1、BRITISH STANDARD BS 6712-1: 1995 ISO 8226-1: 1994 Measurement of hygroexpansivity of paper and board Part 1: Method for the measurement of hygroexpansivity up to a maximum relative humidity of 68 %BS6712-1:1995 This British Standard, having been prepared under the directionof the Sector Board forMat
2、erials and Chemicals, waspublished under the authorityof the Standards Boardand comes into effect on 15 May 1995 BSI 08-1999 First published July 1986 Second edition May 1995 The following BSI references relate to the work on this standard: Committee reference PAI/11 Draft for comment 93/309915 DC I
3、SBN 0 580 24233 1 Committees responsible for this British Standard The preparation of this British Standard was entrusted to Technical Committee PAI/11, Methods of test for paper, board and pulps, upon which thefollowing bodies were represented: British Carton Association British Fibreboard Packagin
4、g Association British Printing Industries Federation British Textile Confederation Envelope Makers and Manufacturing Stationers Association Her Majestys Stationery Office Institute of Paper Conservation Pira International Post Office The Paper Federation of Great Britain University of Manchester (In
5、stitute of Science and Technology) Coopted members Amendments issued since publication Amd. No. Date CommentsBS6712-1:1995 BSI 08-1999 i Contents Page Committees responsible Inside front cover National foreword ii Introduction 1 1 Scope 1 2 Normative references 1 3 Definitions 1 4 Principle 1 5 Appa
6、ratus and materials 1 6 Sampling and preparation of test pieces 2 7 Test procedure 2 8 Expression of results 3 9 Precision 3 10 Test report 3 Annex A (normative) Preparation of salt solutions 4 Annex B (informative) Bibliography 4 Table 1 Test load 2 Table A.1 Saturated salt solutions 4 List of refe
7、rences Inside back coverBS6712-1:1995 ii BSI 08-1999 National foreword This Part of BS6712 has been prepared by Technical Committee PAI/11. It is identical with ISO8226-1:1994 Paper and board Measurement of hygroexpansivity Part1: Hygroexpansivity up to a maximum relative humidity of68%, published b
8、y the International Organization for Standardization (ISO). This edition supersedes BS6712-1:1986, which is withdrawn. 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
9、a British Standard does not of itself confer immunity from legal obligations. Cross-references International Standard Corresponding British Standard ISO 186:1994 BS 3430:1995 Method for sampling to determine the average quality of paper and board (Identical) ISO 187:1990 BS EN 20187:1993 Paper, boar
10、d and pulps Standard atmosphere for conditioning and testing and procedure for monitoring the atmosphere and conditioning of samples (Identical) Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages1 to 4, an inside back cover and a back cover. This sta
11、ndard 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.BS6712-1:1995 BSI 08-1999 1 Introduction Knowledge of the dimensional changes in paper and board to be expected when the ambient humidity chan
12、ges is essential for accurate control of printing and similar processes. The change in dimensions, or hygroexpansivity, is due to stress relaxation of the constituent fibres and swelling or contraction of the fibres caused respectively by absorption or desorption of water. The proportion of the two
13、mechanisms causing hygroexpansivity depends upon the upper limit of relative humidity. For the purposes of this part of ISO8226, an upper limit of68% relative humidity is imposed to minimize the effects of stress relaxation on the hygroexpansivity. Part 2 of this International Standard specifies a m
14、ethod for the determination of hygroexpansivity up to a maximum relative humidity of86%, a value at which stress relaxation may have a significant effect on hygroexpansivity. 1 Scope This part of ISO8226 specifies a method for the determination of the hygroexpansivity of paper and board when subject
15、ed to a change in the relative humidity with which it is in equilibrium from(33 2)% to (66 2)%. This method is applicable to paper and board generally. It is not, however, suitable for crpe papers and corrugated fibreboard. 2 Normative references The following standards contain provisions which, thr
16、ough reference in this text, constitute provisions of this part of ISO8226. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this part of ISO8226 are encouraged to investigate the possibility of applying the most
17、 recent editions of the standards indicated below. Members of IEC and ISO maintain registers of currently valid International Standards. ISO 186:1994, Paper and board Sampling to determine average quality. ISO 187:1990, Paper, board and pulps Standard atmosphere for conditioning and testing and proc
18、edure for monitoring the atmosphere and conditioning of samples. ISO 536:, Paper and board Determination of grammage 1) . 3 Definitions For the purposes of this part of ISO8226, the following definition applies. 3.1 hygroexpansivity change in length that occurs in a given length of paper or board wh
19、en the relative humidity with which it is in equilibrium is raised from a specified lower relative humidity to a specified higher relative humidity the change in length is expressed as a percentage of the given length when the paper or board is in equilibrium with 50% relative humidity NOTE 1A contr
20、action of the test piece is regarded as negative hygroexpansivity. 4 Principle To ensure that all test pieces being tested are brought to the initial relative humidity from an immediate similar moisture level, this method includes a preliminary conditioning step at a very low relative humidity. Prel
21、iminary conditioning of test pieces of paper or board at a specified temperature (preferably23 C 1 C), under zero load and a relative humidity of (22 3)% and then at relative humidities of (33 2)% and (66 2)%. Measurement of the change in length between the latter two relative humidities under a loa
22、d appropriate to the grammage of the sample. The change in length is expressed as a percentage of the length measured at50% relative humidity. 5 Apparatus and materials 5.1 Cabinet, with air circulation, capable of being maintained at one of the temperatures specified in ISO187, preferably23 C 1 C,
23、and attaining the required relative humidities, measured as specified in5.5, uniformly within the whole cabinet and within not more than30min. NOTE 2The cabinet should preferably be located in an environment controlled to a temperature of23 C 1 C. NOTE 3All cabinets, irrespective of the method of re
24、lative humidity generation, are subject to humidity variations within the cabinet unless exceptional care is taken to minimize temperature variations (temperature variations greater than0,4 C can be significant). 1) To be published. (Revision of ISO536:1976)BS6712-1:1995 2 BSI 08-1999 5.2 Saturated
25、salt solutions (seeAnnex A), to provide relative humidities of (22 3)%, (33 2)% and (66 2)% as measured in accordance with5.5. NOTE 4Other methods of generating the required relative humidity may be used provided equivalent accuracy is obtained. NOTE 5The initial length (see7.1) at50% relative humid
26、ity should be determined by maintaining the cabinet in a conditioned test room operating at the preferred atmosphere of ISO187. 5.3 Clamps, upper and lower, or other means of suspending the test pieces vertically within the cabinet such that, when there is no load on the test piece, the distance bet
27、ween the inner clamping faces is a set value, known to within1mm (preferably100mm 1mm). A means shall be provided for tensioning the test pieces with the known loads (seeTable 1), and releasing this tension without removing the loads and without opening the cabinet. 5.4 Loading weights, including th
28、e loads attributable to the mass of the clamps, for application to the test pieces during measurement (seeTable 1). Table 1 Test load 5.5 Means of measuring relative humidity (for example humidity probes) or the air in the cabinet(5.1) with a precision of 1% (maximum error of reading) and an accurac
29、y of 2% (maximum departure from true relative humidity). The measuring probe should be capable of detecting a change of0,5% relative humidity within10s, at the equilibrium relative humidity level. NOTE 6Care must be taken to ensure that the corrosive nature of the “salt mist” does not affect the per
30、formance of any humidity probe. It is recommended that probes be protected by a polytetrafluoroethylene (PTFE) screen or other suitable means. NOTE 7All humidity probes require regular calibration, preferably by a nationally accredited laboratory. Calibration certificates normally quote the known er
31、ror of the instrument. The known error should be used to correct the measured value. 5.6 Means for measuring the temperature in the cabinet (5.1). 5.7 Devices for measuring the length or change in length of the test pieces to the nearest0,01mm. These devices may be mechanical or electronic. 6 Sampli
32、ng and preparation of test pieces 6.1 If a lot is being sampled, select the specimens to be tested in accordance with ISO186. 6.2 From undamaged specimens free from watermarks, folds and wrinkles, cut five test pieces in the machine direction and/or five in the cross direction as required. Each test
33、 piece shall be at least20mm longer than the nominal free span between the clamps, and the minimum free span shall be100mm. The width of the test piece shall be at least15mm. For the determination of hygroexpansivity in the machine direction or in the cross direction, cut the test pieces with the lo
34、nger side parallel to the relevant direction. 6.3 Determine the sample grammage, g, in accordance with ISO536. 7 Test procedure 7.1 Initial length (l 0 ) Set the clamps (5.3) inside the cabinet (5.1) to a span of at least100mm (known to within1mm). Clamp, then condition the unloaded test pieces for
35、at least30min at the selected temperature (see5.1) and at a relative humidity of (50 2)%. Gently apply the appropriate load in accordance with Table 1 and note the readings on the length-measuring devices (5.7) to the nearest1mm. Record this length as (l 0 ). 7.2 Preliminary conditioning of test pie
36、ces Condition the unloaded test pieces for at least30min at a relative humidity of (22 3)%. Gently apply the appropriate load in accordance withTable 1 and note the readings on the length-measuring devices. Remove the load and repeat the conditioning and measurement sequence until the length under l
37、oad changes by no more than0,02% between readings. NOTE 8These readings are not used in the calculation. 7.3 Measurement of hygroexpansivity Change the conditioning atmosphere to (33 2)%, and record the relative humidity value obtained. Condition the unloaded test pieces for at least30min at a relat
38、ive humidity of (33 2)%. Gently apply the appropriate load in accordance with Table 1 and note the readings on the length-measuring devices. Remove the load and repeat the conditioning and measurement until the length under load changes by no more than0,01mm. Record these lengths to the nearest0,01m
39、m (l 33 ). Sample grammage, g Total load Equivalent mass (including clamp) g/m 2 N/m g/15 mm g u 125 125 275 15 1 30 1 50 1 80 1 23 1,5 46 1,5 76 1,5 122 1,5BS6712-1:1995 BSI 08-1999 3 Condition the test pieces in the same way in an atmosphere having a relative humidity of(66 2)%. Note the relative
40、humidity value obtained. Record the new readings (l 66 ) of the test piece lengths to the nearest0,01mm. 8 Expression of results Calculate the hygroexpansivity, X, expressed as a percentage, between33% and66% relative humidity, using the equation: where Express the mean result to the nearest0,05% se
41、parately for the machine direction and/or cross direction as required. Calculate also the standard deviation for the machine direction and/or cross direction respectively. 9 Precision For test results, each of which consisted of the average of five determinations, the following precision data were o
42、btained from an international cross-check involving six laboratories testing five papers. 9.1 Repeatability The repeatability at the 95% confidence level, for the difference between two test results obtained in a single laboratory, was between0,02% and0,03% for samples tested in the machine directio
43、n, and between0,04% and0,06% for samples tested in the cross direction. NOTE 9The range in repeatability values quoted is due to large differences between mean values of different paper samples. NOTE 10All values for repeatability are percent absolute hygroexpansivity. 9.2 Reproducibility There were
44、 insufficient data from different laboratories for reproducibility to be assessed accurately. 10 Test report The test report shall include the following information: a) a reference to this part of ISO8226; b) all information necessary for complete identification of the sample; c) the date and place
45、of testing; d) the test span between the clamps at the start of the test; e) the width of the test piece; f) the mean value for the hygroexpansivity in the machine direction and/or cross direction; g) the standard deviation for the machine direction and/or cross direction; h) the measured values of
46、temperatures and relative humidities used for the test; i) any deviation from the requirements of this part of ISO8226 and any incidents which may have affected the test results. l o is the reading, in millimetres, on the length-measuring device, for the test piece under the appropriate load at a re
47、lative humidity of (50 5)%; l 33 is the reading, in millimetres, on the length-measuring device, for the test piece under the appropriate load at a relative humidity of (33 2) %; l 66 is the reading, in millimetres, on the length-measuring device, for the test piece under the appropriate load at a r
48、elative humidity of (66 2) %.BS6712-1:1995 4 BSI 08-1999 Annex A (normative) Preparation of salt solutions At constant temperature, saturated salt solutions reach equilibrium with the amount of water vapour in the atmosphere in a closed container, thereby maintaining a constant relative humidity. Sa
49、turated salt solutions can absorb or give up large quantities of water without changing the equilibrium relative humidity, making them suitable for studies of water vapour absorption or desorption. A wide range of relative humidity conditions can be obtained, using various salt solutions, as reviewed by Young 1 . Saturated salt solutions should be prepared from reagents of recognized analytical grade and distilled water or water of equivalent purity, since the presence of impurities may affect the e
