Friction is an important property during the converting and end-use of almost every paper product. High friction is essential for sack and corrugated containers during transportation and storage, for controlling the paper roll functionality and to obtain good runnability of the paper in a printing press. The reliability of copiers and printers depends on a constant friction of the paper sheet, especially during sheet feeding. Low paper-paper friction and low paper-metal friction are required for example during the corrugating of fluting.

 

Friction testing is very sensitive to variations in measurement conditions. In order to achieve reproducible results the test variables must be standardized. At Innventia, the development of friction testing equipment has been going on for many years. The work has resulted in a ISO standard for friction testing (ISO 15 359, Paper and Board, Determination of the static and kinetic coefficients of friction- Horizontal plane method) and in the development of a friction tester that follows the guidelines of the ISO standard.

 

The test pieces are 6 cm wide and about 15 cm long and are cut in a special cutting device allowing for contact-free handling of the test area (6x6 cm). Ten test pieces, yielding five replicas are necessary to test a sample. During a friction test three slidings are performed yielding the static and the kinetic coefficients of friction for each sliding. Great care must be taken when preparing and sending the crude samples to the lab, because any physical contact irreversibly alters friction.