Volume 6, Issue 11

The dominant organic green pigments are polyhalogenated copper phthalocyanines (CuPcs). These pigments exhibit similar excellent coloristic and technical performance to CuPc blue pigments and are produced worldwide in large quantities. The green pigments are halogenated CuPcs. There are two pigments with CI designations. CI Pigment Green 7 is a bluish green product, in which the 16 ring hydrogen atoms of the CuPc molecule are replaced virtually completely by chlorine. Products designated as CI Pigment Green 36 incorporate a range of bromo- and bromochlorocopper phthalocyanines and are yellowish-green pigments. CuPc green pigments are manufactured by direct exhaustive halogenation of crude CuPc blue with chlorine or bromine or an appropriate mixture of the two halogens, depending on the composition of the product required. The synthesis is carried out at elevated temperatures in a suitable solvent, commonly a molten AlCl 3 /NaCl eutectic mixture.

This chapter describes some of the fundamental chemical and structural principles underlying the phthalocyanine system. Historically, phthalocyanines had been isolated as insoluble blue products in the early twentieth century, although the structures were not established at the time. After the serendipitous re-discovery of metal complex phthalocyanines by industry, and the elucidation of their structures, copper phthalocyanine (CuPc) pigments were introduced industrially in the 1930s to become, and remain, by far the most important blue and green organic pigments, finding almost universal use as colorants for paints, printing inks, plastics, and a wide range of other applications. The phthalocyanines have become one of the most extensively studied classes of organic compounds, because of their unique molecular structures, light absorption properties that produce strong, bright colors, and their exceptionally high stability. While their dominant use is as colorants, they are also of interest for a range of other applications, for example in electronic devices, biological applications, and as catalysts.

Titanium dioxide (TiO 2 ) is by far the most important white pigment. The extraordinary scattering behavior of TiO 2 together with the lack of absorption in the visible range and the stability in different application systems is the reason why TiO 2 is the most commonly used pigment. Of the three TiO 2 modifications, only rutile and anatase play a role for pigment uses, whereas brookite has no technical importance. Two main processes are used for the production of TiO 2 pigments, the sulfate process and the chloride process. Many TiO 2 pigments are equipped with an additional surface treatment (aftertreatment) to improve weather resistance and lightfastness of the pigment itself and of the pigmented organic matrix. A second aim of the surface treatment is the improvement of the dispersibility of the pigments in the application system.

Oxonitride pigments belong to the inorganic yellow, orange and red colorants. They were developed to complement the yellow, orange and red color range. Oxonitride compositions that are interesting for pigment uses crystallize in perovskite, chalcolamprite and spinel structures. The most suitable compositions for pigment purposes are most probably LaTaON 2 and CaTaO 2 N. The synthesis of oxonitride pigments is technically difficult and takes place using a solid state-gas reaction. The pigments are characterized by excellent optical and application characteristics in particular regarding brilliance and color strength, strong hiding power, good dispersibility, light fastness and temperature stability.

Zinc oxide pigments belong besides titanium dioxide and zinc sulfide pigments to the most important inorganic whites. The pigments are mostly used in paints, coatings, artists’ colors, and cosmetics. Zinc oxide pigments are synthesized using various processes. The direct process (American process), the indirect process (French process), and the wet process have the greatest industrial importance for the production of ZnO pigments.

The aim of this chapter is to provide a compact overview of colorants and their use in coatings including a brief introduction to paint technology and its raw materials. In addition, it will focus on individual colorants by collecting information from the available literature mainly for their use in coatings. Publications on colorants in coatings applications are in many cases standard works that cover the wider aspects of color chemistry and paint technology and are explicitly recommended for a more detailed study of the subject [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18]. Articles or information on paint formulation using coatings which contain colorants are rare [19]. This formulation expertise is often company property as it is the result of many years of effort built up over very long series of practical “trial-and-error” optimization tests and, more recently, supported by design of experiment and laboratory process automation [20, 21]. Therefore, it is protected by rigorous secrecy agreements. Formulations are in many ways part of a paint manufacturer’s capital, because of their use in automotive coatings, coil coatings, powder coatings, and specialist knowledge is indispensable to ensure their successful industrial use [22]. An important source to learn about the use of pigments in different coating formulations are guidance or starting formulations offered by pigment, additive, and resin manufacturers. These are available upon request from the technical service unit of these companies. Coating formulations can also be found scattered in books on coating and formulation technology [4, 5, 18, 23,24,25,26,27]. This overview can in no way claim to be complete, as the literature and relevant journals in this field are far too extensive. Nevertheless, it remains the author’s hope that the reader will gain a comprehensive insight into the fascinating field of colorants for coatings, including its literature and current research activities and last but not least its scientific attractiveness and industrial relevance.