Discussion on the Friction Coefficient of Packaging Materials

In recent years, the development of the flexible packaging industry has progressed by leaps and bounds. At the same time, the quality problems that accompany it have also been highlighted. The complaints from the use unit about the breaking of the packaging film, skidding, and the interruption of the packaging production line are increasing. Many flexible packaging materials The factory and the flexible packaging printing plant have caused huge losses. In fact, the root cause of this phenomenon is the friction performance of the flexible packaging material. Therefore, the friction property of the flexible packaging material is crucial to the production and can effectively test the friction coefficient of the packaging material. To solve the above problem, the friction coefficient must be determined experimentally.

Friction coefficient determination apparatus and method

Test Equipment and Test Standards

Test equipment MC-600 friction coefficient instrument: vmcpp.25μm, hot cover specimen;

2 test standards with reference to GB10006-88.

2. Test methods

1 Take three 8cm x 20cm specimens. Test and harmony test surface requirements should be smooth, no wrinkles, and any scratches that may change friction properties. The test specimen edges should be rounded. The test surface of the specimen should be free of dust. Fingerprints and any possibility Change the surface properties of foreign substances.

Standard Conditioning of the Samples and the Standard Environment for the Test. Sample conditions were adjusted at a temperature of 23±2°C and relative humidity of 45% to 55% for at least 16 hours and then tested in the same environment.

After adjusting the level of the MC-600 Friction Tester, place the test surface of one test piece up and flat on the horizontal test stand. The length direction of the test piece and the test stand should be parallel, and the test surface of the other sample should be downward. , Enclose the slider and fix the specimen on both sides of the slider with tape.

The slider with the sample fixed is placed in the center of the first specimen without impact, and the test direction of the two specimens is parallel to the sliding direction and the force measurement system is exactly free of force.

The MC-600 coefficient of friction instrument parameters were set, and then the test was started. After the two specimens were in contact for 15 seconds, the two specimens moved relative to each other. The first peak of the force was the static friction force - FS. The relative movement of the two specimens was within 6 cm. The average force (excluding static friction) is the dynamic friction force - Fd. This process is automatic control, and the test process shows the curve in real time. The friction coefficient is calculated automatically at the end of the experiment.

After three groups of experiments, the mean μS was 0.543 and μd was 0.478. The experimental data showed that the three groups of experimental data were relatively stable and the static friction coefficient was greater than the dynamic friction coefficient.

Because the MC-600 friction coefficient meter has the function of drawing the friction coefficient curve, it can understand the uniformity of the material according to the drawn curve. According to relevant data analysis, the friction coefficient of flexible packaging materials is generally less than 0.3, which is more suitable for practical production. According to this, the data is biased. Large, this can be achieved by selecting the opening agent in the resin, the type and content of the slip agent to control the friction coefficient.

Then, in the end, the friction coefficient is appropriate. I believe that according to the use of materials at the scene, we must continue to experiment to determine the optimal friction coefficient parameters.

Several problems in the friction coefficient test: 1. In the process of communicating with some companies, it was learned that the measured coefficient of friction is greater than 1, and the provided data, such as Cpp sample μS=1.189, μd=0.591, and For this reason, the author has consulted more information. Only one of the two objects to be measured is placed obliquely as a slope, and the other is placed on the slope body to slide down, gradually reducing the inclination of the slope to a certain degree. Friction coefficient is greater than or equal to 1, according to the conventional test method, the author repeatedly made a lot of experiments with different materials, there is no phenomenon that the friction coefficient is greater than 1.

According to the relevant friction data, the friction force that appears in static friction is called static friction force. When the cutting force gradually increases but the two objects remain relatively stationary, the static friction force increases as the shear force increases. However, the increase in static friction can only reach a certain maximum value. When the shear force is greater than this maximum, the two objects will enter the relative sliding relative to each other. This maximum value of static friction is called the "maximum static friction force." This ultimate friction Force, expressed as fmax. The size of the maximum static friction force is proportional to the positive pressure N between the contact surfaces of the two objects, that is, fmax = μnN. The maximum static friction force is represented by fmax, and N is the positive pressure, where the proportional constant μn is called static friction coefficient. Is a unit without the value .μ0 and contact surface material, smooth roughness, dry and wet conditions and other factors, and the contact surface size has nothing to do. From the above description, static friction coefficient μ0. Should not be greater than 1.

Dynamic friction. The frictional force that appears in dynamic friction is called "dynamic friction force." When the main force applied to an object is greater than the maximum static friction force, the object begins to move. After the motion is applied, if the applied force is reduced, the object stops again. Movement. This situation shows that after the movement of the object, there is the force to stop the movement of the object, that is, there is frictional resistance. The frictional force generated when this object moves is called the friction force. The ratio of the dynamic friction force to the size of the positive pressure. It is called "dynamic coefficient of friction." In the formula, μ is a proportional coefficient. Its value is related to the material and surface roughness of two objects in contact with each other, and the relative speed of relative sliding between two objects. In most cases, dynamic friction The coefficient will decrease slightly with the increase of the relative sliding speed. From the definition, the dynamic friction coefficient must be less than the static friction coefficient, and it will not be greater than 1.

If the friction coefficient is greater than 1 in the actual test of the user, it is not a true reflection of the material, and it should be found from the operation, whether the surface property of the material has been artificially changed, etc.

2. The dynamic friction coefficient measured during use is greater than the static friction coefficient. From the above analysis, the dynamic friction coefficient is definitely less than the static friction coefficient. The result should be an abnormality in the back surface of the test material (such as pinholes, foreign objects, etc.), or testing. The process is subjected to external forces, etc. It is possible to find abnormal mutations here by observing the friction curve.