Application Of Optical Brightening Agent In Wet End And Surface Sizing

In this paper, the application of optical brightening agent adding in wet end and being applied by surface sizing technique were investigated in the laboratory. The law of brightness changing was found, and as a guide to the factory machine. In laboratory, the brightness and whiteness hue impacted by the dosage of OBA were investigated when OBA was added in wet end and being applied in surface sizing technique respectively and cooperatively. In mills, the dosage of OBA used in different machines and environment were fine-tuned. Conclusions are as follows.(1) The ISO brightness could be enhanced by the addition of OBA, in despite of adding in wet end or surface sizing alone or cooperatively. The brightness of the sheet is not continuously enhanced with the increasing dosage of OBA. When the OBA dosage increased to a certain value, the brightness was no longer raise or even decline, and the value was called the yellowing pot. Comprehensive comparison, the 2-sulfonic type of OBA was more effective than 4-sulfonic type when they were used at the wet-end of the papermaking process, and 6-sulfonic type of OBA was more effective than 4-sulfonic type when they were applied by the surface sizing technique. In the corresponding application, the yellowing point of 4-sulfonic type of OBA was higher than 2-sulfonic type, and the yellowing point of 6-sulfonic type of OBA was higher than 4-sulfonic type.(2) The brightness could be enhanced when 2-sulfonic type of OBA used at wet end and 4-sulfonic type or 6-sulfonic type was applied in surface sizing. In a certain dosage of OBA, the brightness reached peak value when the 2-sulfonic type at the right percentage of the total volume.(3) The L*a*b* values of the sheet could be changed with the application of OBA, and the changes conducive to raising the white hue. Meanwhile, the heat yellowing degree of the sheet changed a little.(4) When the dosage of OBA was over the yellowing point, it was also shown that the brightness was no longer increasing, or even decline in mill production process. Under certain conditions, improve the brightness of the base paper sheet can more effectively improve the brightness of high-brightness white paper.Dyes or pigments,which was added into papermaking to improve the color phase of paper sheets, could affect the brightness. In comparison, the pigments helped to improve brightness, while reducing the dosage of OBA and pigments. In a certain dosage of OBA, the brightness fluctuated with the proportion dosage which used at wet end, and the value of the optimum percentage depended on the wet end furnish and the type of OBA.