Complex inorganic coloured pigments cover a wide range of colour and chemical composition. This group of pigments represents crystal classes which can be widely found in nature - principally rutile and spinell. Those crystal lattices host metals, which are the reason of colour effects and crystal (chemical) stability. Important metals are nickel, cobalt, trivalent chromium, zinc, manganese, iron, titanium and antimony. Those metals lose their toxicological and ecological properties once incorporated into the crystalline host lattices.
Pigments and Fillers
The organic pigments can be principally classified into two major groups: azo pigments and polycyclic pigments.
Azo pigments are characterized by the presence of one (monoazo) or two (disazo) azo bonds –N=N–, in the molecule and cover mainly the range of yellow, orange, red violet and brown shades. Azo pigments represent about 70% of all organic pigments worldwide and depending on their properties are used over the entire range of pigment application reaching from all types of coatings to colouring of plastics and printing inks to food and cosmetic colourants.
Titanium dioxide is the white pigment most widely used in the world with a global production of approx. 7,2 Mio tons per year. Some 20 % are produced in western Europe. The market for Titanium dioxide in Germany is the most important within western Europe and counts for approx. 500 Mio €.
Users can be found in merely all fields of applications and all sizes of companies.
Carbon black pigments are produced by thermal oxidative dissociation of suitable oils by the lamp black-, furnace black-, and gas black process. The furnace black process is the most important with about 95 % of the total production.
Primary particle sizes range from 10 to 100 nm and can be reproducibly produced. Carbon black pigments are offered as powders and also in pearled qualities according to the handling requirements. Densities in compacted form are between 100 and 500 g/l.
Fillers are important additives for the improvement of various technical properties in paints, printing inks and plastics. Of special importance are synthetic amorphous silicas and silicates, which are produced in large quantities. Silicas are produced by precipitation of waterglass and acids, whereas silicates are produced by the addition of metal salts to the waterglass-acid-reaction. In both cases fine finely divided, amorphous, white powders are obtained with specific surface areas from 30 to 750 m²/g.
The most widely used coloured pigments worldwide are iron oxide pigments. They are offered in the colours red, yellow and black with remarkable high light resistance and chemical stability. Iron oxides are the oldest known pigments and were used as natural pigments already in the stone ages. Synthetic iron oxides show in relation to natural products higher colour strength, high reproducibility of the colour shade and higher chemical purity and therefore dominate the market.
Major products are Zinc oxide, Zinc sulfide, lithopone and Zinc phosphate.
Large amounts of Zinc oxide is used in the rubber industry. Other fields of application are ceramic glazes, optical glasses, paints, plastics and paper.
Zinc oxide serves as a corrosion inhibitor and is added to lubricants, adhesives and batteries. Zinc oxide is a precursor for Zinc phosphate pigments; today the most widely used corrosion inhibiting pigment.
Many manufacturers of pigments also manufacture pigment preparations. Furthermore, there are companies which largely focus on processing pigments into pigment preparations. These preparations include, by way of example
- powder pigment preparations
- aqueous liquid pigment preparations
- pigment pastes
- dry colour pigments
- masterbatches (see Masterbatches)