Study On UV-curable Adhesives With Nano-TiO₂

UV-curable adhesives have been widely used in areas of national economic production such as automotive, medicine, microelectronics processing, et al, because it is a kind of green and efficient adhesives, and has the advantage of high curing rate, ambient curable condition, high energy efficiency and no emission of volatile organic slovent in curing process. However, there are some shortages in photo-initiated radical UV-curable adhesives, such as low bond strength, high volume shrinkage, low refractive index, poor thermal stability and easy inhibition by oxygen. In this paper, we used the cationic polymerization adhesive as the matrix and used the photoacids generated by the photoinitiators to catalyze sol-gel process of titanium isopropoxide (TIP). UV-curable nanocomposite adhesives with high refractive index and high transmittance were prepared by in-situ sol-gel process.In this paper, the effect of type and content of photoinitiator, structure of monomer, light intensity and the thickness of adhesive on curing rate, tensile strength, volume shrinkage of the cationic UV-curable adhesive were studied. The results show that the adhesives with 3,4-Epoxycyclohexylmethyl-3'',4''-epoxycyclohexanecarboxylate (abbreviated as S-06) as monomer, triphenylsulfonium hexafluorophosphate salt as photoinitiators had short surface drying time (8s), high tensile strength (15.8MPa) and low volume shrinkage (3.2%). Then we added different content of titanium isopropoxide as the inorganic precursor into this system, and we researched the kinetic investigated of different TIP content by TTIR spectroscopy. The result showed that there was less influence on curing rate of nanocomposite adhesive when TIP content was low (<20%). The nano TiO₂ with an average diameter of 20nm generated by sol-gel processing dispersed in polymer matrix under the effect of coupling agent. The refractive index of the nanocomposite adhesive increased from 1.5013 to 1.5439, meanwhile had good transmittance in visible and near infrared region. The nanocomposite adhesive had good thermal stability, and the thermal decomposition temperature rose from 320℃to 365℃.