UV-cured Polyurethane Acrylate Coating

Polyurethane acrylate (PUA) aggregates the excellent properties of polyurethane(PU) and polyacrylate, is well applied in the manufacture of coating and printing which needs UV-cure technology. PUA plays an important role in the industry of woods, special paper, printing polish, surface treatment of plastic and metal and electronic products. Recently, PUA become one of the research hotspots about UV-cure materials in China, while it has been commercial abroad.This thesis aims at the studies on the synthesis of PUA coating by bulk polymerization, using isophorone diisocyanate(IPDI), polyether glycol(PEG) and hydroxyl propyl acrylate(HPA) as the raw materials. The optimum reaction conditions catalyzed by dibutyltin dilaurate(DBTDL) as follows: the ratio of materials was IPDI:PEG:HPA=3:2:2; IPDI and PEG reacted firstly, and capped with HPA; reaction temperature was 50℃; amount of DBTDL was 200ppm of total weight of raw materials.The rate equation that can well fit the experiment data under the optimum reaction conditions follow second order and presented as follows:where, the rate constant k follows:Step 1 k= 2.89 ×10¹³ exp(-82.58/RT)Step 2 k= 4.08 ×10¹⁴ exp(-89.82/RT)This rate equation can well predict the relation between conversion of NCO groups and reaction time in different temperature.By IR and NMR methods, we not only well knew the structure changes of PUA in the recipe(IPDI:PPG:HPA=3:2:2), but also found the selectivity of the two different NCO groups, in which the reaction rate of NCO_sec is 3.50 times faster than that of NCO_prim. We used Gaussian-method and Lorentzian-method to fit the GPC spectrum in multi-peaks. For thisrecipe, we found that the n_max≈12; the weight ratio(f) of high molecular weight will increase with the decrease of the ratio between IPDI and PPG; the molecular weight distribution of PUA will broaden with the increase of soft segment length in overlapping peaks.This thesis also aims at studies on the preparation of UV-cured PUA film. By the analysis of the UV spectrum of different photo initiator, we found TPO and 651 is the best choice, Their absorption lies in 272nm and 309nm. The molar absorptivity of TPO is the highest, k_max(272nrn)=8.671 × 10⁶ L·mol^-1·cm^-1, k_max(309nm)=6.429 × 10⁶ L·mol^-1·cm^-1, and keep PUA film yellow-resistant.Also, we tested mechanical property, adhension and 60° gloss of the PUA film, summarized their influencing factors, optimized the main aspect of the coating process: temperature and humidity, extension time of PUA film, and prohibition of oxygen.