This method is used to measure the air resistance of approximately 6.45 cm² (l in²) circular area of paper using a pressure differential of 1.22 kPa. The recommended range of the liquid column instrument is from 5 to 1800 seconds per 100 mL cylinder displacement. For more impermeable papers the time requirements become so excessive that other techniques are preferable. This method measures the volume of air that passes through the test specimen, along with any possible leakage of air across the surface; therefore it is unsuitable for rough-surface papers which cannot be securely clamped so as to avoid significant surface and edge leakage. For a similar method of measuring air resistance that tests paper at a higher pressure (approx. 3 kPa), and has higher resolution in measuring smaller air volumes, refer to TAPPI T 536. For a method of measuring air permeance at pressures up to 9.85 kPa, using both smaller and larger test areas, refer to TAPPI T 547. 

 

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. 

 

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.

 

To perform adequate testing ten, 8.5” x 11” sheets are requested. Ten replicates requiring an area of 2.0” by 2.0” are to be tested. Areas that contain creases or visible damage can not be tested. If sample quantity is limited, testing can be done by sampling fewer sheets and/or performing fewer replicates. This sampling information should be adequate for four or five TAPPI methods per request. If more methods are requested, please call to verify the necessary amount of sample.                                

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IPS cannot sell or otherwise provide standards, specifications, or test procedures to third parties.