Replacement of lead-based driers in alkyd paints
Lead-based paint is becoming a tool of the past. New paint compositions are safer alternatives for most current and future applications. Replacing lead-based paint is still an ongoing effort, but the industry is trending in the right direction. Companies have relied on a variety of ingredients in place of lead since using lead-based paints has multiple benefits.
Litharge (lead monoxide) has been used as a catalyst at levels of approximately 0.5% by weight in the manufacturing of alkyd resins. In the vast majority of cases – perhaps all litharge has been replaced by less toxic, more efficient esterification catalysts such as lithium.
Driers are sometimes supplied pre-mixed in the metal ratios required or specified by the paint manufacturer. This helps to minimize stock-keeping units and can also make dosing out of the driers simpler and more accurate. The growing environmental concern continues to put increasing pressure on lead-based paint driers. Replacement of lead driers by lower toxicity materials began in the 1970s and out of a limited number of alternatives, strontium and zirconium have developed to be the most prominent choice. Most brands tend to use strontium in place of lead as a drying agent. Strontium is non-toxic in addition to being a more efficient chemical. Zirconium is another alternative to lead but can cause health problems of its own. Zirconium isn’t as useful as Strontium either, meaning other chemicals may need to be added to achieve the same effect as the lead.
Strontium driers provide excellent “Loss of Dry” properties, equivalent to lead in this respect Strontium may be considered a more efficient drier than lead as levels of strontium are generally 33% of that of lead.
Strontium is generally regarded as the best alternative drier to lead. At a replacement level of 1 part of Strontium to 3 parts of lead, comparable performance can be achieved in terms of initial drying time, yellowing, weathering and in-can stability. Other than the possibility of some optimization work, no other changes would be anticipated to the drier package or the formulation as a whole. Compared to lead driers, strontium driers are considered to have the following properties:
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Price differences between strontium and lead driers are dependent on the base metal costs. However, given the low levels of addition of driers and their relatively low contribution to the overall cost structure, the cost of formulations containing strontium driers can be comparable to those formulations containing?lead driers.
Situations may arise where strontium driers are not readily available and there may be a need to replace lead with zirconium driers.
Continue reading to know about zirconium driers.