Packaging penetration and leakage

Abstract : This paper analyzes the penetration and leakage of packaging, and puts forward the viewpoint of examining the sealing performance of packaging 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.
I. Overview Packaging In addition to aesthetics and physical protection, its most important performance is hermetic properties. There are two ways in which water vapor or gas enters or leaks out of packaging: penetration and leakage.
Permeation means that the gas or water vapor enters the surface from the high-concentration region and is desorbed from the other surface of the low-concentration region by diffusion into the material. The speed of infiltration is related to the structure, thickness, thickness uniformity, temperature, humidity, etc. of packaging materials, and it is also related to various types of diffusion. Permeation is two kinds of packaging, one is penetrating the penetration of packaging material, the other is penetration through the packaging material in the packaging (such as: heat sealing the sealing part of the heat sealing). The latter type of penetration is generally small and is often overlooked by people. However, under certain conditions, the overall tightness of the package may be greatly affected. For high barrier packaging, for the entire package has a higher 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 two concepts that are completely different from penetration. Leakage means that water vapour or gas escapes through the cracks in the material, micropores or microwave gaps between the two materials or enters the package. It is composed of convection (forced flow caused by total pressure gradient) and diffusion (molecular motion caused by concentration gradient). The rate of leakage depends on the size of the leaked pores, the pressure within the package, the type of diffusing agent, the temperature, humidity, etc. of the mental environment. In order to reduce leakage, for mechanically sealed packages, the mechanical seal should have enough and lasting pressure, and the mechanical seal interface must have sufficient surface finish and corresponding dimensional accuracy. One of the two mechanical seal materials is best. 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 available to control the time, temperature, pressure, cold pressure 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 most of the infiltration and leakage may exist simultaneously, the test results of most packages penetrate and leak out. At present, our country mainly focuses on the testing of the permeability of materials (oxygen and water vapor), and lacks the inspection methods 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 of its molding, filling, heat sealing, sterilization and storage, transportation, sales and other processes, materials, Barrier performance changes and new leaks occur. Because the most reliable product sealing performance is tested by the final packaging material, in order to give a real evaluation of the packaging.
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 test methods for gas permeability commonly used at home and abroad are shown in Table 1. There are two types of component analysis methods: pressure difference method and electric quantity analysis sensor.

The measurement principle of the differential pressure method is to divide the test film into two separate spaces, one of which (high pressure chamber) is filled with the measuring gas, and the other (low pressure chamber) is evacuated, so that both sides of the sample are There is a certain pressure difference. The gas in the high pressure chamber will permeate through the membrane to the low pressure chamber. By measuring the pressure or volume change in the low pressure chamber, the permeability of the cylinder can be obtained. The differential pressure method has the advantages of simplicity, convenience, ability to measure various gases, and low equipment and equipment costs. China's only national standard for gas transmission rate GB/T1038-2000 adopts the differential pressure method. The current gas transmission rate test instruments used by enterprises and institutions in China are basically foods for differential pressure method. However, we can find that the differential pressure method has the following obvious disadvantages from the experimental principle and the use of food:
(1) The test condition for the differential pressure method is that the diffusion agent in the high pressure chamber is an absolutely dry gas. The relative temperature in the experiment is RH=0%, and many packages are in use. The relative temperature of the environment is not RH=0%. The gas transmission rate of some materials (such as PA, EVOH, etc.) is also very high with the humidity of the environment. relationship.
(2) The test condition for the differential pressure method is that the medium-low pressure chamber is a vacuum. In the actual packaging, only the vacuum packaging meets this condition, and the common pressure inside and outside the packaging is basically the same scale. At the same time, the test result is that the gas molecules pass through the test film under the double action of the pressure difference and the concentration difference, so the measurement result is often too large. Shanghai Medicinal Packaging Materials Testing Institute applied an oxygen permeability tester (with equal pressure on both sides of the test) by the American MOCON (Oxygen Concentration Test) and Germany's differential pressure method oxygen permeability tester to compare the results. The results of the differential pressure measurement method are too large. This is especially noticeable when the oxygen transmission rate is 5.0 ml/m2·24h·latm.
(3) There is a pressure difference between the two sides of the material during the differential pressure test, which will destroy the structure of some of the more fragile materials and produce small cracks.