The Effect of Compatibility between Polymer and Reactive Diluent on Properties of UV Cured Films

In the past decades water based UV curing coatings have been developed based on a wide variety of chemical concepts Binders are being used based on a.o. polyurethanes, polyesters, and
polyacrytates Usually the poJymers are modified with ethylenically unsaturated groups, but in a few cases there is no covalent bond between the polymer and the ethylenically unsaturated groups. In general, reactive diluents, in most cases multi functional acrylic monomers, are being used to enhance the film properties after cure. Many different reactive diluents are described, but so far hardly any attention has been given to the interaction between reactive diluent and latex.
One can imagine that the intimacy of mixing between a reactive diluent network on the one hand and a polymer binder on the other will have a major effect on the properties of the cured coating.
Especially in the case where the polymer emulsion comprises particles with a covalent bond between the polymer backbone and the ethylenically unsaturated groups which can participate in UV crosslinking the effect of having a homogeneous or non-homogeneous mixture of polymer and reactive diluent networks will be very significant. This paper aims at answering at least part of the question about the effect of polymer-reactive diluent compatibility on film properties. Based on a model study comprising non-functionalised latexes the effect of miscibility between reactive diluent and the polymer phase on film properties before and after cure will be described. Miscibility of reactive diluent with the polymer particles was determined by comparing the Tg of the polymer with and without reactive diluent. Partitioning of the reactive diluent between polymer particles and the aqueous phase was determined by measuring the change of the
wet stage Tg as a function of type and concentration of reactive diluent.