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Abstract: Shrinkage performance is one of the important properties that affect the use of the film. This article introduces three test methods commonly used in the film shrinkage performance test: the oil bath method, the oven method, and the air heating method. The comparative analysis of the three methods is Provide reference for testing and quality control of film shrinkage performance.
Keywords: shrinkage, heat shrinkage force, cold shrinkage force, shrinkage performance, shrink film, heat shrinkage tester, film heat shrinkage tester
1. Significance
With the increase of product types and the development of packaging technology and processes, there are more and more types of shrink films, common ones are PE, POF, PVC, BOPP, PETG, PVDC, etc., which are widely used in the packaging field, such as shrink sleeves , Cluster packaging, casing film and other forms are used to package food, medicine, tobacco, electronic products, automobiles, daily necessities and other products. Different products have different shapes and sizes, which requires that the shrink film should have excellent shrink performance. To adapt to different product packaging requirements.
The indicators that affect the shrinkage performance of the film include the shrinkage rate and the heat shrinkage force and cold shrinkage force generated during the shrinkage process. If the three indicators have poor performance or poor applicability to the product, it will cause the film to not shrink tightly and fit tightly. Poor, may even cause the product to be squeezed and deformed. At present, the testing methods of film shrinkage performance mainly include oil bath method, oven method and air heating method.
Figure 1 Examples of common shrink film applications
2. Introduction
The oil bath method refers to the film sample cut into a predetermined size is placed in a certain temperature of thermal oil (such as silicone oil) and heated to shrink, the sample is taken out after a certain period of time, and the size of the sample after shrinking is measured. The ratio of the size before shrinkage is the shrinkage of the sample. Relevant standards are GB / T 13519-2016 "Polyethylene Heat Shrinkable Film for Packaging", which requires an oil bath temperature of 140 ° C and a shrinkage time of 20s. The test equipment is shown in Figure 2.
Figure 2 Heat Shrink Tester
The oven method, as the name implies, refers to placing a sample of a certain size in an oven at a certain temperature, taking out and measuring the size of the sample after reaching a specified time, and calculating the ratio of the change in size to the size before shrinkage as the shrinkage rate of the sample . Relevant standards such as GB / T 12027-2004 "Test method for dimensional change rate of heating of plastic films and sheets", GB / T 10003-2008 "General purpose biaxially oriented polypropylene (PP) film", the former places the sample in kaolin On the bed, the temperature and time of the test depend on the specific sample. The latter requires the sample to be placed on a stainless steel plate. The test temperature is 120 ° C and the time is 120 s.
The air heating method is to use the hot air in the closed cavity to heat the sample, and the shrinkage rate is obtained according to the heat shrinkage time and dimensional change of the sample. The heat shrinkage force and the force value during the heating and cooling process of the sample are calculated. Cold shrinking force. At present, the domestic test method standard GB / T 34848-2017 "Test Method for Shrinkage Performance of Heat Shrinkable Film" will be officially implemented on May 1, 2018. Before the implementation of this standard, refer to ISO14616-2004 "Plastic Polyethylene Vinyl "The shrinkage test of heat shrinkable films of copolymers and their mixtures" is tested. The standard requires that the sample enters the cavity after the set temperature in the test cavity to be heated and shrinks. When the measured shrinkage value reaches the condition of the cavity, After the sample comes out of the cavity, the device continues to monitor the shrinkage and force value of the sample until the test is completed. The shrinkage rate is calculated according to the change of the sample size automatically monitored by the equipment during the entire test process. The maximum force value measured during the heating process in the cavity is the heat shrinkage force, and the maximum force value measured during the cooling process after exiting the cavity For cold shrinking force. The test equipment is shown in Figure 3.
Figure 3 FST-02 film heat shrinkability tester
3. Method comparison
From the test range, the three test methods can test the shrinkage of the film, but the air heating method can also test the heat shrinkage and cold shrinkage indicators of the film; from the test process, the oil bath method and the oven method are required. Manually test the size of the sample after contraction, the air heating method is for the device to automatically measure the change of the sample size and force value, and can display the measured value in the process of the sample in real time; in addition, the oil bath method is to place the sample Heating in thermal oil, the oven method is to heat and shrink on kaolin or stainless steel plate, and the air heating method is to directly expose the sample to the air without contact with any objects. This difference in shrinking environment will affect the shrinking process of the sample, so the shrinkage rates measured by the three methods are not comparable.
4. Summary
When testing the shrinkage of the film, the appropriate test method should be selected according to the material material, product standard, test purpose and other factors. If the product standard clearly stipulates, the test shall be carried out according to the requirements of the product standard. The test method can be selected according to the actual situation. If you need to monitor the shrinkage value of the film or need to complete the test efficiently and automatically, or the shrinkage process of high-temperature steam or hot air duct in the actual application of the film, you can choose the air heating method The equipment FST-02 film heat shrinkability tester is used for testing. Jinan Languang Electromechanical Technology Co., Ltd. is a high-tech enterprise specializing in R & D and production of packaging inspection equipment and packaging inspection services. Existing equipment can meet the requirements of three test methods for film thermal shrinkage performance testing. The more you understand, the more you trust! Labthink looks forward to enhancing technical communication and cooperation with enterprises and institutions in the industry!
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