Water Based Coatings That Keep a Pack inside the Fibre Stream
Water-based dispersion coatings achieve food barrier requirements while maintaining full fiber repulpability and standard mill recovery yields.
Surface Holdout
Coating Porosity
Surface holdout governs the capacity of a paper substrate to retain liquid ink components on the exterior web rather than allowing excessive vehicle penetration into the underlying fibrous matrix. Porosity control requires balancing binder migration against rapid solvent evaporation during the drying phase of offset printing. Excessive absorption reduces final gloss and diminishes optical density because pigment particles lose their protective liquid carrier before film formation finishes.
Calendering pressure alters the interstitial void volume of the base sheet to restrict capillary draw rates. Papermakers measure this property through air permeance testing under standardized pressure differentials across the sheet.
Ink Absorption
Solvent migration depends directly upon the size distribution of capillary networks formed during wet web consolidation and subsequent pressing. Low retention values lead to print mottle because uneven fiber density creates localized variation in binder penetration across the web. Pigment entrapment occurs when starch sizing closes surface pores sufficiently to prevent high molecular weight resins from migrating inward.
Gravure printing demands high retention grades to prevent dot gain and edge raggedness caused by uncontrolled vehicle drainage. Printers adjust fountain solution chemistry to mitigate the adverse effects of variable porosity on ink tack stability.
Print Density
Final color saturation correlates directly with the volume of vehicle remaining available for pigment suspension on the outer boundary. Substrates exhibiting high retention yield sharper halftone dots and higher gloss readings because the ink film dries entirely above the uppermost fiber layer. Insufficient holdout causes pigment starvation within shadow areas, which lowers contrast ratios and introduces a washed appearance to multi-color halftone reproductions.
Laboratory densitometry evaluates these optical gains by comparing solid ink density readings against untreated control samples. Surface holdout determines the economic efficiency of high speed printing by reducing the total volume of ink required to achieve target optical density specifications.