Pastes metallic pigments

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. 

Since the middle of the 1980s metallic pigments have been available as pellets, which offers a number of advantages. They are safer to ship than solvent containing pastes or potentially explosive powders. Because they contain less carrier, the volume of... 

As in Section 14.4.1, all ingredients are predispersed and the already dispersed pellets or pastes of the metallic pigments are then blended with the compound to... 

The metal pigments, gold bronze as well as aluminum, are supplied in the form of powders, pastes (including solvents), granules (including resins), suspensions (VMPs), color concentrates or even press-ready printing inks. 

The analysis of plastics for hazardous metals e.g. Cd, Pb, Cr(total) and Hg is now essential on all products including plastics used in electric and electronic equipment sold within the European states. Directives for these products have been issued under Packaging Directive , End of Life Vehicle (ELV), Reduction of Hazardous Substances (RoHS) and Waste Electrical and Electronic Equipment (WEEE), and have been introduced to control the risk to health and waste disposal in the environment. The listed metals have been used extensively in the past as pigments, stabilisers and catalysts, especially PVC, and these toxic elements can be released over time into the environment. Therefore, polymer producers are advised that future products be lower than EU values or free of these metals. 

In the past, MMO pigments were found to be hard to disperse and the source of color specks. Recently, however, all of the major suppliers have targeted polyamide fibers as a lucrative new market and have greatly improved the particle size distribution and ease of dispersion. Some combinations of metals and the colors produced are given in Table 1. 

Aluminum and bronze pigments offer a wide range of unique coloristic effects, which in relation to their different optieal eharaeteristics will be described. In the past, the chemieal resistance of metallic pigments have always been a problem. During the last few years various modified versions of both aluminum as well as bronze pigments have been developed which open new areas for their applieation in plastics. Their characteristics and advantages will be discussed and how to best incorporate metalhc pigments into the different plastic resins. 

As mentioned, in some cases hydrochloric acid is released during processing of PVC which could attack the metallic pigments if they are not encapsulated. It is, therefore, advisable to use the encapsulated PCR or PCA aluminum pigments or the Resist bronze pigments, which are offered as powder or plasticizer pastes (Table 4). 

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. 

A variety of mineral ores, mostly copper minerals such as malachite and chrysocolla, were probably the most used green pigments in the past. Various green minerals derived from metals other than copper, such as green earth (see below) were used in confined regions. 

Mercury (chemical symbol Hg, from the Latin name of the metal, hydrar-gyrium, liquid silver), previously also known as quicksilver is, at ordinary temperatures, a silvery white liquid metal that boils at 360°C. The metal is occasionally found in nature in the native state. Most mercury has been derived, however, from the red mineral cinnabar (composed of mercuric sulfide) that was also used in the past as a red pigment known as vermilion (see Textbox 41). The Greek philosopher Aristotle, writing in the fourth... 

Azomethine metal complex pigments replace the metal with tin stabilizers, resulting in a change in shade. In the case of manganese-laked pigments trouble can also be expected in the presence of epoxy compounds. Pigment preparations based on epoxidized soya bean oil are normally used instead of diisodecyl phthalate pastes in the automotive sector e.g. for coloring PVC roofs etc. 

A number of resinated grades are produced in order to provide higher transparency and to optimize other aspects of pigment properties in application. For reasons connected with process engineering, the resin is typically incorporated as a metal (calcium) resinate. In the past, types of P.R.57 1 additionally contained certain amounts of barium sulfate. 

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