Unique Solutions to Regulatory Concerns Affecting Cobalt and MEKO
June 2016 www.coatingsworld.com Coatings World | 37
cobalt at low temperatures and also when
used in baking finishes, but not at ambient temperatures. It is mainly used in drying oils in combination with cobalt. As a
cobalt replacement, manganese requires
the addition of a drier accelerator like
1,10-phenanthroline or 2,2’-bipyridyl
chelating additives to approach the activity level of cobalt. Films may develop a
brown colored hue on ageing due to the
color of the manganese drier.
Iron has no catalytic activity at room
temperature in air drying finishes but it is
more active than cobalt at elevated temperatures (130 °C). The dark red color of
iron driers restricts its usage in coatings
to dark colors and red coatings.
Vanadium is efficient at lower temperatures but has a tendency to impart
a greenish stain to films. Unlike cobalt,
vanadium is more stable in its higher
valence state which inhibits its role in
oxidative curing and complex formation.
Higher levels are generally needed.
Cerium can promote oxidative curing
at elevated temperatures but is primarily
used as a through or coordinate drier.
Iron-Complex technology - A new
unique organic complex with iron has
yielded an oxidative drier which magnifies the drying activity of iron so that it
is effective over a wide range of temperatures and drying conditions. This new
iron-complex technology is more active
than cobalt, has a very light color and
promotes oxidative curing both at the
surface and throughout the film in many
binders.
Potential Cobalt Re-
Classification
Cobalt driers have been a regulatory concern for many years. Reproductive toxicity and the long term adverse effects on
aquatic organisms have been well known
and documented. As described above, cobalt driers are true catalysts in the oxidation process of air drying binders in that
they do not become part of the molecular
structure. Cobalt driers do not crosslink
into the film and also have some water
solubility so they will eventually leach
into the ground water supply when the
films come in contact with water. There is
also the growing concern that cobalt (as
R, R’ and R” are organic components of varying composition.
