Published: Jan 2012
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METALLIC SOAPS ARE COMPOUNDS OF ALKALINE metals or heavy metals and monobasic carboxylic acids containing from 7 to 22 carbon atoms. The water-insoluble metallic soaps are of particular interest to the coatings industry, although potassium and lithium soaps have limited water solubility. Basically, the known techniques for preparation of metallic soaps are divided in two processes—a fusion process and a double decomposition process. The fusion process involves reacting a metal oxide or hydroxide with a fused fatty acid such as a triglyceride in the presence of water . The process yields the desired metallic soap and glycerin. The double decomposition process involves reacting an alkali soap that is comprised of an alkaline metal salt or an ammonium salt of a fatty acid with an inorganic metal salt. Both processes are usually carried out in a batch mode; and, as a result, a product contaminated with unreacted starting materials and by-products that must be further purified is formed. To obtain a product essentially free of contamination, a continuous process  involving the double decomposition scheme has been devised. An aqueous solution of the alkali soap and an inorganic metal salt are separately fed onto a rotating impeller surface whereon they are instantaneously mixed. The resulting aqueous slurry is rapidly discharged and a contamination-free metallic soap results. Recently, a process for making basic zirconium carboxylates of branchedchain, five- to ten-carbon, aliphatic monocarboxylic acids has been described . The compounds are useful as driers for paints and inks. The applications of metallic soaps in coatings include their use as driers, catalysts, stabilizers, biocides, bodying agents, and flatting agents. An overview of metallic soap applications is presented in Table 1. An interesting particular end-use for metallic soaps is in the formation of a thin metallic oxide coating on a substrate . A solution of the metallic soap is applied by reverse roll coating and then baked in a manner such that a thin, about 1–10 μm, film of the metallic oxide is formed. Although this chapter concentrates primarily on metallic soaps used as driers, a brief review of bodying and flatting applications for these materials is included.
Schnall, Marvin J.
Coatings Consultant, Chapel Hill, NC