Medium oil alkyd resin

P.O.19 has stimulated only limited industrial interest and is rarely used in Europe. It provides a shade which in white reductions resembles that of P.O.34, but which is much duller. Its full shade is noticeably yellower than that of P.O.34. P.O.19, incorporated in medium-oil alkyd resin systems, is less lightfast, both in full shade and in white reductions, than opaque P.O.34 types. The commercially available type exhibits poor rheological behavior. 

A typical fusion process formation for a medium oil alkyd resin is as follows [46]. 

Attempts to produce a copolymer by heating alpha-methylstyrene and tert-butyl perbenzoate with an alkyd were unsuccessful. However, a graft copolymer was obtained with a 5050 mixture of alpha-methylstyrene, styrene, and tert-butyl perbenzoate heated with the medium-oil alkyd resin. 

Figure B.2. Infrared spectrum of a medium oil alkyd resin.

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. 

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). 

Medium-oil alkyds are typically used in architectural paints and as co-resin in some original equipment manufacturer (OEM) coatings. These alkyds are 46-55% oil and 30—35% phthalic anhydride. They are viscous, soluble in mineral spirits and aromatic solvents, and slightly harder, and have poorer application properties than long-oil alkyds. 

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]. 

A medium oil alkyd (46-55% oil content and 30-35% phthalic anhydride in final resin) is one that has good water impermeability, fair baking and color, usual application, and is soluble in aliphatic solvents such as mineral spirits and naphthas. The modifying oil commonly used here is linseed or soya. 

Compatibility studies have been carried out with Reichhold Beckosol long oil alkyds 10-560 and 10-060, medium oil alkyd 11-035, and short oil alkyd 12-005. Vernonia oil is compatible with all three types of alkyd resins at any ratio. 

Medium oil alkyds are more versatile than short or long oil alkyds. Most alkyd resins are produced by the fatty acid process in which the glycerol, dicarboxylic acid and unsaturated acid are condensed at 392-446°F (200-... 

Silicone resins with high phenyl contents may be used with medium or short oil alkyds as blends in air-dried or baked coatings to improve heat or weather resistance the alkyd component contributes to adhesion and flexibiUty. AppHcations include insulation varnishes, heat-resistant paints, and marine coatings. 

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