1、BRITISH STANDARD BS 2782-8: Method822A: 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 BS2782-0, Introduction, issued separatel
2、y.BS2782-8:Method 822A:1992 This British Standard, having been prepared under the directionof the Plastics and Rubber Standards Policy Committee, was published underthe authority of the Standards Board and comesintoeffect on 31January1992 BSI 08-1999 The following BSI references relate to the work o
3、n this standard: Committee reference PRM/21 Draft for comment91/38172DC ISBN 0 580 20297 6 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Plastics and Rubber Standards Policy Committee (PRM/-) to Technical Committee PRM/21, upon which t
4、he following bodies were represented: British Plastics Federation British Steel Industry British Telecommunications plc British Textile Confederation Department of Trade and Industry (National Physical Laboratory) EEA (The Association of Electronics, Telecommunications and Business Equipment Industr
5、ies) Electrical and Electronic Insulation Association (BEAMA Ltd.) Electrical Installation Equipment Manufacturers Association (BEAMA Ltd.) GAMBICA (BEAMA Ltd.) Ministry of Defence Packaging and Industrial Films Association PIRA Plastic Industrial Containers Association Plastics and Rubber Institute
6、 RAPRA Technology Ltd. Yarsley Technical Centre Ltd. Amendments issued since publication Amd. No. Date CommentsBS2782-8:Method 822A:1992 BSI 08-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Definitions 1 3 Principle 1 4 Apparatus 1 5 Test piece 1 6 Procedure
7、1 7 Expression of results 2 8 Test report 2 Publication(s) referred to Inside back coverBS2782-8:Method 822A:1992 ii BSI 08-1999 Foreword This method has been prepared under the direction of the Plastics and Rubber Standards Policy Committee. It supersedes methods513C and513D of BS2782:1970 which ar
8、e deleted by amendment. Test conditions B and C in this method are equivalent to methods513D and513C respectively. Test condition A has no equivalent in BS2782:1970. The principle is basically similar to that of ISO2528 covering the determination of water vapour transmission rate by the dish method.
9、 WARNING NOTE. This method does not necessarily detail all precautions necessary to meet the requirements of the Health and Safety at Work etc. Act1974. Attention should be paid to any appropriate safety precautions and the method should be operated only by trained personnel. A British Standard does
10、 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 not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an insid
11、e front cover, pagesi andii, pages1 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 will be indicated in the amendment table on the inside front cover.BS2782-8:Method 822A:1992 BSI 08-1999 1 1 Scope This
12、 British Standard describes a method for the 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 suitabl
13、e for testing materials of water vapour transmission not less than1g/m 2 perday. 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 ra
14、te the mass of water vapour transmitted from 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/m 2 perday) at the conditions of temperature an
15、d humidity defined at the two faces of the 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 p
16、lastics film are filled with desiccant, sealed 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 tim
17、e. Water vapour transmission rate is not a 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
18、as close as possible to those under which 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
19、 found to be very similar to those obtained using the dish method. 4 Apparatus 4.1 Environmental chamber, circulating conditioned air at a velocity between0.5m/s and2.5m/s, capable of establishing and maintaining the temperature and relative humidity specified for the test (see6.2), within15min of t
20、he door to the enclosure being closed. NOTEThe door should be kept open for the shortest possible time. 4.2 Balance, accurate to0.1mg. 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
21、a4mm sieve but retained on a1.6mm sieve, or alternatively in the form of a crumbly flaked product1.5mm to2mm 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 of100mm
22、100mm size, placing them one on top of the other and heat sealing three edges to form an open-ended bag with the inner edges of the seals761mm 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 pap
23、er, folded, to fit inside the plastics film bag. Pour approximately15g 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 clause5) and seal t
24、he remaining side of the bag with the heat sealer to form a sachet of nominal area116cm 2 .BS2782-8:Method 822A:1992 2 BSI 08-1999 6.2 Test Set the environmental chamber to the most appropriate of the three conditions A, B or C as follows. Place the sachets in the enclosure controlled to the specifi
25、ed conditions so that both surfaces of each sachet are freely exposed without crumpling. Carry out successive weighings to an accuracy of1% of the change between successive weighings, or to1mg whichever is the larger, at suitable intervals. NOTE 1If the mass increase at each successive weighing is l
26、ess than10mg, then use longer time intervals. If the total mass increase is1.5g per15g of desiccant, or more, use shorter time intervals. Plot the cumulative increase of mass (in mg) of each sachet against total time in the enclosure. When at least three, but preferably four, points lie on a straigh
27、t 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 above2% provided that the total uptake of water is less than1.5g for15g of the desiccant. NOTE 3Precautions should be taken to ensure that,
28、 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 same period, which should be as short as possible. 7 Expression of results Determine from the straight line part of the graph of cumulative
29、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 (ing/m 2per day) from the expression: From the result of each test, calculate and report the mean of these results to two significant figures but not clos
30、er than to the nearest0.2g/m 2per day. 8 Test report The test report shall include the following: a) a complete identification of the material tested, including type, source, manufacturers code numbers, previous history, etc.; b) a reference to this British Standard method (i.e.BS2782:Method822A); c
31、) the test conditions (see6.2); d) the water vapour transmission rate; e) the individual results obtained. Additionally, if requested, the test report shall include the thickness of the material, determined either by a gravimetric or a micrometric method. Condition A: temperature25 0.5 C relative hu
32、midity902% Condition B: temperature38 0.5 C relative humidity902% Condition C: temperature25 0.5 C relative humidity752% where S is the exposed area of the sachet (nominally116cm 2 ) (in cm 2 ); m is the increase in mass (in mg/h). rate 240m S - =BS2782-8:Method 822A:1992 BSI 08-1999 Publication(s)
33、referred to BS2782, Methods of testing plastics. BS2782-0, Introduction. BS2528, Sheet materialsDetermination of water vapour transmission rateDish method. BS 2782-8: Method822A: 1992 BSI 389 Chiswick High Road London W4 4AL BSIBritishStandardsInstitution BSI is the independent national body respons
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