ASTM Friction Test – COF Test Methods for Paper, Film & Packaging

Introduction: What Is the ASTM Friction Test and Why It Matters

Die ASTM friction test is critical in determining how materials interact when in contact—particularly under sliding conditions. This test plays a vital role in assessing the static und kinetic coefficients of friction of materials like plastic films, paper, paperboard, and nonwoven fabrics. In the packaging, medical, and electronics industries, frictional properties influence product performance, machinability, und user safety. Understanding how to properly conduct and interpret these tests ensures quality, consistency, and compliance with global standards.

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ASTM D1894: Friction Testing of Plastic Films and Sheeting

Purpose and Industry Relevance

ASTM D1894—Standard Test Method for Static and Kinetic Coefficients of Friction of Plastic Film and Sheeting—provides a reliable procedure to evaluate the slip properties of plastic materials. These properties are vital in film packaging applications, where ease of handling, machinability, and stackability directly affect manufacturing and consumer experience.

Test Mechanism and Significance

The method involves measuring the force required to initiate and maintain sliding between two surfaces—either film-on-film or film-on-another material—using a standardized sled and plane apparatus.

• Statischer COF represents the force to initiate motion.
• Kinetic COF reflects the force to sustain motion once sliding begins.

Key considerations outlined in ASTM D1894 include:

• Additive behavior: Films like polyethylene often include slip additives that bloom to the surface, influencing surface lubricity over time.
• Environmental sensitivity: Frictional properties change with temperature, humidity, and aging, so consistency in test conditions is critical.
• Directional consistency: The method recommends tests in the machine direction (MD) to ensure reproducibility.
• Surface condition and contamination: Human contact or folding can alter results; films should be handled with care and mounted smoothly.

Procedure Highlights

1. Specimen Preparation: A 250 mm x 130 mm film is secured flatly to the test plane; a 120 mm square is mounted on a sled.
2. Mounting Orientation: Always match machine directions of both plane and sled-mounted films.
3. Sled Setup: The sled is connected to a load cell via nylon filament, ensuring gradual force transmission.
4. Motion Initiation: The apparatus moves at 150 ± 30 mm/min until the sled overcomes static friction and slides.
5. Recording: Peak force during initial motion = Static COF; Average force during continuous sliding = Kinetic COF.

Limitations & Best Practices

• Films with high stick-slip tendencies may require metal tow lines instead of nylon for kinetic COF.
• Specimen reuse is prohibited unless studying aging or surface wear.
• Recorder response time must match the speed of friction development to avoid inaccurate peaks.

Cell Instruments offers automated COF testers designed for ASTM D1894, enabling precise control over speed, force, and temperature to ensure repeatable and valid test data.

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ASTM D202: Friction Testing for Electrical Insulation Paper

Purpose and Application

ASTM D202—Standard Test Methods for Sampling and Testing Untreated Paper Used for Electrical Insulation—addresses the mechanical and surface characteristics of insulation paper, which is used extensively in electrical and electronic devices. Among other physical properties, friction characteristics are assessed to ensure paper consistency during winding, layering, and installation.

Friction-Related Provisions in ASTM D202

While ASTM D202 covers a broad range of paper properties (e.g., tensile strength, thickness), its friction test components are crucial in evaluating:

• Slip resistance during handling.
• Layer-to-layer adhesion in multilayered insulation systems.
• Surface uniformity across production batches.

The friction tests in D202 focus more on coefficient of static friction, using procedures tailored to thinner, more fibrous substrates compared to ASTM D1894.

Key Testing Differences from D1894

• Substrates tested are typically paper-based, not polymer films.
• Testing emphasizes non-coated, untreated paper, ensuring raw material behavior is measured.
• Lower mechanical strength of test pieces requires gentler mounting and loading conditions.

Procedure Enhancements

• Cut specimens with precise dimensions, aligned along the grain direction.
• Avoid creasing or contaminating surfaces to ensure valid frictional readings.
• Use a COF tester with adjustable weights to accommodate lighter specimens.
• Analyze COF changes in humid environments, where cellulose fibers may expand, affecting friction.

Integrating ASTM D202 with COF Instruments

Modern friction testers used for ASTM D202, such as those from Cell Instruments, feature programmable loading, speed variation, and humidity control—critical for simulating real-world storage and operational environments.

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Other Withdrawn ASTM Friction Standards Worth Noting

• ASTM D4521-96 (Withdrawn 2001): Standard Test Method for Coefficient of Static Friction of Corrugated and Solid Fiberboard. This method provided a means to evaluate the static COF of fiberboard materials, helping to assess their handling and stacking performance.
• ASTM D4917-97(2007)e1 (Withdrawn 2010): Standard Test Method for Coefficient of Static and Kinetic Friction of Uncoated Writing and Printing Paper by Use of the Horizontal Plane Method. This method used a horizontal sled and plane setup to measure both static and kinetic COF values for paper substrates.
• ASTM D4918-97(2007) (Withdrawn 2010): Standard Test Method for Coefficient of Static Friction of Uncoated Writing and Printing Paper by Use of the Inclined Plane Method. Unlike D4917, this test used an inclined plane to assess the point at which paper begins to slide under gravity.

These withdrawn standards were once widely used to assess frictional performance in paper and fiberboard products. Though no longer active, they provide foundational insights into material behavior that continue to inform modern friction test methodologies.

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Test Equipment and Instruments from Cell Instruments Co., Ltd.

To ensure precision in the ASTM friction test, selecting the right equipment is essential. Cell Instruments offers:

• Coefficient of Friction Testers with:
  • Real-time force detection
  • Adjustable test speeds (as per ASTM D1894)
  • Temperature-controlled test planes
  • Digital data output and analysis

Our instruments are customizable for unique materials or automation lines, and support friction testing per ASTM D1894, D202, D4917, D4918, und D4521 standards. Industries such as packaging, electronics, pharmaceuticals, and textiles rely on our solutions for consistent, regulatory-compliant results.

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Best Practices for Accurate Friction Testing

To improve accuracy and repeatability in the ASTM friction test:

• Always use fresh specimens for each test run
• Maintain consistent surface contact (machine direction alignment)
• Control environmental conditions (temperature and humidity)
• Avoid contaminating surfaces with fingerprints or dust
• Adjust pulling speed to standard levels (e.g., 150 ± 30 mm/min)

Pro Tip: Friction is a surface-sensitive property. Even subtle changes in surface energy, roughness, or treatment (e.g., corona discharge) will impact results.

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Optimize Material Performance with ASTM Friction Testing

Mastering the ASTM friction test and its associated standards (ASTM D1894, D202, D4917, D4918, and D4521) is essential for professionals in quality assurance, product development, and packaging design. These standardized methods not only validate material usability but also enable performance tuning for safe, efficient, and automated applications. Cell Instruments provides the precision instruments und technical support necessary to implement these tests effectively, enhancing reliability and compliance across industries.