Mechanical Refining Impact on Multi Ply Boxboard Z Direction Tensile Development
Controlled low energy refining of middle ply mechanical pulp yields superior Z direction tensile development without caliper loss in multi ply boxboard.
Ply Bonding
Internal Adhesion
Internal strength of a multi-ply paper structure relies upon the bond force between individual layers. Ply bonding measures the internal stress required to cause delamination through the thickness of a substrate. Standard laboratory testing utilizes a z-directional tensile strength apparatus to pull the paper apart in the thickness dimension.
High levels of internal fiber entanglement prevent separation during aggressive converting processes or high-speed printing operations.
Manufacturing Calibration
Production parameters determine the integrity of the layers as the sheet forms on the wire. Refining intensity dictates the degree of fiber fibrillation and determines how well the mechanical interweaving of filaments occurs at the headbox. Low moisture content at the nip points of a press section increases the contact pressure which forces fibers into a permanent union.
Excessive dryness before the sizing press limits the ability of starch or synthetic adhesives to penetrate the interface and reinforce the connection. Machine direction tension profiles influence the alignment of fibers and sometimes create weak zones where the Z-strength drops below critical thresholds.
Performance Expectation
Finished packaging materials demand high resistance to splitting when subjected to folding or mechanical stress from vacuum suction cups on robotic lines. A weak internal union causes the surface of a box or carton to pull away during the application of self-adhesive tape or labels. Converters verify this physical characteristic to ensure that the material withstands the mechanical loads of high speed folding gluing equipment.
Proper control of the bonding process prevents total failure of a package under the weight of its own contents. A paper with insufficient internal bonding represents a structural risk because the substrate separates under simple handling forces.
Low Consistency Refining Energy Distribution across Fractionated Recycled Furnish
Splitting recycled furnish into long and short fractions before refining concentrates mechanical energy on long kraft fibres, cutting power use while boosting compression.