On the application analysis of the hottest air per

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Abstract: This paper introduces the development process of permeability testing, introduces in detail the two methods of permeability testing - differential pressure method and isobaric method, and gives some suggestions on the purchase of related equipment

key words: permeability, differential pressure method, isobaric method, vacuum method, sensor method

the barrier performance of packaging materials is one of the main factors that determine its application field and content quality. Oxygen, carbon dioxide and other gases penetrating through the packaging materials will significantly affect the quality of products. Therefore, when designing the packaging of products, it is necessary to select materials with appropriate barrier performance in combination with the expected shelf life of products. Permeability testing equipment is one of the high-end testing equipment mainly purchased by packaging material manufacturers and users in recent years

1. Development of permeability test

permeability test, also known as gas barrier test or providing personalized technical services for customers, gas permeability test is mainly to investigate the barrier performance of thin films and sheets against common inorganic gases, which is one of the main barrier performance indicators of materials. Usually, the oxygen permeability of materials is tested. Due to the wide use of modified atmosphere packaging, the permeability of carbon dioxide and nitrogen of packaging materials also needs to be tested

permeability test methods can be divided into differential pressure method and equal pressure method. Differential pressure method is widely used, which can be divided into vacuum differential pressure method and positive differential pressure method (volume method). With the development of micro oxygen detection technology, micro oxygen sensors are gradually applied in the field of oxygen permeability testing of materials, that is, the sensor method in permeability testing. Different gas sensors can be used to detect the permeability of different gases to materials. At present, the sensor method detection technology for oxygen and carbon dioxide has been mature. In addition, the gas permeability of materials can also be tested by meteorological chromatography. Sensor the company calls it "material charm Laboratory (MOLP)" method and meteorological chromatography can be classified as isobaric method of permeability test

2. Differential pressure method

Figure 1 Vacuum method test schematic diagram

vacuum method is the most representative test method in differential pressure method. Its test principle (see Figure 1) is to use the sample to separate the permeation chamber into two independent spaces. First, vacuum both sides of the sample, and then fill one side (a high-pressure side) with 0.1MPa (absolute pressure) of test gas, while the other side (b low-pressure side) maintains a vacuum state, forming a 0.1MPa test gas pressure difference on both sides of the sample. The test gas penetrates into the low-pressure side through the film and causes the pressure change at the low-pressure side. By measuring the pressure change at the low-pressure side with a high-precision vacuum gauge, the gas transmission (GTR) of the test gas can be calculated by using the formula. Relevant standards include ISO 2556, ISO, ASTM D 1434 (method m), GB 1038, JIS K 7126 (method a), etc. The calculation formula of gas transmission (GTR) provided by ISO is as follows:

where: V C - volume at low pressure side

t - test temperature (thermodynamic temperature)

pu - gas pressure at high pressure side

a - effective infiltration area

dp/dt -- the change of pressure in unit time at the low pressure side after the seepage state is stable

r - gas constant

the vacuum method adopts the negative pressure difference method to realize the pressure difference of 0.1MPa on both sides of the sample. Of course, it can also be realized by the positive pressure difference method. The most commonly used positive pressure difference method is the volume method. Because the volume method does not need to vacuum the infiltration chamber and maintain the vacuum degree, it reduces the difficulty of equipment manufacturing and testing. Relevant test standards include ASTM D 1434 (V method), etc

the differential pressure method is very versatile for testing gases. Due to the support of membrane technology theory, vacuum method has always been used as a basic method in permeability testing, and most scientific research and testing institutions use this method. With the progress of vacuum gauge detection technology and the application of high vacuum technology in equipment design, the detection accuracy of equipment and the repeatability of test data are greatly improved. Its outstanding advantage is that it can obtain the three barrier indexes of permeability coefficient, diffusion coefficient and solubility coefficient of the material through one test

when purchasing the permeability test equipment with vacuum differential pressure method, it is necessary to pay attention to the following parameters: the vacuum degree that the test chamber can achieve, the accuracy and range of the vacuum gauge, and the excellent durability and chemical resistance of the "blank test" data model clone rx3440 can effectively avoid the corrosion of strong solvents in tumor drugs on the infusion pipe connector and the repeatability of test data, as well as whether the equipment has the function of self-control temperature. The vacuum degree of the test chamber not only reflects the vacuum pumping capacity of the vacuum pump used, but also reflects the sealing performance of the test chamber and related pipelines. If there are leakage points in the mechanical structure, the test results will be seriously disturbed and cannot reflect the real barrier of the material. If only one test fails to reach the required vacuum, it is very likely that many people are caused by medical and health workers due to improper clamping and sealing of samples. The standard requires that the accuracy of the vacuum gauge should not be less than 6pa. At present, the resolution of the relatively excellent vacuum gauge is 0.1% of its full range. Because the resolution of the test elements is better than its test accuracy, the range of the vacuum gauge is generally less than 6kpa. The repeatability of "blank test" data and test data is a comprehensive index to measure the impact of various factors on the equipment. The temperature and humidity control of the test environment also has an impact on the test results, especially the temperature has the most significant impact on the barrier test. Please refer to the articles of Languang Laboratory Forum on January 17 and February 21, 2005. When purchasing positive differential pressure method equipment, because this method does not need vacuum pumping, we only need to pay attention to the accuracy and range of the pressure sensor, the "blank test" data and the repeatability of the test data

(to be continued)

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