Forming Method
The deliberate separation of different fibre furnishes into distinct layers within a single headbox allows the manufacture of paperboard with tailored structural properties. Through stock stratification, a paper machine can place high-quality virgin fibres on the surface and cheaper recycled fibres in the core of the sheet. This technique utilizes internal vanes or dividers inside the headbox nozzle to prevent the different pulp streams from mixing before they reach the wire.
It enables the production of a multi-ply board with high bending stiffness and excellent printability.
Layer Engineering
The physical process relies on keeping the stock flows parallel and laminar as they exit the slice. By maintaining distinct velocities and pressure zones for each layer, the headbox deposits a structured jet onto the forming section. This method reduces the need for multiple headboxes, which decreases the physical footprint of the forming section of the machine.
It also optimizes the use of chemical additives by concentrating them only in the layers where they are needed.
Interface Limitation
Poor bonding between the layers can lead to delamination during high-speed printing or converting. When the moisture content between the stratified layers varies too much, the internal bond strength drops and the board splits under tension.
