Oil drying agent
Encyclopedia
An oil drying agent is a coordination compound that accelerates (catalyzes
) the hardening of drying oil
s through chemical crosslinking. The catalysts affect the autoxidation
of the oils with air. Typical oil drying agents are derived from cobalt
, manganese
, and iron
and lipophilic
carboxylic acid
s such as naphthenic acid
s to make them oil-soluble.
. These catalysts were traditionally carboxylates of lead
, but cobalt and other driers such as zirconium
, zinc
, calcium
, and iron
have become popular. Most driers are colorless but cobalt
is a deep blue purple color and iron driers are reddish orange. Thus the colored driers are compatible only with certain paints.
Japan drier is a common lay term and generic product name for any oil drying agent that can be mixed with drying oils such as boiled linseed oil and alkyd
resin paints to speed up "drying".
(MEKO), which is called an "antiskinning agent."
Catalysis
Catalysis is the change in rate of a chemical reaction due to the participation of a substance called a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. A catalyst may participate in multiple chemical transformations....
) the hardening of drying oil
Drying oil
A drying oil is an oil that hardens to a tough, solid film after a period of exposure to air. The oil hardens through a chemical reaction in which the components crosslink by the action of oxygen . Drying oils are a key component of oil paint and some varnishes...
s through chemical crosslinking. The catalysts affect the autoxidation
Autoxidation
Autoxidation is any oxidation that occurs in open air or in presence of oxygen and/or UV radiation and forms peroxides and hydroperoxides. A classic example of autoxidation is that of simple ethers like diethyl ether, whose peroxides can be dangerously explosive. It can be considered to be a slow,...
of the oils with air. Typical oil drying agents are derived from cobalt
Cobalt
Cobalt is a chemical element with symbol Co and atomic number 27. It is found naturally only in chemically combined form. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal....
, manganese
Manganese
Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...
, and iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
and lipophilic
Lipophilic
Lipophilicity, , refers to the ability of a chemical compound to dissolve in fats, oils, lipids, and non-polar solvents such as hexane or toluene. These non-polar solvents are themselves lipophilic — the axiom that like dissolves like generally holds true...
carboxylic acid
Carboxylic acid
Carboxylic acids are organic acids characterized by the presence of at least one carboxyl group. The general formula of a carboxylic acid is R-COOH, where R is some monovalent functional group...
s such as naphthenic acid
Naphthenic acid
Naphthenic acid is the name for an unspecific mixture of several cyclopentyl and cyclohexyl carboxylic acids with molecular weight of 120 to well over 700 atomic mass units. The main fraction are carboxylic acids with a carbon backbone of 9 to 20 carbons. The naphtha fraction of the crude oil...
s to make them oil-soluble.
Varieties of drying agents
Oil drying agents are often called salts, but they are probably non-ionic coordination complexes akin to basic zinc acetateZinc acetate
Zinc acetate is the chemical compound with the formula Zn2, which commonly occurs as a dihydrate Zn22. Both the hydrate and the anhydrous forms are colorless solids that are commonly used in chemical synthesis and as dietary supplements. Zinc acetates are prepared by the action of acetic acid on...
. These catalysts were traditionally carboxylates of lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
, but cobalt and other driers such as zirconium
Zirconium
Zirconium is a chemical element with the symbol Zr and atomic number 40. The name of zirconium is taken from the mineral zircon. Its atomic mass is 91.224. It is a lustrous, grey-white, strong transition metal that resembles titanium...
, zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
, calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
, and iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
have become popular. Most driers are colorless but cobalt
Cobalt
Cobalt is a chemical element with symbol Co and atomic number 27. It is found naturally only in chemically combined form. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal....
is a deep blue purple color and iron driers are reddish orange. Thus the colored driers are compatible only with certain paints.
Japan drier is a common lay term and generic product name for any oil drying agent that can be mixed with drying oils such as boiled linseed oil and alkyd
Alkyd
An alkyd is a polyester modified by the addition of fatty acids and other components. They are derived from polyols and a dicarboxylic acid or carboxylic acid anhydride. The term alkyd is a modification of the original name "alcid", reflecting the fact that they are derived from alcohol and...
resin paints to speed up "drying".
Antiskinning
Premature hardening of paint, called skinning, can be inhibited by the addition of volatile ligands that bind to the oil drying agents. One such inhibitor is methylethyl ketone oximeMethylethyl ketone oxime
Methylethyl ketone oxime is the organic compound with the formula C2H5CCH3. This colourless liquid is the oxime derivative of methyl ethyl ketone. MEKO, as it is called in the paint industry, is used to suppress "skinning" of paints: the formation of a skin on paint before it is used...
(MEKO), which is called an "antiskinning agent."