How it works:
A paper absorbency analyzer is an instrument used to quantify the penetration behavior of liquids on the surface of paper. Its core principle is based on capillary action and liquid diffusion kinetics, which evaluates the liquid penetration resistance of paper by measuring the permeation time or diffusion area of the liquid on the surface of the paper under specific conditions. In sizing degree evaluation, the instrument usually simulates the behavior of ink or water on the paper surface and is tested according to standard methods such as GB/T 460 or TAPPI T 441. When the instrument works, a standard test droplet is placed on the surface of the paper, and the time it takes for the liquid to be fully absorbed or diffused to a predetermined radius is recorded using a sensor or image analysis system, which is negatively correlated with the degree of sizing application.
Definition of sizing degree
Sizing degree refers to the ability of paper to resist liquid penetration after sizing treatment, and is a key indicator to measure the durability, printability and performance of paper. High sizing paper can effectively prevent ink bleeding, ensure print clarity, and improve the stability of the paper in humid environments. Evaluating the sizing degree not only helps to optimize the dosage and distribution of sizing agents in the papermaking process, but also provides a basis for the quality control of different applications of paper (such as writing paper and packaging paper). While traditional evaluation methods rely on subjective judgment, the application of absorbance analyzers enables objective and reproducible quantitative evaluation.
Operation process
Standardized steps need to be followed to evaluate sizing degree using a paper absorbency tester. First, the sample is placed on an instrument test platform to ensure that the surface is flat and wrinkle-free. Adjust the ambient temperature and humidity to standard conditions (e.g., 23°C, 50% RH) to reduce external interference. Subsequently, a specified volume of test solution (commonly standard ink or distilled water) is applied to the paper surface through a dosing dropper while the timing device is activated. The instrument automatically monitors the liquid infiltration process and stops timing when the liquid completely disappears or when the diffusion diameter reaches a set threshold. The permeation time t is recorded and may be calculated in combination with the diffusion area A. In general, the degree of sizing can be estimated by the following empirical formula:
S = k / (t × A)
where k is the instrument calibration coefficient. Each set of samples was tested at multiple points to obtain an average value to ensure representative results.
Influencing factors
The test results of the measuring instrument are affected by a variety of parameters and need to be strictly controlled to ensure the accuracy of evaluation. The main parameters include the properties of the test fluid, the height of the droplet, the orientation of the paper, and the environmental conditions. For example, the viscosity and surface tension of the test liquid directly affect the permeation rate. The drop height should be consistent to avoid impact differences. The direction of the fiber arrangement of the paper (longitudinal or transverse) can lead to anisotropic penetration behavior, and bidirectional testing is recommended. In addition, the type of sizing agent (e.g., alkylenone dimer or rosin gum) and the porosity of the paper substrate can also significantly change the absorbency. The following table lists common influencing factors and their control requirements:
| Influencing factors | Control requirements |
| Test fluid temperature | Maintain at 23±1°C |
| Droplet volume | Standard volume 0.1 mL |
| Paper pretreatment | Constant temperature and humidity balance for 24 hours |
| Number of test points | No less than 5 points/sample |
Use Cases:
Paper absorbency tester has been widely used in quality inspection and research and development in the paper industry. For example, in the production of cultural paper, the neutral sizing process can be optimized and the paper printing performance can be improved by measuring the sizing degree. In the world of wrapping paper, testing helps assess the paper's ability to resist moisture, ensuring product protection features. Both domestic and foreign standard systems have detailed regulations on the use of instruments, such as the Chinese national standard GB/T 460 "Determination of paper sizing degree" and the international standard ISO 535 "Determination of paper water absorption". These standards unify test conditions and result presentation, facilitating cross-regional quality comparison. The following table compares the core parameters of some of the criteria:
| Standard name | Main test conditions: |
| GB/T 460 | Standard ink is used, osmotic time method |
| TAPPI T 441 | Water osmosis method, which measures the diffusion diameter |
| ISO 535 | The Cobb method focuses on the quality of water absorption |
Although the paper absorbency tester provides a reliable means for evaluating the degree of sizing application, there are still some limitations. For example, the instrument takes a long time to test paper with high sizing degree, which may affect efficiency; For rough surfaces or coated paper, the liquid diffusion pattern is complex, and it is necessary to combine image analysis technology to improve accuracy. Future development trends include the integration of high-resolution cameras and artificial intelligence algorithms to achieve real-time penetration trajectory tracking and 3D penetration model construction. At the same time, the promotion of green sizing agents requires instruments to adapt to new bio-based test solutions to be closer to actual application scenarios.
References
1. Research on the method of determination of paper sizing degree, Papermaking Science and Technology, 2020.
2. GB/T 460-2008, Determination of sizing degree of paper.
3. TAPPI T 441 om-09，Water absorptiveness of sized paper and paperboard.
4. ISO 535:2014，Paper and board — Determination of water absorptiveness.