Views:75 Author:Site Editor Publish Time: 2017-02-24 Origin:Site
Methods for testing the permeability of plastic bottle containers
At present, the widely used container permeability test method is developed on the basis of thin film permeability test weighing method, using the principle of weighing test, the relevant test standards are GB/T 6981-1986, GB/T 6982-198 6, ASTM D 3079-94, according to the nature of the material divided into flexible packaging plastic bottle container permeability detection and hard packaging container permeability detection, detection of the two types of containers of the specific operating steps have nuances, but the basic test method is consistent.
The test method is as follows: the desiccant (can be used to fit the attachment) into the test container sample, seal the test sample, the test sample after warm-up treatment into the constant wet and hot conditions of the test box (chamber) for wet heat test, after the container material wetting performance of the high and low at an appropriate interval time to weigh the sample weight, when the penetration reached a stable and the sample weight increase to calculate the amount of permeable container.
Although the method was developed on the basis of thin film test weighing method, it is very difficult to realize automatic detection, so the practical application of the method is not easy, the test efficiency is relatively low, the result is not high credibility. This poor outcome is due to the following:
(1) The test time is relatively long. In accordance with the standard requirements for penetration stability judgment must obtain at least three test points of weight data, for this standard recommended the following interval: for packaging containers with high permeability, the recommended minimum weighing interval of 2 to 3 days; It is calculated that even containers made from materials with poor barrier spree take 7 to 8 days to complete a test, and months to complete a test if the container is detected and manufactured by a high barrier material is detected.
(2) When weighing the test sample (or the desiccant and its containing attachment), the test sample (or the desiccant and its containing attachment) needs to be moved back and forth in the test environment and weighing environment, thus causing the test to not be carried out in a stable state. The transmission of water vapor should have been determined in a permeable equilibrium state, but the movement of this weighing process will destroy the penetration balance established under the test conditions, thus affecting the accuracy of the experimental results. And the shorter the weighing interval, the more significant the effect is, as explained in the standard, for example, it is clearly stated that "too frequent weighing affects 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. Because the desiccant placed in the container is limited, generally in the range of 80 to 100g, so when the test has been carried out for a period of time, wherein the desiccant's moisture absorption capacity will be reduced, accordingtoathattesting sample steam pressure difference on both sides will change. When the desiccant's moisture absorption ability is reduced, the desiccant can be replaced to continue the test, but because the desiccant replacement is difficult to achieve complete lyscaling consistency in weight, so the test will affect how much.
(4) Poor seal reliability. Especially for non-repeatable sealed packaging containers, in which to put the desiccant and its attachments need to open on the wall of the container, and after placing the desiccant and attachment must use sealing wax to seal the opening, because each sample weight weighing needs to be removed from the container, so after each weighing needs to carry out wax sealing operation, which not only greatly increases the complexity of the test operation, but also increases the possibility of seal failure.
(5) Poor repetition. The operator's test sample preparation habits and weighing habits have an impact on the results.
(6) Because the accuracy of the load cell is limited by its range, the accuracy of container detection using this method is much worse than that used for thin film testing. At the same time, the test result unit measured by this method is g/m2.30d, which means that the surface area of the container needs to be accurately measured, but for irregularly shaped containers, this is undoubtedly another test problem.