Metal carboxylates are more commonly referred to as driers or siccatives. They are an organometallic salts, formed by the reaction of a metallic raw material and synthetic carboxylic acid(s) dissolved in a hydrocarbon solvent. When added to alkyd based paints they markedly reduce the drying times.
Primary Driers
Act as oxidation catalysts, as their metal soaps exhibit more than one oxidation state. Primary driers catalyse cross linking of the resin and in the process hydroxyl, carbonyl and carboxylic groups are formed.
Through Driers
Ensure that a coating dries at a uniform rate throughout the body of the film. Primary driers without the presence of through driers would mainly dry the surface of the film, whilst the coating underneath would remain wet. Through driers are used to ensure that the coating dries at a uniform rate throughout the body of the film not just at the surface. Through driers link fatty acid chains via oxygen-metal-oxygen bridges leading to cross-links.
Auxiliary Driers
Modify the effect of other driers but do not demonstrate any drying action on their own. Learn More Button (Link to Our Products Page)
Drying Process in Coatings
All driers work through the whole of the coating
Primary driers are most active at the surface where the oxygen content is the highestÂ
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Oxygen from the atmosphere is absorbed by the primary drier at the surface of the coating Solvent and MEKO evaporate
Auxiliary driers act at the surface depending on their functionality.
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Calcium opens the matrix structure to facilitate solvent evaporation and deeper oxygen penetration. Free radical process started at the surface is passed down through the film. Through driers promote drying of the body of the film.
Drier Dosage
General starting point recommendations for individual metals and blends can be provided. The recommendatiosn for a coating based on standard long oil alkyd will differ from that for a short oil alkyd or a high solids coating; similarly the nature of the oil / fatty acid and any hybridisations will change the optimal drier package. The Metchem driers for alkyd based coatings are designed for ease of use, and the type of technology will determine the optimal drier package.
In order to attain maximum performance of a coating the formulator needs to find the right balance of primary, through, auxiliary driers and additives. Specific metals can provide the means for a coating to improve defined qualities; such as increased hardness, higher gloss, better through dry