Research On The Brightness Stability Of Coated Papers Containing Hyp

Due to the rapid development of high yield pulping technology and the unique properties of high-quality high-yield pulp, such as higher bulk and opacity, high-yield pulps are becoming increasingly used to product high value-added fine papers that are traditionally produced with chemical pulps exclusively. However, due to the presence of a large quantity of photochemical reactive lignin, there is a concern on the long term brightness stability of HYP containing papers. Therefore, the study of inhibiting HYP yellowing in order to increase the utilization rate of HYP is one important research direction in the current and future pulp and paper industry.This work used different concentrations of yellowing inhibitors (OBA, TiO2and nano-ZnO) and other pigments to prepare the coatings. Hand-sheets which contain HYP (substitution20%) were coated with different weight on one side. The hand-sheets were accelerated aging with UV light box after air-dried, meanwhile, measured the brightness and other optical properties’changes with optical instruments, in order to study the effect of yellowing inhibitors on the optical stability of HYP-containing hand-sheets.The experimental results indicated that OBA could improve the initial brightness and optical stability of the HYP-containing hand-sheets, the higher the dosage of OBA, the more obvious the effect, but when its dosage exceeded0.4%, the effect was no longer obvious. However, the△E value increased with UV irradiation.In this research, various TiO2was added to coating colors to improve the light fastness properties of coated papers containing high-yield pulps. It was shown that rutile TiO2was especially effective at improving brightness stability of coated papers. At a dosage of3parts of rutile TiO2and5parts nano-ZnO, the brightness stability of coated paper containing20%of HYP was found to be even better than papers made of100%chemical pulp coated with conventional coating color. Besides, the experience results showed that good inhibiting effectiveness also could be obtained when30%HYP was added in coated papers as well as the paper had double coatings(without OBA or nano-pigments in the bottom layer).The work results showed that the viscosity of coating color displayed the same trend as solids content at low rotate rate, while nano-pigments had little effect on the viscosity. The strength properties of the coated papers decreased during UV irradiation. However, the difference was not obvious for different dosage of yellowing inhibitors.