Penetration and leakage of the hottest Package1

  • Detail

Infiltration and leakage of packaging

I. overview

in addition to aesthetics and physical protection, the most important performance of packaging is airtightness. There are three ways for water vapor or gas to enter or escape from the packaging: infiltration and leakage

permeation refers to that gas or water vapor enters the surface from the high concentration area, diffuses to the material, and desorbs from the other surface of the low concentration area. The speed of permeation is related to the structure, thickness, thickness uniformity, temperature, humidity, etc. of the packaging material, as well as the type of diffusing agent. There are two kinds of penetration for packages, one is through the penetration of packaging materials, and the other is through the penetration of the joint of packaging materials in the package (such as the heat joint of the sealing part of heat sealing). The latter kind of penetration is generally small and is often easy to be ignored, but under some specific conditions, it may have a great impact on the overall sealing of the package. For high barrier packaging, in order to have a high sealing performance of the whole package and reduce the penetration of the heat seal, the seal should have sufficient width, and the heat seal material used must have a certain barrier performance

leakage is completely different from infiltration. Leakage refers to the release or entry of water vapor or gas into the package through cracks, pores or tiny gaps between two materials. It is composed of convection (forced flow caused by total pressure gradient) and diffusion (molecular motion caused by concentration gradient). The speed of leakage depends on the size of leakage pores, the pressure in the package, the type of dispersant, and the temperature and humidity of the environment. In order to reduce leakage, for the package with mechanical seal, there should be sufficient and durable pressure outside the mechanical seal, and the mechanical seal interface must have sufficient surface finish and corresponding dimensional accuracy. It is best to have a certain elasticity and small permanent deformation of one of the two mechanical seal materials. For heat sealed packages, in order to avoid leakage at the heat seal, good packaging machinery must be available to control the time, temperature and pressure of heat sealing and the time, pressure and temperature of cold pressing. At the same time, the thickness of heat sealing layer and the thickness of packaging materials must also be appropriate. Of course, the form of packaging bags also has a great impact on leakage. Generally, the leakage probability of three side sealing bags is smaller than that of medium sealing bags, organ bags, self-supporting bags, etc

as a package, because penetration and leakage may exist at the same time, the test results of most packages are the sum of penetration and leakage. In packaging design and application, it is very important to distinguish leakage and penetration, because in the tightness of the whole packaging, one of them is often the main influencing factor. But it should be clear: whether the leakage is the main factor or not, it is very important for the design and manufacture of the whole package to determine whether there is leakage in a package and to understand the location and rate of leakage. China 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 some qualitative inspection methods for the leakage of packages. For the packaging of some products, the test results of packaging materials are satisfactory, but they are often unsatisfactory in the application process. This is because the barrier performance of packaging materials will change and new leakage will occur in the process of forming, filling, heat sealing, sterilization, storage, transportation, sales and so on. Since the most reliable sealing performance of products is obtained by the test of the final packaged products, the author believes that the packaging should be tested as long as possible, not just the two sections of the broken sample aligned with the packaging material at the fracture, so as to give a real evaluation of the packaging

Second, the permeability of packaging

the permeability of packaging is generally divided into two categories: gas permeability and water vapor permeability, and the gas permeability is generally represented by oxygen, which has a great impact on the packaging

1 ﹐ detection of gas permeability

the commonly used gas permeability test methods at home and abroad are shown in Table 1. From the perspective of test principle, there are two types: differential pressure method and component analysis method through electric quantity analysis sensor

The measuring principle of the pressure difference method is to separate the test film into two independent spaces, fill one side (high-pressure chamber) with measuring gas, and vacuumize the other side (low-pressure chamber), so that a certain pressure difference is generated on both sides of the sample, and the gas in the high-pressure chamber will penetrate into the low-pressure chamber through the thin film. The permeability of the gas can be obtained by measuring the pressure or volume change of the low-pressure chamber. Differential pressure method is simple, convenient, can measure all kinds of gases, and the price of instruments and equipment is low. The only national standard of gas transmission rate gb/t 1038-2000 in China adopts the differential pressure method. At present, the gas transmission rate testing instrument used by enterprises and institutions in China is basically the instrument of differential pressure method. However, we can find that the differential pressure method has the following obvious characteristics from the experimental principle and the application practice of the instrument:

① the test conditions of the differential pressure method are: the diffuser in the high-pressure chamber is an absolutely dry gas. The relative humidity in the experiment is rh=0%, while many packages are in use, the relative humidity of the environment is not rh=0%. The gas transmittance of some materials (such as PA, EVOH, etc.) is also greatly related to the humidity of the environment

② the test condition of differential pressure method is that the medium and low pressure chamber is vacuum. In actual packaging, only vacuum packaging meets this condition, and the common internal and external pressure of packaging is basically equal. At the same time, the test result is that when gas molecules pass through the test film under the dual action of pressure difference and concentration difference, the measurement result is often enlarged. Shanghai pharmaceutical packaging materials testing institute applied the oxygen permeating instrument of American Morgan (MOCON) (the pressure on both sides was equal during the test) and the oxygen permeating instrument of German differential pressure method to carry out a comparative experiment. The results showed that the control of the experimental process and data processing by the measurement computer control system of differential pressure method met the requirements of the corresponding national standards for man-made panels, and the result was relatively large, especially when the oxygen permeating rate was less than 5.0ml/m2 It is more obvious at 24.h.1atm

③ there is a pressure difference on both sides of the material in the test process of the pressure difference method, which will destroy the structure of some relatively fragile materials, produce small cracks, pinholes and other defects, and the existence of the pressure difference will also make the material deform, make the material thickness thinner, and increase the air permeability area, thus affecting the experimental results; The existence of differential pressure in the test process is not conducive to the fixation and sealing of the sample, and it is easy to produce leakage, while the external gas enters the low-pressure chamber of the system, and the detection system cannot identify it; There is a pressure difference on both sides of the test material, so the test in the test process is to be carried out under the external force. The stress state of the material will change some microscopic results of the material, which will have a certain impact on the cadmium resistance performance of the material. Although there is no Research Report in this regard at present, it is a problem that cannot be ignored for some materials

④ due to the limitations of its detection means, the differential pressure method generally cannot detect the permeability of packages, and the permeability of packaging is the most reliable for evaluating the tightness of packaging

⑤ due to the limitations of its experimental method, the accuracy of the instrument is relatively low. Generally, the minimum amount of measurement is only 1.0-3.5ml/m2.24h 1atm, at present, the best instrument of this kind is only 0.5ml/m2.24h 1atm, and the repeatability of the experiment is poor under the condition of low permeability and excess

the principle of the electricity analysis type oxygen transmittance tester is to use the test membrane to separate into two independent air flow systems, one side is the flowing gas to be measured (which can be pure oxygen or mixed gas containing oxygen, and the relative humidity can be set), and the other side is the flowing nitrogen with stable relative humidity. The total pressure on both sides of the sample is equal, but the partial pressure of oxygen is different. Under the effect of the concentration difference of oxygen, oxygen penetrates the film. The oxygen through the film is sent to the electrical component sensor under the nitrogen gas flow. The electrical analysis sensor can accurately measure the amount of oxygen contained in the gas flow, so as to calculate the oxygen transmittance of the material

the electricity analysis type oxygen transmittance tester can control the test conditions such as different humidity, temperature and gases with different oxygen content, and can more effectively simulate the actual use conditions of the packaging. During the test, the two test pressures of the samples are the same, which is conducive to reducing the leakage and damage to the samples during the test. Because the electricity analysis type oxygen transmittance tester can accurately determine the composition of oxygen in the transmitted gas, Therefore, the test results are more accurate and reliable. Due to its reasonable design and high sensitivity of the detection probe, the detection accuracy of the electricity analysis type oxygen transmittance tester is quite high. The minimum amount of detection can generally reach the film of 0.01ml/m2.24h 1atm, package: 0.001 ml/tm. For the high-precision detector, the minimum amount of film can reach: 0.001 ml/m2.24h 1atm, the package is 0.00005ml/24h 1atm, its accuracy is 500 times higher than that of differential pressure method. Of course, the instrument also has disadvantages, that is, it is expensive, there are not many manufacturers, and its detection service life is not long. For materials with high oxygen transmission rate, the test process has little impact on the service life of the detection probe, and the test cost is high

for high resistance cadmium packaging materials containing aluminum foil, it is inappropriate to use the differential pressure method to detect the oxygen transmission rate, because its oxygen transmission rate is low, which is generally 0.5ml/m2.24h Below 1atm. It is understood that high resistance cadmium packaging materials containing aluminum foil are often less than 0.2ml/m2.24h, 1atm measured with the electric quantity analysis oxygen transmittance tester of Morgan in the United States. According to the theoretical calculation of the pinhole of aluminum foil, the oxygen transmission rate of generally good aluminum foil composite packaging materials is less than 0.1ml/m2.24h 1atm, the measurement accuracy is 0.3ml/m2.24h 1atm。 Obviously, it can not meet the requirements of detecting high barrier packaging materials containing aluminum foil. In a sampling inspection of a drug packaging material testing station, the oxygen transmission rate was measured by the oxygen transmission rate tester (differential pressure method) of Toyo Seiki, Japan. The results showed that all composite materials containing aluminum foil were unqualified (0.5ml/m2.24h.1atm), while the oxygen transmission rate tester (electric quantity analysis type) of American Morgan was sent to the packaging material scientific research and testing center of Shanghai Drug Administration for testing, but all of them were qualified. For the packaging materials such as PA and EVOH, which have a great impact on the oxygen permeability and environmental humidity, the differential pressure method can only be tested under the condition of relative humidity rh=0%, because generally, the electricity analysis type oxygen passing rate tester should also be used for testing

at present, the oxygen transmission detection instruments used in China are basically differential pressure method, and most of them are Japanese Toyo precision machinery products. There is only gb1038 "test method for gas permeability of plastic films and sheets - differential pressure method" for oxygen transmittance in China. The testing unit also purchased the differential pressure method oxygen transmittance tester for the reason of the standard. At present, it is quite necessary to formulate a national standard for measuring the oxygen transmission rate by electric quantity analysis method similar to astmd3985, which is used to measure the oxygen transmission rate of high barrier and humidity sensitive composite packaging materials

2. Detection of water vapor transmission rate

at present, the commonly used test methods of water vapor transmission rate at home and abroad are shown in Table 2. From the perspective of detection principle, they mainly include weighing method and infrared verification method

the principle of weighing method is to put a certain desiccant (usually anhydrous calcium chloride) into the moisture permeable cup, put the tested film on the moisture permeable cup, and seal it with wax to make it moisture permeable

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