Water Based Coatings That Keep a Pack inside the Fibre Stream
Water-based dispersion coatings achieve food barrier requirements while maintaining full fiber repulpability and standard mill recovery yields.
Gurley Densometer Air Permeability
Porosity Measurement
Air resistance measured by the time required for a specific volume of air to pass through a defined area of paper indicates the tightness of the sheet structure. This gurley densometer air permeability is measured in seconds, where a higher value represents a less porous material. It is a critical metric for paper that will be used in vacuum-fed machinery or for grades requiring specific coating hold-out.
It is often the first check performed when a new batch of paper arrives for a high-speed printing job.
Testing Apparatus
A weighted inner cylinder slides down inside an outer cylinder filled with oil, forcing air through the clamped sample. The resistance provided by the fibre network determines the speed of the descent. Fine-tuned adjustments to the refining process at the mill are used to hit target values for different end uses.
Practical Implication
High porosity is often necessary for papers that must be glued quickly, as it allows the moisture from the adhesive to escape into the sheet. In contrast, a very dense sheet is needed for high-quality printing to prevent the ink from sinking too deeply into the fibres. Excessive air resistance can cause problems with suction-based sheet separation on the press.