ISO 18907 pdf download Imaging materials — Photographic films and papers — Wedge test for brittleness
This InternationalStandard specifies a method for determiningand expressingquantitativelythe brittlenessof photographic film and papers. lt does not, however, specify a universal britleness test for all types ofstress encountered for which special tests can be required to correctly rate the material for brittleness.
The method is applicable to films with or without a gelatin backing and to fibre-based or resin-coatedRC) photographic papers. lt may also be applied to either raw or processed materials although thebrittleness level can be quite different after processing from that before processing.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and areindispensable for its application. For dated references, only the edition cited applies. For undatedreferences, the latest edition of the referenced document (including any amendments) applies.
ISO 483, Plastics — Small enclosures for conditioning and testing using aqueous solutions to maintain thehumidity at a constant value
3 Terms and definitions
For the purposes ofthis document, the following terms and definitions apply.
brittlenessproperty of materials that causes them to break or crack when deformed by bending
4 PrincipleMeasurement of the opening ofa wedge at which a specimen loop fails when subjected to high strains.
5.1 Wedge tester for brittleness
The wedge tester for brittleness consists of two non-parallel metal plates or jaws, which form a wedgeor V as shown in Eigures 1 and 2, A clamp is attached to one jaw at the narrow end of the wedge to holdone end of the specimen. A scale is provided which gives the wedge separation between the two jaws atany point (see Referencel1l).
The dimensions for the wedge tester are standardized for both a narrow and a wide tester. Thenarrow wedge (see Figure 1) has a wedge angle of 9° and a maximum wedge opening of 25 mm. lt isgenerally satisfactory for most films. For more brittle films and papers, a wide wedge (see Figure 2) isrecommended. lt has a wedge angle of 28° and a maximum wedge opening of 74 mm.
5.2 Test chamber
An ar-conditioned box or walk-in room shall be used for both conditioning and testing. The temperatureshall be controlled within + 1 C and the relative humidity to within + 1 % of the specified values. Thelinear air velocity shall be at least 15 cm/s.
NOTETo control the relative humidity to this accuracy usually requires a dew point method.
If a walk-in conditioned room is used, the air velocity shall be adequate to maintain the conditionsspecified.The numberofpersonnel permitted in the room duringtesting shall belimited and precautionsshall be taken to prevent the operator’s breath reaching the material.
6.1 Preparation ofspecimens
Specimens shall be cut in an atmosphere of 20 °C to 23 °C and from 40 % to 55 % relative humidity
NOTEIf the specimens are cut at relative humidities lower than 40 %, it can be difficult to obtain smoothedges.Handling under these conditions can also cause emulsion cracking, which will affect the subsequentbrittleness results. Exposure to relative humidities greater than 55 % can permanently alter the subsequentbrittleness behaviour of some films and photographic papers.
The cutter shall be of a precision type and shall be kept sharp so that the specimens’ edges are smoothand free of nicks. Rubber gloves shall be worn by the operator when handling the specimens, both intheir preparation and testing.