Method for processing silver halide color photographic elements using processors having low volume thin tank designs

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FIELD OF THE INVENTION

This invention relates to the processing of silver halide photographic materials. It more specifically relates to the processing of such materials using a Low Volume Thin Tank processing system.

BACKGROUND OF THE INVENTION

Photographic processing equipment and processing chemicals have evolved dramatically over the last decade to meet the increasing demand for convenient, low cost, and environmentally friendly photoprocessing. Some of the changes have included improved processing chemicals which provide faster processing for both film and paper; and smaller, more streamlined equipment which requires a reduced amount of photochemicals. One of the most popular systems is the minilab which is small enough to allow any corner drugstore to offer photoprocessing and which can process a roll of film and provide prints in less than one hour.

However, even the advent of the minilab has not addressed all the needs and problems of modern photoprocessing. Two areas which particularly need addressing are 1) the increasing demand for photoprocessing capabilities in non-traditional photoprocessing environments and 2) the need to reduce the amount of replenishment necessary to keep a photoprocess system stable, both to decrease cost and to reduce the amount of effluent from processing machines. These two areas are often interrelated. In addition there is the never-ending desire to reduce processing time and/or the amount of chemicals needed to fully process various photographic materials.

The demand for non-traditional photoprocessing environments is being fueled by the increase of digital image processing. As digital image processing becomes more prevalent, there is a growing need for color hard copy from digital sources. Silver halide photographic hard copy can give the highest quality images, but is often found to be less convenient than electrophotographic or thermal technologies. Since the photographic processing of digital images would often be done in an office, home, or other non-traditional photoprocessing environments, the convenience of processing is of upmost importance.

Currently available processors can be inconvenient for home or office processing or for other small operations for the following reasons. First, the volume of the tank solutions that need to be prepared to fill a processor are still somewhat large for small-scale operations. Typical processor tank volumes of 10 to 25 liters for processor tanks require relatively large volumes of solutions to be handled.

Secondly, for low utilized systems, the processing solutions remain in the tank for a long residence time. The lack of `tank-turnovers` with fresh replenisher causes the solutions to evaporate and the components to oxidize, causing the chemical concentrations of the components to change. This leads to process control variability and precipitate formation, both of which can affect sensitometry. Such low utilization problems are one of the largest obstacles for small-scale operations when using traditional processing equipment.

Lastly, the relatively high silver coverages of current films and papers require higher chemical concentrations in the processing solutions, which contributes to the cost of the chemicals. It further results in a concentration of chemicals in the waste from the processor which may make disposal of the waste difficult for a home, office, or other small-scale operations.

The need to reduce the-amount of replenishment is driven by both cost and environmental concerns and is shared by large and small processors. Photographic processors are equipped with replenisher solutions designed to maintain process activity at a steady-state, as sensitized goods are processed. The replenishers contain the necessary components to replace chemicals consumed or lost through oxidation or carryover in developing, bleaching, fixing and washing and/or stabilization of sensitized materials.

In automated systems, as sensitized materials are processed, a signal is relayed to turn on the replenisher pumps, so that fresh solution is added to the process tanks. The rates that the solutions are added to the process are dependent on the concentration of components which can be attained in the replenisher solutions.

The replenishment rate in a processing system is set at the lowest rate possible. This reduces the effluent from the process, lowers handling of chemicals, reduces the amount of chemicals used, and reduces the energy needed to maintain operating temperatures. However, the amount replenishment can be reduced is dependent on the following factors.

1. Replenisher Stability--Once all components are combined into a single solution, the components begin reacting with each other and with oxygen, limiting the usefulness of the solution to the stability of the components. The usefulness of a mixed replenisher is normally 4-8 weeks, but may be as short as a few days. Solution stability may be enhanced by the use of covers which sit on top of the solution, eliminating air space which allows oxidation and evaporation.

2. Concentrate Stability--Because of the reactivity of the various components with each other and with oxygen, it is necessary to separate the replenisher concentrates into two or more parts until they are to be used. Concentrates are normally stable for several years if properly stored.

3. Productivity--The quantity of sensitized material processed daily is of concern, since low replenishment rates cause the tank solutions to be resident in the tanks for longer periods of time, subjecting them to oxidation, evaporation and interaction degradation.

4. Carryover--Carryover is the solution carried over from one tank into the next with the sensitized materials. The lower the carryover, the more stable the solutions. When very little or no solution is carried over into the next tank, less dilution occurs and less replenisher is needed in the next tank and less chemical interaction takes place. If the carryover is high, more solution is carried over and more replenisher is needed to compensate for dilution and chemical interactions. If the carryover out of the tank is greater than the replenishment rate, the tank volume will decrease. This results in a shift in the process activity due to the resulting volume loss. This loss reduces the time the sensitized material is in the solution and could lead to processor malfunction. If tank volume is lost, processing solution must be added to maintain solution level.

5. Evaporation-Oxidation--Evaporation and oxidation take place constantly with all processors. To control them, the area of solution exposed to the air needs be kept to a minimum. A surface which results in considerable evaporation and oxidation is the surface of rollers which are used to transport the sensitized material from one tank to another. Some processors have rollers which are partially submerged in the process solutions. The continual wetting and drying of these rollers increases evaporation and oxidation of the processing solutions. It is advantageous to have rollers either completely submerged or completely out of solution. Another way to reduce evaporation and oxidation is to reduce the flow of air over the solutions.

6. Tank turnover--Tank turnover (TTO) is the time required to replace the process tank solution with fresh replenisher solution. Reducing the replenishment rate of solutions extends the residence time of the solutions in the processor, increasing the time per tank turnover. To reduce the time per TTO and replenishment rate, it is necessary to reduce the volume of the processor tanks or increase the utilization (productivity) of the processor. Reducing the volume of the tanks or increasing the utilization of the processor, will decrease the time per tank turnover and reduce the residence time of the solutions.

7. Precipitation/Crystallization--Components which are present in the tank solutions may increase in concentration due to seasoning (processing of sensitized materials) or because of evaporation. Because of their solubility, the components may precipitate or crystallize from solution. The increase of the level of certain components may cause the precipitation or crystallization of other components by reducing their solubility. The lower the replenishment rate, the more likely that this will occur.

8. Process by-product buildup--Materials washing out of the sensitized product, such as, sensitizing dyes, halides, calcium, silver, which accumulate in the solutions as they season out of the sensitized materials, or as they are formed from reactions during photoprocessing, may also precipitate or crystallize.

9. Pump accuracy--As the replenishment rates are reduced, the need for high accuracy, low-volume pumps becomes imperative.

In particular, the amount of replenishment necessary is dependent on the level of utilization of the processor. When a traditional processing system has low utilization it cannot be operated using a low replenishment regime because the system is not stable.

The industry has attempted to compensate for low utilization problems and disposal problems by adjusting processing chemistry. For example, minilab film and paper processors run through a wide range of utilizations. One unit may experience a wide change of utilizations depending on the time of the year and picture taking opportunities. A variety of developer solutions have been made available to accommodate most situations. EKTACOLOR RA Developer Replenisher was formulated to accommodate the widest range of utilizations or tank turnovers within a given period of time. EKTACOLOR RA Developer Replenisher or EKTACOLOR PRIME Developer Replenisher will perform as designed, if the process maintains one tank turnover every 2 to 4 weeks or less. This product will perform equally as well if the process is run at higher utilizations, but may begin to fail if the developer tank is turned over less frequently than every 4 weeks. In this case, EKTACOLOR