Study On Cationic And Hybrid UV Curing Resin Systems And Their Application

Stereolithgraphy Apparatuses (SLA) has been applied in many fields since it came out.Photocurable resins, an indispensible part for SLA, have impact on photoforming parameters,curing rate and product performances. Therefore, the study on photocurable resins hasprofound significance on promoting SLA. Nowadays, most of the commercial SLAphotosensitive resins are provided by foreign companies, while those developed by domesticcompanies are based on radical polymerizatuion in majority. Their dimensional accuracy andmechanicl properties have a great gap compared to foreign products. In this article UVcationic curing epoxy resin system and UV radical-cationic hybrid curing resin system werestudied. The influence of the content of photoinitiators and photosensitizers, types ofphotosensitizers and ratio of radical and cationic resins on gel content and drying time wereinvestigated. The changes of gel content and mechanical properties with various post curingconditions were examined. The conversion of C=C double bond and epoxy group weremeasured with FT-IR during UV curing process. The curing depths at different exposureenergy were measured, and the penetration depth coefficient (Dp) and critical exposure energy(Ec) were calculated. The thermal stability and degree of crosslinking were characterized withthermogravimetric analyzer (TGA) and dynamic mechanical analyzer (DMA).The results showed that triarylulfonium salt doped resins had higher curing rate thandiaryliodonium salt doped resins if no photosensitizers were added. Gel content ofdiaryliodonium salt doped systems reached83%at exposure time15s, while thediaryliodonium salt system needed exposure time40s to achieve the same gel content. Sixphotosensitizers were selected to sensitize the diaryliodonium salt photoinitiator and theirsensitizing efficiencies are JRCure184≈BDK＞ITX＞MBF＞JRCure819＞anthracene. Theepoxy resins doped with diaryliodonium salt and photosensitizer JRCure184and BDKexhibited high UV curing rate, they could cure after being exposed to UV for15s. But theresin system with BDK exhibited a slight yellowing phenomenon, whereas JRCure184didn’t.JRCure184is superior as photosensitizer for diaryliodonium salt.Orthogonal experiments indicated that the amount of PAG208had outstanding effect on the gel content, synergitic effect between JRCure184and PAG208existed but it was not verysignificant. The optimized formula of the hybrid resin should be R:C=3:2, JRCure184at1phr, PAG208at1.5phr. Gel content of the hybrid would be92%at exposure time of25s.Increasing post curing temperature and time could further enhance the gel content andthe optimum post curing temperature was80℃. After post curing, the sample exhibited highertensile strength, shrinkage ratio and hardness, but slightly lower elongation at break. For theepoxy resins doped with sulfonium salt and sensitized iodonium salt, the hybrid resin ofepoxy and epoxy acrylic resins, the tensile strength were49MPa,47MPa and64MParespectively, whereas the elongations at break were1.4%,1.6%and4.5%, and the hardnesseswere71,71and77Shore’s D, respectively. The volume shrinkages after UV curing were3.5%,3.3%and3.9%, respectively.The absorption of epoxy group and C=C double bond in FT-IR spectra went down withthe increasing UV exposing time. The conversions of the epoxy group and C=C in thehybrid resins were80%and93%respectively, being higher than that of UV cured epoxyresins. The Dp and Ec of the three types of UV curing resins ranked below, Dp: Hybrid resin≈epoxy resin with iodonium salt and sensitizor＞epoxy resin with sulfonium salt; Ec:Hybrid resin＜epoxy resin with sulfonium salt＜epoxy resin with iodonium salt andsensitizer. The Ec of hybrid resin was22.76mJ/cm2, much less than that of UV cationiccuring resins.DMA analysis showed that the glass transition temperatures of radical, cationic andhybrid resins were100℃,83℃and90℃, respectively. The tan δ curve appeared wider thanthe loss curve of radical and cationic cured samples, which indicated radical and cationiccomponents had good compatibility.The Stereolithography for the three UV curable resins were operated on SPS450BStereolithography Apparatus. The hybrid system showed higher curing rate, gel content andoverall performance. It behaved similar to Somos14120from DSM. The Hybrid system wasbetter than the other two UV cationic curing systems. Furthermore, the hybrid system did notshow warpage after photoforming. The prototyped sample exhibited high dimensional accuracy and smooth appearance. The epoxy acrylate/epoxy hybrid resin is suitable for SLA.