A NEW ANALYSIS OF FIBER ORIENTATION EFFECTS ON PAPER FORMATION

The micro-variability of grammage influences the variability of mechan ical and hygro-strain properties of paper. This is of particular impor tance in high-speed multicolour printing, for example. Anisotropy, due to the preferential orientation of fibre axes in the machine directio n, may be thought to interfere with the micro-scale variability of gra mmage for purely geometrical reasons. This has been analysed for stand ard fibre networks with specific anisotropy, using statistical geometr y. The coefficient of variation of grammage has been computed as a fun ction of the orientation ratio for three orientation distribution func tions. For a one- or two-term cosine orientation distribution function , the uniformity of grammage is strictly not influenced by the extent of orientation. For a wrapped Cauchy orientation distribution function , a more oriented paper is slightly less uniform but negligibly so. Fo r a rectancular orientation distribution function, the paper is found to be slightly more uniform when it is more oriented. The overall resu lt of this study is that the uniformity of grammage as measured in pra ctice is not significantly influenced, if at all, by the degree of ani sotropy.