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.
Ink Tack Picking
Surface Cohesion
Adhesive bond strength dictates the resistance a paper substrate offers against film rupture during high speed printing. Ink tack picking occurs when the internal tension of a drying fluid exceeds the surface integrity of the sheet. Fibres lift from the structure because the pull force required for separation outstrips the bonding energy of the cellulose matrix.
Print technicians measure this threshold to calibrate the viscosity of fluids against the physical properties of the stock.
Mechanical Load
Tension develops at the nip point where the plate cylinder transfers an image to the moving web. A sticky ink film creates a drag force that pulls vertically on the paper surface. When the velocity of the press increases, the rate of film splitting triggers a rapid acceleration in the separation force.
Low internal sizing levels or high clay coating porosity lower the resistance of the material. Press operators mitigate damage by adjusting the tack additives in the fountain solution or slowing the production cycle to reduce the mechanical stress placed on the sheet.
Performance Constraint
Material failure results in accumulation on the rubber blankets that ruins image sharpness after brief intervals. Excess debris transfers back into the dampening system and causes contamination of the ink supply. Stable print quality depends upon maintaining a margin between the peak tension of the ink and the threshold of the substrate surface.
Press performance stays within defined bounds only when the chemical nature of the fluid is compatible with the mechanical properties of the paper grade.