PURE ALKYD RESINS

Alkyd resins are produced by reacting 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.  But 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 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.)
 
 
ALKYD TYPE
APPLICATIONS/CHARACTERISTICS
LONG OIL ALKYDS
  • Printing inks, grinding vehicles
  • House paints, enamels and primers
  • Traffic paints, compatible with vinyl resins and chlorinated rubber
MEDIUM OIL ALKYDS
  • Quick-dry enamels, spar varnishes
  • Quick-dry enamel with good color retention
  • Traffic paints, limited compatibility with vinyl resins and chlorinated rubber
  • Plasticizer for nitrocellulose lacquers
SHORT OIL ALKYDS
  • Baked enamels, grinding vehicles
  • Baked enamels, catalyzed lacquer
  • Baked enamels, auto lacquers, wood lacquers
  • White baked enamels with excellent color retention
  • Can Coatings
FLAT ALKYDS
  • Flat wall finishes with excellent brushing and leveling

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