EP0049245A1 - Photographic processing concentrates - Google Patents

Abstract

Photographic processing concentrates containing processing agents such as developing agents, fixing agents, bleaching agents, bleaching-fixing agents, stabilizing agents, etc., prepared in the form of stable pastes intended to be diluted in water or another liquid medium to form active treatment solutions. Treatment concentrates use the association of finely divided solid particles in a stable three-dimensional network, giving them useful physical and chemical characteristics.

Description

PHOTOGRAPHIC PROCESSING CONCENTRATES

This invention relates to new photographic processing concentrates.

The processing of photographic elements,such as elements comprising one or more silver halide emulsion layers, is typically carried out- with aqueous processing solutions comprising one or more processing agents. These solutions are conventionally relatively dilute, and thus, it is not generally feasible, from an economic standpoint, to package, transport and store processing solutions of working strength since this would involve the packaging, transporting and storage of large amounts of water. Heretofore, there have been two distinctly different approaches taken to the problem of packaging photographic processing compositions in a form that is suitable for transporting and storage. One approach involves the preparation of dry powder mixes' hich must be dissolved in water and then diluted to the proper volume before use. The other approach involves the preparation of liquid concentrates, that is, concentrated solutions which merely have to be diluted with water to obtain a working strength solution. Examples of such packaged processing formulations are described in numerous patents and publications; for example, the dry powder developer mixes of U.S. patents 2,843,484 and 2,846,308, the black-and-white developer liquid concentrates of U.S. patents 3,467,521, 3,532,498, 3,854,948 and 4,046,571,. and the color developer liquid concentrates of U.S. patents 3,574,619,

3,647,461, 3,814,606, and published British patent specification 2,016,723.

Each of the prior art procedures possesses both advantages and disadvantages. For example, the use of dry powder mixes avoids the expense involved in shipping and storing of water and enables the preparation of compact light-weight packages that require little storage space. However, dry powder mixes are highly disadvantageous in that they are difficult to handle, create a hazard as a result of the generation of dust, require highly accurate weighing and dispensing techniques which are difficult to control, and often require difficult and time-consuming procedures to bring about dissolution in water during preparation of the working strength solution. On the other hand, liquid concentrates are very convenient to use and much less hazardous, since they eliminate the dust problem, and they can be very readily diluted to working strength without the need for laborious mixing procedures. However, even though these solutions are concentrated, they still contain a considerable amount of water, and it is very expensive to have to transport and store this water. Thus, for example, typical liquid concentrates used in photographic processing are of a concentration such that as much as two-thirds of the total weight is water. Moreover, there is a severe problem involved with such liquid concentrates of photographic processing compositions as there is a tendency for chemical interactions to take place between certain of the components. This frequently prevents- combining all of the components in a single liquid concentrate, and necessitates the separation of the components into two or more parts which must be subsequently combined to form the

« final processing solution. Often, as many as three or four different parts are required, and this greatly complicates the packaging operation and adds

cι. to the expense of manufacture, transport, and storage. For example, black-and-white developers of the hydroquinone/pyrazolidone type are typically packaged as a two-part liquid concentrate system, as described in United States patents 3,532,498 and

3,854,948. However, with developers of this latter type which contain an aldehydic hardening agent, as is typical in machine processing of X-ray films, it is the usual practice to package the hardening agent separately as illustrated, for example, by U.S. patent 4,046,571. Color developers containing aromatic primary a ino color developing agents are typically packaged as a liquid concentrate system comprising at least two parts, and sometimes three or four parts, as illustrated by U.S. patents 3,647,461 and 3,814,606.

It is known to formulate photographic processing agents in tablet form. Such tablets are described in Canadian patent 831,928. This has many advantages but is not, in general, a feasible commercial alternative to the use of dry powder mixes or liquid concentrates. The preparation of tablets is a complex and expensive procedure, and many photographic processing compositions are not amenable to tablet formation. Moreover, tablets usually require the use of large amounts of binding agents, and these agents can make dissolution of the tablet difficult and/or cause adverse sensitometric effects in processing. One approach to the problem of promoting prompt dissolution of photographic processing tablets is to incorporate effervescing agents, however, use of these materials is generally not very effective and introduces additional costs and complexity in the manufacturing operation.

OMPI

Y/I.-Ό - ^* Proposals have been made in the past to formulate photographic processing concentrates as paste-like compositions. For example, British patent 4689 describes black-and-white developer concentrates having the consistency of a paste or cream, Italian patent 427,967 describes black-and-white developer concentrates which are prepared in paste form, U.S. patent 2,735,774 describes fixer concentrates of paste-like consistency, and U.S. patent 2,784,086 describes black-and-white developer concentrates that are formulated in the form of a smooth gel. However, prior art processing concentrates of paste-like consistency have typically depended on the use of suspending, thickening, binding or gelling agents to maintain solid constituents in a uniform suspension, and have lacked the properties necessary to meet high quality performance specifications. Thus, for example: they have suffered from such problems as poor flow characteristics which render them very difficult to handle; lack of chemical stability; a tendency to separate, cake or crystallize; and poor solubility characteristics, such that they have been difficult to dissolve. Use of the suspending, thickening, binding or gelling agents adds substantially to the cost and complexity of the manufacturing operation and can create problems of microbiological growth formation and the formation of scums and residues in processing operations. Moreover, there are very few, if any., agents that will function effectively under conditions of high pH and/or high salt concentration. In some

« instances, paste-like processing concentrates have been prepared without the use of suspending, thickening, binding or gelling agents, but these co positions have exhibited similar disadvantageous characteris ics.

It is thus desirable to provide photographic processing concentrates of paste-like consistency in a form that overcomes the problems of prior art pastes and provides many of the advaptages of dry powder mixes, while, at the same time, provide many of the advantages of liquid concentrates. Such can be achieved in accordance with the invention with a photographic processing concentrate containing a photographic processing agent characterized in that the concentrate comprises a discontinuous solid phase distributed throughout a continuous liquid phase, the solid phase comprising finely divided solid particles associated in a stable three-dimensional network which imparts shear-thinning characteristics to the concentrate, at least one of the liquid phase and the solid phase containing a photographic processing agent, and the liquid phase being present in an amount sufficient to impart a paste-like consistency to the concentrate.

The photographic processing concentrates of the invention can be packaged, transported, and stored in the form of a stable paste that is adapted to be readily dissolved in water or other liquid medium to form a working processing solution. The paste is comprised of a discontinuous solid phase comprising finely-divided solid particles associated in a stable three-dimensional network distributed throughout a continuous liquid phase. The liquid phase is present in an amount which is much less than the amount that would be needed to form a solution of the solid phase and just sufficient to impart a paste-like consistency. One or more photographic processing agents is present in either or both of the liquid and solid phases. The three-dimensional network formed by the association of the finely-divided solid particles provides a high degree of stability to the concentrate, while still permitting it to be readily dissolved in a liquid medium. It also imparts shear- thinning characteristics which greatly facilitate dispensing of the concentrate. The continuous liquid phase can consist of a single liquid or of two or more miscible liquids. It can be comprised of water, or of one or more organic liquids, or it can be a mixed aqueous- organic system. The solid phase typically comprises one -or more of the ingredients of the processing composition which are normally solid materials. While liquid or solid ingredients which are not necessary components of the working processing solution can be incorporated in the paste when needed, it is frequently the case that the paste can be prepared solely from the necessary components ef the processing solution, without the need to delete any ingredients that would be used in the prior art - system of liquid concentrates nor to add any additional ingredients. Formulation of the stable paste is achieved by appropriate selection of the relative proportions of the ingredients, appropriate control of the particle sizes of the ingredients, and appropriate control of the procedures whereby they are combined.

In using the paste form of concentrate described herein, problems of chemical interaction between ingredients, which complicate the use of liquid concentrates, are frequently much less severe. Thus, in many instances, all of the necessary ingredients can be combined together to form a single paste, or the number of separate parts which is needed in a system can be reduced, for example, from three to two or from four to three. Typically, the paste has excellent shelf- life properties, and is capable of being readily diluted with water or other liquid medium to form a working strength solution that performs in a manner indistinguishable from a working strength solution prepared from liquid concentrates. Also, the pastes of the invention are readily adaptable for use in automatic or semi-automatic procedures for delivery to the processing system, and thus are as convenient to use as liquid concentrates, and much more convenient to use than dry powder mixes. The photographic processing concentrates of the invention are stable, non-separating, non-caking, non-crystallizing and readily dissolvable in a liquid medium to form processing solutions. Considering the complexity and inherent sensitivity to deterioration of modern day photo¬ graphic processing compositions, particularly such highly complex compositions as color developers and X-ray developers, it was unexpected to find that a processing concentrate can be formulated in paste form to obtain important advantages in regard to packaging, transport and storage resulting from its excellent stability and low bulk, and yet, the concentrate can be easily converted from the paste form to a processing solution that performs equally as well as solutions prepared from liquid concentrates. It is also unexpected to find that preparation of processing concentrates jin paste form can greatly simplify packaging by enabling all components to be incorporated together, or at least to reduce the number of component parts into which they must be separated.

With photographic processing compositions in which all processing agents are normally solid materials, it is ordinarily feasible to prepare the processing concentrate of the invention by combining these solid materials in finely-divided form in the correct proportion and appropriate order with the appropriate amount of water, or other liquid medium, and thoroughly blending them together, taking care to ensure that the finely-divided solid particles are associated in a stable three-dimensional network. Similarily, with processing concentrates in which some of the processing agents are normally solid materials and others are normally liquid materials, it is ordinarily feasible to prepare the processing concentrates of the invention by combining the solid materials, the liquid 'materials and water, all in the appropriate portions, and thoroughly blending them together. In instances where several of the processing agents are liquids, little or no water may be required. In some instances, it is advantageous in forming the paste to utilize either liquid or solid inert materials which do not have any processing function, i.e., which are not processing agents, but which promote the desired formation of the paste. Thus, either or both of the solid phase and the liquid phase can be composed solely of active agents, and the use of inert materials is optional, depending on the characteristics of the active agents and the properties desired in the concentrate. Preferably, the paste-like- processing concentrates of this invention are prepared without the use of any suspending, thickening binding or gelling agents, as these agents typically exhibit many characteristics which render their use undesirable in photographic

v^j .c processing compositions.

The term "photographic processing agent" is used herein to refer to a material used to develop or otherwise process a photographic element, for example, to develop, fix, bleach, harden, stabilize, etc. Thus, the processing solutions prepared from the processing concentrates of the invention can be any of the solutions used in processing photographic materials such as, for example, black-and-white developing solutions, color developing solutions, fixing baths, bleaching baths, stabilizing baths, stop baths, nucleating baths, mono-baths, bleach-fixes, prehardeners, activators, conditioning baths, toners, neutralizers, and the like. The invention is particularly useful for preparing processing concentrates containing photographic-processing agents useful for processing silver halide photographic elements.

Developing agents of both organic and inorganic types are well known in the photographic art. Useful classes of organic developing agents include hydroquinones, catechols, aminophenols, pyrazolidones, phenylenediamines, tetrahydro- quinolines, bis(pyridone) amines, cycloalkenones, pyrimidines, reductones and coumarins. Useful inorganic developing agents include compounds of a metal, having at least two distinct valence states, which are capable of reducing ionic silver to metallic silver. Such metals include iron, titanium, vanadium, and chromium. The metal compounds employed are typically complexes with organic compounds such as polycarboxylic acids or aminopolycarboxylic acids.

A particularly important class of black- and-white developing agents useful in the invention are the dihydroxybenzenes such as, for example, hydroquinone, chlorohydroquinone, bromohydroquinone, isopropylhydroquinone, toluhydroquinone, methylhydroquinone, 2,3-dichlorohydroquinone, 2,5-dimethylhydroquinone, 2,3-dibromohydroquinone, l,4-dihydroxy-2-acetophenone-2,5-di- methyIhydroquinone, 2,5-diethyIhydroquinone, 2,5-di-p-phenethyIhydroquinone, 2, 5-dibenzoylaminohydroquinone, and

2,5-diacetaminohydroquinone. A further particularly important class of black-and-white developing agents useful in the invention are the 3-pyrazolidones. Useful compounds of this class include those substituted in the

1-position by a monocyclic aryl group of the benzene series, including phenyl and substituted phenyl such as p-tolyl, p-chlorophenyl, etc. A typical compound of this type is l-phenyl-3-pyrazolidone. In addition to this substitution in the 1-position, the pyrazolidone nucleus can be substituted in the 4-position, particularly by lower alkyl and substituted lower alkyl groups such as methyl and hydroxymethyl. Representative compounds of this class are l-phenyl-4-methyl-3-pyrazolidone, l-phenyl-4-hydroxymethyl-3-pyrazolidone, l-phenyl-4, 4-dimethyl-3-pyrazolidone, and l-phenyl-4,4-di

«

(hydroxymethyl)-3-pyrazolidone.

Color developers useful in the invention typically contain primary aromatic amino color developing agents. These color developing agents are well known and widely used in a variety of color photographic processes. They include aminophenols and p-phenylenediamines.

Examples of aminophenol developing agents include o-aminophenol, p-aminophenol, 5-amino-2- hydroxytoluene, 2-amino-3-hydroxy-toluene, 2-hydroxy- 3-amino-l,4-dimethylbenzene, and the like.

Particularly useful aromatic primary amino color developing agents are the p-phenylenediamines and especially the N-N-dialkyl-p-phenylenediamines in which the alkyl groups or the aromatic nucleus can be substituted or unsubstituted. Examples of useful p-phenylenediamine color developing agents include: N-N-diethyl-p-phenylenediamine monohydro- chloride, 4-N,N-diethyl-2-methylphenylenediamine monohydrochloride, 4-(N-ethyl-N-2-methanesulfonylaminoet.hyl)- ' 2-methylphenylenediamine sesquisulfate monohydrate, 4-(N-ethyl-N-2-hydrox ethyl)-2-m th lpheny- lenediamine sulfate, and 4,N,N-die hyl-2,2'-methanesulfonylamino- ethylphenylenediamine hydrochloride.

An especially preferred class of p-phenylenediamine developing agents are those containing at least one alkylsulfoήamidoalkyl substituent attached to the aromatic nucleus or to an amino nitrogen. Other especially preferred classes of .p-phenylenediamines are the 3-alkyl-N- alkyl-N-alkoxyalkyl-p-phenylenediamines_^ and the 3-alkox -N-aIky1-N-aIkoxyalkyl-p-phenylenediamines. These developing agents are described in U.S. patents 3,656,950 and 3,658,525 and can be represented by the formula:

wherein n is an integer having a value of from 2 to 4, R is an alkyl group of from 1 to 4 carbon atoms, and R is an alkyl group of from 1 to 4 carbon atoms or ah alkoxy group of from 1 to 4 carbon atoms. Illustrative examples of these developing agents include the following compounds: N-ethy1-N-methox butyl-3-me hyl-p-pheny¬ lenediamine, N-etbyl- -etboxyethyl-3-metb l-p-pheny- lenediamine, N-ethyl-N-methoxyethyl-3-n-propyl-p-pheny- lenediamine,

N-ethyl-N-methoxyethyl-3-methoxy-p-phenyl- lenediamine, and N-ethy1-N-butox ethy1-3-methyl-p-phenylene¬ diamine. In addition to the primary aromatic amino color developing agent, color developer compositions typically contain a variety of other agents such as alkalines to control pH, bromides, iodides, benzyl alcohol, anti-oxidants, solubilizing agents, sequestering agents, brightening agents, etc. which can be used in the processing concentrates of the invention. «

In the production of color photographic images, it is necessary to remove the silver image which is formed coincident with the dye image. This can be done by oxidizing the silver by means of a suitable oxidizing agent, commonly referred to as a bleaching agent, in the presence of halide ion followed by dissolving the silver halide so formed in a silver halide solvent, commonly referred to as a fixing agent. Alternatively, the bleaching agent and fixing agent can be combined in a bleach-fixing solution and the silver removed in one step by use of such solution. A variety of bleaching agents are known for use in photographic processing, for example, ferricyanide bleaching agents, persulfate bleaching agents, dichromate bleaching agents, permanganate bleaching agents, ferric chloride and water-soluble quinones. Such processing agents can be used in the processing concentrates of the invention.

A particularly important group of photographic bleaching agents are the aminopoly- carboxylic acid bleaching agents. They are typically utilized in the form of water-soluble salts, such as ammonium or alkali metal salts, of a ferric aminopolycarboxylic acid complex. A typical example is the ammonium salt of ferric ethylene- diaminetetraacetic acid (NH,FeEDTA) , which is also known as ammonium ethylenedinitrilotetraacetato ferrate (III). Many other aminopolycarboxylic acids is addition to ethylenediamine tetraacetic acid are also useful such as, for example: nitrilotriacetic acid, diethylenetriamine pentaacetic acid, ortho-diamine cyclohexane tetraacetic acid ethylene glycol bis(aminoethyl) ether) tetraacetic acid, diaminopropanol tetraacetic acid, N-(2-hydroxyethyl)ethylenediamine triacetic acid, and ethyliminodipropionic acid. The aminopolyacetic acids are preferred, as they are readily available and provide particularly good bleaching action. Fixing agents used in photographic processing and which can be used in the processing concentrates of the invention include thioureas, thiocyanates, thiosulfates, mercapto-containing compounds such as mercapto acetic acid, quaternary ammonium salts, polyamines such as tetraethylene pentamine, and the like. In bleach-fix compositions, it is common to employ thiosulfates as fixing agents, typically ammonium thiosulfate or alkali metal thiosulfates such as sodium thiosulfate and potassium thiosulfate.

Bleach and bleach-fix processing agents used in the invention can contain a wide variety of addenda known to the art to be useful in such form¬ ulations, including amines, sulfites, mercapto- triazoles, alkali metal bromides, alkali metal iodides, and the like.

Agents for hardening of gelatin or other hydrophilic colloids employed in photographic elements are often used in processing. Such agents can also be used in the invention. For example, they can be incorporated in fixing baths, or in developing baths or utilized in the form of prehardener solutions. In hardening fix baths, it is common to utilize an aluminum or zirconium salt as the hardening agent. In developers and pre- hardeners, any of a very wide variety of hardening agents can be employed. Such hardening agents include aldehydes such as formaldehyde,^* dialdehydes such as succinaldehyde and glutaraldehyde, α-diketones, sulfonate esters, active halogen compounds, etc. In color reversal processing of photo¬ graphic elements, it is common to utilize nucleating agents to take the place of reversal re-exposure. Nucleating agents can be incorporated in a color developing solution or in a separate bath which is used between first development and- color develop¬ ment. Useful classes of nucleating agents useful in the invention include alkali metal borohydrides, ionic boron hydrides containing two or more boron atoms per molecule, amine boranes, polyamine boranes, phosphine boranes, arsine boranes, stibine boranes, borazines, chelated stannous salts, and the like.

A final step in many color photographic processes involves treatment of the element with a stabilizing bath, which serves to stabilize the dye images. Such baths frequently include a wetting agent, for example, a polyoxyalkylene compound, and an aliphatic aldehyde, for example, formaldehyde, paraformaldehyde, acetaldehyde, aldol, crotonaldehyde and the like. The agents comprising such baths can be used in the processing concentrates of the invention.

While certain common photographic processing agents that can be used in the processing concentrates of the invention have been described in detail above, it should be understood that the present invention is not limited to these particular processing agents, but is broadly applicable to any of the wide diversity of compositions used in the processing of photographic elements.

Processing of black-and-white_^ photographic elements is generally quite simple, involving only the steps of developing and fixing. ^' Color process- ing can involve a two-step process, such as a

:?ι

WH O _, process employing the steps of color developing and bleach-fixing, or more complicated processes such as a process employing a prehardener, a neutralizer, a first developer, a color developer, a bleach, a fix and a stabilizer. The concentrates of the invention can be advantageously utilized with simple processes or with those employing a complicated series of steps. It is useful in black-and-white processing (including X-ray processing and processing of lith- ographic films), in the processing of photographic elements designed for reversal color processing, in the processing of negative color elements, and in the processing of color print materials. The present processing concentrates can be employed with photographic elements which are processed in color developers containing couplers or with photographic elements which contain the coupler in the silver halide emulsion layers or in layers contiguous thereto. The photosensitive layers present in the photographic elements processed with processing concentrates of this invention can contain any of the conventional silver halides as the photo¬ sensitive material, for example, silver chloride, silver bromide, silver bromoiodide, silver chlorobromide, silver chloroiodide, silver chloro- bromoiodide, and mixtures thereof. These layers can contain conventional addenda and be coated on any ofc the photographic supports, such as, for example, cellulose nitrate film, cellulose acetate film, poly- vinyl acetal film, polycarbonate film, polystyrene film, polyethylene terephthalate film, paper, polymer-coated paper, and the like.

The solid material used in preparing the paste-like photographic processing concentrates of this invention is typically comprised of one or more normally solid processing agents, e.g., such solid processing agents as the salts of p-phenylene¬ diamines which are commonly used as color developing agents. However, where the desired processing composition does not require any processing agents which are normally solid, or requires an insufficient proportion of such agents to render the formation of a paste feasible, inert particulate components which do not perform a processing function, but are added solely to facilitate formation of the paste, can be utilized. Useful materials for this purpose include a wide variety of finely-divided photographically inert solid materials such as silicon dioxide, sodium sulfate, and diatomaceous earth. Formation of the paste-like photographic processing concentrates of this invention requires the use of solid particles in very f nely-divided form. Because the solid particles are very finely- divided, they provide a very large .surface area per unit of weight. The amount of surface area is an important factor in determining the physical characteristics of the paste-like concentrate, especially its rheological properties. The desired small particle size and high surface area can be achieved by grinding which takes place during blending of the materials in forming the concentrate, or by grinding individual ingredients prior to blending. The actual particle size employed can vary widely, depending on the particular processing formulation involved. How¬ ever, the photographic processing concentrates of this invention are typically characterized by the presence of particles of very small size. Generally speaking, it is desirable that the finely-divided solid particles have a size less than 100 microns, preferably less than 25 microns, and most preferably

OIvFI \ less than 3 microns.

The liquid phase of the paste-like photographic processing concentrates of this invention can take a variety of forms. In appropriate situations, e.g., those where the processing formulation does not employ any processing agents which are liquids, water can be used as the sole liquid ingredient forming the liquid phase. In other instances, one or more liquid processing agents, or a combination of water plus one or more liquid processing agents can be utilized. Inert water-miscible organic liquids, i.e., those which do not have a processing function, can be added in order to promote formation of the paste, if desired.

The paste-like photographic processing concentrates of the invention are made up of a discontinuous solid phase that is distributed throughout a continuous liquid phase. Thus, the two phases are in intimate association with one another and interact to provide the properties exhibited by the paste. The liquid phase must not be present in either too great or too small an amount in relation to the solid phase or the resulting product will not have the desired paste-like consistency. The actual ratio of liquid to solid in the concentrate can vary widely, depending on the particular processing formulation involved, and such factors as particle size. Generally speaking, it is desirable that the liquid phase be present in an amount of from 0.05 to 0.8 parts per part of solid phase by weight, and more preferably in an amount of from 0.1 to 0.6 parts per part of solid phase by weight.

The photographic processing concentrates of the invention are characterized by a very low ratio of liquid to solid in comparison to prior art photographic processing concentrates. A typical

o example of a color developer liquid concentrate of the prior art is that described in Example 1 of U.S. patent 3,647,461. This developer concentrate contains 2 grams of sodium sulfite and 6.4 grams of 4-amino-N-e hyl-N-(β-methanesuIfonamidoethyl)-m- toluidine sesquisulfate monohydrate dissolved in 11 grams of water. This is a weight ratio of liquid to solid of 1.3 to 1. In comparison, the same formula¬ tion prepared in the form of a paste-like concentrate in accordance with this invention would typically have a ratio of liquid to solid of about 0.6 to 1. A typical example of a black-and-white developer liquid concentrate of the prior art is that described in Example 1 of U.S. patent 3,467,521. This developer concentrate contains 312- grams of potassium sulfite, 15 grams of potassium hydroxide, 90 grams of potassium carbonate, 45 grams of hydroquinone, 1.5 grams of l-phenyl-3-pyrazol- idone developing agent, 10 grams of potassium bromide and 8 grams of ethylenediaminetetraacetic acid dissolved in sufficient distilled water to give a volume of 1 liter. This is a weight ratio of liquid to solid of approximately 1 to 1. In comparison, the same formulation prepared in the form of a paste-like concentrate in accordance with this invention would typically have a ratio of liquid to solid of 0.25 to 1. A typical example of a prior art developer paste is that described in Example 1 of U.S. patent 2,784,086. This developer paste is prepared by adding 24.0 grams of sodium sulfite, 45.0 grams of sodium carbonate, 1.6 grams of onomethyl p-aminophenol sulfate, 4.8 grams of hydroquinone, 1.0 grams of potassium bromide and 2.0 grams of sodium tetraphosphate to 90 milliliters of a 2% solution of the sodium derivative of algin. This is a weight ratio of liquid to solid of approximately 1.1 to 1. In comparison, a comparable developer prepared in the form of a paste-like concentrate in accordance with the invention would omit the algin derivative and would typically have a ratio of liquid to solid of 0.25 to 1.

Photographic processing agents present in the paste-like concentrates of the invention can be present in either or both phases. Frequently, a processing agent which is a solid material will be distributed between the solid and liquid phases, with the amount present in each being determined, in part, by its solubility characteristics. For example, the p-phenylenediamines that are used in color developers will typically be distributed between both phases with a major portion, e.g. , 90% being in the liquid phase, and a minor proportion, e.g., 10%, being in the solid phase.

Typically, the photographic processing concentrates of the invention are prepared in the form of a stiff paste, but the degree of fluidity of these compositions can be varied to a very considerable extent, as desired, so that pastes with either a pourable or non-pourable consistency are within the contemplated scope of this invention. Thickening or suspending agents are not usually needed in the processing concentrates of this invention, but their use is optional, and they can be employed, if desired. Generally speaking, the paste-like concentrates are readily dissolved in water, even with the use of only very simple stirring equipment such as a hand-held paddle. Improved results, however, are usually obtained when they are dissolved with the aid of mechanical stirring devices that provide much higher mixing speeds that can be achieved by hand. While the concentrates disclosed herein can be characterized as being stable, nonseparating, non-caking, non-crystallizing and readily dissolvable in a liquid medium to form a working processing solution, such terms are, of course, relative terms, and it is intended by use of these terms only to indicate that the concentrate possesses these characteristics to a degree sufficient to be useful for its intended purpose.

It should be noted that processing concentrates prepared in the paste form described herein are not intended to be used, as such, in processing photographic materials, but only after being dissolved in the appropriate amount of water or other liquid medium to f'orm a working strength solution. Thus, the objectives and purposes of this invention are clearly different than in the case of prior art inventions where photographic processing compositions have been converted to forms other than true solutions with the intention that they be used in such form in the processing of photographic elements, for example, the processing compositions in the form of a foam as described in U.S. patent 2,860,977, the solid fusible, processing compositions of U.S. patents 3,347,675 and 3,438,776, and the viscous processing compositions of U.S. patent 3,392,019. The processing concentrates of this invention are designed to facilitate packaging, transport and storage, and this involves distinctly different considerations and problems that were involved in the above prior art that were seeking to simplify processing operations per se.

It should also be noted that the paste¬ like concentrates of the invention are characterized by a very low ratio of liquid to solid. It is this feature that provides the desired low bulk character¬ istics that provide substantial cost savings in pack- aging, transport and storage. In this regard, the photographic concentrates of this invention are clearly distinct from photographic processing con¬ centrates of the prior art, which have utilized relatively large portions of water, but have had high viscosity in spite of the high water content because of the presence of large amounts of colloidal thickening, binding, gelling, or suspending agents. The paste-like photographic processing concentrates of the invention are characterized by the presence of f nely-divided solid particles associated in a stable three-dimensional network. A variety of mechanisms can result, separately or in combination, in the creation of such a network. For example, with certain processing formulations, the finely-divided solid particles are present in the form of aggregates or clusters of particles, and such systems can, therefore, be described as flocculated. In such a flocculated suspension, particles associate, through electrical forces, to other particles, and it is this attraction into a network which imparts stability. With other formulations, network formation is dependent upon morphological association. For example, particles of needle-like structure are generated in blending and grinding of the ingredients, and such particles associate in a stable three-dimensional network as a consequence of their shape. In still other form- ulations, certain of the components are present in the form of intermolecular association products which create a stable three-dimensional network through physical and chemical interaction, but readily dissociate when the paste is diluted with water. The term "stable" is used herein with reference to the three-dimensional network in the sense of being descriptive of its capability of functioning to maintain the desired even distribu- tion of materials throughout the paste-like concentrate during a shelf life of adequate duration to meet the requirements of the photographic art.

The presence in a photographic processing concentrate of the stable three-dimensional network described herein is evidenced by a yield point and by rheological behaviour that can be characterized as shear-thinning or pseudoplastic. The network results from the association of finely-divided particulates through mechanisms such as those outlined above. The dimensions of the network are perhaps best characterized by the distances over which a disruption of one point has an effect at another point. These dimensions are dependent on the materials and methods of formulation and can range from a few tens of microns up to many centimeters.

A processing concentrate of the invention in the form of a flocculated colloidal suspension is illustrated by a p-phenylenediamine color developer formulation containing both benzyl alcohol and triethanolamine. Color developers containing these two ingredients are described in U.S. patent 4,170,478. In this system, two immiscible solvents, benzyl alcohol and water, are made miscible by the addition of a third solvent, triethanolamine, which is completely miscible with both of the other solvents. Thus, benzyl alcohol and water are immiscible in any quantity of benzyl alcohol greater than one gram in twenty-five milliliters of water, and of more than one milliliter of water in ten grams of benzyl alcohol. The addition of triethanol- amine increases the solubility of benzyl alcohol in water and vice versa. In this system, flocculation is dependent upon maintaining a low water concentration. This can be explained, in part, by 5 the fact that with a low concentration of water, there is a low ionic strength, since salts present in the formulation will not ionize to a high degree in an organic medium. Under these conditions, flocculation is favored. The result of flocculation

10 is the association of the finely-divided particles in a stable three-dimensional network that is characteristic of the paste-like concentrates of this¹ invention.

The photographic processing concentrates

15 of the invention exhibit good stability character¬ istics from the standpoint of both chemical and physical stability. For example, they are resistant to aerial oxidation and to deleterious changes resulting from chemical reactions between components

20 thereof. They are also highly advantageous in that they are non-separating, non-caking, and non-crystallizing. These advantageous character¬ istics are believed to be imparted to the concentrate by the presence of the aforesaid stable

25 three-dimensional network. Thus, for example, association of the finely-divided particles in a stable three-dimensional network maintains larger particles in suspension, and avoids settling or stratification.

30. Numerous factors relating to the characteristics of the starting materials and the manner in which they are combined to form a .paste¬ like processing concentrate of the invention are believed to interact together to influence the

35 formation of the stable network of associated particles. Such factors include the following: (1) The order in which the ingredients are combined to form the paste.

(2) The temperature during formation of the paste. (3) The type of mixing equipment used in forming the paste and the parameters of mixing such as the degree to which shearing takes place.

(4) The particle size.

(5) The effects of additives which are not processing agents, such as dispersing agents or thickeners.

(6) The effect of pH and the chemical environment during paste formation.

(7) The effect of the ratio of aqueous to organic liquids when both are present.

(8) The effect of the liquid to solid ratio.

Various exothermic and gas-evolving phenomena can take place during mixing to form the paste. These may be explainable in terms of acid-base reactions or other exothermic chemical reactions. An increase in temperature occurs during mixing, in part as a result of chemical reactions, but primarily as a result of the grinding action of the mixer. Care must be taken to prevent the temperature from rising to too high a level, as this can result in depletion of essential components of the formulation.

Characteristic features of paste-like photographic processing concentrates of the invention comprising finely divided solid particles associated in a stable three-dimensionaj network include their shear-thinning properties and high sedimentation volumes. (A shear-thinning material is one which has a high viscosity under low shear conditions, and a low viscosity under high shear conditions). The shear-thinning properties possessed by these concentrates are especially significant in that they greatly facilitate dispensing of the concentrates from the containers in which they are packaged. The particular viscosity and degree of shear-thinning exhibited varies greatly among the very wide range of different processing compositions coming within the scope of the present invention. For example, typical concentrates have an apparent viscosity in the range of from 250 to 1300 centipoises at a shear rate of 800 reciprocal seconds (sec. ) . At a shear rate of 4500 reciprocal seconds, an apparent viscosity in the range of from about 100 to about 500 centipoises is typical. These values refer to viscosity measurements made in a HERCULES HI-SKEAR VISCOMETER (rational concentric cylinder type) at ambient temperature. The rotor or inner cylinder (radius 1.95 cm., height 5.0 cm.) is rotated at a constant angular acceleration of approximately 5.49

2 rad/sec to a maximum angular velocity of 115 rad/sec. This rotation imparts an increasing rate of shear (maximum 4549 sec^" ) to the sample which is contained in the annulus between the inner and outer cylinders (annulus width 0.5 cm.). The torque which is transmitted through the sample to the outer cylinder is measured and used in calculation of apparent viscosity as a function of rate of shear^'. The stable three-dimensional network formed by association of finely-divided solid particles also imparts a high sedimentation volume to the concentrate. Unlike a stable suspension of solid particles, in which the particles act independently, in the concentrates described herein, particles exist in a state of association. As a

c?? consequence, the sedimentation volume is large, whereas the sediment from a stable suspension tends to pack closely, i.e., to approximate closest packing behavior, so as to exhibit a considerably smaller sedimentation volume for particles of the same dimensions. Brownian motion can be observed in a stable suspension, but not in a flocculated system.

The flocculated suspensions have been found to exhibit pronounced thixotropic behavior.

In particular, they tend to become quite fluid when agitated, but return to a stiff paste form when at rest. • In being mixed, they are subject to extreme shearing which prevents extensive association and in consequence, are free-flowing, while upon standing they become quite viscous and "paste-like." In terms of flocculation, it is apparent that standing for a sufficient time allows further association of particles into a network. Given enough time, the system will proceed to its point of equilibrium, i.e., optimal degree of association. The optimum condition is dependent upon the particular formulation involved, that is, the particular ingredients and their proportions. Once in its equilibrium state, the material will not readily dissolve in water. With the application of shearing energy, the network associations, that is, interparticle attractions, are broken, the viscosity decreases, and the material can be readily dissolved in water.

The paste-like photographic processing concentrates of the invention are especially advantageous in the packaging of color developing compositions comprising primary aromatic amino color developing agents. Typically, color developers are packaged and sold in liquid concentrate form, with the chemical formulation for a given process being divided into the least possible number of concentrated parts that will provide good shelf life. Often, the color developer formulation will contain numerous ingredients, sometimes as many as fifteen or more, and it will be necessary to separate it into three or four parts in order to package it in the form of liquid concentrates. Formation of stable paste-like concentrates, in accordance with the teachings herein, will often permit packaging of complex color developers containing as many as fifteen or more ingredients in the form of a single paste or, perhaps, two different pastes. It was particularly surprising to find that problems of chemical interaction between components of complex color developer formulations which complicate the use of liquid concentrates, and necessitate packaging of as many as four separate liquid concentrates, are frequently much less severe with the paste-like concentrates of this invention.

The aromatic primary amino color developing agents are solid materials which will distribute themselves between the liquid and solid phases of the concentrate. In these concentrates, the liquid phase will typically be comprised of water and at least one organic liquid, since organic liquids, e.g. , benzyl alcohol, are necessary components of many currently used photographic color developing compositions.

The starting ingredients for forming the paste-like concentrates can be liquids, powders, or slurries. Typically, the slurries are saturated solutions with excess solutes present as undissolved solids. The ingredients are blended in a high shear

^" mixing vessel and can be conveyed to this vessel by any of several methods. Liquids and slurries are usually pumped, while powders are handled with a screw conveyor or other powder transport system. Agitated storage tanks can be used with the slurries in order to keep the solids in suspension. For uniformity and proper consistency, it is necessary to thoroughly disperse the solids and homogenize the product. This is best accomplished with hydraulic and mechanical shear provided by high speed agitators.

Once the paste has been mixed to the desired consistency, the next step is to convey it to the package-filling apparatus. If mixing is done directly above the filling process, the concentrate can be conveyed by gravity through a vibrated chute. Alternatively, the concentrate can be conveyed by pumping, typically by pumps of the positive-displacement type. Package filling can be carried out with the use of an auger system or a piston system. Packages of a wide variety of types can be utilized and inexpensive packaging materials, for example, thermoplastics such as polyethylene, can be employed. Dispensing of the paste and combining it with water or other liquid medium to form a working processing solution can be carried out by any suitable method. There are two basic approaches which are feasible. The first of these is to dispense and dissolve the entire contents at one time, i.e., a batch-dispensing approach. In this instance, it is not necessary that the paste be entirely homogeneous, since' all of the contents of the package are utilized to form a single batch of processing solution. The second approach is to dispense a portion of the contents of the package intermittently as needed. In this case, the paste must be completely homogeneous, since each portion dispensed must be like every other to give a consistent working solution. - Photographic processing chemicals must be dissolved in water or other liquid medium in very precise amounts in order to prepare working processing solutions. Thus, to be commercially useful, a photographic concentrate must not only possess features facilitating packaging, transport and storage, but must be capable of being dispensed . in such a way as to ensure the necessary precision in the preparation of working processing solutions. It is particularly advantageous for the photographic processing concentrate to be "volumetrically dis¬ pensable." By the term "volumetrically dispensable," as used herein, is meant a 'composition which has flow properties such that it can be dis¬ pensed from a package in a metered amount on a volumetric basis, and which has a high degree of uniformity such that each unit volume dispensed contains essentially the same amount of active agents on a weight basis. With such a concentrate, it is possible to combine a predetermined volume of concentrate with a predetermined volume of liquid, e.g., 100 cubic centimeters of concentrate combined with one liter of water, and consistently obtain the same weight of active agents in the resulting working solution. The dilution ratio employed with the processing concentrate, that is, the amount of water or other liquid used to convert the pas «te to a working processing solution, will vary greatly depending on the nature of the photographic element being processed, the processing procedure, and the particular processing formulation involved. In general, the dilution ratio will be in the range of 1 part of paste to 8 parts by weight of liquid to 1 part of paste to 100 parts by weight of liquid. The term "a photographic processing concentrate" is used herein to refer to a composition comprising one or more processing agents, such as developing agents, bleaching agents, fixing agents, etc. The processing concentrate can be (but not necessarily) complete in the sense that it merely needs to be combined with water, or other liquid medium, to form a working strength processing solution. In some instances, a processing concentrate of the invention can be combined with another photographic processing concentrate, as well as water or other liquid medium, to form a working strength processing solution, this other process¬ ing concentrate suitably being a paste, a powder, or a liquid. For example, a photographic developing solution might comprise five active agents, namely, a developing agent, an alkali, an antifoggant, an anti-oxidant and a sequestering agent. In utilizing processing concentrates of the invention, it may be advantageous to form a first paste containing the developing agent and anti-oxidant, and a second paste containing the alkali, the antifoggant and the sequestering agent, and then to combine the first and second pastes together, along with an appropriate quantity of water, to form a working strength developing solution. In another instance, a photographic processing composition might require several different solid processing agents and one liquid processing agent, and the paste-like concentrate could include only water and the several solid processing agents, while the working strength solution would be prepared by combining the liquid processing agent and the paste, along with an appropriate quantity of water.

While the photographic processing concentrates of the invention have been referred to throughout the specification as "pastes," and this term is aptly descriptive of their character¬ istics, they could also be referred to by a variety of other terms, such as, for example, the terms "semi solid," or "semi fluid" or "plastic." The term "a photographic processing solution," as used herein, is intended to include working solutions, replenisher solutions, starter solutions, and so forth.

The paste-like photographic processing concentrates of the invention can be evaluated by the preparation of rheograms, that is, plots of shear rate versus shear stress. In such plots, the viscosity is inversely proportional to the slope of the curve. For a strictly pseudoplastic or shear-thinning fluid, the values of shear stress obtained during an ascending series of shear rates correspond to those obtained in a descending series of shear rates. In other words, the curve for a descending series retraces the curve for an ascending series. The occurrence of thixotropic loops in a rheogram provides Theological evidence that the composition is a structured fluid, that is, one comprising a three-dimensional network. Thus, . with a thixotropic pseudo-plastic fluid, the rheogram exhibits what can be termed a thixotropic loop or hysteresis loop in that the descending series does not retrace the curve for the ascending • series.

A thixotropic fluid is one which exhibits a time-sensitive viscosity. In other words, the viscosity decreases with increasing shear duration.

OM When a thixotropic fluid is sheared at a constant shear rate, the viscosity decreases with time until some equilibrium value is reached. This is inter¬ preted by rheologists as the breakdown of a structure present in the fluid. When an ascending series of shear rates is imposed on a thixotropic pseudoplastic fluid, and immediately followed by a descending series, the curve is not retraced. A hysteresis loop is produced, with the curve of the descending series displaced toward the shear rate axis. This loop is also known as a thixotropic loop and is due to the breakdown of structure with time. The photographic processing concentrates of the invention comprise finely-divided solid particles associated in a stable three-dimensional network which imparts shear-thinning characteristics to the concentrate. Thus, they can be character¬ ized as thixotropic pseudoplastic fluids.

Low ratios of liquid to solid character- ize the paste-like photographic processing concentrates of the invention. Such low ratios are rendered feasible by proper compounding of the ingredients of the formulation to achieve a stable three-dimensional network of associated particles. In prior art attempts to prepare paste-like photographic processing concentrates, commercial success was not achieved because the concentrates prepared without the use of thickening, gelling, binding or suspending agents would harden to a hard unusable mass in a relatively short time, e.g., a few days, or would separate into two or more phases. On the other hand, when thickening, gelling, binding or suspending agents were emloyed to alleviate these problems, other difficulties were encountered, such as poor flow characteristics, crystallization, and limited solubility characteristics. The present invention is pre¬ dicated on the discovery that thickening, gelling, binding or suspending agents are not necessary in processing concentrates of paste-like consistency, and that the desired shelf stability can be achieved by careful control of the parameters of the manufacturing process, including, in particular, such important parameters as the particle size, the order in which the ingredients are combined, the degree of mixing and the ratio of liquid to solid components.

The invention is further illustrated by the following examples of its practice. Example 1

A photographic processing concentrate intended to be diluted with water to form a color developing solution for developing negative-positive color film was prepared in the following manner: 780 illiliters of a 47% by weight aqueous solution of potassium carbonate and 240 grams of powdered potassium sulfite were added to a 3.8 liter stainless steel Waring Blender, equipped with a cooling jacket, and blended for two minutes at low speed. 516 grams of 4-(N-ethyl-N-2-methanesulfonyl- aminoethyl)-2-methylphenylenediamine sesquisulfate monohydrate color developing agent in the form of a finely-divided powder was then added slowly while stirring with a spatula. 502 grams of powdered potassium carbonate was then added, and the mixture was blended for three minutes at high speed.

The product obtained was a pourable paste having a weight ratio of liquid to solid of 0.16 to 1 which exhibited shear-thinning characteristics. It was diluted with water in a ratio of 50 grams of water to one gram of paste and dissolved readily to produce a working color developing solution.

Example 2 A photographic processing concentrate intended to be diluted with water to form a hardening developer for processing X-ray film was prepared as a two-part paste formulation in the following manner:

To prepare the first part, 787.5 grams of potassium hydroxide (45% aqueous solution), 1545.69 grams of potassium sulfite, 157.5 grams of sodium bicarbonate, 21 grams of boric acid, 35 grams of ethylenediaminetetraacetic acid, 1.26 grams of 5- methylbenzotriazole, 5.25 grams of 5-nitroindazole, 630 grams of hydroquinone developing agent and 175 grams of water were thoroughly blended together.

The product obtained was a pourable paste which had a weight ratio of liquid to solid of 0.22 to 1 and exhibited shear-thinning characteristics.

To prepare the second part, 100 grams of glycerol and 150 grams of water were added to a 0.95 liter Osterizer Blender and blended at slow speed. 31.5 grams of powdered l-phenyl-3-pyrazolidone developing agent was added and blending was continued for about 2 minutes. 317.1 grams of powdered glutaraldehyde bis bisulfite hardener was added slowly, using a spatula to work it into the mixture as necessary, and blending was continued for about 3 minutes. The product obtained was a pourable paste which had a weight ratio of liquid to solid of 0.7 to 1 and exhibited shear-thinning characteristics.

To prepare a working developing solution, 5.6 grams of the first paste and 1.0 grams of the second paste were combined with 30 grams of water. Both pastes dissolved readily to thereby produce a developing solution suitable for the processing of X-ray f i lm .

Example 3 A photographic processing concentrate intended to be diluted with water to form a color developing solution for developing color prints was prepared from the following ingredients:

Components Quantity

1. Benzyl alcohol 493 milliliters 2. l-Hydroxyethylidene-1,1- disphosphonic acid (60% by weight aqueous solution) 40 milliliters

3. Potassium carbonate (anhydrous) 1600 grams

4. Potassium sulfite (anhydrous) 100 grams 5. Potassium bromide 16.7 grams

6. Hydroxylamine sulfate 170 grams

7. 4-(N-ethyl-N-2-methanesulfonyl- aminoethyl)-2-methylphenylene- diamine sesquisulfate monohydrate color developing agent 215 grams

8. Lithium sulfate 89 grams

These ingredients were added in the order specified to a 3.8 liter stainless steel Waring Blender equipped with a cooling jacket. Mixing was carried out at a high speed for times of 30 seconds for addition of ingredient 2, 15 seconds for addition of ingredient 3, 2 minutes for addition of ingredient 4, 1 minute for addition of ingredient 5, 2 minutes for addition of ingredient 6, 3 minutes for addition of ingredient 7, and 1 minute for addition of ingredient 8.

The product obtained was a pourable paste having a weight ratio of liquid to solid of 0.3 to 1 which exhibited shear-thinning characteristics. It was diluted with water in a ratio of 18 grams of water to one gram of paste and dissolved readily to produce a working color developing solution.

Example 4 A photographic processing concentrate tended to be diluted with water to form a color developing solution for developing color prints was prepared from the following ingredients:

Component Weight (grams)

I. Triethanolamine 960.0 2. Benzyl alcohol 1071.0

3. Sulfonated fatty acid surfactant 2.0

4. Potassium hydroxide (45% by weight aqueous solution) 291.2

5. Potassium hydroxide (85% solid) 370.0 6. 1-Hydroxyethylidene-l, 1-di- phosphonic acid (60% by weight aqueous solution) 92.8

7. Potassium bromide 11.2

8. Potassium sulfite 40.0 9. Amino-substituted stilbene brightening agent 240.0

10. Lithium sulfate 224.0

II. Hydroxylamine sulfate 504.0

12. 4-(N-ethyl-N-2-methanesulfonyl- aminoethyl)-2-methylphenylene- diamine sesquisulfate mono- hydrate color developing agent 544.0

13. Potassium carbonate 2000.0

Components 1 to 5 were added to a 6-liter VME-6 mixer manufactured by Fryma-Maschinen AG, and blended while cooling to a temperature of 17°C. The mixer was then started and components 6 to 13 were added through the addition port, allowing about 2 to 5 minutes between additions for thorough mixing. After addition of the first five components, the dissolver (a rotating disk with a saw tooth type configuration) was started, and allowed to run throughout the mixing procedure. The colloid mill (two rotating conical disks) was started after all components had been added, and allowed to run for one hour.

The product obtained was a pourable paste having a weight ratio of liquid to solid of 0.61 to 1 which exhibited shear-thinning characteristics. It was diluted with water in a ratio of 11.75 grams of water to one gram of paste, and dissolved readily to produce a working color developing solution.

The paste described above was analyzed by a technique involving high speed centrifugation to separate the continuous liquid paste and the dis- continuous solid paste, followed by analysis of the separated phases. The continuous liquid phase was analyzed by ultraviolet spectroscopy, gas chromato- graphy, Karl Fischer titration and total alkalinity titrimetry. The discontinuous solid phase was analyzed by ultraviolet spectroscopy, gas chromato- graphy, Karl Fischer titration, total alkalinity titrimetry, and gravimetric sulfate analysis. It was found that about 85% of the triethanolamine, about 95% of the benzyl alcohol, and about 90% of the 4-(N-ethyl- -2-methanesulfonylaminoethyl)-2- methylphenylenediamine sesquisulfate monohydrate were present in the continuous liquid phase. Potassium carbonate was found to be the major constituent of the discontinuous solid phase, with greater than 95% of the total potassium carbonate being found in this phase. Water, including water that was formed in situ, constituted about 4%, of the paste by weight. Particle sizes of solid materials in the paste were in the range of 0.5 to 3 microns. Example 5

A photographic processing concentrate intended to be diluted with water to form a black- and-white developing solution was prepared with the use of a mortar and pestle from the following ingredients: Component Weight(grams)

1. Potassium sulfite, anhydrous 220. . 3

2. Sodium bicarbonate 22 , .4

3. Boric acid 3 . . 0

4. Ethylenediaminetetraacetic acid 5. .4 5. 5-Methylbenzotriazole 0. , 2

6. l-Phenyl-3-pyrazolidone develop¬ ing agent 4. , 5

7. Hydroquinone developing agent 89. . 7

8. Potassium hydroxide (45% aqueous solution) 138. .4

9. Water 25. , 0

Component 1 was ground^' for four minutes and set aside. Components 6 and 7 were each ground for three minutes and were also set aside. Components 1 to 7 were then combined in the mortar and ground for two minutes. Component 8 was added slowly with mixing. Component 9 was then added slowly with mixing. The composition was mixed for three minutes after the final addition. Within five hours, the material had set to a stiff paste. No separation, caking, or crystal¬ lization was evident even after two days. Rheograms of both freshly-prepared and two-hour old composition had distinct thixotropic loops. Example 6

A photographic processing concentrate intended to be diluted with water to foxm a color developing solution was prepared with the use of a mortar and pestle from the following ingredients Component We igh t (grams )

1. Triethanolamine 94.4

2. Benzyl alcohol 93.6

3. Potassium hydroxide, anhydrous 25.6 4. l-Hydroxyethylidene-l,l-di- phosphonic acid (60% by weight aqueous solution) 8.1

5. Sulfonated fatty acid surfactant 0.2

6. Potassium bromide 0.98 7. Potassium sulfite 3.5

8. Amino-substituted stilbene brightening agent 21.0

9. Lithium sulfate 19.6 10. Hydroxylamine sulfate 44.1 11. 4-(N-ethyl-N-2-methanesulfonyl- aminoethyl)-2-methylphenylene- diamine sesquisulfate monohydrate (color developing agent) 47.6

12. Potassium carbonate 175.0 Components 3, 10, 11, and 12 were ground separately and set aside. Components 1 to 5 were added to the mortar in numerical order with mixing. Components 6 to 9 were combined together and then added slowly with mixing. Then components 10, 11, and 12 were slowly added in order with mixing. When all additions were complete, the composition was mixed for five minutes. The total time of mixing was about thirty-three minutes.

Within twenty-nine hours, the material had set to a stiff paste. After several days, there were no signs of separation, crystallization, or caking. Rheograms for freshly-prepared and four- hour old samples had significant thixotropic loops.

Example 7 A photographic processing concentrate intended to be diluted with water to form a fixing solution was prepared with the use of a mortar and pestle from the following ingredients:

Component Weight(grams) 1. Ammonium thiosulfate (807= aqueous solution) fixing agent 423.7

2. Sodium thiosulfate fixing agent 90.0

3. Sodium sulfite ^• 16.2

4. Sodium metabisulfite 19.0 5. Sodium acetate 45.0

6. Acetic acid 22.8

7. Sodium glyconate 8.1

8. Aluminum sulfate 57.8

Components 2 and 5 were ground separately and set aside. All components were added together, slowly, in order, and with mixing. When all addi¬ tions were complete, the composition was mixed for two more minutes.

Within two and one-half hours, the composition had set to a smooth, stiff paste. No signs of separation, caking, or crystallization were apparent even after four days. Rheograms of fresh and two-hour old samples had thixotropic loops. The rheogram of the two-hour old sample had a very distinct loop.

For purposes of comparison with the above examples, a paste-like photographic processing concentrate was made according to the formula and procedure of British patent No. 4689. The concentrate was prepared in a mortar and pestle from the following ingredients:

1. Hydroquinone developing agent 168 grams

2. Potassium metabisulfite 168 grams

3. Potassium bromide 84 grams 4. Water 108 grams Component 1 was ground in the mortar for eight minutes. Components 2 and 3 were ground together for five minutes and then were combined with component 1 and ground for five more minutes. Component 4 was added slowly with mixing; and when all additions were complete, the composition was mixed for three minutes.

Within one day of preparation, the material had separated into a fluid upper layer and a dense sediment and was not useful for preparation of a working photographic processing solution.

For purposes of further comparison with the above examples, a paste-like photographic processing concentrate was made according to the formula and procedure of Example 5 of the U.S. patent 2,735,774. • The concentrate was prepared in a mortar and pestle from the following ingredients:

1. Sodium acetate 30 grams

2. Boric acid 15 grams 3. Sodium citrate 3 grams

4. Ammonium alum 10 grams

5. Sodium bisulfite 10 grams

6. Ammonium thiosulfate (76% aqueous solution) fixing agent ^' 100 milliliters

7. Sodium thiosulfate, anhydrous fixing agent 150 grams

Components 1 to 5 were ground together in the mortar for five minutes. Component 6 was added slowly with mixing. Component 7 was ground separately before adding it to the mixture. When all additions were complete, the composition was mixed for five minutes.

Within 30 minutes, this composition had noticeably stratified, leaving a dense sediment at the bottom of the jar. After three and one-half days, a clear liquid layer had formed at the top of the sample. In addition, rheograms for both freshly prepared and two-hour old composition showed no evidence of thixotropy. The paste-like concentrates of this invention provide many important advantages in the photographic art. For example, they result in a major reduction in the cost for transport and storage of packaged chemicals, as compared to liquid concentrates. This is because of the much lower content of water that is required as compared to liquid concentrates, which results in much less bulk and weight, and thus much lower costs. Many processing chemicals are not sufficiently soluble in water to form highly concentrated solutions, so liquid concentrates often require a substantial water content. With the paste-like concentrates of this invention, a given quantity of processing solution can often be made from a package which has half or less than half of the weight and volume of a corresponding package of liquid concentrate.

A further advantage of paste concentrates, as compared to liquid concentrates, is that they tend to be more, chemically stable and to require less separation of ingredients and, accordingly, fewer separate parts in the total package. Keeping properties are generally significantly better with pastes because of such features as reduced suscept¬ ibility to oxidation, reduced susceptibility to deterioration caused by temperature changes, and reduced tendency for crystallization to occur.

Formation of working solutions from the photographic processing concentrates of the invention is relatively simple, as compared to the" difficult and time-consuming dissolution procedures required with dry powder formulations. Moreover,

_oi-£?ι_ '^' the paste concentrates are amenable to use with processing compositions in which some of the necessary ingredients are normally liquid, and some are normally solid, whereas dry powder formulations are useful only with compositions in which all necessary ingredients are normally solid. Paste formulations also effectively avoid the problems of caking and dusting that plague the use of dry powder formulations. As will be evident from the disclosure and examples herein, the paste-like photographic processing concentrates of the invention combine many of the advantages of liquid concentrates with many of the advantages of dry powder formulations to solve longstanding problems in the art of packaging photographic processing agents. They dissolve easily and speedily to form working processing solutions, for example replenisher solutions, and can be adapted for use in systems in which replenisher solution is held in a storage tank or for direct use in continuous replenishment of processing machines.

Claims

CLAIMS :

1. A photographic processing concentrate containing a photographic processing agent character¬ ized in that said concentrate comprises a discontinuous solid phase distributed throughout a continuous liquid phase, said solid phase comprising finely-divided solid particles associated in a stable three-dimensional network which imparts shear- thinning characteristics to said concentrate, at least one of said liquid phase and said solid phase containing said photographic processing agent, and said liquid phase being present in an amount sufficient to impart a paste-like consistency to said concentrate.

2. A photographic processing concentrate according to Claim 1 characterized in that said liquid phase comprises at least one of water and a water-miscible organic liquid.

3. A photographic processing concentrate according to Claim 1 characterized in that the size of said finely divided solid particles is less than 100 microns.

4. A photographic processing concentrate according to Claim 1 characterized in that the said liquid phase is present in an amount of 0.05 to 0.8 parts per part of said solid phase by weight.

5. A photographic processing concentrate according to Claim 1 characterized in that the viscosity of said concentrate is 100 to 500 centipoises at a shear rate of 4500 reciprocal seconds.

6. A photographic processing_, concentrate according to Claim 1 characterized in that said photographic processing agent is a developing agent or a fixing agent.

7. A photographic processing concentrate according to Claim 1 characterized in that said processing agent is an aromatic primary amino color developing agent.

8. A photographic processing concentrate according to Claim 1 characterized in that said processing agent is a thiosulfate fixing agent.

9. A photographic processing concentrate according to Claim 1 characterized in that said processing agent is a dihydroxybenzene developing agent.

10. A photographic processing concentrate according to Claim 1 characterized in that said processing agent is a 3-pyrazolidone developing agent.

11. A photographic processing concentrate according to Claim 1 characterized in that said finely-divided solid particles comprise said processing agent.

12. A photographic processing concentrate according to Claim 1 characterized in that said finely-divided solid particles comprise a photographically inert material.

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