Printability of Fibres and Vessel Elements from Oak Kraft Pulp

Abstract

The evaluation of printability is usually done on large printed areas; imperfections on a microscopic scale have been mostly ignored, in spite of their obvious importance. The unevenness of the paper surface often originates from non-uniformity in the morphology of the fibrous material. Thick fibres or particles standing out from the paper surface will produce dark spots, while the very thin, small ones will cause ‘valleys’ having lighter tones. With the increased use of hardwoods, which may contain 10-50 per cent by volume or 10 per cent by weight vessel elements of 50-500 μm in diameter, whereas the fibres may be only 15 μm, these problems are even more serious.