SIST ISO 18908:2003

SLOVENSKI STANDARD
01-april-2003
Imaging materials - Photographic film - Determination of folding endurance
Imaging materials -- Photographic film -- Determination of folding endurance
Matériaux pour l'image -- Films photographiques -- Détermination de la résistance au
pliage
Ta slovenski standard je istoveten z: ISO 18908:2000
ICS:
37.040.20 )RWRJUDIVNLSDSLUILOPLLQ Photographic paper, films
IRWRJUDIVNHSORãþH)LOPVNL and cartridges
]YLWNL
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

INTERNATIONAL ISO
STANDARD 18908
First edition
2000-05-15
Imaging materials — Photographic film —
Determination of folding endurance
Matériaux pour l'image — Films photographiques — Détermination de la
résistance au pliage
Reference number
©
ISO 2000
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ii © ISO 2000 – All rights reserved

Contents Page
Foreword.iv
Introduction.v
1 Scope .1
2 Term and definition .1
3 Principle.1
4 Apparatus .1
5 Sampling.2
6 Conditioning and test conditions.2
7 Procedure .3
8 Interpretation of results .3
9 Test report .5
Annex A (informative) Numbering system for related International Standards.6
Annex B (informative) Description of parts of MIT folding-endurance tester.8
Bibliography.9
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 18908 was prepared by Technical Committee ISO/TC 42, Photography.
This first edition cancels and replaces ISO 8776:1988, of which it constitutes a minor revision.
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 – 18999 (see annex A).
Annexes A and B of this International Standard are for information only.
iv © ISO 2000 – All rights reserved

Introduction
Photographic film should have sufficient folding endurance to permit satisfactory performance when used in the
equipment for which it is intended under the atmospheric conditions likely to be encountered in practice.
Photographic film is essentially a laminate of two or more different materials, generally a plastics support and the
photosensitive emulsion. The latter is usually made of image forming chemicals suspended in gelatin or an other
polymeric binder.
The folding endurance of photographic film is affected adversely by both reduced temperature and reduced relative
humidity. In most applications, folding endurance loss at low relative humidity is encountered more frequently than
loss at a low temperature. Moreover, a marked change in film flexibility may occur with only a very small change in
relative humidity below a level of about 25 %. This means that folding endurance tests on photographic film should
be carried out only in an atmosphere that is accurately controlled with respect to both temperature and relative
humidity.
The folding endurance of film is very dependent on the sample thickness decreasing with an increase in thickness
of either the base or the emulsion. For this reason, the thickness of the film layers have to be considered when
comparing the behaviour of different films. The temperatures and relative humidities to which the film has been
subjected between manufacture and testing may also affect the folding endurance even though the sample is
reconditioned to a standard temperature and humidity.
Gelatin is generally more brittle than film base, so that photographic film having a gelatin layer on only one side is
usually more brittle if bent with the gelatin-side out (that is, gelatin under tension). This can affect the folding
endurance, depending on the direction of the first fold.
The folding endurance of photographic film may vary in different directions if the base is oriented more in one
direction than another. There is generally no directional effect in the emulsion.
This International Standard covers the MIT folding endurance test in which the film is subjected to a rapid and
repeated folding action until it breaks.
Different types of failure occur when film is flexed. Failure may consist of very fine cracks in the emulsion (without
a break in the support) which are objectionable when the photograph is viewed. Failure may also consist of cracks
in the support or a complete break.
The wedge brittleness test, standardized in ISO 18907 (see [2] in the bibliography), can generally detect the
presence of emulsion cracks after a single flex. However, emulsion cracks are not visible during the MIT test.
They may occur after relatively few flexes and result in subsequent flexing of only the film base itself with
consequent higher folding endurance. For this reason, the MIT fold test may not necessarily be in agreement with
ISO 18907. The two tests may also disagree because the apparent brittleness (or lack of flexibility) and fatigue
resistance can also be dependent upon the manner in which the photographic film is mechanically treated with
respect to both the degree and the speed of straining. There are a number of folding endurance tests in addition to
the MIT folding endurance test, as described in ISO 5626 (see [1] in the bibliography). Films may be rated
differently according to the different tests.
INTERNATIONAL STANDARD ISO 18908:2000(E)
Imaging materials — Photographic film — Determination of folding
endurance
1 Scope
This International Standard specifies a method for determining and quantitatively expressing the folding endurance
of photographic film. The method is based on the MIT folding-endurance tester described in annex B. It is an
analytical test and is not intended to simulate practical use conditions.
This International Standard is applicable to film with or without a gelatin backing. It may also be applied to either
raw or processed film, although the flexibility level of a given film can be quite different after processing.
Equipment similar to that described in this International Standard may be used provided that a correlation has been
established between the results obtained using such equipment and the results obtained using the equipment
described.
2 Term and definition
For the purposes of this International Standard, the following term and definition applies.
2.1
folding endurance
measure of fatigue resistance after multiple flexing
3Principle
Folding, backwards and forwards in a standardized manner, of a sample of film subjected to a longitudinal stress
until it breaks.
4 Apparatus
4.1 Test chamber
An air-conditioned cabinet or walk-in room shall be used for both conditioning and testing. The temperature shall
o
be controlled to within � 1 C. The relative humidity shall be controlled to within � 1 % at relative humidities below
30 % and to within� 2 % at higher humidities. The linear air velocity shall be at least 150 mm/s.
If a walk-in conditioned room is used, the air velocity shall be adequate to maintain the conditions specified. The
number of personnel permitted in the room during testing shall be limited and precautions taken to prevent the
operator's breath re
...