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TAPPI T 549 Coefficient of friction






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


The TAPPI T 549 Coefficient of friction method describes a horizontal plane procedure for the determination of the coefficient of static and kinetic friction of paper measured when sliding against itself.

The horizontal instrument requires some means of movement of the specimen in relation to the surface upon which it rests. The coefficient of friction (COF) is measured directly from the resistance to tangential motion and the applied weight pressing two pieces of paper together.

Static COF relates to the force required to initiate movement between two surfaces while kinetic COF relates to the force required to cause continuation of the movement at uniform speed.

The determinations of COF for packaging materials is described in TAPPI T 815 “Coefficient of Static Friction (Slide Angle) of Packaging and Packaging Materials (Including Shipping Sack Papers, Corrugated and Solid Fiberboard) (Inclined Plane Method).” In the method for testing packaging materials, the force measurement is often made on the third slip, while in this method the determination is made on the first slip.

Summary of Method

One specimen of the paper sample is clamped to a horizontal plane surface, the other to a specimen sled. The sled is pulled across the surface, or the plane pulled under the stationary sled and the force required to do so is measured. The coefficients of both static and kinetic friction may be determined.

Significance and use

The coefficient of friction of printing and writing papers is an indicator of the ease with which the top or bottom sheets of a stack of paper will slide across the succeeding sheet, such as occurs on the infeed of a printing press or the sheet transport into a copier machine. A minimum value of coefficient of friction is required to prevent double-feeding of any sheets.

Since each sheet is removed from the stack only once, a single slide of each pair of specimens is performed and the value recorded.

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