concept
The tearing degree of paper and cardboard refers to the force required for a certain distance to be torn apart by a sample that has been cut, also known as the internal tearing degree, expressed in mN, and the unit used to be gf (lgf=9.807mN). The edge tearing degree is the force required to tear a certain length of a pre-cut sample along one side of the sample by a force in the same plane, and the unit is N. The work done by tearing paper and cardboard includes two parts, that is, the work done by pulling the fibers apart and the work done by pulling the fibers apart. Fiber length is an important factor affecting the tearing of paper and board. As the fiber length increases, the tearing degree increases, because increasing the fiber length means increasing the work done by pulling the fiber apart. Internal tearing is one of the important testing items for bag paper, packaging paper and packaging cardboard. For banknote paper and candy wrappers, edge tear has specific significance.
Commonly used tear Testers include Elmandorf single tear Tester, LW tear Tester, Brech-Imset double tear Tester and special edge tear Tester.
Factors Affecting Tear
(1) relative humidity
The influence of relative humidity on the general strength properties is that the strength decreases with the increase of humidity, but the tear degree increases with the increase of relative humidity. The tear degree at 65% relative humidity is lower than that of 12% higher at 50% relative humidity.
(2) Instrument accuracy
The accuracy of the scale value, the friction of the pendulum shaft, the friction of the pointer, the shape of the edge of the sample cut by the cutter, etc., all have a significant impact on the tearing degree. In general, the total error caused by the accuracy of the instrument is less than 1%.
(3) Different layers of tearing
Tracing paper and kraft pulp handsheets beaten for 35 minutes have high tightness and strong internal bonding of fibers. In the direction of tearing and the number of layers torn, they are torn along a straight line, and are basically not affected. The effect of tearing layers. However, when the filter paper and unbeaten kraft handsheet were tested for tearing degree at 1-10 layers, it was found that the number of layers was small and the tearing degree was low, and the tearing degree increased with the increase of the number of layers.
(4) Tear radius
According to the measurement results, the tearing radius of 104mm is about 15% higher than that measured by 107mm. Therefore, when using a folding Tester with a tearing radius of 107mm, the test results should be corrected.
