Packaging paper friction coefficient testing measures the static and kinetic slip properties that determine how wrapping papers perform on high-speed packaging lines, during printing and lamination, and in stacked storage and transport. Accurate determination of the coefficient of friction (COF) enables manufacturers to balance machine runnability against stack stability while complying with international standards such as ISO 15359 and ASTM D1894. This technical guide explains the test principle, sample types, measurement procedures, typical acceptance ranges, and practical applications of COF testing for packaging papers.
Technical Overview
The coefficient of friction (COF) is defined as the ratio between the tangential friction force resisting relative sliding motion and the normal force pressing two surfaces together. For packaging paper, two values are measured and reported:
- Static coefficient of friction (μs): the ratio measured at the instant sliding begins, calculated from the peak force required to initiate movement between two paper surfaces or between paper and another material.
- Kinetic coefficient of friction (μk): the ratio measured during continuous sliding at constant velocity, calculated from the average force required to maintain movement.
Friction behavior is a critical quality attribute for packaging paper. If the COF is too low, stacks of bags or sheets may slip, collapse, or shift during palletizing and transport. If the COF is too high, paper may jam, wrinkle, or misfeed in high-speed converting equipment such as vertical form-fill-seal machines, envelope and bag makers, and printing presses. Well-controlled friction therefore directly influences production efficiency, product protection, and end-user safety.
Several recognized standards govern the determination of friction properties for paper and flexible packaging materials:
- ISO 15359 — Paper and board: determination of the coefficients of static and kinetic friction using the horizontal plane method.
- ISO 8295 — Plastics film and sheeting: determination of the coefficients of friction, frequently applied to coated and laminated papers.
- ASTM D1894 — Standard test method for static and kinetic coefficients of friction of plastic film and sheeting, widely used for coated packaging substrates.
- GB/T 10006 — Chinese national method for friction coefficients of films and sheets, technically aligned with ISO 8295.
- TAPPI T 815 — Coefficient of static friction of packaging papers by the inclined plane method.
- TAPPI T 816 — Coefficients of static and kinetic friction of corrugated and solid fiberboard by the horizontal plane method.
Testing Samples
Wrapping and Sack Kraft Paper
Uncoated kraft paper used for grocery bags, industrial sacks, and wrapping applications is tested paper-to-paper to verify stack stability and reliable feeding. Both the outer (print) side and inner side may be evaluated, and measurements are typically performed separately in the machine direction and cross direction because fiber orientation produces anisotropic friction behavior.
Coated and Laminated Packaging Papers
Corrugated Board and Linerboard
Linerboard and corrugated board are tested to predict case erecting performance, stacking friction, and pallet load stability. TAPPI T 816 provides the recognized horizontal plane procedure, while anti-slip liner grades are verified against elevated COF targets.
Sample Preparation and Conditioning
Specimens are cut to the dimensions specified by the selected standard, free from wrinkles, creases, and visible defects, and must not be touched on the test surfaces because fingerprints and contaminants measurably alter results. Unless otherwise agreed, samples are conditioned to equilibrium in the standard atmosphere of 23 °C and 50% relative humidity in accordance with ISO 187, following the sampling principles of ISO 186 for paper and board.
Testing Items
Typical friction measurement programs for packaging paper include the following test items:
- Static coefficient of friction, paper-to-paper, for stack and pallet stability assessment.
- Kinetic coefficient of friction, paper-to-paper, for sliding and feeding behavior prediction.
- Static and kinetic COF of paper against metal, typically stainless steel, simulating packaging machine contact surfaces.
- COF of paper against polymer films, glass, or other package contact materials for multi-material packaging systems.
- Side-specific evaluation, for example outer print surface versus inner sealing surface.
- Direction-specific evaluation in machine direction and cross direction.
As general industry guidance, machine-runability applications typically target kinetic COF values between roughly 0.20 and 0.40, while stack stability applications often require static COF values of approximately 0.40 or higher. Anti-slip papers may be specified with values well above these ranges. Acceptance criteria should always be agreed between supplier and converter based on the actual application.
Testing Methods
Horizontal Plane Method (ISO 15359, ASTM D1894)
A motorized COF tester draws a standardized sled across a flat test bed at constant velocity while a calibrated load cell records the friction force. One specimen is fixed to the horizontal plane and a second specimen is attached to the sled base, with a defined sled mass and contact area, for example the 200 g, 63.5 mm square sled specified in ASTM D1894. The drive speed is prescribed by the method, commonly 100 mm/min in ISO 8295 and GB/T 10006 and 150 mm/min in ASTM D1894. The static coefficient is calculated from the first peak force and the kinetic coefficient from the mean force over the specified sliding distance, in each case dividing the measured force by the normal force.
Inclined Plane Method (TAPPI T 815)
One specimen is clamped to a plane that is tilted slowly until a sled resting on it begins to slide. The static coefficient of friction equals the tangent of the sliding angle. The method is simple and well suited to static friction screening of packaging papers, but it does not yield kinetic friction values.
Instrumentation and Good Testing Practice
- Verify load cell calibration and sled mass before each test series, and handle specimens only with gloves or by non-test edges.
- Clean contact surfaces and the instrument bed between determinations to prevent transfer of coatings, oils, or fibers.
- Perform a minimum of five valid determinations for each surface pairing and direction, reporting individual and mean values.
- Record specimen orientation, side tested, conditioning history, and any deviation from the standard atmosphere, since moisture content strongly influences paper friction.
- For regulatory or commercial disputes, testing can be performed by accredited third-party laboratories operating under ISO/IEC 17025 quality systems.
Applications
Friction coefficient data for packaging paper support a wide range of industrial uses:
- Flexible packaging conversion: verifying that paper and coated substrates feed, form, and seal reliably on vertical and horizontal form-fill-seal lines.
- Printing and finishing: predicting sheet transport behavior on printing presses, cutters, and folding equipment.
- Bag and sack manufacturing: confirming stack stability of finished bags and controlled slip during counting and feeding.
- Corrugated packaging: evaluating case erecting, stacking, and pallet load stability for transport simulation.
- Food and consumer wrapping: qualifying greaseproof, waxed, and laminated papers for hygienic and functional performance.
- Quality control and R&D: incoming material inspection, coating formulation development, and supplier qualification programs.
- Compliance verification: obtaining standardized test reports from accredited third-party laboratories for customer specifications and trade documentation.
FAQ
What is the difference between static and kinetic coefficient of friction?
The static coefficient describes the resistance at the moment sliding starts and is calculated from the peak force, while the kinetic coefficient describes resistance during continuous sliding and is calculated from the average force. Static values are always equal to or higher than kinetic values for the same material pairing.
What friction values are suitable for packaging paper?
There is no universal target because the ideal value depends on the application. As a guideline, kinetic COF of approximately 0.20 to 0.40 supports smooth machine runnability, while static COF of about 0.40 or higher improves stack and pallet stability. Purchase specifications should define limits based on the end use.
Which standard should be used for testing?
ISO 15359 is the primary method for paper and board using the horizontal plane principle. ASTM D1894, ISO 8295, and GB/T 10006 are preferred for coated or film-laminated substrates, while TAPPI T 815 and T 816 cover packaging papers and corrugated board respectively. The standard should be agreed in the test plan before testing begins.
How do humidity and temperature affect the results?
Paper is hygroscopic, and moisture content changes surface properties significantly. Higher relative humidity generally increases the friction of many paper grades. For this reason, specimens must be conditioned at 23 °C and 50% relative humidity in accordance with ISO 187, and all test conditions must be reported with the results.
Can friction between paper and other materials be measured?
Yes. The same horizontal plane instruments can measure COF between paper and stainless steel, polymer films, glass, or other packaging materials, which is essential for simulating real machine and package contact conditions.
How many specimens should be tested?
A minimum of five valid determinations per surface pairing and direction is customary, with additional replicates when variability is high. Mean values, individual values, and any outliers should be documented in the final test report.
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