Metallic pigments surface treatment

When mixed-phase rutile pigments are used in special paint systems, (e.g., stoving or acid-catalyzed lacquers), inorganic surface treatment in an aqueous medium can improve the gloss and flocculation properties. For example, an aqueous pigment suspension is first treated with a surfactant, and then coated with metal hydroxides or oxide hydrates [3.93],... 

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. 

Because the metallic effect is strongly influenced by the pigment surface, its modification has long been a concern. Also, the need for improvement against chemical and physical influences forces the pigment manufacturer to constantly modify the surface treatment to optimize its performance. This includes mechanical after-treatments as well as physical or chemical applied layers. 

The most popular inorganic treatments are those with silica [4], phosphates [5], molybdate [6], and chromate [7], all of which serve mainly to reduce the chemical reactivity of the metallic pigments (Fig. 14.13). This includes corrosion inhibition of the pigment and inhibition of its often catalytic effect as well as a change in the physical surface characteristics, for example, where chargeability is important. 

Primers are pigmented coatings that are applied to new surfaces or to old cleaned surfaces, prior to the application of undercoats or top coats. Its main functions are to achieve adequate adhesion to the substrate and to provide good intercoat adhesion for subsequent coats. They are specifically formulated for particular substrates such as wood, metals, concrete, and other masonry surfaces. Concrete and other masonry surfaces are alkaline and often require special surface treatments. For etching and neutralization of these alkaline surfaces, hydrochloric or phosphoric acid washing is usually done. 

Choice of an appropiate surface treatment and a suitable primer are important because adhesion to the substrates presents difficulties [11.37]. Primers based on modified alkyd resins or two-pack epoxy-resins for derusted ferrous metals mainly contain zinc phosphate and zinc OKide as corrosion protection pigments. Nonferrous metals are first washed with an ammoniacal wetting agent before applying the primer that contains a binder based on synthetic resins (e.g., PVC copolymers, chlorinated rubber) which ensure good adhesion to the substrate. The same primer must be used on zinc or galvanized surfaces because the use of alkyd resins causes embrittlement [11.38] The primed surfaces are largely topcoated with alkyd resin systems. 

Painting can be defined as the coating of a surface with paint (which includes pigment or color). The paint coating can be applied by using brushes, rollers, and spray methods (which are described in chapter Industrial Surface Treatments ). Industrial paint is used to protect metal, wood, and a variety of other materials. It provides a barrier between the substrate s surface and its surroundings. 

When metal particles or metal powder are used instead of a pigment or a dye in an UV curable ink composition, there is a problem in that it is difficult to sufficiently exhibit properties such as gloss provided inherently by the metal. In addition, the storage stability of the composition is lowered. This causes a problem in that the composition is turned into a gel, and thus ejection stability of the composition is lowered due to the increase of the viscosity (10). The negative influence of the metal powder can be eliminated by a surface treatment with a fluorine type silane compoimd or a fluorine type phosphoric add ester. 

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