TAILIEUCHUNG - Coatings Technology Handbook 2010 Part 13

Tham khảo tài liệu 'coatings technology handbook 2010 part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Driers 80-3 coordination compounds such as ortho phenanthroline or di-pyridyl seems to reduce or eliminate such adsorption and prevent loss of dry. This may also be accomplished by using highly basic cobalt compounds that slowly release cobalt into solution. By basic we mean that the metal soap contains more moles of metal than the equivalent moles of acid from which it is formed. To accomplish complete drying of oil films the cobalt drier is used with another that possesses the property of initiating complete dry. Lead soaps are the most effective in this regard but their use has been limited because of toxicity. Calcium and zirconium are the metals used to replace lead. They are considered auxiliary driers. Calcium soaps at one time consisted of the napthenates usually at 4 and 6 calcium concentration. These were highly acidic and quite viscous. They have largely been replaced by calcium octoate a highly basic material low in viscosity and odor and available in solvent solutions in various concentrations. Zirconium 2-ethylhexanoate is also a basic soap usually available in 12 18 and 24 Zr concentrations. It seems to have a catalytic effect on cobalt and manganese driers and is said to have a coordination potential of namely 8 and a low redox potential. When electron-donating groups develop coordination polymerization occurs assisting in the overall drying effect. Barium 2-ethylhexanoate has also been used as a replacement for lead driers but also has found limited use because of its toxicity. Manganese is the other active drier that is widely used in oil paints and in baking finishes. Although active as an oxidant it seems to promote polymerization to a greater extent than cobalt. Solutions of manganese 2-ethylhexanoate rapidly oxidize to a dark brown color on exposure to air. The use of manganese in white paints presents discoloration problems that must be handled by careful formulation. Manganese is often used alone in baking finishes. A number of other metals

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