Containers are packaged directly for liquid packaging. Because the moisture barrier property is one of the key indicators that affect the product shelf life, it is particularly important to accurately measure the moisture permeability of the container. Due to the special shape of the container, it is difficult to detect the moisture permeability of the container. Therefore, the moisture permeability test of the container was first used to estimate the moisture permeability of the container by detecting the container sheet. However, due to the uneven wall thickness of the container, Material properties will change during the production process (in the manufacturing process of the container, the raw materials need to undergo high temperature, cooling and other processing processes), so there will be no small deviation between the estimated results and the actual test results. Later, there was a test method for measuring the moisture permeability of a container, which was the most commonly used traditional method for measuring the moisture permeability of a container. However, this method has many deficiencies both in the test efficiency and in the convenience of operation. Therefore, Jinan Languang has opened up new trails. The introduction of a sensor-based container moisture permeability tester has enabled the rapid and accurate determination of the moisture permeability of containers.
Traditional method of container moisture permeability testing
At present, the commonly used method for measuring the moisture permeability of containers is based on the measurement of the moisture permeability of the film, and the principle of weighing method is used. The relevant test standards are GB/T 6981-1986 and GB/T 6982-1986. ASTM D 3079-94, according to the nature of the material, is divided into a moisture-permeable test for flexible packaging containers and a moisture permeability test for hard-packed containers. There are subtle differences in the specific operating procedures for these two types of containers, but the basic test methods are consistent.
The test method is as follows: Put the desiccant (can be used to contain accessories) into the sample of the test container, seal the test sample, and immediately transfer the test sample into the test chamber (chamber) with constant hot and humid conditions and perform the moist heat test. Afterwards, the weight of the sample should be weighed at an appropriate interval according to the permeability of the container material, and the permeability of the container should be calculated from the increase in the weight of the sample after the penetration has stabilized.
Although this method is developed on the basis of thin film test weighing method, it is very difficult to achieve automatic detection. Therefore, the practical application of the method is not convenient, the test efficiency is low, and the result is not reliable. This bad result stems from the following aspects:
(1) Longer test time. The determination of the osmotic stability in accordance with the standard requirements must obtain weight data for at least three test points. The following intervals are recommended for this standard: For packaging containers with high moisture permeability, the recommended minimum weighing interval is 2 to 3 days. For a packaging container with low moisture permeability, it is recommended to weigh it once for 15 to 30 days. It is estimated that even a container made of a material with poor barrier properties requires 7 to 8 days to complete a test. If a container made of a high barrier material is tested, it takes several months to complete one test.
(2) When weighing the test sample (or desiccant and its accessories), the test sample (or the desiccant and its accessories) needs to be reciprocated in the test environment and the weighing environment, so that the test cannot be performed on one It is done in a stable state. The original water vapor transmission should be measured in a penetrating equilibrium state, but this movement in the weighing process will destroy the established osmotic balance under the test conditions, which will affect the accuracy of the experimental results. And the shorter the weighing interval, the more significant this effect will be. This is also stated in the standard. For example, it is clearly stated that "the weighing too often will affect the accuracy of the test."
(3) It is difficult to maintain a stable water vapor pressure difference on both sides of the test sample for a long time. Since the desiccant placed in the container is limited, it is generally in the range of 80 to 100 g. Therefore, after the test is performed for a period of time, the desiccant's moisture absorption ability will decrease, and the water vapor pressures on both sides of the test sample will be correspondingly reduced. The difference will change. When the desiccant's ability to absorb moisture is reduced, the desiccant can be replaced to continue the test, but since the replacement of the desiccant is difficult to achieve exactly the same weight, it will have an impact on the test.
(4) poor sealing reliability. Especially for non-reusable packaging containers, it is necessary to open the container wall when placing the desiccant and its accessories, and the sealing agent must be used to seal the opening after the desiccant and accessories are put in, because each time The desiccant and its accessories need to be removed from the container when weighing the sample weight. Therefore, the wax sealing operation is required after each weighing. This not only greatly increases the complexity of the test operation, but also increases the sealing. The possibility of failure.
(5) Poor repeatability. The operator's test sample preparation habits and weighing habits all have an impact on the results.
(6) Since the accuracy of the load cell is limited by its range, the accuracy of the container detection method using this method is much poorer than the accuracy of this method for thin film testing. At the same time, the unit of test result measured by this method is g/m2·30d, which means that the surface area of ​​the container needs to be accurately measured. However, this is undoubtedly another testing problem for irregularly shaped containers.
Using Sensor Method to Detect the Water Vapor Permeability of the Container
The principle of measuring the moisture permeability of a container using a sensor method is the same as the principle of detecting the air permeability of a container, so the practical application and promotion of this method is based on a good basis. The specific test method is as follows:
First prepare the test sample. The production method is the same as the method of detecting the oxygen permeability of the container, and the sample placement method differs depending on the specific detection site. The detection of the moisture permeability of the entire container usually includes the moisture permeability detection of the bottle body and the whole moisture permeability detection of the bottle cap and the bottle body. When detecting the moisture permeability of the bottle body, the container should be inverted, the bottle mouth should be fixed downwards in a special bottle holder, and then the bottle mouth should be filled with a special sealed encapsulant to seal the bottle mouth to prevent water vapor from the bottle holder and bottle mouth. The joints penetrate into the bottle body. The test sample produced by this method is shown in Figure 1.
Fig.1 Test sample for moisture permeability testing of finished bottles
When detecting the overall moisture permeability of the bottle cap and the bottle body of the container, firstly, a small hole should be opened in the bottom of the container. The size of the hole is preferably the input pipe and the output pipe that have just been fed with nitrogen gas. Then place the container cap upside down in a special bottle holder and place it in the middle, and then pour the matched potting glue into the bottle body and the wall between the bottle holder to ensure the nitrogen in the recessed part of the bottle bottom. The input and output tubes are filled with potting material, and the finished test sample is shown in Figure 2.
Figure 2 Samples of the overall moisture permeability test of the finished container
Afterwards, the upper cavity of the test method membrane moisture permeability testing apparatus was replaced with a specific housing (supporting the equipment), and then the prepared test sample was installed to separate the permeate chamber into two independent air flow systems (see FIG. 3 ). In this way, the carrier gas (drying) is on the side of the container and the relative humidity on the other side is maintained, so that the concentration of water vapor on both sides of the sample is different, that is, there is a stable concentration of water vapor (relative humidity difference). Under the influence of the difference in water vapor concentration (difference in relative humidity), water vapor is carried into the sensor by the carrier gas flow through the vessel wall. At this time, the sensor accurately measures the water vapor content in the carrier gas flow, and the test sample can be calculated. Water vapor transmission rate.
Fig. 3 Principle of the moisture permeability test of the sensor method container
Labanink's Labthink TSY-W3 Electrolysis Moisture Permeability Tester is Jinan Languang's Labthink TSY-W3 Electrolytic Moisture Tester, which can realize rapid and accurate measurement of the overall moisture permeability of the container. The test accuracy can reach at least 0.001g/pkg·d, and the test time is generally only 3 ~ 4 days. Compared with traditional weighing instruments, the Labthink TSY-W3 Electrolytic Permeability Tester has considerable advantages both in terms of detection accuracy and detection efficiency.
to sum up
The use of conventional methods to detect the overall moisture permeability of the container has the disadvantages of low test efficiency and poor test accuracy, which hinder the development of the overall moisture permeability of the container. Therefore, although this method has been implemented for many years, the actual use effect is still not good. The use of the sensor method to detect the moisture permeability of the container as a whole is a major advancement in the traditional method. This method can detect the moisture permeability of all current flexible packaging items (including flexible packaging bags, paper boxes, bottles, etc.) and can fully examine the packaging. The moisture permeability of the material provides a more accurate and comprehensive test data for the shelf life of the content.
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