Sulfur dyes applications

From an appHcations point of view, the sulfur dyes are between vat, direct, and fiber-reactive dyes. They give good to moderate lightfastness and good wetfastness at low cost and rapid processing (see Dyes, application and evaluation). 

The chemistry of the three most important chemical classes of organic colorants, the azo, carbonyl and phthalocyanine classes, has been dealt with individually in Chapters 3-5 respectively. In this chapter, the chemistry of a further five chemical classes which are of some importance for specific applications is discussed. These classes are the polymethines, arylcarbonium ion colorants, dioxazines, sulfur dyes and nitro dyes. A section of this chapter is devoted to each of these, each individual section contains a description of the principal structural features which characterise the particular colorant type, together with an outline of the chemistry of the main synthetic routes. There are many other chemical types of dyes and pigments that do not fall into the categories previously mentioned, but which are neglected in this text either because they are commercially of little importance or because they have been less extensively investigated. 

Sulfur chloride is a solvent for sulfur and a chlorinating agent. Other applications are vulcanizing rubber an intermediate in making sulfur dyes, synthetic rubber, thionyl chloride, and several other compounds pesticide formulations hardening soft woods and extracting gold. 

Sulfur dyes are used mainly for dyeing textile cellulosic materials or blends of cellulosic fibers (qv) with synthetic fibers such as acrylic fibers, polyamides (nylons), and polyesters. They are also used for silk (qv) and paper (qv) in limited quantities for specific applications. Solubilized sulfur dyes are used on certain types of leathers (qv). 

In the 1995 edition of the Co/our Index, the sulfur dyes are classified according to application method and the structure of the intermediates, into ordinary or conventional dyes, leuco or prereduced dyes, and thiosulfonic derivatives of conventional dyes (solubilized sulfur dyes) (30). 

The low cost of sulfur dyes, coupled with good fastness properties and the ease of application, continues to ensure a high consumption. The number of manufacturers has fallen since the 1960s and production is mainly confined to the United States, U.K., Germany, and Spain. There is one principal producer in each of these countries. There are other, less well-known manufacturers in Russia, the People s Republic of China, South Korea, Japan, and... 

Sulfur Dyes. These dyes arc synthesized by heating aromatic amines, phenols, or nitro compounds with sulfur or. more usually, alkali polysullides. Sulfur dyes are used for dyeing cellulosic fibers. They are insoluble in water and are reduced to ihe water-soluble leuco form for application to the substrate by using sodium sulfide solulion, The sulfur dye proper is then formed within the fiber pores by atmospheric oxidation. Sulfur dyes constitule an important class of dye lor producing cost-effective tertiary shades, especially black, on cellulosic fibers. 

Sulfur dyes are a special class of dyes with regard to both preparation and application, and knowledge of their chemical constitution [1], They are made by heating aromatic or heterocyclic compounds with sulfur or species that release sulfur. Sulfur dyes are classified by method of preparation as sulfur bake, polysulfide bake, and polysulfide melt dyes. Sulfur dyes are not well-defined chemical compounds but mixtures of structurally similar compounds, most of which contain various amounts of both heterocyclic and thiophenolic sulfur. 

The term pseudo (or synthetic) sulfur dyes refers to dyes that have application properties similar to those of sulfur dyes but are obtained by the insertion of mer-capto groups or their precursors into the dye precursors or pigments rather than by the classical sulfurization method. These dyes thus have some of the characteristics of sulfur dyes. 

With a few exceptions, sulfur dyes [1] are employed to dye cellulosic fibers. The main applications are the dyeing of corduroy, velveteen, denim articles, twill work clothes, tarpaulins, and backpack fabrics. The dyeing of the cellulosic fiber component of blended fabrics (polyester/cotton blends above all) is increasingly important. 

Leuco Sulfur Dyes (C.I. Leuco Sulphur). These liquid dyes already contain the reducing agent required for dyeing. They must simply be diluted with water before application. Ecologically more favorable, low-sulfide types have come onto the market recently. 

With respect to both application and fastness, a distinction is made between sulfur dyes and sulfur vat dyes. The latter include dyes of the type Hydron Blue C.I. Vat Blue 43, 53630 [1327-79-3]) and Indocarbon C.I. Sulphur Black 11, 53290 [1327-14-6]). 

Recently, the electrochemical reduction of sulfur dyes was studied. For continuous processes a mediator is not necessary. In discontinuous application it is possible to reuse dyebaths [72],... 

Disperseand Sulfur Dyes (see also Section 4.7.3). The thermosol pad steam process is the primary method for application of disperse and sulfur dyes. The sulfur dyes that are used preferentially in the ready-for-dyeing soluble form, and are especially inexpensive for muted shades, must be applied after the thermosol step because of their incompatibility with disperse dyes. 

For commercial printing onto nonporous, hydrophobic materials such as plastics, metals, and glass, rapidly drying solvent inks which adhere to these substrates are needed. A typical solvent for these applications is methyl ethyl ketone (MEK). However, alternative alcoholic solvents tike ethanol and N-propanol have been introduced for ecological and safety reasons. The predominant color for industrial marking is black, and solvent soluble 2 1 azo chromium(m) complex, polyazo, Nigrosine, and sulfur dyes are used. Typical formulation of an... 

Fig. 13.20. Steps involved in the application of sulfur dyes to cotton.

Fig. 13.21. Two-step chemistry employed in the application of C.l. Solubilized Sulfur dyes (top) and a representative dye structure (bottom).

Applications Sodium sulfide is mainly used in tanning as a hair-removing agent (so-called asher). It is also utilized in ore flotation, dyeing with sulfur dyes in the textile industry and in the chemical industry e.g. for the precipitation of heavy metal ions. Anhydrous sodium sulfide is also utilized in the manufacture of polyphenylenesulfide (PPS), a high temperature-resistant plastic. The current production of sodium sulfide in Western Europe is estimated to be ca. 50 10- t/a. 

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