BS ISO 18924:2013 download

06-30-2021 comment

BS ISO 18924:2013 download.Imaging materials Test method for Arrhenius type predIctions.
BS ISO 18924 specifies a test method For the prediction of certain physical or chemical property changes of imaging materials.
BS ISO 18924 is applicable to the Arrhenius test portion of ISO 18901, ISO 18905, ISO 18909, ISO 18912. and ISO 111919
BS ISO 18924 Is applicable to the prediction of the optical-density (D) loss or gain of imaging materials. Photographic dye images may be produced by chromogenic processing, by Formation oldiazo dyes. orby non-chromogenic methods such as dye diffusion and silver dye-bleaching processing. BS ISO 18924 also covers density changes caused by
— residual coupler changes in dye Images,
— excess residual processing chemicals in silver black-and-white materials,
— temperature effects on thermally processed silver Images.
BS ISO 18924 Is applicable to the prediction of support degradation. One such example is the generation of acetic acid by degradation of cellulose acetate film support. Mother example Is the change in tensile energy absorption of black-and-white paper support.
2 Terms and definitions
For the purposes of BS ISO 18924, the Following terms and definitions apply.
Arrhenlus plot
plot of the logarithm of the time for a given change In a characteristic proportional to the reaction rate (dye loss, tensile strength change, Dminyellowing, etc.) versus the reciprocal of the temperature, in kelvins
Note Ito entry: The Arrhenius plot may be used to predict behaviour at a temperature lower than those at which the tests are run.
glass transition
reversible change in an amorphous polymer from, or to, a viscous or rubbery condition to. or from, a hard and relatively brittle one
glass transition temperature
approximate mid-point of the temperature range over which glass transition takes place
Note Ito entry: T5can be determined readily only by observing the temperature at which a significant change takes place in a specific electrical, mehanicaI, or other physical property-Ill
Note 2 to entry: T can aLso he sensitive to the moisture content of the polymer (see 4,4, &nn&A. and 8.3 of Annex B for anformation)
Note 3 to entry: For imaging materials containing gelatin, T5is very humidity dependent.
Irrelevant physical or chemical reactions
chemical or physical reactions that take place only at high temperatures and/or humidities and do not take place at the temperatures at which the Arrhenius predictions are to be made
Note I to entl-y: Such reactions may nevertheless affect the quality of the Image, binder, or support.
morphological changes
changes in the physical structure of the association of the molecules
thermodynamic temperature
temperature measured on the absolute scale which Is based on absolute zero (-273.15 ‘CI and having an Interval of measurement that Is equivalent to degrees Celsius
Note Ito entry; The temperature unit in the absolute scale is the kelvin.
3 Background and theory
3.1 Background
In the 1890s. Svante Arrhenius discovered that the rate of some chemical reactions is proportional to the reciprocal of the absolute temperature. This relationship has been used with phenomena related to a chemical change, such as the loss of a particular physical property or the change in the optical density ol fIlm. If a linear relationship exists between the logarithm of the time for a change of a particular property and the reciprocal of the temperature, then this plot can be extrapolated to lower temperatures than those used in laboratory studies. This allows the predIction of the time required for the change to happen at room temperature or lower.
This relationship was first used for the rates of chemical reactionsl2l and was later applied to paper materialsjiql This theory became the basis for TAPPI Standard 453.(] The approach was also applied to textiles(iJ and to physical properties of photographic film supports.(7.J More recently, t has been used to predict the lading of both chromogenic and non-chromogenic photographic dyes 19.111
Predictions based on the Arrhenius equation require the reactions to be run under a series of temperatures at either constant relative humidity (free.hanging) or constant moisture content inside the enclosure. The investigator shall determine which of the above conditions is more relevant to the system being tested.
There may also be cases where elevated temperatures cause different reaction pathways from those occurring at ambient or sub-ambient conditions. In these cases, the plot of the logarithm of time versus the reciprocal of the absolute temperature will be nonlinear and great caution shall be taken in drawing conclusions. Only the linear and lower temperature portion of the plot can be extrapolated to ambient conditions or below.
The drawback to elimination of higher temperature data is that the experiment will then take longer because of the slow reaction rate at lower temperatures. Patience Is the only solution br getting the correct answer when this happens. When incubations are limited to a few of the higher temperatures. this can lead to Incorrect or misleading results and shall be done with extreme caution.
Confidence In the Arrhenlus methodology is obtained when predictions [or phenomena with reasonably short lifetimes correspond to the real-time results. Such data do exist for the fading of photographic dyesLiLuJ and the stability of cellulose ester film supports.lUJ4I
4 Experimental procedures
4.1 OutlIne of Arrhenius test
An Arrhenius test should have the following steps that are explained in more detail in several of the references41.jJI
a) Prepare specimens: 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 dther the free-hanging or the sealed-bag technique (see ii).
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 of Arrhenius plots are given In Annex C.
4.2 Requirements for a meaningful Arrhenius test
Although a straight line can be drawn between two points and an Arrhenius prediction maybe made by plotting the results of two different incubation temperatures, there can be no evaluation of the 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 lour temperatures shall be run for each prediction.
lithe 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
Two test methods, known as the sealed-bag and the free-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-equilibratlon 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 Annex A.

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