Dissolved substances from coated broke

A paper machine made coating base paper over a cycle in which the grammage declined as in the top graph. The machine ran a neutral pH with added soda ash to improve the curing of the alkyl ketene dimer (AKD) size. The conductivity reflected the freshwater baseline (about 0.4 mS/cm) plus the added alkalinity giving a total conductivity of 2-3 mS/cm. The retention aid program comprised a low molecular weight cationic polymer followed by a polyacrylamide with fairly constant doses on output. The machine experienced variable sizing (Top graph) despite increased addition of AKD and deposition problems at the press section, which were both most severe during production of the lower grammage base paper.

The size press pick up and coating formulation varied quite considerably, leading to an increase in the concentration of dissolved solids in the recycled coated broke. There were several factors involved in the significant decline in wire retentions (Middle graph), which played a large part in the sizing and deposition problems, including the following:

The drop in grammage

Increased thick stock fines content

The increased anionicity of the broke due to the rising content of pigment dispersant (Bottom graph).