Construction of self-crosslinking core-shell acrylic emulsions and their effect on water-based ink
Self-crosslinked core-shell acrylic emulsions were prepared by two-step emulsion polymerization with acrylic acid(AA),butyl acrylate(BA),methyl methacrylate(MMA),hydroxypropyl acrylate and hydroxyethyl methacrylate as monomers,ethylene glycol dimethacrylate(EGDMA)and glycidyl methacrylate(GMA)as cross-linking monomer,and further bonded to synthesize water-based ink.The influencing factors on the water resistance and adhesion of the ink were investigated.The self-crosslinked core-shell acrylic emulsions and their corresponding films were characterized by TEM,FTIR,TG,DSC,optical contact angle measuring instrument and universal test machine,while the effects of GMA mass fraction in shell monomers on emulsion particle size,stability,ink adhesion and water resistance were analyzed.The results indicated that the mass ratio of AA in core-layer to AA in shell-layer(core-shell acrylic acid ratio)showed a significant effect on the adhesion of ink,while the ratio of the mass ratio of MMA to BA in core-layer to the mass ratio of MMA to BA in shell-layer(core-shell softness/hardness ratio)showed a significant effect on the water resistance of ink.The optimal formulation of self-crosslinking core-shell acrylic emulsion was as follows:mass ratio of mixed monomers in core-layer to those in shell-layer(core-to-shell mass ratio)2.00∶3.00,core-to-shell softness ratio 3.00∶0.75,core-to-shell acrylic ratio 0.50∶2.50,and the amount of internal crosslinking monomer EGDMA 0.75 g.When the mass fraction of GMA in the shell-layer monomers was 1.5%,the self-crosslinked core-shell acrylic emulsion exhibited an average particle size of 112.2 nm,polydispersity index of 0.108,maximum thermal decomposition rate at 409℃,the glass transition temperatures of the core-layer and shell-layer of 28.5 and 51.7℃,respectively,optimal dispersion stability,latex film water absorption rate of 34.55%,ink adhesion of 99%,and water resistance of 50 times.