The air permeance of papers has a major importance in the specifiction of materials for the packaging and printing industries. The air permeance is the flow of air through unit area under unit pressure difference in unit time. This is under specified test conditions and is expressed in u m/(Pa.s).
The Densometer is very user friendly due to it's built-in computer. It is also extremely reliable due to it's fully automatic operation. This ensures preventing the risk of human errors. It offers complete statistics using an exclusive testing software. It also has a parallel port for the connection of a local printer. And a RS232 serial port for the connection to a computer.
Gurley Method of measuring air permeance of paper
This method measures the amount of time required for a certain volume of air to pass through a test specimen. The air pressure is generated by a gravity-loaded cylinder that captures an air volume within a chamber using a liquid seal. This pressurized volume of air is directed to the clamping gasket ring, which holds the test specimen. Air that passes through the paper specimen escapes to atmosphere through holes in the downstream clamping plate.
Importance of measuring Air permeance for paper materials
The air resistance of paper may be used as an indirect indicator of Z-directional fluid permeance, as well as other variables such as: degree of refining, absorbency (penetration of oil, water, etc.), apparent specific gravity, and filtering efficiency for liquids or gases. Air resistance is influenced by the internal structure and also the surface finish of the paper. Internal structure is controlled largely by the type and length of fibers, degree of hydration, orientation, and compaction of the fibers; as well as the type and amount of fillers and sizing. The measurement of air resistance is a useful control test for machine production; but due to the number and complexity of factors outlined above; careful judgment should be used in the specification limits for air resistance.
What is Air permeance?
Air resistance is the resistance to the passage of air, offered by the paper structure, when a pressure difference exists across the boundaries of the specimen. It is quantified by obtaining the time for a given volume of air to flow through a specimen of given dimensions under a specified pressure, pressure difference, temperature, and relative humidity.