| Films from acrylate emulsion have excellent physical properties such as light stability,weather resistance and adhesion on various substrates.Great improvement in digital printing area has been achieved in that latex acts as the binder of aqueous ink-jet inks,and latex particles are deposited on substrate surface during ink-jet printing.The latex films on various substrates entrap and protect colorants in latex ink,which improved durability of image.However,their water-based acrylate emulsion polymers are of poor hydrophobicity,which should be modified to water resistance.Acrylate emulsion polymers with core-shell structures were synthesized via semi-continuous seed emulsion polymerization in this research.The hydrophobicity of latex cast film was modified by particle structure and fluoroacrylate.At first,Ethyl acrylate(EA)was utilized to prepare the core,and methyl methacrylate(MMA),butyl acrylate(BA),and methacrylate acid(MAA)were employed to constitute the shell,the effects of reaction temperature,emulsifier,particle structure,and amount of MAA on polymer properties were investigated in detail.The optional synthesis conditions of the core-shell latex were reaction temperature 80?,amounts of emulsifiers,initiator,and MAA were 4 wt%,0.6 wt%,and 3 wt%,respectively.So the yielded latex particles had the soft core and hard shell.The particle construction and sizes were observed by transmission electron microscopy(TEM)and light scattering(LS).The average particle size was less than 100 nm and the core-shell structure was clear.The long term stability of latex was perfect.The latex exhibited viscosity plateau of Newtonian fluid behaviors and viscous behavior dominated in the latex.Then the hexafluorobutyl methacrylate(HFBM)wan introduced into the shell by copolymerization,which was used to improve of cast films the hydrophobic.The core-shell structure of the latex particles were confirmed by TEM and LS.The zeta potential showed that the latex particles had high thermodynamic stability.Fluorinated side chains could migrate to the interface during film formation,which decreased substantially the surface energy of the cast films.The hydrophobicity of the emulsion film was improved by introduction of HFBM and increased with content of HFBM.Because most of fluorine had migrated to the interface between the cast film and air,and little migrated to the other opposite side.So the hydrophobicity was derived from the fluorine enrichment phenomena on the top side of the cast films.However,the fluorine concentration on cast film surface gradually approached to saturation with the increase of the amount of HFBM,and the hydrophobicity of film tended to its equilibrium.The core-shell fluoroacrylate latex was utilized in aqueous ink-jet ink as the binder.It was found that there were slight difference between latex and latex ink on rheological properties.Finally polymer latex particles were synthesized with multilayer core-shell structure via emulsion polymerization to enhance hydrophobicity further.The latex particles had cross-linked core coated by a two layers of shells.The inner shell was PEA and the outermost layer of shell was copolymer from MAA,BA,MAA and HFBM.Ethylene glycol dimethacrylate(EGDMA)was used as the cross-linking agent in the synthesis of the core,which prevented the chain migration during film formation.Hence,the core kept sphere while the shells formed film.The roughness of the film surface was improved compared with film surface from common core-shell latex.The topography of film was similar with lotus leaf surface.Moreover,the outermost shell layer was modified with fluoroacrylate to reduce surface energy of the latex films.So the hydrophobicity of emulsion film was achieved for the synergistic interaction of the cross-linked core and fluorine that higher than fluorine-containing acrylate without cross-linked core.However,the mechanical properties of the films declined slightly due to stress concentration from the rigid cross-linked cores embedded into the continuous films from the shell layers. |
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