Instrument principle
The core measurement principle of the Schopper air permeability meter is based on Poisel's law, which describes the relationship between the flow rate of a fluid through a porous medium in a laminar flow state and the pressure difference. For porous materials such as paper, its air permeability is usually expressed in terms of air permeability, that is, the volume of air passing through a specimen per unit area per unit time under a certain pressure difference. The instrument calculates the air permeability or permeability of paper by measuring the air flow rate through a specified area of paper at a constant pressure difference, or by measuring the pressure difference required at a fixed air flow. The process is carried out under standardized temperature and humidity conditions to ensure comparability and accuracy of results.
Standard method
The measurement process strictly follows relevant international and national standards, such as ISO 5636 series or GB/T 458 series standards. Key parameters include test area, applied differential pressure, measurement time, and ambient temperature and humidity. Typically, the test area is fixed at 10 cm², and the differential pressure is selected from 1.0 kPa to 2.5 kPa, depending on the paper type. The instrument uses precision pressure sensors and flow meters to automatically record data and calculate the final result. Air permeability units are often expressed in μm/(Pa·s) (breathable resistance) or mL/min (air permeability), depending on the standard method used.
Operation process
The instrument is mainly composed of a test head, a pressure regulation system, a flow measurement unit, a control panel and a data processing module. The test head is equipped with a ring clamp to ensure that the specimen is held flat and without side leakage. During operation, the specimen is first placed in the test area and the air tightness check is initiated. The system then automatically applies a set differential pressure and measures the stabilized air flow. The entire process is controlled by a microprocessor, reducing human operating errors. After the measurement is completed, the screen displays the results directly and can be connected to a computer for data export and further analysis.
Applications:
Paper air permeability is an important energy indicator for packaging paper, filter materials, special industrial paper and cigarette paper. For example, the air permeability of cigarette paper directly affects the combustion rate and composition of the flue gas; The air permeability of filter paper is related to filtration efficiency and resistance; The air permeability of the wrapping paper affects the freshness and protection performance of the product. By accurately measuring air permeability, manufacturers can optimize process parameters, control product quality, and meet the specific needs of downstream applications.
Notes:
The accuracy of the measurement results is influenced by several factors. The uniformity of the test body, temperature and humidity conditions, fixture pressure and system air tightness need to be strictly controlled. The ambient temperature and humidity should be kept within the standard range, usually 23±1°C and 50±2% RH to avoid changes in air permeability caused by changes in paper moisture content. In addition, the instrument needs to be calibrated regularly using standard reference materials to ensure traceability of the measurement chain. Operators should follow standard procedures to avoid wrinkling or damage during specimen clamping.
With the increase in sensor technology and automation, modern Schopper analyzers continue to improve in terms of measurement accuracy, speed and data integration. Some of the new instruments have fully automated test sequences, real-time environmental compensation, and networked data management functions. In the future, data analysis combined with artificial intelligence may help to more deeply correlate air permeability with paper microstructure, providing more powerful tools for material development and online quality control.
References
ISO 5636-2: Determination of air permeance (medium range).
GB/T 458-2008: Determination of air permeability of paper and cardboard.
Paper Physics: A Review of Key Concepts and Testing Methods.