1、BRITISH STANDARD BS 6712-2: 1991 ISO 8226-2: 1990 Measurement of hygroexpansivity of paper and board Part 2: Method for measurement of hygroexpansivity up to a maximum relative humidity of 86 %BS6712-2:1991 This British Standard, having been prepared under the directionof the Paper and PrintingStand
2、ards Policy Committee, was published underthe authorityofthe Standards Boardand comes into effect on 29 March 1991 BSI 07-1999 The following BSI references relate to the work on this standard: Committee reference PAM/11 Draft for comment 89/44548 DC ISBN 0 580 19438 8 Committees responsible for this
3、 British Standard The preparation of this British Standard was entrusted by the Paper and Printing Standards Policy Committee (PAM/-) to Technical Committee PAM/11, upon which the following bodies were represented: British Fibreboard Packaging Association British Paper and Board Industry Federation
4、(PIF) British Printing Industries Federation British Telecommunications plc Envelope Makers and Manufacturing Stationers Association Her Majestys Stationery Office Man-made Fibres Producers Committee Ministry of Defence Pira (the Research Association for the Paper and Board, Printing and Packaging I
5、ndustries) Post Office Society of British Printing Ink Manufacturers University of Manchester Institute of Science and Technology Amendments issued since publication Amd. No. Date CommentsBS6712-2:1991 BSI 07-1999 i Contents Page Committees responsible Inside front cover National foreword ii 1 Scope
6、 1 2 Normative references 1 3 Definition 1 4 Principle 1 5 Apparatus 1 6 Sampling and preparation of test pieces 2 7 Procedure 2 8 Expression of results 2 9 Precision 2 10 Test report 2 Annex A (informative) Preparation of salt solutions 4 Table 1 Test loads 1 Table A.1 Saturated salt solutions 4 Pu
7、blication(s) referred to Inside back coverBS6712-2:1991 ii BSI 07-1999 National foreword This Part of BS 6712 has been prepared under the direction of the Paper and Printing Standards Policy Committee. It is identical with ISO 8226:1990 “Paper and board Measurement of hygroexpansivity Part 2: Hygroe
8、xpansivity up to a maximum relative humidity of 86 %”, published by the International Organization for Standardization (ISO). The international standard has an introduction which is as follows. The measurement of dimensional changes in paper and board with changes in the ambient humidity is necessar
9、y for accurate control of printing and similar processes. The change in length, or hygroexpansivity, is due to stress relaxation of the paper fibres and swelling or contraction of the fibres by absorption or desorption of water. The proportion of the two mechanisms effective to produce hygroexpansiv
10、ity depends upon the upper limit of relative humidity of the environment. For the purpose of this part of ISO 8226 an upper limit of relative humidity of 86 % is imposed to accommodate the effects of stress relaxation on the hygroexpansivity. ISO 8226-1 describes a method for the measurement of hygr
11、oexpansivity at 68 %. The relationship between hygroexpansivity and relative humidity above approximately 68 % is non-linear, partly due to the effects of stress relaxation of the test piece above this humidity. A two-point measurement of hygroexpansivity can be used with humidities greater than 68
12、%, but no attempt should be made to interpolate or correct measurements in the range 33 % r.h. to 84 % r.h. to other relative humidity ranges, by simple arithmetical procedures. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are
13、responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Cross-references International Standard Corresponding British Standard ISO 186:1985 BS 3430:1986 Method for sampling to determine the average quality of paper and
14、board (Identical) ISO 187:1990 BS 3431:1973 Method for the conditioning of paper and board for testing (Technically equivalent) ISO 8226-1:1985 BS 6712 Measurement of hygroexpansivity of paper and board Part 1:1986 Method for measurement of hygroexpansivity up to a maximum relative humidity of 68 %
15、(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 standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table o
16、n theinside front cover.ISO8226-2:1990(E) BSI 07-1999 1 1 Scope This part of ISO8226 specifies a method for the determination of the hygroexpansivity of paper andboard when subjected to a change in the relative humidity with which it is in equilibrium from (33 2) % to (84 2)%. The purpose of this pa
17、rt of ISO8226 is to cover applications of paper and board intended to be used in high humidity conditions, e.g. as found in tropical countries. It may also be useful in determining the effect of excessive moisture to which paper may be subjected for short periods during some printing processes, e.g.
18、 offset printing. 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, through reference in this text, constitute provisions of this part of ISO 8226. A
19、t the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this part of ISO 8226 are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and ISO ma
20、intain registers of currently valid International Standards. ISO 186:1985, Paper and board Sampling to determine average quality. ISO 187:1990, Paper, board and pulps Standard atmosphere for conditioning and testing and procedure for monitoring the atmosphere and conditioning of samples. ISO 8226-1:
21、1985, Paper and board Measurement of hygroexpansivity Part 1: Hygroexpansivity up to a maximum relative humidity of 68 %. 3 Definition For the purposes of this part of ISO 8226, the following definition applies. hygroexpansivity the increase in length relative to the initial length that occurs when
22、the relative humidity with which the test piece of paper or board is in equilibrium is raised from a specified lower relative humidity to a specified higher relative humidity NOTE 1A contraction of the test piece is regarded as negative hygroexpansivity. 4 Principle To ensure that all test pieces be
23、ing 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. Preliminary conditioning of test pieces at a specified temperature (preferably23C 1 C), under zero load and a rela
24、tive humidity of (22 3)% and then at relative humidities of (33 2)% and (84 2)%. Measurement of the change in length between the latter two relative humidities under a load appropriate to the grammage of the test pieces. 5 Apparatus 5.1 Cabinet, with air circulation, capable of beingmaintained at on
25、e of the temperatures specified in ISO187, preferably23C 1 C. It shall be possible to attain uniform relative humidities of (22 3)%, (33 2) %, (50 5)% and(84 2)% within the whole cabinet and within a short time, for example,30min. Any method which will provide the specified relative humidities withi
26、n the tolerances indicated may be used, for example, the saturated salt solutions given inAnnex A. 5.2 Clamps, or other means for suspending the test pieces vertically in the cabinet (5.1) and provided with some means of ensuring the unloaded test pieces are free from tension. 5.3 Loading weights, f
27、or application to the test pieces during measurement (seeTable 1). Table 1 Test loads 5.4 Means for measuring the relative humidity of the air in the cabinet (5.1) with a precision of 1% (maximum error of reading) and an accuracy of2% (maximum departure from true relative humidity). 5.5 Means for me
28、asuring the temperature in the cabinet (5.1). 5.6 Device for measuring the increase in length of the test pieces to the nearest0,01mm. This device may be mechanical or electronic. Test piece grammage, A A Total load (including clamps) Equivalent mass g/m 2 N/m g/15 mm A Au 125 15 1 23 1,5 125 A Au 2
29、00 30 1 46 1,5 200 A Au 275 50 1 76 1,5 275 A A 80 1 122 1,5ISO8226-2:1990(E) 2 BSI 07-1999 6 Sampling and preparation of test pieces 6.1 Where possible, sample in accordance with ISO186. 6.2 From undamaged specimens free from watermarks, folds and wrinkles, cut five test pieces in the machine direc
30、tion and/or five in the cross direction as required. Each test piece shall be at least20mm longer than the nominal free span between the clamps, and the minimum free span shall be 100mm. The width of the test piece shall be at least15mm. For the determination of hygroexpansivity in the machine direc
31、tion or in the cross direction, cut the test pieces with the longer side parallel to the relevant direction. 7 Procedure 7.1 Initial length (l o ) Set the clamps (5.2) inside the cabinet (5.1) to a span of at least100mm (known to within1mm). Clamp, then condition the unloaded test pieces for at leas
32、t30min at the selected temperature (see5.1) and at a relative humidity of (50 5)%. Gently apply the appropriate load in accordance with Table 1 and note the readings on the length-measuring devices (5.6) to the nearest0,01mm. Record this length as l 0 . 7.2 Preliminary conditioning of test pieces Co
33、ndition the unloaded test pieces for at least30min at a relative humidity of (22 3)%. 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
34、 no more than0,02% between measurements. NOTE 2These readings are not used in the calculation. 7.3 Measurement of hygroexpansivity Change the conditioning atmosphere to one of(33 2)%, and record the relative humidity value obtained. Condition the unloaded test pieces for at least30min at a relative
35、humidity of (33 2)%. 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 until the length under load changes by no more than0,01mm. Record these to the nearest0,01mm (l 33 ). Co
36、ndition the test pieces in the same way for a minimum of18h in an atmosphere having a relative humidity of (84 2)%. Note the relative humidity value obtained. Record the new readings(l 84 ) of the test pieces to the nearest0,01mm. NOTE 3Shorter conditioning times at a relative humidity of84% may be
37、used by agreement, but this fact should be noted in the test report. 8 Expression of results The hygroexpansivity, X, expressed as a percentage, between33% and 84% relative humidity, is given by the equation where Express the mean result to the nearest0,05%, separately for the machine direction and
38、the cross direction as required. Calculate also the standard deviations for the machine direction and cross direction respectively. 9 Precision No information is as yet available on the repeatability or the reproducibility of this method. 10 Test report The test report shall include the following in
39、formation: a) reference to this part of ISO 8226; b) all the information necessary for complete identification of the sample; c) the date and place of sampling and testing; d) the test span between the clamps at the start of the test; l o is the reading, in millimetres, on the length-measuring devic
40、e, for the test piece under the appropriate load at a relative 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 84 is the reading, in millimetres, on the length-measuring devi
41、ce, for the test piece under the appropriate load at a relative humidity of (84 2)%; R 1 is the recorded lower relative humidity, i.e. (33 2)%; R 2 is the recorded higher relative humidity, i.e. (84 2)%. X 51 R 2 R 1 - l 84 l 33 ()100 l o - =ISO8226-2:1990(E) BSI 07-1999 3 e) the width of the test p
42、iece; 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 temperatures and relative humidities used for the test; i) any deviation from the requirements of th
43、is part of ISO 8226 and any incidents which may have affected the results.ISO8226-2:1990(E) 4 BSI 07-1999 Annex A (informative) 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, t
44、hereby maintaining a constant relative humidity. Saturated 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
45、 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 equilibrium relative humidity. In most cases,
46、 the solution can be prepared by dissolving a quantity of the salt in excess of that required to saturate the solution, at a temperature slightly above the required testing temperature. Because certain salts can change their hydrated form, care should be taken to avoid dissolving at elevated tempera
47、tures. The approximate solubility values at23C and the relative humidities given by salts recommended for use in this part of ISO8226 are listed in Table A.1. Table A.1 Saturated salt solutions 1) Young, J.F. J. Appl. Chem. 17 September 1967:241. Salt Solubility Relative humidity g/100 cm 3 % Potass
48、ium acetate (KC 2 H 3 O 2 ) 262 22 3 Magnesium chloride (MgCl 2 .6H 2 O) 170 33 2 Potassium chloride (KCl) 36 84 2BS6712-2:1991 BSI 07-1999 Publication(s) referred to See national foreword.BS 6712-2: 1991 ISO 8226-2: 1990 BSI 389 Chiswick High Road London W4 4AL BSIBritishStandardsInstitution BSI is
49、 the independent national body responsible for preparing BritishStandards. It presents the UK view on standards in Europe and at the international level. It is incorporated by Royal Charter. Revisions BritishStandards are updated by amendment or revision. Users of BritishStandards should make sure that they possess the latest amendments or editions. It is the constant aim of BSI to improve the quality of our products and
