Permeation and leakage of packaging (1)

Abstract This paper analyzes the penetration and leakage of packaging and puts forward the viewpoint that the sealing performance of packaging should be examined from the whole process of packaging materials, packaging process, transportation and sales. For the current domestic and international common oxygen transmission rate, water vapor transmission rate testing methods were analyzed and compared, pointed out their advantages and disadvantages and some problems in the actual operation process, the article also gives a common leak detection method, The reasons for the leakage were discussed.
Key words: packaging leakage oxygen permeability water vapor transmission rate test methods First, packaging In addition to aesthetic and physical protection, the most important performance is the closed performance, water vapor or gas into or out of packaging there are three ways: Penetration and leakage.
Permeation means that the gas or water vapor enters the surface from the high-concentration zone and is desorbed from the other surface of the low-concentration zone by diffusion to the material. The speed of infiltration and the structure, thickness, thickness uniformity, temperature, and humidity of the packaging material. And so on, but also related to the type of diffusing agent. There are two kinds of penetration for the package, one is through the penetration of the packaging material, and the other through the packaging material infiltration at the junction of the packaging material (such as: heat sealed sealing part of the heat sealing). The latter penetration is generally small and often overlooked by people. However, under certain conditions, the overall tightness of the package may have a great impact. For high-barrier packaging, for the entire package has a high sealing performance, reduce the penetration of the heat seal, the seal should have a sufficient width, the use of heat sealing material must have a certain barrier properties.
Leakage is a completely different concept from penetration. Leakage is the diffusion of water vapor or gas through the material's cracks, pores, or small gaps between two materials or into the package. It is the diffusion of convection (forced flow caused by the total pressure gradient) (molecular motion caused by the concentration gradient). The two functions are composed together. The rate of leakage depends on the size of the leaked pores, the pressure within the package, the type of diffusing agent, and the temperature, humidity, etc. of the environment. In order to reduce leakage, mechanically sealed packages should have adequate and durable pressure outside the mechanical seal. The mechanical seal interface must have sufficient surface finish and corresponding dimensional accuracy. It is best to have one of the two mechanical seal materials. The material has a certain elasticity and a small permanent deformation. For heat-seal sealed packages, in order to avoid leaks at the heat seal, good packaging machinery must be in place to control the time, temperature, pressure, cold-press time, pressure, temperature, etc. of the heat-seal, and the thickness of the heat-seal layer. And the thickness of the packaging material must also be appropriate. Of course, the form of the packaging bag also has a great influence on the leakage. Generally, the three-sided sealing bag is less likely to leak than the middle sealing bag, the organ bag, and the self-supporting bag.
As a package, because both penetration and leakage may exist simultaneously, the test results for most packages are the sum of penetration and leakage. In packaging design and application, it is very important to separate leaks from infiltration, because in the tightness of the whole package, often one of them is the main influencing factor. However, it should be clear that regardless of whether the leakage is the main factor, it is very important for the design and manufacture of the entire package to determine whether there is a leak and to know the location of the leak and the leak rate. Our country is mainly focused on the testing of the permeability of materials (oxygen and water vapour), and lacks an inspection method for the overall sealing performance of packages and products. There are only a few qualitative test methods for the leakage of packages. Some product packaging, packaging materials test results are satisfactory, but often unsatisfactory in the application process, this is because the packaging material in the molding, filling, heat sealing, sterilization and storage, transportation, sales, etc. The barrier properties of the material can change and new leaks can also occur. Since the most reliable product sealing performance is obtained by testing the final packaged product, the author believes that the package, not just the packaging material, should be tested whenever possible, so as to give a real evaluation of the package.
Second, the packaging of the penetration of the permeability of the package is generally divided into two types of gas permeability and water vapor transmission rate, while the gas transmission rate is generally represented by the impact of oxygen on the packaging.
1. Detection of gas transmission rate At present, the commonly used methods for measuring gas permeability at home and abroad are shown in Table 1. There are two types of methods: differential pressure method and component analysis method using a coulometric sensor.
Table 1 Test Method for Gas Permeability

The measurement principle of the differential pressure method is to use a test film to separate into several generations of independent space, one side (high pressure chamber) is filled with the measuring gas, and the other (low pressure chamber) is evacuated. There is a certain pressure difference between the two sides, and the gas in the high pressure chamber will pass through