Downgauging Folding Boxboard without Losing Compression Strength
Downgauging folding boxboard demands increasing core bulk and outer ply elastic modulus to preserve caliper and bending stiffness under McKee formula laws.
Refining Intensity
Specific Energy
The amount of mechanical energy applied per impact to pulp fibres during stock preparation controls the swelling and bonding potential of the fibres. The process variable known as refining intensity determines the balance between fibre shortening and external fibrillation. It is measured in watt-seconds per metre or joules per gram of pulp.
This parameter does not predict the behavior of different wood species under the same refining conditions, because hardwoods and softwoods have different structural limits. It is used instead to control the consistency of a single pulp grade.
Fibre Modification
High energy impacts cut the fibres and reduce their average length. By controlling refining intensity, mills can choose to bruise and swell the fibres rather than cutting them. This bruising increases the surface area available for hydrogen bonding when the paper sheet dries.
It improves the tensile strength of the sheet.
Property Tradeoff
Pulp drainage and bulk decrease as fibres are more refined. If refining intensity is too high, the pulp becomes slow-draining and the resulting board is too dense. Mills adjust the disc gap and speed of the refiner to keep this variable in the target range.
This adjustment helps maintain the bulk of the board.