Introduction
The air permeability of paper is a key indicator for evaluating its structural density and suitability, especially in the fields of packaging, filtration and specialty papers. The Bentsun method and the Geerle method are two widely used classic methods for determining paper air permeability, and their principles, measurement parameters and application scenarios are significantly different. This article will systematically explain the differences between the two methods, in order to provide a clear technical reference for related detection work.
Differences between method principles and measurement parameters
The Bentson method mainly measures the flow of air through paper, while the Görley method measures the time it takes for air to pass through paper. The Bentegen method characterizes air permeability by the volume of air passing through a unit area of paper per unit of time at a specific pressure, and the result is usually expressed in milliliters per minute. The Görley Rule characterizes resistance by measuring the time it takes for a fixed volume of air to pass through a defined area of paper, and its results are usually expressed in seconds, with higher values indicating tighter paper.
Instrument structure and test process comparison
The thermometer is usually composed of a pressure regulation system, a measuring head and a flow meter, and a fixed pressure difference is formed on both sides of the specimen during the test to measure the air flow velocity. The Geerley instrument is composed of a closed cylinder, a specimen holding device and a timer, which measures the time it takes for air to pass through the specimen under constant pressure to equilibrate the pressure in the cylinder. The calibration methods and specimen preparation requirements of the two instruments also have their own emphasis, with the Benter method focusing more on the precise control of the pressure difference and the Geerlet method emphasizing the tightness of the system.
Standard system and applicable fields
The two methods correspond to different standard systems and are suitable for different types of paper. The special method is more common in the evaluation of loose papers such as filter paper and absorbent paper. Görley's law is more suitable for testing high-density papers such as parchment paper and high-barrier packaging paper.
| method | Mainly suitable for paper types |
| Bent's method | Filter paper, absorbent paper, certain printing papers |
| Geralfa | Parchment paper, high-density wrapping paper, greaseproof paper |
Data relationships and conversion considerations
Theoretically, the physical quantities measured by the two methods are correlated and can be approximately converted by formulas. Factors such as paper structure, test conditions, and instrument characteristics are considered for conversion, and empirical formulas or comparison tables are often relied upon in practical applications, and direct conversion may be biased.
The conversion relationship can be approximated as:
T ∝ 1 / Q
where T is the Gehlet value (seconds) and Q is the Bentsen air permeability (mL/min).
Conclusion
There are clear differences between the Bentley method and the Geerley method in terms of principle, instrument, applicable object and data expression. The selection method should be based on paper characteristics, industry standards and specific testing purposes. Understanding the differences between the two can help assess the breathability of paper more accurately and ensure that the test results are valid and comparable.
References
ISO 5636-2: Determination of air permeability of paper and paperboard (Bentegen method)
TAPPI T460: Standard Test Method for Air Permeability of Paper (Görley Method).
Handbook of Test Methods for Paper Industry, China Light Industry Press