Imaging materials — Polyester-base magnetic tape — Storage practices

This International Standard provides recommendations concerning the storage conditions, storage facilities, enclosures, and inspection for recorded polyester-base magnetic tapes in roll form. It covers analog and digital tape and includes tape made for audio, video, instrumentation and computer use. This International Standard is applicable to medium-term and extended-term storage of magnetic tape as defined in 3.18 and 3.7 and also is applicable to magnetic-tape records intended as master tapes, which should not be in frequent use. Deviations from these recommendations, whether before or after recording, may result in shortened life expectancy. For example, adverse conditions during shipment, handling, or usage. This International Standard is not applicable to "work" or "use" copies (see informative annex C).

Matériaux pour image — Bande magnétique à base de polyester — Pratiques d'emmagasinage

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14-Jun-2000
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INTERNATIONAL ISO
STANDARD 18923
First edition
2000-06-01
Imaging materials — Polyester-base
magnetic tape — Storage practices
Matériaux pour image — Bande magnétique à base de polyester —
Pratiques d'emmagasinage
Reference number
ISO 18923:2000(E)
©
ISO 2000

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ISO 18923:2000(E)
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ii © ISO 2000 – All rights reserved

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ISO 18923:2000(E)
Contents Page
Foreword.v
Introduction.vi
1 Scope .1
2 Normative references .1
3 Terms and definitions .2
4 Environmental conditions.5
5 Materials .7
6 Enclosures.7
7 Preparation.8
8 Storage housing.9
9 Storage rooms.9
10 Fire-protective storage.10
11 Identification, inspection, and cleaning .10
Annex A (informative) Numbering system for related International Standards.11
Annex B (informative) Stability of cellulose triacetate base.12
Annex C (informative) Distinction between master tapes and work copies .13
Annex D (informative) Temperature/relative humidity relationship .14
Annex E (informative) Temperature and humidity acclimatization .15
Bibliography.17
Table 1 Maximum temperature and relative humidity for storage.6
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ISO 18923:2000(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO
member bodies). The work of preparing International Standards is normally carried out through ISO technical
committees. Each member body interested in a subject for which a technical committee has been established has
the right to be represented on that committee. International organizations, governmental and non-governmental, in
liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical
Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
Draft International Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
International Standard ISO 18923 was prepared by Technical Committee ISO/TC 42, Photography.
This International Standard is one of a series of standards dealing with the physical properties and stability of
imaging materials. To facilitate identification of these International Standards, they are assigned a number within
the block from 18900 to 18999 (see annex A).
Annexes A to E of this International Standard are for information only.
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ISO 18923:2000(E)
Introduction
Magnetic tape is an important material in the capturing of information and has had widespread use in audio, video,
and computer applications over the past 60 years. Preservation of this information is becoming of increasing
concern to society, particularly as the recorded information becomes older and frequently of greater value to
libraries, archives, museums, government agencies, and commercial organizations. Magnetic tape is also widely
used by individual consumers to preserve records of personal or entertainment value.
The retrievability of the information on magnetic tape is dependent upon that of the complete magnetic system.
This includes the stability of the tape itself, the equipment on which it is run and, in some systems, upon the
necessary software. It is recognized that tape records will eventually have to be copied or transferred to another
material when the system becomes obsolete. Nevertheless, it is advantageous to prolong the tape life so that the
material does not become the controlling factor.
Although there have been many studies of tape stability, International Standards do not exist against which tape life
can be evaluated. Likewise, International Standards are not available on the life expectancy of hardware and the
problems associated with hardware wearing out or becoming obsolete. Therefore, the best approach for tape users
is to store magnetic tape under conditions that will extend its life and to handle tape so that it will not be subjected
to stress and undergo physical breakdown during use. This International Standard addresses the concerns of
storage.
A major component of magnetic tape is the plastic base. Early audio-magnetic tape was manufactured on a variety
of base materials, including paper, various vinyl esters, and cellulose esters. After extended storage, or storage
under adverse conditions, the cellulose-triacetate base decomposes and produces acetic acid (see informative
annex B). However, since the 1960s, magnetic tape has been coated onto a polyester base that has excellent long-
term stability. This International Standard was developed specifically for polyester-base tapes. However, it is also
applicable to the storage of triacetate-base tapes even though the triacetate base is not as stable.
The second component of magnetic tape is the oxide (or metal particle) binder layer which determines the
magnetic characteristics. A magnetic characteristic of importance in the aging behaviour of tape is the development
of print-through of analog tape. However, both research and use have clearly demonstrated that the critical
concerns are primarily changes in physical properties, not the loss of magnetic characteristics. Upon use and
aging, there may be changes in the friction properties, abrasivity, binder-base adhesion, and binder cohesion that
render the tape unusable. Many of these changes occur as a result of binder degradation. Unfortunately, the user
has no practical means of determining the stability of the composite tape and must rely on the studies of the
manufacturer.
Regardless of the inherent stability of the binder layer, it is known that good storage conditions will extend the life of
all tapes. While a good storage environment cannot reverse all the degradation that has already occurred, it can
slow down additional deterioration.
NOTE Some degraded tape can be rendered temporarily playable by a variety of specialized procedures.
Two storage conditions are described in this International Standard. Medium-term storage conditions are
recommended for tape with an expected useful life of ten years, while extended-term storage conditions are
intended for tape with an expected life of fifty years. The conditions given in this storage recommendation represent
a compromise between maximizing the tape life, considerations of convenience, and the cost of building and
maintaining a storage facility.
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INTERNATIONAL STANDARD ISO 18923:2000(E)
Imaging materials — Polyester-base magnetic tape — Storage
practices
1 Scope
This International Standard provides recommendations concerning the storage conditions, storage facilities,
enclosures, and inspection for recorded polyester-base magnetic tapes in roll form. It covers analog and digital
tape and includes tape made for audio, video, instrumentation and computer use.
This International Standard is applicable to medium-term and extended-term storage of magnetic tape as defined in
3.18 and 3.7 and also is applicable to magnetic-tape records intended as master tapes, which should not be in
frequent use.
Deviations from these recommendations, whether before or after recording, may result in shortened life
expectancy. For example, adverse conditions during shipment, handling, or usage.
This International Standard is not applicable to "work" or "use" copies (see informative annex C).
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of
this International Standard. For dated references, subsequent amendments to, or revisions of, any of these
publications do not apply. However, parties to agreements based on this International Standard are encouraged to
investigate the possibility of applying the most recent editions of the normative documents indicated below. For
undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC
maintain registers of currently valid International Standards.
1)
NFPA 75-1995, Electronic computer/Data processing equipment.
1)
NFPA 90A-1996, Installation of air conditioning and ventilating systems.
1)
NFPA 232-1995, Protection of records.
2)
ASHRAE, Equipment. 1988.
2)
ASHRAE, Handbook of fundamentals. 1988.
2)
ASHRAE, Systems. 1987.
1) Available from the National Fire Protection Association, 1 Batterymarch Park, P.O. Box 9101, Quincy, MA 02269-9101,
USA.
2) Available from the American Society of Heating, Refrigeration and Air Conditioning Engineers, 1791 Tullie Circle, NE
Atlanta, GA 30329, USA.
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ISO 18923:2000(E)
3 Terms and definitions
For the purposes of this International Standard, the following terms and definitions apply.
3.1
aperture
window
opening on the flange that is used to facilitate threading of magnetic tape on the hub and inspection of the wind
3.2
base
support in a recording material on which the magnetic layer (and, if necessary, the back layer) is coated
3.2.1
cellulose-acetate base
base for recording materials composed mainly of cellulose esters of acetic acid
3.2.2
polyester base
base for recording materials composed mainly of a polymer of ethylene glycol and terephthalic acid (also referred
to as polyethylene terephthalate), or a polymer of ethylene glycol and 2,6 naphthalene dicarboxylic acid (also
referred to as polyethylene naphthalate)
3.3
cartridge
housing for a roll of recording material, such as photographic film or magnetic tape, attached to a single hub or reel
SEE cassette (3.4).
3.4
cassette
housing for a roll of recording material, such as photographic film or magnetic tape, whose ends are attached to
two hubs or reels
3.5
container
box, can, or carton used for storage and shipping of recording materials
EXAMPLE The box into which a reel, cassette, cartridge or shell is placed is a container.
NOTE Reels, cassettes, cartridges or shells are not containers.
3.6
dew-point
temperature at which moisture begins to condense on a surface, corresponding to saturation for a given absolute
humidity
EXAMPLE The more humid the air, the higher the dew-point temperature.
3.7
extended-term storage conditions
storage conditions suitable for the preservation of information recorded on the majority of magnetic tapes for
50 years
3.8
fire-protective storage
facilities designed to protect records against excessive temperatures, water and other fire-fighting agents, and
steam developed by insulation of safes or caused by the extinguishing of fires and collapsing structures
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ISO 18923:2000(E)
3.9
flange
fixed or removable circular disc, which is connected to the hub to make a reel for the purpose of protecting the roll
of recording material
SEE reel (3.21)
3.10
heads out
configuration of magnetic tape stored on its reel, or in its cassette, such that the tape is positioned to play from the
beginning of the recorded information
3.11
hub
cylindrical object at the centre of the tape reel, around which the recording material is wound
3.12
leader
flexible plastic or paper strip which can be spliced to either end of a roll of recording material
3.13
leafing
multiple popped strands in a magnetic-tape wind
SEE popped strand (3.19) and stepped pack (3.29)
3.14
life expectancy
LE
length of time that information is predicted to be retrievable in a system
3.15
loose pack
undesirable pack condition in a roll of recording material, such that the outer portion of the roll can be moved and
tightened by pulling on the end
3.16
magnetic field intensity
level of the magnetic field at a point in space
3.17
medium
media,pl
material on which the information is recorded
3.18
medium-term storage conditions
storage conditions suitable for the preservation of recorded information for a minimum of 10 years
3.19
popped strand
lateral displacement of a single strand or wrap of magnetic tape extending beyond the plane of the tape pack
SEE leafing (3.13) and stepped pack (3.29)
3.20
print-through
unwanted transfer of a magnetic field and its signal from one tape lap to another within a roll of magnetic tape
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ISO 18923:2000(E)
3.21
reel
spool
hub or core with flanges (protective sides) onto which recording material is wound
3.22
relative humidity
RH
ratio, defined as a percentage, of the existing partial vapour pressure of water to the vapour pressure at saturation
NOTE It is usually, but not always, equal to the percentage of the amount of moisture in the air to that at saturation.
3.23
shell
cassette/cartridge housing for magnetic tape
3.24
slot
spaceor slitinthehubor reelsurface
3.25
splice
union of two pieces of recording material to form a single piece
3.26
splicing tape
paper or plastic strip coated with a thermal-or pressure-sensitive adhesive, used in splicing
3.27
spoking
deformations in a roll pack that appear radially outward and disrupt the circular nature of the wind
3.28
staging
process of conditioning material from one set of temperature/moisture conditions to another
3.29
stepped pack
multiple adjacent strands of magnetic tape extending beyond the level of a tape pack
SEE leafing (3.13) and popped strand (3.19)
3.30
storage environment
conditions for storing materials, i.e., temperature, relative humidity, cleanliness of facilities, and atmospheric
pollutants
3.31
storage housing
physical structure supporting materials and their enclosures
NOTE It may consist of drawers, racks, shelves or cabinets.
3.32
system
material, hardware, software and documentation necessary for recording and/or retrieving information
3.33
tape pack
length of magnetic tape wound on a reel or hub
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ISO 18923:2000(E)
3.34
tails out
configuration of magnetic tape stored on its reel or in its cassette, such that the tape should be fully rewound in
order to correctly play from the beginning of the recorded information
3.35
wind
�appearance� physical appearance and tension of the magnetic tape pack
3.36
wind
�process� process of transferring a roll of recording material from one spool or reel to another
4 Environmental conditions
4.1 Humidity and temperature limits
4.1.1 Medium-term storage environment
The average relative humidity of a medium-term storage environment shall not exceed 50 % RH and shall not be
lower than 15 % RH. The maximum temperature for prolonged periods shall not exceed 23 °C (see Table 1). The
peak temperature for short time periods shall not exceed 32 °C. Tape should not be stored below 8 °C due to a
potential problem with lubricant separation from the binder.
o
Cycling of temperature shall not be greater than � 2 C over a 24 h period. Cycling of relative humidity shall not be
greater than � 10 % over a 24 h period. Protection increases by storing tape at low temperature and/or low relative
humidity.
4.1.2 Extended-term storage environment
The rate of chemical reactions, such as the degradation of the tape base and the polymer binder layer, is lowered
with decreasing temperature and decreasing relative humidity. Consequently, life expectancy is increased as
storage temperature and/or storage humidity are lowered within the range of recommended storage.
A lower storage temperature can compensate for a higher humidity to provide the same life expectancy (see
informative annex D) and a wider relative humidity range can be tolerated. For this reason, several relative
humidity/temperature combinations can be used for an extended-term storage environment as specified in Table 1.
The majority of tapes fail due to hydrolysis of the binder. The storage conditions given in Table 1 are based on
predictions of binder stability for the majority of polyester-base tapes. The maximum temperature shall not exceed
23 °C and storage of tape below 8 °C is not recommended. When low-temperature storage is used, attention shall
be given during warm-up to avoid moisture condensation (see 7.1). Cycling of relative humidity in the storage
environment shall not be greater than � 5 % and cycling of temperature shall not be greater than � 2°C over a 24h
period. It should be recognized that while tape reaches temperature equilibrium quickly, it takes a long time for a
tape pack to attain moisture equilibration (see informative annex E).
It is impossible to specify the best relative humidity and storage temperature for any facility since they depend upon
the value of the material, the past storage history, the length of time that the tape is to be kept, the size of the vault,
the cost of various options, and the climate conditions where the facility is located. Lower temperatures with the
specified relative humidity range may be difficult to achieve with air-conditioning equipment operating at normal
humidity and may require a specialized installation.
Properly controlled air conditioning may be necessary for maintaining humidity and temperature within the limits
specified. The fundamentals of air conditioning are given in the three ASHRAE publications listed in clause 2.
Automatic control systems are recommended, and they shall be checked frequently enough to determine that the
temperature and humidity limits specified in Table 1 are not being exceeded. A reliable hygrometer may be used
for humidity measurements.
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ISO 18923:2000(E)
Where air conditioning is not practical, high humidities may be lowered by dehumidifiers of the electrical
refrigeration type controlled with a hygrostat. Inert desiccants, such as chemically pure silica gel, may be used,
provided the dehumidifier is equipped with filters capable of removing dust particles down to 0,3 �m (microns) in
size and is controlled to maintain the relative humidity given in Table 1. Dehumidification may be required in
storage areas, such as basements and caves, that have inherently low temperatures but frequently exceed the
upper humidity limit.
The recommended humidity and temperature conditions can be maintained either within individual storage
housings or within storage rooms containing such housings.
Table 1 — Maximum temperature and relative humidity for storage
Medium-term storage Extended-term storage
Maximum temperature Maximum relative humidity Maximum Maximum relative
c, e a, d
c, e a, b temperature humidity
o
o
C %
C %
23 50 23 20
17 30
11 50
a
The moisture content of the tape to be stored shall not be greater than that of tape in moisture equilibrium with these
relative humidities. The minimum relative humidity is 15 %, because of possible transport problems due to static
b
Cycling shall not exceed �10 % RH over a 24 h period.
c
Cycling shall not exceed � 2 °C over a 24 h period.
d
Cycling shall not exceed �5%RHovera24hperiod.
e Storage of tape below 8 °C can cause lubricant separation from the tape binder. The manufacturer should be
consulted to determine if this is a potential problem.
4.2 Gaseous impurities
The most practical technologies shall be used to ensure minimization of gaseous impurities such as ammonia,
chlorine, sulfides, peroxides, ozone, oxides of nitrogen, smoke, and acidic gases.
4.3 Magnetic fields
Within a storage area, the peak intensity of external DC fields shall not exceed 4 kA/m (see [1] in the bibliography)
and the peak intensity of external AC fields shall not exceed 800 A/m.
External magnetic fields are most frequently observed near motors and transformers (i.e., elevator installations in
commercial buildings). Most of these installations are localized and the field intensity falls off rapidly with
separation. A few feet of separation from the source will usually provide sufficient protection.
External fields of a more unanticipated nature are produced by some headphones, speakers, microphones,
magnetic cabinet latches, or magnetized tools.
See 7.2 for a discussion of print-through.
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ISO 18923:2000(E)
5 Materials
The materials used for hubs, flanges, reels, cassettes, cartridges, containers, and storage housing shall be
chemically stable, non-debris producing and shall meet the requirements of clause 10. They shall be free from
warpage and distortion. Metals shall be non-magnetic. Plastics are suitable for flanges, hubs, cassettes and
cartridges but they shall be sufficiently strong to not distort or break under conditions of use. Plastics are not
recommended for open reels.
6Enclosures
6.1 Reels
6.1.1 Hubs
Hubs shall be cylindrical and composed of materials that are resistant to distortion. Hubs are preferred without
slots, irregularities, or deformations on the surface in contact with the tape.
Hubs shall be constructed to minimize deformation or damage of the tape. Hubs shall have as large a diameter as
is practical, since larger diameter hubs yield better resistance to inner tape-pack distortions.
6.1.2 Flanges
Flanges with small apertures are recommended in preference to flanges with large apertures. Flanges shall not be
padded. It is recommended that flanges be removable and replaceable.
6.2 Cassettes and cartridges
6.2.1 Cassette and cartridge shells
Cassette and cartridge shells and their components shall be impact resistant. They shall be constructed so as not
to damage the tape and shall be able to be disassembled and reassembled.
6.2.2 Hubs
Hubs shall be cylindrical and shall have the largest possible diameter. They shall be constructed to minimize pack
irregularity caused by the attachment of the tape/leader tape to the hub.
Hubs shall lock in such a way that the tape pack is held in place without loosening when the cassette is not in the
machine. Those shells which do not provide such locking devices shall be stored in containers that provide locking
mechanisms.
6.3 Containers
Containers shall be resistant to impact, moisture, and dust intrusion. Containers made of paper or cardboard are
not recommended.
Containers shall be designed so that the flanges are not load bearing when the containers are stored in their
correct vertical position. Containers shall not be able to be deformed in the defined storage conditions. The
container lid shall be capable of being latched, attached or locked to prevent accidental opening.
6.4 Labelling
Reels, cassettes, cartridges and containers shall provide a means for labelling that allows identification of the
recorded information contained within. The labelling shall be non-acid, non-debris and non-oxidant producing, and
shall be attached to or affixed in such a manner that it will remain for the life expectancy of the material.
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ISO 18923:2000(E)
The number and size of labels shall be kept to a minimum to reduce the possibility of adhesive migration. Bulk
information shall be on the container label. Labels shall be small enough to avoid adhesive contamination of the
tape and shall not overlap the tape.
The original manufacturer's product identification shall be maintained with the tape. The magnetic tape or leader
tape shall not be marked, labelled, embossed or identified.
6.5 Supplementary materials
Other materials shall not be stored in the tape container.
7 Preparation
All preparation of tape for storage shall be done in areas having an environment of approximately 20 °C and
50 % RH. All tapes shall be stored on reels, cartridges or cassettes, and in appropriate containers.
7.1 Acclimatization
A tape pack shall be acclimatized for temperature to prevent moisture condensation when it is transferred from a
cold environment outside the storage facility, or when being removed from an extended-term storage area to an
access or production area. These materials shall be allowed to warm up to a temperature above the dew point at
medium-term storage conditions for the equilibrium times given for information in annex E. Tape packs shall be
kept in appropriate containers during acclimatization. Tapes shall not be rewound when they are cold.
A tape pack may require moisture acclimatization to ensure that it will play properly. When tape is in equilibrium
with a low-temperature or low-humidity environment, it will have reduced dimensions and may not play properly.
High-density helical scan tape may be susceptible to mistracking problems due to inadequate moisture
acclimatization. This can be corrected by allowing the tape to reach partial humidity equilibrium (see informative
annex E) or by rewinding the tape several times on a machine.
7.2 Tape wind and tape pack
Prior to storage, tape should be played continuously end-to-end, or continuously wound at a tension that
approximates the play tension so as to ensure a smooth and even-tensioned pack. Both too loose and too tight a
pack shall be avoided. Too loose a pack can cause slippage or cinching of the tape on the hub and subsequent
damage to the tape. Too tight a wind can cause stretching and deformation of the tape, especially if temperature
and humidity variations are significant.
Tapes in cassettes or cartridges shall be wound so that all the tape is on one hub. A tape pack shall not have
leafing, stepped pack, spoking, or any other pack abnormality.
Tape rolls that are wound at room temperature and/or humidity, then stored at a lower temperature and/or humidity,
can have a looser wind. Additional care in handling may be required to avoid slippage, p
...

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