Paint and Coatings

Description

For architectural (decorative) paints, enamels, primers, road-marking paints, baked enamels, automotive and wood lacquers, etc.

Alkyd resins are produced by the reaction of a polybasic acid (phthalic anhydride, maleic anhydride, etc.) with a polyhydric alcohol (glycerine, pentaerythritol, ethylene glycol, etc.) and an oil or a fatty acid. The reaction may be further modified with the addition of rosin and/or phenol-formaldehyde resin. Various polybasic acids, polyhydric alcohols, oils, fatty acids and modifying agents may be combined to produce alkyds with specifically desired properties.

Originally, alkyd resins were merely the reaction products of phthalic anhydride and glycerine. However, these products were too brittle to make satisfactory coatings. The use of oils or unsaturated fatty acids in combination with the brittle alkyds resulted in the air-drying coatings which revolutionized the chemical coating industry. Further developments led to the use of completely or partially saturated oils and fatty acids for baking finishes and lacquers.

The oil or fatty acid portion of the alkyd is one of the factors which determine the paint formulator’s choice of resin to be used. In general, the lower the phthalic content of an alkyd, the higher the amount of oil used. For this reason, low phthalic unmodified alkyds (under 27%) are designated as “long oil”, medium phthalic alkyds (27-30%) as “medium oil” and high phthalic alkyds (over 30%) as “short oil”. Alkyds produced by the interaction of polybasic acids, polyhydric alcohols and oils or fatty acids are referred to as “unmodified alkyds”.

The incorporation of rosin, phenol-formaldehyde and vinyl or acrylic monomers into the alkyd during the reaction produces a modified alkyd. (See rosin/phenol modified alkyds and vinyl/urethane modified alkyds.)