BS ISO 18924:2013 pdf download

BS ISO 18924:2013 pdf download.lmaging materials —Test method for Arrhenius-type predictions.
4 Experimental procedures
4.1 OutlIne of Arrhenlus test
An Arrhenius test should have the lollowing steps that are explained in more detail in several of the references.LLJ.Zl
a) Prepare spectmens; this may include exposing, processing, cutting, trimming, etc.
b) Take Initial readings of the property of Interest on the non-Incubated specimens.
c) Incubate the specimens at a minimum of four temperatures, using either the free-hanging or the sealed-bag technique (sec 4.3).
d) Measure the property of interest on the incubated specimens after different incubation times.
e) Determine the incubation time at each incubation temperature for the property of interest to reach a predetermined level.
f) Plot the log of the incubation time determined in e) against the reciprocal of the thermodynamic temperature to obtain an Arrhenius plot.
g) Predict the time for the property of interest to change the desired amount at the desired temperature by extrapolation of the Arrhenius plot.
h) Examples ofArrhenius plots are given inAiinexC.
4.2 Requirements for a meaningful Arrhenius test
Although a straight line can be drawn between two points and an Arrhenlus prediction may be made by plotting the results of two different incubation temperatures, there can be no evaluation ofthe statistical significance of this experiment unless three or more temperatures are used. Because a smaller number of data points is apt to lead to a strongly biased prediction, a minimum of four temperatures shall be run for each prediction.
If the effect of relative humidity needs to be considered, experiments at different relative humidities shall be studied. The relative humidities shall be at least 10 % RH apart and preferably should be 20 % RH apart. The tests shall be run at a humidity range representing the anticipated storage of the material.
4.3 Sealed-bag versus free-hanging testing
iWo test methods, known as the “sealed-bag’ and the Iree-hanging methods, are available for accelerated stability testing. These kinds of test conditions tend to give somewhat different results.
In the sealed-bag method, the photographic material is stored in a sealed container with very little air. Pre-equilibration of the samples to a constant relative humidity Is necessary before they are sealed. This test simulates real-life storage conditions in which substances released by the photographic material are trapped inside the container and can interact with the image or support layers. For example, with cellulose-acetate-base motion picture films stored in sealed bags or closed metal or plastic cans, the fading of the dye images may be accelerated by the presence of acetic acid generated by the degradation of the acetate film base.
In the free-hanging method, the specimens are suspended in a relatively large humidity-controlled test chamber at a sufficient distance from each other to ensure free access of circulating air to all surfaces. This test would be appropriate to simulate storage conditions In which photographic materials are stored in vented containers and circulating air is used to remove any released substances.
The advantages and disadvantages of each method are discussed In informative AnnexA.
4.4 Effect of heating on sealed bags containing photographic film or paper
If photographic paper or film containing significant amounts of gelatin is incubated in a sealed foil bag.. the relative humidity (RH) of the environment will increase with increasing temperature, even though the moisture content of the overall system remains constant. In some systems, this increase of humidity can also cause physical changes such as the transformation of the gelatin conformation to the above 7 state (see 2.3).
Experimental evidence has shown that this increase of relative humidity results in more staining on paper and, in some cases, more dye fading in colour photographs. For example, if a processed black-and- white paper Is Incubated In the free-hanging mode, thermal yellowing will be considerably less than if it is incubated in a sealed foil bag. Thus, in order to establish the same environmental conditions for both the sealed bag and free-hanging test methods, one shall choose pre-equilibration RH levels for the bagged samples which compensate for the RH increase that occurs at the elevated test temperature.
The amount of RH compensation required may he sample dependent, since different materials can have different moisture-sinking propcrties.lll From a practical standpoint, the determination of correct RH values for sealed-bag incubations may require a few trial runs where RH measurements are taken inside bags containing representative materials prior to commencement of the actual tests.
4.5 DeterminatIon of test Increments
If the free-hanging method is used, time increments of treatment can be accumulated upon the same samples and they can be returned to the oven until the failure point has been reached. However, foil-hag testing requires that the increments be determined In advance. since all the bags arc pre-equilibrated and prepared at the same time.
It Is strongly recommended that the initial increments [or [oil-bag testing be somewhat conservative so as not to overshoot the failure point, and that subsequent increments be adjusted once data have been obtained on the first few increments. Adjusting the schedule in this way increases the probability that the failure point Is neithcr underreached nor overreached.