Study On Synthesis Of Polyurethane-Acrylate Core-Shell Emulsion For HIPS Plastic Coatings

Emulsions used for HIPS plastic coatings mainly refer to Polyacrylate (PA) Emulsion and Polyurethane (PU) Emulsion. While the PA emulsion and its film possess excellent weatherproof property and can provide high rigidity and considerable water & alcohol resistance, they show an unsatisfactory film-forming ability. In contrary, PU emulsion owns nice film-forming ability and the film is of optimum elasticity, glossiness, wearability and impact-resistance at low temperature, but it suffers from poor performance in hardness, water and alcohol resistance. On this basis, Polyurethane-Acrylate(PUA) hybrid emulsion has well integrated the advantages of PU and PA emulsion, and avoided their shortcomings. As the basic material of HIPS plastic coating, PUA emulsion still needs improvement on its adhesion and hardness. Therefore, in this paper, a kind of core-shell structured cross-linking PUA hybrid emulsion is studied, with“Similar structure, Close Polarity”principle, according to HIPS plastic surface-adhesion theory.Core-Shell Polyurethane-Acrylate (PUA) hybrid emulsion (with PA as the core and the PUA as shell part) was composed through adding a double functional groupβ-hydroxypropyl methacrylate, adopting the solution polymerization and emulsion polymerization in situ to ingraft the acrylate monomers to PU (including dimethylol propionic acid DMPA): Acrylic acid (AA), Butyl Acrylate (BA) and Styrene (St), a crosslinking. Firstly, isophorone diisocyanate (IPDI), polyether glycol (N210), dimethytolpropionic acid (DMPA) were used as main materials to prepare PU prepolymer, in which crosslinking agent HEMA was joined, thus PU prepolymer with end vinyl was obtained. Then by adding vinyl monomers AA, BA and St in droppings for graft copolymerization, PUA prepolymer in shell was prepared, followed by using water dispersion and ethylenediamine chain extension, together with vinyl monomers to form intermediate dispersions. At last, through core monomers radical emulsion polymerization, Polyurethane-Acrylate (PUA) hybrid emulsion was eventually synthesized.The effect to the performance of emulsion and film caused by each technological and proportioning factor in the three stages of this core-shell structure synthesis process has been analyzed. These factors include those in shell PUA prepolymer preparation: NCO/OH total molar ratio, hydrophilic group (-COOH) content, HEMA amount and its reaction temperature and time, dibutyl tin dilaurate (DBT) amount, inhibitor types, adding amount , methods and rate of vinyl monomer, adding amount of initiator; those in PUA/A intermediate dispersion preparation: neutralization degree, ethylenediamine content, dispersion process; those in monomer emulsion polymerization: types and content of core monomers etc.The emulsion synthesis process and product structural performance have been examined, characterized and analyzed, and the results show that the emulsion and film present favorable adhesion force and hardness. Infrared spectrum tracking analysis and transmission electron microscopy analysis also have proved the core-shell structure’s generation. Through laser particle size analyzer and comprehensive thermal analysis, we got a set of PUA core-shell emulsion with PUA as the shell and PA as the core, which was reasonable processed, of good proportion and distributed in narrow particle size (100nm particle size on average).