Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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Fig. 2. Polyisocyanate structures. Adducts made with IPDI trimer (Fig. 2) were introduced in the late 1960s. Due to a different monomer structure, these trimers are higher in viscosity, high- er in color, higher in free monomer content, and lower in crosslinkability (crosslink sites per unit molecular weight)than the HDI trimer. Table I summarizes the important physical properties of polyisocyanate adducts used for metal coat- ings. The performance of the finished coating depends on several factors: the adduct (HDI trimer or HDI biuret), polyol, solvents, and catalyst. Table II rates and ranks the coating performance (performance test methods described in Fig. 86

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