Patent Publication Number: US-3879203-A

Title: Process for bleach-fixing color photographic silver halide material

Description:
United States Patent Schranz et al.  
 [ Apr. 22, 1975 PROCESS FOR BLEACH-FIXING COLOR PHOTOGRAPl-llC SILVER HALIDE MATERIAL {75] Inventors: Karl-Wilhelm Schranz,  
 Odenthal-Hanenberg: Reinhard Miiller, Leverkusen; Erwin Schiin.  
 Leverkusen; Wolfgang l-lunicke. Leverkusen. all of Germany Agfa-Gevaert Aktiengesellschatt, Leverkusen, Germany [22] Filed: Apr. 9, 1973 [21] Appl. No.: 349,229  
 [73] Assignee:  
 [30] Foreign Application Priority Data Surash 96/50 A Newman 96/50 A Primary E.\&#39;aminerMary F. Kelley Anorney, Agent, or Firm-Connolly and Hutz [57] ABSTRACT The process of avoiding color-fog in bleach-fixed color photographic materials and also reducing the silver content in the effluent from the bleach-fix solution by flowing the solution countercurrent to the direction of movement of the developed photographic material through at least two separate zones in the bleach-fix operation. The bleach-fix solution is introduced into the bleach-fix operation at a zone where it has high oxidizing power and acts to bleach the developed material which has previously had a greater percentage of the silver removed in a first step. The solution is then passed to the first stage where its oxidation value is diminished by lowering the pH or adding reducing agents and wherein the oxidizing agent effects a removal of a greater amount of silver than occurs in the subsequent stage.  
 The agent can be removed from the first stage and after the excess of silver is removed reused by introduction into the subsequent stage.  
 5 Claims, 2 Drawing Figures l x l A r l I 7 l 77 78 I4 75 [5 PATENTEDAPRZZiQTS F IG. 7  
 FIG. 2  
  PROCESS FOR BLEACH-FIXING COLOR PHOTOGRAPHIC SILVER HALIDE MATERIAL This invention relates to a process for bleach-fixing color photographic silver halide material which is particularly suitable for use in rapid processing machines.  
  For the rapid processing of color photographic materials, in which it is aimed to shorten the time taken by the whole photographic process, it is usual to employ high bath temperatures, vigorous agitation of the baths and high concentrations of active substances in the baths and to shorten the treatment times in the individual baths. Particularly the washing processes between stages are much shorter then in conventional processes or may even be eliminated. Instead of being washed between the different stages, the material is frequently only stripped to remove bath liquid adhering to it or squeezed off between rollers It is impossible to prevent completely some of the bath of one stage from being carried into the bath of the next stage. frequently with the result that the quality of the image suffers. This applies particularly to the transfer from the color developer to the bleach-fix bath which follows. As is known, the function of the bleach-fix bath is to dissolve all the silver in the layer of the photographic material out of the layer. the image silver formed by color development being first oxidized by the bleaching agent present. Dissolved silver therefore accumulates in the bleach-fix bath.  
  The oxidizing power of bleach-fix baths is. however, sufficient also to oxidize color developer remaining in the layers of the color photographic material so that unwanted color coupling takes place. A general color fog is thereby produced which falsifies the colors of the image and spoils the quality of the image whites. On the other hand. the bleach-fix bath is required to have a high oxidizing power not only to ensure complete bleaching of the image silver but also to produce a sufficient color density, especially that of the cyan dye which is reduced to a substantial extent to the leuco form by the reduced form of the bleaching agent in the bleach-fix bath, which is a powerful reducing agent.  
  Another problem in processing color photographic materials and especially in bleach-fixing is that of conforming to the regulations concerning the contamination of effluent water. Bleach-fix baths are in many cases basically non-toxic or at least the quantity of substances entering the effluent water or wash water from the bleach-fix bath can be kept low by constantly recirculating and thus reusing the bleach-fix baths and .regenerating them as required. However, it is precisely when a cyclic process is used that the bath continuously accumulates silver so that even the small quantities of bleach-fix bath remaining in the gelatine layers may, when entering the limited volume of wash water in which the layers are washed after bleach-fixing, result in concentrations of silver ions in the effluent water which are above the tolerance limits. Conforming to the regulations relating to effluent water therefore requires the concentration of silver ions in the bleach-fix bath to be kept very low, which is not possible in the cyclic process described above.  
  It is therefore an object of this invention to find a bleach-fix process for the rapid processing of color photographic material which will not only give excellent results in the finished image but will keep the contamination of the effluent water within tolerable limits, especially as regards the silver concentration.  
  It has now been found on the basis of a series of tests that in a bleach-fix bath installation most of the silver and residual silver halide goes into solution during the first part of the treatment time and only very small quantities of remaining silver need to be dissolved towards the end of the treatment.  
  If, for example, the color developed material. instead of being bleach-fixed in a single tank, is passed through a series of tanks which all start with the same quantity of bleach-fix bath, then the major quantity of silver is found in the first tank or tanks while in the last tank the quantity of silver is so small that after the addition of wash water the silver ion concentration remains below the tolerance limit.  
  It was also found that if a bleach-fix installation is subdivided into separate bleach-fix baths as described above, the oxidizing power of the bleach fix-bath at the beginning of the installation can be sufficiently diminished to prevent substantially oxidation of the color developer carried into the bath and hence prevent the formation of color fog without impairing the bleaching and fixing action of the bleach-fix bath. The dimunition in oxidizing power is achieved either by reducing the pH or by adding reducing agents or by a combination of these two measures.  
  This invention relates to a process for bleach-fixing developed color photographic material using bleach-fix baths which contain as bleaching agent a heavy metal complex of a complex-forming aminopolyacetic acid and as fixing agent a silver salt solvent. the developed color photographic material being passed through a length of bleach-fix bath.  
  in summary, according to this invention the process comprises the bleach-fixing of the developed color photographic silver halide material in a bleach-fix installation containing two or more means or chambers. The bleach-fix installation and its operation consists of a plurality of means or chambers for applying a bleachfixing solution to the developed color photographic material. This plurality of application means is physically arranged so that the respective means are juxtaposed with respect to each other and successively receive the developed color photographic material, The bleach-fixing solution is employed in each of the application means and is carried by liquid flow through the respective application means in the opposite direction to the movement of the color photographic material, otherwise referred to as countercurrent. To obtain this through-put by liquid flow of the bleach-fixing solution, a certain amount of bleach-fix regenerator solution is introduced into the flow of the bleach-fixing solution at the end of the bleach-fix installation, opposite to the end at which the color photographic material is introduced. Similarly, an amount of the bleach-fix solution is removed from the application means where the color photographic material is introduced. Accordingly, a similar amount of bleach-fix solution is moved through the installation in the opposite direction to the movement of the color photographic material. This regenerator or added supply for replenishment has a low silver content, preferably of less than 10 mg of silver per liter. It is a feature of this invention that by the time the bleach-fixing solution is flown to application means where the color photographic material is introduced, its oxidizing power is sufficiently diminished by reduction of pH and/or addition of reducing agents so that the formation of a color fog is effectively suppressed.  
  The process is preferably applied using the usual bleach-fix baths in which the bleaching agents consists of the cobalt(lll), copper(ll) or preferably iron(lll) complex of a complex-forming aminopolyacetic acid, preferably ethylene diaminetetraacetic acid and the fixing agent is preferably sodium thiosulfate.  
  On leaving the bleach-fix bath, the color photographic material carries a certain amount of bleach-fix bath with it. Losses may also occur by splashing or evaporation, especially if the individual tracts of the bleach-fix bath are open and if elevated temperatures are employed to accelerate the process.  
  These losses are compensated for by the addition of bleach-fix bath regenerator which contains little or no silver to the last zone of the bleach-fix bath. The regenerator containing the above mentioned bleaching agent and a fixing agent may even be added in excess so that the bleach-fix bath flows in the opposite direction to the color photographic material. By overflow or by means of pumps, the bleach-fix bath flows from the last zone into the preceding zone against the direction of flow of the color photographic material, and from there onwards to the beginning of the bleach-fix bath. If the process is carried out continuously, a high-silver con centration is established at the beginning of the length of bleach-fix bath (up to 10 g/l) but this is considerably reduced in the following zones and falls to within tolerable limits at the end of the length of bleach-fix bath.  
  The reduction in concentration depends mainly on the ratio of quantity carried out of the bath by the photographic material a [ml/m to the quantity of regenen ator agent flowing in counter-current b [ml/m If one neglects the quantity of silver dissolved out of the photographic material in the following tracts of the bleachfix bath, then at a first approximation the reduction of silver concentration from tract to tract is b/a. Since the quantity of bath carried out by the color .photographic material is given, the number of zones arranged in series and/or the quantity of regenerator b may be so chosen that the silver concentration is reduced to a tolerable level in a wash water having the quantity w [ml/m The silver concentration in the last zone c,, may then be where c, the tolerance concentration in the wash water.  
  The word zones is used in the context of this invention to mean parts of the whole length of the bleach-fix bath. The zones may be individual tanks arranged in a cascade in series and in which the color photographic material is passed through the bleach-fix bath by a process of immersion or they may be spray chambers arranged in series in which the bleach-fix bath is applied to the photographic material by spraying. The zones may be dimensioned so that the times of stay of the color photographic material in the individual tracts are identical. On the other hand, it may be advantageous to make individual zones in different sizes so that the color photographic material stays for different lengths of time in the different zones.  
  The subdivision of the length of the bleach-fix bath into several zones also makes it possible to diminish the oxidizingpower of the bleach-fix bath in the first zone following the color development. According to the invention, dimunition in the oxidizing power is achieved either by adding an acid to the bleach-fix bath to reduce the&#39;pH or by adding a reducing agent to reduce the redox potential. A combination of these two methods may also be used. The optimum conditions in the first zone of the length of bleach-fix bath may advantageously be maintained by monitoring and control with the aid of electrometric measuring chains.  
  In the usual bleach-fix baths which are preferred to have a very high oxidizing power, the pH is generally between 6 and 8. It has been found that the pH can be reduced to about 5 without impairing the bleaching and fixing action and that in fact exceptionally rapid bleaching takes place at a pH of about 5.5. At the same time, however, the oxidation of color developer carried into the bath is suppressed. Reduction of the pH in the first zone of the length of bleach-fix bath can be achieved by adding inorganic or organic acids, e.g., phosphoric acid or acetic acid. Control of the pH is preferably carried out fully automatically, either continuously or intermittently, by means of a pH measuring chain consisting, for example, of a glass electrode and a calomel electrode and the potential of which controls the supply of acid by means of a simple control device and magnetic valve.  
  As already indicated above, dimunition of the oxidizing power of the bleach-fix bath can also be achieved by adding a reducing agent to the first zone of the length of bleach-fix bath. Suitable reducing agents are,  
 for example, hydrazine, hydroxylamine, dithionite, formaldehyde, sulfoxylate and their water-soluble salts. If this method is used, constant conditions may again be maintained in the first zone of the length of bleach-fix bath by fully automatic control, e.g., to keep the rH- value (redox value) constant by adding reducing agent at the appropriate rate to compensate for the changes in the bleach-fix bath due to color developer entering the bleach-fix bath with the color photographic material and due to the inflow of regenerator in the opposite direction. A similar measuring and control arrangement may be used as that described above for pH- control, but the measuring chain used in this case may be, for example, a glass electrode and platinum electrode. At pH values of between 5 and 8 the optimum redox potential to be maintained by addition of reducing agent in the first zone is between 0 and 100 mV more positive than the redox potential of the equivalence point defined by the 1:1 mixture of reduced and oxidized forms of the redox system used as bleaching agent. a  
  FIG. 1 is a schematic representation of such a measuring and control arrangement. in this diagram, the reference numeral 11 indicates zone 1 of the length of bleach-fix bath. The two measuring electrodes 12 and 13 of the electrometric measuring chain dip into the bleach-fix bath. 12 is a glass electrode; 13 is a calomel electrode for pH-control or a platinum electrode for rH-control. The potential measured by the measuring instrument is amplified in the measuring amplifier 14 pH-con trol) or a reducing solution (for rH-control).  
 The rate of inflow 19 into zone lis controlled by the magnetic valve 17.  
  An overflow of bleach-fix bath enriched in silver is drawn off from the first zone. The quantity drawn off depends on the quantity of bleach-fix bath regenerator added in the last zone. The overflow can be desilvered by known methods, e.g., by electrolysis. by precipitation with sulfide or by cementation with iron, and can then be worked up into bleach-fix bath regenerator to be reused by adding to the last zone. This working-up may be carried out batchwise or continuously. Since most methods of desilvering inevitably also reduce the bleaching agent. it is advisable first to reduce the overflowing bleach-fix bath by adding reducing agent to the first zone for the sake of obtaining higher yields.  
  The process according to the invention of subdividing a length of bleach-fix bath into two or more separate zones, regenerating in counter-current to the direction of movement of material and reducing the oxidizing power in the first zone has the following advantages over previous processes in which only a single bleach-fix bath is used or in which several are used but regeneration is not carried out in cascade formation:  
 1. The silver concentration in the last zone can be kept so low before washing that the tolerance limits in the effluent water are not exceeded.  
 2. The quantities of water required to keep the silver ions in the effluent water within the tolerance limits can be kept small.  
 3. The accumulation of silver in the first zone to high concentrations provides for efficient desilvering with small volumes.  
 4. Diminishing of the redox potential and/or of the pH in the first zone effectively prevents oxidation of color developer carried into the zone and hence production of a color fog. Excellent results are obtained in the finished image.  
 5. Diminishing of the redox potential in the first zone of the length of bleach-fix bath facilitates recovery of the silver from the overflow.  
 6. The possibility of high oxidizing power in the second and following zones of the length of bleach-fix bath ensures adequate bleaching of the silver and complete reoxidation of the dyes of the color photographic material.  
 7. The total recovery of silver and possibility of constant rejuvenation of the bleach-fix bath in a cyclic process results in a particularly economical process.  
  The process according to the invention may be used in tank installations and tank baths, for spray processes or also for roller application processes. It may be carried out with bleach-fix baths in which, for example, copper, cobalt or iron chelates of an aminopolyacetic acid, quinone or complex iron (III) cyanide are used as EXAMPLE 1 Color photographic paper 9 cm in width and having an overall surface area of 6 m was exposed imagewise, developed normally in a color developer and then bleach-fixed at 20C in a bleach-fix bath of the following composition:  
 ethylene diaminotetraacetic acid 3.0 g Na HPO 20 g Na PO 4 g Na-iron-lIl-EDTA 30 g N21 50: 8 g ammonium thiosulfate 120 g Na=CO 6.0 g water 1000 ml glacial acetic acid up to pH 7.7.  
  The bleach-fix bath was distributed among six separate tanks through which the band of developed color photographic material was passed in succession in the course of 4 minutes. The color photographic material was free from silver on leaving the last tank. Then the silver contents in the individual tanks were as follows:  
 tank 1 L12 g/l 427: of the total silver 2 0.97 3671 of the total silver 3 0.38 14% of the total silver 4 0.13 5% of the total silver 5 0.06 2.257: of the total silver 6 0.02 0.75% of the total silver These results show that 78% of the silver were a]- ready dissolved in the first third of the length of bleachfix bath and 9 272&#39;in the first half.  
 EXAMPLE 2 In this example. a length of bleach-fix bath subdivided into three tracts is described and the silver concentrations present when a state of equilibrium has been reached in continuous operation are calculated.  
  FIG. 2 shows schematically a length of bleach-fix bath consisting of three chambers 21, 22 and 23 and a washing chamber 24 adjacent thereto. After color development at 25, the color photographic material is introduced into chamber 21, passes successively through the individual chambers of the length of bleach-fix bath and then moves from the last chamber 23 into the washing chamber 24. In the figure, A [g/m denotes the quantity of silver introduced per m of color photographic material; a [l/m denotes the quantity of bath removed per m of color photographic material by uptake into the emulsion layers, and b [l/m denotes the quantity of regenerator 26 per in of color photographic material which flows into the last chamber 23 and is carried in countercurrent to the direction of movement of the photographic material into the front part of the length of bleach-fix bath and is removed as overflow 27 from the first chamber 21. W [l/m is the quantity of wash water 28 per m of color photographic material which reduces the silver concentration of the bath leaving the last chamber 23 by the factor a/w. 29  
 Y is the effluent water leaving the washing chamber 24.  
  The times required for the flow through chambers 21 to 23 and hence the length of flow paths are so calculated that of the silver from the photographic layer is dissolved in chamber 21 and the remaining 10% in chamber 22 while chamber 23 serves mainly for the reoxidation of cyan dye. In the calculations shown below, e denotes the proportion of silver which is dissolved out of the emulsion layers in the first chamber 21, i.e., e 0.90.  
  The following data were used for the length of bleach-fix bath described in this example:  
 quantity of silver contained in the material per rn quantity removed from the bath by the materiakper m of material quantity of regenerator per m quantity of wash water per in proportion of silver dissolved in the first tract From a determination of the equilibrium ratios within the processing system. the following equations are obtained for the silver concentrations C C C in chambers 21-23:  
 and the following equation is obtained for the silver concentration in the wash water (chamber 24):  
  Given the data indicated above, the numerical results of the equations are as follows:  
  These values agree with the values obtained in a practical experiment within a limit of error of A silver concentration of 0.2 to 1 mg/l in the effluent water is regarded as tolerable.  
  If bleach-fixing were carried out in a single region distinct from adjoining parts as has previously been customary. the silver concentration obtained in the effluent water then using the same proportions as in the example would be 12.2 mg/l, i.e., 65-times as high.  
 We claim:  
  1. The method of bleach-fixing developed color photographic silver halide material comprising passing developed color photographic material into the plurality of separate means arranged in series for applying bleach-fix solution to the developed color material, passing the developed color material into the first means for applying bleach-fix solution and from the first means to and through at least one later means for applying a bleach-fix solution to the developed color material, introducing into said last bleach-fix applying means a bleach-fix solution having an oxidizing power at a pH of between 6 and 8 and a low silver content and containing a heavy metal complex of a complex forming aminopolyacetic acid as bleaching agent and a silver salt solvent as fixing agent first into the last means continuously passing the bleach-fix solution from one application means to the next adjacent application means countercurrent to the photomaterial passage by initially passing a portion of this last application means to the next adjacent means so that a portion is passed to the first means countercurrent to the direction of movement of said developed color photographic material; and diminishing the oxidizing power of the bleachfix solution in the first means by decreasing the pH to 5.5 or less, or adding a reducing agent to lower the redox potential to a value between 0 and mV more positive than the potential of the equivalence point defined by the l:l mixture of reduced and oxidized forms of the redox system; a portion of the bleach-fixing solution of the first means is passed out of the installation and a corresponding amount of regenerator bleach-fix solution is added to the last of the means in a cycle wherein the developed photographic material is treated in the first means to remove a greater percentage of silver from the developed material than in any latter means and the developed material is treated in at least one latter means at a redox potential of more than 100 mV more positive than that of the equivalence point and at a pH of between 6 and 8 to remove the residual silver from the color photographic material.  
  2. The process of claim 1, wherein the added portion of regenerator bleach-fixing solution to the last of the means produces a surplus of bleach-fixing solution in the first means.  
  3. The process of claim 1, wherein the amount of the overflow of bleach-fix solution of the first means is desilvered to form a regenerator bleach-fixing solution of a low silver content.  
  4. The process of claim 1, wherein the pH of the bleach-fixing solution in the first means is maintained within a given pH range by an automatic controlling means comprising an electrometric pH measuring chain and a dosing device for adding an acid.  
  5. The process of claim 1, wherein the redox potential of the bleach-fixing solution in the first means is maintained within a given range of redox potential by automatic controlling means comprising an electromet ric redox potential measuring chain and a closing device for adding a reducing agent.