Dimensional stability

Paper is hygroscopic, i.e., it can absorb or release moisture, and this property enables it to reach a moisture equilibrium with the surrounding air. As a side effect of this, the paper expands when it absorbs moisture and shrinks when it releases it. In other words, highly dimensionally stable paper is paper that only experiences minor dimensional changes when subjected to changing ambient humidity conditions.

Dimensional changes often have one or more negative effects. One example is in laminated composites with various layers, where the changes can result in the composite rolling up, as well as in poor layflat performance. Above all, however, poor dimensional stability leads to problems when it comes to printing processes. The reason for this is that paper moisture often changes between individual printing units as a result of the ink drying process, which in turn results in the paper losing moisture. When this moisture loss results in excessive shrinkage, it becomes impossible to print the color of the next printing unit with the correct dimensions.

This is why an MG cylinder with a diameter of more than 7,300 millimeters, the biggest of its kind worldwide, has been installed at Koehler Paper’s Production Line 8. This cylinder is a drying cylinder that smooths and dries paper surfaces without stretching the web lengthwise, resulting in a significant improvement in dimensional stability.