1、BRITISH STANDARD BS 7476:1991 Specification for Polyethylene film for covering silageBS7476:1991 This British Standard, having beenprepared under the directionof the Plastics and RubberStandards Policy Committee, was published underthe authority of the Standards Board and comes intoeffect on 30 Sept
2、ember 1991 BSI 10-1999 The following BSI references relate to the work on this standard: Committee reference PRM/75 Draft for comment 91/37185 DC ISBN 0 580 19960 6 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Plastics and Rubber Stan
3、dards Policy Committee (PRM/-) to Technical Committee PRM/75, upon which the following bodies were represented: British Plastics Federation Her Majestys Stationery Office Institute of Trading Standards Administration Ministry of Defence Packaging and Industrial Films Association PIRA International A
4、mendments issued since publication Amd. No. Date CommentsBS7476:1991 BSI 10-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Definitions 1 3 Composition 1 4 Appearance and finish 1 5 Conditioning of test specimens 1 6 Dimensional tolerances 1 7 Minimum weight 1
5、8 Tensile properties 2 9 Marking of packaging material 2 Publication(s) referred to Inside back coverBS7476:1991 ii BSI 10-1999 Foreword This British Standard has been prepared under the direction of the Plastics and Rubber Standards Policy Committee. It is based on an Industry Standard issued by BA
6、HPA in 1986 under the reference BAHPA 5/86. Polyethylene film used for covering silage, in common with other plastics materials, is adversely affected by exposure to ultraviolet radiation, e.g. sunlight. These effects may be mitigated by the addition of suitable stabilizers or carbon blacks and the
7、normal expected service life of approximately one year exposed out of doors can readily be achieved. However, in the absence of an agreed method of test for weatherability, which reliably correlates with natural weathering, it is not possible to include a definitive performance requirement clause co
8、vering this aspect. BS 7344 specifies requirements for reeled low density polyethylene film (for general purpose application), the widths of which are not covered by the scope of this standard. A British Standard does not purport to include all the necessary provisions of a contract. Users of Britis
9、h 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, pages 1 and 2, an inside back cover and a back cover
10、. 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.BS7476:1991 BSI 10-1999 1 1 Scope This British Standard specifies the requirements for, and the dimensional tolerances of, flexible
11、non-reinforced polyethylene film suitable for covering silage, available in widths above 4 m and thicknesses greater than 125 4m. 2 Definitions For the purposes of this British Standard the following definitions apply. 2.1 tensile strength the maximum tensile stress per unit area, calculated from th
12、e maximum load during a tension test carried to break, and the original cross-sectional area of the specimen 2.2 percentage elongation at break the increase in the distance between reference lines on a test specimen, arising during a tension test carried to break, expressed as a percentage of the in
13、itial distance between the reference lines 2.3 machine direction the direction parallel to the direction in which the film is extruded during manufacture 2.4 transverse direction the direction at right angles to the machine direction 3 Composition The polyethylene film shall be manufactured from a b
14、ase material consisting of polyethylene, linear low density polyethylene or a copolymer in which ethylene is the major constituent. NOTEThe material may contain stabilizers, pigments or other additives. 4 Appearance and finish The film shall be in the form of sheet and shall be free from defects and
15、 mechanical damage. NOTE 1The film may be supplied folded in any form as agreed between the purchaser and the supplier. NOTE 2The film should be of a homogeneous nature and all pigments or other additives should be uniformly dispersed. 5 Conditioning of test specimens All samples shall be conditione
16、d at 23 2 C for not less than 1 h before testing or the measurement of dimensions, and all testing and measurements shall be carried out at 23 2 C. NOTEPolyethylene films are insensitive to changes in the relative humidity of the atmosphere and there is no necessity for the preconditioning of sample
17、s to a standard relative humidity. 6 Dimensional tolerances 6.1 Length The length of film on a reel shall be not less than the nominal length. Any method shown to give accurate results may be used but in cases of dispute the reference method shall be BS2782:Method 632A. There shall be no joins. 6.2
18、Width The width of the film shall be within 2% of the nominal width of the film. Any method shown to give accurate results may be used but in cases of dispute the reference method shall be BS2782:Method632A. 6.3 Thickness 6.3.1 Nominal thickness The nominal thickness shall be not less than1254m. 6.3
19、.2 Spot thickness The minimum spot thickness, when measured in accordance with BS2782:Method630A, shall be not less than 80% of the nominal thickness. 6.3.3 Average thickness The average thickness of the film, when tested in accordance with section 1 of BS2782:Method631A:1982, shall be not less than
20、90% of the nominal thickness. For the purposes of this specification, the density of natural unpigmented films shall be taken as 924 kg/m 3and the density of black films shall be taken as940 kg/m 3 . For other colours, the exact density of the film shall be determined in accordance with BS2782:Metho
21、d620D and this density shall be used in the calculation to determine average thickness. 7 Minimum weight The minimum weight of any pack or reel, excluding packaging or core if present, shall be not less than95% of the nominal weight calculated from the nominal length, width and thickness using the d
22、ensity specified in6.3.3.BS7476:1991 2 BSI 10-1999 8 Tensile properties 8.1 Tensile strength at break The tensile strength of the film, when measured in accordance with BS2782:Method 326B in both machine and transverse directions, shall be not less than15 MPa. 8.2 Percentage elongation at break The
23、percentage elongation at break, when measured in accordance with BS2782:Method 326B in both machine and transverse directions, shall be not less than450%. 9 Marking of packaging material The outer packaging of each pack or reel shall be marked with the following information: a) the number and date o
24、f this British Standard, i.e. BS7476:1991 1) ; b) the name of the manufacturer; c) a description of the product; d) the nominal length, width and thickness of the film and the minimum net weight; e) batch number or code or other means of identification. 1) Marking BS 7476:1991 on or in relation to a
25、 product represents a manufacturers declaration of conformity, i.e. a claim by or on behalf of the manufacturer that the product meets the requirements of the standard. The accuracy of the claim is therefore solely the responsibility of the person making the claim. Such a declaration is not to be co
26、nfused with third party certification of conformity, which may also be desirable.BS7476:1991 BSI 10-1999 Publication(s) referred to BS 2782, Methods of testing plastics. BS 2782:Methods 326A to 326C, Determination of tensile strength and elongation of plastics films. BS 2782:Method 620D, Determinati
27、on of density of solid plastics excluding cellular plastics (density gradient column method). BS 2782:Method 630A, Determination of thickness by mechanical scanning of flexible sheet. BS 2782:Method 631A, Determination of gravimetric thickness and yield of flexible sheet. BS 2782:Method 632A, Determ
28、ination of length and width of flexible sheet. BS 7344, Specification for reeled low density Polyethylene film for general purpose application 2) . BAHPA 5/86, Polyethylene film suitable for covering silage in the United Kingdom 2) . 2) Referred to in the foreword only.BS 7476:1991 BSI 389 Chiswick
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