In recent years, the development of the flexible packaging industry has advanced by leaps and bounds. At the same time, the subsequent quality problems have also become prominent. The complaints of users about the packaging film breaking, slipping, and packaging production line interruption are increasing. Many flexible packaging material factories and flexible packaging printing factories have caused huge losses. In fact, the root cause of this phenomenon lies in the friction properties of flexible packaging materials. Therefore, the friction performance of flexible packaging materials is essential to production. The above problems can be effectively solved by testing the friction coefficient of packaging materials. The size of the friction coefficient must be determined by experiment.
Equipment and method for determination of friction coefficient
Test equipment and test standards
Test equipment MC-600 friction coefficient instrument: vmcpp.25μm, hot cover sample;
â‘¡The test standard is conducted with reference to GB10006-88.
2. Test method
①Take three 8cm × 20cm samples. The required sample of the test auspicious and test surface should be smooth, without wrinkles and scratches that may change the friction properties. The edge of the sample should be rounded. The test surface of the sample should be free of dust. Fingerprints and any foreign substances that may change the surface properties.
Condition adjustment of the sample and standard environment of the test. The condition of the sample is adjusted for at least 16 hours under a standard environment of temperature 23 ± 2 ° C, relative humidity 45% -55%, and then the test is conducted in the same environment.
After adjusting the level of the MC-600 Friction Coefficient Apparatus, the test surface of one sample is upwards and fixed flatly on the horizontal test bench. The length of the test specimen and the test bench should be parallel, and the test surface of the other specimen is downward , Wrap the slider, and fix the sample on both sides of the slider with tape.
Place the slider fixed with the sample in the center of the first sample without impact, and make the test direction of the two samples parallel to the sliding direction and the force measuring system is just unstressed.
Set the parameters of the MC-600 friction coefficient meter, and then start the test.After the two samples are kept in contact for 15 seconds, the two samples move relatively, and the first peak of the force is the static friction force-FS. The two samples move relatively within 6 cm. The average value of force (excluding static friction force) is dynamic friction force-Fd. This process is automatically controlled, and the curve is displayed in real time during the test process. The friction coefficient is automatically calculated at the end of the experiment.
After the average of the three groups of experiments, μS = 0.543, μd = 0.478. From the experimental results, the three groups of experimental data are relatively stable, and the static friction coefficient is greater than the dynamic friction coefficient.
Because the MC-600 friction coefficient instrument has the function of drawing a friction coefficient curve, you can understand the uniformity of the material according to the drawn curve. According to relevant data analysis, the friction coefficient of the flexible packaging material is generally less than 0.3, which is more suitable for the actual production. Large, so that the friction coefficient can be controlled by selecting the opening agent in the resin and the type and content of the slip agent to meet user requirements.
So, in the end, what is the appropriate friction coefficient? The author believes that it is necessary to continuously determine the optimal friction coefficient parameter based on continuous use of materials on site.
Several problems in the friction coefficient test: 1. During the communication with some companies, I learned that the measured friction coefficient is greater than 1, and the data provided, such as Cpp sample μS = 1.189, μd = 0.591, and others For this reason, the author consulted more information, only one of the two objects to be measured was placed obliquely as a slope, and the other was placed on the slope body and slid down along it, gradually reducing the slope of the slope to a certain point. The friction coefficient is greater than or equal to 1. According to the conventional test method, the author has repeatedly done many experiments with different materials and the friction coefficient is not greater than 1.
It is known from the relevant data of friction: the friction force that occurs in static friction is called static friction force. When the tangential external force gradually increases but the two objects remain relatively still, the static friction force increases with the increase of the tangential external force. However, the increase in static friction can only reach a certain maximum value. When the tangential force is greater than this maximum value, the two objects will move from relatively stationary to relative sliding. This maximum value of static friction force is called "maximum static friction force." This limit 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. Use fmax to express the maximum static friction force, N represents the positive pressure, where the proportional constant μn is called the static friction coefficient It is a value without units. Μ0 is related to the material of the contact surface, smoothness and roughness, wet and dry conditions, etc., and has nothing to do with the size of the contact surface. From the above introduction, the static friction coefficient μ0. Should not be greater than 1.
Dynamic friction. The friction force that occurs in dynamic friction is called "dynamic friction force." When the main force applied to the object is greater than the maximum static friction force, the object starts to move. After the movement, if the applied force is reduced, the object stops again. Movement. This situation shows that after the object moves, there is a force that prevents the object from moving, that is, friction resistance. The friction force generated when this object moves is called the dynamic friction force. The ratio of the dynamic friction force to the positive pressure It is called "dynamic friction coefficient." In the formula, μ is the proportionality coefficient, and its value is related to the material and surface roughness of the two objects in contact, and the relative sliding speed between the two objects in contact. 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 is definitely smaller than the static friction coefficient, and it will not be larger than 1.
The friction coefficient greater than 1 appears in the user's actual test, which is not a true reflection of the material. It should be found from the operation, whether the surface properties of the material have 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 that the surface of the test material is abnormal at the rear end (such as pin holes, foreign objects, etc.) In the process of being subjected to external forces, etc. You can find an abnormal mutation here by observing the friction curve.
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