Shaping process, metallic pigments

The VMPs (vacuum metallized pigments) differ very much from these traditional pigment flakes. Due to the original PVD-process, they are extremely thin (ca. 0.03 pm) and provide a very smooth, highly reflective surface. The particle shape has a tremendous influence on the metallic effect (see below). 

Nonoriented Tedlar SP films (Types 8 and 9) offer excellent conformability to almost any shape or substrate while maintaining the durability, chemical resistance, and ease of cleaning expected of PVF film.1 ] Nonoriented films are available as multilayer films without adhesives or heat sealing. Multilayer technology allows for effects such as pearlescent or metallic colors. The Tedlar SP process allows a pigmented base layer to be covered with an integral clear top layer. 

The chemistry of the aqueous sol-gel process is quite complex due to metal and the double role of water as ligand and solvent as well as due to the large number of reaction parameters that have to be stricdy controlled (hydrolysis and condensation rate of the metal oxide precursors, pH, temperature, method of mixing, rate of oxidation, the nature and concentration of anions, etc.) in order to provide good reproducibility of the synthesis protocol. Another fundamental problem of aqueous sol-gel chemistry is that the as-synthesized precipitates are generally amorphous. The required postsynthetic annealing step to induce the crystallization process prevents any subtle control over crystal size and shape. For the preparation of bulk metal oxides, like the ceramic pigment case, these limitations play only a minor role however, in the case of nanoparticle synthesis, they constitute a major concern. 

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