Ambient crosslinking latex binders: Effects of alkali-soluble resin dosage on ethanol resistance, adhesion and crosslinking reaction

The performance of polyacrylate latexes synthesized using alkali-soluble resin (ASR) is generally superior to that of traditional latexes synthesized using small molecule emulsifiers. Herein, self-crosslinking polyacrylate latexes, which can be used as binders in waterborne inks, were synthesized using alkali-soluble resin (ASR) as the surfactant and diacetone acrylamide (DAAM) and adipic acid dihydrazide (ADH) as crosslinking systems. Transmission electron microscopy (TEM) and dynamic mechanical analysis (DMA) results confirmed that latex particles have core-shell structures. Effects of ASR dosage on the morphology of latex particles, shell thickness and size were investigated. Effects of ASR dosage on the ethanol resistance, crosslink density, activation energy for viscous flow, and adhesion of the latex were also examined. As ASR dosage increases, the shell thickness and size of the self-crosslinking polyacrylate latex particles increase, indicating that the mechanism of action of ASR is quite different from the micelle theory using emulsifiers. The increased ASR content improves ethanol resistance of latexes and significantly decreases the crosslink density and degree of crosslinking of latex films. When ASR content increases, the activation energy first decreases then increases, whereas the non-Newtonian index gradually increases. The estimated work of adhesion between latexes and BOPP films was calculated using Young-Dupré equation; in addition, the adhesion of corresponding inks on BOPP films was also measured directly. Both values increase with increasing ASR content. Our findings are essential in understanding the structure-property relationships that is crucial to the synthesis and application of latexes utilizing ASR as surfactants.