An Examination of Various Evaluation Tests for Paper Sizing - A Proposal to Use the Klemm Test for Sizing Evaluation

This study compared various sizing evaluation tests, including the Stockigt and Cobb tests as the most popular methods, by using papers of varied basis weight and varied dose of sizing agent. Many tests, including Stockigt, Hercules, KBB and Cobb, are severely affected by basis weight. None of these except Cobb are sufficiently sensitive to evaluate light sizing, because they measure water penetration in the Z-direction and the distance is quite small. The Klemm test, which has been used for water absorptiveness of non-sized paper, determines the absorptiveness in the X-Y direction and is sufficiently sensitive to evaluate even light sizing as an absolute sizing degree. The interconnected pore structure of paper makes the absorptiveness in the X-Y direction equivalent to that in the Z-direction. The Standard Klemm test gives the absorptiveness height for 10 min testing and is independent of basis weight. A shorter testing time than 10 mm could be used but the absorptiveness height is too small to detect for heavy sizing. Further, the heading edge of water uptake is often vague, and thus the absorptiveness height can be replaced by the weight increase due to water absorption (absorptiveness weight) as a more accurate measure. Furthermore, the absorptiveness weight measured by the Klemm test which was linearly proportional to basis weight could be normalized with basis weight and specimen width (1.5 cm), and thus was indicated as absorptiveness height. This test was proposed as an absolute evaluation for sizing degree (Klemm test for sizing evaluation) in this report because it is independent of basis weight and is sensitive enough to measure sizing degree accurately even with light sizing.