Standardized Laboratory Methods for Evaluating Matte Print Coating Burnishing
Standard laboratory burnish evaluation uses controlled sled friction and 60-degree delta gloss measurements to quantify matte coating asperity degradation.
Asperity Deformation
Surface Compression
Topographical flattening under nip pressure describes the mechanical alteration of microscopic paper surface high points during calendering or printing. Mill operations measure asperity deformation to quantify how peaks in the fibre network collapse into adjacent void spaces under high loading. This structural shift determines the final smoothness of coated or uncoated boxboard before fluid application.
Excess nip load crushes internal fibre bonds and reduces bulk yield.
Contact Mechanism
Pressure distribution across the contacting roll faces governs how individual surface features yield elastically or plastically during conversion. When paperboard enters a steel or soft nip, shear stresses concentrate on projecting fibre structures before the bulk sheet compresses. Hydraulic pressure from trapped moisture within the web can resist local collapse at high speeds.
High temperature softens lignin and hemicellulose, accelerating plastic flow of micro-peaks at lower mechanical force. Lowering line load preserves board stiffness while altering surface micro-topography.
Calendering Limit
Printing press performance depends on maintaining uniform ink transfer without sacrificing bending stiffness through over-densification. Uncontrolled asperity deformation flattens surface features completely but degrades Z-direction tensile strength and box stacking strength. Laboratory testing uses liquid penetration methods and optical profilometry to monitor peak height reduction across varied nip temperatures.
The alteration of surface topography ceases to improve print gloss once microscopic voids are fully sealed, leaving further mechanical force to purely destroy bulk volume.