Measurement index of air permeability test of

How to measure the testing index of air permeability of packaging machinery?

1. Influencing factors of air permeability test 　　

There are many factors affecting the air permeability test, such as sensor accuracy, effective range, system leakage, sample processing, material characteristics, test environment, hardware design, software processing, etc. Many of these factors are determined by the innate nature of the design. From an application point of view, users are not concerned with how manufacturers improve these conditions, but what requirements are met and what conditions are met before they can obtain objective and accurate Test data, this article introduces two main measurement indicators-'blank test' and repeatability of test results.

2. Data of 'Blank Test' 　　

1. 'Blank test' 　

'Blank test' is a reflection of the comprehensive error of the equipment. The test error is due to the fact that there are influencing factors that cannot be effectively improved in the gas permeability test, such as system leakage and other unpredictable factors. Although there is no clear 'blank test' in the air permeability test standard, the testing work on the 'blank test' has been widely recognized by the society.　　

2. VAC-V1 'blank test' data 　　

In order to obtain the comprehensive impact value of all factors, VAC-V1 uses a sample that is considered to be completely airtight to test according to normal operating procedures, and then observe the comprehensive impact of the system leakage and other factors on the entire equipment. The 'blank test' value obtained by this method is more reliable to determine the quality of the equipment.　　

Labthink VAC-V1's 'blank test' uses 55μm copper foil (thick aluminum foil sample can also be used) as the sample for the test, strictly sealed, the system is evacuated for 48h (before entering the test state, the vacuum degree of the upper and lower chambers should be 10Pa or less), use the conventional volume of VAC-V1 (the device has an optional expansion volume function) for testing. In order to analyze the impact of changes in ambient temperature and humidity on the test, there is no automatic temperature control function of the device. The obtained pressure time curve is shown in Figure 1. (In addition, there are temperature time and humidity time curves, which will not be repeated here)

The test lasts 12 days (including vacuum time), the temperature is between 18 and 23 ℃, and the ambient humidity is 50 ± 8% RH (such as using the device's self-temperature control function, the test effect is better). After entering the test state, the pressure in the lower chamber increased by 6.0Pa, and the test result was 0.023ml/m2・24h・0.1MPa (if the extended volume or fuzzy test mode is selected, the comprehensive impact of the above factors can be effectively reduced. The test results will be more accurate). Cooperating with the data list to analyze the entire test curve, it is not difficult to conclude that the effect of temperature and humidity changes on the test is very small.

Within the first 60h, the pressure change was relatively large, rising from 0Pa to 3.84Pa. In the subsequent 180h, the pressure increase decreased gradually, and the equivalent air permeability was 0.012ml/m2・24h・0.1MPa. The reason why this phenomenon occurs is related to the degassing state. The test proves that extending the vacuum time can effectively improve the impact on the test results.

Three, data repeatability

1. Elements of data repeatability As each manufacturer implements a certain test method, the components used vary greatly, so the data repeatability of the device is also an important indicator for evaluating the device. By analyzing the data repeatability of the device, you can better understand the error and fluctuation of the device's test data and improve the test efficiency. Data repeatability includes: S (standard deviation), CV (percent coefficient of variation), and LSD (least significant difference between two individual test results based on a 95% confidence level).

2. Measured data 　

Five samples A, B, C, D, E were selected for oxygen permeability test, and Labthink VAC-V1 gas permeameter was used. The test temperature, O2GTR value and test results of the five samples are shown in Table 1: 　　

A and D samples are provided by Thailand Packaging Inspection Center 　　

Sample B is provided by Mecadi Laboratories in Germany 　　

As the O2GTR values ??of the oxygen permeability of the five samples increase in sequence, the standard deviation increases and the data volatility gradually decreases. The main reason is that when testing high-barrier samples, the degassed state of the sample and the influence of the comprehensive factors on the test chamber are more obvious than when testing low-barrier samples, for example, a certain oxygen permeability of samples B and E The results of the sex test differ from their respective average O2GTR values ??by 0.4. For sample B, the effect of data fluctuations accounts for 2.06%, while for sample E, it is only 0.0332%. Therefore, it is somewhat one-sided to discuss the value of volatility separately. Pay attention to the barrier properties of the sample.　

The 'blank test' data and the repeatability of the test results are important indicators for measuring the permeability testing equipment. The test error is not purely determined by the equipment, but also related to the test principle. It is generally believed that the quality of the equipment blank test results has a greater impact on the detection of high-barrier samples, but the repeatability of the equipment data is a comprehensive reflection of the data errors obtained by the equipment in any range of air permeability.