Recycling spent hydroquinone developer and a recycled hydroquinone developer

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BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a process of recycling a spent photographic developer wherein the spent developer is collected and reconstituted and can be re-used without detrimental effect on films processed therein.

Photographic developers are well-known in the art. The development of exposed silver halide photographic elements comprises a multiple step process of development, fixing, washing and optionally a stopping step. The development step is conventionally undertaken with an aqueous alkaline developer composition (or developer) which includes a developing agent either singly or with one or more additional developing agents. A comprehensive list of developing agents is provided in C. E. K. Mees, The Theory of the Photographic Process Chapters 14-15 (rev. ed. 1959). The most commonly used developing agent, particularly for processing black-and-white photographic silver halide elements is hydroquinone. The hydroquinone or other suitable developing agent serves as a strong silver reducing agent to reduce silver halide grains containing a latent image to yield a developed photographic image.

Hydroquinone-based developers have been successfully employed for many years, but in recent years, various guidelines and regulations have been imposed that impact on the use of these conventional developers. This is due to the toxicity and environmental hazards associated with the hydroquinone and other components comprising the developer, as well as the generally alkaline nature of the developer.

In view of the current environmental concerns surrounding the discharge of spent photographic developers into the environment and the likelihood of increased environmental regulations, it is highly desirable to eliminate or reduce the introduction of the spent developer effluent into the environment by recycling the used developer. Apart from the obvious environmental benefits of recycling, there are also financial advantages to recycling the spent developer due to a reduction in the amount of raw materials needed and in the cost of compliance with environmental regulations.

A major obstacle to recycling, however, is being able to reconstitute the developer such that the performance of photographic materials in the recycled developer is equivalent or substantially equivalent to the performance of the photographic materials in fresh developer. Conventional hydroquinone-based developers typically have been poor recycling prospects because certain oxidation products of hydroquinone (formed during development of photographic materials) produce large, dark (almost black in color) polymeric compounds which are difficult to quantitatively analyze and separate from the developer. The presence of these undesirable oxidation products in developers contributes to sludge formation and staining of photographic elements processed therein.

The aforementioned environmental and cost issues have been addressed by recycling reconstituted used developers containing ascorbic acid and derivatives thereof as described in U.S. patent application Ser. No. 08/170,595, filed Dec. 21, 1993, which is a continuation-in-part of U.S. patent application Ser. No. 07/941,343, filed Sep. 4, 1993.

However, hydroquinone is a widely used developing agent and, further, there are photographic applications in which ascorbic acid developers are not typically as suitable as hydroquinone developers would be, for example, in the development of hydrazine-containing films to achieve satisfactory speed, contrast and image quality. As such, there also is a great need for recycling spent hydroquinone developers.

SUMMARY OF THE INVENTION

In accordance with this invention there is provided a process for recycling a spent black-and-white photographic developer comprising the steps of:

a) determining a volume, V.sub.i, of the spent developer resulting from use of a fresh developer wherein the fresh developer comprises

(1) a developing agent selected from a group consisting of hydroxybenzene compounds, derivatives of hydroxybenzene compounds, and mixtures thereof, and

(2) a compound which provides a sulfite concentration of 0.65 to 1.5 molar;

b) analyzing the spent developer to determine the pH and the concentration of critical components, which are primary developing agents, secondary developing agents, bromides, antifoggants, sulfites, and alkanol amines;

c) reconstituting the spent developer for reuse, based on results of a) and b), comprising:

(1)determining a final volume, V.sub.f, of reconstituted developer based on the relationship:

V.sub.min =(V.sub.i .times.B.sub.i)/B.sub.a

where

V.sub.min =minimum volume of reconstituted developer and V.sub.f is greater than or equal to V.sub.min

B.sub.a =aim concentration of bromide in the reconstituted developer

B.sub.i =analyzed concentration of bromide in the spent developer,

(2)diluting the spent developer with water and/or a special developer such that: a volume of water, V.sub.w, is greater than or equal to zero;

a volume of special developer, V.sub.s, is greater than or equal to zero; and

V.sub.w +V.sub.s =V.sub.f -V.sub.i,

(3)adding amounts of the critical components in sufficient quantity to achieve aim concentrations as determined from the equation,

Amount of critical component to add=(V.sub.f .times.CC.sub.a)-(V.sub.i .times.CC.sub.i)-(V.sub.s .times.CC.sub.s)

where

CC.sub.a =aim concentration of critical component

CC.sub.i =analyzed concentration of critical component in spent developer

CC.sub.s =concentration of critical component in special developer with the proviso that the total amount of critical component added is greater than or equal to zero,

(4)adding amounts of non-critical components as determined from the equation,

Amount of non-critical component to add={(V.sub.f -V.sub.i).times.NC.sub.a }-(V.sub.s .times.NC.sub.s)

wherein

NC.sub.a =aim concentration of non-critical component

NC.sub.s =concentration of non-critical component in special developer with the proviso that the total amount of non-critical component added is greater than or equal to zero,

and wherein steps c)(1), c)(2), c)(3) and c)(4) can be performed in any order.

In another aspect, the present invention comprises a black and white photographic developer capable of being recycled according to the above process. In yet another aspect, the present invention comprises a recycled, black-and-white photographic developer made according to the above process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

This invention is a process for recycling spent hydroquinone-type developers wherein the spent developer is analyzed and reconstituted so that the recycled developer will perform substantially equal to fresh developer. The invention is also a developer that can be recycled according to the process and the recycled developer resulting from the process.

DEVELOPERS

The benefits of the present process are achieved for developers containing hydroquinone-type developing agents. Here the term developer is meant in a general sense to encompass certain categories of developers that will be specifically referred to later in this application. For example, the term "fresh developer" denotes a developer which is newly mixed, and/or which has not been used to develop any film, and/or which has not been held at elevated development temperatures, i.e., about 95.degree. F. to about 110.degree. F., for any extended period of time, that is, up to about 12 hours. Fresh developer includes components with each having an original starting concentration. The term "spent developer" as used herein, means a developer which has been used to process photographic film or which otherwise has lost some of its development activity as compared to fresh or virgin developer. A "working developer" may also be referred to in this application. A working developer is one that is in a processor at any given time and being used to develop photographic material in the processor. It is understood that at some period in time during its use in processing a sufficient quantity of film that fresh developer will become spent developer. To be a successful candidate for recycling, the developer must be one which avoids the combination of disadvantages that previously has been presented by the presence of hydroquinone-type developing agents.

The developer comprises hydroxybenzene-based primary developing agents which include hydroquinone and other such compounds suitable for use as developing agents. It should be noted that certain oxidation products of hydroquinone, such as hydroquinone monosulfonic acid and hydroquinone disulfonic acid are acceptable (unlike those noted above) because even though they are oxidation products that form during processing and add to the complexity of the developer, they are also developing agents. These compounds are considered critical components for the purpose of this invention. The developer also comprises secondary developing agents, antifoggants, bromides, alkanol amines and antioxidants which are considered critical components for the purpose of this invention. The pH of the developer is also considered critical. A critical component or characteristic is one whose concentration is critical to developer performance and/or whose concentration changes significantly either in storage or as a result of the physical or chemical action of the developer on the film during processing. Non-critical components are those having some effect, but are usable over a broad range of concentrations and are not appreciably affected by storage or reaction with the film.

CRITICAL COMPONENTS

The primary developing agents include, but are not limited to, hydroquinone, pyrocatechol, methyl hydroquinone, and other hydroxybenzene compounds suitable for use as developing agents.

Secondary developing agents include, but are not limited to, pyrazolidone, N-Methyl-p-aminophenol sulfate (metol), and derivatives thereof, with metol being particularly preferred.

Antifoggants are present to prevent formation of minimum density in areas where development is not intended. Antifoggant agents include, but are not limited to, benzotriazole, phenylmercaptotetrazole, benzimidazole, indazole, nitroindazole, and derivatives thereof, used alone or as mixtures.

Soluble bromides, particularly alkali metal bromides are also used as antifogging agents. Potassium bromide and sodium bromide are the preferred.

Antioxidants, such as sulfites, are typically present in developers as preservatives and/or accelerating compounds. It has been known for some time that sulfite inhibits oxidation of hydroquinone. See Lazaridis, Hydroquinone Oxidation in Lithographic Developers, 20:1 Photographic Science and Engineering 2 (January/February 1976). It has been found that a significantly higher level of sulfite than typically used in hydroquinone developers limits the rate of formation of the dark-colored oxidation products of hydroquinone. The formation of these dark-colored oxidation products has prevented hydroquinone from being a good candidate for recycling heretofore. A relationship between molarity of sulfite and oxidation of hydroquinone exists and it has been found that a three-fold to four-fold increase in the sulfite content above that typically observed in hydroquinone developers can result in a ten-fold increase in stability of the hydroquinone, with stability meaning resistance to oxidation. Examples of useful compounds include, but are not limited to, alkali metal sulfites, bisulfites, metabisulfites and carbonyl-bisulfites adducts. A preferred antioxidant is sodium bisulfite.

Alkanol amines which act as development enhancers are critical components in this invention. A particularly preferred alkanol amine is 3-diethylamino-1,2-propanediol (DEAPD). The alkanol amines can include primary, secondary, or tertiary amines.

An anti-sludge agent is added to the developer to prevent undesirable deposits on rollers of a processor or on the film. A preferred anti-sludge agent is 2-mercaptobenzothiazole (2-MBT).

The pH of the developer is a critical characteristic and is adjusted in the range of about 9.5 to 12.5, preferably 11.1 to 11.6. The pH is adjusted by adding alkali metal hydroxides or sodium hydrogen sulfite. The sodium hydrogen sulfite is particularly suitable for adjusting pH in this invention considering that it is also used as an antioxidant as noted above. There are many other substances that can be used to adjust pH known to one of ordinary skill in the art.

Critical components were defined above, however it should be noted that depending on the desired commercial application, that some substances not listed herein as critical could be deemed as such for the particular application. For example, the claimed invention does not incorporate a development accelerator which is often included in a developer to increase developer activity. However, in a different commercial application, such a substance could be deemed as a critical component and, as such, would be considered as falling within the scope of this invention. Further, non-critical components in a particular application could be deemed critical in some other application, and alternatively critical components in a particular application could be deemed non-critical in some other application. This provides flexibility for situations where a particular photographic application or a particular performance of the developer is desired.

A suitable hydroquinone developer whether designated as fresh or working developer may comprise the following critical components:

______________________________________ Usable Range Preferred Range Component (moles/liter) (moles/liter) ______________________________________ Sulfite Ion 0.65 to 1.50 0.70 to 1.00 Bromide Ion 0.01 to 0.15 0.05 to 0.10 Pri. Dev. Agent(s) 0.10 to 0.50 0.20 to 0.30 Sec. Dev. Agent(s) 0.001 to 0.04 0.005 to 0.01 Antifoggants 0.00001 to 0.01 0.0001 to 0.005 Antisludge Agent(s) 0.00 to 0.002 0.0001 to 0.0005 Alkanol Amine(s) 0.01 to 0.50 0.05 to 0.25 Adjusted pH 9.5 to 12.5 11.1 to 11.6 (in pH units) Water to make one liter ______________________________________

The categories of compounds listed immediately above are critical components. It is understood that water does not meet the strict definition of critical as offered above but water is a critical component in that its presence is necessary to the functioning of the developer. However, water will not be handled in the same way as other critical components as will be addressed later. There are, of course, other components which are non-critical that may be added.

NON-CRITICAL COMPONENTS

The developer may also contain a multitude of other adjuvants that are desirable, but not critical to developer performance, such as, sequestering agents, swelling control agents, anti-foaming agents and buffers. Such adjuvants are well known to those of ordinary skill in the art and this list is not to be considered as exhaustive.

Small amounts of sequestering agents (or chelating agents) are generally employed to sequester trace metal ions, e.g., copper and iron ions, present in the water or chemicals used to produce the developer and in the films. Preferred sequestering agents are sodium salts of ethylenediaminetetraacetic acid (EDTA).

Other materials that may be added to the developer, include antifreezing agents, such as ethylene glycol and polyethylene glycol. An anti-foaming agent may also be added, such as Dow 2210, a silicone emulsion made by Dow Chemical Co.

A typical and preferred fresh or working developer with both critical and non-critical components will comprise:

______________________________________ Component Preferred Range (grams) ______________________________________ Sodium Sulfite 85 to 105 Tridosium salt of EDTA 3.0 to 4.0 Potassium Bromide 6.5 to 8.5 Hydroquinone 20.0 to 30.0 Metol 1.5 to 2.5 Glucono-delta-lactone 0.75 to 3.00 Benzotriazole 0.30 to 0.60 Phenylmercaptotetrazole 0.04 to 0.07 2-Mercaptobenzthiazole 0.03 to 0.06 3-Diethylamino-1,2-propanediol 25.0 to 55.0 Adjusted pH (in pH units) 11.1 to 11.6 Water to make one liter ______________________________________

COLLECTING SPENT DEVELOPER

A process for recycling spent photographic developer in accordance with the present invention comprises the steps of determining the volume of the spent developer and reconstituting the spent developer so that it can be used in the same way that a fresh developer would be used.

Spent developer may conveniently be collected in an off-line tank when purged from a developer tank of a processor such as, during processing and/or during automatic replenishment. The spent developer is collected until a sufficient quantity is available for recycling in accordance with the present invention. It is to be understood that the process of the present invention does not require that any particular amount of spent developer be collected for recycling. It is desirable for the present invention to be practiced in batch quantities. In fact, it would be expected that in practice spent developer from many different film processors would be collected for recycling at some central location.

It is advantageous and indeed preferred that any particulate matter present in the collected spent developer be separated from the liquid. It is common for spent developer to contain a variety of foreign particulate matter, such as gelatin, conglomerates of silver, hair, dirt, paper clips, etc. The separation of liquid developer from particulate matter may be practiced in any conventional manner, such as by decanting or filtration.

RECONSTITUTION

After a convenient quantity of spent developer has been collected and its volume determined, the next step in the present process comprises reconstituting the developer for recycling. By "reconstitute", it is meant that the concentration of the critical components in the spent developer is adjusted (i.e., either increased or decreased) to obtain an aim concentration of such components so that the performance of the recycled developer would be substantially equal to performance of the original fresh developer. Reconstitution can be described as a remanufacture of the spent developer.

It should be noted that reconstitution is differentiated from such conventional processes as replenishment, in that the latter refers to the well-established practice of, for example, periodically adding quantities of fresh developer to the working developer present in a processor to make up for losses due to evaporation and/or carry-out by the film. Some of the components contained in the working developer can also be consumed through aerial oxidation and by reaction with the film being processed. In conventional replenishment, a quantity of fresh developer is added based on the amount of film processed and/or the period of time since the last replenishment addition. In practice, the quantity of fresh developer added typically must be greater than the sum of the volume of working developer carried out of the developer section of the processor plus the volume of developer lost by evaporation in order to maintain control of sensitometric and chemical parameters in the working developer in the processor. Because the volume of fresh developer added in the replenishment process exceeds the volume of working developer lost by film carryout and evaporation, the developer section of processors are typically equipped so that this excess developer flows out through an overflow tube. Ordinarily, this overflow is the spent developer that is disposed of in the sewer or through other waste disposal methods. In the present process, this overflow is collected for recycling.

While, in principle, any amount of spent developer might be collected for recycling, it is typically most advantageous to collect the spent developer from many processors and even many geographical sites. This collected developer is combined into a master batch and transformed into a recycled developer that is equal or substantially equal in performance to a fresh developer by addition of critical components and/or dilution. As will be demonstrated, the recycled developer in accordance with this invention can be used the same as a fresh developer is used, that is, either for replenishing working developer during normal processing or for initially charging a processor.

An analysis step is performed prior to, or as part of, the reconstituting step. The analysis step, as the name implies, comprises an analysis of the spent developer to determine the concentration of the various critical components which are to be increased or decreased. A determination of the pH is included as part of the analysis step. Conventional analytical methods that are used include, but are not limited to, titration, extraction, surface tension, spectroscopy and chromatography.

In particular, the spent developer is analyzed for the concentration of critical components i.e., developing agents (both primary and secondary), bromides, sulfites, alkanol amines and antifoggant(s). Primary and secondary developing agents can also be referred to as total reducing substances.

Typically, no analysis is made of non-critical components because their concentrations are assumed to remain constant.

Based on the analysis results, and depending upon the particular developer being recycled, the reconstituting step can involve the addition of certain critical components to increase the concentration thereof and/or the dilution of the spent developer to decrease the concentration. Based on conventional replenishment rates for developer, it is typically the case that the critical components are present in the spent developer in amounts from about 50% to 150% of their original starting concentrations in fresh developer. In most cases, the concentration of such components in spent developer would be lower than the original concentration in fresh developer. Those components which are lower in concentration than the original starting concentration in the fresh developer are added to the spent developer in an amount sufficient to achieve aim concentrations. However, because of evaporation of the working developer, for example, it can be possible that some critical components exhibit increased concentrations in the spent developer compared to the original starting concentrations in the fresh developer. Those components which have higher concentrations in the spent developer than original starting concentration in the fresh developer have their concentrations decreased to an aim level by diluting.

It is well known that bromide, for example, is a critical component that can be higher in concentration in spent developer than in fresh developer. With bromides, this increase is due to the use of the developer to process films which contain silver bromide grains. It may be necessary to dilute the spent developer in order to compensate for the higher concentration of the bromide or to compensate for the evaporation losses in the developer due to high temperature processing. It is important to maintain the concentration of the bromide ion due to its restraining effect; the greater the bromide concentration, the more the development of film is restrained. The concentration of the bromide in the spent developer is generally dependent upon the mix of films processed in the developer, i.e., the proportion of the processed films which are totally or partially silver bromide grain films. It should be understood that if all the films processed in the developer are entirely silver chloride grain films, for example, then the spent developer may not need to be diluted to the extent that the spent developer would if some of the films processed contained silver bromide. Another factor which can influence the concentration of bromide in the spent developer includes the amount of developed density, i.e., the proportion of the imaged film which is high density and low density.

In such instances when bromide is higher in concentration in the spent developer, the reconstituting step would involve diluting the spent developer (e.g., with water) to reduce the concentration of bromide to the aim level. Sufficient water is added to the spent developer to dilute bromide to its aim value and thereby arrive at a final volume of the reconstituted developer. Amounts of the critical components other than bromide would then be added to achieve the aim concentrations based on the final volume of reconstituted developer. For most applications, both an addition and dilution will be necessary to reconstitute the spent developer. In those circumstances, it may be convenient to combine the addition and dilution steps as may be required by formulating a specia