The air permeability of the stretched film is mainly expressed by the gas permeability and the gas permeability coefficient. Gas permeation refers to the volume of gas that permeates through a unit area of the tested film in a unit time under the action of a constant temperature and a unit pressure difference, when stable permeation. The gas permeability coefficient refers to the constant temperature Under the difference of unit pressure, when stable permeation, the gas volume per unit thickness and unit area per unit time permeates the film under test. The air permeability test of the stretched film is carried out on a special instrument. The method is to divide the high-pressure chamber and the low-pressure chamber Open and seal well. There is a test gas of about 105 Pa in the high-pressure chamber. The volume of the low-pressure chamber is known. Use the real air in the low-pressure chamber at the beginning of the test. The empty pump is pumped out, the pressure is close to zero, and then the pressure rise and change in the low-pressure chamber are detected with a pressure gauge. The following items should be paid attention to when testing the air permeability of thin stretched film: 1 The temperature should be strictly controlled during the test. 2. It takes a long time for degassing and venting during the tensile film test. The pressure in the low-pressure chamber should be tested after reaching a stable permeation. Before recording. 3. The test inspection process is carried out under the condition of the pressure difference between the two high and low pressure chambers. Therefore, in order to ensure the accuracy of the test data Must pay attention to the tightness of each system in the working instrument.
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