Stalagmite Formation in LWC-Paper Coating, 1993 Coating Conference Proceedings

Olli T. Suontausta

"Stalagmites" refers to coating colour bleeding from beneath the blade and accumulating behind the blade. The purpose of the present study was to investigate the formation of stalagmites occurring during the production of LWC paper. The aim was to investigate how stalagmite formation is influenced by coating colour viscosity and elasticity, and by the conditions prevailing under the blade.

The formation of stalagmites behind the blade was detected by photographs, which were taken of the blade at one minute intervals. The amount of stalagmite formation was measured using an image analyzer.

No correlation was found between coating colour viscosity and stalagmite formation. Increasing elastisity caused, however, a certain increase in stalagmite formation. One of the basic factors affecting stalagmite formation

appears to be the shear forces acting in the coating colour layer under the blade. These forces increase as the coater speed is raised and as the gap between blade and paper (coat weight) is reduced. The shear forces in the coating colour also increase with increasing solids volume concentration in the coating colour.