1、| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | BRITISH STANDARD BS 7948 : Part 1 : 1997 I
2、CS 55.040; 83.140.10 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW Specification for Film for wrapping rubber bales Part 1. Non-strippable high melting point filmsBS 7948 : Part 1 : 1997 This British Standard, having been prepared under the direction of the Sector Board for
3、Materials and Chemicals, was published under the authority of the Standards Board and comes into effect on 15 March 1997 BSI 1997 The following BSI references relate to the work on this standard: Committee reference PRI/50 Draft for comment 95/123604 DC ISBN 0 580 27074 2 Amendments issued since pub
4、lication Amd. No. Date Text affected Committees responsible for this British Standard The preparation of this British Standard was entrusted to Technical Committee PRI/50, Natural and synthetic rubbers, upon which the following bodies were represented: British Rubber Manufacturers Association Ltd. C
5、hemical Industries Association Tropical Growers AssociationBS 7948 : Part 1 : 1997 BSI 1997 i Contents Page Committees responsible Inside front cover Foreword ii Specification Introduction 1 1 Scope 1 2 Normative references 1 3 Material 1 4 Physical properties 1 Annex A (normative) Determination of
6、melting characteristics of bale wrappings by DSC (differential scanning calorimetry) 2 List of references Inside back coverii BSI 1997 BS 7948 : Part 1 : 1997 Foreword This Part of BS 7948 was prepared by Technical Committee PRI/50. Other Parts of this standard will cover films suitable for low temp
7、erature mixing and strippable films. 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. BSI 1997 1 BS 7948 :
8、 Part 1 : 1997 Specification Introduction Considerable quantities of natural and general purpose synthetic rubber are prepared in crumb form. The crumbs are dried and then pressed into bales whilst still warm, at approximately 60 C. The bales are then wrapped in a film and packed, often automaticall
9、y, into crates. The wrapping film should be strong enough to withstand the stresses encountered during the wrapping and packing operations. It should not adhere to the film on the other bales under the combined effects of the heat from the rubber and the weight of the bales. During storage, the rubb
10、er will flow and the film should be able to withstand the stresses generated. Any failure of the film will cause rubber-to-rubber adhesion, which in a 30-bale crate leads to a one-tonne bale. The prime purpose of the film is to keep the bales separate at all times so that they may be easily removed
11、from their packaging for use. However, because it is difficult and uneconomic to strip the film from each bale, an essential feature is that the film should disperse in the rubber compound during mixing. This means that its melting point has to be lower than the temperatures attained in internal mix
12、ing cycles, typically 120 C to 160 C. Unfortunately, there is no acceptable or reproducible dispersal test available to measure this important property directly. Mixes carried out on a two-roll mill or in a single-stage internal mixer cycle might not reach the required temperature for dispersion. If
13、 this happens, then an option would be to strip the film from the bales. Films suitable for low temperature mixing and strippable films will be covered in other Parts of BS 7948. 1 Scope This Part of BS 7948 specifies the material and physical property requirements for non-strippable high melting po
14、int film for wrapping natural and general purpose synthetic rubber bales, intended to keep the bales separate during storage. 2 Normative references This Part of BS 7948 incorporates, by dated or undated reference, provisions from other publications. These normative references are made at the approp
15、riate places in the text and the cited publications are listed on the inside back cover. For dated references, only the edition cited applies: any subsequent amendments to or revisions of the cited publication apply to this Part of BS 7948 only when incorporated in the reference by amendment or revi
16、sion. For undated references, the latest edition of the cited publication applies, together with any amendments. 3 Material The film shall be manufactured from one of: a) low-density polyethylene (polyethene) (PE-LD); b) low-density polyethylene blended with ethylene/vinyl acetate copolymer (E/VAC);
17、 or c) an appropriate grade of E/VAC copolymer. NOTE. Antioxidants, slip agents and anti-blocking agents may be present. 4 Physical properties 4.1 Thickness When measured using a thickness gauge, the film shall have a thickness between 0.035 mm and 0.065 mm. 4.2 Melt flow rate When tested in accorda
18、nce with BS 2782 : Method 720A at 190 C, the melt flow rate shall be greater than 1 g/10 min. 4.3 Vicat softening temperature When tested in accordance with BS 2782 : Method 120A, the Vicat softening temperature shall be no greater than 93 C. 4.4 Melting point by differential scanning calorimetry (D
19、SC) When tested in accordance with the method given in annex A, melting shall be complete before 110 C.BS 7948 : Part 1 : 1997 2 BSI 1997 Annex A (normative) Determination of melting characteristics of bale wrappings by DSC (differential scanning calorimetry) The method falls into two stages; a cali
20、bration phase and a measurement phase. A.1 Calibration Calibrate the DSC over the range of 50 C to 200 C by the use of stearic acid and indium standards which have melting points at 68.0 C and 156.6 C respectively. The two standards are heated individually at the heating rate to be used for the meas
21、urement of the test sample. This is normally at a rate of 20 C/min. On completion of each temperature scan, measure the maximum of the melting endotherm. The peak maxima obtained for the two standards are then input into the instrument calibration program. A.2 Sample measurement Heat the sample over
22、 the required temperature range at the same rate as for the calibration standards. The onset, maximum and end point of the sample melting are then read from the instrument. The onset of melting is defined as the intersection of the baseline and the tangent to the peak. The endpoint is where the peak
23、 ends (returning to the baseline). As a final check on temperature, the indium standard is scanned again and corrections to the sample melting values made where necessary. BSI 1997 BS 7948 : Part 1 : 1997 List of references (see clause 2) Normative references BSI publications BRITISH STANDARDS INSTI
24、TUTION, London BS 2782 Methods of testing plastics BS 2782 : Part 1 Thermal properties BS 2782 : Methods 120A, 120B, 120D and 120E : 1990 Determination of Vicat softening temperature of thermoplastics BS 2782 : Part 7 Rheological properties BS 2782 : Method 720A : 1979 Determination of melt flow rat
25、e of thermoplasticsBSI 389 Chiswick High Road London W4 4AL | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
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