Immobilization Cell for CVO Series Rheometers

Allows the measurement of the rheological properties of coatings applied to a porous substrate during the immobilization process. A vacuum may be used to generate a controlled pressure drop across the substrate.

Water retention and immobilization are key properties for successful paper coating mixes. Paper coatings are aqueous dispersion of binder, pigments and co-binders (water retention aids / rheology modifiers). During the coating process these are applied onto an absorbent, porous base. Water in the coating can be adsorbed into the base. If this absorption is too rapid, coating defects can occur due to drying and immobilization of the coating, which would give streaks in blade coating and excessive orange peel in metered size presses for example. Conversely, if a coating has too high a water retention, it will not immobilize and penetrate into the base, losing base coverage and the functional properties of the coating are reduced. Coating mixes are therefore formulated to give good water retention.

A common method of measuring water retention is gravimetrically, whereby pressure is applied to a known volume of the coating mix and the amount of water removed is measured via an absorbent paper. This static method gives a quick and easily understood number but does not replicate the kinetics of the dynamic situation on a coating machine. The Immobilization Cell is able to reproduce a de-watering environment under shearing conditions giving measurements of any rheological parameter.

For studying the effect on immobilization due to changes in: