Лако-красочные материалы — производство

Alkyd resins have been used in surface coatings for more than eight decades. They have been the workhorse of the binders for solventbased architectural coatings and to a considerable extent for industrial coatings because of their low cost, good performance properties, and versatility of applications. In the beginning of the 20th century, the esterification product of glycerine with phtha — lic anhydride (glyptal) was produced as a synthetic hard resin. However, owing to its brittleness and incompatibility with oils, it was of not practical utility in coatings at that time. In the late 1920s, Kienle et al. made a significant contribution to alkyd resin techno­logy by developing a process to chemically incorporate vegetable oil in the polymer backbone using an alcoholysis technique. This development led to the commercial availability of alkyd resins with good solubility and film forming characteristics. The term alkyd resin originally was proposed to describe the reaction product of polyhydric alcohols with a polybasic acid as a euphonic contraction of ‘al’ from ‘alcohol’ and ‘cid’ from ‘acid’ (changed to ‘kyd’ for aiding pronunciation). Although this does not make any reference to the fatty acid component, alkyd resins are generally understood as oil modified polyesters.

According to DIN 53183, “Alkyd resins are synthetic polyester resins produced by esterifying polyhydric alcohols with polybasic carboxylic acids where at least one of the alcohols must be tri — hydric or higher. Alkyd resins are always modified with natural fatty acids or oils and/or synthetic fatty acids and may be addi­tionally modified with compounds such as resin acids, benzoic acid, styrene, vinyltoluene, isocyanates, acrylic, epoxy, or silicone compounds.”

Despite the development of a vast variety of other synthetic resins, alkyd resins have remained a large fraction of the resins for the paint industry because of a number of reasons. They are a single­pack system with excellent storage stability; they are relatively inexpensive as well as soluble in inexpensive solvents; they are versatile and can be engineered for a wide variety of properties ranging from hard, fast-drying compositions to softer, more fle-

xible slow-drying resins; they can be chemically modified by a number of other resins to improve their film properties; and they possess excellent wetting characteristics for pigments as well as the surfaces they’re applied to. On the other hand, being polyesters, their main limitation is their sensitivity to water, alkali and acid due to hydrolysis of ester linkages of the polymer backbone.