Rationale
Water absorption analyzers are key devices used to quantify the absorption performance of paper and cardboard liquids. Its core principle is based on capillary action and liquid osmotic kinetics, which evaluates the hydrophilicity of a material by measuring the mass or liquid rise height of a standard liquid (usually distilled water or a specific solution) absorbed per unit area of the specimen under specific conditions. Common assays include the Klemm method (Cobb value method) and the capillary suction height method (Klemm method). Instruments typically consist of specimen holding devices, liquid tanks, timing devices, and weighing or altimetry systems to ensure that the testing process meets standardized time, pressure, and liquid contact conditions.
Application in toilet paper inspection
For toilet paper, water absorption is an important indicator of comfort and functionality. When determining, the Creem method is usually used according to standards (such as GB/T 461.1, ISO 535). The sample with a specified area is in contact with the water surface for a specific period of time (e.g., 60 seconds) at standard pressure, and then the excess liquid on the surface is quickly removed and the mass difference before and after water absorption is weighed to calculate the water absorption per unit area (Cobb value). This value directly reflects the rapid water absorption capacity of toilet paper, affecting its performance as a wiping material. Testing requires strict control of water temperature, contact time, and operational consistency to ensure comparable results.
Application in cardboard inspection
Absorbency testing of cardboard focuses on evaluating its resistance to liquid penetration, which is crucial for the protective properties of packaging materials. In addition to the Krem method, capillary suction height method is also commonly used to evaluate the capillary effect of the fiber structure inside the cardboard. According to the standard (such as GB/T 1540, ISO 5637), the lower end of the vertically suspended specimen strip is immersed in the liquid, and the height of the liquid rising along the specimen is measured within the specified time to characterize the diffusion rate of the liquid inside the material. This parameter helps predict the strength retention and barrier performance of cardboard in wet environments.
Operational points
To ensure the accuracy of the measurement, a number of parameters need to be standardized:
Liquid properties: Distilled or deionized water is usually used, and the temperature is controlled at 23±1°C.
Contact time: Depending on the type of material, it can range from seconds to minutes, and needs to be accurately timed.
Specimen pretreatment: The specimen needs to be balanced under constant temperature and humidity conditions (such as 23°C, 50% RH).
Operational consistency: including specimen placement, excess liquid removal and weighing speed.
The formula for calculating the test results is as follows:
C = (m₂ - m₁) × 100
where C represents the water absorption of the crem (g/m²), and m₁ and m₂ are the masses (g) before and after water absorption of the sample, respectively.
Instrument maintenance and calibration
Regular maintenance is the basis for ensuring the long-term stable operation of the absorbency tester. The liquid tank and clamping device should be cleaned daily to prevent residue from affecting the test. Calibration includes verifying the accuracy of the timing device, checking the accuracy of the weighing system (using standard weights), and confirming that the holding pressure of the specimen meets the standard requirements. It is recommended to calibrate periodically according to the instrument manual and national metrology regulations, and keep records.
The water absorption data provide a basis for the production quality control and application selection of toilet paper and paperboard. For toilet paper, proper water absorption helps balance softness with wet strength; For cardboard, lower water absorption tends to mean better moisture resistance. Producers can optimize this metric by adjusting the slurry ratio, slurping degree, or adding additives. The test data should be comprehensively evaluated in combination with other physical properties (such as tensile strength and thickness) to meet the needs of different application scenarios.
FAQs
| Problem manifestations | Possible causes and suggestions |
| The test results are poorly repeated | the sample is not fully balanced; fluctuations in liquid temperature; The operation time is inconsistent. |
| The water absorption value is abnormally high | The excess liquid on the surface of the specimen is not effectively removed; Weighing delay results in evaporation loss. |
| Instrument readings are unstable | The weighing platform is affected by vibration or airflow; Electronic components need to be checked. |
| The liquid rises unevenly | The cutting direction of the specimen is inconsistent; Fiber orientation affects capillary paths. |
References
GB/T 461.1 Determination of capillary aspirate height on paper and paperboard
GB/T 1540 Determination of water absorption of paper and paperboard (Krem method)
ISO 535 Paper and cardboard – Determination of water absorption – Creem method
ISO 5637 Paper and paperboard—Determination of water absorption—Water immersion method
TAPPI T441 Determination of Water Absorption of Paper and Cardboard (Krem Test)