TUNING THE MECHANICAL-PROPERTIES OF UV COATINGS TOWARDS HARD AND FLEXIBLE SYSTEMS

The standard resins of radiation-curable coatings provide either hard or flexible coatings dependent on the type of chemistry used. Whereas aromatic epoxide acrylates usually give hard and brittle coatings, ure thane acrylates are known for their flexibility, Since the radiation c urable systems should not contain solvents, the desired low viscosity for the specific application is adjusted with reactive monomers. This normally prevents the use of flexible high-molecular-weight polymers. On the other hand, the viscosity of dispersions is determined by the s olid content only and not by the molecular weight of the polymers used . Thus, waterbased W-curable coatings are one strategy out of this dil emma in order to combine the flexibility of higher-molecular-weight po lymers with the hardness of highly crosslinked acrylates. The mechanic al data of conventional and waterbased UV coatings are discussed in de pendency on glass transition temperature and elastically effective cha in length between crosslinks. (C) 1997 Elsevier Science S.A.