Particle Distribution
Particle movements through the forming fabric of a paper machine alter the distribution of small fibres and mineral fillers within the sheet. During the dewatering process, wet-end fines migration causes these tiny particles to move toward the wire side of the paper. This movement creates a difference in composition between the top and bottom surfaces.
Dewatering Interaction
The speed of the machine and the type of drainage elements used on the table influence the severity of the particle shift. Rapid water removal pulls more material through the fibre mat, whereas a gradual drainage allows the fines to be trapped more evenly. This effect is a primary cause of two-sidedness in paper, where one side is smoother or more absorbent than the other.
Structural Influence
Uneven particle distribution affects the way the paper curls when it is exposed to moisture or heat. If wet-end fines migration is not controlled with retention aids, the resulting sheet may exhibit poor surface strength on one side. This condition leads to linting or dusting during the printing process.
It also impacts the penetration of adhesives and coatings, making it difficult to achieve a uniform finish across both sides of the substrate. Laboratory tests on the ash content of each layer help mill operators adjust the foil angles to minimize these gradients.
