Tone Value Increase Target Derivation for Uncoated Papers
Deriving uncoated paper TVI targets demands separating optical light scattering from capillary ink absorption using M1 spectral data to set inverse RIP curves.
Paper Porosity
Air Permeability
Volumetric gas flow measurement determines internal pore volume and void structure within paper webs. Standardized testing measures the time required for a specified volume of air to pass through a defined sheet area under fixed pressure differentials. Evaluating paper porosity predicts liquid absorption rates, adhesive penetration, and vacuum handling characteristics during converting operations.
Paper mills adjust refining and wet end pressing to control void space distribution.
Void Architecture
Gurley densometer testing records seconds needed for one hundred cubic centimetres of air to pass through one square inch of paper. Bendtsen porosity units express airflow in millilitres per minute through a standardized test surface area. Dense calendering flattens surface fibres and collapses internal voids, reducing overall sheet permeability.
High porosity allows rapid ink vehicle absorption, setting offset inks quickly while potentially lowering surface gloss. Low porosity retains ink vehicle on the surface, improving print gloss but extending ink drying times. Packaging converting machines rely on consistent air permeability to hold sheets against vacuum transport belts during high-speed feeder operations.
Coating applications seal surface pores, converting high-porosity base paper into smooth, impermeable printing substrates.
Fluid Limit
Excessive porosity causes ink pinholing and vehicle strike-through on thin paper grades. Extremely non-porous synthetic substrates prevent ink absorption entirely, demanding oxidative or ultraviolet curing systems. High humidity expands paper fibres, altering void geometry and changing air permeability test results.