High Shear Rheology Calibration Procedures for Aqueous Latex Anilox Evacuation
Calibrating capillary rheometers with Bagley and Mooney corrections ensures precise aqueous latex transfer from anilox cells, preventing spatters and excess coat weight.
Pinhole Defects
Barrier Discontinuity
Microscopic void channels penetrating functional coating layers degrade the containment properties of packaging substrates. On barrier-coated paper and paperboard, pinhole defects represent localized discontinuities where liquids, gases or oils bypass protective polymers to wet underlying cellulose fibres directly. These microscopic apertures form during liquid application, drying or hot extrusion lamination when film integrity fails locally.
Standard dye stain tests, such as turpentine or red oil penetration protocols, detect these imperfections by visual tracking of bleeding through the back of the sheet. Modern optical scanners identify them down to micron scales on operating converting lines.
Defect Genesis
Air entrainment within liquid coating formulations creates microscopic bubbles that burst during drying, leaving behind crater-like passages that fail to close before solidification. Rough base paper topography exacerbates the problem when outstanding surface fibres puncture thin coating films during rod or blade application. If drying rates are set too aggressively, rapid boiling of residual moisture blows open pinhole defects in semi-solidified functional layers.
In extrusion lamination, moisture present within the paperboard vaporises upon contact with molten polymer extrudates, rupturing the continuous film. High-porosity raw stock requires pre-calendering or primer coats to smooth the fibre bed and prevent structural punctures.
Packaging Consequence
Gas transmission barriers drop substantially when microscopic channels breach the continuous synthetic layer. Oxygen transmission rates surge beyond target specifications, degrading sensitive food products through rancidity and microbial oxidation. Liquid packaging cartons holding juices or dairy products suffer structural softening when fluids wick along pinhole defects into the paperboard structural core.
Grease-resistant fast food containers exhibit unsightly grease staining along fold lines where pinholes coalesce into tears. Eradicating pinhole defects requires optimized wet coat weights, anti-foaming chemistry and regulated baseboard formation.