**5.2 UV hybrid epoxy adhesives**

Most widely used UV cure adhesives are acrylate compositions [39–41]. Acrylate based UV cure adhesives are mainly composed of acrylate monomer, acrylate oligomer and radical photo-initiator. Acrylate based UV cure adhesives can be cured instantly, within seconds. Limitations of UV cure acrylate adhesives are surface cure issue, shadow cure problem, high cure shrinkage and poor humidity reliability. By combination of UV acrylate composition with thermal cure epoxy composition, UV and thermal cure hybrid epoxy adhesives have been developed and commercialized for over two decades [42–44]. Acrylate monomer, epoxy resin, photo-initiator and epoxy curing agent are primarily formulated in the UV and thermal cure hybrid adhesives. UV hybrid epoxy adhesives combine advantages from both UV acrylate proportion and thermal cure epoxy part. Adhesion reliability performance could be much improved by introduction of epoxy composition with compared to normal UV acrylate adhesives. In the meantime, production efficiency could be much improved by shortening the fixture time to seconds via UV radiation with compared to at least dozens of minutes needed for thermal cure epoxy adhesives. Surface cure issue, shadow cure issue and cure shrinkage problem of acrylate UV adhesives could also be improved to certain degree because of lower contents of free radical curable acrylate compositions. In some cases, thermal initiator such as peroxide is also formulated in the hybrid adhesive to assure curing remained acrylate compositions after UV radiation or those at shadow areas where UV light cannot reach.

Successful development and industrialization of so called ODF (One Drop Fill) process for large size LCD (liquid crystal panel) panel production was one important technology revolution in early 2000s that have made a big impact on our modern life. Development and commercialization of LCD ODF main sealant, an UV hybrid epoxy adhesive, played a key role in its mass production success [45–47]. LCD ODF main sealant is an adhesive material that is used to bond two glass substrates and seal liquid crystal material between them. It is a UV hybrid epoxy adhesive, typically composed of acrylate monomer, photo-initiator, partially acrylate epoxy resin and latent curing agent. Main steps for the adhesive use in this process are: (1) dispensing LCD main sealant; (2) dropping off liquid crystal materials into each cell; (3) alignment and assembly; (4) UV cure the sealant; and (5) thermal cure the sealant. The author has invented initiator free UV hybrid thermal cure epoxy adhesives by combination with bismaleimides that shows much better compatibility with liquid crystal material and high performance [48–50].
