A New Method for Testing the Thermal Shrinkage Performance of Shrink Film

The current situation of shrinking film packaging products with many types and different shapes requires different shrinkage properties, so it is particularly important to strengthen the research and monitoring of shrink film heat shrinkability. 1. Test principle This test adopts the air heating principle for testing. When the temperature in the heating chamber of the equipment reaches the set value, the sample enters the heating chamber for a shrinkage test. The changes in size and force produced during the shrinking process are changed by displacement. The sensor and the force sensor carry out real-time monitoring. When the force value drops to the set value, the sample exits the cavity and continues to monitor the size and force value changes of the sample. The shrinkage rate is the percentage of the ratio of the decrease in the length of the sample before and after the test to the length of the sample before the test. The force generated during the heating of the sample is the heat shrinking force, and the force generated during the cooling of the sample out of the cavity is the value Cold shrinkage force.　　2, test equipment and samples 　　 The test equipment used in this article is the FST-02 film heat shrinkability tester independently developed by Labthink. The equipment has a high-precision force sensor and displacement sensor, which can accurately measure the heat shrinkage performance parameters of the sample. The shrinkage force range is 0.2 ~ 30 N, the measurement accuracy is ±0.2%, and a wider range of force can be customized according to special needs Value; heat shrinkable displacement range is 0.125 ~ 70 mm, measurement accuracy is ±0.125 mm; heating chamber working temperature range is room temperature ~ 210℃, temperature control accuracy is ±0.5℃; 1 ~ 3 groups of samples can be tested simultaneously The sample size is 130 mm × 15 mm. The equipment meets a number of national and international standards, such as ISO 14616, DIN 53369, and can accurately and quantitatively determine the heat shrinkage force, cold shrinkage force and shrinkage rate of plastic films during heat shrinkage.　　3. Test process 　　3.1 Cutting samples 　　 Cut 10 specimens with a width of 15.0 mm across the OPS sample. The length should ensure that there is an effective length of 100 mm between the clamps. Two round holes are formed on the surface of each sample with a special sample preparation device to facilitate the clamping of the sample. Every 2 specimens are a group, which are used to test the shrinkage rate and shrinkage force of the specimens.　　3.2 Sample loading 　　 Take any three sets of samples and clamp them on the three sets of fixtures of the equipment. Each set of fixtures includes two sample fixtures equipped with force sensors and displacement sensors. The clamped sample should be completely flat and the force sensor should not be stressed.　　3.3 Parameter setting　　Set the test parameters such as test temperature and end temperature, click the start test option, and the test will start. 3.4 Test process When the temperature in the heating cavity of the equipment reaches the test temperature, the sample enters the cavity automatically, and the test starts timing. The sample shrinks under heat and generates heat shrinkage force. When the force value drops to 15%~30% of the maximum heat shrinkage force When, the sample automatically exits the cavity, and the force generated thereafter is the shrinkage force. The equipment automatically records and displays the heat shrinkage force, cold shrinkage force and shrinkage rate of the sample from entering the cavity to the end of the test in real time. After the test, the equipment displays the shrinkage rate, maximum heat shrinkage force, and maximum cold shrinkage force of each group of samples. Clamp the remaining two sets of samples to the equipment for testing.　　 Label: pof heat shrinkable film