Fine Chemicals: Dyes and Coloring Materials

James Richard Fromm


The coloring industry traditionally divides into two areas: the dyeing of fabrics, and the covering of surfaces with paints, inks, lacquers, or varnishes. Its division is thus into dyes, which are soluble coloring materials, and pigments, which are insoluble coloring materials, and their related chemicals.

Pigments

The primary use of pigments is in paints, which are suspensions of pigment particles in a liquid medium. The components of paint are the pigment, the binder, and the solvent. A typical oil-base white house paint may consist of 45% pigment (often TiO2, PbCO3, ZnO, or a mixture of these), 17% talc used as an extender pigment for gloss (Mg(SiO3)2), 31% linseed oil as the binder, and 8% mineral spirits to permit drying. Such paints have long been known and used. Modern paints may use synthetic resins (plastics) as binders rather than natural linseed oil or resin obtained from pine and similar trees. Pigment may be either organic or inorganic. White pigments are based on oxides of titanium, zinc, lead, or antimony, while colored and black pigments may be either inorganic or organic materials. Naturally occurring pigments such as cadmium sulfides, iron compounds, and other transition metal compounds have long been used; additional colors from synthetic materials are becoming available. Binders used, if not natural materials such as linseed oil or natural resins, are acrylic resins (appliance finishes, automobile enamels), alkyds, or oil-modified phthalate resins (general paints), cellulosics such as cellulose nitrate or cellulose acetate (lacquers), methanes, vinyls or modified polyvinyl chlorides, rubber-base and latexes.

Dyes

Dyes are one of the oldest components of the fine chemicals industry. Useful dyes by 1850 still included only the natural materials such as cochineal, kermes, madder, indigo, logwood, Brazil wood, fustic, weld, cutch, and saffron. The first synthetic dye, aniline purple or mauve, was accidentally discovered by W.H. Perkin in 1856 in the course of an attempt to prepare drugs similar to quinine from coal tar. Further dyes of similar structure, such as magenta (1859) soon followed, and work began on synthetic methods of manufacture of the natural dyeing materials as well.

Modern dyes are generally synthetic organic compounds of some complexity, and no general synthetic formulation can be given. Raw materials were once coal tar, but many of the materials produced from this are now produced more cheaply from petrochemical sources.


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Copyright 1997 James R. Fromm