Deinking evaluation using near infrared narrow band digital image analysis

The current deinking evaluation methods include visual image analysis (manual and digital) and optical reflectance (using the Kubelka-Munk equation). The mechanism of image analysis is simple: dark ink (mostly black) is isolated from the light background (fiber) and then captured visually or by digital devices. The image analysis methods have inherent limits, such as poor correlation with paper optical properties, and have large variances from sample to sample and side to side. In this paper, an innovative approach that employs a band of near infrared light and a digital imaging device was applied to address these limitations. This approach has advantages for isolating specks from backgrounds, obtaining high quality raw data, and significantly reducing the variances among the handsheets and their sides. By using the ink elimination equation derived from image analysis, reliable ink elimination rates were obtained that were well correlated with paper optical properties. This system was also applied to newspaper deinking evaluation with positive results.