Research On Modification Of Fast Ultraviolet-Curing Polyurethane Acrylate

Ultraviolet(UV)-curable coatings are energy-saving and environmentally friendly,and have great application value in the future market.Polyurethane acrylate(PUA)coating has excellent comprehensive performance and increasing the curing rate is a research hotspot in recent years.The curing time of PUA has been shortened to a few seconds by modifying the structure of the oligomer or synthesizing new oligomers.In the fields of papermaking,architectural coatings,etc.,maintaining a high UV-curing rate and imparting flame-retarding properties to PUA materials have important practical significance.However,the research on flame-retarding and fast curing PUA system under the condition of low intensity of UV power is relatively rare.So we synthesized a flameretarding PUA oligomer for flame retardant modification.In addition,the curing of the light-shielding portion is usually incomplete when the UV-curable coatings were used.The thermal treatment after UV irradiation may compensate for such defect.So we have also carried out the modification work of the UV/thermal dual curing PUA system.In the flame-retarding modified part,we synthesized a new phosphorus-containing PUA oligomer(FRPUA)using a phosphenanthrene derivative(2DOPO-DHBP),1,3-propanediol-glycidyl methacrylate monomer and isophorone diisocyanate.Then we mixed FRPUA with HPCP,etc,to prepare the FRPUA-n HPCP(n=0,10,15,20)system.The system were characteristic of improved flame retardant properties when maintaining a fast curing rate.It was found that FRPUA-15/20 HPCP liquid resin(with the thickness of 1 mm)can be cured within 2 s under UV light(400 W).Both 2DOPO-DHBP and HPCP can improve the combustion properties of PUA resin:the limiting oxygen indexes for PUA and FRPUA-20 HPCP cured samples were 19.0% and 23.3%,respectively.2DOPO-DHBP and HPCP exhibited synergistic flame retardant effect in PUA resin: the peak value of heat release rate(PHRR)and the total heat release(THR)of FRPUA-20 HPCP cured samples were 475.2 W/g and 26.4 k J/g respectively,which were significantly lower than the PHRR value(760.4 W/g)and the THR values(29.2 k J/g)of PUA-20 HPCP cured samples.In the UV/thermal dual curing section,we added two different thermal initiators,namely thiol or heat curing agent,to the UV curing PUA system.Then we prepared twodifferent UV/thermal dual curing PUA systems.Both systems exhibited a faster surface drying rate and low volatile organic compounds emissions(less than 1.5 wt.%).At the same time,they all exhibited different modification advantages over UV curing PUA systems(NAS).For the UV/thermal dual curing system with thiol added: a shore hardness value(D)decreased from 78 to about 30;the glass transition temperature was also significantly reduced.For the UV/thermal dual curing system with thermal curing agent added:(1)the dual curing system has excellent acid resistance and alkali resistance while the corresponding performance of the NAS were a little bad;(2)the initial decomposition temperature of NAS system(curing condition was 1 min for UV irradiation)and the dual curing system(curing conditions were curing at 100℃ for 10 min after 1 min of UV irradiation)were 269.4℃ and 318.2℃,respectively.A UV/thermal dual curing system with thiol added can be used when the important point focuses on the soft performance.If the sample is required to have excellent chemical resistance or thermal stability,the UV/thermal dual curing system with a thermal curing agent system added can be considered.