Description

TAPPI T 648 – Viscosity of Coating Clay Slurry

1.1 This method describes a procedure for the determination of the low- and high shear viscosity of coating clays. This is accomplished by the preparation of a completely dispersed 70% solids aqueous clay suspension with incremental introduction of dispersant to obtain the optimum dosage (minimum viscosity) for the low and high shearing rates.

1.2 At 70% solids’ content, not all clay slurries are sufficiently fluid to permit viscosity determinations with the usual instruments. The test as written is thus substantially limited in its applicability to the type of coating clays suitable for high solids coating. A similar test procedure using lower solids content is informative in the case of clays such as calcined and delaminated coating clay that are not suited to testing at 70% solids. In each case the solids content should be maintained at as high a level as possible to accentuate differences between the clays in question.

1.3 Coating clays are available in predispersed slurry form, generally at 69.5-70.5% solids. The procedure for determining the viscosity characteristics of these clay slurry shipments is also incorporated in this method.