Derived from Kubelka-Munk theory using R0, R-infinity and grammage, it reflects the total area of fiber-air and pigment-air interfaces in the sheet. Bleached chemical pulps typically fall around 20 to 40 m2/kg, mechanical pulps run higher, and fine pigments such as PCC or titanium dioxide much higher still. Refining, wet pressing and calendering all lower it by bonding fibers together and closing air gaps.
Scattering coefficient fell from 42 to 36 when they pushed refining, which explains the opacity loss.
Filler gains taper off: past a certain loading the particles crowd together, and each extra percent buys less scattering.
Also heard as
- scattering coefficient
- s
- specific scattering coefficient
Related terms
Kubelka-Munk theory
Two-flux light model linking a sheet's reflectance and opacity to its scattering and absorption coefficients.
Light-absorption coefficient
Per-grammage measure of how much light a paper absorbs, written k and given in square meters per kilogram.
Opacity
A sheet's ability to hide what lies behind it, expressed as a percentage from readings over black and white backings.
Filler
Fine mineral powder added to papermaking stock to raise opacity, brightness and smoothness and to cut cost.
Fines
Fiber fragments and small particles that pass a fine screen and have an outsized effect on sheet optics.