Ink Holdout and Dot Gain When a Stock Changes Grade
Changing stock grades alters micro-porosity and light scattering, shifting ink holdout and dot gain, requiring immediate press curve and ink film adjustments.
Ink Vehicle Absorption
Substrate Porosity
Hydraulic fluid penetration within a paper sheet defines this parameter, identifying the velocity at which a non-pigmented carrier liquid migrates through a fibrous network. This ink vehicle absorption quantifies the interaction between surface sizing agents and base sheet voids during high speed offset printing. It dictates the rate at which binders and resins enter the capillaries of a substrate immediately following the nip.
The measurement requires a controlled contact time where a drop of standardized oil encounters the paper surface under gravity. Boundary conditions apply to stocks with heavy mineral coatings or barrier films that prevent fluid ingress by blocking the surface pores completely.
Surface Capillarity
Differential pressure across the sheet thickness drives the liquid deeper into the bulk structure as the mechanical press force ceases. Through ink vehicle absorption, a mill manages the drying speed of traditional oil based formulations by modifying the internal pore distribution of the paper matrix. Low penetration values lead to high gloss holdout because the pigments remain elevated on the print surface instead of sinking into the sheet.
High values generate matt finishes but risk strike through where the carrier fluid migrates to the reverse side of the packaging board. Process variables include refining intensity in the paper machine wet end and the chemistry of the size press application. Calendering pressure alters these void geometries, changing the rate of fluid uptake during the subsequent converting phases.
Processing Tolerance
Tight limits on this flow property prevent mottling or picking issues during multicolour production runs on lithographic equipment. Excessive ink vehicle absorption creates uneven colour density across the printed image because the substrate steals the fluid before the tack can balance properly. Printers monitor these variations to adjust the drying temperature and ink viscosity in real time.
Converters demand specific target windows to ensure that coatings bond correctly to the sheet surface without lifting the underlying fibres. Uniformity of the measurement across a master roll proves that the sheet chemistry remains stable during the entire manufacturing run. An optimal rate provides sufficient adhesion of the print layer while maintaining the aesthetic finish of the final package.