EP0046927A1 - Process for producing dispersions and photographic materials - Google Patents

Abstract

A process for the preparation of photographic emulsions, consisting of water-immiscible or water-insoluble organic substances and an aqueous solution of an organic binder, characterized in that the hydrophilic and hydrophobic phases are heated separately from one another to the respective temperatures above their liquefaction point and then continuously metered into a dispersion chamber are supplied, the outlet of which is provided with a throttle point, so that the dispersion can take place under pressure and is therefore carried out at temperatures above the boiling point of the individual components or of the azoetrops which may form.

Description

The invention relates to a process for the production of dispersions and photographic materials which contain dispersions according to the invention. In particular, the invention relates to the production of dispersions of organic, hydrophobic substances in an aqueous phase.

In the following, dispersions are understood to mean apparently homogeneous systems which contain at least 2 phases in finely divided form. Examples of dispersions are e.g. Emulsions and suspensions.

To produce such dispersions, it is known to mix organic substances, in particular color couplers, in solid or liquid form with high-boiling solvents referred to as oil formers, optionally to add a low-boiling auxiliary solvent, and this mixture with the aid of an emuls gators with an aqueous solution, generally a gelatin solution. Such methods are described in U.S. Patent 2,322,027; The examples in US Pat. No. 2,322,027 show that relatively low temperatures are maintained during the dispersion. The use of low-boiling auxiliary solvents has been described many times, but has the major disadvantage that the low-boiling auxiliary solvent must be distilled off from the disperse phase after dispersion. This requires a relatively large technical effort to remove the solvent completely. The removal is generally carried out at reduced pressure and low temperatures in order to avoid agglomeration of the disperse phase and thermal stress on the mostly temperature-sensitive binders.

From DE-PS 1 143 707 it is also known to emulsify color components with a melting point below 75 ° C. in a gelatin solution heated to 90 ° C. with the aid of an emulsifier. From GB-PS 1 151 590 it is also known to use color couplers with a melting point below 100 ° C., the color couplers being melted together with a dispersant. From GDR patent specification 139 040 it is known to use color couplers with a melting point above 75 ° C. by mixing these couplers with a high-boiling solvent and then emulsifying them in water which contains a wetting agent. It can then be mixed with a gelatin solution at low temperature.

A disadvantage of such processes is that the color couplers used may have a melting point of at most 100 ° C. Although there is no need to separate off a low-boiling auxiliary solvent, on the other hand one is limited to color couplers which have a correspondingly low melting point or which may be achieved by mixing with other color couplers or oil formers. In addition, in both the solvent-free dispersion process and in the process using an oil former, the dispersing step by grinding cannot be used for all color couplers. This is because it is technically difficult to intercept the heat generated during the grinding by the cutting work. This difficulty is all the more serious the finer the color coupler particles are to be dispersed and the narrower the required distribution width, i.e. the deviation of the individual particles from the average grain size. Most of the compounds to be dispersed, like gelatin, are relatively sensitive to temperature. Gelatin shows slightly irreversible changes at high temperatures, which are manifested in poorer casting behavior and poorer sensitometric values. In the known processes, the phases to be dispersed are mixed before the dispersion and run together into the dispersing device.

A process is known from US Pat. No. 3,850,643, in which a copper / oil-forming mixture is dissolved in a solvent at 137.8 ° C. and this solution internally half a minute in a gelatin / emulsifier solution.

For this purpose, a special entry device is used, consisting of a fixed ring-shaped plate and a perforated plate with webs. The solvent is then washed out of the solidified emulsion.

The method has the disadvantage that a special apparatus must be used, which requires special alignment. Further disadvantages are the use of solvents, which have to be removed in a subsequent double operation, and the very long entry time.

The object of the invention is to find a dispersion process which avoids the disadvantages of the known processes. In particular, the invention was based on the object of specifying a dispersing process which ensures gentle treatment of the dispersed compounds.

A process has now been found for producing dispersions from at least one liquid organic phase which contains a hydrophobic, photographically active compound and at least one aqueous phase which comprises a binder, in which both phases are combined with dispersion. According to the invention, the two phases are left separate from one another in a suitable disperser Run in the yaw device.

In a preferred embodiment of the method, the organic phase is the pure melt of a photographic substance or the solution of the photographic substance in an oil former and the dispersion takes place above the liquefaction temperature of this fogographically active substance or solution.

The aqueous phase can contain dissolved binders and the dispersion can take place above the liquefaction temperature of this binder temperature. The dispersion can also take place above the liquefaction temperatures of both phases.

In a preferred embodiment, the dispersion is carried out at a temperature which is above the boiling point at atmospheric pressure of the lower-boiling phase or of the azeotrope which may form. The organic phase preferably contains a photographically active substance which is essentially immiscible with water at pH 7. In a preferred embodiment, a high-boiling oil former can additionally be contained.

The photographically active compound can be a color coupler, a stabilizer or a UV absorber.

A particularly advantageous procedure is characterized in that the residence time of a particle of the organic phase in the shear zone of the dispersing device is only a maximum of 6 seconds. The temperature in the dispersion room is advantageously at least 100 ° C. and the pressure in the dispersion room is at least 1 bar. A special method is that the temperature of the organic phase is between 100 and 140 ° C, the temperature of the aqueous phase is between 70 and 85 ° C and the temperature in the dispersion zone is between 60 and 140 °.

The process according to the invention is outstandingly suitable for producing dispersions in an aqueous medium from organic hydrophobic substances which are photographically active. Examples of such substances are, for example, hydrophobic couplers of the most varied types (4-equivalent couplers, 2-equivalent couplers, DIR couplers, mask couplers, white couplers, competitive couplers), dyes or other coloring compounds, e.g. for the color diffusion transfer process, UV absorbers, stabilizers and other photographic additives.

The aqueous phase contains, to improve the stability of the dispersions, hydrophilic colloidal binders, e.g. Gelatin. The gelatin can also be replaced in whole or in part by other natural, synthetic or semi-synthetic binders, e.g. by derivatives of alginic acid or cellulose, by polyvinyl alcohol, polyacrylates, partially saponified polyvinyl acetate or polyvinyl pyrrolidone.

According to the invention, the organic phase is heated above its melting point to such an extent that a thin liquid solution is formed. This is dispersed in the aqueous phase, the residence time in the shear zone of the dispersing device generally being less than one second. The aqueous phase is introduced into the dispersing device at a temperature which is preferably below the boiling point at normal pressure. The temperature of the aqueous phase is preferably 70 to 95 ° C. While the aqueous phase can circulate through the dispersing device before the actual dispersion step, the organic phase is only introduced directly into the shear zone of the dispersing device at the start of the dispersion at high temperature.

According to the invention, the temperature of the organic phase is above the melting point of the organic substance to be dispersed, for example the coupler or the mixture of a coupler and a high-boiling oil former. Couplers with melting points up to 180 ° C can be processed without problems according to the invention. The temperature of the organic phase is preferably 100 ° C to 140 ° C. The temperature of the organic phase only cools to the surrounding temperature during or after the dispersion has taken place. The temperature in the shear zone of the dispersing device is generally 60 ° C. to 140 ° C., in particular 80 ° C. to 120 ° C. The temperature in the dispersing device can optionally be controlled via additional devices will. In order to avoid boiling of the aqueous phase in the dispersing device, an excess pressure can be maintained in the dispersing device. The overpressure is then measured so that it does not boil, and results from the boiling diagrams of the selected systems. The overpressure can be, for example, between 0-3 bar, possibly also at a higher value.

The usual machines can be used as the dispersing device, e.g. High-speed stirrers, so-called mixing sirens or ultrasound devices. In a preferred embodiment, the residence time in the shear zone of the dispersing device is only 0.02 to 0.4 seconds. Dwell time is understood to mean the time from the entry of the dispersing partners into the shear zone of the dispersing device to the exit. However, it is also possible to have the dispersion run through the shear zone several times by superimposing a circulation system on the product line. In this case, the effective residence times are generally between 0.2 and 6 seconds. The dispersing partners are sent several times through the shear zone of the dispersing device, so that the residence times add up to an average or effective residence time. These residence times are far below the residence times previously used for the production of such emulsions.

The average particle size in the dispersions obtained is a function of residence time, mixing performance and dispersion temperature. In general, the influence of the residence time decreases with higher mixing performance. At higher temperatures, finer dispersions can generally be obtained than at lower temperatures. In principle, any particle sizes can be obtained, particularly preferred are particle sizes from 200 to 600 nm, in particular from 300 to 350 nm.

Relatively temperature-sensitive substances can also be dispersed in the dispersing device at high temperatures. Another advantage of the process according to the invention is that highly concentrated dispersions can be produced with a high space / time yield.

The space / time yield is based on known manufacturing processes and known use concentrations. E.g. normally a dispersant used with 5% active ingredient, which must be prepared in a kettle, so that the aqueous phase (gelatin solution) can be initially charged with 25% and the organic phase is concentrated, a correspondingly smaller apparatus can be used. This results in a space / time yield that is better by a factor of 3 simply by taking the smaller boiler volume into account. In addition, since mixing times of 10 minutes are usually used, mixing times of 6 seconds (as explained above) result in a further improvement by a factor of 100.

The pressure in the disperser should be above the vapor pressure of the aqueous phase. Among other things, determined by the temperature of the organic phase (e.g. 120 ° C corresponding to 2 bar overpressure), which cools down to the dispersion temperature during dispersion. If you do not want to run the batch phase of the aqueous phase as a pressure vessel, you must ensure that the temperature is below 100 ° C. Or you disperse at temperatures higher than 100 ° C and - in the event that you want to return the dispersate to the batch kettle - cool down to temperatures below 100 ° C before relaxing. The dispersion effect itself is not dependent on pressure, provided that it is ensured that no evaporation takes place.

The ratio of organic matter (color coupler, UV absorber, etc.) to oil former is not a critical parameter for the success of the process. The oil former (high-boiling solvent) is not absolutely necessary, but it is advantageous not to exceed the viscosity of 1000 mPas at the preferred dispersion temperature. A corresponding setting is possible by adding oil formers.

The oil formers are substances which generally boil above 180 ° C. and have good dissolving power for the hydrophobic substance to be dispersed. These include the esters of glutaric acid, adipic acid, phthalic acid, sebacic acid, succinic acid, maleic acid, fumaric acid, isophthalic acid, terephthalic acid and phosphoric acid or the esters of glycerin, as well Paraffin and fluorinated paraffin are preferably used because these compounds are chemically stable and very easily accessible, can be handled very easily and have no adverse effect on the light-sensitive materials when the dispersions are used for photographic purposes. The following are particularly preferably used as oil formers according to the invention: tricresyl phosphate, triphenyl phosphate, dibutyl phthalate, di-n-octyl phthalate, di-2-ethylhexyl phthalate, glycerol tributyrate, glycerol tripropionate, dioctyl sebacate. Paraffin and fluorinated paraffin. Succinic acid derivatives are also preferred. Examples are given below.

In the formulas given, the symbol R stands for a longer aliphatic radical with at least 8 carbon atoms. This is preferably one of the following, monounsaturated aliphatic radicals - _{C12H23 '} -C ₁₅ H ₂₉ or -C ₁₈ H ₃₅ .

The method according to the invention can be carried out with devices according to FIGS. 1 and 2, but is of course not restricted to the use of these devices. According to FIG. 1, the aqueous phase is metered in from a stirrable and heatable boiler 1 with pump 2 via a dispersing machine 3 with a defined flow rate.

The organic phase is metered from a likewise heatable and stirrable kettle 4 with a pump 5 via a filter 6 directly into the shear zone of the dispersing machine.

The dispersing machine 3 can also optionally be switched to bypass 7.

In the heat exchanger 8, the dispersion produced in the dispersing machine can be cooled to such an extent that it leaves the pressure-maintaining valve 9 down to a temperature below the evaporation point. cooled at normal pressure and can be introduced into the boiler 10.

The device can be operated in a continuous as well as in a discontinuous mode of operation.

Rotor / stator machines are preferably used as dispersing machines, since these enable the organic phase to be introduced directly into the shear zone and the organic phase can thus be dispersed at temperatures higher than that specified by the average dispersion temperature.

Figure 2 shows another embodiment, 1 represents a batch boiler. 2 is a pump that conveys the aqueous phase to the dispersing machine 3. The organic phase is metered in from the boiler 4 via the pump 5. The cooler 8 allows the emulsified mixture to be cooled to temperatures below 100 ° C., so that pressure can be passed through the valve 9 after relaxation.

The dispersions prepared according to the invention are outstandingly suitable for the preparation of light-sensitive photographic materials which contain silver halide. The dispersions can be introduced into such materials in a manner known per se. The dispersions can be introduced both in layers containing silver halide and in layers free of silver halide.

The usual silver halide emulsions can be used, which can be prepared by the usual known methods. Gelatin can be used as a binder for the photographic layers, but can be replaced in whole or in part by other binders. Stabilizers such as triazole derivatives, thiocarbonic acid derivatives of thiodiazole or azaindenes can be added to the emulsions as antifoggants. The silver halide emulsions can also be sensitized with the usual chemical sensitizers; the usual for optical sensitization

Sensitizers as described, for example, in the work of S.M. Hamer "The Cyanine Dyes and Related Compounds" (1964), Intersience Publishers John Wiley & Sons.

The photographic layers are hardened under conditions which do not adversely affect the image tone, but which allow the layers to be processed quickly even at higher temperatures. Suitable curing agents are, for example, formalin, dialdehydes, divinyl sulfone, triazine derivatives, if appropriate in the presence of tertiary amines, and also instant curing agents such as carbamoylpyridinium compounds or carbodiimides. The usual substrates can be used, e.g. Polyolefin-coated underlays, for example polyethylene-coated paper, suitable polyolefins and paper, polyester, triacetate.

example 1

An aqueous 25% gelatin solution is prepared in a heatable kettle equipped with a slowly running stirrer. After a clear solution has been formed, 0.90 kg of triisopropyl naphthalenesulfonate is added. This aqueous solution is then heated to 80 ° C.

von 20°C und 6,00 kg Kuppler der FormelIn a second heatable and stirrable vessel, 16.00 kg of tricresyl phosphate are heated to 120 ° C. and then, for example, 14.00 kg of couplers of the following formula

of 20 ° C and 6.00 kg coupler of the formula

2- (2'-α-Methyltridecyl-4'-chlorophenoxyacetylamino) -4,6-dichloro-5-methylphenol

added and stirred. A clear solution is formed at 120 ° C.

Now the aqueous gelatin solution is pumped through the dispersion zone of a continuous mixer (Dispax reactor, type ^p 3/6/6) by means of a pump with a flow rate of 150 kg / h, in the working space of which a pressure of 2 bar by means of a cross-sectional constriction (valve) is set at the outlet and first in the fore position boiler of the aqueous solution is returned so that the pipeline and mixing zone are filled with liquid and brought to temperature. Then the circulation of the aqueous gelatin solution is ended.

The second solution is then fed to the mixing zone at a flow rate of 60 kg / h by means of a heatable pump through a heatable pipeline. A temperature of 110 to 115 ° C arises at the outlet of the mixing zone. The pressure is kept at 2 to 2.5 bar. This pressure is about 1 bar higher than the pressure necessary to avoid the boiling of the aqueous phase, but promotes a particularly uniform emulsion formation.

Example 2

The two solutions of Example 1 are prepared in a 10-fold amount, but the difference is that the aqueous solution in the kettle is kept at 40 ° C. and only flows through a heat exchanger in which the temperature is just before being pumped into the dispersing machine the solution is raised from 40 to 80 ° C.

In addition, the solid, powdery couplers from Example 1 are mixed and placed in the shaft of a dissolving screw, to which the tricresyl phosphate heated to 120 ° C. is fed at the same time, so that the solution is produced continuously, the residence time at high temperature of 115 ° C. being only a few Seconds.

Example 3

auf 140°C aufgewärmt und 50,00 kg Kuppler der Formel

zugegeben und so lange gerührt, bis bei 130°C eine klare Lösung (Lösung II) entstanden ist.25.00 kg of 25% gelatin solution and 1.02 kg of triisopropyl naphthalenesulfonate (solution I) are prepared at 60 ° C. in accordance with Example 1 in a heatable and coolable kettle with a slow-moving stirrer, and are placed in a second heating and Stirable kettles are 50.00 kg of dibutyl phthalate and 25.00 kg of a compound of the formula

warmed up to 140 ° C and 50.00 kg coupler of the formula

added and stirred until a clear solution (solution II) is formed at 130 ° C.

Both solutions are metered continuously with piston metering pumps to a continuous mixer based on the rotor / stator principle, which is operated at a speed of 10,000 rpm, namely solution I with a Material flow of 120 kg / h and solution II with a material flow of 60 kg / h.

The continuous mixer is connected with a circuit. At a pressure of 2 bar and a temperature of 110 to 120 ° C, a fine-particle emulsion is formed in the continuous flow, which is cooled to 80 ° C in a downstream cooler and then processed after passing through a pressure-maintaining valve that is set to 2 bar to become. An emulsifier with an average particle size of 337 nm is obtained.

The dispersant obtained is added to a silver halide emulsion containing 60 g / 1 silver halide in a manner known per se. The dispersion thus obtained is provided with hardening and wetting agents and cast onto a base in a known manner. The material obtained is exposed imagewise and developed in a conventional color developer.

For comparison, a corresponding photographic material is produced from the same silver halide emulsion with the same dispersed compounds, but the dispersion was not carried out according to the invention but according to US Pat. No. 2,322,027. The procedure is such that the amounts of coupler and oil former specified above are dissolved in 150 kg of diethyl carbonate. A mixture is prepared by stirring into the 10% gelatin solution (amount corresponding to 25 kg gelatin) mixed with the above-mentioned amount of wetting agent. This mixture is repeated several times by one Mixing siren skillfully while dispersing. The solvent is then evaporated off in vacuo. The emulsifier obtained is added to the silver halide emulsion.

The comparison material was processed in the same way as that of the invention.

The sensitometric data listed in the table below show that, according to the invention, a higher sensitivity, gradation and maximum density is obtained.

A decrease in the sensitivity value by 0.3010 units corresponds to a doubling of the sensitivity.

Example 4

25.00 kg of gelatin solution and 0.5 kg of triisopropyl naphthalenesulfonate are prepared at 60 ° C. in a heatable and coolable kettle with a slow-moving stirrer in accordance with Example 1 (solution I). The concentrations of the gelatin solutions are chosen to be 7.5%, 10%, _15% and 20%. The gelatin solutions are introduced and 5 kg of tricresyl phosphate and 5 kg of a compound are in a second heatable and stirrable kettle

Warmed up to 140 ° C and stirred until a clear solution (solution II) is formed.

Both solutions are continuously metered in with piston metering pumps to a continuous mixer based on the rotor / stator principle, which is operated at a speed of 10,000 rpm, namely solution I with a material flow of 120 kg / h and solution II with a material flow of 60 kg / h.

The continuous mixer is connected with a circuit. At a pressure of 2 bar and a temperature of 11o to 120 ° C, a finely divided emulsion is formed in the continuous flow, which is cooled to 80 ° C in a downstream cooler and then processed after passing through a pressure control valve that is set to 2 bar to become.

Emul gates with particle sizes between 625 and 350 nm are obtained.

Example 5

aufgeheizt und so lange gerührt, bis eine bei 130°C klare Lösung mit einer Viskosität von 750 mPas entstanden ist. Beide Lösungen werden kontinuierlich mit Kolbendosierpumpen einem Durchlaufmischer nach dem Rotor/Stator-Prinzip, der mit einer Drehzahl von 10 000 U/min betrieben wird, zudosiert, und zwar Lösung I mit einem Stoffstrom von 120 kg/h und Lösung II mit einem Stoffstrom von 60 kg/h.53.1 kg of 10% gelatin solution and 5.3 kg of 50% solution of the sodium salt of dodecylbenzenesulfonic acid and 21.3 kg of water at 60 ° C. are prepared in accordance with Example 1 in a heatable and coolable kettle with a slow-moving stirrer ( Solution I), submitted and in a second heatable and stirrable vessel 20.9 kg of a compound of the formula

heated and stirred until a clear solution with a viscosity of 750 mPas is obtained at 130 ° C. Both solutions are continuously metered in with piston metering pumps to a continuous mixer based on the rotor / stator principle, which is operated at a speed of 10,000 rpm, namely solution I with a material flow of 120 kg / h and solution II with a material flow of 60 kg / h.

The continuous mixer is connected with a circuit. At a pressure of 1 bar and a temperature of 95 ° C, a finely divided emulsion is formed in the continuous flow, which is cooled to 80 ° C and processed further.

Claims (13)

1) Process for the preparation of dispersions from at least one liquid organic phase which contains a hydrophobic, photographically active substance, and at least one aqueous phase which contains a binder, by combining the phases with dispersion in a dispersing device, characterized in that the two Phases enter the dispersing device simultaneously, but separately from one another. 2) Method according to claim 1, characterized in that the organic phase is the pure melt of a photographically active substance and that the dispersion takes place above the liquefaction temperature of this photographically active substance. 3) Method according to claim 1, characterized in that the organic phase is the solution of a photographically active substance in an oil former (high-boiling solvent) and that the dispersion takes place above the liquefaction temperature of this solution. 4) Method according to claim 1, characterized in that the aqueous phase contains dissolved binder and that the dispersion takes place above the liquefaction temperature of this binder solution. 5) Method according to claim 1, characterized in that the organic phase and the aqueous phase are dispersed at a temperature above the liquefaction temperatures of both phases. 6) Method according to claim 1, characterized in that the dispersion is carried out at a temperature above the boiling point at normal pressure, the lower boiling phase or the azeotrope which may form. 7) Method according to claim 1, characterized in that the organic phase contains substances which are essentially immiscible or insoluble in water at pH 7 and that the aqueous phase contains gelatin. 8) Method according to claim 1, characterized in that the organic phase contains an oil former in addition to the photographically active substance. 9) Method according to claim 1, characterized in that the photographically active compound is a color coupler, a stabilizer or a UV absorber. 10) Method according to claim 1, characterized in that the residence time of a particle of the organic phase in the shear zone of the dispersing device is a maximum of 6 seconds. 11) Method according to claim 1, characterized in that the temperature in the dispersion chamber is at least 100 ° C and a pressure of at least 1 bar is maintained in the dispersion chamber. 12) Method according to claim 1, characterized in that the temperature of the organic phase between 100 and 140 ° C, the temperature of the aqueous phase between 70 and 95 ° C and the temperature in the dispersion zone between 60 and 140 ° C. 13) Photographic material from a layer support, at least one silver halide emulsion layer and optionally further layers, characterized in that a dispersion prepared according to claim 1 is contained in at least one layer.

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