Лако-красочные материалы — производство

Although they are not the only type used, difunctional aromatic acids are most commonly used in alkyd resins, of which phthalic anhydride is the most important and commonly used diacid because of its avai­lability, low cost, relatively low melting point, and high reactivity. Isophthalic acid is another dibasic acid that is frequently used for alkyds with improved hardness and heat resistance, but its high melting point (342 °C) makes it difficult to process resins at normal temperatures. Partial replacement of phthalic anhydride with maleic anhydride improves drying time and color of resins. Aromatic acids and maleic anhydride contribute to hardness, chemical resistance, and durability of alkyds. On the other hand, long-chain dibasic acids, such as adipic acid, sebacic acid and azelaic acid, are sometimes used in minor quantities to plasticize alkyds and provide flexibility. Bio-based succinic acid has recently gained interest among alkyd manufacturers due to its renewable nature and sustainability. An important trifunctional acid worth mentioning i s trimellitic anhydride, which is often employed in water-reducible alkyd resins and in high — solids alkyds. Some examples of commonly used carboxylic acids and anhydride are shown in Figure 2.11.