Study On The Synthesis And Stability Mechanism Of Internal Crosslinking Polyurethane-Epoxy Hybrid Emulsion With Core-shell Structure

Waterborne polyurethanes(WPU) are replacing conventional solvent-borne polyurethanes as the tendency and emphasis of paint industry. Presently, the main problems existing in WPU in our country are the relatively poor water resistance, solvent resistance, etc. These problems have restricted the use of WPU. Resins with high molecular weight are good for the film properties, but is disadvantageous for the dispersion stability. It is a conflict. Crosslinking modification is one of the most effective measures to improve the water resistance and mechanical properties of WPU, and has important academic and practical significance.In this paper, a kind of internal crosslinking polyurethane-epoxy hybrid emulsion with core-shell structure has been prepared. Firstly, the prepolymer was synthesized; secondly, it was modified by epoxy resin and blocked; thirdly, the prepolymer was emulsified in water; and the crosslinking reaction occurred in the emulsion particles lastly. The blocked -NCO radicals locate in the inside of the emulsion particles because of its hydrophobicity, so the crosslinking reactions occur in the particles mostly. In this way, the crosslinking density of the resin increases and the dispersion stability remains uninfluenced. The emulsion can cures at room-temperature without solidified agent or heat. Anticorrosive coatings product has been prepared with home-made polyurethane-epoxy hybrid emulsion. The results show that the anticorrosive paint made in this paper has alike good properties of solvent-borne polyurethane products. It has 4H pencil hardness, 1 grade flexibility, 50cm impulsion resistance, surface drying in 1.5h, film drying in 48h, 1 grade adhesive power, <10% water absorption, >30d water resistance, >21d salt water resistance and salt spray test data >600h.The influence of adding mode of epoxy resin on the polyurethane-epoxy hybrid emulsion has been studied. The sample prepared with grafting copolymerization method is less stable than the sample prepared with mixing modification method. The sample prepared with grafting copolymerization method has better solvent and water resistance, higher tensile strength and lower break elongation. The type and dosage of epoxy resin also influence the emulsion and film properties. In grafting copolymerization, with the epoxy equivalence of epoxy resin increases, the storage stability drops. The film acquires higher hardness degree and tensile strength, lower break elongation and better water resistance at the same time. The best content is 7-10%. In mixing modification, the type of epoxy resin has little effect. Modulus and water resistance increase with epoxy resin content, which can attain 20%.The chain extension reaction of the resin with amine has been studied carefully. The kind of amine chain extender impacts the stability of emulsion notably. The emulsion prepared...