Mica pigment, silica coated

The dominant class of lustre pigments is based upon oxide coatings of mica platelets, but newer materials have appeared e.g. silica and alumina flakes from Merck, with better performance characteristics than traditional mica." " There has also been developments in the technology for the coating of reflective metal platelets, e.g. aluminium, with oxides using chemical vapour deposition that has led to exciting new products. ... 

Improved color strength and very high luster are produced by the combination of precise thickness silica flake substrate materials, selected for their interference chro-maticity, and by deposition of titania or iron oxide coating layers of the precise thickness required to generate the same interference color. These pearl luster pigments show stronger chromaticity L a b -values than can be produced with mica-based designs. 

The choice of antiblocking additive depends on the polymer, the desired film quality, and whether there is a pigment. Several inorganic substances are used, including synthetic amorphous precipitated silica, diatomaceous earths, nepheline syenite, calcined clay, coated calcium carbonate, magnesium carbonate, magnesium sulphate, mica, talc and various zeolites. Calcium carbonate particles are approximately spherical, but silica ones are irregular mica forms sheets and talc is plate-like. 

Figure 7-7 shows a cross-sectional diagram of metal oxide coated on mica and metal oxide deposited on silica flake pigments. The new properties available with silica flake pigments can be summarized as follows. 

In practice, platelet crystals are synthesized with a layer thickness d calculated to produce the desired interference colors (iridescence). Most pearlescent pigments now consist of at least three layers of two materials with different refractive indices. Thin flakes (thickness ca. 500 nm) of a material with a low refractive index (mica, silica, alumina, glass) are coated with a highly refractive metal oxide (Ti 2, FejOj, layer thickness ca. 50-150 nm). This results in particles with four... 

Paint and coating manufacturers use over 40 different t)q)es of extenders, fillers, and pigments, in construction, perhaps more than in any other industry.These materials are added to lower the cost, except for pigments and minerals added for gloss or flatness of finishes. Titanium dioxide pigment is the most important mineral in paints. Other t)q)es of fillers include alumina hydrate, barite, calcium carbonate, kaolin, mica, silica, and talc.t l... 

The first interferential pigments were created on the basis of natural muscovite mica as a substrate and coated with titanium or iron oxide. Other substrates have subsequently been used in this type of pigment, notably the silica flake and the alumina flake. The substrate provides the necessary platelet shape, while the interference colour is determined by the thickness of the metal oxide layer and its refractive index. 

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