Metallic pigments shapes

Metallic Pigments. These pigments are metal flakes of various sizes made up of aluminum, copper, zinc, and/or their alloys. The aluminum flakes develop the silver metallic colors, whereas the copper, zinc, and aluminum alloys produce the gold, copper, brass, and bronze colors. The metal effect is modified, not only by shape and size, but also by perticle size distribution within a given product. Since aluminum, in particular, as a fine dry powder, can form explosive mixtures with air, most of these materials are commercially available in paste or liquid concentrates. In addition, surface treatments of these materials enhance their appearance and performance. Flakes of other metals, such as stainless steel, are used for surface protection purposes such as corrosion resistance and electrical conductivity. 

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). 

If you ever had the opportunity to use almninum pigments in plastics, you are familiar with the fact that you are not dealing with spherical pigments, but with flakes. Because of their shape, metallic pigments appear to behave in regard to their optical properties in almost every way opposite to non-metallic pigments. Here are some examples ... 

Aluminum pigments are the most often used metallic pigment in surface coatings. They are prepared from high purity aluminum metal by ball milling fine aluminum powder in the presence of a hydrocarbon solvent and grinding aids such as stearic acid and then formed into platelet-shaped particles. They are normally supplied as pastes in hydrocarbon solvents and occasionally in powder form. 

The stable form of arsenic is the gray or metallic form, although other forms are known. Cooling the vapor rapidly produces yellow arsenic, and an orthorhombic form is obtained if the vapor is condensed in the presence of mercury. Arsenic compounds are used in insecticides, herbicides, medicines, and pigments, and arsenic is used in alloys with copper and lead. A small amount of arsenic increases the surface tension of lead, which allows droplets of molten lead to assume a spherical shape, and this fact is utilized in the production of lead shot. 

For all the pigments of this class, metal-free phthalocyanine, and those containing Mg, Al, Cu, and Fe, the kinetic spectra exhibit a similar shape and behavior (Fig. 16). There is at all photon energies a maximum of fast electrons at 0.8-1.0 e.v. There are besides at large values of the energy losses E two maxima at 3 e.v. and at 5.5 e.v., respectively, which are especially conspicuous in the case of Mg-phthalocyanine. The fine structure of these maxima is real. 

Production. Metallic iron pigments are commercially produced by the reduction of acicular (needle-shaped) iron compounds [5.30], As in the production of magnetic iron oxide pigments, the starting materials are iron oxide hydroxides (see Section 3.1.1) or iron oxalates, which are reduced to iron in a stream of hydrogen either directly or via oxidic intermediates. 

The metal effect depends not only on particle size and particle size distribution, but also on the orientation of the metal flakes within the coating film, particle shape, the transparency of the binder matrix, and the presence of colored pigments or dyes. 

Metal effect pigments are flake-shaped metallic particles supplied in the form of powders, pastes, pellets, suspensions or color concentrates [5.166-5.168]. Typical metal effect pigments include aluminum ( silver bronze ) and copper- and copper/zinc-alloys ( gold bronze ). 

The anisotropic shape of the metallic flakes should be considered during dispersion and application of these pigments high shear forces may damage the pigments and the effect and should therefore be avoided. 

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