Leather Reactive Dyes

On leather, reactive dyes attach to the amino group of lysine and hydroxyly-sine moieties of collagen. A tanning effect may occur if one reactive group reacts with leather. However, the reaction of the electrophilic group of reactive dyes with water (hydrolysis) competes with the fixation reaction of forming a covalent bond between the dye and the substrate. The hydrolyzed dye cannot react with the fiber. Leather absorbs the noncovalently bound dye like a conventional anionic dye. Unlike on textiles, these hydrolyzed dyes cannot be easily washed off. That is the reason why sometimes no decisive wetfastness improvement can be achieved. 

Dyes for leather Dyes, natural Dyes, reactive Dyes, sensitizing... 

Phthalocyanine Dyes. In addition to their use as pigments, the phthalocyanines have found widespread appHcation as dyestuffs, eg, direct and reactive dyes, water-soluble dyes with physical or chemical binding, solvent-soluble dyes with physical or chemical binding, a2o reactive dyes, a2o nonreactive dyes, sulfur dyes, and wet dyes. The first phthalocyanine dyes were used in the early 1930s to dye textiles like cotton (qv). The water-soluble forms Hke sodium salts of copper phthalocyanine disulfonic acid. Direct Blue 86 [1330-38-7] (Cl 74180), Direct Blue 87 [1330-39-8] (Cl 74200), Acid Blue 249 [36485-85-5] (Cl 74220), and their derivatives are used to dye natural and synthetic textiles (qv), paper, and leather (qv). The sodium salt of cobalt phthalocyanine, ie. Vat Blue 29 [1328-50-3] (Cl 74140) is mostly appHed to ceUulose fibers (qv). 

Sulfonic Acid-Based Dyestuffs. Sulfonic acid-derived dyes are utilized industrially in the areas of textiles (qv), paper, cosmetics (qv), foods, detergents, soaps, leather, and inks, both as reactive and disperse dyes. Of the principal classes of dyes, sulfonic acid derivatives find utiUty in the areas of acid, azoic, direct, disperse, and fiber-reactive dyes. In 1994, 120,930 t of synthetic dyes were manufactured in the United States, of which 5,600 t were acidic (74). The three largest manufacturers of sulfonic acid-based dyes for use in the United States are BASF, Bayer, and Ciba-Geigy. 

In Chapters 3-6, the commercially important chemical classes of dyes and pigments are discussed in terms of their essential structural features and the principles of their synthesis. The reader will encounter further examples of these individual chemical classes of colorants throughout Chapters 7 10 which, as a complement to the content of the earlier chapters, deal with the chemistry of their application. Chapters 7, 8 and 10 are concerned essentially with the application of dyes, whereas Chapter 9 is devoted to pigments. The distinction between these two types of colorants has been made previously in Chapter 2. Dyes are used in the coloration of a wide range of substrates, including paper, leather and plastics, but by far their most important outlet is on textiles. Textile materials are used in a wide variety of products, including clothing of all types, curtains, upholstery and carpets. This chapter deals with the chemical principles of the main application classes of dyes that may be applied to textile fibres, except for reactive dyes, which are dealt with exclusively in Chapter 8. 

The nomenclature given for these componnds is a nniversally recognised system for the naming of dyestuffs devised by the Society of Dyers and Colourists as part of their Colour Index (Cl). The Cl Generic Name is made up of the application class, the hne and a nnmber. Acid dyes are nsed on wool and polyamide, direct dyes on cel-lulosic fibres, paper and leather, disperse dyes on polyester fibres, reactive dyes on cellnlosic fibres and basic dyes on polyacrylonitrile and paper. 

To provide an overview chemical constitution and synthesis are combined in this section. The various application media for metal-complex dyes are a further ordering principle, which generates overlap of some sections with reactive dyes (Section 3.1), leather dyes (Section 5.1), and paper dyes (Section 5.3), demonstrating the typically complex interrelationship of constitution and application of dyes. 

Reactive dyes are colored compounds that contain groups capable of forming covalent bonds between dye and substrate. Approximately 80-90% of reactive dyes are azo dyes. The other chromogenic classes are anthraquinones, dioxazines, phthalocyanines, and some 1 1 copper azo complexes. Reactive 1 2 complex leather dyes were also commercially manufactured for a short time. Constitution and producer have not been disclosed. 

Although reactive dyes have the potential to provide the best fastness to wet treatments, this potential has only been realized in some small segments. Since 1951, when the first reactive dyes were designed for cotton, many reactive dyes including complete ranges have been offered for leather. However, no major breakthroughs have been achieved to date. 

Synthetic dyes are mainly aromatic organic compounds, and they can be classified as cationic (basic dyes), anionic (direct, acid, and reactive dyes), or nonionic (disperse dyes) type [134]. Synthetic dyes are mainly used in the textile industries, but they have many other applications such as in printing, leather, papermaking, drug, and food industries [85]. Total world colorant production is estimated to be... 

Materials used for leather dyeing are usually acid dyes, direct dyes, mordant dyes (Thorstensen, 1993) and reactive dyes (Shao and Zhao, 1984). Basic dyes are primarily used for dyeing vegetable tanned leather (Sandoz, 1949). 

Saville B P (1999), Physical Testing of Textiles, Cambridge, Woodhead Publishing Ltd. Shao Y and Zhao S M (1984), Leather dyeing with reactive dyes . Leather Science And... 

Acid dyes Azoic colouring matters Basic dyes Developers Direct dyes Disperse dyes Fluorescent dyes Food dyes Ingrain dyes Leather dyes Mordant dyes Natural dyes Oxidation dyes Pigments Reactive dyes Reducing agents Solvent dyes Sulphur dyes Condense sulphur dyes Vat dyes... 

Molecular structures of the above mentioned dyes are presented in Figure 5. The dyes were purchased from Sigma-Aldrich (Germany) and used witliout further purification. These dyes were selected for the studies because they are extensively used in the textile industry. C.I. Acid Orange 7 is applied for fibers such as silk, wool and nylon using neutral to acid dye baths. Direct Blue 71 is used for cotton, paper, leather, wool, silk and nylon dyeing. Reactive dyes, e.g. RB5, are by far the best choice for dyeing of cotton and other cellulose fibers. 

Estlander T (1988) Allergic dermatoses and respiratory diseases from reactive dyes. Contact Dermatitis 18 290-297 Estlander T, Kanerva L, Jolanki R (1990) Occupational allergic dermatoses from textile, leather, rubber and fur dyes. Am J Contact Dermat 1 13-20... 

Acid dyes Reactive dyes Basic Direct dyes Mordant dyes Disperse dyes Vat dyes Solvent dyes Fluorescent brightners Other dye classes Nylon, sUk, wool, paper, inks and leather Cotton, wool, sUk and nylon Paper, polyacrylonitrile, modified nylon, polyester and inks Cotton, rayon, paper, leather and nylon Wool, leather and anodised altiminirun Polyester, polyamide, acetate, acrylic and plastics Cotton, rayon and wool Plastics, gasoline, varnishes, lacquers, stains, inks, fats, oils and waxes Soaps and detergents, aU fibres, oils, paints and plastics Food, drugs and cosmetics, electrography, direct and thermal transfer printing... 

A series of water-soluble fiber-reactive xanthene dyes has been prepared from the reaction of ben2oxanthenedicatboxylic acid anhydride disulfonic acid with, for example, 3-aminophenyl-P-hydtoxyethyl sulfone to yield dyes, with high brilliance and good fastness properties for dyeing of or printing on leather, wool, sHk, or ceUulosic fibers (53). 

Pseudomonas luteola Reactive azo dyes, Direct azo dyes and leather dyes The 59-99% color removal after 2-6 days static incubation, at dye concentration of 100 mg L 1, monoazo dyes showing fastest rate of decoloration [78]... 

Chromium and cobalt are the metals most commonly used in dyestuffs for polyamide fibres and leather because of their kinetic inertness and the stability of their complexes towards acid. Since the advent of fibre-reactive dyestuffs, chromium and cobalt complexes have also found application as dyestuffs for cellulosic fibres, particularly as black shades of high light-fastness. Copper complexes are of more importance as dyes for cellulosic fibres and are unsuitable for polyamide fibres because of their rather low stability towards acid treatments. 

Oxazine, azine and thiazine dyes are named for the characteristic heterocyclic ring systems 1,4-oxazine, 1,4-diazine, and 1,4-thiazine. The dyes are generally cationic (basic) or acid dyes. They also can be reduced to colorless forms, then oxidized back to the dye, as in vat dyeing. The dyes also have been used to a limited extent in disperse and fiber reactive applications. They are used as titration indicators and may be applied to acrylic fibers and leather. 

While the development of direct dyes was essentially completed in the 1930s, it was reactivated in the 1960s and 1970s, when it was found that benzidine, an important direct dye intermediate at the time, is carcinogenic. Benzidine dyes are used for some yellows and reds and mostly for black. In view of the ensuing concern, the leading dye producers withdrew benzidine-based dyes preemptively to protect their workers, dyers, and consumers. Studies to find alternative dyes were undertaken, and this work led eventually to many of today s most important black dyes for leather, e.g,C.I. DirectBlack 168, 30410 [85631-88-5] (16). 

Another reactive component for leather (major use dyeing wool) is thea-sul-fatoethylsulfonyl group, as in e.g., C.l. Reactive Violet 4, 17965 [12769-08-3] (1 1 Copper 21), as well as acryloamido, e.g., a-bromoacryloamido groups. 

---