When issues such as unstable paper feeding, double-sheet feeding, misaligned cartons, or inconsistent fold positioning occur during the processing of paper and paperboard, it is often difficult to quickly identify the specific cause. Feeder settings, roller pressure conditions, ambient humidity, paper flatness, variations between material batches, and the friction properties of the material’s surface can all contribute to these abnormalities. Paper and paperboard COF testing provides objective, quantifiable data that helps manufacturers identify the root causes of these issues and ensure stable, productive operations.
A broader understanding of COF testing for packaging materials can help manufacturers evaluate friction behavior across different materials, applications, testing standards, and production conditions.
Where Does Surface Friction Matter in Paper and Paperboard Packaging?
Surface friction affects the performance of paper and paperboard throughout their entire lifecycle—from surface treatment of raw materials through processing, packaging, stacking, and transportation. Throughout their lifecycle, paper and paperboard frequently come into contact with other surfaces, and the resulting friction affects production stability as well as the performance of the final packaging.
- Paperboard Production and Storage: Maintaining Sheet Stability
Paper and paperboard are typically produced, stored, and transported in stacks of individual sheets. The friction between sheets of paper or paperboard helps maintain stability under external forces such as vibrations and handling impacts.
- Printing, Coating and Finishing: Changing Surface Interaction
Paper and paperboard typically undergo surface treatments such as printing, coating, varnishing, and lamination; however, these processes alter the surface properties of the material, affecting its friction characteristics when in contact with other surfaces. Smooth coated surfaces reduce sliding resistance, while certain coatings increase surface friction.
Friction coefficient testing can be used to determine whether the friction characteristics of modified surfaces meet the requirements for subsequent production stages.
- Sheet Feeding and Separation: Controlling the Balance Between Holding and Releasing
During automatic paper feeding, friction must provide sufficient traction to ensure stable paper transport and smooth separation between sheets. If friction is too high, it may cause double or multiple sheets to be fed at once, paper jams, and other issues; if friction is too low, the paper may slip, resulting in unstable feeding.
- Conveying and Positioning: Transferring Motion and Maintaining Accuracy
As the sheets move through the rollers, conveyor belts, and guide systems, friction helps transfer motion and maintain their position. This prevents slippage or positioning errors.
- Folding, Die Cutting and Converting: Preventing Unwanted Material Movement
During die-cutting, creasing, folding, and gluing, friction helps keep the cardboard in place under mechanical force. Insufficient friction may cause the material to shift, resulting in inconsistent forming results. Excessive friction increases resistance and reduces processing efficiency.
- Finished Package Handling, Stacking and Transportation: Preventing Sliding Under External Forces
After production, finished cardboard boxes and paper products are subjected to vibrations, acceleration, and handling forces during stacking and transportation. Appropriate friction helps prevent the packaging from shifting or collapsing, ensuring stability during stacking and transportation.
Paper and Paperboard Materials Requiring COF Testing
- Coated Paper and Paperboard: coatings can change surface slip behavior
- Folding Carton Board (FBB/SBS): commonly used for folding cartons and consumer packaging
- Corrugated Board and Containerboard: where friction can affect conveying and stacking
- Kraft Paper and Packaging Paper: where surface structure and moisture may affect handling
- Recycled Paper and Paperboard: where material variation can influence surface behavior
- Printed, Varnished, and Laminated Paperboard: where finishing processes can significantly change the final surface
Why Printing and Coating Change the Friction Behavior of Paper and Paperboard?
The original surfaces of paper and paperboard consist of fiber structures, pores, and microscopic topographical features; these surface characteristics determine how the material interacts with other surfaces when in contact or sliding against them.
During coating, printing, and other surface treatment processes, newly applied materials—such as coatings, inks, and varnishes—cover the original fiber structure and form a surface layer with varying hardness, smoothness, and adhesion properties. At the same time, subsequent processing steps such as calendering and lamination further alter the texture and roughness of the paper’s surface.
Due to changes in surface structure and material composition, paper or paperboard exhibits different friction characteristics before and after treatment.
Should You Test Paper and Paperboard Before or After Printing?
Whether to conduct testing before or after printing depends primarily on your testing objectives.
Testing Before Printing
Testing unprinted paper or cardboard provides insight into the substrate’s inherent friction properties. It is typically used for:
- Raw material quality control
- Comparing paper grades
- Monitoring production consistency
- Determining material specifications prior to processing
Testing After Printing and Finishing
Evaluating the friction properties of the final product. This is typically used to assess:
- The effects of ink or coatings;
- The performance of the finished paper;
- Whether the processed material meets downstream processing requirements.
If additional processes such as coating, varnishing, or lamination are applied after printing, the COF evaluation should generally be performed after the final surface treatment because this represents the actual condition of the material in use.
Should You Test Both Before and After Printing?
In fact, this largely depends on the purpose of the evaluation.
Pre-printing tests help manufacturers understand the inherent friction characteristics of base paper or cardboard, which is very useful for assessing the consistency of raw materials and selecting materials suitable for processing.
Post-printing tests, on the other hand, provide a more practical evaluation of the finished material, particularly in situations where the printed surface comes into direct contact with other sheets of paper, machine parts, or packaging materials during production and use. This helps identify potential issues caused by changes in surface friction, such as unstable paper feeding, stacking problems, or handling difficulties.
Factors Affecting Paper and Paperboard COF Testing Results
Surface Structure and Roughness
The surface structure of paper and paperboard depends not only on their appearance but is also influenced by their internal fiber network, pore structure, and microscopic surface topography. Factors such as fiber composition, papermaking processes, calendering methods, and surface smoothness can alter the contact conditions on the material’s surface, thereby affecting its friction properties.
Printing, Coating, and Surface Finishing
Processes such as printing, coating, varnishing, and lamination, which act on the material’s surface, alter the friction characteristics of paper and paperboard. The application of ink and other materials may change the surface roughness of the material, creating new surface properties.
Moisture Content and Environmental Conditions
Paper and paperboard are materials highly susceptible to humidity; changes in humidity affect fiber flexibility, surface structure, and interactions between contacting surfaces.
The friction characteristics of materials tested under dry conditions may differ from those of the same materials tested under conditions of higher humidity.
Material Composition and Paper Grade
Fiber type, recycled content, fillers, and board structure influence surface interaction. Different materials, such as coated board, kraft paper, and corrugated board, naturally exhibit different friction characteristics.
Contact Surface and Material Pairing
COF represents the friction between two contacting surfaces rather than a single material property. Paperboard-to-paperboard, paperboard-to-metal, and paperboard-to-polymer interactions may produce different friction results.
Test Conditions and Measurement Parameters
Factors such as sliding speed, applied load, specimen preparation, and test procedures can influence coefficient of friction results. Variations in test parameters alter the contact pressure and sliding behavior between surfaces, leading to differing coefficient of friction results.
How to Diagnose Paper and Paperboard Packaging Line Problems: Is Surface Friction the Root Cause?
When faults such as double feeding, slippage, misalignment, and unstable stacking occur with paper or cardboard on a production line, the root cause is not always related to friction. Factors such as equipment parameter settings, changes in material, or variations in surface friction can all lead to production failures.
Manufacturers should first identify the failure behavior, evaluate possible causes, and then use COF testing to verify whether material friction is affecting performance.
A Systematic Troubleshooting Approach
| Production Symptom | Possible Causes to Investigate | When to Suspect Surface Friction | How to Verify |
| Double-sheet or multiple-sheet feeding | Feeder settings, suction force, sheet flatness, moisture variation, stacking conditions | The issue occurs only with certain paper grades, suppliers, or after printing/coating processes | Compare sheet-to-sheet static COF between stable and problematic materials under the same production conditions |
| Paperboard slipping during feeding or conveying | Roller wear, insufficient contact pressure, conveyor condition, machine speed settings | Slipping appears after changing paperboard surface properties or using different finishes | Evaluate paperboard-to-feeder or conveyor surface COF to determine whether traction is sufficient |
| Position deviation during printing, die cutting, or folding | Machine alignment, guide settings, material dimensional changes, feeding accuracy | Material movement becomes unstable even though equipment conditions remain consistent | Compare COF values between normal and problematic batches and check for friction variation |
| Packaging line performance changes after printing, coating, or varnishing | Coating thickness, curing condition, ink properties, surface contamination | The same paperboard performs differently before and after surface treatment | Measure COF before and after finishing processes to identify changes in surface friction behavior |
| Paperboard stacks or finished cartons shift during handling | Stacking method, package design, vibration, load conditions | Products move even though handling conditions remain unchanged | Test paperboard-to-paperboard or package-to-package COF under relevant conditions |
COF testing helps manufacturers determine whether material surface friction is contributing to production problems. By comparing stable and problematic materials under the same conditions, manufacturers can identify friction-related issues and establish suitable COF control ranges for reliable processing.
Which COF Test Standard Applies to Paper and Paperboard?
- ISO 15359:1999 — Paper and board — Determination of the static and kinetic coefficients of friction — Horizontal plane method is specifically applicable to paper and board.
- TAPPI/ANSI T 549 covers static and kinetic friction of uncoated writing and printing paper using a horizontal-plane method.
- TAPPI T 815 addresses the coefficient of static friction, or slide angle, of packaging and packaging materials, including shipping sack papers, corrugated and solid fiberboard, using an inclined-plane method.
How to Choose the Right COF Tester for Paper and Paperboard Applications?
When selecting a coefficient of friction tester, be sure to choose one that is compatible with the material properties of the test specimen, the friction behavior in the intended application, and the ultimate testing objective.
Step 1 : Match the Paper or Paperboard Application
The coefficient of friction tester must be capable of testing the types of materials you need to test. For example, kraft paper, folding cartons, and corrugated cardboard.
Step 2 : Measurement of Dynamic and Static Coefficients of Friction
The static coefficient of friction and the kinetic coefficient of friction describe the friction characteristics of a material at different stages, respectively. If you are investigating sheet separation and continuous conveying, a tester capable of measuring both static and kinetic COF provides greater testing flexibility.
Understanding the Difference Between the Coefficient of Static Friction and the Coefficient of Kinetic Friction→Static vs Kinetic Coefficient of Friction
Step3 : Match the Actual Friction Interface and Test Conditions
The selected tester should be capable of evaluating relevant friction interfaces—such as contact between paper and paper, cardboard and equipment, or cardboard and cardboard—to ensure that the test results effectively reflect actual production behavior or material performance.
Step 4 : Ensure Measurement Sensitivity and Stability
The friction behavior of paper and paperboard materials may undergo relatively minor changes due to coating, printing, humidity, or material variations. A coefficient of friction (COF) tester should possess sufficient sensitivity to ensure that subtle changes can be detected. High stability helps minimize measurement deviations and ensures that test results accurately reflect actual surface friction characteristics.
Step 5 : Support for Relevant Test Standards
A coefficient of friction tester should comply with relevant testing standards to ensure the reliability and comparability of test results.
Saicheng MXD-02 Coefficient of Friction Tester for Paper and Paperboard Testing
The Saicheng MXD-02 Coefficient of Friction Tester is specifically designed to evaluate the static and dynamic friction properties of sheet materials. It helps users analyze how surface friction affects material handling, feed stability, processing performance, and stacking behavior.
This tester supports coefficient of friction evaluations for various paper and cardboard applications, including coated cardboard, folding carton materials, corrugated cardboard, and the surfaces of finished packaging products. With its stable measurement performance and repeatable test results, the MXD-02 helps manufacturers compare material differences, evaluate the effectiveness of surface treatments, and establish friction control requirements for specific applications.
Conclusion
In paper and paperboard applications, surface friction is a critical factor that affects material separation, feeding stability, converting performance, and stacking reliability. By using Saicheng’s COF Tester, manufacturers can accurately evaluate the static and kinetic friction characteristics of different paper and paperboard materials, helping identify friction variations caused by material composition, coating, printing, or surface finishing processes.