Preparation And Properties Of UV-Curable Coating Based On Titanium Dioxide With High Weather Resistant

UV-curable coatings have attracted wide attention due to their advantages of low VOC emissions,energy saving and high efficiency.However,the poor weather resistance of UV-curable coatings restricts the application of UV-curable coatings in outdoor environments.Titanium dioxide（TiO₂）is most commonly used in the field of weather-resistant coatings due to its low cost and excellent UV absorption capacity.However,most of them are based on solvent-based coatings and waterborne coatings,and are rarely used in UV-curable coatings,as the UV shielding effect of TiO₂ will compete with photoinitiators.The effect of TiO₂ addition on the curing process and weather resistance of UV-curable coatings has not been studied in detail.In this work,TiO₂ particles was modified by dispersant and inorganic coating and employed as fillers to prepare UV-cured coatings with high weather resistance.The effect of the addition of TiO₂ particles on the curing process and weather resistance of UV curing coating was systematically explored.In addition,a series of multifunctional microspheres based on TiO₂ were prepared by combining photopolymerization technology and emulsion polymerization method.By exerting the synergistic effect of physical structure and chemical composition,it is expected to obtain high weather-resistant multifunctional UV-curable coatings.The specific research contents are as follows:（1）TiO₂ was modified by dispersant and added to the UV-curable coating.The effect of TiO₂ addition on the curing process of UV-curable coating was analyzed by gel content test and real-time infrared test.The effect of TiO₂ addition on the weather resistance of the coating was analyzed by UV accelerated aging test and salt spray test.The results showed that the curing rate and double bond conversion rate of the coating decreased with the increase of TiO₂ content.However,the effect of TiO₂ addition on the curing degree of the UV-curable coating could be neglected by controlling the TiO₂ content（≤5 wt%）and film thickness（≤30μm）.The color difference values（ΔE）of the pure resin coating after UV aging for 1000 h was 21.25,the surface gloss loss was 27%,and the surface was cracked,indicating the poor weather resistance of the pure resin coating.In contrast,theΔE of the coating with TiO₂ after UV aging for 1000 h was only 3.65,the surface gloss loss decreased to 6.5%,and there was no cracking on the surface of the coating,indicating that the addition of TiO₂ could effectively improve the weather resistance of the coating.The corrosion resistance of the coating before and after aging was studied by salt spray test.The results showed that a large area of red corrosion products appeared on the surface of the aged pure resin coating after salt spray test,while there were no corrosion points,blisters and red corrosion products on the surface of the aged TiO₂ coating after salt spray test,which further demonstrated that the addition of TiO₂ could improve the weather resistance of the coating.This work provided an effective way to prepare environmentally friendly coating with high weather resistance by improving the weather resistance of the coating by adding TiO₂ with ultraviolet absorption and scattering ability.（2）TiO₂ was modified by in-situ hydrolysis condensation of tetraethyl silicate on the surface of TiO₂.TiO₂ particles with different SiO₂ shell thickness（TiO₂@SiO₂）were prepared by controlling the hydrolysis condensation time of tetraethyl silicate.The results showed that the SiO₂ shell on the surface of TiO₂ could not only effectively inhibit the photocatalytic activity of TiO₂,but also improve its dispersion.The results of gel content test and real-time infrared test showed that SiO₂ coated TiO₂ could reduce its influence on the curing rate and curing degree of the coating.In addition,compared with TiO₂ particles,the incorporation of TiO₂@SiO₂ could further reduce the changes of gloss and surface morphology of the coating after UV aging.When the concentration of TiO₂@SiO₂ was 10.0 wt%,theΔE of the coating after UV aging for 1000 h was 3.4,the surface gloss loss was only 2.0%,and the surface did not crack,suggesting that the coating had the best weather resistance.This work effectively inhibited the photocatalytic activity of TiO₂ without sacrificing its UV shielding ability by inorganic coating modification,which was of great significance for improving the weather resistance of the coating.（3）TiO₂ hollow microspheres were prepared by photopolymerization and emulsion polymerization.In this chapter,oil phase droplets composed of photocurable prepolymer,TiO₂particles,photoinitiator and organic solvent were prepared.Upon exposure to UV irradiation,the simultaneous photo-polymerization of UV-curable prepolymer and the migration of TiO₂particles to the oil-water interface contributed to form microsphere shell.After removing organic solvent,cavities was left in microspheres,leading to TiO₂hollow microspheres.The morphology of TiO₂ hollow microspheres was modulated by tuning the types of photoinitiator,the hydrophilicity of TiO₂ particles and the amount of solvent.The hollow structure of the microspheres could block the heat propagation path,reduce the heat conduction rate of the coating,and improve the thermal insulation performance of the coating.The TiO₂ particles in the shell could absorb and scatter ultraviolet light,thereby improving the weather resistance of the coating.The TiO₂ hollow microspheres were used as fillers to construct thermal insulation and weathering coatings.The results showed that the thermal insulation and UV shielding properties of the coatings were better with the decrease of the shell thickness of TiO₂ hollow microspheres.When the concentration of TiO₂ hollow microspheres was 15.0 wt%,the thermal conductivity of the coating was 0.132 W/m K,which was 40%lower than that of the pure resin coating,and the internal temperature of the building model could be reduced by 4^oC.The addition of TiO₂ hollow microspheres could improve the UV durability of the coating.TheΔE of the coating after UV aging for 1000 h was 5.1,and the surface gloss loss was 4.6%,showing the excellent weather resistance.The TiO₂ hollow microspheres prepared in this work could not only improve the thermal insulation performance of the coating,but also improve the weathering resistance of the coating,which provided a feasible solution for preparing high-performance thermal insulation and weathering coatings.（4）TiO₂ porous microspheres encapsulating phase change material（butyl stearate）were prepared by photopolymerization and emulsion polymerization.Photocurable resin,TiO₂particles,phase change materials and photoinitiators were added to organic solvents to prepare oil phase droplets.TiO₂ porous microspheres encapsulating butyl stearate were obtained after solvent removal and UV curing.The butyl stearate loaded in the microspheres could absorb,store and release a large amount of energy during the phase change process,thus giving the coating temperature adjustment ability.The TiO₂ particles in the microspheres could absorb and scatter ultraviolet light,which could improve the weather resistance of the coating,and the TiO₂particles had high thermal conductivity,thereby improving the thermal response rate of the phase change material.The results showed that the prepared TiO₂ porous microspheres encapsulating butyl stearate had fast thermal response rate,high thermal cycle stability and good UV shielding performance.After 100 cycles of heating-cooling,the loss rate of phase change enthalpy was only 1.58%,and the reflectivity in the ultraviolet region was 8.3%.The TiO₂ porous microspheres encapsulating butyl stearate were used to construct a heat storage and weathering coating.The coating with TiO₂ porous microspheres encapsulating butyl stearate had a significant temperature hysteresis region at 36^oC-48^oC during heating and cooling,indicating that the addition of TiO₂ porous microspheres encapsulating butyl stearate could effectively improve the temperature regulation ability and thermal management ability of the coating.The addition of TiO₂ porous microspheres encapsulating butyl stearate could improve the weather resistance of the coating.TheΔE of the coating after UV aging for 1000h was 4.6,and the surface gloss loss was 3.5%.The TiO₂ porous microspheres encapsulating butyl stearate prepared in this work could not only improve the temperature regulation ability of the coating,but also improve the weather resistance of the coating.Its heated storage performance and weather resistance were of great significance for the thermal energy storage and service life of the coating.