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Abstract
Fibres that acquire a z-direction tilt in the forming process help bond adjacent strata of the paper sheet, increasing z-direction shear. Fibre tilt manifests itself as a measurement difference when directionally sensitive tests are conducted “toward headbox” or “toward reel.” Seven of eight different paper grades ranging in grammage from 73 to 268 g/m
2 were found to show this difference for Scott-internal-bond tests, directional-brightness tests, or both. Test results were compared for 180° rotations in the machine direction and cross-machine direction. Three-eights of the rotations showed significant directional effects at the 75–100% confidence level, including roughly equal numbers of Scott bond and brightness tests. However, the two tests did not reinforce each other strongly, possibly because of depth variations in z-direction tilt. A model emphasizing tilt of MD fibres caused by rush or drag conditions was well supported by Scott-bond testing. Directional effects in CD testing appear to require a more complex model based on cross flows in the forming section.
Keywords
Fibre tilt,
grain,
felting,
z-direction,
directionality,
running direction,
extension,
shear,
Scott internal bond,
brightness,
tape pull,
fibre pull,
ply-bond,
sheet-splitting,
Student’s t-test,
confidence,
significance,
Fourdrinier,
rush,
drag,
cross flows,
paper,
mechanical properties,
testing,
papermaking,
orientation,
fibers,
optical measurements,
optical properties,
fiber analysis,
fiber properties,
dimensional stability,
shear strength,
microfibril angle,
brightness,
fiber orientation
Citation
Vahey, David W.; Considine, John M. 2010. Tests for z-direction fibre orientation in paper. Appita Journal. 63(1): 27-31, 41.
