Optimizing Score Line Geometry for Low-Fibre-Length Recycled Substrates
Low-fibre recycled board requires widening female matrix channels to 1.8 times caliper and reducing penetration depth to prevent top-liner rupture.
Moisture Conditioning ISO 187
Atmospheric Standard
Standardized atmospheric control ensures reproducible physical testing of paper, board and pulps across international testing laboratories. The standard protocol for moisture conditioning ISO 187 specifies a constant laboratory environment maintained at 23 degrees Celsius and 50 percent relative humidity with continuous air circulation. This pre-test conditioning process brings cellulose materials into moisture equilibrium before measuring physical properties like tensile strength and bursting resistance.
It establishes uniform baseline testing conditions that eliminate variations caused by changing ambient weather or storage environments. The boundary of this standard applies to physical laboratory testing conditions and does not govern industrial web drying settings on paper machines.
Equilibrium Process
Cellulose fibers exhibit hygroscopic behavior, absorbing or desorbing water molecules until internal moisture balances with ambient air humidity. Under moisture conditioning ISO 187, test specimens are suspended individually to allow unhindered air contact across all exposed surfaces until successive weighings show constant mass. Reaching true moisture equilibrium requires sufficient exposure time, typically ranging from 4 hours for lightweight paper grades to 24 hours for heavy paperboard substrates.
Variations in relative humidity during physical testing alter fiber swelling, board caliper and internal bond strength measurements. Laboratory technicians monitor wet-bulb dry-bulb psychrometers or calibrated electronic sensors to verify ambient stability before running strength evaluations. Standardizing sample moisture content ensures valid comparisons between board samples manufactured at different mill sites or tested across distinct seasonal periods.
Hysteresis Behavior
Desorption paths yield higher equilibrium moisture content than absorption paths at identical relative humidity levels due to sorption hysteresis. Skipping pre-conditioning treatment invalidates comparative physical test results between competing paperboard grades.