Detailed analysis of the UV‐adjustment techniques used in paper and graphic industries

Abstract

AbstractMany commercial materials (papers and boards) contain optical brightening agents also known as fluorescent whitening agents. Adequate adjustment of the UV content of a measurement device (e.g., spectrophotometers) is essential for accurate color measurement. As specified in the ISO standards, the UV content is adjusted against an assigned value of an international reference transfer standard, for example, CIE whiteness (D65/10°) for the CIE illuminant D65 or ISO brightness for the C illuminant. Because of the simplicity, these approaches have gained great popularity in papermaking industry. Yet, there has been little evidence indicating how accurate the total spectral radiance factor corresponding to the single assigned value is reproduced. Hence, we present a method that quantitatively evaluates the accuracy of the UV‐adjustment technique, through comparing the total spectral radiance factors obtained from UV adjustment with the assigned ones. This method has been applied to three second‐level international reference transfer standard illuminated by three standard illuminants, D65, C, and D50. We found that the major differences between the assigned spectra and those obtained from the UV adjustments occur in the blue band where fluorescence is strong. At a few wavelengths, the differences may be up to 4–5%. Nevertheless, their color differences corresponding to the assigned spectra and those obtained from the UV adjustments are still smaller than unity (1 ΔE*) for all of the illumination conditions. Two instruments using the representative UV adjusting techniques, for example, the conventional UV‐adjusting with an adjustable (GG395) UV filter and the numerical UV‐filtering, have been studied. © 2016 Wiley Periodicals, Inc. Col Res Appl, 42, 19–26, 2017