Uncoated Writing Coefficient of Friction Test: TAPPI T549 Guide

Importance of Friction Testing for Uncoated Writing Papers

The coefficient of friction (COF) is a critical property that influences how well paper behaves in high-speed feed and transport mechanisms. Too much friction can cause paper jams; too little can lead to double-feeding or slippage. Uncoated writing papers, often used in desktop printers, copiers, and notepads, require just the right friction characteristics for reliable performance.

TAPPI T549 outlines the standard method for measuring the static and kinetic COF of these materials. Unlike packaging materials tested using inclined plane methods (TAPPI T815), this method applies a horizontal plane testing setup, allowing precise and consistent results with minimal variability.

Coefficient of Friction Measurement Device for Paper Testing

Choosing the right coefficient of friction measurement device is essential to comply with TAPPI T549. The test setup involves a horizontal plane surface and a metal sled equipped with rubber backing. The sled is placed over a paper specimen and moved at a constant speed, typically 150 ± 30 mm/min.

Cell Instruments offers the COF-01 Coefficient of Friction Tester, designed specifically to deliver reliable, repeatable measurements of static and kinetic COF for papers and films. This equipment ensures:

  • Stable horizontal motion
  • High-precision load sensing
  • Fully programmable test cycles
  • Real-time display and data export

By using a high-quality device like COF-01, paper manufacturers and quality control teams can confidently assess material properties and improve converting or printing performance.

Step-by-Step TAPPI T549 Testing Procedure for Uncoated Writing

Uncoated Writing Sample Preparation

  • Sample Selection:
    Use a finished ream or lift sample from a roll. Follow TAPPI T400 for sampling protocols.
  • Specimen Cutting:
    Cut pairs of specimens—one larger (100 × 215 mm) and one smaller (75 × 130 mm)—ensuring proper machine direction alignment.
  • Conditioning:
    Precondition and test samples in a controlled environment as defined in TAPPI T402.

Test Setup and Execution

  • Mounting Specimens:
    • Place the larger specimen on the horizontal test plane with the felt side up.
    • Attach the smaller specimen to the sled with the wire side facing down.
  • Starting the Test:
    • Gently place the sled onto the specimen without applying lateral movement.
    • Begin horizontal movement using the instrument’s mechanical power unit.
  • Recording COF Values:
    • Static COF: Measure the peak force required to initiate movement.
    • Kinetic COF: Record the average force over approximately 130 mm of sliding.

Uncoated Writing COF Calculations

The coefficients are calculated as:

  • Static COF = Initial Force (mN) / (Sled Mass × 9.80665)
  • Kinetic COF = Average Force (mN) / (Sled Mass × 9.80665)

These values are unitless and offer a clear indicator of paper performance during feeding and handling operations.

Why Choose Cell Instruments COF-01 for Paper Friction Testing

uncoated writing coefficient of friction test

Professionals seeking compliance with TAPPI T549 and dependable test accuracy trust the Cell Instruments COF-01. Key benefits include:

  • Conformance to international standards like TAPPI T549, ISO 8295, and ASTM D1894
  • High-resolution load cells for detecting minimal frictional forces
  • User-friendly software with automatic COF calculations
  • Modular design adaptable for various materials beyond uncoated writing paper

Whether in R&D labs, production QA, or independent testing agencies, the COF-01 streamlines friction analysis and supports consistent paper quality.

Applications of COF Testing in Paper Industry

Understanding and controlling the coefficient of friction in uncoated writing papers impacts several operational areas:

  • Printing press feeds: Prevent misfeeds and increase run-time efficiency

  • Copier performance: Avoid sheet overlap and jamming

  • Packaging stackability: Ensure reliable stacking during transport or retail display

  • Die-cutting and converting: Support accurate registration and alignment

With the proper coefficient of friction measurement device, manufacturers can meet performance expectations, reduce downtime, and maintain competitive quality levels.

Conclusion

The uncoated writing coefficient of friction test using the TAPPI T549 standard provides a reliable framework for assessing how paper interacts with itself during typical operations. By following the proper procedures, using calibrated equipment like Cell Instruments COF-01, and maintaining standard environmental conditions, paper manufacturers and quality inspectors can ensure optimal friction characteristics for real-world applications.

For expert support or to learn more about our friction testing solutions, contact Cell Instruments today.

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