Abstract
In recycled paper processes, stickies are at the origin of many production disturbances, such as machine breaks, defects in paper and converting problems. At the end of the recycling process, the most abundant and disturbing macro contaminants are fragments of pressure sensitive adhesives. These particles adhere to machines clothes, and clog the felts or even cause the break of the running paper web. The contamination is typically evaluated by measuring the total stickies concentration in the pulp after screening. However, industrial experience shows that it is difficult to correlate this stickies concentration with the occurrence of process disturbances. We suggest that only the amount of stickies that is effectively exposed at the surface of the sheet to the machine clothes is disturbing and is at the origin of runnability problems. In this work, we recall the definition of the stickies exposure, and use it to anticipate the effect of geometrical parameters on the fraction of stickies that are exposed at the surface of the sheet. Parameters such as stickies length and thickness, sheet thickness, or stickies orientation in the z-direction, are investigated. A new sensor is developed to characterise stickies in their 3 dimensions (without prior pressing), and discriminate them from other type of contaminants. Improvements compared to classical stickies measurements methods are discussed. The exposure of real stickies populations to machine clothes is measured in handsheets, and compared with results from the modelling.
Download PDF