Improving the performance of polyacrylate latex binders for water-based inks through the application of reactive emulsifiers and nanosized zinc oxide

The poor redissolution and low ethanol resistance stability of room temperature self-cross-linking polyacrylate latexes (RTSPLs) made from conventional emulsifiers are the main obstacles for their industrial application in water-based inks. To address these issues, in this study, anionic SR-10 (allyloxy polyoxyethylene ammonium sulfate) /nonionic ER-10 (allyloxy fatty alcohol polyoxyethylene ether) dual-reactive composite emulsifier is developed to replace the conventional 2A1 (sodium dodecyl diphenyl ether disulfonate) /TX-30 (alkyl phenol polyoxyethylene ether) non-reactive composite emulsifier for the synthesis of polyacrylate latexes, and a certain mass of nanosized zinc oxide (ZnO) was added into as-prepared latexes as an ionic cross-linking agent to partially replace the cross-linking monomer of diacetone acrylamide (DAAM). Properties of the latexes and the latex films, with emphasis on redissolution, stability against ethanol, and adhesion on biaxially oriented polypropylene (BOPP) and polyethylene (PE) substrates, were evaluated to study the effect of the reactive emulsifiers and the nanosized ZnO. The application of the reactive composite emulsifier eliminates the disadvantages associated with the desorption from the latex particles and migration during film formation of the non-reactive emulsifier, thus improving the ethanol resistance stability of latexes and adhesion of their inks on BOPP substrate. The introduction of a certain amount of nanosized ZnO to replace DAAM in equimass amounts improves the redissolution but reduces the cross-linking density and water resistance of the latex film. Surprisingly, the addition of nanosized ZnO substantially improves the ethanol stability of latexes. When ZnO replaces DAAM, accounting for approximately 1 wt% of the total monomers, not only the prepared latex exhibits excellent alcohol dilution stability, but also the latex film has a relatively high cross-linking density, good redissolution, and good comprehensive properties. These findings provide an effective, yet simple way to balance the redissolution and high cross-linking degree of latex films while ensuring that the latexes have good ethanol resistance stability.