Study On The Synthesis And Modification Of Waterborne Polyurethane For UV-curable Coating

In recent years, the control of volatile organic compounds （VOC） emission is becomingmore and more strict along with the people environmental protection consciousness. Thetraditional solvent-based coating is gradually replaced by some environmental protectioncoating. These coating become the hot spot of the current research. UV-curable waterbornecoating combines the characteristics of waterborne coating and UV-curable coating with theadvantage of green environmental protection, no pollution, energy saving, fast curing speed,low cost and highproduct quality. And it is rapid development in recent years. UV-curablewaterborne polyurethane coating （WPUA） has been wide researched, reported, and applied.The home-made polyester glycol （PETG）, and polyether glycol （PPG1000）, isophoronediisocyanate （IPDI）,2,2-dimethylol propionic acid （DMPA）,2-Hydroxyethyl methacrylate（HEMA） and pentaerythritol triacrylate （PETA） are used as the materials to synthetize WPUA.Then the modified nano-SiO₂is used to modify WPUA. The properties of WPUA/nano-SiO₂are measured. The conclusions with practical reference value are obtained:1.1,6-adipic acid, phthalic anhydride,1,4-butanediol and triethylene glycol are used forthe preparation of PETG in the first preparation. The effects of many factors such as reactiontime, reaction temperature, catalyst on syntheses and properties of WPUA are studied. TheFourier infrared spectrometer （FTIR） and thermogravimetric analyzer （TGA） are used to testits structure and properties. The PETG, IPDI, DMPA are used to synthesis WPUA by solutionmethod （acetone method）. The structure and properties of WPUA emulsion and coating filmare discussed. The experimental results show that the preparation of PETG is through thetemperature programmed mode without any catalyst. When1,6-adipic acid and phthalicanhydride molar ratio is6.5:1, the particle size of WPUA emulsion is54.6nm, and theemulsion is stability. Tensile strength of the coating film is6.34MPa, and the hardness is2H.2. PETG, PPG1000, IPDI, DMPA, HEMA and PETA are used to prepare WPUA. Theeffects of many factors such as R value, namely, n-NCO/n-OH（witout-OH of HEMAand PETA）,n（HEMA）/n（PETA）on syntheses and properties of WPUA emulsion and coating film are studiedwith the help of FTIR, TGA, universal testing machine and gel permeation chromatograph（GPC）. The research shows that: the stability of emulsion, the mechanical properties, waterresistance and heat resistance of coating film are improved when R value between1.4and1.5.when n（HEMA）/n（PETA）=3:1, the hardness of coating film is2H, the tensile strength is7.01MPa and the elongation at break is394.42%, the decomposition temperature is increased.3. WPUA still exists deficiencies in curing film hardness, mechanical properties, solventresistance and water resistance, etc, so it need to be modified. Preparing of different particlesizes of nano-SiO₂, and determine the better conditions to modify the surface of nano-SiO₂through orthogonal test: KH-570as the modifying agent, its dosage is10%, the modifiedtemperature is60℃, the modified time is7h. To study on preparation of WPUA/nano-SiO₂emulsion and coating film by changing the content of modified nano-SiO₂. The researchshows that: the emulsion is stability, the mechanical properties, water resistance, solventresistance of coating film are improved when the partical size of nano-SiO₂is56nm and its dosage is1.0%.WPUA in this article compatibles with good water resistance of the polyether type ofWPUA and excellent heat resistance, mechanical properties of the polyester type of WPUA.At the same time, by adjusting the proportion of HEMA and PETA regulating the content ofC=C, the mechanical properties and thermal stability properties are obviously better thanWPUA by HEMA only. The water resistance, solvent resistance and hardness of WPUA areimproved by adding modified nano-SiO₂. The application scope of WPUA is expanded. Theresearch provided a certain theoretical basis and experimental evidence for the further studyof WPUA.