Optimizing Creasing Tool Geometry for Barrier Coated Boxboard Converting
Optimizing creasing geometry for barrier board requires expanding female channel width and applying polished male rule radii to prevent barrier film splitting.
Cobb Testing ISO 535
Water Absorption Method
Cobb Testing ISO 535 defines the standardized laboratory procedure for determining the quantity of water absorbed by paper and board surfaces under specified conditions over a given time frame. Mill operators apply this protocol to quantify sizing efficiency and liquid penetration resistance across corrugated containerboards and packaging substrates. Liquid absorption values dictate how a substrate accepts water based flexographic inks or aqueous barrier coatings during converting operations.
Production lines require strict adherence to these limits because excessive absorption causes adhesive failure on sealing machines and structural softening in humid storage environments. Testing blocks a fixed area of test material beneath a metal ring, pours a measured liquid volume onto the surface for a standard duration, and removes surplus moisture with a calibrated roller before weighing the dry sheet against the post test mass. Grams of water absorbed per square meter establish the final metric value.
Surface Sizing Boundary
Paper mills alter internal chemical additives and surface starch application levels to control the rate of fluid uptake during high speed converting runs. Substrates destined for liquid packaging carton production demand exceptionally low absorption rates to prevent fluid migration through cut edges, whereas absorbent newsprint requires entirely different sizing thresholds. Low Cobb values indicate high hydrophobic resistance, preventing glue starvation during high speed box folding and gluing.
High absorption leads to warping on automated corrugated laminating lines and poor print density when aqueous pigment dispersions sink too deeply into the fibrous matrix. Sizing chemistry parameters must balance penetration against surface ink drying speeds to maintain print clarity without sacrificing lamination strength.
Gravimetric Calculation
Laboratory technicians execute this gravimetric procedure by clamping conditioned samples onto a flat rubber mat beneath a cylindrical metal ring with a defined internal cross section. Liquid flows onto the upper surface for durations typically spanning sixty seconds or one hundred eighty seconds depending on the specific product grade specification. Technicians invert the assembly onto absorbent blotting paper immediately after the exposure period ends, rolling a heavy metal cylinder across the back of the test piece to remove excess surface moisture without extracting liquid from within the sheet structure.
Analytical balances measure mass differentials to milligram precision. Final calculations convert mass gains into standardized absorption figures that converters use to verify incoming raw material compliance against purchasing specifications.