Calcium is an auxiliary drier. It is used both in combination with lead
and as a partial replacement for lead in vehicles that show poor tolerance
for lead. Calcium prevents formation of basic lead phthalates in alkyds
systems. When used along with zirconium in lead free systems, calcium
driers find important application as pigment wetting agents and reduce
loss of dry problems.
Zinc has been found to give harder films in many coatings films and
baking enamels keeping the film 'open' and preventing surface wrinkling
agent and reduce loss of dry when incorporated early in the grind phase of
Lead functions as a powerful drier by promotion polymerization of
drying oils, causing the film to dry in its entire thickness.; in other
words the drying of the surface and inside the film is catalyzed
uniformly. Lead is, therefore called a "through" drier like
cobalt is known as the top drier. Lead also improves the flexibility,
toughness, durability, water resistance and salt spray resistance of the
film. Lead is always used in conjunction with others such as cobalt and
calcium. It is also used as a deleafing additive for aluminum pastes.
However, lead is seldom used these days due to environmental hazards.
Iron is a specialty drier which is active only at bake temperatures
above 120º C although it effects little or no polymerization at ambient temperatures.
Iron can be used only in darkly pigmented coatings as it contributes a
brownish red color. Iron is a good wetting agent for carbon black
pigments, thus yielding better grinds. It also helps to avoid loss of dry
problems. Iron has also been reported to reduce the tendency for orange
peeling in black automotive bake finishing.
Cerium promotes polymerization and through drying, cerium, more active at
higher temperatures, does not stain the film although it imparts less
hardness than iron. Cerium is a preferred drier in long oil alkyd vehicles
and alkyd/epoxy systems. Cerium also performs as an effective auxiliary
drier in coatings dried at low temperature and high humidity. Cerium is
particularly recommended for baking finishes for white or overprint
varnishes where color retention is important.
Lithium is generally used in conjunction with cobalt in high solids
coatings as a substitute for lead. These resins are necessarily of low
molecular weight, so designed to comply with VOC regulations. Lithium
promotes through drying with improved hardness reducing the tendency
of high solids coatings to wrinkle. It is also used as an etherification
catalyst for alkyds
-particularly with coconut oil alkyds.
DURA also offers metals carboxylates of barium, copper, rare earth and
many others in addition to the principal drier metals previously