Primer alkyd based

Air-drying alkyds may also be used for the production of primers and undercoats. In the case of primers, the shorter the oil length of the binder the faster the drying, but the lower the tolerance for wire-brushed rusted-steel surfaces. Alkyd-based undercoats are not significantly different in performance from those based on oil varnishes the choice is frequently dictated by economic considerations. 

Binders based on linseed oil and other oils have been used for many years in anticorrosive primers. Alkyd binders, especially those with high fatty acid contents, perform similarly. The main disadvantages of these binders is their limited chemical resistance and their slow drying. 

Prime coating is either a two-pack, zinc-rich epoxy primer with a DFT of ca. 30-40 pm, or a chromate-free, two-pack epoxy primer. Topcoats based on PVC copolymerisates, chlorinated rubber, silicone-reinforced epoxy esters, or alkyds were used for many years. Now, the standard European topcoat is based on acrylic resins with terminal epoxy groups that are cross-linked with amine adducts or aminoamide resins. 

Nitrocellulose based lacquers often contain short or medium oil alkyds to improve flexibiUty and adhesion. The most commonly used are short oil non drying alkyds. Amino resins or urethane resins with residual isocyanate functional groups may be added to cross-link the coating film for improved solvent and chemical resistance. The principal appHcations are furniture coatings, top lacquer for printed paper, and automotive refinishing primers. 

Oleo-resinous primers plus alkyd finish Aluminum-based primer plus alkyd finish Emulsion-based primer plus alkyd finish Wood stains... 

Aluminum-based primer plus alkyd finish The binder for these primers is normally oleo-resinous but the pigmentation is aluminum flake. This type is preferred for hardwoods and softwoods where knots or resinous areas predominate. They do not give such a smooth surface as primers without aluminum. 

Emulsion-based primer plus alkyd finish These are based on acrylic resin dispersions and have the advantage of a rapid rate of drying. They generally have excellent adhesion and flexibility but lack the sealing properties of aluminum primers. 

Paints are complex formulations of polymeric binders with additives including anti-corrosion pigments, colors, plasticizers, ultraviolet absorbers, flame-retardant chemicals, etc. Almost all binders are organic materials such as resins based on epoxy, polyurethanes, alkyds, esters, chlorinated rubber and acrylics. The common inorganic binder is the silicate used in inorganic zinc silicate primer for steel. Specific formulations are available for application to aluminum and for galvanized steel substrates. 

With these lacquers, nitrocellulose-based primer-surfacers are used. As well as liquid plasticisers, a wide range of materials are used as plasticising resins short oil alkyds, maleinised oils, ester gum, rosin and bodied castor oils. Pigmentation is usually inert. Thermoplastic acrylics are often preferred under acrylic lacquers these are based on acrylic resins and cellulose acetate butyrate. 

Coating materials may be based on short or medium-oil alkyds (e.g. primers for door and window frames) nitrocellulose or thermoplastic acrylics (e.g. lacquers for paper or furniture finishes) amino resin-alkyd coatings, with or without nitrocellulose inclusions, but with a strong acid catalyst to promote low temperature cure (furniture finishes) two-pack polyurethanes (furniture, flat boards) unsaturated polyester resins in styrene with free-radical cure initiated by peroxides (furniture) or unsaturated acrylic oligomers and monomers cured by u.v. radiation or electron beams (coatings for record sleeves paperback covers, knock-down furniture or flush interior doors). 

Nitrocellulose-based lacquers often contain short or medium oil alkyds to improve flexibility and adhesion. The principal applications are furniture coalings, top lacquer for printed paper, and automotive refinishing primers. 

Inhibitive Primers. The traditional primers are red lead and linseed oil, alkyd resins and zinc potassium chromate, proprietary epoxy, alkyd, urethane and latex systems with modified phosphate, borate and molybdate pigments. Chromate-based pigments, although in use in aircraft coatings, automotive primers and coil coating primers, are subject to environmental concern on the toxicity of hexavalent chromium which is likely to result in their replacement by innocuous products. 

A further progress perspective in the field of water-based paints could be their use for painting ships [205]. However, these studies are only in the beginning. The main difficulty is corrosion prevention. Maximum protection from stress corrosion cracking is ensured by alkyd paints combined with phenolic epoxy paints during a 6.5-year exposure [206]. These data were obtained on pre-contaminated steel plates. In Russia now water-based dispersion primers with anticorrosive properties have been developed and manufactured [207]. This was possible after incorporation of corrosion inhibitors combined with surfactants into the formulations. 

Oxygen-induced Polymerized Coating Alkyds. These are oil-based primers and topcoats. Alkyds are based on fish or vegetable oils blended with pigments and catalysts in a solvent. The film is formed when the oil reacts with oxygen assisted by the catalyst followed by the evaporation of the solvent. Most paints sold in cans are alkyds. Drying oils consist of penetrating oils and lacquers that form a thin protective film. 

Side and cross members are pretreated by blasting and phosphating. An electrode-posited primer coating follows and is sometimes immediately overcoated with a topcoat based on an air-drying alkyd or epoxy ester, or on an oven-drying alkyd-melamine resin combination. After assembly of the truck, a third layer (i.e., a second topcoat) is applied that serves as a supply finish. These finishes are mostly two-pack acrylic aliphatic isocyanate topcoats. Water-based two-pack systems and powder coatings are the most recent developments. 

Coil coatings are normally applied by roller coating machines, but are sometimes sprayed. The topside of the metal band is normally painted with a primer (DFT ca. 5 pm) and a topcoat (DFT 20-22 pm). Zinc-rich coil coatings are applied with a DFT of 5-20 pm, plastisol films have a DFT of 80-400 pm. The reverse side of the coils is coated with backing coats based on binders, such as alkyd, polyester, and epoxy resins (DFT 8-10 pm). 

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. 

A one-pack primer based on chlorinated rubber or chlorosulfonated polyethylene (as is conventional with galvanized surfaces) or a two-pack epoxy primer is then applied. The primer can be coated with a topcoat system that is usually formulated with medium or long oil alkyd resins [11.39]. 

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