Volume 7, Issue 2

Disazo condensation pigments were developed in the mid-twentieth century as a range of high-performance azo pigments to meet the stringent demands placed on the technical properties required for applications in growing markets such as automotive paints, plastics, and fibers. The commercial products vary in shade from yellow through red to brown. Structurally, the pigments are related to the classical yellow azoacetoacetanilides or red azonaphthols by synthetically connecting two monoazo derivatives by a condensation reaction involving an aromatic diamine. The resulting pigment molecules are of extremely large molecular size with the presence of several amide groups, factors that determine their excellent set of fastness properties. The procedures used in their manufacture involve complex and demanding multistage processes, and this explains the higher cost of these pigments. The application performance attributes provided by the individual commercial products are discussed in detail in the final section.

Special effect pigments are in the very most cases synthetic pigments, characterized by high luster, brilliance and iridescent colors known from optically thin films. The visual appearance has its origin in reflection and refraction of light at thin single and multiple layers. The pigments are either transparent, semitransparent or light-absorbing platelet-shaped crystals or layer systems. They can consist of single crystals, but also of monolayer or a multilayer structures in which the layers have different refractive indices and light absorption properties. Pigment based on the layer-substrate principle represent the technically most important class of special effect pigments. There are many variation and combination possibilities for the layer and substrate materials used. Special effect pigments based on platelets of natural or synthetic mica, on alumina, silica, or borosilicate flakes are the main representatives of layer-substrate pigments. They are manufactured in most cases by wet chemical processes combined with high-temperature processes. The production of substrate particles includes mechanical processes, but also crystal growth, glass formation, and web coating.

This chapter surveys the structural and synthetic chemistry and the industrial applications of quinacridones, a small but extremely important group of high-performance carbonyl (or polycyclic) organic pigments. They are based on one of the most important new chromophoric systems developed specifically for pigment applications after the introduction of the phthalocyanines, and currently occupy a prominent position in the red to violet shade areas. A historical perspective on the discovery and commercial development of the quinacridones is presented initially. There then follows an illustrated discussion of the structural chemistry of the pigments, encompassing both molecular and crystal structures. Throughout the chapter, specific features of their molecular structures and the nature of the intermolecular association within the crystals are related to their influence on the color and technical performance in application, in which they exhibit some of the highest standards of heat stability, solvent resistance, and fastness to light and weather encountered in organic pigments. Finally, a survey of the principal current applications of the specific individual commercial quinacridone pigments is presented.

Ceramic colors or stains consist mainly of pigments, glaze or body, and opacifiers. They are used for the decoration of porcelain, earthenware bone china and other ceramics. Glazes and enamels are the main application systems for ceramic colors. Pigments are the color giving components in the composition of a ceramic color. High temperature and chemical stability as well as high tinting strength are characteristics of stains. Technically important ceramic colors are cadmium sulfide and sulfoselenides (occluded in zircon), metals such as gold, silver, platinum, and copper (as colloidal particles), metal oxides (α-Fe 2 O 3 , Cr 2 O 3 , CuO, Co 3 O 4 /CoO, MnO 2 /Mn 2 O 3 , and NiO/Ni 2 O 3 ), mixed metal oxides and silicates, zirconia-based and zircon-based compositions. Ceramic colors are often produced using solid state reactions.

The chromium(III) oxide pigments Cr 2 O 3 (chromium oxide green) and CrOOH (chromium oxide hydrate green) are representatives of the inorganic green and blue–green pigments. Cr 2 O 3 pigments are very important for the coloration of paints, coatings, plastics, building materials and other application systems. CrOOH pigments have lost their technical importance because of the low thermal stability. Chromium oxide green pigments are characterized by excellent application properties. They are synthesized starting from alkali dichromates or ammonium dichromate by reduction in liquid or solid phase.

Carbon black pigments are manufactured today mainly by modern chemical processes in industrial scale production. They are the most important representatives of black pigments. Carbon black pigments have a number of advantages compared with other inorganic black pigments and with black organic colorants. Hiding power, color stability, solvent resistance, acid and alkali resistance as well as thermal stability are excellent good properties that are not achieved from other blacks. Carbon black pigments are applied in most of the pigment relevant systems, such as printing inks, paints and coatings, plastics, and cosmetics. They are produced by several industrial processes. Furnace blacks, channel blacks and gas blacks have the highest importance among the various carbon blacks. Particle size, particle size distribution, surface quality and structure determine the coloristic and application technical properties of the individual pigments. Oxidative aftertreatment is used in many cases to modify the surface of the pigments concerning the stability and the compatibility with the application system. Particle management, aftertreatment and the provision of pigment preparations are suitable ways for the improvement of the pigments and the optimization of the dosage form.