The Influences on the Optical Properties of Paperboard Due to Dye Additives

Abstract: In the paper industry the appearance and optical performance of coated and uncoated paperboard is important, therefore colour dyes are widely used to enhance the paperboard. In order to enhance the appearance of paper products, the dyes are added directly into the pulp and/or in the coating. This addition can lead to dye buildup in the white water system. The white water system recirculates back to the pulp and contains both chemicals, dye and fibers. A general assumption is, when the concentration of dyes builds up in the system, it can lead to changes of the optical properties. Previously studies have been conducted to investigate the white water system at Iggesund Paperboard Workington Ltd. mill. Suspicion of a potential dye buildup in the white water system arose because of notable changes in the optical properties of the collected samples. An assumption was, when the concentration of dye increases in the white water system, it led to changes of the optical properties. The purpose of this project was therefore to investigate if/how potential dye buildup occurred in the white water system at Iggesund paperboard Workington Ltd. Mill. The system will be analyzed for dye buildup and to see if it influences the optical properties of the coated paperboard as a final product as well as how quickly it builds up in the system. This report contains a theoretical background for relevant knowledge about the white water system and optical properties of paperboard. The methodology for this project was to collect samples from the boardmachines’ white water system and analyze them through laboratory trials. Collected data is presented in the form of diagrams, trends have been investigated to validate assumptions. The dye dosage point was also analyzed through laboratory trials, to confirm or deny whether it is possible to achieve an optimal dosage point. The analysis showed that there were changes in the optical properties in the white water over time, as a result of dye buildup. Due to the complex system and different parameters that may affect the system, the sample collection needs to be extended further for a more precise conclusion. Such as how the dye responds to longer shuts and addition of polymers. Apart from what influenced the optical changes in the white water system and may have affected the paperboard, when the top coating from the production is applied, no changes or variations cannot be seen. Therefore giving the conclusion, that the changes of the optical properties do not influence the paperboard as a final product.