Preparation And Properties Of UV Curable Materials Containing Mercapto Groups

It is well known that UV curable coatings have found wide applications inthe fields of electric products, paper, wood, automobile etc. due to its fast curingspeed, high coatings quality, less environmental pollution, low energyconsumption and convenient operation. However, the oxygen inhibition duringthe curing process limited the UV curable coatings application, especially forthe coatings thickness and surface drying.The introduction of mercapto group into UV curable coatings, not only caneffectively reduce the oxygen inhibition effect of UV curing process, but alsocan form the photoinitiated thiol-acrylate click reaction, which have graduallybecame a new research direction in the UV curable field. However, it is difficultto realize in the industrial application due to the serious odor and residure ofsmall molecular merchant compounds. Therefore, how to effectively anchor thesmall molecular merchant compounds onto the component of UV curablecoatings, investigate the theory of photoinitiated thiol-acrylate and discuss theeffect of merchant groups on the properties of UV curable coatings are animportant research topics in the UV curing field.Based on the above limitiations of small molecular merchant compound inthe UV curing process, in this paper, some common small molecular merchantcompounds were anchored onto the some basic components used in the UVcurable coatings by chemical grafting method. The specific preparation process and main conclusions are as follows:1. Preparation of modified nanosilica with KH590and study its propertiesin UV curable coatings3-mercaptopropyl trimethoxysilane (KH590) was successfully anchoredonto the nanosilica surface by conventional method via condensation reactionbetween Si-OH. The anchoring (or grafting) mode of KH590onto the nanosilicasurface was determined by combing the conventional instrument analysis andquantum chemical calculations.The results show that the mercapto group concentration of nanosilicasurface firstly increases and then decreases with the increasing amount ofKH590. The highest grafting ratio is16.8%and mercapto group concentration is0.9mmol/g. The grafting mode is relate to the amount of KH590, Themono-grafting mode is favorable with the lower concentration of MPTMS,while the grafting mode may be transferred into ladder like grafting mode whenmore MPTMS introducing the system. The dispersion and aggregation ofnanosilica in the UV curable coatings were significantly improved. Comparedwith the modification before and after, the curing speed, anti oxygen inhibitionand merchanical performances are different.2. The thiol-acrylate click reaction based on the nanosilica surfaceOn the basis of modified nanosilica, the thiol-acrylate click reaction on thenanosilica surface was studied. At the same time, the synthesized silanecoupling agents was firstly prepared by KH590and TMPTA and then graftedonto the nanosilica surface. The difference between two treating methods wascompared. The results show that the mercapto group on the nanosilica surfacecan participate in the UV curing process by click reaction. The grafting ratio is21.9%for the former method and143.2%for the latter method. The differencein grafting ratio leads to the difference in the UV curing kinetics, viscosity andhardness of UV curable coatings. 3. Preparation of modified nanosilica with the macromolecular mercaptocompound and study its properties in UV curable coatingsWith the modified nanosilica as starting point, the macromolecularmercapto compound was anchored onto the nanosilica surface by repeatedthiol-acrylate click reaction. The grafting degree and terminal groupd waschanged with the click reaction process, and the effect of terminal acrylate andmercapto group on the UV curing process was investigated.The grafting ratio and the anchoring molecule weight increased with thegrafting process, and the final grafting ratio was45%with multiple terminalmercapto groups. Both terminal acrylate and mercapto goups can participte inthe UV curing process by polymerizable groups or click reaction, in addition,the mercapto group is more effective to UV curing process by reducing oxygeninhibition.4. Preparation of mercapto groups termined polyurethane and study itsproperties in UV curable coatingsThe multifunctional thiol-terminated PU was prepared by polyether diol,IPDI and Tetrathiol, and the terminal functional group of PU was1.95mmol/g.At the same time, the multifunctional acrylate-terminated PU was prepared soas to investigate the difference of functional groups in UV curable coatings.The reaction between mercapto group and NCO is easily to carry out, butthe obtained thiol-terminated PU is complicate and with higher molecularweight due to part tetrathiol is used as crosslinker. With the different levels ofprepared PU as main resin in UV curable coatings, their differences in curingkinetics, viscosity, volumetric shrinkage and adhesion were investigated. Thethiol-terminated PU exhibited significant better properties than correspondingacrylate-terminated PU, including remarkable anti-oxygen inhibition.5. Preparation of photoinitiator containing mercapto group and study itsphotoinitiated properties The mercapto group was anchored onto the photoinitiator1173with IPDIas bridge. Compared with1173, the modified photoinitiatorhad lower migrationand lower residual agent after UV curing. The odor problems of small molecularmercapto alone also improved; in addition, the presence of thiol group canreduce the addition amount of photoinitiator UV curing coatings. Thesynergistic effect is palyed between mercapto groups and photoinitiator.