1、T 464 om-12 TENTATIVE STANDARD 1944 OFFICIAL STANDARD 1973 OFFICIAL METHOD 1979 REVISED 1985 REVISED 1990 REVISED 1995 REVISED 2001 REVISED 2006 REVISED 2012 2012 TAPPI The information and data contained in this document were prepared by a technical committee of the Association. The committee and th
2、e Association assume no liability or responsibility in connection with the use of such information or data, including but not limited to any liability under patent, copyright, or trade secret laws. The user is responsible for determining that this document is the most recent edition published. Appro
3、ved by the Standard Specific Interest Group for this Test Method TAPPI CAUTION: This Test Method may include safety precautions which are believed to be appropriate at the time of publication of the method. The intent of these is to alert the user of the method to safety issues related to such use.
4、The user is responsible for determining that the safety precautions are complete and are appropriate to their use of the method, and for ensuring that suitable safety practices have not changed since publication of the method. This method may require the use, disposal, or both, of chemicals which ma
5、y present serious health hazards to humans. Procedures for the handling of such substances are set forth on Material Safety Data Sheets which must be developed by all manufacturers and importers of potentially hazardous chemicals and maintained by all distributors of potentially hazardous chemicals.
6、 Prior to the use of this method, the user must determine whether any of the chemicals to be used or disposed of are potentially hazardous and, if so, must follow strictly the procedures specified by both the manufacturer, as well as local, state, and federal authorities for safe use and disposal of
7、 these chemicals. Water vapor transmission rate of paper and paperboard at high temperature and humidity 1. Scope1.1 This method is for the gravimetric determination of the water vapor transmission rate (WVTR) of sheet materials at 37.8C (100F) with an atmosphere of 90% RH on one side and a desiccan
8、t on the other. 1.2 It is generally suitable for any material up to 3 mm (1/8 in.) thick, although it may be used with caution for thicker materials if the edges of the specimen are completely sealed. 1.3 For testing at other conditions see TAPPI T 448 “Water Vapor Transmission Rate of Paper and Pap
9、erboard at 23C (73F) and at 50% RH.” 1.4 This test can be used for both creased and uncreased specimens. See TAPPI T 465 “Static Creasing of Paper for WVT Tests” or TAPPI UM 590 “Creasing of Paperboard for Water Vapor Transmission Rate (WVTR) Testing.” 2. Significance 2.1 This method provides a mean
10、s for measuring the ability of a material to protect contents, that are enclosed within the material, from undesirable changes due to the transmission of water vapor to or from the surrounding environment. 2.2 The influence of temperature and humidity on the water vapor transmission rate of paper or
11、 paperboard is seldom linear, so test results obtained at lower temperatures and humidities cannot safely be extrapolated to apply to warmer, more humid conditions. 2.3 If sheet materials are not homogeneous, there may be a considerable difference in the transmission rate depending on which side fac
12、es the high humidity. Usually the test is made so as to simulate the use of the material in practice; for example, a material for enclosing a dry product would be tested by exposing to the dry atmosphere that surface which would face the product in the package. T 464 om-12 Water vapor transmission r
13、ate of paper and / 2 Paperboard at high temperature and humidity 3. Definitions The water vapor transmission rate (WVTR) of a sheet material is the mass of water vapor transmitted per unit time per unit area from one face of the sheet to the other under specified steady conditions. The standard unit
14、 is g/m2 day and for this method, the specimen has an atmosphere approaching 0% RH on one face and 90% RH on the other, at a temperature of 37.8C (100F). NOTE 1: WVTR is a distinctive characteristic, often erroneously termed “permeability” or “moisture-vapor transfer” (MVT). 4. Apparatus14.1 Test di
15、sh, a light, shallow, non-permeable dish, that can be weighed on an analytical balance, having an opening as large as is practical, with an area of at least 50 cm2 (about 8 in.2) and an inside depth of 10 - 15 mm (0.4 - 0.6 in.). The design of the test dish is such that a wax seal made between the d
16、ish and the specimen is impervious to water vapor and clearly defines the test area. A suitable design is shown in Fig. 1. Fig. 1. Design of test dish. 4.2 Template, to define the test area and the location of the wax seal. It is made of a circular metal disk 3-6 mm (about 1/8 - 1/4 in.) thick, with
17、 its edge beveled at an angle of approximately 45. The diameter of its smaller, bottom face defines the test area and must be measured accurately. It is approximately equal to, and not greater than, the diameter of the effective opening of the dish in contact with the specimen. There is a small hole
18、 through the disk to allow air passage, and a handle to facilitate removal of the disk after the wax solidifies. Positioning lugs may help to center the template in the dish. 4.3 Balance, of 200-g capacity, sensitive to at least 0.5 mg, with a pan large enough to hold the test dishes. 4.4 Testing ro
19、om or cabinet, maintained at 37.8 0.6C (about 100F) and 90 2% RH, with air continuously circulated over the exposed surface of the test specimens at a speed of at least 30 m/min. (about 100 ft/min.). The test area must be such as to avoid the dripping of any condensate on the assemblies during the t
20、est. NOTE 2: Take care to ensure by actual measurement that the air circulated over the test specimen is actually between 88 and 92% RH and between 37.2 and 38.4C during normal operation. If the test specimen assemblies cannot be weighed inside the 37.8C (100F), 90% RH cabinet, it is recommended tha
21、t the cabinet be located in a controlled constant temperature-humidity environment e.g., 23C (73F) and 50% RH in which the weighing can also be performed. 4.5 Cutting template, a circular disk to cut specimens of such a size that they lie flat over the groove on the dish for sealing. 4.6 Weighing co
22、vers. If the test specimen assemblies must be removed from the conditioned enclosure for weighing, covers may be used to prevent appreciable change in weight of the assemblies during weighing (see 8.7.2). The covers are circular disks of aluminum, 1 2 mm (about 1/32 3/32in.) thick, with a knob in th
23、e center for lifting. The circumference of each cover fits the inside beveled surface of the annular wax ring just above the plane of the specimen and is smoothed so as not to remove any wax when lifted. A numbered cover is required for each correspondingly numbered test dish. 1Names of suppliers of
24、 testing equipment and materials for this method may be found on the Test Equipment Suppliers list, available as part of the CD or printed set of Standards, or on the TAPPI website general Standards page. 3 / Water vapor transmission rate of paper and T 464 om-12 paperboard at high temperature and h
25、umidity 5. Materials 5.1 Desiccant, anhydrous calcium chloride in the form of small lumps that will pass a No. 8 screen (2.38 mm), but free from fines that will pass a No. 30 screen (595 m), and preferably pre-dried at 200C (392F) before use. The permissible moisture gain during the test is limited
26、to 10% of its initial weight. Silica gel may be used if its moisture gain is limited to 4%. Caution: Do not use the highly oxidative (explosive) magnesium perchlorate as a desiccant. 5.2 Wax, for sealing, that adheres tenaciously to both the dish and the specimen and is not brittle, hygroscopic, nor
27、 subject to oxidation. The weight of a surface of 50 cm2of freshly melted wax when exposed to the test conditions for 24 h should not increase more than 0.001 g. A mixture of 60% of refined laminating-type microcrystalline wax and 40% refined crystalline 57C (135F) m.p. paraffin wax is usually satis
28、factory. If the above waxes are not available, other sealants may be used as long as they (a) are highly resistant to the passage of water and water vapor and (b) do not lose weight to, or gain weight from, the atmosphere in an amount that would affect the test result by more than 2% over the requir
29、ed period of time. 5.3 Petrolatum (petroleum jelly), for coating the beveled edges of the templates to facilitate their removal after the wax has been applied and cooled. 6. Sampling and test specimens 6.1 To determine conformance to product specifications, obtain a sample of the sheet material in a
30、ccordance with TAPPI T 400 “Sampling and Accepting a Single Lot of Paper, Paperboard, Containerboard, or Related Product.” Otherwise, obtain a sample appropriate to the reason for testing. 6.2 With the appropriate cutting template, cut three typical specimens from each test unit and identify the sur
31、faces. 7. Conditioning Conditioning of the sample before assembly of the test plates is normally not required. If there is a possibility that undue shrinkage may occur after assembly, causing the wax seal to break, the sample should be preconditioned according to TAPPI T 402 “Standard Conditioning a
32、nd Testing Atmospheres for Paper, Board, Pulp Handsheets, and Related Products” before cutting the specimen disks. 8. Procedure 8.1 Place sufficient desiccant inside the dish to cover the bottom to a depth of at least 8 mm (about 3/16in.), and when leveled, to be within 6 mm (about 1/4in.) of, but n
33、ot touching the under surface of the specimen. Determine the rough weight of the desiccant to stay within the weight gain limitation of 5.1. The exact weight is not essential; however, each cup should contain approximately the same amount of desiccant. 8.2 Center the specimen over the top of the dis
34、h with the sides oriented properly (see 2.3). 8.3 Apply a thin film of petrolatum to the beveled edge of the waxing template. Wipe off the excess so as to avoid contaminating the specimen. Center the template over the specimen and dish with the smaller face adjacent to the test specimen, and apply a
35、 firm downward pressure. 8.4 Heat the wax to 80C (176F) and flow the molten wax into the annular space around the beveled edge of the template. A special pipet may be used for this, rotating the dish if convenient, but adding the wax neatly and quickly. Two pours may be used, if desired, to minimize
36、 cracks and air bubbles, but in either case, the wax should form a slight meniscus above the upper edge of the template and not flow over the edge. NOTE 3: Firm downward pressure on the template and the use of wax that is at a temperature not over 85C (185F) will minimize the formation of bubbles. 8
37、.5 When the wax has set and shrunk slightly, a slight twist will release the template. Examine the seal for bubbles and cracks, and discard any assembly with a faulty seal. NOTE 4: After the wax has cooled, melting a narrow groove of wax next to the side of the cup can repair or reduce the possibili
38、ty of any cracks forming between the wax and the metal. A soldering iron works well for this. T 464 om-12 Water vapor transmission rate of paper and / 4 Paperboard at high temperature and humidity 8.6 Place the assembled dishes in the test atmosphere, specimen up, and allow the conditioned air to ci
39、rculate over the specimens at least overnight before starting to weigh the assemblies. NOTE 5: This technique avoids the possibility of the desiccant coming into contact with the specimen. NOTE 6: If procedure 8.7.3 is used, a preliminary tare weighing of the assemblies can be made before preconditi
40、oning to expedite the establishment of a reasonable weighing schedule. NOTE 7: With specimens having a high rate of transmission, it may be necessary to make the first and subsequent weighings at shorter intervals to keep the weight gain of the desiccant within limits. A very poor barrier may cause
41、this limit to be passed overnight. NOTE 8: Under some circumstances, a wax seal made at 23C will fail by internal pressure when exposed to 37.8C. If this occurs, the seal can be made at a temperature close to 37.8C or a small glass capillary can be inserted and sealed with care to allow the internal
42、 atmosphere to equalize at the higher temperature. The capillary is suitably sealed off with flame or wax after conditioning at 37.8C for about 4 h. 8.7 Three weighing procedures are acceptable, depending on available facilities. 8.7.1 Weigh the test assemblies directly in the test atmosphere. 8.7.2
43、 Weigh the test assemblies with the weighing cover. In this case, first cover the dish in the cabinet with its corresponding cover. Remove each assembly and weigh to the nearest 0.001 g. Replace the assemblies in the cabinet and remove the covers. Between weighings, keep the covers in a dust-free pl
44、ace, preferably resting flat on three-point supports. Always weigh the assemblies in the same order. 8.7.3 Weigh the test assemblies on a precise weighing schedule. For this, the test cabinet must be in a controlled atmosphere (e.g., as 23C, 50% RH). With a direct reading balance adjacent to the tes
45、t cabinet, and with preliminary tare weights as suggested in Note 7, each dish can be weighed in the same order and at the same time interval ( 5 s) from the start of the weighing. The procedure is: Shut off circulation and open the test cabinet; then start a stopwatch. Remove the first assembly and
46、 rough weigh (using the tare value to expedite the weighing). At a precise time (60 s is a reasonable interval) record the weight to 0.001 g and return the assembly to its place in the cabinet. Immediately remove and rough weigh the second assembly, record its weight to 0.001 g at the next time inte
47、rval, and continue in this fashion until all assemblies are weighed. The identical sequence and timing must be followed each time the dishes are weighed. NOTE 9: For some test cabinets, a significant drop in RH occurs when the cabinet is opened. Recovery to 90% RH can be slow. Therefore, the last as
48、sembly to be weighed can be subjected to significantly lower RH just prior to weighing. Although this is not likely to cause a change in test results or precision, it could if a large number of specimens were being tested at the same time. 8.8 Record the successive weights of each assembly to the ne
49、arest 0.001 g. Repeat the weighings at recorded time intervals, usually 24 h, until a constant rate of gain is obtained. This can be determined from the data when the increase of mass per unit time becomes constant to within 5% for two successive weighings. NOTE 10: A common procedure is to weigh after a preliminary overnight conditioning and to make a final weighing three days later. This appears to give reproducible results on similar samples, but any failure to reach a steady state during the preliminary conditioning period will be m
