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ABC's of Package Tests: Tear

A tear tester has a stationary clamp and a movable clamp on a pendulum, means for holding this pendulum in a raised position, then quickly releasing it, and a scale that registers the arc through which the released pendulum swings.

Samples of paper or fil are clamped into the tester and nicked to start the tear; then the pendulum clamp is released. This tears the sample and the scale registers the arc, As the arc i sproportional to the tear strength of sample, calibration of the arc gives the tear strength.

Tear strength is reported in grams/mm of thickness. It is the force necessary to continue tearing a sample after a nick has been made. This test is very importnat for all films as well as paper. High tear values may be needed for machine operations or for package strength. However, low tear values are necessary and useful for easy opening of some package types.