TAPPI T549 Coefficient of Friction Testing Machine for Paper

Coefficients of static and kinetic friction of uncoated writing and printing paper by use of the horizontal plane method

In the paper and packaging industry, understanding surface interactions is essential for ensuring smooth performance in printing, converting, and handling processes. TAPPI T549 is the recognized method for determining the static and kinetic coefficients of friction of paper when sliding against itself. This standard is especially important for printing paper and uncoated writing grades, where issues like sheet feeding and double-feeding can significantly affect product quality and equipment functionality.

Importance of Coefficient of Friction Testing in Paper

Coefficient of friction (COF) testing is a crucial metric that indicates how easily sheets of paper slide over each other. TAPPI T549 specifically focuses on the horizontal plane method, offering a quantitative way to evaluate both:

Static coefficient of friction: the force needed to initiate movement.
Kinetic friction testing: the force needed to maintain movement at a constant speed.

These values are critical in printing paper and uncoated writing applications, particularly in sheet-fed presses and copiers. Too low a COF can result in double-feeding, while too high a COF might cause jams or resistance in paper transport systems.

Test Procedure: How to Perform a TAPPI T549 Test

Preparation
Place the coefficient of friction testing machine on a stable, vibration-free surface. Level the equipment and zero the force measurement system.
Specimen Alignment
- Cut the samples according to grain direction (machine direction or cross-machine direction).
- Place the larger specimen (felt side up) on the horizontal plane and secure it.
- Position the smaller sample (wire side down) under the sled, avoiding any premature horizontal motion.
Static Friction Test
- Attach the sled to the motor or gauge cable.
- Start the device and record the initial peak force as the static coefficient of friction.
Kinetic Friction Test
- Continue movement over approximately 130 mm (5 inches).
- Record the average force over this distance as the kinetic COF.
Repeatability
- Do not reuse test pairs unless required for variable comparisons.
- Maintain consistent timing between sled placement and movement initiation.

Test Method Summary According to TAPPI T549

TAPPI T549 outlines a straightforward but precise horizontal sliding method:

One paper sample is attached to a flat test plane.
A second sample is fixed to a sled with a standardized weight and surface area.
The sled is pulled (or the plane moved beneath the sled) using a constant-speed motor or pulley system.
The maximum force before movement begins gives the static COF.
The average force during steady movement provides the kinetic COF.

This method allows consistent, reproducible testing—ideal for quality control and production line evaluation.

Applications of TAPPI T549 in the Industry

Printing Paper: Ensures efficient sheet feeding in high-speed printing presses.
Uncoated Writing Paper: Prevents sticking or misfeeds in copiers and office printers.
Packaging Quality: Though TAPPI T549 is for paper-to-paper testing, it complements inclined plane methods like TAPPI T815 for broader packaging applications.

By understanding friction behavior, manufacturers can modify surface properties or coatings to meet application needs and equipment compatibility.

Why TAPPI T549 Matters for Quality Control

Maintaining the right COF levels ensures:

Smooth paper feeding in printers and copiers
Reduced machine wear due to fewer jams or misfeeds
Improved product consistency from batch to batch
Better customer satisfaction by avoiding common handling issues

TAPPI T549 provides the methodology to quantify friction behavior, offering data that drives smarter decisions in production and material design.

COF-01 Coefficient of Friction Testing Machine

To comply with TAPPI T549 with precision and reliability, Cell Instruments offers the COF-01 Coefficient of Friction Testing Machine, specially designed for:

Static and kinetic COF evaluation
Horizontal plane friction testing
Application in printing paper, uncoated writing, and other textile and packaging materials

Its constant-speed movement and digital force recording ensure TAPPI-standard results that are reproducible and highly accurate. For professionals in quality control or R&D, the COF-01 ensures your testing aligns with TAPPI T549 and production goals.