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(also siccative), a substance that catalyzes the oxidative polymerization (drying) of vegetable oils; any of the constituents of boiled oils, oil varnishes, and alkyd, epoxyester, and other oil-containing paint and varnish materials that accelerate the formation of a film at room and higher temperatures. By chemical composition, driers can be salts of metals (most often lead, manganese, cobalt), salts of fatty acids of such oils as linseed oil and tall oil (whose corresponding salts are called linoleates and tallates), or salts of resin acids of rosin (resinates), naphthenic acids (naphthenates), and 2-ethylhexoic acid (octoates).
Driers dissolve in oils when heated to 120°-150°C and in volatile organic solvents. The reactivity of the drier is determined primarily by the type of metal and by the metal’s concentration, which usually amounts to 0.01–0.5 percent of the oil’s weight. For each metal there is an optimum concentration at which quick-drying coatings are obtained that do not crack under prolonged use. It is fairly common to use composite driers, containing ions of two or more metals, as well as mixtures of different driers. For example, the formation of a film is accelerated by using Pb with Mn or Pb with Co; the quality of coatings obtained by cold drying is improved by substituting Zr for part of the Mn or Co. Certain properties of driers, as well as the cost, are dependent on the type of acid. Thus, naphthenates and octoates are more stable during storage than hnoleates, resinates, and tallates. Octoates offer two advantages over the less expensive naphthenates: they are colorless and odorless. Resinates are less expensive and are more readily soluble in oils than linoleates. Films made from materials containing resinates are more lustrous than films with linoleates but exhibit a lower degree of flexibility and strength. Linoleates of lead, manganese, zinc, and cobalt are the main driers used in oil painting.
Driers are classed as fused or precipitated, depending on the method of preparation. Fused driers are more readily obtained but are less homogeneous, have a deeper color, and contain more impurities than precipitated driers. Driers are generally produced as solutions in white spirits or turpentine but are also available as powders, pastes, and concentrated solutions in oil.
REFERENCESEntsiklopediia polimerov, vol. 3. Moscow, 1977.
Kiplik, D. I. Tekhnika zhivopisi[6th ed.]. Moscow-Leningrad, 1950.
M. M. GOL’DBERG