Driers
Aluminum driers, in combination with standard oxidative surface driers, provide enhanced through dry, better pigment wetting and dispersion, greater water resistance higher gloss retention and less discoloration. A limitation to the use of alumi-num driers is that they are more resin specific and tend to build viscosity in systems high in acid number and/or hydroxyl number.
Since calcium has little drying action in itself but is very useful in combination with active driers, it is known as an Auxiliary drier.
In vehicles that show poor tolerance for lead, it is possible to replace part of the lead with a larger amount of calcium to prevent the precipitation of the lead and maintain drying efficiency. Calcium is often used to replace lead where the toxicity of lead must be avoided For example: toy enamels, baby furniture finishes and sanitary finishes.
Calcium driers are also useful as pigment wetting and dispersing agents and help to improve hardness and gloss and reduce "silking." When ground with drier adsorbing pigments, calcium minimizes loss-of-dry by being preferentially adsorbed.
Cobalt is without a doubt the most important and most widely used drier metal in coatings. It is primarily an oxidation catalyst and as such acts as a "surface" or "top drier." Used alone, it may have a tendency to cause surface wrinkling; therefore, to provide uniform drying, cobalt is generally used in combination with other metals, such as manganese, zirconium, rare earth, calcium and combinations of these metals.
Due to the fact that it is necessary to add only very small amounts of cobalt driers, cobalt minimizes discoloration in paints and enamels as compared with other drier metals. Additionally, cobalt does not discolor white paints, since the deep blue color of the cobalt counteracts the yellow of the oils and resins and thereby enhances the whiteness of the paint. Cobalt is almost always used as a drier in white coatings.
Owing to their high activity, cobalt driers should preferably be added as near to the end of the manufacturing process as possible.
While iron exhibits very little drying at room temperature, it becomes very active at elevated temperatures, and is therefore extensively used in baking finishes. Iron driers provide tough, durable, yet very flexible films with extremely good gloss.
In air-dry finishes, iron is particularly useful in eliminating the after-tack common to oxide pigmented paints and unprocessed fish-oil compositions.
Iron also functions as a wetting agent and helps to obtain quicker and better grinds when used with carbon black pigments.
Because of their dark color and high staining power, iron driers are used primarily in dark-colored baking enamels. In addition, they are generally used to replace lead driers in aluminum paints since iron does not adversely affect the leafing of aluminum pigments.
Manganese driers are intermediate in activity, and they have both oxidizing and polymerizing properties. Used alone, manganese has a tendency to produce films that may be too hard and too brittle. When used in combination with lead, hard, tough, durable films are produced. Lead-manganese drier combinations are often employed for enamels, outside paints, floor finishes and baking finishes.
One disadvantage in the use of manganese driers is their relatively dark color, which has a tendency to stain or discolor white or light finishes. OMG's new Light-Colored Manganese Driers overcome this problem. Manganese performance and stability can be significantly enhanced by the incorporation of selected chelates, such as DRI-Rx ®. The chelated manganese is a very active drier, especially in "long oil's vehicles. The manganese chelate also works well under marginal drying conditions making it a very useful drier.
Rare earth driers, containing high levels of lanthanum, neodymium or cerium, promote polymerization and through drying. These driers are used to replace lead and zirconium. Rare earth driers are especially effective for drying coatings under low temperature and high humidity conditions. Generally, one-half of the rare earth metal is required to obtain the same drying activity as that furnished by lead or zirconium. Rare earth driers are more active than lead or zirconium in oleoresinous and alkyd baking finishes, epoxyesters, styrenated alkyds and silicone alkyd formulations. They also contribute to improved gloss and gloss retention.
Our most popular Tin compound is Dibutyl Tin Dilaurate (DsTDL), which is used mostly as a catalyst to produce polyurethane Products such as flexible foams used in upholstery and solid PU Products. Other uses of DBTDL include a room temperature curing agent for silicone elastomers, an esterification and transesterification catalyst, and a catalyst for peroxycarbamate formation. Tin carboxylates are also available from OMG for proprietary catalytic applications. Other tin organics are usually used as polymerization catalysts.
Zinc is among the group of metals known as "auxiliary" driers, used in conjunction with the redoxmetals. The primary function of zinc is to keep the film "open" by retarding surface dry, thus permitting hardening throughout and preventing surface wrinkling, particularly in cobalt-containing films and enamels.
Zinc is a powerful wetting and dispersing agent, and when incorporated early in the formulation, it greatly reduces the time of mixing and grinding. Because of its extremely light color, zinc can be added without discoloring the film.
While zirconium driers have long been in use, this metal has come to the forefront with legislation restricting the use of lead driers in many countries. Zirconium, like lead and rare earths, serves as a through drier; and, is generally used in combination with cobalt, manganese and/or calcium. Three-quarters of a pound of zirconium will usually replace one pound of lead (based on metal). However, when substituting zirconium for lead, maximum drier performance can best be determined by experimentation. Unlike lead, zirconium is a poor pigmentwetting and dispersing agent; therefore, the use of calcium or our SPURSO may be called for when using zirconium vs. lead.
OMG (OM Group, Inc.), 50 Public Square, Cleveland, OH 44113. Tel: 216-781-0083; Fax: 216-263-7492.