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NOVEMBER 1982 PIGMENT AND RESIN TECHNOLOGY 3 New alkyds and not so new chlorinated rubber Tw o technical developments are in the news this month , one new and one old . The new development, which comes from Battelle's Columbus, Ohio, laboratories, is an improved process for pre paring air-driable alkyd resins widely used in paints, inks, and coatings. It is said to improve the quality of the resins while reducing the energy and time necessary to prepare them. Battelle recently received a U.S. patent (U.S. 4,335,027 ) for the process and now hopes to commercialise it. It was developed as part of an internally supported research programme. Wit h the new Battelle process, the organic anhy drides and glycidyl esters that constitute air drying alkyds, initiall y are mixed with metal salt catalysts. The mixture is heated in reactors at temperatures not exceeding 100°C for between two and four hours. In the reactors the compounds polymerise and form a resin. With conventional processing different compounds are used as the resin feedstock. These compounds require heating at between 230°C and 250°C for as long as 12 hours. In addition to energy and time savings, the new pro cess is said to offer several other advantages over conven tiona l methods. First, under the new process the resins are colourless. This is important if the resins are used in white or light- coloure d paints. Under conventional methods the finished resins take on a darker colour that is difficult to remove. The colour often results because substantial amounts of side products are produced during the long heating periods. Also, the alkyd resins produced with the new Battelle process have a narrower molecular weight range, imparting excellent level ling or flow-out characteristics to coatings formulated using these resins. The older development we referred to is that Bayer's Pergut chlorinated rubber celebrates its 50th anniversary this year. Developed to meet the paint industry's requirements for a raw material with water and chemical resistance com bined with weatherability, it is still in demand today despite the competition from more recent coating materials. If our memor y serves us correct, ICI's Alloprene chlorinated rubber paint is now coming up to its 50th anniversary. Prior to the introduction of Pergut, the paint industry had not been slow in attempting to exploit naural rubber's properties in the production of chemical resistant finishes. They were beset by a number of problems, however: firstly, the rubber didn't possess sufficient weather resistance; secondly, its high viscosity made the paints difficult to brush on ; thirdly, its compatibility with the commonly used surface coating raw materials was inadequate. Chlorination solved these problems, but initially caused an additional one with a tendency to split off hydrogen chloride. In Pergut (as with Alloprene), the paint industry had a product which provided paints and varnishes with excellent resistance to water and chemicals, and much improved light- and weather-stability compared to competing materials.
Pigment & Resin Technology – Emerald Publishing
Published: Nov 1, 1982
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