WATER-BASED RADIATION-CURABLE LATEXES

Film-forming polystyrene/poly(n-butyl acrylate-co-glycidyl methacrylat e) [PS/P(BA-co-GMA)] core-shell latex particles were prepared via a tw o-stage emulsion polymerization procedure using a polystyrene latex se ed. Delayed addition of GMA was used in order to locate functional epo xy groups close to the particle surfaces. It was found that a temperat ure of 25 degrees C at the second-stage polymerization, in combination with a redox initiator system, was essential for the formation of a u niform shell of BA-GMA copolymer around the PS core. The latex particl e morphology was investigated by transmission electron microscopy (TEM ). Reactive double bonds were introduced into the particle shells in o rder to produce a film-forming latex system that could be cured by ult raviolet (UV)-radiation without any need to use reactive multifunction al monomers or oligomers as crosslinkers. The surface-bound epoxy grou ps were used as grafting sites for amine or carboxyl functional unsatu rated monomers, respectively. The grafting was demonstrated by Fourier transform infrared (FTIR) spectroscopy. Films prepared from modified and unmodified latexes were exposed to UV radiation in the presence of a photoinitiator. Crosslinking was tested by thermal mechanical analy sis (TMA) and by determination of swelling and gel content of exposed films. It was demonstrated that films from the modified latexes after irradiation had significantly higher stiffness and gel content and sho wed lower swelling than unmodified ones. (C) 1996 John Wiley & Sons, I nc.