ASTM D and ASTM E96 both address the determination of the water vapor transmission and permeance of coatings. ASTM E96/E96M. ASTM D Standard Test Methods for Water Vapor Transmission of Organic Coating Films. Buy ASTM D R TEST METHODS FOR WATER VAPOR TRANSMISSION OF ORGANIC COATING FILMS from SAI Global.
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The permeability is calculated by multiplying the permeance by the thickness of the material. Your email address will not be published. For the wet cup method, two results, each the mean of triplicate trials, are expected to differ by less than adtm How precise is the testing? What is water vapor? Essentially, the test determines how much vapor is lost through the film in the wet cup method or how much vapor the desiccant attracts or draws through the film for the dry cup method.
The Significance of the Permeability of Paints | KTA UniversityKTA University
The WVT d6153 determined by dividing the rate of weight change, which is the slope of the plot, by the area of the test specimen. If the cup is filled with water, the dish loses water over the course of the test so the plot points downward. The wet cup method can produce higher results than the dry cup method when the same coating is tested under the same air temperature and humidity conditions.
The steam that you see consists of very small droplets of liquid water suspended in air. The permeance and permeability may be calculated from the WVT.
For example, the units might be grams per hour or nanograms per 24 hours. It can be used to test paper, plastic films, other sheet materials, fiberboards, gypsum and plaster products, d163 products, and plastics.
If the container is filled with desiccant, the method is called the dry cup method or the desiccant method. The Water Vapor Permeance is often simply call the permeance, and the water vapor permeability is often simply called the permeability. Dd1653 a Reply Cancel reply Your email address will not be published. If a sample is tested twice by the dry cup method, and each test consists of three replicate trials, the difference between the permeance results from the two tests are expected to be less than a quarter of a perm if the permeance is less than 1 perm.
The weight data is plotted versus time. ASTM E96 covers many materials, including coatings. Verify that the units are the same Method: This includes personalizing content and advertising. These three terms are used atsm describe how quickly water vapor diffuses through a solid material. Leave this field empty. They run essentially the same kinds of tests as in the ASTM methods, but do so instrumentally.
The Water Vapor Transmission WVTpermeance, and permeability are very closely related in that one is calculated from the other. ASTM D does not discuss this correction.
ASTM D – 13 Standard Test Methods for Water Vapor Transmission of Organic Coating Films
Hence, the water vapor transmission characteristics of coatings are important in assessing their performance in practical use.
What should one consider when comparing the permeance of coatings? Water vapor can be produced by the evaporation of water or the sublimation of ice or snow. First the WVT is determined. The system may at first gain or lose weight more quickly, and then settle into a constant or steady-state rate of weight change after a couple of days, or longer, depending on the type of material being tested. In the gas phase, water molecules move very rapidly and are not bound together.
The answer to the question posed is based on the substrate and the service environment. Historical Version s – view previous versions of standard. In general, the more permeable a coating is to the passage of moisture as is typical of many water-reducible coatings, the greater its affinity for water and the greater the increase in transmission when tested in and exposed to high humidities.
Water in the gas phase is invisible.
The Significance of the Permeability of Paints
Referenced Documents purchase separately Ast documents listed below are referenced within the subject standard but are not provided as part of the standard. See the slide below for more information about the correction. The method that most closely approaches the conditions of use should be selected.
However, it appears that no side-by-side tests have been run comparing results from measurements with such instruments to these ASTM methods for precision and accuracy.