Water Proof
Gravimetric method-the method of arbitration of water vapor permeation tests
Abstract: This article examines defining parameters and developing test methods for testing permeation of water vapor.
Keywords: method arbitration, the gravimetric method, the method of sensor, the water vapor permeation, calibration
Water vapor permeation test method is primarily into two categories: the gravimetric method and the sensor, with the latter method is oldest used. Gravimetric method is the method of arbitration testing permeation of water vapor. Data System methodology sensor must be calibrated with the gravimetric method.
Vapor permeation 1.Water materials
permeation of moisture of materials is the main index into the property valuation water proof packaging materials such as sheet and film. This can be determined by testing permeation of water vapor.
The indexes frequently used to evaluate the water barrier property of materials are the water vapor transmission rate? WVT? And permeation of water vapor (Pv). WVT is the amount of water to pass through the steam per square meter of the sample with a thickness of some in the 24 hours. It is measured at a required temperature, relative humidity and vapor pressure. The unit is · g/m2 24h. permeation of water vapor represents the amount of water vapor transmitted through per unit area and per unit thickness of the sample temperature required and the relative humidity in the unit of water vapor pressure inside per unit of time. The relationship between PV and WVT is indicated below
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Where: d is thickness of the sample? P is the pressure difference of water vapor on both sides of the sample, that has nothing to do with the relative humidity on both sides. The value of 1.157 × 10-9 is used for the transfer unit. It is clearly described in ASTM E 96 as the index of water vapor permeation of materials is defined in accordance with the gravimetric method.
2. Development of methods for water vapor permeation test
2.1 Method Gravimetric
In the mid-nineteenth century, barrier property of materials has become a new index for evaluating the performance of materials. The first standard for permeation tests, ASTM E 96, has been published in 1953. This standard defines the permeation of water vapor parameters of materials using the principle and the definition of method parameters Gravity. At that time, the testers permeation of water vapor built using the gravimetric method not only necessary accessories diversified complex, more probation and was lower in tests of efficiency, farmers also need training rigorous.
Gravimetric method at present has made obvious progress. Newest Gravimetric permeation testers water vapor has combined environmental testing and weighing only one condition, which not only improves test accuracy and simplifies instrument operation operators but also greatly reduce the failure rate for the test. At the same time, the development of components and a weight on technology significantly improves test accuracy and effectiveness of the gravimetric method.
2.2 Method of sensor
method detection method includes relative humidity, infrared and test method electrolytic method Test sensors, which are successively introduced since 1770.
Dynamic method relative humidity can be used for a quick comparison of the permeation water vapor specimens. In addition, the test environment is adjustable so that the actual state of implementation of the package can be better simulated. This method measures directly is not the amount of water vapor Micro, but the time or the speed of transmission of water vapor specimen. Therefore, the data system of the tester are calibrated based on film repository completely, which is also mentioned in ASTM E 398-03 as follows: Standard Films, who have been using gravimetric calibration ... ... A standard, whose film calibration WVTR was determined by gravimetry according to the method of dehydrating test methods ISO 15106-1 E96 ... also specifications clear about the source data referential film. It is necessary for the system data should be consistent with the gravity method.
In the test method infrared, infrared detection technology is applied to test the permeation of water vapor. process adopts the electrolytic smelting technology for high precision tests of the water vapor amount of micro. These two methods vary considerably in terms of sensor, but the principle is similar in structure testing, both to test directly the amount of water vapor to pass through the sample. In addition, these two methods to test the entire water vapor permeation of the package. While the gravimetric method can not be taken into consideration both the weighing range and accuracy of test when testing overall package, it always takes film repository calibrate its data system. In ISO 15106-2, it is clearly specified that the reference film and test data should be obtained as a function of gravimetric means. "Reference Sample: a sample with a transmission rate of water vapor is known, or for which the rate of transmission of water vapor has been determined in accordance with ISO 2528. "
3. The method of arbitration
Since there are several methods water vapor permeation test existing simultaneously, an arbitration method becomes necessary when an action is brought on dispute concerning the data of the permeation of water vapor. The method of arbitration should be the basic method and requires no system additional data to calibrate their own data system. It should be scientific and test technology for simple procedures. In addition, the method arbitration should have a better repeatability of data and error test ideal. Is a goal-based analysis of the characteristics of each method.
First, as noted above, the calibration of these methods must reference film sensor for the calibration data, whether they are testing the amount of water vapor transmission or not directly. Data permeation of water vapor Film reference are obtained by gravimetric method? ISO 2528 or ASTM E 96?. In addition, despite the fact that the test method adjustable infrared is accepted in ASTM F 1249 Conditional Authorization (concerns over should be obtained in advance) as a method of arbitration, its data system must be calibrated by gravimetric means. Clearly, the system calibrated data from the infrared method is consistent with that of the gravimetric method. Therefore, if the infrared method can be used as a method of arbitration, there no reason that his method of calibration of reference, the gravimetric method, can not be the method of arbitration. Moreover, water vapor quantity of micro sensors in the method adopted sensor belongs to the type of consumption. It must be calibrated by the reference film regularly. The data systems of these methods sensors calibrated by reference film is a unified system for data mutual substitution. But they are not qualified as a test method of arbitration.
Second, since the repeatability data is concerned, data presented in multiple standards are very similar? E 96 ASTM / E 96 M-05? ASTM E 398-03 and ASTM F 1249-06?. Regarding the error test, ASTM E-96 / M E-96-05 gives this description: "This test method has no bias because the water vapor transmission documents is defined in terms of this test method. 'To test the method error of sensor, ASTM 1249-06 gives an explanation as follows: the measured values are from comparison with films of known reference value. The precision of this method depends on the validity of the value attributed to the reference films.
In conclusion, the vapor permeation tests, the gravimetric method is not only the approach most widely used, but also the method of arbitration. It is the standard for these systems data obtained by vapor permeation of water from other test methods.
About the Author
Labthink, the excellent provider of testing instruments and testing services, is devoted to provide most excellent and complete quality control solutions for pharmaceutical, foodstuff, cosmetics, packaging, printing, adhesive, automotive, petrochemistry, environment, biology, new energy, construction, aviation and electronic industries worldwide.
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