The Preparation Of Polyurethane Electrophoretic Paint Embedded By Chemical Cross-linking

Two component water-borne polyurethane coating is a kind of using water as the medium of the new environmental friendly coatings, and the low volatile organic compounds（VOC） content of the aqueous coating and the high performance of the two-component solvent coatings are combined by it. Two component waterborne polyurethane coating has been become a hot research because of its excellent corrosion resistance, solvent resistance, weather resistance and other properties. A hydrophilic cross-linking agent was studied in this paper,which was embeded in the electrophoresis polyurethane resin. The electrophoretic resin was got by high speed stirring and the emulsification. The film would be fully cross-linked, when the baking temperature reached a certain value, so its properties and appearance would be greatly improved.The following three parts was included in the the specific research.In the first part, the preparation and properties of cross-linking cured polyurethane electrophoretic resin was explored in detail. The preparation of hydrophilic curing agent was characterized by FT-IR and effects of the dosage of trimethylolpropane（TMP） and E-12 synthesis of epoxy resin and ethylene glycol butyl ether（BCS）,emulsion solids, as well as neutralization degree on the appearance and properties of the film were investigated respectively. It turned out that the the isocyanate group had been completely closed and it was found that the desirable properties and appearance for the film could be obtained under the condition 0.49 % of TMP, 2.33 % of E-12 synthesis of epoxy resin, 15 % of emulsion solids and 100 % neultralization degree,without BCS.In the second part, the preparation of two-component thermosetting coating and optimization of electrophoresis process was explored in detail. An cationicpolyurethane（PU） resin was compounded with oligomer polyol and isophorone diisocyanate（IPDI） as raw materials, then TMP as a modifier. The deblock process of waterborne polyurethane cross-linking agent was detected by in-situ fourier transform infrared（FT-IR）. Effects of the dosage of TMP, the molar ratio of resin to cross-linking agent, deblock temperature of water-borne polyurethane cross-linking agent, process parameters on the appearance and properties of the film were investigated respectively.It was found that the desirable property and appearance for the film could be obtained under the condition of the wt % of TMP was about 0.50 %, 1:1.5 for the functional groups molar ratio of resin to cross-linking agent, deblock temperature of waterborne polyurethane cross-linking agen was 100 ℃, baking temperature and time were80 ℃×30 min, 140 ℃×1 h, 60 V for the electrophoresis voltage, 50 s for the electrophoresis time.In the third part, the preparation and properties of waterborne hybrid polyurethane resins by polymer modified montmorillonite was explored in detail. The sodium montmorillonite（MMT） was modified activated and hydroxyl-modified montmorillonite（HPMMT） was prepared. The novel active organic montmorillonite（OMMT） was used as the reinforcing body of polyurethane matrix, and the cationic polyurethane hybrid resins were prepared, then it was mixed with the cross-linking agent by high speed stirring. The nano-hybrid electrophoretic resin was got by the emulsification. The polyurethane films were prepared by the electrophoresis process,and the chemical corrosion resistance of the polyurethane electrophoretic resins had been improved much. Small-angle X-ray diffraction（XRD）, FT-IR and thermogravimetry（TG） were used to study the structures and properties of the novel organic montmorillonite and the morphology of organic montmorillonite in electrophoretic emulsion was characterized by transmission electron microscope（TEM）. The effect of the content of organic montmorillonite and ratio of n₍（TMP-OH）_/n_{（PTMG-OH）} on the properties and appearance of the films had been studied. The results showed that the inter lamellar space of novel OMMT was enlarged from 1.309 nm to2.154 nm. After modified by hydroxyl-terminated cationic polyurethane,the properties of electrophor- esis film were improved much when the wt % of OMMT was about0.3 % and the ratio of n（TMP-OH） /n（PTMG-OH） was about 3.