Preparation And Application Of UV Light-Cured Modified Polyurethane Acrylate Waterborne Coatings

UV curing technology is an environmentally friendly curing technology with low energy consumption and fast curing speed.Epoxy acrylate,polyester acrylate and polyurethane acrylate are common oligomers in UV curing coatings.Waterborne polyurethane acrylate（WPUA）meets the requirements of environmental protection and has the excellent properties of both polyurethane and acrylate,so it has become the focus of current scholars.Its advantages are mainly shown in its strong toughness,but its hardness needs to be improved,and it is easy to produce oxygen inhibition,uneven cross-linking and other major defects in the curing process of UV,so this paper aims to prepare UV curing waterborne coatings with high hardness,high light transmittance and excellent curing properties by modifying WPUA,and explore its application properties.In view of this,this paper uses epoxy resin to modify the emulsion properties,mechanical properties and hardness of the polymer.Secondly,thiol click chemistry is introduced in the preparation process,thiol-isocyanate and thiol-ene reaction are combined to reduce the oxygen inhibition in UV curing.The characteristic functional groups were determined by Fourier transform infrared spectroscopy（FTIR）and Raman spectroscopy（Raman）.The optimum contents of trimethylol propane tris（3-mercaptopropionate）（TMPMP）and pentaerythritol tetraacrylate（PETTA）were discussed from the aspects of emulsion stability,hydrogen bonding degree,UV-curing properties,thermal stability and mechanical properties.Finally,organic-inorganic nanocomposites were prepared by blending modified silica to further improve its hardness and thermal stability and expand its application range.The results are as follows:（1）In this study,bisphenol An epoxy resin（E-51）was selected to modify WPUA.When the dosage of E-51 was 4wt.%of the total solid content,the mechanical properties were the best,the tensile strength increased by 68.78%,and the elongation at break still reached 212.55%.The hardness also increased significantly,the pencil hardness increased from 2B to H,and the Shaw hardness D value increased from 34 to 54.（2）The UV-curable waterborne thio-polyurethane acrylate coating was prepared by thiol click chemistry,and its characteristic functional groups were determined by Fourier transform infrared spectroscopy and Raman spectroscopy.Through the study of the UV-curing properties of the cured film,it is found that when the content of TMPMP reaches 16wt.%and the content of PETTA is28wt.%,the thioether bond formed in the polymer main chain has good effect of anti-oxygen inhibition,the UV curing time is shortened,and the double bond conversion rate can reach 100%,and the light curing efficiency is improved.In the exploration of TMPMP,it was found that when its content reached 16wt.%,the formed intermediate had the highest degree of hydrogen bonding and the best mechanical properties.Finally,the pencil hardness of the cured film reached 3H and the Shaw hardness D value reached 62,indicating that the improvement of UV-curing efficiency is beneficial to improve the hardness of the material.（3）The nano-silica（Si O₂）was modified by silane coupling agent KH570.When adding KH570silane coupling agent of 10%solution volume,the dispersion of nano-particles was the best,and the average particle size of the dispersion was 50.75 nm.A UV curable waterborne polyurethane hybrid emulsion with stable properties was obtained by adding KH570-Si O₂before the resin emulsification.The SEM analysis showed that when the doping amount of KH570-Si O₂ reached 3 wt.%,the compatibility between inorganic phase and polymer phase was better.Coating on PET substrate,by testing the hardness of the film,found that the hardness of the pencil reached 4H,Shore hardness D reached 68,the overall rigidity is strong,the mechanical strength is good;the initial decomposition temperature reached 297.61℃,indicating that the thermal stability has been greatly improved;secondly,the film has a good light transmittance,its light transmittance is 94.14%.In summary,a UV curing waterborne modified polyurethane acrylate with high hardness and high light transmittance was prepared.