Study On Localized Crosslinking Core/Shell Polyacrylate Emulsion Adhesive

With the features of rich source and the higher cohesive force to some laminated films, the acrylate emulsion adhesives not only can satisfy the demand of high adhesive strength to those films, but also possess good heat resistance, excellent weather-resistance and better color maintaince and so on. In recent years, the acrylate emulsion adhesives are widely applicated in the packing laminated films. Whereas, several problems of the ordinary polyacrylate emulsion adhesives remain to be solved at present:Firstly, its cohesive energy is low and adhesion to the low surface energy films such as polypropylene is weak; Secondly, the property of water resisting and adhesion decreases because the small emulsifier transfers easily; Thirdly, the food will be contaminated by the small emulsifier, and it cannot well meet the need of packing material cleaness for edible.In order to improve the capability of polyacrylate emulsion adhesives and enlarge the range of applcation, espacially to the low surface energy films, acrylic acid ester monomer with long chain of alkyl was introduced which can improve the wetting quality and the adhesion property of the emulsion on matrix with low surface energy. The heat-resistance and cohesion intensity of adhesive is improved by adding functional monomer which generate appropriate crosslinking reaction. Appropriate reactive cationoid emulsifier is utilized to participate in the polymerization of monomers. This reactive emulsifier not only has the function of conventional emulsifier, but also will turn to be a part of the adhesive macromolecules, so it can avoid the emulsifier dividing from the polymer particles or transfering in the latex film and the property of glue film is improved.Based on the above idea, localized crosslinking and core/shell polyacrylate emulsion adhesive was prepared by seed emulsion polymerization using n-butyl acrylate(BA), methyl methacrylate(MMA),2-ethylhexyl acrylate(EHA), vinyl acetate(VAc), functional monomer with epoxy group and functional monomer with carboxylic group as main reagents, non-ionic and cationic emulsifier as composite emulsifier in this work. Transmission electron microscope, infrared spectropic analysis, thermal analysis, measuring the peeling strength et al were used to characterize the morphology of latex particles, the chemical structure and heat-resistance, the peeling strength of latex film of adhesive. The effect of the amount emulsifier and initiator, ratio of monomers and core/shell on the property of adhesives were studied. The polyacrylate emulsion that is blended with tackifier resin and species and amount of tackifier resin emulsions was studied. The main conclusions were summarized as follows:(1) The prepared latex particles is core/shell structure which was connected by chemical bonding force, and the localized crosslinking strcture also exist in the particles;(2) The reactive emulsifier which linked to the adhesive macromolecules via covalent bond participated in copolymerization; the ratio of the OP-10 and FY which varied from 0.5:1.0 to 1.5:1.0 had little influence on the the conversion of monomer and gel, solid-content and stability of the emulsion. When the ratio of the OP-10 and FY is 0.5:1.0 and the total amount of emulsifier is 3%, the monomer conversion and solid-content is 95.71%,44.05%, respectively, and the latex is obtained with fine comprehensive performance.(3) When the amount of emulsifier and initiator is 3wt% and 0.25wt% of the monomers, respectively, the amount of functional monomer with epoxy group and functional monomer with carboxylic group both were 6wt%, the ratio of soft/hard monomer in core and shell respectively is both 65:35, the ratio core/shell is 6:4, the comprehension performance of latex is excellent. The 180°peeling strength of PET/LDPE and BOPP/LDPE reached 5.81 N/25mm and 4.68 N/25mm respectively, and they showed mixed fracture mechanism.(4) Importing BF-225 tackifier resin emulsion to the core/shell polyacrylate emulsion adhesives could improve the adhesive ability remarkably; the adhesive ability of polarity-nonpolarity and nonpolarity-nonpolarity plastic films is quite well: the 180°peeling strength of PET/BOPA, PET/BOPP, PET/LDPE got the increase of the 1.07 times,1.34 times,1.12 times respectively of pure polyacrylate emulsion adhesives, showed mixed fracture mechanism. (5) The morphology and chemical structure are effected by drying temperature. As the drying temperature increased, the 180°peeling strength increased. When the amount of emulsion is 5 g/m2 and the drying temperature is 80℃, the 180°peeling strength of PET/BOPA, PET/BOPP and PET/LDPE reached to 4.40 N/25mm,3.18 N/25mm and 5.66 N/25mm, respectively, and they showed mixed fracture mechanlsm.(6) The peeling strength was influenced by the gelatinized quantity per unit area: the peeling strength increased as the gelatinized quantity increased, but the strength is nearly unchanged when the gelatinized quantity reached a certain degree.