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1、BRITISH STANDARD BS 2782-8: Method 822A: 1992 Methods of testing Plastics Part 8: Other properties Method 822A: Determination of water vapour transmission rate of plastics films (sachet method) IMPORTANT NOTE. Before reading this method it is essential to read BS 2782-0, Introduction, issued separat
2、ely. Licensed Copy: London South Bank University, London South Bank University, Tue Dec 12 08:42:03 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 2782-8:Method 822A:1992 This British Standard, having been prepared under the direction of the Plastics and Rubber Standards Policy Committee, was publish
3、ed under the authority of the Standards Board and comes into effect on 31 January 1992 BSI 08-1999 The following BSI references relate to the work on this standard: Committee reference PRM/21 Draft for comment 91/38172 DC ISBN 0 580 20297 6 Committees responsible for this British Standard The prepar
4、ation of this British Standard was entrusted by the Plastics and Rubber Standards Policy Committee (PRM/-) to Technical Committee PRM/21, upon which the following bodies were represented: British Plastics Federation British Steel Industry British Telecommunications plc British Textile Confederation
5、Department of Trade and Industry (National Physical Laboratory) EEA (The Association of Electronics, Telecommunications and Business Equipment Industries) Electrical and Electronic Insulation Association (BEAMA Ltd.) Electrical Installation Equipment Manufacturers Association (BEAMA Ltd.) GAMBICA (B
6、EAMA Ltd.) Ministry of Defence Packaging and Industrial Films Association PIRA Plastic Industrial Containers Association Plastics and Rubber Institute RAPRA Technology Ltd. Yarsley Technical Centre Ltd. Amendments issued since publication Amd. No.DateComments Licensed Copy: London South Bank Univers
7、ity, London South Bank University, Tue Dec 12 08:42:03 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 2782-8:Method 822A:1992 BSI 08-1999i Contents Page Committees responsibleInside front cover Forewordii 1Scope1 2Definitions1 3Principle1 4Apparatus1 5Test piece1 6Procedure1 7Expression of results2 8
8、Test report2 Publication(s) referred toInside back cover Licensed Copy: London South Bank University, London South Bank University, Tue Dec 12 08:42:03 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 2782-8:Method 822A:1992 ii BSI 08-1999 Foreword This method has been prepared under the direction of t
9、he Plastics and Rubber Standards Policy Committee. It supersedes methods 513C and 513D of BS 2782:1970 which are deleted by amendment. Test conditions B and C in this method are equivalent to methods 513D and 513C respectively. Test condition A has no equivalent in BS 2782:1970. The principle is bas
10、ically similar to that of ISO 2528 covering the determination of water vapour transmission rate by the dish method. WARNING NOTE. This method does not necessarily detail all precautions necessary to meet the requirements of the Health and Safety at Work etc. Act 1974. Attention should be paid to any
11、 appropriate safety precautions and the method should be operated only by trained personnel. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does no
12、t of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 and 2, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This
13、will be indicated in the amendment table on the inside front cover. Licensed Copy: London South Bank University, London South Bank University, Tue Dec 12 08:42:03 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 2782-8:Method 822A:1992 BSI 08-19991 1 Scope This British Standard describes a method for t
14、he determination of the water vapour transmission rate of thermoplastics material in the form of film which can be heat-sealed, where the water vapour transmission through the seal is known to be considerably less than through the film. The method is suitable for testing materials of water vapour tr
15、ansmission not less than 1 g/m2per day. NOTEThe titles of the publications referred to in this standard are listed on the inside back cover. 2 Definitions For the purposes of this British Standard the following definition applies. water vapour transmission rate the mass of water vapour transmitted f
16、rom one face to the other, under constant conditions of vapour pressure at the two faces, expressed per unit of surface area and during a given time NOTEThe rate is expressed in grams per square metre per day (g/m2per day) at the conditions of temperature and humidity defined at the two faces of the
17、 sheet. The rate is dependent on, but not usually proportional to, the thickness and permeability of the constituent material or materials and the conditions of temperature and humidity under which the test is carried out. 3 Principle Sachets made from the plastics film are filled with desiccant, se
18、aled and placed in an atmosphere with controlled temperature and relative humidity. The sachets are weighed at suitable intervals of time. The water vapour transmission rate is found from the increase in mass when this has become linearly proportional to time. Water vapour transmission rate is not a
19、 linear function of temperature nor, generally, of relative humidity difference. A determination carried out under certain conditions is not, therefore, necessarily comparable with one carried out under other conditions. The test conditions chosen should be as close as possible to those under which
20、the test material is expected to be used. The test conditions specified in this method have been chosen as being the most suitable for the comparison of films made from different materials. Results obtained on polyethylene film by the sachet method have been found to be very similar to those obtaine
21、d using the dish method. 4 Apparatus 4.1 Environmental chamber, circulating conditioned air at a velocity between 0.5 m/s and 2.5 m/s, capable of establishing and maintaining the temperature and relative humidity specified for the test (see 6.2), within 15 min of the door to the enclosure being clos
22、ed. NOTEThe door should be kept open for the shortest possible time. 4.2 Balance, accurate to 0.1 mg. 4.3 Heat sealer, of the type conventionally used for sealing thermoplastics film. 4.4 Desiccant, which is anhydrous calcium chloride in the form of granules passing a 4 mm sieve but retained on a 1.
23、6 mm sieve, or alternatively in the form of a crumbly flaked product 1.5 mm to 2 mm in size. NOTEIt is essential that the calcium chloride is free from moisture. 5 Test piece The test piece shall be in the form of a bag made by cutting from the test film two squares of 100 mm 100 mm size, placing th
24、em one on top of the other and heat sealing three edges to form an open-ended bag with the inner edges of the seals 76 1 mm apart. At least two test pieces shall be used for each determination. 6 Procedure 6.1 Preparation of the sachets Make a bag from blotting paper or filter paper, folded, to fit
25、inside the plastics film bag. Pour approximately 15 g of calcium chloride into the paper bag and secure the edges with paper clips. NOTEFilled bags of desiccant should be stored in a desiccator until required for use. Place a bag of desiccant in the film bag (see clause 5) and seal the remaining sid
26、e of the bag with the heat sealer to form a sachet of nominal area 116 cm2. Licensed Copy: London South Bank University, London South Bank University, Tue Dec 12 08:42:03 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 2782-8:Method 822A:1992 2 BSI 08-1999 6.2 Test Set the environmental chamber to the
27、 most appropriate of the three conditions A, B or C as follows. Place the sachets in the enclosure controlled to the specified conditions so that both surfaces of each sachet are freely exposed without crumpling. Carry out successive weighings to an accuracy of 1 % of the change between successive w
28、eighings, or to 1 mg whichever is the larger, at suitable intervals. NOTE 1If the mass increase at each successive weighing is less than 10 mg, then use longer time intervals. If the total mass increase is 1.5 g per 15 g of desiccant, or more, use shorter time intervals. Plot the cumulative increase
29、 of mass (in mg) of each sachet against total time in the enclosure. When at least three, but preferably four, points lie on a straight line, a constant rate of gain has been attained and the test may be discontinued. NOTE 2For calcium chloride the relative humidity in the sachet will not rise above
30、 2 % provided that the total uptake of water is less than 1.5 g for 15 g of the desiccant. NOTE 3Precautions should be taken to ensure that, if removed from the enclosure for weighing, the sachets are weighed under the same conditions at each successive weighing and are out of the enclosure for the
31、same period, which should be as short as possible. 7 Expression of results Determine from the straight line part of the graph of cumulative increase in mass against time, the increase in mass of each sachet over a given interval of time and calculate the water vapour transmission rate (in g/m2 per d
32、ay) from the expression: From the result of each test, calculate and report the mean of these results to two significant figures but not closer than to the nearest 0.2 g/m2 per day. 8 Test report The test report shall include the following: a) a complete identification of the material tested, includ
33、ing type, source, manufacturers code numbers, previous history, etc.; b) a reference to this British Standard method (i.e. BS 2782:Method 822A); c) the test conditions (see 6.2); d) the water vapour transmission rate; e) the individual results obtained. Additionally, if requested, the test report sh
34、all include the thickness of the material, determined either by a gravimetric or a micrometric method. Condition A:temperature 25 0.5 C relative humidity 90 2 % Condition B:temperature 38 0.5 C relative humidity 90 2 % Condition C:temperature 25 0.5 C relative humidity 75 2 % where S is the exposed
35、area of the sachet (nominally 116 cm2) (in cm2); m is the increase in mass (in mg/h). rate 240m S - -= Licensed Copy: London South Bank University, London South Bank University, Tue Dec 12 08:42:03 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 2782-8:Method 822A:1992 BSI 08-1999 Publication(s) refer
36、red to BS 2782, Methods of testing plastics. BS 2782-0, Introduction. BS 2528, Sheet materials Determination of water vapour transmission rate Dish method. Licensed Copy: London South Bank University, London South Bank University, Tue Dec 12 08:42:03 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 278
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