Application of Paper Absorbency Tester in Sizing Process

Rationale

Paper absorbency tester is a special instrument used to quantitatively evaluate the penetration and absorption behavior of liquids on the surface of paper. Its core principle is based on capillary action and fluid dynamics, which measures the time, absorption, or permeation rate required for a liquid to be absorbed by simulating the contact process between a liquid (usually water or a specific reagent) and paper under specific conditions. Common testing methods include the Cobb value method, Klemm method, etc., which follow international standards (such as ISO 535, TAPPI T441) or national standards (such as GB/T 1540) to ensure the comparability and repeatability of test results. The instrument is usually composed of a sample holding device, a liquid supply system, a timing device and a measuring unit, which can accurately control key parameters such as liquid contact area, pressure and temperature.

Influence mechanism

Sizing is a key process in the papermaking process, aiming to change the hydrophilic water balance on the surface of paper fibers by adding sizing agents (such as alkyl enone dimer, rosin gum, etc.), thereby regulating the resistance of paper to liquids. The effect of the sizing process directly determines the final application properties of the paper, such as printing suitability, writing impermeability, and packaging moisture resistance. Sizing agents form a hydrophobic film on the surface of the fibers, reducing the capillaries between the fibers or changing their surface energy, thereby delaying or preventing the penetration of liquids. The paper absorbency tester plays the role of a "diagnostic tool" in this process, helping process personnel evaluate the impact of parameters such as sizing uniformity, sizing agent dosage and drying conditions by quantifying absorbency indicators (such as Cobb value, g/m²). There is a clear correlation between absorbency data and sizing process parameters, for example, an increase in sizing agent concentration usually leads to a decrease in Cobb value, which can be approximated as a linear or exponential model:

C = C₀ · e^-k·ρ

where C is the absorbency measurement, C₀It is the absorbency benchmark of the unsizing paper, k is the constant related to the type of sizing agent and process conditions, and ρ is the concentration of the sizing agent. This model helps optimize the process window and avoid performance defects caused by under- or over-sizing application.

Application Practice

In the development of sizing process and production control, the application of paper absorbency tester runs through multiple links. First, in the R&D stage, the paper absorbency under different sizing formulas, addition amounts and processing temperatures can be systematically tested to quickly screen out the process scheme that meets the target performance. Secondly, on the production line, regular sampling tests can monitor the sizing stability in real time and detect absorption abnormalities caused by raw material fluctuations, equipment wear or process drift in a timely manner. For example, if the Cobb value is continuously elevated, it may indicate that the sizing agent is uneven dispersion or the temperature of the drying section is insufficient, and the process parameters need to be adjusted. In addition, the meter can be used to evaluate the synergistic effect of compound sizing (e.g., surface sizing combined with internal sizing) or to study the effect of recycled fiber content on sizing efficiency. Here are some examples of how common sizing issues correlate with absorbency testing:

Through this data feedback, process personnel can implement targeted adjustments, such as optimizing the sizing agent emulsification process, calibrating the amount of coating, or improving the drying curve, thereby reducing raw material waste while ensuring product quality.

Test Standards

To ensure the effective application of absorbency assay results in the sizing process, standardized testing procedures must be strictly followed. This includes sample pretreatment (e.g., temperature and humidity balance), instrument calibration (e.g., liquid volume accuracy, timing accuracy), and operational specifications (e.g., contact time control, surface residue removal). Differences in test conditions between standards (e.g., liquid type, contact time, sample size) can cause results to be not directly comparable, so the standard version used should be clear when benchmarking processes. When interpreting the data, it is necessary to combine auxiliary parameters such as paper quantification, thickness and pore structure for comprehensive analysis to avoid misjudgment of a single index. For example, high-dosing paper may show lower absorption per area, but the actual penetration depth may still be large. It is recommended to establish long-term data trend graphs and correlate them with process logs to identify cyclical changes or incremental shifts. In cross-departmental communication, absorbent data should be presented in clear graphs with descriptions of test conditions to facilitate collaborative decision-making.

Epilogue

As the paper industry evolves towards intelligence and sustainable development, the technology of paper absorbency testers is also constantly upgrading. The new instrument is integrating automated sample injection, in-line testing, and data cloud synchronization to make it more suitable for continuous production environments. At the same time, for emerging processes such as bio-based sizing agents and nano-modified coatings, testing methods may need to be extended to non-aqueous liquids or specific chemical reagents to more comprehensively characterize the performance of functionalized paper. In the sizing process, absorbency analyzers have changed from a simple quality inspection tool to a key support for process optimization and innovation. Through precise measurement and scientific analysis, it helps the industry play a substantial role in improving product performance and reducing energy and material consumption, reflecting the value contribution of testing technology to the manufacturing process.

References

1. International standard ISO 535:2014, Paper and cardboard – determination of water absorption (Cobb method).

2. Papermaking Technology (3rd ed.), Light Industry Press, Chapter: Sizing and Dring.

3. Review of Paper Physical Properties Testing Technology, Journal of China Paper Society, 2020.

4. TAPPI T441 standard, water absorption of paper and cardboard (Cobb test).