Study On Preparation And Properties Of UV-Curable Polyurethane Acrylate Hardening Coatings

Plastic is an indispensable material in modern society,which has been widely used in the fields related to high-tech products,such as the flexible electronic screens and the shell of electronic products.But the surface hardness of plastic is low and easy to be scratched,so it is necessary to harden the surface of plastics.Polyurethane acrylate(PUA)coating is a commonly used hardening material on plastic surface.In our work,various PUA coatings were prepared,their structures were characterized and the surface properties of the coatings coated on polycarbonate(PC)sheet were studied.(1)A rigid branched core containing six terminal hydroxyl groups,TAC-MTGL,was synthesized by thiol-ene click chemistry and used for the subsequent preparation of branched compounds with multifunctional double-bond.Subsequently,the isocyanate-containing intermediate product was obtained via the reaction of IPDI,4-hydroxybutyl acrylate and trimethylolpropane diallyl ether.Finally,the branched polyurethane acrylate(BPUA-TAC)was synthesized through the reaction of TAC-MTGL and the isocyanate-containing intermediate product.The other two different branched cores(TAT-MTGL and TMPTA-MTGL)and corresponding BPUA branched compounds(BPUA-TAT and BPUA-TMPTA)were also synthesized to investigate the effect of rigid branched cores on the properties of the resultant coatings.The structures of branched cores and BPUA were characterized by 1H NMR.A series of UV-curable coating solutions(S1,S2 and S3)were prepared by mixing BPUA,photo initiators and IPA.For purpose of further promoting the crosslink density and reducing internal stress of coatings,PETMP was added into the above-mentioned coating solutions to obtain another series of coating solutions(S1-1,S2-1 and S3-1).All of resultant coating solutions were coated on PC sheet to obtain hardening coatings under UV-irradiation.The properties of BPUA coatings were characterized by the tests of FT-IR,gel content,water absorption,dynamic mechanical property,mechanical property,TG and surface properties.Meanwhile,the effects of the rigid branched core and the addition of PETMP on the properties of coatings were also studied.The FT-IR results showed that the conversion of double-bond increased with the decreased rigidity of branched cores,and the gel content tests revealed the consistency of change between the double-bond conversion and the chemical crosslink density.The DMA results indicated that the introduction of PETMP increased the total crosslink density of coatings.Additionally,compared with the crosslink density,the rigid branched core can endow coatings with higher Tg value.All of the prepared coatings exhibited good thermal properties with a decomposition temperature of higher than 150?.The S1-1 coating displayed superior performance among all of the prepared coatings,such as 5H of pencil hardness,5B of adhesion and 6.76 MPa in ? and 49.2%strain in ?.Compared to the coating prepared with commercially available PUA-6 resin that possesses pencil hardness of 4H,the prepared coatings showed higher pencil hardness.(2)The reaction of IPDI and PETA was carried out to obtain the isocynate-containing intermediate product,which was subsequently reacted with norbornane dimethylamine(NDMA)to synthesize the rigid PUA-NDMA branched compounds containing six terminal acrylate groups.The other two PUA branched compounds(PUA-PZ and PUA-EDA)with different diamines(PZ and EDA)were prepared to investigate the effect of rigid diamines on the properties of PUA coatings.The structures of PUA were characterized by 1H NMR.A cluster of UV-curable coating solutions were prepared by mixing PUA,photo initiators and IPA,and then they were coated on PC sheet to obtain hardening coatings under UV-irradiation.The properties of PUA coatings were characterized by the tests of FT-IR,viscosity,XRD,AFM,DMA,mechanical property,TG and surface property.Meanwhile,the effect of the rigid diamines on the properties of the resultant coating was also studied.The FT-IR results showed that flexible diamines and low viscosity of coating solutions can improve the conversion of double-bond.The micro-structure analysis revealed that the hydrogen bonding of PUA-NDMA coating were mainly formed between hard and hard segments,resulting in micro-phase separation and rough surface of the coating.However,PUA-PZ and PUA-EDA coatings mainly generated phase mixing,and their coating surface was relatively uniform.The DMA results indicated that the rigid diamines endowed coatings with higher Tg value than the crosslinking density.Additionally,the prepared coatings displayed good thermal properties with a decomposition temperature of higher than 150?.The tensile test showed that the PUA-PZ coating with highest crosslinking and rigid diamines posessesed excellent mechanical property with 20.7±0.2 MPa in ?and 6.8±0.8%in ?.The pencil hardness of the prepared PUA-PZ coating could reach to 5H,and it also showed good adhesion(5B)and flexibility(<2 mm).(3)The titanate coupling agent(PN-102)was used as the surface modifier to prepare the modified SiO2 nanoparticles(Si-PN 102-5)with small particle size and good dispersion ability in PUA-6 resin.The roughness of the PUA/SiO2 composite coating was compared by adjusting the dosage of Si-PN 102-5,from which the optimal amount of Si-PN102-5 was determined.Accordingly,hydrophilic SiO2(Si-380)and hydrophobic SiO2(Si-115)were introduced into PUA-6 resin to prepare the corresponding composite coatings.The properties of PUA/SiO2 composite coatings were characterized by the tests of FTIR,AFM,SEM,DMA,mechanical property,TG and surface property.Meanwhile,the effects of SiO2 nanoparticles modified with different surface modifiers on the properties of PUA/SiO2 composite coatings were also studied.The FTIR and XPS results showed that the titanate coupling agent(PN-102)had functionalized the Si-PN 102-5 particle surface successfully.The TEM test displayed that the particle size of SiO2 was almost unchanged before and after modification,and was maintained at about 20-30 nm.The AFM and UV-vis results indicated that the optimal addition of Si-PN 102-5 particles in the composite coating was 5 wt%.The SEM,DMA and tensile test revealed that Si-PN 102-5 can not only block the interaction and accumulation of nanoparticles,but also enhance the interface interaction with polymer chains through chain entanglement because of its large PN-102 structure.Additionally,due to its good dispersion in PUA-6 resin,it significantly improved the tensile strength and toughness of the coating,whose ? and ? could reach to 11.0±0.1 MPa and 9.4±3.0%,respectively.The pencil hardness of the prepared Si-PN102-5-5%composite coating could reach to 5H which was higher than the commercial PUA-6 coating,and it also dsiplayed good adhesion(4B)and flexibility(3 mm).The TG results showed that the type of modified SiO2 hardly influence the thermal stability of the resultant composite coatings,and the prepared composite coatings displayed good thermal stability with a decomposition temperature of higher than 250?.