Comparative Study of Brightness/Whiteness Using Various Analytical Methods on Coated Papers Containing Colorants

Abstract

Fluorescent Whitening Agents (FWA), dyes and pigmented inks are used extensively in the paper industry to enhance the appearance and optical performance of coated and uncoated papers. There are several different systems in use for the description and specification of color and optical properties of paper, using colorimeters, spectrophotometers and brightness meters. CIE and TAPPI are the most commonly used color systems in the paper industry. In this study, three different colors (blue, black and red), and FWA were added into coating formulations from three to five addition levels. Coated LWC papers were measured for their optical properties with two different spectrophotometers and a brightimeter. The CIE whiteness formulation (1996) was analyzed on slightly colored papers. It was found that in some cases, calculated CIE whiteness values increased with increasing amount of colors in the coating layer, although the papers appeared darker or redder to the observers. Small deviations in measured CIE tristimulus functions X, Y, and Z often caused significant changes in calculated CIE, and Ganz whiteness values. Hunter whiteness values also followed the same pattern as CIE and Ganz whiteness, although it is less sensitive to small changes in the tristimulus values. The results show the deficiencies in the current measurement techniques for assessment of brightness and whiteness of wood