Title
Effect of cobinders for coating on the performance of fluorescent optical brightening agents
Authors
YUAN-SHING PERNG EUGENE I-CHEN WANG and CHIH-PING CHANG

Received March 21, 2013
Published Volume 49 Issue 2 February
Keywords fluorescent brightening agent, brightness, whiteness, co-binder, starch, carboxymethyl cellulose (CMC), soy protein

Abstract
The proportions of bleached chemi-thermomechanical pulp (BCTMP) in the pulp mix need to increase with the trend toward lighter paper grammage, leading to a decrease in the brightness of coated paper, which also influences the quality of the paper. Adding fluorescent optical brightening agents (OBAs) to coating formulas can increase the whiteness of the coated paper. If suitable co-binders can be found as carriers of the OBAs to exert a synergistic effect, then the whiteness of the paper can be further increased. Our experimental design selected a typical coating formula for art paper, and three kinds of typical co-binders (starch, carboxymethyl cellulose (CMC), and soy protein) were tested. Four different types of OBAs (di-, tetra-, and 2 kinds of hexa-sulpho-OBAs) were applied at dosages of 0.25, 0.5, 1.0, 2.0, and 4.0 parts (with the total coating pigment as 100 parts). The brightness, whiteness, and CIE L*a*b* values of the coated papers were then evaluated. The experiments comprised 63 sets of treatments. Results indicated that for the starch co-binder, and relatively low brightness demand, 4S-OBA was optimal, while for relatively high brightness demand, however, 6S-B-OBA was more suitable. With CMC as the co-binder, the respective OBAs of choice were 2S-OBA and 6S-B-OBA; and with soy protein as the co-binder, these were either 2S- or 4S-, and 6S-B-OBA, respectively. As for the choice of co-binders, when using 2S-OBA, the option of soy protein was optimal, followed by starch; in matching 4S-OBA, starch was the co-binder of choice, followed by CMC. When 6S-A-OBA was used, for relatively low-whitening demands, soy protein was optimal; and for high-whitening demands, starch was the choice. When 6S-B-OBA was used, the lower brightness requirements called for soy protein, while higher requirements called for soy protein or starch as co-binders.