Metallic pigments processing

Sanding is carried out at this stage and, after clean-up, the final colour or top-coat is applied. There is some variation in the resin chemistry used. Alkyds crosslinked with melamine-formaldehyde are widely used for non-metallic pigmentation. Metallics are usually based on acrylics for better durability. The acrylic may be thermoset with melamine-formaldehyde or a thermoplastic lacquer (plasticised copolymer of methyl methacrylate). A thickness of about 50ftm is applied and stoved for 20 min at 130°C (lacquers receive a bake-sand-bake process for a smoother appearance). 

Studies of the metal-exchange process of P.R.49 (Na) to P.R.49 1 (Ba) [1] revealed that the process, apart from the temperature, is not only influenced by the crystal structure and the concentration of the barium ions but also by the amount of rosin soap. Colophony-based rosin which is assumed to act as a surfactant, is converted during the laking process into colorless insoluble rosinate salts. These salts are incorporated in the pigment til up to 30% by weight without a loss of tinctorial strength. Very often the color strength is even increased, accompanied by a color shift to more bluish reds. 

During the ball milling process, a lubricant is added to prevent cold fusion it also determines the wetting properties of the metallic pigment, i.e., leafing or nonleafing . 

The universal pigment concentrates offered by some pigment manufacturers contain 50% to more than 95% metallic pigment. They can be added directly for a final pigment loading of about 1% and will in most cases keep the processing cost down and result in a brilliant product. 

Both injection blow molding and pinch tube processes are especially suitable for metallic pigments, because the expansion of the plastic during the blowing process causes further orientation of the metallic pigment parallel to the surface. 

The pressing processes do not provide any dispersing action for the metallic pigments. The premixed components are only brought into the desired form and then sintered (melted). The homogenous appearance therefore depends totally on the preblend of all powdered components. 

The SCORIM Process. It is possible to attach the SCORIM unit to the injection molder to manipulate the filling process of the mold so that in the area of the weld lines the resin is mixed [16]. This will improve the structural strength substantially and at the same time the unwanted orientation of metallic pigments is prevented. This process typically requires a 10-15°C higher temperature of the resin and the mold. The process is based on a prolonged flow ability of the polymer. 

Pb, Hg, As, Cd, Sn, Zn, and Cu are widely used in industry, particularly in metal-working and metal-plating processes, and in products such as batteries, electronic components, certain pesticides, and medicines. Owing to the brilliant colors of certain heavy metal compounds, they are also used in paint pigments, glazes, inks, and dyes. 

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). 

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