Mineral Coating Pigment Packing Micro Geometry and Pore Volume Distribution
Pigment micro-geometry and particle packing dictate coat pore volume distribution, controlling ink vehicle absorption rate, print gloss, and coat strength.
Coating Consolidation Mechanics
Pore Network Formation
Structural phase transitions during the removal of water from aqueous pigment and binder slurries govern the development of paper coating porosity and surface finish. Initial drying draws water through evaporation and base paper absorption until coating consolidation mechanics drive suspended mineral pigments and latex spheres into mutual contact at the first critical immobilization point. At this juncture, the fluid suspension transforms into a rigid, fluid-saturated gel structure that resists further hydrodynamic leveling.
Continued dewatering introduces air into the interstitial voids, establishing the permanent pore network and bulk density of the mineral layer. Final mechanical properties depend directly on the packing geometry established during this transition.
Shrinkage Stress
Capillary forces generated within the narrowing liquid menisci compress the porous mineral network during secondary dehydration. These contraction forces induce substantial in-plane stresses, which can cause micro-cracking if the binder glass transition temperature exceeds the local drying temperature. Understanding coating consolidation mechanics allows paper chemists to balance fast drainage rates against the formation of uniform, closed pigment matrices.
High binder levels cushion pigment contact points, distributing internal stresses and preventing localized surface fissuring.
Structural Boundaries
Base paper absorptivity and the solids content of the initial suspension govern the rate and location of the immobilization boundary. Highly absorbent raw paper accelerates liquid dewatering from below, creating a consolidation front that moves upward through the wet layer. Non-absorbent synthetic films force consolidation to occur exclusively from the top surface downward, altering the ultimate pore morphology.
The consolidation process terminates when all free liquid menisci recede and the binder polymer hardens fully.