ASTM D1894 determines the amount of force required to initiate movement of a loaded sled against a film surface and to continue movement. These two forces determine whether a film will feed through a form-fill-seal machine properly or jam, and whether a stack of bags can be separated or will block. MatX Lab performs friction testing on packaging films, coated substrates, and sheets in accordance with ASTM D1894.
What Is ASTM D1894?
ASTM D1894 is the standard test method for static and kinetic coefficients of friction of plastic film and sheeting. A sled of defined mass and contact area rests on a specimen and is pulled across it at constant speed while force is recorded.
Each trace yields two results. The first is the static friction coefficient. It is determined from the first peak when the sled leaves the ground. The second is the kinetic friction coefficient. It is obtained from the average of the force during steady movement.
Test pairing is part of the result. Film against itself, film against the metal of a machine surface, and outer face against inner face all give different values, and a coefficient reported without its pairing cannot be used.
ASTM D1894 Scope and Applications
This test measures the frictional force between two surfaces, both dynamic (in motion) and static (at rest).
- Slip additive control. Tracking how much a slip package has bloomed to the surface, which is the usual reason friction changes between lots.
- Blocking and stacking behavior. Assessing whether film layers will separate cleanly, which film-to-film friction predicts reasonably well.
- Coating and treatment verification. Measuring the friction effect of a coating, corona treatment, or matte finish.
- Incoming film verification. Confirming a delivered lot matches the friction specification the converting line was set up for.
ASTM D1894 Test Procedure
Slip additive migration makes this test time-dependent in a way most people underestimate. The same roll gives different numbers a week apart.
| Step | What happens |
| Sample logging | Roll identification, production date, and time since manufacture are recorded, because slip additive continues blooming and friction falls with age. |
| Specimen cutting | Cut specimens for the sled and the plane, handle them at the edges, and keep them flat. Surface contact is what is being measured. |
| Pairing definition | The contact pair is defined and recorded: film to film with faces named, or film to a specified metal or other surface. |
| Conditioning | Specimens are conditioned at standard laboratory temperature and humidity, since both affect additive behavior and surface response. |
| Sled preparation | Mount the specimen to the sled without wrinkles and without adhesive contamination reaching the contact face. |
| Plane preparation | The mating specimen or surface is fixed flat to the horizontal plane, free of trapped air and creases. |
| Sliding | Pull the sled at the specified speed, commonly 150 mm/min, and record force through the initial peak and the steady region. |
| Calculation | Take the static coefficient from the initial peak and the kinetic coefficient from the average of the steady region, both divided by the sled weight. |
Limitations: The slip additive moves to the surface over time, so the film measured right after production will differ from the film measured a month later, and both are correct. Both temperature and humidity influence the measurement, so comparisons between laboratories can happen only under identical conditioning conditions. Some films have stick-slip characteristics that cause the measurement to show a saw-toothed pattern instead of a stable zone; averaging such a measurement would hide what really happens. The sled needs to be perfectly horizontal; otherwise, even a wrinkle underneath it will influence the contact and thus the measurement. Multiple passes on the same path change the surface, so each sample gets only one pass.
ASTM D1894 Specimen Requirements and Test Conditions
| Parameter | Typical requirement |
| Sled | 63.5 mm square contact face, 200 g total mass |
| Sliding speed | 150 mm/min |
| Specimen size | Sufficient for the sled plus a sliding distance in the steady region |
| Contact pair | Defined explicitly, with faces identified |
| Replicates | Five per pairing minimum |
| Conditioning | Standard laboratory atmosphere; temperature and humidity recorded |
| Sample age | Production date recorded, since friction changes with additive bloom |
| Material required | Enough for the replicate count in each pairing plus spares |
Send film with its production date and store it flat. Friction on a slip-modified film measured at three days and at thirty days can differ substantially, and without the date the result cannot be compared against anything.
ASTM D1894 Test Results and Reporting
Your report gives static and kinetic coefficients of friction per specimen with the mean for each, and the contact pairing stated as part of the result.
We supply force traces on request, since the shape carries information the coefficients do not. Conditioning temperature and humidity, sled mass, sliding speed, film face orientation, and the sample production date all appear with the data.
Where stick-slip occurred, we describe it and show the trace rather than presenting a smoothed kinetic value. The behavior of a film that talks with its mouth sealed is not the same as the behavior of a film that travels smoothly at an equal average coefficient.
ASTM D1894 FAQs
Why did my film's friction change since the last lot?
Slip additive level or age is the usual answer. Additive blooms to the surface over time, so both formulation changes and a different time since production will move the number.
What is a good coefficient of friction for packaging film?
This completely depends on the nature of the line. A low coefficient of friction allows easy feeding but is liable to slip through the drive, while a higher one will grip but will pull. Your machine setting defines the target rather than the method.