Method for replenishing a photographic fixing agent

Description

BACKGROUND OF THE INVENTION

[0001] This invention concerns a method for replenishing a photographic fixing agent designed for the processing of photographic materials, particularly color processing. More specifically, the invention concerns a method to reduce the quantity of water necessary for the photographic processing, and thereby the quantity of effluent discarded from said processing, by adding to the fixing bath a concentrated replenishment solution (also called maintenance solution or regenerating solution) of a fixing agent.

[0002] In color photographic film processing, after the development step, a fixing step is used to complex and thereby dissolve undeveloped silver halides remaining in the photographic material. In the case of color photographic materials, a bleaching step is used in order to oxidize developed silver which is then fixed. The fixing step is accomplished with a fixing bath, which comprises a fixing agent, the most usual of which is thiosulfate, together with various other constituents.

[0003] The sensitometric characteristics of the processed materials depend on the values of the process parameters; temperature, pH, and concentrations of the constituents. These parameters must therefore be monitored continuously. Because the processing itself also consumes the reagents initially supplied to the baths, these baths have to be maintained or replenished. For this purpose the process manuals indicate replenishment bath formulations, in particular for developing and fixing baths. These replenishment baths are supplied systematically, after the developing bath has been in operation for a certain number of hours, or after a certain quantity of film has been processed, or continuously.

[0004] Photographic processing comprises successive immersions in different baths separated by washing tanks. Such processing therefore consumes much water and generates much effluent that has to be treated before being recycled or discarded. The replenishment of such fixing baths is usually carried out using solutions prepared from kits comprising concentrates. These concentrates are diluted at time of use and then added to the fixing bath. The necessary replenishment of the baths further increases the water consumption and thereby the effluent produced. Many methods have been proposed for the treatment and(or) the recycling of the effluents.

SUMMARY OF THE INVENTION

[0005] The present invention provides a solution to the problem of reducing the water consumption without adversely affecting the sensitometric results of the photographic process.

[0006] The object of this invention is a method for the maintenance and replenishment of fixing baths using concentrated solutions.

[0007] The method of the invention for the maintenance of a photographic fixing bath comprises the addition of a concentrated aqueous solution of a fixing agent to the fixing bath during the processing in a photographic processing. The terms "concentrated solution" mean a solution containing at least 200 g/l preferably at least 500 g and more preferably at least 800 g of 60 % ammonium thiosulfate per liter. A concentration of 800 g/l of 60 % ammonium thiosulfate corresponds to 3.25 mole/l.

[0008] A further object of this invention is a method of photographic processing comprising at least one developing step and one fixing step wherein the fixing step is carried out using a fixing agent the maintenance of which is achieved using a concentrated solution.

DETAILED DESCRIPTION OF THE INVENTION

[0009] The fixing agents are well known, and are described for example in " Chimie et Physique Photographiques " by P. Glafkidès, p.174 et seq., Ed. P. Montel, Paris, 4th edition, 1976. The most commonly used fixing agents are alkali metal or ammonium thiosulfates. The fixer can also comprise sulfite and(or) bisulfite, an anti-calcium agent, a buffer, etc.

[0010] The pH of the fixing agent is generally between 5.5 and 7, and it must be strictly controlled to assure sensitometric quality, that is, maintaining sensitometric values such as speed, contrast, Dmin, Dmax with the ranges indicated in the processing manuals.

[0011] According to this invention, it was found that such prior dilution was unnecessary, and that the fixing agent could be replenished by adding a concentrated solution directly, without adversely affecting the sensitometric results, as the example below shows. This addition of a concentrated replenishment solution to the fixing bath allows the flow rate of the replenishment solution to be reduced. Whereas with a replenishment solution at the usual dilution (200 g/l of 60% weight thiosulfate), this flow rate is more than 20 l/hour (i.e., given the run-through speed of the film, 1.33 l/100 m of 35 mm of motion picture film), it is possible with a concentrated solution to reduce this flow rate to 5 l/hour (0.33 l/100 m of 35 mm of film processed, such as 35 mm motion picture film), or even to 1 l/hour (0.07 l/100 m of 35 mm motion picture). The concentration of the thiosulfate replenishment solution can be in the range of from 0.8 to 5 mole/l and preferably of from about 2 to about 4 mole/l. This latter molar concentration represents from about 500 g/l to about 1000 g/l of a 60 weight % aqueous solution of ammonium thiosulfate. The concentrate can also contain all the components of an usual fixer replenisher, for instance sulfite, bisulfite, ammonia, a buffer, an anticalcium agent, a biocide, etc. The more concentrated the replenishment solution is, the more the replenishment flow rate can be lowered. This lowered flow rate also affords a considerable saving in bath reagents. According to the Manual for Processing Eastman Motion Picture Film, Module 7 Process ECN specifications, EKC, 1990, the composition of the fixing bath used in the processing machine has to remain constant, for example 185 ml of 58% thiosulfate per liter and 20 g of sulfite per liter. With a normal diluted replenishment solution added at 20 I/hour, flow rates are 185 x 20 ml for thiosulfate and 20 x 20 g for sulfite per hour. With a concentrated replenishment solution added at 1 l/hour, flow rates are only 185 ml for thiosulfate and 20 g for sulfite per hour, respectively.

[0012] The method of the invention finds a particularly advantageous application in the processing of color motion picture films. Such processing concerns large quantities of film, and therefore large-sized machines that consume large quantities of water and solution, and generate large quantities of effluent waste. In view of the current standards concerning water consumption allowed per m² of processed film, it is important to minimize the quantity of water used in such processing, while not adversely affecting the sensitometric values of the processed film.

[0013] The following example illustrates the invention.

EXAMPLE

[0014] ECN® Eastman Color Negative film was processed using the process ECN-2.

[0015] The initial fixing bath had the following composition, as prescribed in " Manual for Processing Eastman Motion Picture Film ", Module 7, Process ECN-2 specifications, EKC, 1990 page 24.

Water	700 ml
59% Ammonium thiosulfate	185 ml
Sodium sulfite	10 g
Anhydrous sodium bisulfite	8.4 g
pH at 27°C	6.5

[0016] The replenishment of the fixing bath is usually carried out using a solution with the composition below, as prescribed by the Manual cited, this solution being added continuously.

Water	700 ml
59% Ammonium thiosulfate	200 ml
Sodium sulfite	22 g
Anhydrous sodium bisulfite	4 g
pH at 27°C	7.2

[0017] According to the invention, instead of using the above solution for the replenishment, the concentrated solution detailed below was used:

59% Ammonium thiosulfate	861.86 g
ANTICAL N° 8 anticalcium agent	32.9 g
43% Ammonium bisulfite	46.2 g
Anhydrous sodium sulfite	154.2 g
20% Ammonia	25.74 g
Acetic acid	8.55 g
Water QSP 11

[0018] This concentrated solution was added directly to the fixing bath in a continuous manner at a flow rate of 1 l/hour, in the course of ECN-2 processing. The sensitometric results obtained under steady state conditions were:

	Speed	Contrast (shoulder)	Dmin
Red	530	0.50	0.16
Green	536	0.59	0.58
Blue	521	0.56	0.96

[0019] These results comply with the ECN-2 processing standards.

[0020] After this replenishment method was continued for four months, with a continuous operation of the processing machine, the bromide and iodide levels remained stable within the tolerance limits of the ECN-2 process, i.e., less than 25 g/l of bromide and less than 2 g/l of iodide. The quantity of thiosulfate in the fixing bath was adjusted by regulating the flow rate of the replenishment solution. As prescribed for the ECN-2 process, the pH must not fall below 5.5, and when below this value, was readjusted to 6.5 with ammonium hydroxide. Likewise, the quantity of sulfite must not fall below 15 g/l of fixing bath, and when below this value, was readjusted to 20 g/l by adding sulfite. Sensitometric data were not modified.

[0021] The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

Claims

1. Method for replenishing a photographic fixing bath, comprising the addition to said fixing bath, during its use, of a concentrated aqueous solution of a fixing agent.

2. Method according to claim 1, characterized in that the fixing agent is an alkali metal or ammonium thiosulfate.

3. Method according to claim 2, characterized in that the concentration of the fixing agent in the concentrated aqueous solution is 0.8 to 5 mole/l.

4. Method according to claim 3, characterized in that the concentration of the fixing agent in the concentrated aqueous solution is 2 to 4 mole/l.

5. Method according to any of claims 1 to 4, characterized in that the addition of the concentrated aqueous solution is carried out continuously during the fixing, with a flow rate between 0.2 and 5 1/100 m of film processed.

6. Method according to claim 5, characterized in that the addition of the concentrated aqueous solution is carried out at a flow rate between 0.5 and 1.5 1/100 m of film processed.

7. Method according to any of claims 1 to 6, characterized in that the pH of the fixing bath is maintained at a value between 5.5 and 7.

8. Method according to any of claims 1 to 7, characterized in that the sulfite concentration of the fixing bath is maintained between 15 and 20 g/l.

9. Method for the processing of a photographic material comprising a development step and a fixing step, characterized in that the fixing step is carried out in a fixing bath the maintenance of which is achieved by a method according to any of claims 1 to 8.

10. Method according to claim 9, characterized in that the development step comprises the processing of the photographic material in a color developer, and in that the method also comprises a bleaching step after the development step and before the fixing step.