In the field of paper production and processing, the friction properties of paper surfaces are one of the key physical parameters that affect their stacking, conveying, packaging and printing suitability. This property is often intuitively referred to as "slippery", and its quantified value is the coefficient of friction. Accurate measurement of the static and dynamic coefficients of friction of paper is essential for predicting the paper performance on high-speed presses, evaluating the sliding behavior of packaging materials on automated production lines, and ensuring the stability of finished product stacking. Measurement practices need to refer to a number of technical standards to ensure data consistency and comparability.
Measurement principle
The coefficient of friction is measured based on the classical law of friction. Static friction coefficient (μsis the ratio of the maximum tangential force to normal pressure required to activate two relatively stationary paper surfaces; and the dynamic friction coefficient (μkis the ratio of the force required to maintain constant sliding between the surface of the paper to the normal pressure. Its basic relationship can be expressed as:
μ = F / N
where μ represents the friction coefficient, F is the friction force, and N is the normal force perpendicular to the contact surface.
The mainstream measurement method is the planar sliding method. The paper sample under test is fixed flat on a horizontal platform, and another standard slider, usually covered with the same or specific dual material, is placed on it with a specified area and weight. The instrument drives the platform or slider to move at a constant speed, and the sensor accurately records the maximum force at the moment of start-up (corresponding to static friction) and the average force during sliding (corresponding to dynamic friction). Measurements should be performed under standard atmospheric conditions with constant temperature and humidity to eliminate interference with the moisture content and surface condition of the paper by ambient temperature and humidity.
Influencing factors
To obtain true, repeatable coefficient of friction values, the following variables must be tightly controlled:
Paper surface condition: The coating process, filler distribution, surface roughness and whether or not there is calendering will significantly change the surface energy and smoothness. Even for the same batch of paper, there may be microscopic differences between rolls or parts.
Environmental conditions: Relative humidity directly affects the hygroscopicity of paper fibers, thereby altering the softness and surface friction characteristics of the paper. Tests are usually conducted according to the temperature and humidity pretreatment and test conditions specified by ISO 187 or similar standards.
Test parameters: Slide quality (determining normal pressure), contact area, pull speed, and texture orientation of the paper (portrait or transverse) are all preset test parameters that must be consistent with the standard method employed and clearly stated in the report.
Sample handling and installation: The sample should be flat and wrinkle-free, with no visible defects. When fixing, ensure that it fits snugly against the test platform without bubbles or sagging, and prevents contaminants such as hand grease from affecting the test area.
Measurement standards
The internationally recognized paper friction coefficient test standards mainly include ASTM D4917, TAPPI T549 and ISO 15359. These standards provide detailed specifications for instrument calibration, sample preparation, test speed, slider characteristics, and result calculation. The following table compares some of the core requirements of these standards:
| Standard name | Main scope of application |
| ASTM D4917 | Static and dynamic friction coefficients between paper and cardboard (including corrugated cardboard). |
| TAPPI T549 | Coefficient of static friction between paper and cardboard (horizontal plane method) |
| ISO 15359 | Paper and cardboard Determination of static and dynamic friction coefficients |
| Common test speeds | 150 ± 30 mm/min |
| Common slider quality | 200 ± 5 g (contact area is typically 40 cm² or 64 cm²) |
| The results show | Means, standard deviations, and test surfaces, texture orientation, and humidity conditions are typically reported |
Data interpretation
The measured friction coefficient value needs to be interpreted in conjunction with the specific application scenario. For example, in high-speed rotary printing, too high a static friction coefficient may lead to difficulty in paper separation and cause double-sheet feed failure; while too low dynamic friction coefficient may cause the paper to slip during conveying, affecting the overprinting accuracy. For packaging stacking, a moderate static friction coefficient ensures the stability of the stack, prevents collapse, and facilitates manual or mechanical sorting and extraction. Systematic coefficient of friction testing allows manufacturers to optimize coating formulations and process parameters, while end users can scientifically predict the behavior of materials on their production lines, reducing downtime, reducing losses, and improving the quality consistency of the final product.
Conclusion
The measurement of the coefficient of friction on paper is a rigorous standardized physical test. It quantifies "smoothness" and transforms subjective feel into objective data, providing key quality control and performance prediction tools for the entire paper chain from production to application. The key to ensuring authentic measurements lies in strict adherence to standard methods, precise control of test conditions, and a deep understanding of the physical meaning behind the data. Continuous technical practices help to promote paper products that are more in line with the actual needs of downstream industries.
References
ASTM International. ASTM D4917-21 Standard Test Method for Coefficient of Static and Kinetic Friction of Uncoated Writing and Printing Paper by Use of the Horizontal Plane Method.
TAPPI Press. TAPPI T549 om-19 Static coefficient of friction of corrugated and solid fiberboard (horizontal plane method).
International Organization for Standardization. ISO 15359:1999 Paper and board — Determination of the static and kinetic coefficients of friction — Horizontal plane method.
Mark, R.E., Habeger, C.C., Borch, J., & Lyne, M.B. (Eds.). (2002). Handbook of Physical Testing of Paper. Marcel Dekker.