Temperature influence factors and development trend of sealing test of flexible packaging

Abstract: This paper introduces the test method of the sealing property of soft packaging and the important influencing factors At the same time, it gives a detailed description of the new development and application of the test technology in combination with the market demand Key words: leakage, sealing, packaging, storage, broken bag When choosing soft packaging form and soft packaging materials, many indexes need to be considered, such as the barrier of packaging to light and gas, the size of top gap space, the cost of packaging, the cost of transportation and storage, the convenience of use, the environmental protection of materials, etc The comprehensive score of these indexes is the basis for choosing packaging, while the sealing test (or the sealing test of the sample after simulated test such as aging test and vibration test) is the veto in the evaluation of soft packaging Because the sealing is the premise of realizing the packaging functionality, and it is also the comprehensive embodiment of whether the selected soft packaging materials match each other and the selected packaging forms in mechanical properties, thermal properties and optical properties The packaging with poor airtightness will lead to deterioration of goods due to gas or liquid entering and leaving the packaging, and may also cause pollution to the environment or surrounding goods For functional packaging, leakage will also cause the loss of packaging functionality, which will bring serious losses to users 1 There are two kinds of sealing test methods, positive pressure method and negative pressure method In the positive pressure method, gas is injected into the sample to increase its internal pressure, and then the leakage is judged according to the change of the internal pressure of the sample The negative pressure method is to place the sample in the water of the test chamber By vacuuming the test chamber, the internal and external pressure difference of the sample immersed in the water will be generated, and the situation of the gas overflowing or the water penetrating into the sample will be observed, so as to determine whether the sample has sealing defects The sealing test data of soft packaging is an important basis for setting conditions and evaluating results in the simulation tests of commodity storage, stacking and vibration Compared with other inspection items, the tightness test is the smallest The main feature is that it is applicable to a wide variety of detection objects, while the detection objects of other tests are often relatively single, for example, tensile test can only detect film or sheet, kneading test can only detect film, headspace gas test can only detect packaging, and sealing test can not only detect various packaging, but also test packaging semi-finished products, samples can be just The finished product can also be the sampling in any link of the circulation process At the same time, by using the test accessories, the types of the samples can be expanded, and the restrictions on the shape and size of the samples can be further relaxed 2 The influence factors of the sealing property of soft packaging is the comprehensive embodiment of whether the selected soft packaging materials match each other and the selected packaging forms in mechanical properties, thermal properties and optical properties External force, temperature change, light radiation and other factors can directly affect the sealing of soft packaging In addition, some factors may not have a direct impact on it, but they will lead to the reduction of material strength, the deterioration of the thermal sealing layer fastness, the leakage of additives in soft packaging materials and other problems, and then affect the sealing of soft packaging However, it must be noted that the specific impact of each influencing factor on different packaging forms and packaging materials is not the same If we want to analyze the actual effect of each influencing factor on the sealing of soft packaging one by one, it will greatly increase the workload and cost of testing Therefore, it is difficult for us to take all the influencing factors into account in the actual testing, but for the most prominent The influencing factors must be taken into account and even reflected as one of the test conditions, otherwise the practicability of the test results will be restricted Practical experience shows that temperature is the key factor to affect the sealing performance of flexible packaging during its manufacture and subsequent storage and transportation On the one hand, for the soft packaging materials with heat sealing, whether the heat sealing temperature is appropriate directly affects the strength of the sealing place, and the flatness of the bag may also affect the actual sealing effect of the soft packaging due to the heat deformation On the other hand, for the finished soft packaging materials, the environmental temperature still has a significant impact on their sealing, because the current commonly used soft packaging materials are composite films, some of which are even composed of three or more kinds of materials, such as polymers, metals, paper, and so on, while the thermal properties of different materials are often different After the change of the external environment temperature, the difference of the material expansion coefficient will lead to the separation or deformation between layers of the composite material, or the reduction of the strength of the material itself, so the strength of the sealing part of the soft package will also be greatly reduced Therefore, the sealing performance of many soft packages under the conditions of high or low temperature is far lower than the test data in the normal temperature environment, which leads to The leakage of packaging is common Therefore, we should pay more attention to the influence of environmental temperature change when testing the sealing property of soft packaging It is necessary to control the temperature of the samples for sealing test and realize the actual test at a specified temperature 3 New changes in sealing test Nowadays, all kinds of new packaging have been launched into the market, but the inspection requirements for the tightness of soft packaging have not been reduced, but more attention has been paid than before, because the more expensive packaging, the less you want to cause the failure of packaging functionality due to leakage, whether in brand image or cost, it is crucial to enhance the inspection means to ensure the tightness of packaging In order to meet the needs of this market, the sealing test equipment has greatly improved in the control of test conditions and test accuracy First of all, it is to introduce the sealing detection equipment with temperature control function As mentioned earlier, the change of ambient temperature during the test can indeed bring significant impact on the sealing test results, but in fact, the impact of temperature on the sealing of flexible packaging has also attracted the attention of packaging designers, especially the current long-distance transportation of goods makes many goods experience significant temperature changes from the completion of production to the use of consumers Some of them Products will experience temperature fluctuations in circulation, and some products are stored in high or low temperature However, it is not uncommon that the packaging of these products is qualified in the laboratory environment, but leakage occurs in actual application Now we can accurately detect the sealing property of the soft package by simulating the change of temperature environment to preprocess the sample or controlling the temperature in the test chamber However, because the change of temperature and the change of pressure in the package mostly occur at the same time, the test data obtained by controlling the temperature in the test chamber to simulate the actual environment is more practical At present, we have been able to achieve the temperature control of the test chamber from room temperature to 60 ℃, which has been able to meet the storage environment simulation requirements of most commodities Secondly, improve the detection accuracy and quantitative detection index Sealing test is a destructive test, it is impossible to test all commodities, so it is very important to use limited samples to get as many effective test data as possible for sealing test However, in the past, only two conclusions were passed and failed in the sealing test, which could not provide more effective and valuable data Therefore, when the actual storage and transportation environment is a little more harsh, the number of packages with leakage may increase significantly Now we can use the positive pressure test equipment to measure not only the minimum bursting pressure of the soft package sample, but also the minimum pressure that the soft package sample can bear without rupture under the specified pressure For a long time, in addition, it can also realize the sealing test of the designated position of the sample through the test accessories, effectively enhance the practicability of the test data, and help to analyze the weak links in the packaging structure, provide the basis for improving the packaging structure, selecting more appropriate packaging materials, and provide more accurate damage critical conditions for the stacking, storage, transportation, impact and other test models 4 As an important test item of soft packaging, the sealing test equipment has greatly improved the test environment control and test accuracy, enhanced the practicability of sealing test data, and played a greater role in improving the structure of soft packaging and selecting soft packaging materials In the future, with the diversification of soft packaging forms, the sealing detection technology of soft packaging will have further development, and play a greater role in the evaluation of soft packaging with other detection indicators.