1、BRITISH STANDARD BS2782-6: Method643A: 1976 Methods of testing Plastics Part6: Dimensional properties Method643A: Shrinkage on heating of film intended for shrink wrapping applications IMPORTANT NOTE. Before reading this method it is essential to read the foreword, general introduction and instructi
2、ons to BS2782, issued separately. UDC678.5/.8:678.01:536.416:620.192.52BS2782-6:Method643A:1976 BSI08-1999 The following BSI references relate to the work on this standard: Committee reference PLC/17 Draft for comment68/11485 ISBN 0 580 09092 2 A British Standard does not purport to include all the
3、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 inside front cover, pages i and ii, p
4、ages1 and2and 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. Amendments issued since publication Amd. No. Date CommentsBS2782-6:Method643A:1976 BSI 08-1999 i Contents
5、 Page 1 Scope 1 2 References 1 3 Principle 1 4 Apparatus 1 5 Test pieces 1 6 Conditioning 1 7 Procedure 1 8 Test report 1 Figure 643 A.1 Specimen holder 2 Figure 643 A.2 Light wire mesh cage with lid 2ii blankBS2782-6:Method643A:1976 BSI 08-1999 1 1 Scope This method describes a procedure for determ
6、ining the extent to which plastics films shrink when heated in an unrestrained state. For films of different materials, appropriate test temperatures are specified. It should be appreciated that for some materials, the shrinkage obtained in industrial use may differ from the values obtained by this
7、test method. The shrinkage of film as determined by this method is usually measured in two directions at right angles to each other in the plane of the film. 2 References The following British Standards are referred to in this method. BS2782:1975, Methods of testing plastics Foreword, general introd
8、uction and instructions. BS3412, Polyethylene materials for moulding and extrusion. 3 Principle The method consists of heating a measured length of film in a bath at a stated temperature, remeasuring and calculating the percentage reduction in length. 4 Apparatus The following apparatus is required.
9、 4.1 Heating bath, of depth sufficient for the test piece to be fully immersed and containing a liquid that will not affect the material under test at the test temperature nor decompose at this temperature. 1)It shall be possible to control the temperature of the bath to within 0.5 C of the specifie
10、d temperature. 4.2 Test piece holder, that will permit the test piece to be fully immersed in the liquid in the bath e.g.a pair of metal tongs or the device, made from heavy-gauge wire, shown in Figure 643 A.1 or a light wire mesh cage with lid as shown in Figure 643 A.2. 4.3 Stop watch 5 Test piece
11、s Use a10 1mm wide test piece. If the apparatus shown in Figure 643 A.1 is used, cut the test piece100mm in length plus an amount necessary for holding it. Mark the test piece (for example, by drawing a line across its width) at a distance of100 1mm from one end. If the apparatus shown in Figure 643
12、 A.2 is used, cut the test piece100 1mm in length. Use five test pieces for each direction of testing (seeparagraph on direction of testing in BS2782: Introduction:1975). 6 Conditioning Unless otherwise specified, the test pieces do not require to be conditioned. 7 Procedure Immerse the test piece f
13、ully for20 1s in the bath, at the temperature specified below for the material (see note1). Remove the test piece from the bath and, without delay, place it horizontally (see note2) on a sheet of absorbent material, such as tissue or blotting paper, to cool. Measure the distance from the end of the
14、test piece to the mark or the total length of the test piece, as appropriate, to the nearest1mm (l 1 mm). Express the shrinkage on heating of the test piece as a percentage of the original length(100mm), i.e.as(100l 1 )%. Report the shrinkage in a particular direction of the material under test as t
15、he mean of the values obtained on the five test pieces cut in that direction (see note3). NOTE 1It is intended to add to the list of test temperatures as experimental evidence becomes available for films of other compositions. NOTE 2If the test pieces are held in a vertical position to cool they may
16、 stretch and give a false result. NOTE 3The length of the test piece is normally reduced by the heat treatment, in which case the shrinkage is reported as a positive value. If the test piece extends under the heat treatment, the shrinkage is reported as a negative value. 8 Test report The report sha
17、ll include the following particulars. a) The shrinkage on heating of the material for each direction of testing. b) The direction of the long axis of each group of test pieces in relation to some feature of the film. 1) Glycerine or silicone oil is a suitable liquid. PVC film 90 0.5 C Polyethylene f
18、ilm of density not greater than0.925 115 0.5 CBS2782-6:Method643A:1976 2 BSI 08-1999 c) Temperature of test. d) The individual test results. e) The method used to hold the test piece. Figure 643 A.1 Specimen holder Figure 643 A.2 Light wire mesh cage with lidblankBS2782-6: Method643A: 1976 BSI 389 C
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