3. Precautions
The permeability of packaging materials, whether it is water vapor transmission rate or oxygen transmission rate, should pay attention to the following issues in the application process of detection and detection results:
1 The concept of permeability is based on the film's Fic Rian condition. For oxygen, it is generally consistent with Hooke's law except for individual oxygen absorbing materials. However, due to the interaction of water vapor and organic substances with many polymers, it generally belongs to non-Hooke's law diffusion.
2 For composite materials, the structure is not necessarily symmetrical, so there are problems with the positive and negative sides of the sample. Some materials, such as PVDC coated BOPP or PVDC and PVC composite hard plates, have significant differences in the oxygen transmission rate measurement on the front and back, and sometimes even one time difference. This is because during the actual test, the measured result is the sum of the penetration through the sample and the penetration of the seal. PVDC and PVC composite hard sheets used in pharmaceutical blister packaging, some manufacturers use PVDC and PTP aluminum foil heat sealing, some manufacturers use PVC and PTP aluminum foil heat sealing, from the principle, it should be high resistance cadmium layer PVDC and PTP aluminum foil heat sealing is only reasonable because it can most effectively seal the drug.
(3) For absorbent hygroscopicity packaging materials, the effects of adsorption and desorption on the experimental results should be considered during the test, and it should be clear that the equilibrium time is generally longer, and even in the same environment, through different processes. The state of equilibrium is not necessarily the same, which means that the equilibrium state of the material is not only related to the balanced environment but also to the process.
4 Leakage problems in the testing process should be highly valued. The water vapor transmission rate and oxygen transmission rate obtained from any experiment are the sum of penetration and leakage. Only when the leakage is negligible, the measured penetration rate is high. Is accurate. The details of the operation and some auxiliary materials (such as sealing wax, vacuum grease, etc.) all have a significant impact on the leakage during the test.
5 Packaging materials and packaging are two different concepts. With high-resistance cadmium-based packaging materials, it is not always possible to produce high-barrier packaging. From the packaging material to the package, from the package to the consumer, many factors in the process can affect the final barrier properties of the product.
Third, the leakage of packaging
Leakage of packaging generally has two types: one is the inevitable leakage due to the design and structure itself (such as the leakage of bottles and caps), and such leakage must be solved by changing the design and structure of the packaging ( For example, the leakage of bottles and caps can be solved by adding heat-seal gaskets on the bottle mouth; the other is leakage due to defects caused during the manufacture, transportation, etc. of the package, which does not change the design and structure. Under the conditions, adjustments can be resolved. Determining if there is a leak in a package and determining the location of the leak is important for the packaging project. The current domestic and international commonly used packaging leakage testing methods are shown in Table 3. From the point of view of the test method, the leakage of the packaging is generally qualitative. The purpose of the inspection is mainly to detect whether there is a certain package in the production of packaging materials, molding, filling, heat sealing, sterilization, and storage, transportation and sales. Some defects cause product leakage.
There are generally two types of leaks caused by defects in products: press-through and leak-sealing. Press-through refers to the packaging material being pressed by an external force to form a penetrating hole or crack. The reasons for this are generally: 1 The heat seal pressure is too high. In the process of heat sealing, if the heat sealing pressure or the heat sealing mold is not parallel, the local pressure is too large, and some relatively fragile packaging materials are often pressed through. 2 heat sealing mold rough, angular or foreign body. Poorly manufactured heat-sealing molds often crush the packaging materials. Some heat-sealing molds will produce sharp edges after impact, and they can easily press through the packaging material. 3 The thickness of the packaging material was not selected correctly. Some packaging machines require thickness of the packaging material. If the thickness is too large, some locations of the packaging bag may be pressed through. For pillow type packaging machines, the thickness of the packaging material should not exceed 60 цм. If the packaging material is too thick, it can be easily broken in the sealing area of ​​the pillow type packaging. 4 Wrong choice of packaging material structure. Some packaging materials have poor compression resistance and cannot be used to package some hard, angular materials. For example, a paper-aluminum-plastic composite material is used to package granular granules. 5 Improperly designed packaging mold. In the design process, if the die hole of the heat seal film does not conform to the shape and size of the packaged material, and the mechanical strength of the packaging material is different, it is easy to press through or fracturing the packaging material during the packaging process.
Leakage seal is due to some factors, so that should be through the melting of the fusion of the site, not sealed, leak seal generally have the following reasons: 1 heat seal temperature is not enough. The same sealing materials require different heat sealing temperatures in different heat sealing locations, different packaging speeds require different heat sealing temperatures, different packaging temperature requirements require different heat sealing temperatures, and the sealing equipment requires vertical and horizontal sealing temperatures. Differently, in the same heat-sealing mold, the temperatures of different parts may not be the same. These are problems that must be considered in the packaging. For the heat sealing equipment, there is also a problem of temperature control accuracy. At present, domestic packaging equipment has poor temperature control accuracy, and generally has a deviation of ±10°C, that is, if the temperature we control is 140°C, the actual The temperature during the packaging is between 130°C and 150°C. Many companies' airtightness inspections use random sampling in finished products to check. In fact, this is not a good method. The most reliable method is to sample the lowest temperature point within the range of temperature change, and it should be continuously sampled so that the sample can cover the longitudinal and lateral parts of the mold. 2 The sealing area is contaminated. In the filling process of the packaging, the sealing position of the packaging material is often contaminated by the packaging material, and the pollution is generally divided into liquid pollution and dust pollution. To solve the problem of contaminants in the sealing area can be solved by improving the packaging equipment and using anti-pollution and anti-static heat sealing materials. 3 equipment and operation problems. If the heat seal film has foreign matter, the heat seal pressure is not enough, and the heat seal film is not parallel. 4 Problems with packaging materials. If the corona crosses the surface, there are too many heat-sealable lubricants causing poor heat seals.
There is also a “half leak†in the actual leakage of packaging, which means that in the process of molding, filling, heat-sealing, sterilizing, and transporting and selling of packaging products, although there is no perforation leakage between the inside and outside, but its high barrier Layers (such as aluminum foil, SIOx barrier coating or plating) produce cracks or pinholes, and "semi-leakage" will seriously affect the overall sealing performance of the package, which is a non-negligible factor in the packaging process. I have done some research work on the pinhole of aluminum foil and its influence on barrier properties, and obtained the theoretical formula for calculating oxygen permeability and water vapor transmission rate of aluminum foil and its composite materials from pinhole parameters of aluminum foil. . How to reduce the cracks and pinholes of the barrier layer in the process of packaging and distribution of packaging materials in the aspects of packaging design, material selection, and packaging equipment coordination; how to detect the crack resistance of packaging materials and how to evaluate barrier layer folding The impact of cracking on packages is a very significant issue in practice.
Fourth, the conclusion
In the long-term production and practice, the author encountered many problems in the penetration and leakage of packaging, and felt that it involved a wide range, including the production and use of packaging materials, supporting of packaging equipment, storage, transportation and sales of packaging products, and ultimately The whole process of consumer use. At present, there are many problems in the detection of water vapor and oxygen permeation in the country. Therefore, in writing this article, I hope that I can start with some suggestions for the formulation of standards for infiltration and leakage and the actual production and use of packaging materials.
Author: Liaoqi Zhong
From: (Guangzhou Economic and Technological Development Zone Aluminum Foil Co., Ltd.)