Synthesis And Application Of Hyperbranched Polyurethane In UV-curable Coatings

UV-Curable coating is one of the research hotspots in environment-friendly coatings for its distinguish advantages,such as environmental friendly,fast curing and low temperature operation et al.Polyurethane acrylates(PUA)is one of the widely used oligomer in the field of UV-Curable coatings due to its excellent properties.However,the low tensile strength and scratch hardness limit its engineering applications in some fields.So,enhancing these properties of PUA is priority.Hyperbranched polymers have unique three-dimensional molecular structures,advantages of low viscosity,good compatibility and high reactivity,as well as a large number of end-group functionality.Thus,this kind of molecules can be good candidates of crosslinker,forming the linear polymers into three-dimensional network,to meet the performance requirement of UV-Curable coatings by enhancing the mechanical properties,hardness and abrasion resistance of PUA curing resin.In this work,a novel hyperbranched polyurethane acrylate(HBPUA)was synthesized as crosslinker of UV curing system,and a series of high-performance UV-curable coatings were prepared by incorporating different amounts of HBPUA.The main work in this thesis as follows:(1)The structure characteristics,properties,synthetic methods and applications of hyperbranched polymer and polyurethane acrylate were introduced briefly in this paper.A novel hyperbranched polyurethane acrylate and a linear polyurethane acrylate were also designed in this paper.Two-step method was used to synthesis PUA and HBPUA and "di-n-Butylamine-Toluene" method was used to monitor the reactions.The preferred temperature and time of the first reaction to synthesis PUA and HBPUA was 75 ?,75 ?,1.5 h,2 h,respectively.The preferred temperature and time of the second reaction to synthesis PUA and HBPUA was 55 ?,55 ?,8 h,6 h,respectively.The structure of PUA and HBPUA was characterized by Fourier transform infrared spectroscopy(FTIR)and hydrogen nuclear magnetic resonance(1H NMR).Results indicated that the isocyanate groups(-NCO)disappeared completely during the reaction,in addition,PUA and HBPUA were synthesized successfully.(2)Irgacure 184 and TMPTA-SiO2 were incorporated into PUA,with different amounts of HBPUA as crosslinker,and then a series of UV curing system were obtained after mixing them to a homogenous state.Viscosity test results show that the viscosity of the UV curing system increased constantly with the increased of HBPUA content,and it could reach 13 Pa s by adding 20 wt%HBPUA.Rheological properties test results demonstrated that the UV curing system had strong viscosity at a lower shear rate.But when the shear rate was increased,all samples perform typically pseudoplastic and the shear-thinning characteristics,which was conducive to the storing and conduction of coatings.Curing kinetics test result indicated that the degree of double bond conversion reached the highest value when 10 wt%HBPUA was added,besides,the gel content was also reached to the highest value of 99.7%.(3)A series of UV cured films with different amounts of HBPUA were prepared by UV radiation curing.Mechanical properties test results showed that the tensile strength increased constantly and the elongation at break declined constantly with increasing HBPUA contents.However,the cured film with around 10 wt%HBPUA exhibited the better mechanical property.The DMA results show that HBPUA had good compatibility with the base resin PUA.When 10 wt.wt%HBPUA was added,Tg of the cured film reached a maximum of 50 ? and E' of the cured film reached maximum,too.(4)A series of UV cured coatings with different amounts of HBPUA were prepared on PC and PVC substrates.Surface properties results indicated that all prepared coatings exhibited good adhesion(level 0)on PC and PVC sheets.Pencil hardness of the cured coating could reach 9 H and the abrasion resistance achieved the best performance when the content of HBPUA was up to 10 wt%.Thermal properties results showed that all samples displayed a similar process of thermal decomposition,appearing two main weight loss regions with peak maxima around 330 ? of hard segment decomposition and 420 ? of soft segment decomposition,respectively.Accordingly,the thermal stability was enhanced with the addition of HBPUA,but not by much.Optical properties results illustrated that the existence of HBPUA only slightly effected the transmittance of the cured coatings,and all of them presented high transparency(above 90%)throughout the visible light range.UV-Curable coatings prepared in this paper with the advantage of favorable mechanical properties,high hardness,good abrasion resistance,excellent optical properties and environment-friendly et al,could be used in the field of automotive coatings and 3C electronics et al,which has a widely range of applications background and market demand.