Test method For Moisture Permeability of General Plastic Packaging Bottles
The commonly used food packaging bottles and plastic cosmetic bottles container moisture permeability test methods are developed on the basis of the film moisture permeability test weighing method, using the weighing method test principle. The specific operation steps for the moisture permeability test of flexible packaging plastic bottle containers and the moisture permeability test of rigid packaging containers are slightly different, but the basic test methods are the same.
The test method is as follows: put the desiccant (containing accessories that can be used) into the test container sample, seal the test sample, preheat the test sample, and immediately transfer it to a test box (chamber) under constant humidity and heat conditions for a humid heat test. Afterward, the sample weight needs to be weighed at appropriate intervals according to the moisture permeability of the container material, and the moisture permeability of the container is calculated based on the increase in the sample weight when the penetration is stable.
However, the practical application convenience of this method is not good, the test efficiency is relatively low, and the reliability of the results is not high. This bad result stems from the following aspects:
(1) The test time is relatively long. The weight data of at least three test points must be obtained when judging the penetration stability according to the requirements of the standard. For packaging containers with high moisture permeability, the recommended minimum weighing interval is 2 to 3 days; for packaging containers with low moisture permeability, it is recommended to weigh once every 15 to 30 days. If it is to test a container made of a high-barrier material, it will take several months to complete a test.
(2) When weighing the test sample (or desiccant and its containing accessories), the test sample (or desiccant and its containing accessories) needs to move back and forth in the test environment and the weighing environment, which will damage the test conditions. The osmotic balance established under the environment affects the accuracy of the experimental results. And the shorter the weighing interval, the more significant this effect will be.
(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 put in the container is limited, the moisture absorption capacity of the desiccant will be reduced, and the water vapor pressure difference on both sides of the test sample will change accordingly.
(4) Poor sealing reliability. Especially for non-re-sealable packaging containers, an opening on the container wall is required when the desiccant and its containing accessories are put into it. A wax sealing operation is required after each weighing, which not only greatly increases the complexity of the test operation, but also increases the possibility of sealing failure.
(5) Poor repeatability. The operator's test sample preparation habits and weighing habits all have an impact on the results.
(6) The accuracy of the load cell is limited by its range.
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