UV-Curable Alkyd Resins

Technological developments and market demands in the paints and coatings sector have begun to increase the use of clean technologies and environmentally-friendly products. Due to legal requirements and legislation introduced by the European Union regarding hazardous chemicals and substances, restrictions on the use of volatile organic solvents employed in paints and varnish formulations have come into focus. For this reason, in recent years there has been a shift toward UV technology, which enables faster and more efficient production while also being environmentally friendly. This technology, which has long been used in Europe for wood protection systems, represents a developing market for our country. With the widespread adoption of products that cure and dry in seconds under UV radiation, acrylate oligomers, one of the main raw materials used in the production of these products, have gained importance. Only a limited number of companies worldwide produce and market acrylate oligomers commercially. Acrylate oligomers, one of the main components of coating systems that can be cured with UV radiation, directly affect the costs of UV products.1-3 Building on the knowledge and experience of Kayalar Kimya in alkyd resins, one of its main areas of activity, the aim has been to develop new binders (alkyd resins) that can be cured with UV radiation. Alkyd resins are polymers obtained as a result of the polyesterification reaction of polyols with polyfunctional acids in the presence of oils and/or fatty acids. Depending on the type of oil and/or fatty acids in their structure, alkyd resins with widely differing properties are synthesized, and they find applications in many sectors ranging from plasticizers to adhesives, inks, and coating systems. For the paints sector, alkyd resins still carry great importance and the use of alkyd resins based on highly unsaturated fatty acids is preferred. However, in some cases alkyd resins do not exhibit all the desired properties on the final product in coating systems. By combining different polymers, it is possible to obtain polymers with different performances and properties. This approach yields successful results in the production of paints suitable for various purposes and are defined as modified alkyds.4 UV-curable alkyd resin synthesis studies have been carried out through acrylation of alkyd resins with acrylic monomers. Depending on the type of alkyd resin and acrylic monomer used, the final product properties vary. In the step of modifying alkyd resin with acrylic resin, the Diels-Alder addition reaction mechanism is utilized. In the Diels-Alder reaction, the reaction of a conjugated diene with an unsaturated compound called a dienophile results in the formation of a six-membered ring. In UV-curable alkyd resin synthesis, during the Diels-Alder addition reaction stage, the alkyd resin serves as the diene group while the acrylic monomer is used as the dienophile. Therefore, the oil and/or fatty acids in the alkyd resin structure must contain conjugated double bonds. Tung oil, which contains approximately 80% eleostearic acid in its structure, is one of the oils with the highest proportion of conjugated double bonds. Therefore, attention was paid to ensuring that the alkyd resin to be synthesized would be tung oil-based.

UV-curable alkyd resin synthesis reaction takes place in 3 main steps:

I. Monoglyceride formation, II. Condensation reaction, III. Acrylation reaction via Diels-Alder addition reaction mechanism. The reaction mechanisms are presented sequentially in Figure 1 and Figure 2.5-6

Figure 1. Reactions occurring during tung oil-based alkyd resin synthesis Turkcoat

   

Figure 2. Reactions occurring during the synthesis of tung oil-based UV-curable alkyd resin.

  After the resin synthesis steps are completed, 1H-NMR analysis is performed to verify whether the Diels-Alder addition reaction has occurred. Subsequently, FTIR and GPC analyses of the resin are performed, and in accordance with the results obtained, UV paint and varnish formulations containing the resin are prepared and UV curing properties are examined. The test results obtained demonstrated that UV-curable type alkyd resin synthesis was successfully synthesized as a result of the modification of alkyd resins. This will enable Kayalar Kimya to diversify the product range and performance in UV coating systems, one of its important production lines. Çağrı Ağın Senior Chemical Engineer Kayalar Kimya Research and Development Center References [1] R. Bongiovanni, F. Montefusco, A. Priola, N. Macchioni, S. Lazzeri, L. Sozzi, B. Ameduri, Prog. Org. Coat. 45 (2002) 359–363. [2] C. Deckera, F. Massona, R. Schwalm, Polym. Degrad. Stabil. 83 (2004) 309– 320. [3] R. Mehnert, A. Pincus, I. Janorsky, R. Stowe, A. Berejka, UV & EB Curing Technology & Equipment, John Wiley and Sons Inc., New York, 1998. [4] M.Y. Cheong, T.L. Ooi, S. Ahmad, W.Md.Z.W. Yunus, D. Kuang, J. Appl. Polym. Sci. 111 (2009) 2353–2361. [5] K. Zou, M.D. Soucek, Macromol. Chem. Phys. 205 (2004) 2032–2039. [6] D.H. Parker, Principles of Surface Coating Technology, Interscience Publisher, New York, 1965.