Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03C—PHOTOSENSITIVE MATERIALS FOR PHOTOGRAPHIC PURPOSES; PHOTOGRAPHIC PROCESSES, e.g. CINE, X-RAY, COLOUR, STEREO-PHOTOGRAPHIC PROCESSES; AUXILIARY PROCESSES IN PHOTOGRAPHY
  • G03C1/00—Photosensitive materials
  • G03C1/005—Silver halide emulsions; Preparation thereof; Physical treatment thereof; Incorporation of additives therein
  • G03C1/015—Apparatus or processes for the preparation of emulsions
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03C—PHOTOSENSITIVE MATERIALS FOR PHOTOGRAPHIC PURPOSES; PHOTOGRAPHIC PROCESSES, e.g. CINE, X-RAY, COLOUR, STEREO-PHOTOGRAPHIC PROCESSES; AUXILIARY PROCESSES IN PHOTOGRAPHY
  • G03C1/00—Photosensitive materials
  • G03C1/005—Silver halide emulsions; Preparation thereof; Physical treatment thereof; Incorporation of additives therein
  • G03C1/015—Apparatus or processes for the preparation of emulsions
  • G03C2001/0157—Ultrafiltration

Definitions

• the present invention relates to a process for the precipitation of silver halides.
• Another known process for the preparation of silver halides is the so-called "twin jet" tank process, in which an aqueous solution of a silver salt and an aqueous solution of a metal halide are simultaneously introduced into a reaction vessel which contains a dispersing medium.
• the precipitation of the silver halide grains advantageously takes place in two distinct stages. In the first stage or nucleation stage, silver halide grains start to form, then in the second stage, or growth stage, an additional quantity of silver halides is formed as a reaction product which precipitate on the silver halide grains formed in the first step, resulting in the growth of these silver halide grains.
• the double jet, silver tank precipitation methods are usually carried out with vigorous stirring of the reagents whose volume in the reaction vessel increases continuously during the precipitation of the silver halides.
• Continuous twin jet precipitation methods are known in the art, as described in British Patent 1,302,405 and United States Patent 3,801,326 and 4,046,576, where the volume of the reaction vessel remains constant during precipitation of silver halides, due to continuous elimination of dispersion silver halides, which gives a practically constant working condition.
• U.S. Patent 3,790,386 describes a variant of the process for the preparation of silver halides, by continuous jet, in which the dispersion of silver halides is continuously removed from a container. constant volume reaction and introduced into a separate container from the dispersion container, this second container serving for maturation and having a volume at least equal to ten times the volume of the reaction container.
• this second container serving for maturation and having a volume at least equal to ten times the volume of the reaction container.
• Analogous, continuous, double-jet precipitation methods and devices are described in US Pat. Nos. 3,897,935, 4,147,551 and 4,171,224.
• the present invention relates to a method for precipitating silver halides which consists in forming a dispersion of photosensitive silver halides by reaction of a silver salt in solution and a metal halide in solution, this reaction allows both to form seeds of silver halides and soluble salts in the presence of a dispersing medium, then to grow the grains of silver halides in a reaction vessel where the seeds of silver halides and the dispersion medium are present, this process being characterized in that, while the silver halides present in the dispersion medium are grown, during the grain growth stage, the volume of the dispersion is reduced by withdrawing a fraction of the dispersion medium, maintaining the silver halide grains in the residual dispersion.
• the method according to the invention makes it possible (1) to avoid the tendency to the continuous formation of grains of silver halides during the growth stage of the precipitation process, i.e. avoids renucleation, (2) to reduce the crystal imperfections of the silver halide grains, (3) to reduce the formation of the haze by reduction in the silver halide grains, and (4) to obtain silver halide grains which are more reproducible in sensitivity.
• the process according to the invention makes it possible to operate with a more constant volume of reaction medium, in comparison with the usual precipitation methods, in tanks, of the prior art.
• This result makes it easier to balance the volume of the reaction vessel with the volume of the reaction medium.
• peptizing agents such as hydrophilic colloidal binders, which are usually used in the preparation of silver halide dispersions, make it possible to avoid flocculation of the latter.
• hydrophilic colloids in the dispersion medium has certain drawbacks in the preparation of the silver halide grains, in particular as regards the crystal structure of the silver halides, the size distribution of the silver halide grains and the nature and distribution of crystal defects, as described in the book "The Theory of the Photography Process” by Mees and James, 2nd Ed., p. 85 and 4th Ed. P. 29 to 31.
• the presence of hydrophilic colloids in the reaction medium can also interfere with the addition of photographic adjuvants in the silver halide grains.
• FIG. 1 represents a diagram of the double-jet precipitation method according to the invention where the receptacle 1 for forming silver halides initially contains a dispersion medium 3, the reaction medium being stirred by a agitator 5. The reaction medium is stirred, then a solution of a silver salt is introduced into the reaction medium by jet 7, and simultaneously a solution of a metal halide is introduced into the reaction medium by the second jet 9.
• a third jet 11 is shown, the use of which will be described later.
• the stirring system allows the saline solutions to mix almost instantly with the dispersion medium.
• the metal halide solution contains a water soluble halide which reacts with the water soluble silver salt contained in the silver salt solution to form a silver halide as the main product of the reaction.
• a practically uniform dispersion of grains of silver halides is formed.
• the formation of additional silver halide grains during the step of grain growth is minimized, but when preparing dispersions of polydispersed silver halides, the formation of additional silver halide grains continues, while the silver halides formed in step previous continue to grow, and thus obtain silver halide grains whose size varies over a wide range.
• the volume of the medium contained in the reaction vessel can be controlled by removing a fraction of the dispersion of silver halides by the stream 13 which is directed to an ultrafiltration device 15.
• This ultrafiltration device makes it possible to reduce the volume of the silver halide dispersion, separating part of the dispersion medium represented by stream 17, while maintaining the silver halide grains in the residual silver halide dispersion which is returned to the reaction vessel by the stream 19.
• the ultrafiltration device comprises the central ultrafiltration unit 15, the streams 13, 17 and 19, as well as other elements, not shown, in FIG. 1, for example pumps, valves, volumeters, etc.
• the ultrafiltration operation is particularly effective during the growth stage, but the ultrafiltration device can be started during the nuelization stage or even before the introduction of the silver salt.
• a peptizing agent such as a hydrophilic colloidal binder
• This peptizing agent may be present in the reaction medium before the introduction of the saline solutions.
• the peptizing agent can be introduced by the third jet 11 or by the jets 7 and / or 9 which serve to introduce the aqueous solutions of the silver salts and metal halides.
• This peptizing agent is not essential during the lubrication step, but it is advantageously present during at least a fraction of the ultrafiltration step.
• this peptizing agent is advantageously present during the two stages, that is to say during the oiling stage and during the stage of growth of the halide grains of money.
• the ultrafiltration device 15 removes practically no fraction of the peptizing agent but selectively eliminates the aqueous solution of soluble salts formed as by-products of the precipitation of silver halides.
• a silver nitrate solution is used as the aqueous silver salt solution which reacts with an alkali metal halide to form a substantially water-insoluble silver halide as the main product.
• an alkali metal nitrate is also obtained as a by-product of the reaction, the ultrafiltration making it possible to remove both the liquid dispersion medium and the alkali metal ttitrate in solution in the dispersion medium.
• the elimination by ultrafiltration of the soluble salts formed as by-products of the precipitation of silver halides is particularly important when the process according to the invention is used to prepare aqueous dispersions of photosensitive silver halides, in particular the absence of a peptizing agent.
• the additional addition of dispersing medium and the carrying out of the ultrafiltration act together to reduce the concentration of soluble salts in the reaction vessel.
• the contribution of this addition of dispersion medium to the container where the aqueous dispersion of silver halides is prepared is at least partially counterbalanced by the elimination of the dispersion medium in the ultrafiltration device.
• This additional dispersion medium can be introduced into the container where the precipitation reaction of the silver halides is carried out by operating by any suitable means.
• this third jet 11 is used to introduce a dilute solution of a metal halide, advantageously a solution of a metal halide whose molarity is equal to or. less than 0.01.
• the concentration of soluble salts, formed as by-products of the precipitation of silver halides, in the reaction is less than 0.1 mole per liter, advantageously less than 0.05 mole per liter and preferably less than 0.01 mole per liter.
• concentration of soluble salts formed as by-products can reach the values usually encountered in the processes for preparing silver halides, this concentration possibly reaching, for example, up to 3 moles per liter of reaction medium.
• the ultrafiltration operation can be carried out at any stage of the precipitation of silver halides, but it is advantageously started during at least part of the stage of growth of the halide grains of silver, and very advantageously it is carried out during this whole stage of growth of the silver halide grains. Although it was reasonable to think that the ultrafiltration operation should be postponed until the end of the oiling stage, it appeared that one could start this ultrafiltration operation even during the lubrication step or even from the start of the implementation of the process according to the invention before the start of precipitation of the silver halides.
• the ultrafiltration technique used during the precipitation of silver halide grains has a certain number of particular advantages and avoids certain disadvantages of the other known separation methods;
• a particular advantage of the ultrafiltration technique is that the dispersion of silver halides withdrawn from the reaction medium can be returned to the reaction vessel after a very short period of time.
• the duration of the ultrafiltration operation is advantageously less than 10%, very advantageously less than 1% of the total duration of the reaction for preparing the silver halides.
• the risk of significantly stopping the growth of the silver halide grains by subtracting a fraction of the reaction medium in order to subject it to the ultrafiltration operation is slight.
• Another particular advantage of the ultrafiltration operation resides in the fact that it is necessary to withdraw a very small proportion of the dispersion of the silver halides contained in the container where the precipitation reaction takes place.
• the quantity of silver halides contained in the ultrafiltration device represents less than 50%, and advantageously less than 25%, of the silver halides contained in the reaction vessel.
• any usual dispersion medium may be present at the start of the reaction in the container where the precipitation of the silver halides will take place.
• the volume of the dispersion medium present at the start of the reaction in the container where the precipitation will take place silver halides represents approximately 10% to 90%, advantageously 20% to 80% of the volume of the dispersion of the silver halides to be prepared.
• the dispersion medium is advantageously water or a dispersion of a peptizing agent in water, which may contain other adjuvants such as one or more agents for maturing silver halides as described more fully below. .
• the process according to the invention is carried out in the presence of a peptizing agent, it is advantageously present in the dispersion medium, at the start of precipitation, at a concentration at least equal to 10%, and advantageously at least equal to 20% of the total amount of peptizing agent present at the end of the preparation of the silver halides, the additional peptizing agent being added during the addition of the silver salt and the metal halide, soluble in the water.
• a small proportion, for example a proportion of less than 10% of one of the solutions of the silver salt and of the metal halide is also present in the reaction medium, at the start of the precipitation of the silver halides, to adjust the concentration of silver ions in the reaction medium, at the start of precipitation of the silver halides.
• the silver ion concentration is measured by the inverse logarithm of the silver ion or pAg concentration.
• the water-soluble silver salt and metal halide solutions can be used and used for their simultaneous introduction into the reaction medium, using the solutions and methods known from the prior art for preparing silver halide emulsions by the double jet method.
• Article 17643 of the journal "Research Disclosure", Vol. 176, December 1978, paragraph I, and U.S. Patents 2,222,264, 3,655,394, 3,672,900 and 3,761,276 as well as German Patent Application 2,107,118 describe methods of precipitating silver halides by double jet, useful for implementing the process according to the invention.
• the silver salt solution is an aqueous solution of a water soluble silver salt such as silver nitrate and a solution of a metal halide which is usually an aqueous solution of one or more halides of alkali metals such as sodium or potassium or of an alkaline earth metal such as calcium or magnesium. or an ammonium halide.
• Useful halides include chlorides, bromides and iodides. The proportion of iodide is usually less than 20% by mole, advantageously less than 6% by mole relative to all of the halides present.
• metal halides When several metal halides are used, they can be introduced either in the form of a single jet, or separately, into the reaction medium.
• aqueous solutions of a silver salt and aqueous solutions of metal halides at a concentration of between 0.1 mole and 2 moles per liter are used.
• sensitizing compounds which may be present, either at the start of the reaction in the reaction medium, or introduced via one or more jets, according to the usual methods.
• Sensitizing compounds such as copper, thallium, lead, bismuth, cadmium, zinc, medium chalcogens such as sulfur, selenium, tellurium, and noble Group VIII metals, may be present during the precipitation of the silver halides, as described in the patents of the United States of America 1 195 432, 1 951 933,
• the reagents can be introduced into the reaction vessel by reaction, conduits opening at the surface or under the surface of the medium from / by gravity feed, or by other means making it possible to control the rates of introduction as well as the pH. and / or the pAg of the reaction medium, as described in US Pat. Nos. 3,821,002 and 3,031,304, and in the article in the journal Photographische Korrespondenz, 102, No. 10, p. 162 (1967).
• reaction vessel 1 represented in FIG. 1 has its open upper surface, it is also possible to envisage a closed reaction vessel leaving only passage for the currents represented by the arrows 7, 9, 11, 13 and 19.
• the reaction vessel can be completely filled with liquid during the entire preparation of the silver halide dispersion.
• This mode of realization offers the particular advantage of avoiding that the air or any other ambient atmosphere is entrained in the dispersion during its preparation.
• This embodiment allows, in addition, a much greater stirring speed via the stirring mechanism 5, since in a closed reaction vessel filled with liquid, the risk of vortex formation and d entrainment of air in the dispersion of silver halides, resulting in the formation of foams, is eliminated.
• the silver halide grains prepared by the process according to the invention may comprise silver halide grains of various sizes, that is to say large grains, medium grains or fine grains, of which the crystallization planes are advantageously the planes 100, 111 or 110, these silver halide grains can be prepared by various specific techniques, as described in the work "Photographic Emulsion Chemistry” by GF Duffin, pages 57 to 82 (1966) and in VL's “Making and Coating Photography Emulsions" Zelikman and S.N. Levi pages 69 to 160 and 219 to 228 (1964).
• the silver halide grains formed as the main product of the reaction advantageously have a relatively narrow size distribution, that is to say that the dispersions of silver halides formed are advantageously monodispersed.
• the dispersions of silver halides formed are advantageously monodispersed.
• a monodisperse silver halide emulsion is often defined more briefly, indicating that at least 95% by mass or number of the silver halide grains have a diameter which varies by less than about 40% relative to the mean diameter, this variation being advantageously less than 25% and preferably less than 10%.
• the diameter mentioned here is the effective diameter, that is to say the diameter of a circle with an area equivalent to that of the grain of silver halides as observed under a microscope or on a photomicrograph. The measurement of the size of the silver halide grains is described more fully in the work "The Theory of the Photography Process", by Mees and James, 3rd edition, p. 36-43 (1963).
• Polydispersed photosensitive silver halide grains are particularly useful in photographic applications that require wide exposure latitude and low contrast, while monodispersed silver halide grains are useful for a number of applications photographic, for example applications where high contrast is desired, the formation of grains with a core and external envelope by physical maturation, applications in which mixtures are produced the formation of a haze or of uniform sensitization.
• Monodispersed photosensitive silver halide grains are particularly advantageous in the field of Graphic Arts and in positive-direct emulsion applications, since monodispersed silver halide grains have a more uniform size distribution than that of the polydispersed silver halide grains, it is possible to treat them more effectively in most photographic applications than the polydispersed silver halide grains.
• concentrations of peptizing agent of between 0.2% and about 10% can be used, relative to the total mass of the constituents of the emulsion contained in the reaction vessel. It is preferable to maintain the concentration of peptizing agent in the reaction vessel, before or during the formation of the silver halides, at a value of less than approximately 6% by mass. It is common practice to maintain the concentration of peptizing agent in the reaction medium in a range of between approximately 2% and 6% by mass, before and during the formation of the silver halides, then to adjust the concentration by binding up 'to the optimum value by introducing additional quantities of binder.
• the emulsion prepared by the process according to the invention contains approximately 5 g to 50 g of peptizing agent per mole of silver halides, advantageously approximately 10 g to 30 g of peptizing agent An additional quantity of binder can then be introduced to bring the concentration of the latter up to a value of up to 300 g per mole of silver halides, but the concentration of binder in the final emulsion is advantageously less than 50 g. per mole of silver halides.
• the binder represents approximately 30% to 70% by mass of the emulsion layer.
• binders including the p ⁇ ptisants agents, mboles compounds usually used in emulsions photosensitive to silver halides.
• peptizing agents are advantageously hydrophilic colloids which can be used alone or in combination with hydrophobic substances.
• Suitable hydrophilic compounds include natural substances such as proteins, protein derivatives, cellulose derivatives such as cellulose esters, gelatin, for example bone or skin gelatin treated in basic medium or gelatin of pigskin treated in an acid medium, gelatin derivatives, for example acetylated and phthalylated derivatives of gelatin, etc., as described in the patents of the United States of America
• hydrophilic colloidal binders it is possible to use, in combination with these hydrophilic colloidal binders, other substances, in particular in the form of latex, which include synthetic polymeric peptizing agents, such as described in the patents of the United States of America 3 679425, 3 706 564, 3,813,251, 2,253,078, 2,276,322, 2,276,323, 2,281,703, 2311058, 2414207, 2484456,
• the silver halide grains are subjected to maturation in the reaction vessel during the formation of the silver halides.
• the usual silver halide solvents can be used to promote this maturation.
• ammonia and halide ions in excess relative to the stochiometric amount necessary for the formation of the silver halides to promote the maturation of the silver halides. it therefore appears that the metal halide solution introduced into the reaction vessel can itself promote this maturation.
• this ripening agents can be introduced into the reaction vessel via one or more of the silver salt, metal halide or peptizing agent solutions.
• this curing agent can be introduced independently of the silver salt and metal halide solutions.
• Maturing agents which are particularly useful are those which contain sulfur, in particular the maturing agents of the thioether class, such as those which are described in the patents of
• Solvents for silver halides from the class of organic thioethers, useful as maturing agents are those which correspond to the following formulas:
• r and m are whole numbers from o to 4
• n is an integer from 1 to 4
• p and q are whole numbers from o to 3
• X represents an oxygen or sulfur atom, a carbamyl radical - CONH-, a carbonyl radical -CO-, or a carboxy radical -COO-,
• Aging agents for silver halides of the thioether class which are particularly useful for preparing photographic emulsions by the process according to the invention include the compounds which correspond to the following formulas:
• thiocyanates can be used, in particular the alkali metal thiocyanates, usually potassium and ammonium thiocyanates. Although these thiocyanates can be used at any usual concentration, the most advantageous concentrations are usually between 100 mg and 20 g of thiocyanate per mole of silver halides. Maturing agents of the thiocyanate class are described in the above-mentioned US Patents 2,222,264, 2,448,534 and 3,20069.
• the ultra-filtration technique constitutes a particularly advantageous means in the implementation of the process according to the invention.
• the known ultrafiltration techniques are very varied.
• the ultrafiltration device 15 can represent any usual ultrafiltration device, such as those described in the journal Research Disclosure, Vol. 102 article 10208, October 1972, Research Disclosure, Vol. 131, article 13122, March 1975, and Research Disclosure, Vol. 135, section 13577, July 1975, and German patent application 2,436,461 and to the United States patent 2,495,918.
• the ultrafiltration operation can be carried out by pumping out the silver halide dispersion contained in the reaction vessel and sending it in contact with a semi-permeable membrane contained in the ultrafiltration device, applying a pressure difference across the semi-permeable membrane.
• the semi-permeable membranes have pores whose size is such that they can be crossed by molecules having a well-defined size while retaining the larger molecules as well as the grains of silver halides contained in the dispersion.
• Useful membranes are those which stop molecules whose molecular mass is between approximately 500 and 300,000 or more, advantageously between approximately 00 and 50,000.
• the choice of a m ⁇ mbrane having a determined permeability is usually a function of the size of the silver halide grains at the start of the ultrafiltration process and is also a function of the substance with the lowest molecular weight which must be retained in the dispersion after removal of the dispersion and / or soluble salts by ultrafiltration.
• the molecular mass of the soluble salt formed by the reaction of the silver salt and the metal halide, soluble salt which is usually an alkali nitrate inevitably has a mass low molecular, which facilitates its passage through the membrane which selectively retains the silver halide grains, and the peptizing agent in the case where such an agent is present in the dispersion medium.
• the pressure exerted on the dispersion of silver halides which is pumped into the ultrafiltration device can vary considerably, but the pressure at the inlet of the device advantageously has a value of approximately 700 kPa while the pressure at the exit from the residual silver halide dispersion can reach up to about 70 kPa.
• the pressure difference across the membrane is advantageously between 280 kPa and 420 kPa, but the ultrafiltration operation can be carried out using pressures outside these values, depending on the nature of the ultrafiltration device, the viscosity of the dispersion, the concentration and the degree of purity of the dispersion of silver halides which leaves the ultrafiltration device to return to the reaction vessel, etc.
• the ultra-filtration device is advantageously used at a temperature which is within the range of temperatures usually used to precipitate the silver halides.
• the membranes used in the ultrafiltration device are advantageously anisotropic membranes which comprise a very thin texture layer with extremely fine pores, this layer being supported by a thicker porous material.
• Membranes useful in the ultrafiltration device can be prepared from a wide variety of polymers such as polyvinyl chlorides, polyvinylcarboxylates, for example polyvinyl vinyl and polyvinyl acetate, polyvinyl alcohols, polysulfones, polyvinyl ethers, polyacrylamides and polymethacrylamides, polyimides, polyesters, polyfluoroalkylenes, for example polytetrafluoroethylene, polyvinylidene fluoride, cellulose polymers such as cellulose, cellulose esters, for example cell acetate - lose, cellulose butyrate and cellulose acetobutyrate.
• the method according to the invention has been described with reference to a single ultrafiltration device, one can also use two or more ultrafiltration devices in series, or in parallel, or else mixed. For example, if an ultrafiltration device 15 which has a relatively high permeability is used, the dispersion medium withdrawn by current ultrafiltration 17 can be sent to a second ultrafiltration device having a significantly lower permeability. The dispersion of silver halides retained by this second ultrafiltration device can then return to the reaction medium.
• the proportion of the dispersion medium containing the soluble salts removed by the ultrafiltration device by the current 17 can be adjusted to the desired value by usual adjustments concerning the flow rates and the pressures exerted in the ultrafiltration device.
• the volume of the dispersion of silver halides formed at the end of the addition of the solutions of the silver salt and the halides can be varied considerably, depending on the total volumes of solutions added, according to the particular characteristics which it is desired to provide for the dispersion of silver halides.
• the proportions of the dispersion medium removed by ultrafiltration can be extremely high, this proportion of dispersion medium, which comprises the salts in solution formed as by-products of the precipitation of silver halides, being between approximately 10% and 90% of the total volume of the solutions introduced. It is usually advantageous for the proportion of dispersed medium removed to represent at least 50% of the total volume of the solutions introduced into the reaction medium.
• the dilute aqueous metal halide solution as described above, is introduced by the third jet, at a flow rate which is 10 to 30 times greater than all the flow rates of the solutions.
• silver salt and intro metal halide picked by the first and second jets are introduced by the third jet, at a flow rate which is 10 to 30 times greater than all the flow rates of the solutions.
• silver salt and intro metal halide picked by the first and second jets are introduced by the third jet and the ultrafiltration device cooperate so as to significantly reduce the concentration of soluble salts in the dispersion of silver halides.
• the large amounts of dispersing medium introduced by the third jet can be easily removed by ultrafiltration and can be particularly useful for ensuring optimal flow in the ultrafiltration device.
• the third jet it is particularly useful to continue the introduction of the dilute metal halide solution by the third jet, as well as the ultrafiltration operation, after the end of the introduction.
• first and second jets It is also possible to alternate stages of operations in which the first and second jets and / or the third jet are activated respectively, or only the third jet.
• the use of the third jet and the ultrafiltration device can together reduce the concentration of soluble salts in the reaction medium during the formation of the silver halides and during the stages in which the formation of the silver halides is stopped. and / or after the end of the formation of the silver halides.
• the flow rate of the third jet can be increased gradually as the preparation of the silver halides progresses. It is also possible to interrupt the arrival of the silver salt and metal halide solutions by the first and second jets, with more frequent, as the preparation of the silver halides progresses. .
• the arrivals of the silver salt and metal halide solutions are stopped.
• One of the saline solutions can then be added to adjust the pAg of the silver halide dispersion to the desired value.
• the ultrafiltration operation can be stopped at the same time as the addition of the saline solutions of silver salt and metal halide, or the ultrafiltration can be continued to remove an additional quantity of the soluble salts from the dispersion medium. , either that the dilute halide saline solution is introduced by the third jet, or that it is not.
• the dispersion of silver halides is removed from the container where the preparation was carried out to be further treated according to the usual methods, for example to be washed as described in the Research Disclosure, article 17643, supra, Section II.
• the nuelization step and the stage of growth of the silver halide grains are carried out in the same reaction vessel, using a double jet precipitation method. , in a single tank. It is well known, however, that it is possible to stop the precipitation of silver halides, especially after the end of the grain growth stage.
• the single reaction vessel as described above can be replaced by two separate reaction vessels.
• a closed nucleation vessel can be used in which the reagents are introduced and mixed, upstream from the downstream reaction vessel, as described, for example, in the United States patents. America 3,790,386, 3,897,935, 4,147,551 and 4,171,224 above.
• the contents are recycled from the downstream reaction vessel where the grain growth takes place to the reaction vessel upstream where the watering takes place.
• the process according to the invention it is possible to independently control different parameters used to control the formation and growth of the silver halide grains, parameters such as pH, pAg, temperature , the maturation, the residence time, etc., both in the storage container and in the reaction container for the growth of the grains, when two separate containers are used. If it is desired that the halogenation of the silver halides is entirely independent of the growth of the silver halide grains carried out in the grain growth container downstream of the nuelization container, it is necessary not to recirculate the dispersion of silver halides present in the grain growth container to the nucleating container.
• the nuelization step of the process for preparing the silver halides according to the invention can be independent of the grain growth step, it follows that the nuelization step can be carried out by one of the various processes for precipitation of the usual silver halides, in addition to the double-jet precipitation method, in the tank, for example by a single-jet precipitation method or by a continuous double-jet precipitation method, methods as described in the references of James, Trivelli and Smith cited above, as well as to the patents of the United States of America 3 801 326 and 4 046 576 cited above.
• the silver salt solution can be introduced independently, either into the gel container alone, or into both the gel container and the grain growth container.
• the aqueous solutions of metal halides may be initially present in the nuelization container or else introduced into the latter. Since the water-soluble halides can be removed by ultrafiltration and it is usually desirable to carry out the growth step of the silver halide grains in the presence of an excess of halide ions over In most cases, water-soluble halides will be added to the stoichiometric amount in the grain growth container, either from the nuelization container or directly by an independent jet.
• the third jet can be introduced, as described above, either to introduce a solution of peptizing agent or to dilute the water-soluble salts, in the oiling container or in the grain growth container or in the two containers.
• the third jet When the third jet is used to dilute the dissolved salts formed by the precipitation reaction of the silver halides, it is preferable that the third jet is introduced into the grain growth container.
• the ultrafiltration device When using a nuelization container and a grain growth container, it is preferable that the ultrafiltration device is connected to the grain growth container, as shown in Figure 1, so that the dispersion is withdrawn into the grain growth container to be directed to the ultrafiltration device and then returns from the latter to the grain growth container.
• the ultrafiltration device can be used to return the dispersion, initially received from the grain growth container, to the oil container. It is possible to implement other embodiments.
• the silver halide dispersions prepared by the process according to the invention can be mixed with other silver halide dispersions, either prepared by the process according to the invention or prepared by other processes; these mixtures can be carried out immediately after the precipitation of the silver halides or at any stage before coating on a support.
• the silver halide dispersions prepared by the process according to the invention can be used by operating according to the usual methods as described in the journal "Research Disclosure", art. 17643 cited above They can be sensitized chemically by operating as described in the above-mentioned article, paragraph III. They can also be sensitized spectrally or desensitized spectrally as described in the aforementioned article, paragraph IV. One can add to them other usual photographic adjuvants, as described in the aforementioned article, paragraph V. One can add adjuvants to the silver halide dispersions using the usual methods as described in the aforementioned article, paragraph XIV.
• Spectral sensitizing dyes can also be introduced into the reaction medium before the precipitation of the silver halides or during the precipitation of the silver halides, advantageously during the stage of growth of the silver halide grains, as described, by example, to the patent of the United States of America 3,628,960.
• the peptizing agent can be added to the dispersion of silver halides, after the end of the addition of the photographic adjuvants, since the activity of these photographic adjuvants can be more effective when they are introduced into the dispersion of silver halides in the absence of a binder.
• Tanning agents can be used in combination with binders, as described in the above-mentioned article, paragraph X.
• the silver halide dispersions prepared by the process according to the invention can be used to prepare most of the silver halide photographic products of the prior art, as described in the journal "Research Disclosure", art. 17643 cited above, paragraphs VII, VIII, XI, XII, XVI, XVII, XX to XXVII.
• the silver halide dispersions and the other solutions can be applied to prepare these photographic products by operating, for example, according to the methods described in the abovementioned article, paragraph XV, then exposing and treating them by the usual methods such as as described in the aforementioned article, paragraphs XVIII and XIX.
• the following examples illustrate the invention.
• EXAMPLE 1 This example illustrates a method of preparing aqueous dispersions of silver halides in the absence of colloidal binder.
• Step 1 Nuelation.
• the container 1 in which the precipitation of the silver halides will be carried out, contains, initially, 48 liters of an aqueous 0.005 M potassium bromide solution, in such a way as to form the initial reaction medium 3.
• An aqueous 1.00 M silver nitrate solution and an aqueous 1.01 M potassium bromide solution are then introduced simultaneously by the first jet 7 and the second jet 9, respectively. whose flow rates are constant and equal to 40 ml per minute.
• the duration of the lubrication step in which seeds of silver halides are formed which are useful, in the subsequent step, for forming the silver halide grains by growth of seeds is equal to 30 one.
• the temperature of the reaction medium is maintained at 40oC, the pH value, measured at 40oC, at 5.5, and the silver potential VAg, measured at 40oC, at 62 mV, ie a pAg equal to 9.28.
• Step 2 Washing of the silver halide germs.
• Step 3 Growth of the silver halide crystals
• Step 4 Washing the silver halide crystals.
• Step 5 Growth of the silver halide crystals.
• the final dispersion obtained is used to prepare a photosensitive emulsion with silver bromide.
• phthalylated gelatin is added to the final dispersion, then the emulsion is washed, after coagulation, followed by redispersion, using the usual method. These coagulation and redispersion operations are repeated a second time. Water and an aqueous gelatin solution are then added so as to adjust the concentration and density of the emulsion so that a volume of 3.8 l of emulsion contains one mole of silver bromide and gelatin at a concentration of 5% and weighs 4 kg.
• the emulsion is then chemically sensitized to sulfur and gold by operating by a usual method. Examination under the microscope of the emulsion does not reveal the formation of any agglomerate, shows that the emulsion obtained is monodispersed and contains silver halide crystals whose average size is equal to 0.3 Jim.
• the sensitometric characteristics of the emulsion are determined, which are similar to those of a control emulsion prepared by precipitation in the presence of gelatin.
• EXAMPLE 2 This example illustrates the preparation of a dispersion of silver halides in the presence of a peptizing agent.
• Example 1 A device similar to that described in Example 1 is used.
• the container 1 initially contains solution A defined below. Solutions B and C defined below are then added simultaneously, with vigorous stirring, the duration of the addition being equal to 36 min, during which the pAg of solution A is maintained at 8.7.
• Step 2 Growth of the silver halide crystals.
• a fraction of the reaction medium is removed, at a flow rate of 1.8 kg / min, which is passed through an ultrafiltration device comprising a semi-permeable polysulfone medium, with an average molecular weight of 1,000 and in the form of two spirally wound tubes 1 m long and 5 cm in diameter.
• the solution containing the soluble salts is eliminated at a flow rate equal to all of the flow rates for the introduction of solutions B and C, so as to keep the volume of the reaction medium constant, ie 608 l, throughout the precipitation stage. .
• the emulsion is cooled to 37.8 ° C, then it is passed through the ultrafiltration device described above, but with a semi-permeable membrane as a polysulfone whose average molecular mass is equal to 20,000, until the pAg of the emulsion is equal to 8.2. Then add 12.24 kg of gelatin, then heat the emulsion to 43.3oC, stir until the gelatin dissolves, then add an additional amount of water to bring the total mass of the emulsion to 72.0 kg. The emulsion is then cooled, it is chemically sensitized, then it is applied to a support and its sensitometric characteristics are determined, operating as described in Example 1.
• the photographic properties of the emulsion are similar to those of an emulsion which has been washed after coagulation by a usual method.

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• 1980
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