Pretreatment for painting

Chromate conversion coatings are used widely on aluminum alloys as a pretreatment for painting, though in some applications, where noncondensing atmospheric exposure is expected, they may be used as the primary means of corrosion protection. Chromate conversion coatings are used on magnesium, cadmium, and zinc, and on galvanized steel to suppress the formation of white rust. 

Amorphous phosphate films are formed during the process of alkali phosphat-ing [1]. This type of film is generally used on iron and steel and may he used for temporary corrosion protection or as a lowphosphate layers are a mixture of iron phosphate (Fe3(P04)2-8H20), iron oxides, and hydroxides. The treatment haths consist of phosphoric acid solutions of pH 3-5 with minimal or no divalent cations present. Nitrate or other additives are used as accelerators. 

Magnesium CCCs are usually formed in acidic solutions in which Mg surfaces are easily activated. Nitric acid-and chromic acid-based mixtures are common. Because of the high corrosion susceptibility of Mg alloys, CCCs are more often used as a surface pretreatment for paint than as stand-alone corrosion-resistant coatings. 

Some part of the cellulose fraction is redirected to make cellulose derivatives, such as cellulose acetate, methyl and ethyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose. These derivatives find multiple applications, for instance, as additives in current products (e.g., paints, lacquers) of chemical industry. Typically, the preparation of cellulose derivatives takes place as a two-phase reaction cellulose is pretreated, for example, with alkali, and a reagent is added to get the substitution. Usually no catalyst is needed [5]. 

In order to obtain maximum corrosion protection for painted metal articles, the metal parts are pretreated with an inorganic conversion coating prior to the painting operation. These zinc or iron phosphate coatings greatly increase both paint adhesion and corrosion protection. Traditionally, a chromic acid post-treatment has been applied to these phosphatized metal surfaces to further enhance corrosion protection. 

Polyolefin injection mouldings are printed less frequently than films and bottles but requirements for treatment for this purpose do occur, and also for pretreatment for other purposes (like metallizing or being painted so as to match other components). Several different methods are available and may be used in practice, including ... 

Aluminum Several authors have compared the efficiency of various pretreatments for aluminum and its alloys [173, 186-189]. Typical pretreatments for aluminum prior to paint appKcation are chromating and anodization (Ref [168] and references therein). 

Uses Corrosion inhibitor, adhesion promoter for paints or coatings onto metal substrates, for use in baking and air-drying systems with alkyds, polyesters, acrylics, urethanes metal pretreatment Properties Yellowish liq. very strong odor partly sol. in water sp.gr. 1.08 dens. 9.03 Ib/gal vise. 17,000 cps b.p. 137 C flash pt. (PMCC) 38 C 66% NV... 

---