A number in parentheses indicates the year of last reapproval. This standard has been approved for use by agencies of the Department of Defense. The films may be free filmsor they may be applied to porous substrates. The methodthat most closely approaches the conditions of use should beselected.
|Published (Last):||4 August 2012|
|PDF File Size:||16.12 Mb|
|ePub File Size:||17.76 Mb|
|Price:||Free* [*Free Regsitration Required]|
A number in parentheses indicates the year of last reapproval. This standard has been approved for use by agencies of the Department of Defense. The films may be free filmsor they may be applied to porous substrates. The methodthat most closely approaches the conditions of use should beselected. The values given in parentheses are mathematicalconversions to SI units that are provided for information onlyand are not considered standard. Factors for conversion arestated in They run essentially the same kinds of tests as in theASTM methods, but do so instrumentally.
However, it appearsthat no side-by-side tests have been run comparing results frommeasurements with such instruments to these ASTM methodsfor precision and accuracy. It is the responsibilityof the user of this standard to establish appropriate safety andhealth practices and determine the applicability of regulatorylimitations prior to use.
Referenced Documents2. Acceptedinch-pound unit is grains per square foot per hour. Accepted SIunit is grams per square metre per 24 h. Acceptedinch-pound unit is grains per square foot per hour per inch ofmercury called a perm. Accepted SI unit is grams per squaremetre per 24 h per millimetre of mercury called a metricperm.
Summary of Test Methods4. Current edition approved June 1, Published July Originally approvedin Last previous edition approved in as D — 03 United States1desiccant, and the assembly placed in a test chamber with acontrolled atmosphere. Two sets of exposure conditions areacceptable for this test method. Two sets of exposure conditions are acceptable forthis test method Significance and Use5.
In some services, for example, exteriorwood and masonry, the coating has to allow moderate amountsof water vapor to pass through the film without damage to it. Hence, the water vapor transmission characteristics of coatingsare important in assessing their performance in practical use.
These values are for use in design,manufacture, and marketing. In general, the more permeable a coatingis to the passage of moisture as is typical of many water-reducible coatings, the greater its affinity for water and thegreater the increase in transmission when tested in and exposedto high humidities. Absorption of water may make a coatingless dense, thus allowing moisture to diffuse easily and cause amuch higher moisture vapor transmission rate, WVTR thanwould occur in drier environments.
Ifthe cup or dish is made of aluminum, it must be anodized orgiven a protective clear coating to prevent corrosion. The contacting facesof the flanges shall be ground to such flatness that when thefilm is in position, moisture transfer can occur only through theexposed film area. For hard films, or films having a very roughsurface, a soft rubber gasket may be inserted between the filmand the flange.
The flanges shall then be held together withsuitable clamps. Air shall be circulatedthroughout the chamber to maintain uniform conditions at alltest locations. For low or high humidity conditions, a standarddesiccator or other suitable cabinet may be used. For maintain-ing constant relative humidity by means of aqueous solutions,refer to procedures outlined in Practice E Reagents and Materials7.
Use caution in handling magnesiumperchlorate because of possible chemical reaction that may beproduced if it comes in contact with some organic materialsand is subsequently heated to regenerate the anhydrous salt. It must be highly resistant tothe passage of water vapor.
It must not affect the vapor pressure in a water-filled dish. NOTE 1—Among acceptable sealants are 1 a mixture ofmicrocrystalline wax and refined crystalline parafin wax, 2 tissueembedding wax, and 3 a mixture of beeswax and rosin. Your comments will receive careful consideration at ameeting of the responsible technical committee,1which you may attend. Supportmaterials such as paper charts,5filter paper, and glass clothhave been found satisfactory in some instances.
Such supportcan have an effect on the test results. Test Specimens8. Apply air drying coatings to substrates usingone of the methods described in Practices D or D NOTE 2—Special test conditions may require that the coating be appliedby brushing, roller coating or other special methods.
Permeancemay vary with the baking schedule or the time of air drying. If the material is to betested as a free film, remove it from the substrate and allow thepreviously unexposed surface to dry for an additional 7 days. The drying schedule may be modified as recommended bymanufacturer.
NOTE 4—Examine test films for the presence of pinholes or otherdefects before commencing the test. It may be advisable to apply the testmaterial in two coats, applying the second coat perpendicular to the firstcoat and allowing for an adequate drying period between coats to achievethe desired film thickness.
Coatings should not be applied toboth sides of a support. Glass cloth is preferred for coatingsthat are cured by baking. Test Conditions9. Thoroughly seal the frame to the edge of thecup at the temperature to be used in the test.
If the coating is ona substrate or support, place the coated side away from thedesiccant in the cup. NOTE 5—Imperfections in the film that are not readily visible mayproduce inconsistent results; consequently make sure that the test isalways run at least in triplicate. Record time, temperature, and relative humidity. Coatings expected to have high WVTratings, over 10 perms, may require weighings more frequentlythan once a day.
More D In some services, for example, exterior wood and masonry, the coating has to allow moderate amounts of water vapor to pass through the film without damage to it. Hence, the water vapor transmission characteristics of coatings are important in assessing their performance in practical use. These values are for use in design, manufacture, and marketing. 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. Absorption of water may make a coating less dense, thus allowing moisture to diffuse easily and cause a much higher moisture vapor transmission rate, WVTR than would occur in drier environments. Scope 1.