1、BRITISH STANDARD BS1133-19: 1986 Packaging code Section 19: Use of desiccants in packaging UDC621.798.02:66.047.8BS1133-19:1986 This British Standard, having been prepared under the direction of the Packaging and Freight Containers Standards Committee, was published under the authority of the Board
2、of BSI and comes into effect on 31December1986 BSI 02-1999 First published December1953 First revision July1968 Second revision December1986 The following BSI references relate to the work on this standard: Committee reference PKM/584 Draft for comment84/41479DC ISBN 0 580 15454 8 Committees respons
3、ible for this British Standard The preparation of this British Standard was entrusted by the Packaging and Freight Containers Standards Committee (PKM/-) to Technical Committee PKM/584 upon which the following bodies were represented: British Plastics Federation Chemical Industries Association Expor
4、t Packing Service Ltd. Institute of Packaging Ministry of Defence Timber Packaging and Pallet Confederation Coopted member Amendments issued since publication Amd. No. Date of issue CommentsBS1133-19:1986 BSI 02-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 D
5、efinitions 1 3 General 1 4 Humidity 1 5 Desiccated packages 2 6 Factors governing choice of desiccant 2 7 Factors determining quantity of desiccant 3 8 Calculation of quantity of desiccant required 4 9 General packaging considerations 6 Appendix A Examples of calculating the required quantity of des
6、iccant 7 Appendix B Examples of labels for desiccated packages 9 Figure 1 Labels for desiccated packages 9 Table 1 WVTR of various materials at38C and90% r.h. 4 Publications referred to Inside back cover BS1133-19:1986 ii BSI 02-1999 Foreword This Section of BS1133 was first issued in1953, revised i
7、n1968 and has now been revised to take into account current recommendations on desiccant quantities. This edition of the code supersedes BS1133-19:1968, which is withdrawn. A list of the current Sections of the packaging code is given below and the importance of preventing access of moisture to the
8、content of the packages is stressed in these. One of the methods of minimising the effect of moisture is the use of the desiccants in conjunction with materials of very low water vapour permeability and this Section has been prepared to give guidance on this subject. The packaging code consists of t
9、he following Sections all of which are published separately with the exception of Sections1 to3 which are published in one volume. Sections1 to3: Introduction to packaging; Section 4: Mechanical aids in package handling; Section 5: Protection against spoilage of packages and their contents from atta
10、ck by micro-organisms, insects, mites and rodents; Section 6: Temporary protection of metal surfaces against corrosion (during transport and storage); Section 7: Paper and board wrappers, bags and containers; Section 7-7.1: Wrapping papers; Section 7-7.2: Bags and envelopes; Section 7-7.3: Cartons a
11、nd boxes; Section 7-7.5: Fibreboard cases; Section 8: Wooden containers; Section 9: Textile bags, sacks and wrappings; Section 10: Metal containers; Section 11: Packaging felt; Section 12: Cushioning materials (excluding packaging felt); Section 13: Twines and cords for packaging; Section 14: Adhesi
12、ve closing and sealing tapes; Section 15: Tensional strapping; Section 16: Adhesives for packaging; Section 17: Wicker and veneer baskets; Section 18: Glass containers and closures; Section 18-1: Terminology; Section 21: Regenerated cellulose film, plastics film, aluminium foil and flexible laminate
13、s; Section 22: Packaging in plastics containers. 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 a British Standard does not of itself confer immunity from legal oblig
14、ations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages1 to 10, 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 on t
15、he inside front cover.BS1133-19:1986 BSI 02-1999 1 1 Scope This Section of BS1133 gives guidance on the use of desiccants in packaging for general use. NOTEThe titles of the publications referred to in this standard are listed on the inside back cover. 2 Definitions For the purposes of this Section
16、of BS1133 the following definitions apply. 2.1 desiccant a material possessing a high affinity for water vapour and used to control relative humidity in sealed packages 2.2 dunnage any hygroscopic material within the barrier other than the packaged item, e.g.packing or blocking materials, instrument
17、 cases, etc. 2.3 hygroscopic capable of exchanging water vapour with the surrounding atmosphere. Exchange will continue until an equilibrium is reached and this is dependent upon the conditions of temperature and relative humidity of the atmosphere. Hygroscopicity is a reversible process, the hygros
18、copic material absorbing or desorbing water vapour to maintain equilibrium with the surrounding atmosphere 3 General Dampness in the atmosphere encourages corrosion and the growth of moulds and bacteria even when liquid water is absent. Steps can often be taken to reduce the deleterious effect of mo
19、isture on a packaged article by such means as the application of a temporary protective against corrosion (seeBS1133-6) to a metal surface or the proofing of textiles. However such direct protection is not practicable for all articles, for example, for certain electrical components or scientific and
20、 optical instruments. A method of providing protection in such cases is by using a completely sealed package. There may, however, still be damp air inside the container and moisture may be given off by the cushioning or bracing material used to hold the articles in position; moreover, few materials
21、used in making sealed packages are completely resistant to the penetration of water vapour and a certain amount of moisture will reach the article through the walls of the package. Additionally temperature fluctuations can cause unacceptable humidity levels within the package without any change in a
22、bsolute humidity (see4.1). 4 Humidity 4.1 Moisture in air Air naturally contains moisture in the form of vapour. The quantity of moisture present in a unit volume is known as the absolute humidity. At any particular temperature, air can hold only a limited amount of water vapour, the higher its temp
23、erature the more water vapour it can hold. Air containing as much water vapour as it can hold is said to be saturated. If saturated air is cooled, it will give up by condensation just enough of its moisture as liquid water to leave it saturated at the lower temperature. The maximum quantity of moist
24、ure which can be held in vapour form by atmospheric air is determined by the temperature. Maxima for a whole range of temperatures have been accurately determined and are published as hygrometric tables and charts. 4.2 Relative humidity Normally air is only saturated with water vapour when it is in
25、close contact with liquid water. The actual amount of water vapour present in air (i.e.the absolute humidity), expressed as a percentage of the amount the air contains when saturated at the same temperature and pressure, is called relative humidity(r.h.). For example, if1m 3of air contains5g of wate
26、r vapour and that air, if saturated at the same temperature and pressure, contains20g of water vapour, then the relative humidity of the air, expressed as a percentage, is: 5 20 -100 25% =BS1133-19:1986 2 BSI 02-1999 Saturated air has a relative humidity of100%. The relative humidity of the atmosphe
27、re is the dominant factor in determining whether the corrosion of metals, mould growth, rottingetc., will occur. It is known, for example, that the corrosion of iron is extremely slow at relative humidities below60% but becomes rapid at higher humidities. Mould growth does not normally take place, o
28、r is extremely slow, unless the relative humidity exceeds70%. Generally for engineering products50%r.h. has been found to be an acceptable maximum. 5 Desiccated packages 5.1 General It has been stated in clause 3 that the deterioration of many articles can be minimized by applying suitable treatment
29、 to the article itself during or after manufacture. Sometimes such treatment is not practicable or desirable and yet it is still necessary to protect the contents; one method of doing this is to ensure that the relative humidity of the atmosphere within the package never exceeds a safe limit (see 5.
30、2). 5.2 Reduction of humidity within the package The safe limit referred to in 5.1 is generally taken to be50%r.h. A package that contains sufficient desiccant to ensure that the relative humidity within it will not exceed this value when stored in predicted conditions for a specified period is call
31、ed a desiccated package. An essential requirement of such a package is that it contains a sufficient quantity of a desiccant to reduce the relative humidity within the package to50% or less and maintain this for the desired period. To assist in maintaining this reduced level of humidity the entry of
32、 water vapour is retarded. There are various ways of achieving this. Sealed metal containers may be used, or the container may incorporate or be made from a water vapour barrier, i.e.a material with a high resistance to the passage of water vapour (seeBS1133-21). It is rarely possible to exclude air
33、 from such packages or to avoid the use of interior packaging materials that contain some moisture. 5.3 Sources of moisture 5.3.1 General. For any package there are four sources of moisture as follows: a) the air inside the barrier; b) the air outside the barrier; c) hygroscopic materials inside the
34、 barrier including the article itself; d) water trapped within the article. 5.3.2 The air inside the barrier. Air inside the barrier contains some water vapour. 5.3.3 The air outside the barrier. Air outside the barrier is likely to be the most important source of moisture because not even a sealed
35、container, except a perfectly sealed metal or glass container, is completely proof against water vapour. The way in which the water passes through the barrier is not important but “waterproof” material is not necessarily even moderately proof against water vapour. Air-tightness is an even less relia
36、ble criterion than water-proofness. The implication of this is that, if the relative humidity outside the package is higher than that inside there is a tendency for moisture to pass into the package. In many countries the relative humidity is often80% to100% and since the atmosphere inside the packa
37、ge is to be kept below50%, the transmission of water vapour may be considerable. 5.3.4 Hygroscopic materials inside the barrier. Hygroscopic materials inside the barrier are a source of moisture. For example, wood and paperboard are both hygroscopic and will give up moisture when the temperature ris
38、es. The packaged item itself may create a problem if it is made in part from hygroscopic materials. 5.3.5 Trapped water. There is always a possibility of water being trapped, for example in pumps after testing, or water being suspended in any oil remaining in an oil bath. Certain non-hygroscopic mat
39、erials used for packaging contain water as a result of their manufacturing process. Expert guidance should be sought to deal with this problem. 6 Factors governing choice of desiccant 6.1 General A desiccant maintains a safe relative humidity inside a package by absorbing most of the moisture from t
40、he air and any moisture arising from the goods or internal hygroscopic materials. It will continue to absorb any moisture which enters the package through the barrier but only for a calculable period. 6.2 Management of the desiccant The desiccant should be supplied in dustproof containers that will
41、allow the desiccant to absorb the moisture from within the package. There are many dehydrating agents that can be used, but certain properties such as moisture-absorbing capacity, chemical inertness, etc., make some materials more suitable than others for use as desiccants in packaging. Desiccant co
42、ntainers should be evenly distributed and firmly secured inside the package.BS1133-19:1986 BSI 02-1999 3 6.3 Choice 6.3.1 General. The major factors to be considered when choosing a desiccant for a package are: a) its moisture absorbing capacity in relation to bulk and mass; b) its stability and phy
43、sical form; c) the influence of temperature (within the range usually experienced) on the moisture absorbing capacity; d) the means of containing the desiccant. 6.3.2 The moisture absorbing capacity in relation to bulk and mass. To maintain a safe relative humidity inside a desiccated package, it is
44、 essential to have present sufficient desiccant to cater for all possible sources of moisture. In order to minimize the space required in the package for the desiccant it is necessary to use materials of high moisture absorbing capacity. 6.3.3 Stability and physical form of the desiccant. The physic
45、al form of the desiccant should be such as to expose the maximum surface of desiccant and allow diffusion of the package atmosphere through its mass. The desiccant container should be designed to minimize hindrance to such diffusion. These conditions are best satisfied when the desiccant is availabl
46、e in the form of coarse granules, beads or extrudates. The desiccant should retain its form throughout the performance of its function, i.e.,it should remain solid and dry to the touch and suffer little or no disintegration. The material should be such that the absorption of moisture is not accompan
47、ied by chemical changes that will cause it to corrode or otherwise damage its container or the article packed. It should not produce liquid or gas or cause a rise in temperature. 6.4 Desiccant materials The desiccants most commonly used for packaging are: a) silica gel; b) activated clays; c) activa
48、ted alumina. For packaging where very low relative humidities, e.g.below10%, are to be maintained, molecular sieve desiccants should be used. The equations used for determining the quantity of basic desiccant used in a package cannot be applied to molecular sieve desiccants. Advice should therefore
49、be sought from suppliers of molecular sieve desiccants as to the appropriate conditions and mode of use in each case. In some circumstances any of these materials may be suitable, but in others the choice can be made only taking account of the nature of the article to be packed. Care should therefore be taken to consult a specialist before finally selecting a desiccant for a particular commodity. Further information on the use of silica gel and activated alumina as desiccants is given in BS2540 and BS2541. 7 Factors determi
