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Dyes types and reactive dyes

Spring 2009

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Direct Dyes.

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water-soluble anionic dyes, when dyed from aqueous solution in the presence of electrolytes, are substantive to, i.e., have high affinity for, cellulosic fibers. Their principal use is the dyeing of cotton and regenerated cellulose, paper, leather, and, to a lesser extent, nylon. Most of the dyes in this class are polyazo compounds, along with some stilbenes, phthalocyanines, and oxazines.

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Aftertreatments, frequently applied to the dyed

material to improve wash fastness properties, include chelation with salts of metals (usually copper or chromium), and treatment with formaldehyde or a cationic dyecomplexing resin.

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Vat Dyes.

water-insoluble dyes applied mainly to cellulosic fibers as soluble leuco salts after reduction in an alkaline bath, by sodium Hydrosulphite Following exhaustion onto the fiber, the leuco forms are reoxidized to the insoluble keto forms and aftertreated, usually by soaping, to redevelop the crystal structure. The principal chemical classes of vat dyes are anthraquinone and indigoid.

Sulfur Dyes. These dyes are applied to cotton from an alkaline reducing bath with sodium sulfide as the reducing agent. Numerically this is a relatively small group of dyes. The low cost and good washfastness properties of the dyeings make this class important from an economic standpoint However, they are under pressure from an environmental viewpoint.

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water-soluble cationic dyes are applied to paper, polyacrylonitrile (e.g. Dralon), modified nylons, and modified polyesters. Their original use was for silk, wool, and tanninmordanted cotton when brightness of shade was more important than fastness to light and washing. Basic dyes are water-soluble and yield colored cations in solution. For this reason they are frequently referred to as cationic dyes. The principal chemical classes are diazahemicyanine, triarylmethane, cyanine, hemicyanine, thiazine, oxazine, and acridine. Some basic dyes show biological activity and are used in medicine as antiseptics.

Cationic (Basic) Dyes.

Acid Dyes. These water-soluble anionic dyes are applied to nylon, wool, silk, and modified acrylics. They are also used to some extent for paper, leather, inkjet printing, food, and cosmetics. Solvent Dyes. These water-insoluble but solvent-soluble dyes are devoid of polar solubilizing groups such as sulfonic acid, carboxylic acid, or quaternary ammonium. They are used for coloring plastics, gasoline, oils, and waxes. The dyes are predominantly azo and anthraquinone, but phthalocyanine and triarylmethane dyes are also used.

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Reactive Dyes

The first commercially available dye capable of covalent reaction with a textile fibre is believed to be Supramine Orange R (CI Acid Orange 30). For wool 1930 It contained a chloroacetylamino substituent from which the labile chlorine atom can be readily displaced under conventional weakly acidic dyeing conditions at the boil to form a dye­fibre bond

1952 Hoechst marketed two Remalan vinylsulphone dyes that were capable of reacting with wool. Near Neutral Conditions Nucleophilic addition across the activated double bond of the vinylsulphone group. 1950 ICI developed dichloro-s-triazine reactive system Alkaline condition + salt additions salt enhances substantivity and lowering of the pH to minimise hydrolysis of the highly reactive dichlorotriazine system,

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DCT later developed less reactive aminochloro-s-triazine derivatives, which ultimately became the most successful of all reactive dye systems.

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Dyes of the aminochlorotriazine type were launched simultaneously as Cibacron (Ciba) and Procion H (ICI) brands shortly after the dichlorotriazine dyes had been introduced More stable pad liquors could be formulated using these less reactive dyes.

Reactive Systems

The characteristic features of a typical reactive dye molecule include: (1) the chromogen, contributing the colour and much of the substantivity for the fibre; (2) the reactive system, enabling the dye to form a covalent bond with the fibre and often also contributing some substantivity; (3) a bridging group that links the reactive system to the chromogen and often exerts important influences on reactivity, stability and substantivity; (4) one or more solubilising groups, usually sulphonic acid substituents on the aryl rings of the chromogen; (5) in some instances, as with the important aminochlorotriazine system, a colourless arylamino or other residue attached to the reactive grouping that also modifies solubility and substantivity.

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Important reactive systems for cellulosic dyeing

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