Polymer-metal adhesion promoters in UV curable coatings

Different types of acrylic monomers containing functional groups able to improve adhesion on steel substrates were prepared and introduced in a typical UV curable epoxy-acrylic system based on a bisphenol-A-diglycidyl-ether diacrylate with a reactive diluent mixture. The adhesion properties of the films obtained after UV curing were measured and related to the presence of different types of functional groups in the resin. Monomers like esters of phosphoric acid with hydroxy-alkyl-acrylates, adducts of hydroxy-alkyl-acrylates on 2-methyl-2,5-dioxo-1-oxa-2-phospholane, acrylic and methacrylic acids and their esters containing free carboxylic groups were taken into account. The results obtained show that the adhesion properties depend on the type of functional group present and on the structure of the monomer. Humidity and solvent resistance tests were performed on film containing the additives homogeneously mixed or added as a thin layer on the substrate surface. The results obtained in the different conditions are reported and discussed.