Лако-красочные материалы — производство

1.2.1

Fundamental Aspects [1.6]

1.2.1.1

Chemical Composition

With few exceptions, inorganic pigments are oxides, sulfides, oxide hydroxides, sili­cates, sulfates, or carbonates (see Tables 1.3 and 1.4), and normally consist of single­component particles (e. g., red iron oxide, a-Fe2O3 with well-defined crystal structures. However, mixed and substrate pigments consist of non-uniform or multicomponent particles.

Mixed pigments are pigments that have been mixed or ground with pigments or extenders in the dry state (e. g., chrome green pigments are mixtures of chrome yellow and iron blue). If the components differ in particle size and shape, density, reactivity, or surface tension, they may segregate during use.

In the case of substrate pigments, at least one additional component (pigment or extender) is deposited onto a substrate (pigment or extender), preferably by a wet method. Weak, medium, or strong attractive forces develop between these pigment components during drying or calcining. These forces prevent segregation of the components during use.

Special substrate pigments include the aftertreated pigments and the core pig­ments. To produce aftertreated pigments the inorganic pigment particles are covered

with a thin film of inorganic or organic substances to suppress undesirable prop­erties (e. g., catalytic or photochemical reactivity) or to improve the dispersibility of the pigments and the hydrophilic or hydrophobic character of their surfaces. The particles can be coated by precipitation (e. g., aftertreated TiO2 pigments, see Section 2.1.3.4), by adsorption of suitable substances from solutions (usually aqueous), or by steam hydrolysis.

To produce core pigments, a pigment substance is deposited on an extender by pre­cipitation or by wet mixing of the components. In the case of anticorrosive pigments (see Section 4.2.1), whose protective effect is located on their surfaces, the use of core pigments can bring about a significant saving of expensive material. Extender particles are also treated by fixing water-insoluble organic dyes on their surfaces via lake formation.

1.2.1.2