THERMOOXIDATIVE BEHAVIOR OF WATER-BORNE INK BINDERS IN THE PRESENCE OF MONOVALENT METAL-ION

As a part of continuing studies on the change in solubility characteri stics of water-borne flexo ink binders, the thermal behaviour of unneu tralized and partially or completely neutralized acrylic copolymer and styrene-maleic anhydride copolymer has been examined relative to a wa ter-based ink binder having no carboxylic acid or anhydride group. Fil ms of ink binder and the inks prepared with these binders were aged at 105 degrees C before or after adding sodium hydroxide. Solubility beh aviour as determined by a swelling study revealed that water solubilit y of acrylic binder decreased significantly after acid group neutraliz ation and ageing. Styrene-maleic anhydride copolymer also showed simil ar behaviour but the effect on solubility was less significant. Thermo gravimetric and FTIR analyses results suggested a crosslinking reactio n by acyclic anhydride formation due to alkali catalysed heating of ac rylic and maleic binders. By contrast, the presence of univalent metal ion in a sulfopolyester-based flexo ink binder did not show any cross linking effect and the water solubility of this binder remained practi cally unchanged.