An effect of optical brightening agent degradation due to heat and moisture

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.