and to render the dyes more stable to resist washing and general use. Different classes of dye are used for different types of fiber and at different stages of the textile production process from loose fibers through yarn and cloth to completed garments.

Acrylic fibers are dyed with basic dyes, nylon and protein fibers such as wool and silk are dyed with acid dyes, polyester yarn is dyed with disperse dyes. Cotton is dyed with a range of dye types including vat dyes which are similar to the ancient natural dyes and modern synthetic reactive and direct dyes.

Methods

Dyeing in Fes, Morocco.

Dyes are applied to textile goods by dyeing from dye solutions and by printing from dye pastes.

Direct application

This section requires expansion.

The term "direct dye application" stems from some dyestuff having to be either fermented as in the case of some natural dye or chemically reduced as in the case of synthetic vat and sulfur dyes before being applied. This renders the dye soluble so that it can be absorbed by the fiber since the insoluble dye has very little substantivity to the fiber. Direct dyes, a class of dyes largely for dyeing cotton, are water soluble and can be applied directly to the fiber from an aqueous solution. Most other classes of synthetic dye, other than vat and sulfur dyes, are also applied in this way.

The term may also be applied to dyeing without the use of mordants to fix the dye once it is applied. Mordants were often required to alter the hue and intensity of natural dyes and improve their color fastness. Chromium salts were until recently extensively used in dying wool with synthetic mordant dyes. These were used for economical high color fastness dark shades such as black and navy. Environmental concern has now restricted their use and they have been replaced with reactive and metal complex dyes which need no mordant.

Yarn dyeing

There are many forms of yarn dyeing. Common forms are: at package form and at hanks form. Cotton yarns are mostly dyed at package form, and acrylic or wool yarn are dyed at hank form. In continuous filament industry, polyester or polyamide yarns are always dyed at package form, viscose rayon yarns are partly dyed at hank form because of technology ^[1].

The common dyeing process of cotton yarn with reactive dyes at package form is given below in short: firstly the raw yarn is wound on a spring tube to achieve package suitable for dye penetration. Then, these softened packages are loaded on a dyeing carrier's spindle one on another. The packages are next pressed up to a desired height to achieve suitable density of packing. The carrier is then loaded on the dyeing machine and the yarn is dyed. After dyeing, the packages are unloaded from the carrier into a trolly. Next, all the packages are hydro extracted to remove the maximum amount of water. All the packages are then dried to achieve the final dyed package. At last the dyed yarn packages are packed and delivered.

Removal of dyes

In order to remove natural or unwanted colour from material, the opposite process of bleaching is carried out.

If things go wrong in the dyeing process the dyer may be forced to remove the dye already applied by a process that normally known as stripping. This normally means destroying the dye with powerful reducing agents (sodium hydrosulphite) or oxidizing agents (Hydrogen peroxide or sodium hypochlorite). The process often risks damaging the substrate (fiber), where possible it is often less risky to dye the material a darker shade, black is often the easiest or last option.

History

Early evidence of dyeing comes from India where a piece of cotton dyed with a vegetable dye has been recovered from the archaeological site at Mohenjo-daro (3rd millennium BCE).^[2] The dye used in this case was madder, which, along with other dyes—such as Indigo—was introduced to other regions through trade.^[2] Contact with Alexander the Great, who had successfully used dyeing for military camouflage, may have further helped aid the spread of dyeing from India.^[2]

See also

Look up dyeing in Wiktionary, the free dictionary.

Wikimedia Commons has media related to: Dyeing

• Textile manufacturing terminology

References

1. ^ Farer Thread
2. ^ ^{a b c} Bhardwaj, H.C. & Jain, K.K., "Indian Dyes and Industry During 18th-19th Century", Indian Journal of History of Science 17 (11): 70-81, New Delhi: Indian National Science Academy.

External links

• Fabric Dyeing Tips

v • d • e Dyeing Techniques: Batik · Dyeing · Kalamkari · Katazome · Leheria · Mordant · Reactive dye printing · Resist · Ring dyeing · Shibori · Tie-dye · Tsutsugaki Types of dyes: Dyes · Natural · Acid · Reactive · Solvent · Substantive · Sulfur · Vat Traditional textile dyes: Brazilin · Cochineal (Polish cochineal) · Cudbear · Dyewoods · Fustic · Henna · Indigo · Kermes · Logwood · Madder · Saffron · Tyrian purple · Weld · Woad History: Trade and use of saffron  · Traditional dyes of the Scottish Highlands Craft dyes: Dylon · Procion Other: Prepared for dyeing

v • d • e Textile arts Fundamentals: Applique · Crochet · Dyeing · Embroidery · Fabric (textiles) · Felting · Fiber · Knitting · Lace · Nålebinding · Needlework · Patchwork · Passementerie · Plying · Quilting · Rope · Sewing · Spinning · Tapestry · Textile printing · Weaving · Yarn History of... : Clothing and textiles · Silk · Quilting · Textiles in the Industrial Revolution · Timeline of textile technology Related: Blocking · Fiber art · Mathematics and fiber arts · Manufacturing · Preservation · Terminology · Textile industry · Textile Museums  · Units of measurement · Wearable fiber art

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Common misspelling(s) of dyeing

• dieing