Coefficient of Friction Testing for Paper and Paperboard
Paper and paperboard friction directly controls whether sheets feed cleanly through digital printers, whether corrugated cases slide safely on conveyor lines, and whether palletized loads stay stable during shipping. Too low a COF between stacked sheets causes misfeed and double-pulls in sheet-fed presses; too high a COF between carton surfaces creates jams on high-speed erecting equipment. The MXD-02A Coefficient of Friction Tester measures paper-to-paper and paper-to-surface friction to TAPPI T816, ASTM D1894, and ISO 15359, delivering the traceable QC data mills and converters need to release rolls and sheets with confidence.
Quick Answer
COF testing for paper uses a sled pulled across a flat substrate at a defined speed to measure the initial breakaway force (static COF) and the sustained sliding resistance (kinetic COF). TAPPI T816 is the primary North American standard for paper and paperboard, specifying a 200 g sled at 150 mm/min under controlled temperature and humidity. Results guide coating formulation, surface sizing decisions, and release-liner specification.
Why Friction Matters in Paper Converting
Sheet feeding in digital presses and offset litho presses depends on controlled friction between sheets in the feeder stack and between the bottom sheet and the feed roller. If static COF between sheets is too low, multiple sheets are pulled simultaneously, causing misfeed jams. If it is too high, the sheet sticks and slips, creating marking and registration error. In corrugated and folding carton converting, high-speed case erectors and gluing machines require predictable surface friction for reliable blank transport. For label stock, the dynamic friction between the release liner and the face stock governs unwind tension on press, directly affecting print registration and die-cut accuracy. COF measurement is therefore a routine incoming and in-process QC test at mills, coaters, and converters.
TAPPI T816 Testing Method
TAPPI T816 is the primary friction standard for paper and paperboard in North America. The procedure is conceptually similar to ASTM D1894 — a 200 g sled wrapped with the test specimen is pulled across a flat platen at 150 mm/min while a load cell records the friction force. Key TAPPI T816 requirements include conditioning at 23°C and 50% RH for a minimum of 24 hours before testing, and the use of a metal platen surface unless the test specifically calls for paper-on-paper. The MXD-02A supports TAPPI T816 with its included 200 g sled and standard polished stainless steel platen. The software calculates static COF from the initial peak and kinetic COF as the average force over the 100 mm travel zone after initial breakaway, consistent with TAPPI T816 calculation provisions.
Paper Types and Expected COF Ranges
Uncoated offset paper typically measures static COF of 0.45–0.65 against itself — sufficient grip for sheet-fed presses. Clay-coated or cast-coated paper surfaces are significantly lower, often 0.25–0.40 static, which is why coated papers are prone to double-sheet feeding if feeder suction is not calibrated. Kraft linerboard against itself commonly shows 0.40–0.60 static, with the corrugated side measuring higher due to its fluted texture. Tissue and hygiene paper can vary widely (0.20–0.80) depending on creping ratio and surface treatment. Silicone-coated release liners are intentionally very low — typically 0.05–0.20 kinetic — to allow label stock to unwind cleanly. Thermal paper for point-of-sale rolls generally targets static COF below 0.30 to prevent stacking adhesion on humid days.
Coated vs Uncoated Surface Testing
Coating changes the friction profile of paper significantly. A light clay coating (5–10 gsm per side) can reduce static COF by 0.10–0.20 compared to the base sheet by smoothing the micro-roughness that drives mechanical interlocking. Heavy cast-coated or pigment-coated surfaces can be even lower, approaching values typical of smooth plastic films. Aqueous dispersion coatings used for water resistance or grease resistance on food-service paperboard often raise COF, sometimes above 0.60 static, which can create problems on packaging lines designed for uncoated substrates. When a new coating formulation is introduced, the MXD-02A allows side-by-side testing of the coated and uncoated base sheet under identical conditions — same sled, same speed, same conditioning — to quantify the COF delta and predict downstream performance.
QC Protocol for Paper Mills and Converters
A robust paper COF QC protocol typically includes three test types per lot: paper-on-paper (face-to-face), paper-on-metal (simulating machine contact surfaces), and — for label or release products — paper-on-release-liner. Five specimens per test type are recommended by TAPPI T816 to account for within-roll variability, and results from the two edges and center of the roll are commonly reported separately. Control charts tracking kinetic COF by lot, with upper and lower specification limits, allow mills to detect coating weight drift or slip agent depletion before rolls ship. The MXD-02A supports this workflow through its SPC export: raw force-time data and calculated COF values export to CSV for import into any SPC software package. Operators can also create named test programs for each paper grade so parameters are fixed and not operator-adjustable.
Selecting the Right MXD-02A Configuration for Paper Testing
Standard paper and paperboard testing is fully covered by the base MXD-02A with the 0–5 N load cell, the 200 g sled, and the stainless steel platen. The 5 N range provides sufficient sensitivity to resolve COF values as low as 0.05 (release liner) and as high as 0.80 (tissue or rough kraft) with the 200 g sled. For testing corrugated board or thick folding carton stock, the extended 10 N or 30 N load cell option accommodates the higher friction forces these substrates generate, particularly in the machine direction where liner fibers are well-aligned. If your lab also tests plastic film laminates on paper (e.g., poly-coated paperboard), the same instrument and sled kit supports ASTM D1894 testing without additional hardware. Contact KHT for guidance on the appropriate load cell for your specific paper grades.
Frequently Asked Questions
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