1、Designation:F124906 (Reapproved 2011)F124913 Standard Test Method for Water Vapor Transmission Rate Through Plastic Film and Sheeting Using a Modulated Infrared Sensor 1 This standard is issued under the xed designation F1249; the number immediately following the designation indicates the year of or
2、iginal adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A superscript epsilon () indicates an editorial change since the last revision or reapproval. 1. Scope 1.1 This test method covers a procedure for determining the rate
3、of water vapor transmission through exible barrier materials. Themethodisapplicabletosheetsandlmsupto3mm(0.1in.)inthickness,consistingofsingleormultilayersyntheticornatural polymersandfoils,includingcoatedmaterials.Itprovidesforthedeterminationof(1)watervaportransmissionrate(WVTR),(2) the permeance
4、of the lm to water vapor, and (3) for homogeneous materials, water vapor permeability coefficient. NOTE 1Values for water vapor permeance and water vapor permeability must be used with caution. The inverse relationship of WVTR to thickness and the direct relationship of WVTR to the partial pressure
5、differential of water vapor may not always apply. 1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of r
6、egulatory limitations prior to use. 2. Referenced Documents 2.1 ASTM Standards: 2 D374Test Methods for Thickness of Solid Electrical Insulation (Withdrawn 2013) 3 D1898Practice for Sampling of Plastics (Withdrawn 1998) 3 E96/E96MTest Methods for Water Vapor Transmission of Materials E104Practice for
7、 Maintaining Constant Relative Humidity by Means of Aqueous Solutions E177Practice for Use of the Terms Precision and Bias in ASTM Test Methods E178Practice for Dealing With Outlying Observations E691Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method 3. Term
8、inology 3.1 Denitions: 3.1.1 water vapor permeability coeffcientthe product of the permeance and the thickness of the lm. The permeability is meaningful only for homogeneous materials, in which case it is a property characteristic of bulk material. 3.1.1.1 Discussion This quantity should not be used
9、 unless the relationship between thickness and permeance has been veried in tests using several thicknesses of the material.An accepted unit of permeability is the metric perm centimeter, or 1 g/m 2 per day per mm Hgcm of thickness. The SI unit is the mol/m 2 sPamm. The test conditions (see 3.1) mus
10、t be stated. 3.1.2 water vapor permeancethe ratio of a barriers WVTR to the vapor pressure difference between the two surfaces. 3.1.2.1 Discussion 1 ThistestmethodisunderthejurisdictionofASTMCommitteeF02onFlexibleBarrierPackagingandisthedirectresponsibilityofSubcommitteeF02.10onPermeation. Current e
11、dition approved Aug. 1, 2011Oct. 1, 2013. Published November 2011November 2013. Originally approved in 1989. Last previous edition approved in 20062011 as F124906.F124906 (2011). DOI: 10.1520/F1249-06R11.10.1520/F1249-13. 2 ForreferencedASTMstandards,visittheASTMwebsite,www.astm.org,orcontactASTMCus
12、tomerServiceatserviceastm.org.ForAnnualBookofASTMStandards volume information, refer to the standards Document Summary page on the ASTM website. 3 The last approved version of this historical standard is referenced on www.astm.org. This document is not anASTM standard and is intended only to provide
13、 the user of anASTM standard an indication of what changes have been made to the previous version. Because it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version of the st
14、andard as published by ASTM is to be considered the official document. Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA19428-2959. United States 1An accepted unit of permeance is the metric perm, or 1 g/m 2 per day per mm Hg. The SI unit is the mol/m 2 sPa. Sin
15、ce the permeance of a specimen is generally a function of relative humidity and temperature, the test conditions must be stated. 3.1.3 water vapor transmission rate (WVTR)the time rate of water vapor ow normal to the surfaces, under steady-state conditions, per unit area. 3.1.3.1 Discussion An accep
16、ted unit of WVTR is g/m 2 per day. The test conditions of relative humidity and temperature where the humidity is the difference in relative humidity across the specimens, must be stated. 4. Summary of Test Method 4.1 A dry chamber is separated from a wet chamber of known temperature and humidity by
17、 the barrier material to be tested. The dry chamber and the wet chamber make up a diffusion cell in which the test lm is sealed. Water vapor diffusing through the lmmixeswiththegasinthedrychamberandiscarriedtoapressure-modulatedinfraredsensor.Thissensormeasuresthefraction of infrared energy absorbed
18、 by the water vapor and produces an electrical signal, the amplitude of which is proportional to water vapor concentration. The amplitude of the electrical signal produced by the test lm is then compared to the signal produced by measurement of a calibration lm of known water vapor transmission rate
19、. This information is then used to calculate the rate at which moisture is transmitted through the material being tested. 5. Signicance and Use 5.1 The purpose of this test method is to obtain reliable values for the WVTR of plastic lm and sheeting. 5.2 WVTR is an important property of packaging mat
20、erials and can be directly related to shelf life and packaged product stability. 5.3 Data from this test method is suitable as a referee method of testing, provided that the purchaser and seller have agreed on sampling procedures, standardization procedures, test conditions, and acceptance criteria.
21、 6. Apparatus 6.1 This method utilizes water vapor transmission apparatus 4 (Fig. 1) comprised of the following: 6.1.1 Diffusion CellAn assembly consisting of two metal halves which, when closed upon the test specimen, will accurately dene a circular area. A typical acceptable diffusion cell area is
22、 50 cm 2 . The volume enclosed by each cell half, when clamped, is not critical; it should be small enough to allow for rapid gas exchange, but not so small that an unsupported lm that happens to sag or buckle will contact the top or bottom of the cell. A depth of approximately 6 mm (0.250 in.) has
23、been found to be satisfactory for 50-cm 2 cells. 4 The sole source of supply of the apparatus known to the committee at this time is Mocon/Modern Controls, Inc., 7500 BooneAvenue North, Minneapolis, MN 55428. If you are aware of alternative suppliers, please provide this information toASTM Internati
24、onal Headquarters.Your comments will receive careful consideration at a meeting of the responsible technical committee, 1 which you may attend. FIG. 1 Measuring System F124913 26.1.1.1 Diffusion Cell ORing An appropriately sized groove machined into the humid chamber side of the diffusion cell retai
25、ns a neoprene Oring. The test area is considered to be the area established by the inside contact diameter of the compressed Oring when the diffusion cell is clamped shut against the test specimen. 6.1.1.2 Diffusion Cell Sealing SurfaceA at rim around the dry side of the diffusion cell. This is a cr
26、itical sealing surface against which the test specimen is pressed; it shall be smooth and without radial scratches. 6.1.1.3 Diffusion Cell Air PassagesTwo holes in the dry half of the diffusion cell. This is necessary only in the earlier model WVTRinstrumentsthathaveaseparateconditioningrackandtesti
27、ngchamber.TheseshallincorporateOringssuitableforsealing the diffusion cell to the test chamber pneumatic ttings for the introduction and exhaust of air without signicant loss or leakage. NOTE 2Use of Multiple Diffusion CellsExperience has shown that arrangements using multiple diffusion cells are a
28、practical way to increase the numberofmeasurementsthatcanbeobtainedinagiventime.Aseparateconditioningrack(Fig.2)maybeusedthatcontainsamanifoldwhichconnects the dry-chamber side of each individual diffusion cell to a dry-air source. Dry air is continually purging the dry chamber of those cells that a
29、re connected to the conditioning rack while the humid chamber side is held at a specic relative humidity by distilled water or a saturated-salt solution. It is desirable to thermostatically control the temperature of the conditioning rack as described in 6.1.3. 6.1.2 TestChamberAcavityintowhichthedi
30、ffusioncellisinserted.Again,thisisnecessaryonlyintheearliermodelWVTR instruments that have a separate conditioning rack and testing chamber. The test chamber shall incorporate means for clamping the diffusion cell in accurate registration with pneumatic system openings to the dry-air source and the
31、infrared detector. The chamber shall also provide a thermometer well for the measurement of temperature. 6.1.3 Diffusion Cell Temperature ControlIt is desirable to thermostatically control the temperature of the diffusion cell to within61F.Asimple resistive heater attached to the station in such a m
32、anner as to ensure good thermal contact is adequate for thispurpose.Athermistorsensorandanappropriatecontrolcircuitwillservetoregulatethetemperatureunlessmeasurementsare being made close to ambient temperature. In that case it may be necessary to provide cooling coils to remove some of the heat. 6.1
33、.4 FlowmeterA means for regulating the ow of dry air within an operating range of 5 to 100 cc/min is required. 6.1.5 Flow-Switching Valves, for the switching of dry-gas ow streams of the water vapor transmission apparatus. 6.1.6 Infrared SensorA water vapor detector capable of sensing 1 g/L of water
34、, or, in other terms, 1 ppm by volume, or 0.002% relative humidity at 37.8C. 6.1.7 RecordingDeviceAmultirangestripchartrecorderorotherappropriateinstrumentformeasuringthevoltagedeveloped by the signal amplier. 6.1.8 Desiccant Drying System, shall be capable of reducing the concentration of water vap
35、or in the gas source down to less than 0.5 ppm by volume or 0.001% relative humidity at 37.8C. In earlier model WVTR equipment, a separate desiccant drying system is needed for the conditioning rack and test chamber. 6.1.9 Flow-Metering ValveA ne-metering valve capable of controlling the dry-gas ow
36、rate to the test cell when the apparatus is in the measure mode of operation. 7. Reagents and Materials 7.1 Desiccant, 4,5 for drying gas stream. 7.2 Absorbent Pads (not critical), such as lter pads of 30 to 75 mm in diameter. Necessary only in earlier model WVTR equipment that utilizes distilled wa
37、ter or saturated salt solutions to generate the desired relative humidity. 5 Linde Molecular Sieve, Type 4Aor Type 5A, in the form of 1 8 in. pellets as may be obtained from the Union Carbide Co., Linde Division, Danbury, CT 06817-0001. FIG. 2 Conditioning System F124913 37.3 Distilled Water, for pr
38、oducing 100% relative humidity, or various saturated salt solutions to produce other relative humidities as described in Practice E104. Newer WVTR equipment does not require saturated salt solutions. Refer to the manufacturers instructions for generating relative humidity. 7.4 Reference Film, known
39、WVTR material for system calibration. 7.5 Sealing Grease, a high-viscosity, silicone stopcock grease or other suitable high-vacuum grease is required for lubrication of Orings and to seal the specimen lm in the diffusion cell. 7.6 Nitrogen Gas, shall be dry and contain not less than 99.5% nitrogen.
40、Needed only with certain WVTR instruments. 8. Sampling 8.1 Select material for testing in accordance with standard methods of sampling applicable to the material under test. Sampling may be done in accordance with Practice D1898. Select samples considered representative of the material to be tested.
41、 If the material is of nonsymmetrical construction, the orientation should be noted. 9. System Calibration With Reference Film 9.1 Follow the manufacturers instructions for calibrating the WVTR instrument with a reference lm. 10. Test Procedure 10.1 PreparationofApparatus(Fig.1)Ifprecedingtestshavee
42、xposedtheapparatustohighmoisturelevels,outgasthesystem to desorb residual moisture. 10.2 Number of Specimens TestedTest enough specimens to characterize package permeation rates but never less than three per sample. 10.3 Preparation of Test Samples: 10.3.1 Cut the test specimen to approximately 10 c
43、m by 10 cm (4 in. by 4 in.). 10.3.2 Measure specimen thickness at four equally spaced points within the test area and at the center in accordance with guidelines described in Test Method D374. 10.3.3 Lightly grease the cell sealing surface and the cell Oring. 10.3.4 For earlier model WVTR systems th
44、at require the use of distilled water or saturated salt solutions, insert one to three absorbent pads into the lower half-cell and dampen with distilled water or a desired salt solution. Otherwise, for newer WVTR instruments, follow the manufacturers instructions for generating the desired relative
45、humidity. 10.3.5 Affix the test lm to the diffusion cell following the manufacturers instructions. Fig. 3 shows the type of diffusion cell usedinearliermodelWVTRequipmentthatconsistedofaseparateconditioningrackandtestingchamber.Diffusioncellsinnewer WVTR equipment are similar to the lower half of th
46、e cell displayed in Fig. 3. 10.3.6 If using a separate conditioning rack, clamp the assembled cell in the conditioning rack.Allow the lm to condition in the diffusion cell until steady state has been attained. If unfamiliar with the material being tested, the operator should investigate the effect o
47、f conditioning time to be certain that sufficient time has been allowed for the material to equilibrate under the test conditions (see Note 3). 10.4 Measure the WVTR of the lm specimen following the manufacturers instructions. NOTE 3When testing materials for which the operator has no previous histo
48、ry, additional time must be allowed to assure that true equilibrium has been reached. When in doubt, retest after an additional conditioning interval of several hours. 10.5 Recordtemperatureofeachtestwithreferencetoathermometerorthermocoupleinstalledinthetestchamberthermometer well. Temperature is a
49、 critical parameter affecting the measurement of WVTR. During testing, monitor the temperature, periodically, to the nearest 0.5C. Report the average temperature and the range of temperatures observed during the test. FIG. 3 Film Diffusion Cell F124913 410.6 Standby and Shutoff Procedures: 10.6.1 Follow the manufacturers instructions for putting the instrument in standby when not being used. 10.6.2 When the system is not to be used for an extended period and there are no lms that require conditioning,
