Effect of Optical Brightening Agent Degradation Due to Heat and Moisture, 1997 Coating Conference Proceedings

Relatively little is known about the effects of heat and moisture on optical brightening agents (OBA:s). In this work, heat and moisture was found to have an influence on the performance of the OBA. This was measured by changes in brightness and relative reflectance from a one-side double coated solid bleached sulphate (SBS) paperboard. Very high temperatures can destroy completely the OBA:s. Moderately high temperatures may destroy the OBA:s partially and can thus lead to optical mottle. For the OBA type used in this study moisture had little effect. Colour space values (CIE-L* a*b*) showed that heat caused the hue of the double coated SBS to move in the direction of less white and towards the red-yellow area. It was found that the b* value may be the most difficult to control because of its high standard deviation with increasing temperature. In addition to optical mottle, this phenomena may seriously affect a printed greybalance if the heat induced effects are not defined accurately, prior to printing for the pre-press reproduction. Future paper and paperboard production processes using higher temperatures may increase the risk for mentioned degradation effects from the OBA:s.