Study On Shrinkage Stress Reduction Of UV-curable Acrylic Resin With Functional Microspheres

UV-curing technology has been widely used in coatings,adhesives and electronic manufacturing due to its remarkable advantages such as energy saving,high efficiency and environmental friendly.In the process of rapid photopolymerization of UV-curable acrylic resin,the molecular spacing is shortened rapidly.the UV-cured materials show volume shrinkage and shrinkage stress,resulting in low coating adhesion of coatings and poor dimensional accuracy of 3D printing materials,which is one of the most difficult problems in the field of UV-curing technology.It is of great significance to study the mechanism and influencing factors of photopolymerization shrinkage stress of resin and develop a UV-curable resin with low shrinkage stress for improving the comprehensive properties of UV-curable materials and expanding the application range of UV-curable resin.In this thesis,the factors affecting the shrinkage stress of UV-cured resin were systematically studied.Porous microspheres,p Hresponsive microspheres and UV-responsive microspheres were prepared.The shrinkage stress of resin was reduced by the deformation of microspheres or the generation of microbubbles to compensate for the volume of resin polymerization shrinkage.The specific research contents were as follows:(1)The influencing factors of shrinkage stress of UV-curable acrylic resin were investigated by RT-MIR-photo-rheology technology.By analyzing the polymerization process of UV-cured acrylic resin under different curing conditions and system components,the influencing factors of curing shrinkage stress were clarified.The test results showed that when UV intensity decreases,the molecular chain can move before curing to release the shrinkage stress;The decrease of the functionality or the decrease of the content of the active monomer can reduce the content of the reactive group and reduce the shrinkage stress of UV-curable acrylic resin;The increasing of molecular chain length of the active monomer can improve the flexibility of the resin system,releasing the concentrated shrinkage stress during polymerization.Microspheres with different structures were prepared by Pickering emulsion template method combined with UV-curing technology,added to UV-curable resin as functional components.The elastic deformation of microspheres was used to reduce the shrinkage stress of UV-curable resin.The results showed the addition of 5 wt % elastic porous microspheres could reduce the polymerization shrinkage stress of the UV-curable acrylic resin by 28 %,with little effect on the final double bond conversion of the resin.In this work,the RT-MIR-photo-rheology technology was used to explore the influencing factors of the shrinkage stress of the UV-curable resin.It was found that the shrinkage stress of the resin could be effectively reduced by reducing the UV intensity,reducing the functionality and content of the active monomer,increasing the molecular chain length of the active monomer,and adding porous microspheres with elastic deformation ability,providing theoretical support for the design of the subsequent microspheres.(2)Microspheres with strong deformation ability and p H responsiveness were prepared by soap-free emulsion polymerization.The photoacid generator and p H-responsive microspheres were added to the UV-curable acrylic resin to effectively reduce the shrinkage stress.p Hresponsive microspheres with significantly increased particle size in an acidic environment were prepared by adjusting the type and content of end-capping agent and the content of crosslinking agent.The photoacid generator produced super protonic acid after UV irradiation,which reduced the p H of the UV-curable resin and increased the particle size of the p Hresponsive microsphere,decreasing the shrinkage stress by compensating for the shrinkage volume of the resin.The results showed that adding 5 wt % p H-responsive microspheres and 2wt % photoacid generator could reduce the shrinkage stress and shrinkage rate of the UV-cured resin by about 40 %,without affecting the pendulum hardness and final double bond conversion of the resin.This work significantly reduced the shrinkage stress of UV-cured resin by exerting the synergistic effect of photoacid generator and p H-responsive microspheres,and provided a new idea for the design of subsequent microspheres.(3)UV-responsive microspheres were prepared by Pickering emulsion template method combined with solvent evaporation method.The UV-responsive microspheres were added to the UV-curable acrylic resin to reduce the shrinkage stress of the resin.UV-responsive microspheres with nano-calcium carbonate particles in the shell and photoacid generator inside were prepared by adjusting the shell content,the content and dispersion position of the emulsified particles,and emulsification speed in the oil phase.The photoacid generator loaded in the microsphere produced protonic acid after illumination,and reacted with the calcium carbonate particles densely distributed in the shell to form microbubbles,which compensated for the polymerization shrinkage volume of the UV-cured resin and reduces the shrinkage stress.The results showed that the shrinkage stress and shrinkage rate of the UV-cured resin can be reduced by about 50 % by adding only 2 wt % of the UV-responsive microspheres.In this work,UV-responsive microspheres that produce microbubbles after illumination can greatly reduce the shrinkage stress of UV-curable acrylic resin without affecting the mechanical properties of the resin and the basic properties of the coating,which had industrial application potential.