ASTM E96-00e1 材料的水蒸气渗透性标准测试方法

Designation: E 96 – 00e1 Standard Test Methods for Water Vapor Transmission of Materials1 This standard is issued under the fixed designation E 96; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript epsilon (e) indicates an editorial change since the last revision or reapproval. This standard has been approved for use by agencies of the Department of Defense. e1 NOTE—Table 2 was editorially revised in March 2002. 1. Scope 1.1 These test methods cover the determination of water vapor transmission (WVT) of materials through which the passage of water vapor may be of importance, such as paper, plastic films, other sheet materials, fiberboards, gypsum and plaster products, wood products, and plastics. The test methods are limited to specimens not over 11⁄4 in. (32 mm) in thickness except as provided in Section 9. Two basic methods, the Desiccant Method and the Water Method, are provided for the measurement of permeance, and two variations include service conditions with one side wetted and service conditions with low humidity on one side and high humidity on the other. Agreement should not be expected between results obtained by different methods. That method should be selected which more nearly approaches the conditions of use. 1.2 The values stated in inch-pound units are to be regarded as the standard. Metric inch-pound conversion factors for WVT, permeance, and permeability are stated in Table 1. All conversions of mm Hg to Pa are made at a temperature of 0°C. 1.3 This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user of this standard to establish appro- priate safety and health practices and determine the applica- bility of regulatory limitations prior to use. 2. Referenced Documents 2.1 ASTM Standards: C 168 Terminology Relating to Thermal Insulating Materi- als2 D 449 Specification for Asphalt Used in Dampproofing and Waterproofing3 D 2301 Specification for Vinyl Chloride Plastic Pressure- Sensitive Electrical Insulating Tape4 E 691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method5 3. Terminology 3.1 Definitions of terms used in this standard will be found in Terminology C 168, from which the following is quoted: “water vapor permeability—the time rate of water vapor transmission through unit area of flat material of unit thickness induced by unit vapor pressure difference between two specific surfaces, under specified temperature and humidity conditions. 3.1.1 Discussion—Permeability is a property of a material, but the permeability of a body that performs like a material may be used. Permeability is the arithmetic product of per- meance and thickness. “water vapor permeance—the time rate of water vapor transmission through unit area of flat material or construction induced by unit vapor pressure difference between two specific surfaces, under specified temperature and humidity conditions. 3.1.2 Discussion—Permeance is a performance evaluation and not a property of a material. 3.2 water vapor transmission rate—the steady water vapor flow in unit time through unit area of a body, normal to specific parallel surfaces, under specific conditions of temperature and humidity at each surface.” 1 These test methods are under the jurisdiction of ASTM Committee C-16 on Thermal Insulation and are the direct responsibility of Subcommittee C16.33 on Thermal Insulation Finishes and Vapor Transmission. Current edition approved April 10, 2000. Published July 2000. Originally published as E 96 – 53 T. Last previous edition E 96 – 94. 2 Annual Book of ASTM Standards, Vol 04.06. 3 Annual Book of ASTM Standards, Vol 04.04. 4 Annual Book of ASTM Standards, Vol 10.01. 5 Annual Book of ASTM Standards, Vol 14.02. TABLE 1 Metric Units and Conversion FactorsA,B Multiply by To Obtain (for the same test condition) WVT g/h·m2 1.43 grains/h·ft2 grains/h·ft2 0.697 g/h·m2 Permeance g/Pa·s·m2 1.75 3 107 1 Perm (inch-pound) 1 Perm (inch-pound) 5.72 3 10−8 g/Pa·s·m2 Permeability g/Pa·s·m 6.88 3 108 1 Perm inch 1 Perm inch 1.45 3 10−9 g/Pa·s·m AThese units are used in the construction trade. Other units may be used in other standards. BAll conversions of mm Hg to Pa are made at a temperature of 0°C. 1 Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States. 4. Summary of Test Methods 4.1 In the Desiccant Method the test specimen is sealed to the open mouth of a test dish containing a desiccant, and the assembly placed in a controlled atmosphere. Periodic weigh- ings determine the rate of water vapor movement through the specimen into the desiccant. 4.2 In the Water Method, the dish contains distilled water, and the weighings determine the rate of vapor movement through the specimen from the water to the controlled atmo- sphere. The vapor pressure difference is nominally the same in both methods except in the variation, with extremes of humid- ity on opposite sides. 5. Significance and Use 5.1 The purpose of these tests is to obtain, by means of simple apparatus, reliable values of water vapor transfer through permeable and semipermeable materials, expressed in suitable units. These values are for use in design, manufacture, and marketing. A permeance value obtained under one set of test conditions may not indicate the value under a different set of conditions. For this reason, the test conditions should be selected that most closely approach the conditions of use. While any set of conditions may be used and those conditions reported, standard conditions that have been useful are shown in Appendix X1. 6. Apparatus 6.1 Test Dish—The test dish shall be of any noncorroding material, impermeable to water or water vapor. It may be of any shape. Light weight is desirable. A large, shallow dish is preferred, but its size and weight are limited when an analytical balance is chosen to detect small weight changes. The mouth of the dish shall be as large as practical and at least 4.65 in.2(3000 mm2x). The desiccant or water area shall be not less than the mouth area except if a grid is used, as provided in 12.1, its effective area shall not exceed 10 % of the mouth area. An external flange or ledge around the mouth, to which the specimen may be attached, is useful when shrinking or warping occurs. When the specimen area is larger than the mouth area, this overlay upon the ledge is a source of error, particularly for thick specimens. This overlay material should be masked as described in 10.1 so that the mouth area defines the test area. The overlay material results in a positive error, indicating excessive water vapor transmission. The magnitude of the error is a complex function of the thickness, ledge width, mouth area, and possibly the permeability. This error is discussed by Joy and Wilson.6 This type of error should be limited to about 10 to 12 %. For a thick specimen the ledge should not exceed 3⁄4 in. (19 mm) for a 10-in. (254-mm) or larger mouth (square or circular) or 1⁄8 in. (3 mm) for a 5-in. (127-mm) mouth (square or circular). For a 3-in. (76-mm) mouth (square or circular) the ledge should not exceed 0.11 in. (2.8 mm) wide. An allowable ledge may be interpolated for intermediate sizes or calculated according to Joy and Wilson.6 A rim around the ledge (Fig. X1.1) may be useful. If a rim is provided, it shall be not more than 1⁄4 in. (6 mm) higher than the specimen as attached. Different depths may be used for the Desiccant Method and Water Method, but a 3⁄4-in. (19-mm) depth (below the mouth) is satisfactory for either method. 6.2 Test Chamber—The room or cabinet where the as- sembled test dishes are to be placed shall have a controlled temperature and relative humidity. The temperature chosen shall be between 21 and 32°C (70 and 90°F), and shall be maintained constant within 61°C (6 2°F). A temperature of 32°C (90°F ) is recommended (Note 1). The relative humidity shall be maintained at 50 6 2 %, (When extremes of humidi- ties are desired, the temperature shall be 38 6 1°C (100 6 1.8°F ) The relative humidity shall be 90 6 2 %. Both temperature and relative humidity shall be measured fre- quently7, or preferably recorded continuously. Air shall be continuously circulated throughout the chamber, with a veloc- ity sufficient to maintain uniform conditions at all test loca- tions. The air velocity over the specimen shall be between 0.02 and 0.3 m-s-1(0.066 and 1ft/s). Suitable racks shall be provided on which to place the test dishes within the test chamber. NOTE 1—Simple temperature control by heating alone is usually made possible at 32°C (90°F ). However, it is very desirable to enter the controlled space, and a comfortable temperature is more satisfactory for that arrangement. Temperatures of 23°C (73.4°F) and 26.7°C (80°F) are in use and are satisfactory for this purpose. With cyclic control, the average test temperature may be obtained from a sensitive thermometer in a mass of dry sand. The temperature of the chamber walls facing a specimen over water should not be cooler than the water to avoid condensation on the test specimen. 6.3 Balance and Weights—The balance shall be sensitive to a change smaller than 1 % of the weight change during the period when a steady state is considered to exist. The weights used shall be accurate to 1 % of the weight change during the steady-state period. For example: -perm (5.7 3 10−11kg·Pa−1·s−1·m−2) specimen 10 in. (254 mm) square at 80°F (26.7°C) passes 8.6 grains or 0.56 g/day. In 18 days of steady state, the transfer is 10 g. For this usage, the balance must have a sensitivity of 1 % of 10 g or 0.1 g and the weights must be accurate to 0.1 g. If, however, the balance has a sensitivity of 0.2 g or the weights are no better than 0.2 g, the requirements of this paragraph can be met by continuing the steady state for 36 days. An analytical balance that is much more sensitive will permit more rapid results on specimens below 1 perm (5.7 3 10−11kg·Pa−1·s−1·m−2) when the as- sembled dish is not excessively heavy. A light wire sling may be substituted for the usual pan to accommodate a larger and heavier load. 7. Materials 7.1 Desiccant and Water: 7.1.1 For the Desiccant Method, anhydrous calcium chlo- ride in the form of small lumps that will pass a No. 8 (2.36-mm) sieve, and free of fines that will pass a No. 30 (600-µm) sieve, shall be used (Note 2). It shall be dried at 400°F (200°C) before use. 6 Joy, F. A., and Wilson, H. G., “Standardization of the Dish Method for Measuring Water Vapor Transmissions,” National Research Council of Canada, Research Paper 279, January 1966, p. 263. 7 The minimum acceptable is to preform this measurement each time the sample is weighed. E 96 – 00e1 2 NOTE 2—If CaCl2 will react chemically on the specimen, an adsorbing desiccant such as silica gel, activated at 400°F (200°C), may be used; but the moisture gain by this desiccant during the test must be limited to 4 %. 7.1.2 For the Water Method, distilled water shall be used in the test dish. 7.2 Sealant—The sealant used for attaching the specimen to the dish, in order to be suitable for this purpose, must be highly resistant to the passage of water vapor (and water). It must not lose weight to, or gain weight from, the atmosphere in an amount, over the required period of time, that would affect the test result by more than 2 %. It must not affect the vapor pressure in a water-filled dish. Molten asphalt or wax is required for permeance tests below 4 perms (2.3 3 10−10kg·Pa−1·s−1·m−2). Sealing methods are discussed in Appendix X2. 8. Sampling 8.1 The material shall be sampled in accordance with standard methods of sampling applicable to the material under test. The sample shall be of uniform thickness. If the material is of nonsymmetrical construction, the two faces shall be designated by distinguishing marks (for example, on a one- side-coated sample, “I” for the coated side and “II” for the uncoated side). 9. Test Specimens 9.1 Test specimens shall be representative of the material tested. When a product is designed for use in only one position, three specimens shall be tested by the same method with the vapor flow in the designated direction. When the sides of a product are indistinguishable, three specimens shall be tested by the same method. When the sides of a product are different and either side may face the vapor source, four specimens shall be tested by the same method, two being tested with the vapor flow in each direction and so reported. 9.2 A slab, produced and used as a laminate (such as a foamed plastic with natural “skins”) may be tested in the thickness of use. Alternatively, it may be sliced into two or more sheets, each being separately tested and so reported as provided in 9.4, provided also, that the “overlay upon the cup ledge” (6.1) of any laminate shall not exceed 1⁄8 in. (3 mm). 9.3 When the material as used has a pitted or textured surface, the tested thickness shall be that of use. When it is homogeneous, however, a thinner slice of the slab may be tested as provided in 9.4. 9.4 In either case (9.2 or 9.3), the tested overall thickness, if less than that of use, shall be at least five times the sum of the maximum pit depths in both its faces, and its tested permeance shall be not greater than 5 perms (3.3 metric perms). 9.5 The overall thickness of each specimen shall be mea- sured at the center of each quadrant and the results averaged. Measurement of specimens of 0.125 in. or less in thickness shall be made to the nearest 0.0001 in. Measurement of specimens greater than 0.125 in. in thickness shall be made to the nearest 0.001 in. 9.6 When testing any material with a permeance less than 0.05 perms or when testing a low permeance material that may be expected to lose or gain weight throughout the test (because of evaporation or oxidation), it is strongly recommended that an additional specimen, or “dummy,” be tested exactly like the others, except that no desiccant or water is put in the dish. Failure to use this dummy specimen to establish modified dish weights may significantly increase the time required to com- plete the test. Because time to reach equilibrium of water permeance increases as the square of thickness, thick, particu- larly hygroscopic, materials may take as long as 60 days to reach equilibrium conditions. 10. Attachment of Specimen to Test Dish 10.1 Attach the specimen to the dish by sealing (and clamping if desired) in such a manner that the dish mouth defines the area of the specimen exposed to the vapor pressure in the dish. If necessary, mask the specimen top surface, exposed to conditioned air so that its exposure duplicates the mouth shape and size and is directly above it. A template is recommended for locating the mask. Thoroughly seal the edges of the specimen to prevent the passage of vapor into, or out of, or around the specimen edges or any portion thereof. The same assurance must apply to any part of the specimen faces outside their defined areas. Suggested methods of attachment are described in Appendix X2. NOTE 3—In order to minimize the risk of condensation on the interior surface of the sample when it is placed in the chamber, the temperature of the water prior to preparation of the test specimen should be within 62°F (61.1°C) of the test condition. 11. Procedure for Desiccant Method 11.1 Fill the test dish with desiccant within 1⁄4 in. (6 mm) of the specimen. Leave enough space so that shaking of the dish, which must be done at each weighing, will mix the desiccant. 11.2 Attach the specimen to the dish (see 10.1) and place it in the controlled chamber, specimen up, weighing it at once. (This weight may be helpful to an understanding of the initial moisture in the specimen.) 11.3 Weigh the dish assembly periodically, often enough to provide eight or ten data points during the test. A data point is the weight at a particular time. The time that the weight is made should be recorded to a precision of approximately 1 % of the time span between successive weighing. Thus, if weighings are made every hour, record the time to the nearest 30 s; if recordings are made every day, a time to the nearest 15 min would be allowed. At first the weight may change rapidly; later a steady state will be reached where the rate of change is substantially constant. Weighings should be accomplished without removal of the test dishes from the controlled atmo- sphere, but if removal is prescribed necessary, the time the specimens are kept at different conditions, temperature or relative humidity, or both, should be kept to a minimum. When results of water vapor transmission are expected to be less than .05 perm, a dummy specimen is strongly recommended. Such a dummy specimen should be attached to an empty cup in the normal manner. The environmental effects of temperature variation and buoyancy variability due to barometric pressure fluctuation can be arithmetically tared out of the weighing values. This precaution permits earlier and more reliable achievement of equilibrium conditions. Analyze the results as prescribed in 13.1. E 96 – 00e1 3 11.4 Terminate the test or change the desiccant before the water added to the desiccant exceeds 10 % of its starting weight (Note 1 and Note 3). This limit cannot be exactly determined and judgement is required. The desiccant gain may be more or less than the dish weight-gain when the moisture content of the specimen has changed. NOTE 4—The WVT of some materials (especially wood) may depend on the ambient relative humidity immediately before the test. An apparent hysteresis results in higher WVT if the prior relative humidity was above the test condition and vice versa. It is therefore recommended that specimens of wood and paper products be conditioned to constant weight in a 50 % relative humidity atmosphere before they are tested. Some specimens may be advantageously preconditioned to minimize the mois- ture that the specimen will give up to the desiccant. This applies when the specimen is likely to have high moisture content or when it is coated on the top (vapor source) side. 12. Procedure for Water Method 12.1 Fill the test dish with distilled water to a level 3⁄4 6 1⁄4 in. (19 6 6 mm) from the specimen. The air space thus allowed has a small vapor resistance, but it is necessary in order to reduce the risk of water touching the specimen when the dish is handled. Such contact invalidates a test on some materials such as paper, wood, or other hygroscopic materials. The water depth shall be not less than 1⁄8 in. (3 mm) to ensure coverage of the dish bottom throughout the test. However, if the dish is of glass, its bottom must be visibly covered at all times but no specific depth is required. Water surges may be reduced in placing a grid of light noncorroding material in the dish to break the water surface. This grid shall be at least 1⁄4 in. (6 mm) below the specimen, and it shall not reduce the water surface by more than 10 % (Note 4). NOTE 5—For the Water Method, baking the empty dish and promptly coating its mouth with sealant before assembly is recommended. The water may be added most conveniently after the specimen is attached, through a small sealable hole in the dish above the water line. 12.2 Attach the specimen to the dish (see 10.1). Some specimens are likely to warp and break the seal during the test. The risk is reduced by preconditioning the specimen, and by clamping it to the dish ledge (if one is provided). 12.3 Weigh the dish assembly and place it in the controlled chamber on a true horizontal surface. Follow the procedure given in 11.3. If the test specimen cannot tolerate condensation on the surfa