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Advantages of Gas Permeability Test Using Equal-pressure Method -from empirical research experiences

Advantages of Gas Permeability Test Using Equal-pressure Method -from empirical research experiences
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Advantages of Gas Permeability Test Using Equal-pressure Method -from empirical research experiences - 1

Advantages of Gas Permeability Test Using Equal-pressure Method -from empirical research experiences Abstract: based on Labthink’s empirical research and its long term operating of equal-pressure method gas permeability testers, this article introduces advantages of equal-pressure method gas permeability testing in some special fields. Key Words: equal-pressure method, differential-pressure method, package, contact lenses Equal-pressure method was gradually developed in the 1970s to determine oxygen permeability of packaging materials. Although equal-pressure method has limitation in its actual application and still needs improvement to challenge the fundamental position of differential-pressure method in gas permeability testing, it possesses test advantages of its own, which expand the application fields of equal-pressure method. 1 The Research and Development of Equal-pressure Method Instrument in Labthink Since the application of package oxygen permeability testing, differential-pressure method has always been the most fundamental and most widely used test method. However, equal-pressure method is a newly developed method in North America in the 1970s. These two methods are based on completely different test principles using different units. That is why test results obtained using these two methods cannot be compared directly. Since equal-pressure method possesses test merits of its own, sometimes it forms effective complementation with differential-pressure method. For this reason, Labthink began to develop equal-pressure method gas permeability testers since 2004. Before its research and development of equal-pressure instruments, Labthink has accumulated much research experience to develop gas permeability testing instruments in aspects of sealing, processing of test cells, designing pipeline and etc. Because domestic micro oxygen probing technology has a short development period and the expanding and application of sophisticated high precision products are not commonly seen, there are some difficulties in the initial research period of such instruments. After Labthink’s unremitting efforts of more than two years and through its cooperation with top ranking international micro oxygen probing corporations, Labthink has made breakthrough development in micro oxygen probing technology. It now has manufactured oxygen permeability test instruments using equal-pressure method completely meeting ISO international standards. 2 Advantages of Equal-pressure Method The theoretical basis of equal-pressure method is not as profound as that of differential-pressure method instruments. It still needs improvement in terms of the richness of test indexes and conveniences of actual application. For example, equal-pressure method can only test the self-property of specimen, i.e., oxygen (or carbon dioxide) permeance. It is unable to test diffusion coefficient and solubility coefficient. Moreover, there are others problems existing such as the unicity of test gas and higher cost of instrument operation. However, the unique characteristics of equal-pressure method give it some incomparable advantages in some special testing www.labthinkinternatio nal.com.cn

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Advantages of Gas Permeability Test Using Equal-pressure Method -from empirical research experiences - 2

fields. 2.1 Container Packaging Testing Oxygen permeability testing of container packaging can be considered as the salient merit of equal-pressure method. Oxygen permeance of package was previously estimated by testing oxygen permeance of packaging sheeting. However, container package is not uniform in thickness and the property of materials has changed during production. Therefore, the estimated results and actual test results vary very much. In equal-pressure method, pressures on both sides of specimen are standard pressure, so the two sides have equal pressure, in which case package...

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Advantages of Gas Permeability Test Using Equal-pressure Method -from empirical research experiences - 3

packaging any more. Equal-pressure method has got some new application in other fields, such as the oxygen permeability testing of contact lenses. Oxygen permeability of contact lenses, directly influencing the wearing comfort of users and in turn affecting distribution of the lenses, is one of the important indexes in evaluating contact lenses. That is why oxygen permeability attracts particular attention of lens manufacturers. ISO has issued special test standards for contact lenses. Among these standards, test principle and test instruments of ISO 9913-2 is very close to the...

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