Quantifying Surface Elevation Variance along Score Lines Using Optical Profilometry
Optical profilometry quantifies score elevation variance down to sub-micron resolution, identifying die wear and coating micro-fractures before carton assembly.
Peak Height Sz
Surface Roughness
Profile roughness measurement defines the micro geometry of paper and board substrates before and after converting operations. Peak height sz represents the maximum profile peak height within a sampling length evaluated on a stylus profilometer trace. Secondary converting machinery relies upon this topographical parameter to predict ink transfer efficiency and adhesive wetting behavior across coated paper surfaces.
High peak height sz values generate micro voids beneath printing plates, which causes dot skipping and incomplete ink coverage during high speed flexographic runs. Substrate manufacturers control calendering nip pressure to suppress excessive peak heights without crushing internal fiber networks.
Coating Adhesion
Specialized barrier emulsions flow into valleys and around asperities during blade coating applications on packaging boards. Peak height sz dictates the minimum dry coat weight required to achieve complete encapsulation of surface fibers. Insufficient coating thickness leaves towering peaks exposed to moisture penetration and gas transmission, which compromises grease resistance in food packaging applications.
Converters measure this parameter after pigment application to verify that smoothing stations level the base sheet adequately for subsequent extrusion lamination.
Print Quality
Gravure printing cylinders demand rigorous control over paper micro topography to prevent ink starvation in fine halftone screens. Peak height sz establishes the upper boundary for surface irregularities that doctor blades and impression rollers must accommodate without causing print mottle. Excessive local peaks prevent uniform contact between the substrate and the printing blanket, leading to missing dots and reduced optical density in solid printed areas.
Press operators adjust impression cylinder force when incoming paper batches exhibit elevated peak height sz values, compensating for surface variations to maintain register and color fidelity.