Test of helium permeability of three polymer films

This article proposes a method to measure the permeability of polymer films by using a helium mass spectrometer leak detector, that is, through polyethylene terephthalate (PET), polydimethylsiloxane (PDMS), polyimide (PI) After measuring the permeability of three polymer films to helium (He), calculate the corresponding permeability of the film according to Fick's law, and analyze and compare the permeability of the three films to He. The experimental results show that the permeability of the three polymer films (PET, PDMS, PI) to helium are: 1.07×10-7 Pa·m3/s, 2.01×10-6 Pa·m3/s, 1.04× 10-5 Pa·m3/s, due to the difference in glass transition temperature, the permeability of the three films is as follows: PDMS>PI>PET, the PET with the highest glass transition temperature has the lowest permeability to He. The relative synthetic uncertainty of the test method in this paper is 5.79%, and the test system for membrane permeability testing has the advantages of short measurement time, simple operation and accurate results.

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Due to the diffusibility of gas molecules and material defects, gas permeation in polymer films is a common phenomenon. In recent years, polymer films have been widely used in food packaging, military, light-emitting display and other fields, so the measurement of film permeability has become more important. In the food packaging industry, the plastic film for packaging fresh food should have a high permeability; in order to preserve greasy food, the permeability of the packaging film to oxygen is required to be extremely small, while the film used for nitrogen-filled packaging requires almost no permeability to other gases ; In light-emitting displays, polymer films are widely used in organic light-emitting diodes (OLED); stratospheric airships used in the military, the permeability of the polymer materials that make up the airship must meet certain requirements to ensure a good overall airship Leak rate, so as to ensure the good performance of the airship, so the study of membrane permeability to helium in this paper has practical significance.

At present, the gas accumulation method is the main method for testing the gas permeability of membranes at home and abroad. Gas accumulation method: In the initial stage of the test, a certain degree of vacuum must be maintained on both sides of the film; during the test, the test gas fills the cavity (high pressure chamber) connected to one side of the film and maintains the pressure at 1atm; the test gas penetrates through the film to the other On the other side, and use a vacuum gauge to record the pressure of the cavity connected to the other side of the film (inspection chamber) over time. Xue FengYao et al. used this method to study the theoretical method of calculating the gas permeability of the membrane, and Inseok Yeo also used this method to study the gas permeability of the vacuum insulation panel (VIP).

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Due to the long measurement time of the gas accumulation method, the background leakage rate in the tested room is an important factor affecting the results, and the fluctuation of the ambient temperature also affects the accuracy of the results. Therefore, the vacuum technology network (http://www.chvacuum.com/) believes that the test method requires the experiment to be performed in a constant temperature room, and the background leakage rate in the tested room needs to be measured separately. The measurement process is more complicated and the measurement time is long.

In this paper, helium mass spectrometer leak detector is used to measure the overall leakage rate of polymer film to He. According to Fick's law, the permeability of polymer film to He is calculated, and three common polymers (PET, PDMS, PI) are compared and analyzed for He The size of the permeability.

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Gas passing through the film mainly involves the following three steps (such as): 1. Gas molecules are adsorbed on one side of the film; 2. Gas molecules diffuse to the other side of the film; 3. Gas molecules are desorbed from the other side of the film.

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In this experiment, helium mass spectrometer leak detector and Fick’s first law were used to measure and calculate the permeability of three polymer films (PDMS, PET, PI) to He. The experimental results show that k(PDMS)>k(PI)>k(PET). This is because for the same test gas, the permeability of the film to the gas is mainly determined by its glass transition temperature. Vacuum Technology Network (http:/ /www.chvacuum.com/) believes that the experimental results are basically consistent with the theory. This paper also found that the overall relative uncertainty of the test system is 5.79%, which verifies the accuracy of the experiment, and the test system is used to measure membrane permeability with high accuracy, short test time, simple and convenient operation, etc. advantage.

Founded in 2015,Zunhua Baorui Titanium Equipment Co.,Ltd. is a manufacturer specializing in pvd vacuum ion coating equipment. The company’s products mainly include large plate coating machine, large tube collating machine, tool coating machine and LOW-E glass production line. Mr.Wang baijiang ,general manager of the company ,has been engaged in vacuum coating industry for more than 30 years. He continuously improve production technology, improve product performance and devote himself to provide customers with better product experience and higher production efficiency.