With the wide application of flexible packaging materials, people gradually realized the packaging function and the change of packaging form brought by it. For example, although the barrier properties of plastic films are not as good as those of metal materials and glass, the barrier properties of high barrier materials can be used to meet the packaging requirements of most foods and their mechanical properties are better. Excellent bending performance, suitable for the purpose of food flexible packaging, can realize the appearance of light and beautiful package appearance, and bring convenience to display and printing of goods.
Food safety is directly related to consumer safety, and the safety of food packaging is an important factor in food safety. However, no material is absolutely safe to use. Plastic film is also the same. Therefore, the detection of flexible packaging materials for food is absolutely necessary and very important.
First, the test focus and necessity Plastic film is a high polymer, in order to make the actual packaging used by the film material has a certain degree of practical performance, usually in the manufacturing process to add some additives and additives to achieve. For example, the hardness of plastics is generally high. Therefore, in order to make the plastic film more suitable for the application of flexible packaging, it is necessary to add certain additives to the polymer to improve the flexibility of the film. The overall performance of a single material is not good, so the modification and compounding of materials are the most effective ways to improve the overall performance of the material. Material modification and multi-layer composites have their own application fields, but due to the relatively high price of modified materials, composite plastic films are more widely used.
In summary, although the plastic film itself has some drawbacks that are unfavorable for the application, these problems can now be improved by the later processing. Therefore, at present, the plastic films we use can be conveniently used for printing, laminating, processing, packaging, etc., and the wide application of multi-layered composite materials truly realizes the control of packaging costs according to the needs of packaging.
Although some processing techniques can be used today to solve the defect of the overall performance of plastic film materials, due to the fact that the polymer itself will react under certain conditions or when it comes into contact with some substances, the free monomer will precipitate, and at the same time A series of auxiliaries and additives added during the material manufacturing process also have problems of precipitation during the storage and actual use of the material (its components are often harmful to the human body), and therefore require special attention, and it is particularly worth noting that The glue used in the compound packaging bag and the residual solvent problem during the printing process will cause no guarantee for the hygienic performance of the material if these problems occur. If these materials are in direct contact with the food, the precipitated substances will enter the food directly. Seriously jeopardize the health and safety of consumers, such as the previous incident of toxic food packaging bags. Therefore, strict physical and chemical properties must be tested on soft packaging materials for food packaging. At the same time, it should also be noted that with the precipitation of the monomer, the physical properties of the material will also change, and these changes are often detrimental to the packaging function of the material. For example, if a substance is precipitated in the adhesive component of the composite film, the film is more prone to delamination, and its original physical properties will be greatly reduced, such as the sealing effect of the package, the mechanical strength, and the like. It can be imagined that if the physical indicators are not closed, the basic protection of the packaging will be reduced, so that the probability of packaging damage during the transport and storage of the packaging will increase. However, if the packaging is damaged, it will not only have a protective effect on the food, but it will also have a serious impact on other items that are stored together, and further increase the loss. Therefore, the physical properties are also the focus of the testing of packaging materials, and sufficient testing needs to be performed before packaging.
Second, the main test items The scope of soft packaging materials, including non-composite film, composite film, of course, also includes paper packaging (especially plastic coated cardboard packaging). However, plastic sheets and plastic containers with large thickness and high hardness are very similar to the raw materials, the main inspection indicators and the film packaging, and therefore often fall into this range. For soft packaging materials, the main testing items can be divided into three categories: sensory, physical testing indicators, and physical and chemical testing indicators, which should be tested in accordance with the manufacturing standards of the corresponding food-grade products. Physical and chemical testing items include evaporation residue (4% acetic acid, 65% ethanol, n-hexane), potassium permanganate consumption, heavy metals, decolorization test (ethanol, cold meal oil, soaking solution). Each of the physical and chemical tests is related to the health and safety of the packaging and is therefore very important. The use of gas chromatographs for the detection of solvent residues in packaging materials not only helps the users of the materials in the safety of the additives, additives, and solvents used in the printing and compounding of the materials (whether or not they contain ingredients that do not meet the requirements of composite use). Or if the content of a certain component is excessive, there is an overall awareness, and it can also effectively solve the problem of "odor" (residual solvent) in some packaging materials. Therefore, the package can be well controlled through this test. safety. Physicochemical indicators are items that should be tested for any material that comes in contact with food. However, depending on the material's manufacturing process and application area, some tests can be performed selectively, such as evaporation residue tests and decolorization tests. Physical testing is mainly used to test the mechanical properties, barrier properties, thermal properties, and optical properties of materials. The main inspection items include tensile strength, elongation at break, tear strength, peel strength, dart drop performance, and sealing performance. , Heat sealing performance, heat shrinkage, gas transmission rate (including oxygen, carbon dioxide, nitrogen, air, etc.), water vapor transmission rate, light transmittance, haze and so on. For different types of materials and differences in application areas, the specific test items for each material are also different. For example, for the container, the torque force required for opening the cap is also required to be tested. Gas permeability detection of materials is often not necessary to detect a variety of gases, should be based on the actual packaging applications to choose from, for example, if oxygen is the main cause of deterioration of the contents of food, the packaging material should have good barrier properties of oxygen, The oxygen permeability of the material should be checked. As for the detection of gases such as carbon dioxide and nitrogen, it is not necessary here. If not only oxygen, but also carbon dioxide and nitrogen are involved in the quality of the contents, then not only the oxygen permeability of the material but also the nitrogen gas transmission rate and the carbon dioxide gas transmission rate need to be measured when examining the barrier properties of the material. However, the objective detection situation is that only the equipment based on the differential pressure method is currently used in the gas permeability testing equipment. There is no selectivity for the test gas, which can achieve the test for the permeability of the test gas without increasing the detection difficulty and the detection cost. However, breathability testing equipment based on other test methods cannot do it. The results of physical testing will directly affect the actual protection function of the packaging, and should be based on the detection of basic indicators.
The actual situation (characteristics of the contents of the package, the storage environment, and the determination of the value-preservation period, etc.) perform a comprehensive inspection of the properties of the packaging material.
III. Summary Nowadays, the total consumption of packaging materials in packaging materials used in Europe and the United States and other developed countries is between 20% and 25%, and it is increasing year by year. The direction of future development is to promote high cost performance and environmental protection. The new varieties, new materials, and plastic films are already one of the most important packaging materials in use today. Closely related to the development of plastic packaging is to conduct a comprehensive inspection of various properties of packaging materials, and should not only emphasize the performance of some of the material, but ignore the potential harm caused by certain performance degradation, but also to prevent the detection of non-compliance The phenomenon of packaging, because food packaging security and food safety are closely related.