A new instrument for measurement of the out-of-plane dimensional stability of paperboard, PaperCon 2010 Conference

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Curl is a dimensional stability phenomenon common to all paper grades. In spite of its adverse effects on runnability in converting and on end-user properties, curl is often characterized with primitive methods with poor repeatability and accuracy. Research activities on paperboard at Innventia resulted in a new instrument prototype, which has been tested in the production control laboratories of three Scandinavian paperboard mills. The prototype houses multiple samples placed on a rotary table and it is equipped with an infra-red dryer to trigger the out-of-plane deformation of the samples.

The prototype identifies the samples, corrects for misplacement and misalignment and calculates the curl components implementing modern imaging technology based on a 3D-camera. We designed the prototype as a quality control instrument with high sample throughput (30–40 samples per hour) and high levels of automation. The instrument can be used for any paper grade with sufficient stiffness to minimize measurement artefacts due to the influence of gravity.

In the standard configuration, testing takes place on square samples with a surface of 100 cm². Yet, the 3D-camera system has been used to extend testing to samples of complex shapes and user-defined sizes.