Abstract:
A powdered, uniformly-mixed photographic processing composition is prepared with intense mixing of dry photoprocessing chemical components, and by forming uniformly sized agglomerates of the mixed powder. During agglomeration, a hot melt binder polymer is applied in a controlled manner to enable the uniformly-mixed powder particles to stick together with little residue in the final composition. With this process, the mixed powder and agglomerates each have the desired uniformity in size and chemical composition. The resulting dry composition is highly stable, dissolvable and substantially free of dust.

Description:
RELATED APPLICATIONS 
     Commonly assigned U.S. Ser. No. 09/048,619, filed on even date herewith by Gurney, Brayer and Gamble, and entitled &#34;Uniformly Mixed Dry Photographic Developing Composition Containing Antioxidant and Method of Preparation&#34;. 
     Commonly assigned U.S. Ser. No. 09/048,433, filed on even date herewith by Brayer, Gamble and Gurney, and entitled &#34;Uniformly Mixed Dry Photographic Processing Composition and Method of Preparation&#34;. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a uniformly mixed, dry photographic processing composition, and to a method of preparing it. In particular, it relates to powdered black-and-white or color photographic processing compositions having two or more dry photoprocessing chemical components that are uniformly mixed therein. 
     BACKGROUND OF THE INVENTION 
     Conventional images are prepared from imagewise exposed photographic silver halide materials by subjecting them to one or more photographic processing solutions that include the various photochemical components necessary for providing a black-and-white and/or color image. At the very least, such materials require photochemical processing in a developer (to &#34;develop&#34; a silver image from exposed silver halide grains) and a fixer (to &#34;fix&#34; and remove unexposed silver halide). Color photographic processing requires additional steps in order to provide an acceptable dye image, for example a silver bleaching step between color development and fixing. 
     The various chemical formulations used in conventional photoprocessing steps have been prepared in both liquid and solid form. Many of the necessary photochemical components are already in solid form, and in early years of photography, solid processing compositions were common. However, it was often difficult to mix the solid components in a uniform fashion, and long mixing times were often then required for preparing aqueous working strength solutions. In addition, some of the photochemical components were reactive with each other, and could not be kept together without severe losses in activity, providing evidence of poor shelf life or stability. 
     More recently, commercial compositions have been prepared, shipped and used as aqueous solutions. Sometimes, they are provided in concentrated form in order to minimize costs associated with weight and volume, but they then require dilution upon use. 
     Even though concentrates provide some advantage in economy, they are usually storable for only a limited period of time, and the reduced amounts of solvent contained therein still increases shipping and storage costs. Thus, the photographic industry has long sought ways to provide stable photoprocessing formulations in dry form. Various manufacturers have developed powders, granules, solid tablets and other dry forms in recent years in response to these needs. 
     To date, solid compositions have not been widely accepted in the trade. One reason is that fine powdered compositions pose health risks to workers trying to formulate working solutions when the fine dust becomes airborne in the workplace. In addition, powdered chemicals are difficult to mix uniformly and consistently on a small scale, for example, in smaller photoprocessing labs. To achieve high uniformity, high energy mixing is required, and many photoprocessing customers cannot afford the needed mixing equipment or space. As the powders are made more fine, the dust problem increases and solubilization becomes more difficult. 
     In response to these problems, various means have been used in the industry to make powdered or granulated photochemicals, for example, fluidized bed agglomerators (see U.S. Pat. No. 4,923,786 of Kuhnert et al), extrusion processes (see U.S. Pat. No. 3,981,732 of Emoto et al), and freeze drying (U.S. Pat. No. 4,816,384 of Fruge et al). 
     Solid tablet chemistries have also been developed in the industry (see for example, U.S. Pat. No. 5,316,898 of Ueda et al), but the tablets lack widespread acceptance because they are more expensive than conventional photochemical compositions. 
     Clearly, there is a need in the art for dry, uniformly mixed photoprocessing compositions that are affordable, easy and safe to use, and readily prepared using readily available equipment and procedures. This invention is directed to solving these problems and meeting these needs. 
     SUMMARY OF THE INVENTION 
     The present invention provides a powdered, uniformly-mixed photographic processing composition comprising two or more photoprocessing chemical components, wherein: 
     less than 0.2 weight % of the powdered, uniformly mixed photographic processing composition is composed of agglomerates having a diameter of less than 20 μm, and 
     the composition has less than 1 weight % solvent, and less than 3 weight % of a hot melt binder polymer. 
     This composition can be prepared using a method comprising the steps of, in order: 
     A) mixing two or more dry photoprocessing chemical components to form a dry uniform mixture thereof, the mixing being carried out sufficient to provide an aim uniformity of the two or more dry photoprocessing chemical components, the aim uniformity being present when two or more random, same-size samples of the dry uniform mixture are within ±4% of the aim weight % for each photoprocessing chemical component, and 
     B) forming agglomerates of an aim size by agglomerating the dry uniform mixture while simultaneously applying to it a hot melt binder polymer, the hot melt binder polymer application being carried out under conditions to provide agglomerates of the aim size, the agglomerates also having the aim uniformity, and the amount of the hot melt binder polymer in the resulting powered, uniformly mixed photographic processing composition is less than 3 weight %. 
     The present invention can be readily carried out using commercially available equipment to produce highly uniform photographic processing compositions containing photochemicals in uniformly sized and mixed agglomerates. The resulting agglomerates are large enough to avoid a dust problem, but small enough to be readily soluble when the working solutions are made. The powdered compositions may contain all or some of the components that are needed for a given processing bath. Thus, the compositions can form a single-part photoprocessing kit, or be one component of a multi-part photoprocessing kit. 
     The agglomerates within the composition of this invention are free-flowing, readily stored and metered into aqueous solutions, relatively inexpensive, readily soluble in water, and stable during shipping and storage. 
     These advantages are achieved by the unique combination of manufacturing steps and conditions described herein. While the specific equipment used in the method of this invention is not new, it has not heretofore been used to provide the photoprocessing compositions with the requisite properties described above. Specifically, the dry photoprocessing chemical components are mixed in such a manner using specific equipment to meet an &#34;aim&#34; uniformity required for a given composition, so that samples within the composition are substantially the same in composition and proportion of the components. That is, randomly obtained samples of the composition vary in composition by no more than ±4% of a specific or &#34;aim&#34; weight % of the components needed for that composition. 
     By &#34;aim&#34; weight % is meant that, for a given processing composition, there is a desired or aim formulation with specific desired or aim amounts (for example, weight %) of each photoprocessing chemical component. Thus, each photoprocessing chemical component should be within that composition at a specific aim weight %, and the present invention provides formulations wherein the components are present within ±4 of the aim weight % for each component. 
     Once the uniform mixture is obtained, its particles are agglomerated while a hot melt binder polymer is applied to achieve an aim size of agglomerates without losing the aim uniformity achieved during the mixing step. The various details for practicing these steps are provided below with exemplary conditions, equipment and procedures. 
     The use of the hot melt binder in the agglomeration step has several advantages. It reduces the need for drying the composition after agglomeration compared to the use of an aqueous binder mixture as described in U.S. Ser. No. 09/048,619 of Brayer et al and U.S. Ser. No. 09/048,433 of Gurney et al, both noted above. Also, when the aqueous binder mixtures are used, there is a higher potential for oxidation of some of the photoprocessing chemical components, but the use of a hot melt binder reduces that problem. Thus, there is less need for applying a separate antioxidant during agglomeration, and the present invention is more advantageous for preparing compositions that are naturally less stable in the presence of water or air. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The powdered, uniformly mixed photographic processing compositions of this invention comprise at least two dry photoprocessing chemical components, and may include up to 15 such components for the more complicated photoprocessing steps (for example, color development). All of these chemical components are uniformly mixed, meaning that for a given composition, an &#34;aim uniformity&#34; is met during the mixing step (described below). 
     As used herein, &#34;photochemicals&#34; and &#34;photoprocessing chemical components&#34; are used interchangeably to mean chemical materials or compounds that directly or indirectly affect the performance of a particular photoprocessing step, to provide a desired image in an exposed photographic element. 
     The photoprocessing chemical components are generally supplied for mixing in a suitable dry form, either powder or granules, and can be supplied as a single or multiple parts. Usually, multiple formulation &#34;parts&#34; are used when some of the chemical components are not readily compatible with each other. 
     By &#34;aim uniformity&#34; is meant that when two or more random, same-size samples of the dry mixture are analyzed, the samples have substantially the same aim weight % of each of the various photoprocessing chemical components therein, that is within ±4% of that aim weight %, preferably within ±2% and more preferably within ±1%, of that aim weight %. The &#34;aim weight %&#34; is determined by the activity and properties desired for a given composition. For example, the aim weight % for each of the components of a developer composition will likely be different than that for each component included within a fixing composition. One skilled in the art can readily ascertain what aim weight % would be appropriate for a given component of a given composition. Thus, uniformity of chemical composition and effectiveness is insured throughout the composition. 
     Such high uniformity is achieved by intensive mixing of the photoprocessing chemical components (or various formulation parts) in a suitable piece of equipment. One suitable means for such intensive mixing is what is known as a &#34;V-blender&#34; that is commercially available from such sources as Patterson Company and Patterson-Kelly Company. This &#34;V-blender&#34; may also include internal baffles or &#34;intensifier components&#34; or &#34;bars&#34; that make the mixing more intense, that is, impart more shear to the mixing operation. 
     Uniform mixing may be also possible using a double cone blender with an intensifier bar. 
     The key to such mixing is to have sufficiently high shear for a sufficient time to achieve the uniformity noted above. The uniformity can be evaluated during the mixing operation, if desired, by taking random, same-size samples and analyzing them for the weight ratios of various photoprocessing chemical components. A skilled photochemist would have a desired weight % in mind for the components based on their activity and use in photoprocessing. If the random samples are within the required variations (e.g. ±4% of aim weight %), then uniform mixing has been accomplished. If the two samples are outside the required variations, additional mixing time is required. After routine experimentation, the suitable mixing times and conditions would be readily determined and used for future mixing operations. Suitable mixing times will vary depending upon the specific equipment used, but may be as little as 10 minutes and up to several hours. 
     Another benefit of such intense mixing is a uniform size distribution. Preferably, the powder particles produced from the mixing have an average diameter of from about 40 to about 80 μm. This uniform size distribution contributes to the uniformity of the resulting agglomerates formed after mixing. 
     Specific equipment and procedures for mixing are described below in the examples. 
     Following the intense mixing noted above, the powder particles are agglomerated into larger particles that are uniform in size and composition. These agglomerates have an average diameter generally of more than 20 μm, and preferably of more than 100 μm. Thus, no more than 0.2 weight % of the powdered composition is composed of particles or agglomerates that are less than 20 μm in size. 
     On the other end of the scale, the agglomerates are generally no larger than 1000 μm, and preferably less than 900 μm. A preferred range of agglomerate aim sizes is from about 125 to about 850 μm for at least 95% of the agglomerates. No more than 1% of the total dry composition weight is composed of agglomerates having a size of 1000 μm or more. 
     Each agglomerate has the same uniformity in weight ratio of photochemicals (that is &#34;aim uniformity&#34;) achieved in the intense mixing step. 
     Agglomeration can be carried out using conventional agglomerating equipment such as a disk pellitizer that can be obtained from a number of commercial sources (including Ferro-Tech Company and Teledyne-Read Co.). Alternatively, agglomeration can be achieved using a &#34;rolling plane&#34; pelletizer, such as those commercially available from the same commercial sources. The particular conditions and procedures for using such equipment would be readily apparent from the instructions provided with the equipment, and could be modified as described herein to achieve the desired result in size and uniformity. Specific procedures and equipment are described below in Example 1. For example, in a rolling plane pelletizer, adjusting the rotation speed and angle of the pan can be used to control the size of the agglomerates. 
     During agglomeration, the dry mixture is contacted (for example, sprayed) with a hot melt binder polymer that, upon cooling, effectively adheres composition particles together to form the agglomerates. 
     The useful hot melt binder polymers generally have a melting temperature above 40° C., preferably above 60° C., and more preferably at or above 80° C. Generally, the binder polymers can have any melting temperature above 40° C. as long as that temperature is not so high as to adversely affect (for example, photochemical activity or other required function) the photoprocessing chemical components in the dry uniform mixture being agglomerated. In addition, the useful polymers must either be water-soluble or -dispersible (when dissolved in working strength photoprocessing solutions) or readily filterable, and they must be inert to the photoprocessing chemical components when they are in the working strength solutions. 
     Blends of hot melt binder polymers can also be used. Representative examples of hot melt polymers are polyethylene glycols, polypropylene glycols, polyvinyl alcohol and polyvinyl pyrrolidones. The polyethylene glycols are preferred. 
     The hot melt binder polymers are generally applied to the dry mixture of particles as a spray of hot droplets. 
     It is important that there not be too little or too much hot melt binder polymer in the resulting dry composition of this invention. If there is too little binder polymer, the agglomerates will likely be too small and composition &#34;dust&#34; will be a problem. If there is too much binder polymer, the agglomerate size will be too large and there will likely be less uniformity of the photoprocessing chemical components. Generally, the amount of hot melt binder polymer in the finished dry composition should be at least 0.25, and preferably at least 0.5, weight %, and generally no more than 3 and preferably no more than 1, weight %, based on total composition weight. 
     Unlike other agglomeration procedures, a separate antioxidant (or preservative) need not be applied to the dry uniform mixture, in order to prevent oxidation of chemical components in the composition. 
     It is also important for composition stability that the dry composition of this invention comprise less than 1%, preferably less than 0.5%, of solvent based on total composition weight. This may require a drying step after the formation of the agglomerates, using suitable drying equipment and conditions that will not adversely affect the photoprocessing chemical components in the composition. However, one advantage of using the hot melt binder is that less moisture is added to the composition, so the need for drying is considerably reduced. In many cases, it will not be needed at all. 
     It is also an important feature of the dry processing compositions of this invention that they be readily dissolvable in water so they can be used immediately in photographic processes with minimum mixing or agitation. Dissolvability can be determined by observing if a 1 g sample of the composition will dissolve within 120 seconds in 100 g of water at ambient temperature while being stirred at 350 rpm with a 1 inch (2.54 cm) stirring bar. Faster dissolution is more desirable. In some instances, dissolvability can be enhanced by the presence of additional &#34;parts&#34; of a multi-part photoprocessing kit. 
     The dry photographic processing compositions of this invention can be the sole composition needed for a given processing step, or they can be parts of a multi-part photographic processing kit that includes two or more dry or liquid components that are mixed in order to carry out a given processing step. 
     The compositions can include photographic developer compositions (either black &amp; white or color), bleaching compositions, bleach-fixing compositions, fixing compositions, dye image stabilizing compositions, or any other composition can may be useful for providing images in black &amp; white or color negative or reversal films or papers, motion picture films or prints, radiographic films, graphic arts films, or any other photographic silver halide imageable material. 
     The chemical components and layer structures of such materials are well known, for example as described for example, in Research Disclosure, publication 38957, pages 592-639 (September 1996), and the many publications listed therein. Research Disclosure is a publication of Kenneth Mason Publications Ltd., Dudley House, 12 North Street, Emsworth, Hampshire PO10 7DQ England (also available from Emsworth Design Inc., 121 West 19th Street, New York, N.Y. 10011). This reference will be referred to hereinafter as &#34;Research Disclosure&#34;. 
     The various photoprocessing chemical components needed for the various processing compositions of this invention are also well known, as described in the noted Research Disclosure and publications noted therein. 
     For example, black &amp; white developer compositions generally include one or more developing agents including, but not limited to dihydroxybenzene developing agents, and ascorbic acid (and derivatives thereof). Such materials are well known in the art, for example, in U.S. Pat. No. 4,269,929 (Nothnagle) and U.S. Pat. No. 5,702,875 (Opitz et al), both incorporated herein by reference. Hydroquinone is the preferred dihydroxybenzene developing agent, and ascorbic acid is a preferred ascorbic acid type developing agent. 
     The developer compositions generally also include one or more co-developing agents (also known as auxiliary or super-additive developing agents), such as the preferred 3-pyrazolidone compounds (also known as &#34;phenidone&#34; type compounds) described in U.S. Pat. No. 5,264,323 (Purol et al), incorporated herein by reference, as well as in Opitz et al noted above. Other common components include antioxidants (such as sulfites), buffers (such as carbonates and borates), antifoggants, surfactants, anti-sludging agents, and metal ion chelating agents. Other details of black and white developer compositions are provided in Research Disclosure, Section XIX. 
     Color developer compositions are also well known. They generally include one or more color developing agents (such as primary aromatic amino color developing agents including p-phenylenediamines) as described for example in U.S. Pat. No. 4,892,804 (Vincent et al) and Research Disclosure, Section XIX. Such compositions also generally include one or more antioxidants (or preservatives) such as sulfite and hydroxylamines as described above, antifoggants, metal ion chelating agents (also known as sequestering agents), surfactants, buffers, biocides or anti-fungal agents, anti-sludging agents, optical brighteners (or stain-reducing agents), water-solubilizing agents, development accelerators, and other components known to one skilled in the art, as described in Research Disclosure, Section XIX, noted above. 
     Bleaching, bleach-fixing and fixing solutions are generally used after development of photographic materials, and the components of such solutions are well known, as described in Research Disclosure Section XX. Bleaching and bleach-fixing solutions generally contain one or more bleaching agents and/or fixing agents. Bleaching agents include peroxides, periodates, persulfates, metal (such as ferric) salts and complexes of carboxylic acids. Fixing agents can include thiosulfates, thiocyanates and other compounds that solubilize silver halide in the photographic material. Such solutions can also include rehalogenating agents, buffers, metal ion chelating agents, biocides, bleaching accelerators, fixing accelerators and other components well known to a skilled worker in the art. 
     Stabilizing solutions are also known from Research Disclosure, noted above. They may include one or more surfactants, dye image stabilizing compounds, metal ion chelating agents, optical brightening compounds, stain-reducing compounds, anti-scumming agents, biocides, buffers and other components known to a skilled artisan. 
     For all of the compositions of this invention, a skilled artisan would know the various amounts of photoprocessing chemical components to be mixed in a given composition for a given photoprocessing purpose. An important aspect of this invention is that, for a given composition, the mixing and agglomeration steps provide desired uniformity of the photoprocessing chemical components consistent with a desired &#34;aim weight ratio&#34; of one component to another. 
     The various examples shown below are representative of several of the dry photographic processing compositions of this invention. Some of them are prepared as &#34;single-part&#34; compositions while others are included as multi-part photoprocessing kits. 
    
    
     EXAMPLE 1 
     Preparation of Black &amp; White Radiographic Developer 
     A two-part black &amp; white developer useful for processing radiographic films was prepared in the following manner. Each &#34;part&#34; was prepared as a dry powder and can be packaged as a component of a processing kit. The individual &#34;parts&#34; contained the following chemical components: 
     
         ______________________________________Part A:Ascorbic acid developing agent                     6.11 kg4-Hydroxymethyl-4-methyl-1-phenyl-                    0.477 kg3-pyrazolidoneBenzotriazole            0.038  kgPotassium bromide (powdered)                    0.764  kgSodium sulfite            7.6 kgDiethylenetriaminepentaacetic acid,                    0.328 kgpentasodium saltPart B:Potassium carbonate buffer______________________________________ 
    
     Part A was mixed for 20 minutes under ambient conditions in a commercially available V-blender (Patterson-Kelly Company) containing a disintegrator (or intensifier), at 16 rpm for the shell and 2300 rpm for the disintegrator. The resulting highly mixed powder was then introduced to a commercially available Ferro-Tech rolling plane pelletizer, where agglomeration was carried out under ambient conditions for 30 minutes. During agglomeration, polyethylene glycol 800 (800 mol. wt.) was sprayed as a hot melt onto the dry uniform mixture at a rate of about 16 mg/min. No antioxidant was applied to the dry uniform mixture. 
     The resulting agglomerates, random samples were determined to have the desired uniformity of chemical components (within ±2% of the aim weight %), and no more than 0.2 weight % of the composition consisted of agglomerates or particles having a diameter of less than 20 μm, and less than 1 weight % were composed of agglomerates having a diameter greater than 1000 μm. The resulting agglomerates contained less than 3 weight % of the polyethylene glycol 800, based on total composition weight. 
     EXAMPLE 2 
     Preparation of Color Developer 
     A three-part color developer useful for processing color negative films was prepared in the following manner. Each &#34;part&#34; was prepared as a dry powder and can be packaged as a component of a processing kit. The individual &#34;parts&#34; contained the following chemical components: 
     
         ______________________________________Part A:CD4 color developing agent*                    4.189 kgHydroxylamine sulfate antioxidant                     2.47 kgSodium sulfite           3.429 kgSodium bromide          175.397 gPropylenediaminetetraacetic acid                    2.414 kgPart B:Potassium bicarbonate bufferPart C:Potassium carbonate buffer______________________________________ *CD4 is 4(N-ethyl-N-hydroxyethylamino)-2-methylaniline sulfate 
    
     Part A was mixed and agglomerated using the equipment and procedures described in Example 1, except using polyethylene glycol 900 as the hot melt binder, with similar good results. 
     EXAMPLE 3 
     Preparation of Ammonium Fixing Composition 
     A black &amp; white film fixing composition was prepared as a single-part composition in the following manner with the following chemical components: 
     
         ______________________________________Ammonium thiosulfate     4.617 kgTetrasodium ethylenediamine tetraacetic                      49 gacidSodium sulfite             930 gCitric acid                634 gAmmonium thiocyanate     5.684 kg______________________________________ 
    
     This formulation was mixed and agglomerated using the procedures and equipment described in Example 1 with good results. 
     EXAMPLE 4 
     Preparation of Sodium Fixing Composition 
     A sodium based fixing composition was similarly prepared having the following components: 
     
         ______________________________________Sodium thiosulfate       14.37  kgSodium tetraborate, pentahydrate                      151 gSodium metabisulfite     1.216  kgSodium citrate, dihydrate                      81 gAmmonium alum sulfate, dodecahydrate                    2.437 kgBoric anhydride (60 mesh)                      202 gCitric acid, anhydrous     72 gSodium acetate, anhydrous                    1.467 kg______________________________________ 
    
     This formulation was mixed and agglomerated using the procedures and equipment described in Example 1 with good results. 
     The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.