Radiation imagery chemistry: process – composition – or product th – Including control feature responsive to a test or measurement
Reexamination Certificate
2000-02-01
2001-06-05
Le, Hoa Van (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Including control feature responsive to a test or measurement
C430S399000
Reexamination Certificate
active
06242143
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the treatment of silver halide photographic materials for the purpose of converting the latent images obtained by light exposure into developed, fixed and stabilized visible images.
PRIOR ART
The processing of photographic materials comprises a development step followed by a fixing step in the case of black-and-white development. The development step is carried out by immersion of the exposed photographic material in a developing bath containing a silver halide developing agent, the function of which is to reduce the exposed silver halides to metallic silver. After fixing, the photographic material is washed and dried.
During use the developing bath becomes gradually depleted in developing agent through the silver halide development reaction, and also by additional oxidation of the developing agent. This consumption of the developing agent, and the ensuing decrease in the concentration of the developing agent, causes the activity of the developing bath to decrease, thereby adversely affecting the sensitometric characteristics of the processed photographic materials. A way to make up for this loss of activity is to add to the ‘seasoned’ developing bath a certain amount of new developing solution, known as replenishing solution. However, the optimum timing of replenishment and the optimum quantities of replenishing solution to be added are difficult to determine. This is because a photofinishing laboratory treats a wide range of films and so the quantities of replenishing solution are in practice set at values that are significantly higher than is necessary. Clearly, it is desirable to add the minimum quantity of replenishing solution that is compatible with the maintenance of the specified sensitometric characteristics. Another positive outcome of minimizing replenishment is a reduction in the volume of effluent. The problem therefore is to be able to know when to replenish the developing solution, i.e., to determine when the activity of the developing bath is too low to ensure that the sensitometric characteristics will be maintained at the values that are specified for any particular photographic process. An essential parameter of the developing bath activity is the concentration of developing agent, which therefore has to be measured.
Various methods are known for measuring the concentration of developing agents. Many of these methods require prior extraction of the developing agent, and so are not suitable for preferably automated in-process monitoring of the concentration of a developing agent throughout the photographic processing. This extraction has been deemed necessary owing to the complex composition of the seasoned developing bath, and the presence in it of a large number of substances liable to react with analytical reagents or respond to analytical tools. The methods for determining the concentration of the developing agent are chemical, e.g., colorimetry, electrochemical, e.g., voltametry, or physical, e.g., chromatography. These methods are described in ‘Chimie et Physique Photographiques’ by P. Glafkidèds, 5th edition, pages 171-178 and 943-944. For on-line determinations, measuring the optical density of the developing bath has also been advocated. A new developing solution is limpid and pale yellow, whereas after a certain time in use it becomes turbid and dark in color. The increase in optical density can therefore be correlated with the seasoning of the developer, affording a way of determining when the developer has to be replenished. Such a method is described, for example, in U.S. Pat. No. 5,489,961. However, it is not a direct accurate measurement of the concentration of the developing agent, which is the main parameter that the activity of the developing bath depends on. Clearly then, the measurement of the concentration of the developing agent has to meet two conditions: the measurement must be accurate, and the measurement has to be performed on-line in a simple way, so that the result of this measurement can be exploited, especially to order replenishing of the developer if necessary.
The object of this invention is to provide a method that solves this problem.
SUMMARY OF THE INVENTION
There is provided a method comprising developing a previously exposed silver halide photographic material, using a developing solution containing a first silver halide developing agent, wherein the developing activity of which is monitored by measuring the concentration of said developing agent by ultraviolet spectrophotometry.
There is also provided a device for monitoring the developing activity of one or more photographic processing lines, said device comprising a system for measuring the concentration of a developing agent by spectrophotometry, and means to preselect the range of wavelength of the spectrophotometric measurement according to the developing agent the concentration of which is to be measured.
The method of the invention is based on the fact that certain constituents of the developing baths, especially the developing agents, absorb electromagnetic radiation in certain characteristic wavelength ranges of the electromagnetic spectrum. Thus, it is possible, for such developing agents, to find at least one wavelength range in which interfering absorption by other constituents of the developing bath is minimal. In this range a spectrophotometric measurement can be made which, after calibration, affords a direct read-off of the concentration of the developing agent that absorbs radiation in that particular range. Depending on the concentration to be measured, and the presence of substances liable to hinder measurement, cells are used that optimize the optical path length of the light absorbed. The power of the radiation source, and the sensitivity of the detector, can also be adjusted.
REFERENCES:
patent: 4857750 (1989-08-01), Millis et al.
patent: 5489961 (1996-02-01), Burbury et al.
patent: 0 585 792 A2 (1994-03-01), None
Goumont Claude G.
Roussilhe Jacques
Eastman Kodak Company
Le Hoa Van
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