PHOTOGRAPHIC DISPERSION MANUFACTURE

Abstract: A process for manufacturing a photographic coupler dispersion. The process involves mixing a coupler and a solvent to form a coupler/solvent mixture, and then subjecting the coupler/solvent mixture to microwave energy to heat the mixture and so cause dissolution of the coupler. In an alternative arrangement, a batch mixture of the coupler and solvent is placed in a microwave heating station so as to heat the batch mixture.

Description: TITLE OF THE INVENTION PHOTOGRAPHIC DISPERSION MANUFACTURE BACKGROUND OF THE INVENTION Field of the Invention This invention relates generally to the manufacture of photographic dispersions, and in particular to a process for manufacturing dispersions incorporating active photographic ingredients used in photographic products. The process is applicable to dispersions used to incorporate couplers or dye-forming materials into emulsions during the production of color films and papers. It will be convenient to hereinafter disclose the process in relation to this exemplary application, although it should be appreciated that the invention is not limited to that application. Description of the Related Art A conventional process for incorporating couplers into photographic emulsions involves dissolving a coupler in a solvent which is then dispersed in a surfactant/gelatin/water solution forming an emulsion base. Dissolution usually occurs at high temperature which requires having to hold the coupler solution at . elevated temperatures for relatively long periods. This has been found to lead to significant coupler decomposition. In such processes where the coupler being incorporated is particularly prone to thermal degradation, high concentrations of solvent are used to enable the dissolution of the coupler at low temperatures. However, the excess solvent must then be removed from the solution, such as by washing or evaporation. This leads to increased waste discharge and consequent production cost increases. These dispersions have smaller particle sizes than those produced with less solvent - a desirable property in such preparations. SUMMARY OF THE INVENTION An object of the present invention is to alleviate these disadvantages with an alternative, improved dispersion manufacturing process, particularly suitable for coupler dispersed emulsions. Another object is the provision of a process for producing a photographic coupler solution in which the likelihood of thermal degradation of the coupler during production is reduced. A further object of the present invention is to provide a process in which photographic coupler dispersions can be manufactured on a continuous basis. Another object is to provide an improved process for preparing a coupler solution, which process can form part of a conventional batchwise dispersion manufacturing process. With these objects in mind, the present invention broadly provides a process for manufacturing a photographic coupler dispersion, including: mixing a coupler and a solvent to form a coupler/solvent mixture; and, subjecting the coupler/solvent mixture to microwave energy to heat the mixture and thereby cause dissolution of the coupler. The application of microwave energy achieves relatively rapid heating of the mixture, compared with conventional convection or conduction heating. This has the benefit of rapidly dissolving the coupler into a coupler solution and thereby minimising the likelihood of thermal degradation of the coupler. It will be appreciated that the period of time during which the coupler/solvent mixture is subjected to microwave energy will vary depending on a number of factors, including the microwave energy output and the volume of the mixture being heated. By way of example, however, in at least one embodiment the coupler/solvent mixture is subjected to microwave energy for a period of less than about 2 minutes. In at least one embodiment, the coupler/solvent mixture is fed on a continuous basis through a heating station at which the mixture is subjected to the microwave energy. In an alternative embodiment, the coupler/solvent mixture can be batch-placed at the heating station for subjecting to the microwave energy. In at least one embodiment, the process further includes mixing the coupler with an emulsion base. In one arrangement, mixing occurs between the coupler solution and the emulsion base. Thus, as the coupler solution emerges, or is removed, from the heating station it is mixed with the emulsion base. In an alternative arrangement, coupler and emulsion base constituents such as water and surfactant are mixed together prior to their heating with the microwave energy. Solvent may also be included in this arrangement. The combined coupler solution and emulsion base produces a crude emulsion or premix. A premix with particle diameter of about 0.5 micrometres is provided in one embodiment. In at least one embodiment of the process, the emulsion base is also separately prepared on a continuous basis. In an alternative embodiment, the emulsion base is batch prepared. That preparation is coordinated with the preparation of the coupler solution to enable appropriately timed mixing together. That mixing preferably occurs without substantial holding times following separate preparation of the coupler solution and the emulsion base. Moreover, where the coupler solution and emulsion base are prepared on a continuous basis, then their preparation is co-ordinated to enable progressive mixing together. The emulsion base is of any suitable composition well known to those skilled in the relevant art. In one embodiment, the emulsion base comprises a gelatin/water solution. A surfactant may also be included in the solution, in this embodiment. Where the emulsion base is mixed with the heated coupler solution then, in at least one embodiment, the emulsion base is separately pre-heated prior to mixing. That emulsion base heating occurs immediately prior to mixing with the coupler solution, in one embodiment. An initial heating of the gelatin/water solution may occur prior to mixing with the surfactant. That heating is achieved by subjecting the emulsion base to any suitable energy source, including microwave energy, and convected or conducted heat energy. In at least one embodiment, the process further includes homogenising the coupler solution/emulsion base premix to form an emulsion formulation. The emulsion formulation may then be chilled and stored prior to use, or transported directly to a coating station of a photographic film manufacturing line. DESCRIPTION OF THE PREFERRED EMBODIMENT The following description refers to one example of a continuous manufacturing plant used in carrying out a preferred embodiment of the process of the present invention. To facilitate an understanding of the preferred process invention, reference is made to this apparatus as schematically shown in the accompanying drawing. It is to be understood that the process is not limited to the use of this exemplary plant. Referring to the drawing, there is generally shown a schematic layout of a plant 1 for use in a process of producing a photographic emulsion formulation having a coupler dispersion. The plant 1 includes separate supply sources of a coupler and solvent. The coupler is supplied from a supply container 2 through a supply line 3. A conveyor device 4, such as a screw conveyor 5 driven by a drive motor 6 coupled thereto, meters the coupler through the line 3. Constituents of the solvent are supplied from separate containers 7 through supply lines 8. Control valve 9 installed within lines 8 enable controlled supply of those constituents. The plant 1 also includes a coupler mixture preparation apparatus 10 at which the coupler and solvent are mixed together. Apparatus 10 includes a preparation vessel 11 into which a measured batch of the coupler and solvent are supplied through the lines 3 and 8. This vessel 11 may be mounted to ensure precise measurement of the coupler and solvent in each batch. To that end, the vessel 11 may be mounted on load cells or other measurement equipment 12. The preparation apparatus 10 also has a mixing device 13 for mixing the batch of coupler and solvent. The device 13 includes at least one mixing blade 14 rotatably connected to drive motor 15 to cause rotation in order to thoroughly mix the coupler and solvent. The preparation apparatus 10 provides for mixing of the coupler and solvent at ambient temperature. However, it should be appreciated that in alternative applications mixing may occur at other specified temperatures. Elevated mixing temperatures may involve pressurising the preparation vessel 11 and other components of the plant 1 in which the process proceeds. The preparation vessel 11 has an outlet 16 therefrom and the preparation apparatus 10 also includes a supply pump 17 connected to the outlet 16 for withdrawing the coupler/solvent mixture batch. The pump 17 includes a screw pump 18 driven by a suitable motor 19. As shown, the plant 1 can include a holding apparatus 20 in which the coupler/solvent mixture can be held prior to further processing. This apparatus 20 includes a holding vessel 21 into which the mixture is pumped by pump 17 through transfer line 22. A further mixing device 23, comprising at least one rotatable mixing blade 24 driven by a drive motor 25, is provided to maintain the mixture consistency within the holding vessel 21. A return line 26 may be connected into transfer line 22 through control valve 27, in order to allow return of at least part of the coupler/solvent mixture to the preparation vessel 11. This return may be used to provide make-up feed for vessel 11 and thereby improve blending of the coupler/solvent mixture between batches. The holding vessel 21 has an outlet 28 therefrom, and the holding apparatus 20 includes a supply pump 29 connected to the outlet 28 for withdrawing the coupler/solvent mixture as required. The plant 1 further includes heating means 30 for subjecting the coupler/solvent mixture to microwave energy to form a coupler solution. The heating means 30 includes a heating chamber 31 through which a feed line 32 from the supply pump 29 passes. The feed line 32 has a heating section 33 within the heating chamber 31, and it is in that section 33 that the coupler/solvent mixture is subjected to the microwave energy. In this embodiment, the heating section 33 of the feed line 32 has a coil formation. This provides a heating section 33 of sufficient length to achieve satisfactory heating within a relatively small heating chamber 31, having regard to the rate of feed of the coupler/solvent mixture and the power of the microwave energy. It will be appreciated that other heating section formations may be equally suitable. The heating means 30 includes a microwave heating unit 34, providing the chamber 31. The heating unit 34 has suitable controls (not shown) for controlling the supply of microwave energy to the chamber 31. At least the heating section 33 of the feed line 32 is composed of a material transparent to microwave radiation. That material may include plastics materials, such as TEFLON. The heating unit 34 has a heating capacity suitable for rapidly heating the coupler/solvent mixture passing along the " heating section 33. Two examples of heating units 34 have 600 Watt and 3 Kilo Watt power outputs to achieve heating of the mixture in less than about 2 minutes. The plant 1 may include a surge vessel 35 into which the heated coupler solution flows for deaerating and holding prior to further processing. Surge vessel 35 has a feed line 36 from which the solution may be drawn as required. The plant 1 further provides for the separate preparation of an emulsion base to be mixed with the coupler solution in order to form a dispersed coupler formulation. The emulsion base preparation involves separate supply sources of emulsion base constituents including gelatin, water and a surfactant. Gelatin is supplied from a supply container 37 through a supply line 38. A conveyor device 39 such as a screw conveyor 40 driven by a drive motor 41 coupled thereto, meters the gelatin through the line 38. Water and other constituents for the emulsion base are supplied from separate containers 42 through supply lines 43. Control valves 44 installed within lines 43 enable controlled supply, including coarse or fine feed, of those constituents. An emulsion base preparation apparatus 45 is provided for mixing together the gelatin, water and other constituents provided through supply lines 38 and 43. The apparatus 45 includes a preparation vessel 46 into which a measured batch of the constituents are supplied. The preparation apparatus 45 also includes a mixing device 47 for mixing the emulsion base constituents in vessel 46. That device 47 includes at least one mixing blade 48 rotatably connected to a drive motor 49 to cause rotation to thoroughly mix the constituents. The preparation vessel 46 has outlet 50 therefrom, and the preparation apparatus 45 includes a supply pump 51 connected thereto through transfer line 52 for withdrawing the emulsion base. The preparation apparatus 45 includes a heating device 53 for heating the emulsion base during preparation. In the plant 1 as shown, the heating device 53 is located externally of the vessel 46, and the emulsion base is recirculated through the heating device 53. To that end, a recirculating line 54 is connected between the transfer line 52, downstream of the pump 51 through control valve 55, and preparation vessel 46. This recirculating line 54 contains the heating device 53 so that the emulsion base can be circulated from the preparation vessel 46 through the heating device 53 and back to the preparation vessel 46. The heating device 53 is of any suitable construction. In that regard, the device 53 may be a microwave heating unit, or a convection or conduction heating unit. The preparation apparatus 45 may be provided with a holding apparatus 56 in which the emulsion base can be held prior to further processing. The holding apparatus 56 includes a holding vessel 57 into which the emulsion base can be supplied through transfer line 52. A further mixing device 58, comprising at least one rotatable mixing blade 59 driven by a drive motor 60, is provided to maintain consistency within the emulsion base. The holding vessel 57 has an outlet 61 from which a feed line 62 extends. The emulsion base preparation apparatus 45 further includes a supply of surfactant. That surfactant is supplied from a supply container 63, through supply line 64, connecting with feed line 62. The preparation apparatus 45 may include a further heating device 65 for reheating the emulsion base downstream of the surfactant addition. To that end, the heating device 65 is installed in feed line 62 downstream of the connection with the supply line 64. Again, the heating device 65 can be of any suitable construction. The plant 1 also has a premix apparatus 66 in which the coupler solution and emulsion base are mixed together. The premix apparatus 66 includes a premix stirrer 67 to which the feed lines 36 and 62 are connected. The premix stirrer 67 is operable to intimately mix the coupler solution and emulsion base. The stirrer 67 may be of a rotor-stator high speed type having a flow through attachment. The connection of the feed lines 36 and 62 may be through a metering device 68, operable to meter correct proportions of the coupler solution and emulsion base into the stirrer 67. This metering device 68 may include a metering pump 69, through which feed lines 36, 62 and 64 pass. The plant 1 may also include an homogeniser or similar milling device (not shown) for homogenising the premix to produce a coupler formulation. This homogeniser may be incorporated into the premix apparatus 66, and in particular the stirrer 67 to simultaneously mix and homogenise the coupler solution and emulsion base. Alternatively, a separate homogeniser may be provided to subsequently homogenise the crude emulsion or premix. In using the plant 1 to prepare a coupler dispersion formulation according to the process of the present invention, a coupler and solvents are mixed in preparation vessel 11 to form a uniform paste mixture. This mixture is conveyed by supply pump 17 to holding vessel 21. Simultaneously, an emulsion base is prepared by preparation apparatus 45. Emulsion constituents are supplied to preparation vessel 46 where they are mixed together and heated by heating device 53. This emulsion base is then supplied through transfer line 52 into holding vessel 57. The coupler/solvent mixture and the emulsion base are then separately drawn from their holding vessels 21 and 57 on a continuous basis. The coupler/solvent mixture is pumped continuously by supply pump 29 through feed line 32 which passes through microwave heating unit 34. The flow rate of the mixture can be varied, but normally the residence time of the mixture in the microwave heating chamber 31 is about 1 minute. At the exit from the heating chamber 31, the coupler has been completely dissolved to form a coupler solution. The coupler solution then passes through the surge vessel 35 and metered through pump 69 to the premix stirrer 67. The emulsion base is drawn from its holding vessel 57 and is metered through metering pump 69 and heating device 65 into the premix stirrer 67. The coupler solution and emulsion base are mixed continuously in the premix stirrer 67 to form a crude emulsion or premix. From the premix stirrer 67, the premix may be passed to a homogeniser in which the particle size is reduced to desired levels. In one example of a batch process of the present invention, one kilogram of a coupler, the 5-[2-(2,4-Di-tert-amylphenoxy)-hexanamido]-2-(p-cyanophenyl- ureido)phenol was mixed at room temperature with one kilogram of a solvent, dibutyl phthalate, to form a uniform paste. An emulsion base having the following composition was also prepared: Gelatin 231 grams Water 1802 grams Alkanol XC (10% solution) 257 grams and held at a temperature of 66°C. The coupler/solvent mixture was then pumped through a microwave heating unit at a rate of 42 grams per minute. The mixture was heated to 138°C in the heating chamber and emerged as a clear liquid, with all of the coupler dissolved. The residence time of the mixture in the heating chamber was approximately 1.7 minutes. The heated coupler solution was then run into the emulsion base whilst being stirred for a sufficient time to add 400 grams. The crude emulsion or premix thus formed was then given a single pass through an homogeniser. The resulting emulsion formulation had a mean particle diameter of 0.28 micrometres and showed no significant coupler crystallisation. Spectrophotometric measurement of the microwave heated coupler solution samples showed an absorbance at 450 nanometres, approximately /7 of that of a sample of a conventionally heated solution, indicating a much lower level of coupler decomposition and formation of colored impurities. In a second example of the process the crude emulsion or premix as prepared above was passed repeatedly through an homogeniser. The particles obtained were as follows: No. Passes Particle Piam (nanometres) 1 0.26 2 0.18 3 0.16 4 0.15 5 0.15 6 0.15 The particle size obtained after two passes was comparable to that obtained with washed formulations. The process of the present invention exhibits several advantages over conventional processes for producing coupling dispersion formulations. Those advantages are related to both the manner of heating of the coupler/solvent mixture and the continuity of the process. It may be seen that microwave heating can be advantageously applied as part of a novel, continuous manufacturing process as described herein. Alternatively, it can form a stage of a conventional batch process. The microwave energy heating of the mixture occurs very rapidly in the present process. Moreover, there is no contact of the mixture with high temperature surfaces, so that generally uniform heating occurs. As a result, there is reduced thermal degradation of the coupler when compared with heating in conventional processes. The use of microwave energy also achieves efficient heating of the mixture. The use of reduced quantities of solvent in coupler solutions, compared with prior art processes involving the use of excess solvent which is subsequently washed or evaporated, provides reductions in operating costs, reduced waste discharge and improved physical qualities in the solution. The continuous version of the process avoids formulation variations evident in batch-to-batch formulations. Moreover, the ability to produce formulations as required for use in manufacturing photographic products, can improve overall manufacturing productivity and reduce wastage. The need to chill store the formulations may be reduced where "just-in-time" production and supply of the formulations is established. The cycle time involved in batch processing may also be reduced through the implementation of the continuous process, leading to operating efficiencies. Finally, it will be appreciated that various modifications and/or additions may be made to the process without departing from the ambit of the invention as defined in the claims appended hereto.

Claims: CLAIMS : 1. A process for manufacturing a photographic coupler dispersion, including: mixing a coupler and a solvent to form a coupler/solvent mixture; and, subjecting the coupler/solvent mixture to microwave energy to heat the mixture and thereby cause dissolution of the coupler. 2. A process as claimed in claim 1, wherein subjecting the coupler/solvent mixture to microwave energy includes progressively feeding a continuous mixture of the coupler and solvent through a microwave heating station so as to progressively heat the continuous mixture. 3. A process as claimed in claim 1, wherein subjecting the coupler/solvent mixture to microwave energy includes placing a batch mixture of the coupler and solvent in a microwave heating station so as to heat the batch mixture. 4. A process as claimed in claim 1, and further including mixing the coupler with an emulsion base. 5. A process as claimed in claim 4, wherein the emulsion base is mixed with the coupler/solvent mixture following the heating causing dissolution of the coupler. 6. A process as claimed in claim 5, and further including heating the emulsion base prior to mixing with the coupler solution. 7. A process as claimed in claim 4, wherein constituents for the emulsion base are mixed with the coupler prior to the heating causing dissolution of the coupler. 8. A process as claimed in claim 4, wherein the combined coupler solution and emulsion base produce a crude emulsion having a particle diameter of about 0.5 micrometres. 9. A process as claimed in claim 2, and further including mixing the heated coupler solution with an emulsion base, the emulsion base being progressively introduced into and mixed with the continuously fed coupler/solvent mixture following emergence of the heated coupler solution from the heating station. 10. A process as claimed in claim 9, and further including heating the emulsion base prior to mixing with the heated coupler solution. 11. A process as claimed in claim 3, and further including mixing the heated coupler solution with an emulsion base, a batch of the emulsion base being introduced into and mixed with the batch heated coupler/solvent mixture following removal of the heated coupler solution from the heating station. 12. A process as claimed in claim 11, and further including heating the emulsion base prior to mixing with the heated coupler solution.

Inventors: COOPES IAN HENRY, ELDER DAVID WILLIAM, MAHKRI ABDUS SATTAR SAMAD, TANG DONALD TAT-ON, COOPES, IAN, HENRY, ELDER, DAVID, WILLIAM, MAHKRI, ABDUS, SATTAR, SAMAD, TANG, DONALD, TAT-ON
Applicants: EASTMAN KODAK CO, EASTMAN KODAK COMPANY
Application year: 1992
Main classification: G03C7
IPC codes: G03C1, G03C7