For several decades now, radiation curing technology has been successfully used in numerous wood and paper coating applications as well as in printing inks. The radiation curing formulations are 100 % solid, environmentally friendly compositions which produce no volatiles and require less energy and space for coating than conventional solvent based technologies. These advantages also make radiation curing formulations interesting for metal coating markets. In the case of the most demanding metal applications where excellent adhesion, flexibility and corrosion resistance are required, some performances improvements are needed. Typical radiation curable formulations are based on (meth)acrylated oligomers and reactive diluents which when cured form a highly cross-linked network having good surface properties such as chemical resistance, scratch resistance, abrasion resistance and surface hardness. A high cross-link density is also associated with limited flexibility and a certain level of film shrinkage; this reduces adhesion to non porous metallic substrates. Recently new tailor made (meth)acrylated oligomers have been developed which have significantly improved performance, hence broadening the uses of the radiation curing technology in metal coating applications.

In this paper, three fairly simple clear-coat systems are studied.

They are characterized and ranked in terms of conversion, molecular characteristics such as molecular weight and double bond content, shrinkage, swelling and visco-elastic characteristics measured on 100 µm free-standing films.

Their barrier properties on hot dip galvanized steel at thicknesses between 20 and 100 µm are studied by electrochemical impedance spectroscopy.

Finally, practical performance tests (solvent resistance, Erichsen, T-bend, reverse impact, salt-spray tests) are performed on the three systems on coatings of 20 and 100 µm applied on hot-dip galvanised steel. These are the tests which are used to set up coating product profiles in the metal industry. The results will be discussed within the framework of the preceding observations.

^a Cytec Surface Specialties, Anderlechtstraat 33, B-1602 Drogenbos, Belgium
^b Faculté Polytechnique Mons, Rue de l’Epargne, 56, B-7000 Mons, Belgium
^c Materia Nova, Rue de l’Epargne, 56, B-7000 Mons, Belgium