MEASUREMENT OF SMALL-SCALE PERMEANCE VARIATION, PaperCon 2010 Conference

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A probe for the measurement of small-scale air permeability was developed. The air permeability of a circular measurement area with a diameter of 2 mm is measured. The measurement conditions can be adjusted to be similar to that of standard laboratory method. The probe is mounted on an x-y table which allows the measurement of permeance variations of a sample area with a size of up to 200 mm x 200 mm. The distance between the centers of the measurement locations is 2.7 mm. This corresponds to approximately 6000 individual measurement results that can be presented as a 2-dimensional permeance map. Permeability measurements on different paper grades show that small-scale permanence variation exists that cannot be detected with the standard laboratory devices. The variation can be large with a typical coefficient of variation in the order of 25 to 50%. Interestingly, the typical size of the permeance variation can be different from that of the sheet formation. Furthermore, both positive and negative correlation with formation can be found. This suggests that several mechanisms exists that give rise to permeance variation. An investigation on a printed sack paper sample showed, that printing can have a considerable influence on the permeance of the final product.