GB2106885A - Process for preparing aqueous dispersion of carbon black - Google Patents

Abstract

An aqueous dispersion of carbon black is prepared in a tank equipped with a high speed agitator by means of, (a) Carbon black, an organic solvent eg. ethylacetate or methanol and a dispersant are mixed and agitated to form a dispersion; (b) water is added to the dispersion in amount of 0.1 to 10 parts by volume per part of the organic solvent, and (c) the organic solvent is removed by a reduced pressure means optionally with heating by a jacket. As dispersant, various surfactants are disclosed, e.g. polyalkylbenzene sulfonates. A water-soluble binder may be added in step (a) or (b) or the final dispersion.

Description

SPECIFICATION Process for preparing aqueous dispersion of carbon black The present invention relates to a process for preparing a dispersion of carbon black and, more particularly, to a process for preparing an aqueous dispersion by dispersing carbon black in water or a water solution of a water soluble binder.

An aqueous dispersion of carbon black is very often used as an ingredient of a coating material, ink, a cosmetic or a photographic light-sensitive material for the purpose of imparting mainly black color or a light intercepting property thereto.

There are generally known methods of preparing an aqueous dispersion of carbon black. In accordance with these known methods the carbon black is produced in a powder form or bead from using a process such as a thermal black process, an acetylene black process, a channel black process, a furnace process or lamp black process. The carbon black is then added to water in which an appropriate dispersing agent is dissolved. The carbon black is then dispersed coarsely so that the mean grain size of the carbon black becomes 10 to 100 pm. This is done using a coarse disperser such as a high speed agitator type like the dissolver described in published unexamined Japanese Patent Application No. 129136/80.The carbon black is then dispersed finely to such an extent that the mean grain size of the carbon black becomes about 0.1 to 10 ym. This is done using a fine disperser such as a sand grinder, a homogenizer or a colloid mill. In addition, as occasion demands, a water soluble binder may be admixed with the above described dispersion at the time of coarse dispersion or fine dispersion, or after preparation of the aqueous dispersion of carbon black is finished. However, such a dispersing process as described above suffers from the following defects: 1. In order to obtain an aqueous dispersion of carbon black having a small mean grain size, it is necessary to continue the processing for coarse dispersion for a long time. For example, the time for running the dispersion ranges from 5 to 50 hours.The amount of dispersion time needed depends on factors such as the primary size of the grain, the presence of secondary cohesion and the like, and whether the carbon black used received any surface treatment, e.g., for imparting hydrophilicity thereto.

2. Strong shearing stress, even if it is transitory stress, once applied to carbon black grains in the process of long range dispersion causes a so-called overdispersing phenomenon and, therefore, the mean grain size of the aqueous dispersion grows all the larger.

3. The dispersing apparatus is equipped with two different systems of dispersers, i.e., one being a coarse disperser and the other being a fine disperser. Accordingly, the carbon black material being dispersed must be emptied out of one disperser into another. When this is done, carbon black remains in these dispersers in considerable amounts because it sticks to the wall of disperser due to its generally high viscosity. Therefore, the yeild rate in the preparation of the aqueous dispersion is lowered and it takes a long time to wash the interior of the disperser after switchover.

An object of the present invention is to present a method for producing an aqueous dispersion of carbon black which eliminates the defects inherent in conventional methods.

Another object of the present invention is to provide such a method which can be performed in a relatively short period of time.

Yet another object of the present invention is to provide a novel dispersing process for producing an aqueous dispersion of carbon black wherein the carbon black has a small mean grain size.

Still another object of the present Invention is to provide a process for producing an aqueous dispersion of carbon black wherein the process utilizes simple devices.

The above described objects are attained by a process of preparing an aqueous dispersion of carbon black using a tank equipped with a disperser of high speed agitator type. The process includes the steps of mixing and agitating carbon black together with an organic solvent and optionally a dispersing agent to form an oily dispersion of carbon black. Water or a combination of water and a water soluble binder is then added together with a dispersing agent, if necessary, to the oily dispersion of carbon black with mixing and stirring. The organic solvent is then removed from the resulting dispersion.

One embodiment of the present invention is described below in detail with reference to the accompanying drawing. However, this invention is not limited to this embodiment.

The drawing shows schematically an apparatus for use in the process of the present invention.

The apparatus comprises a tank 11 equipped with a disperser of the high speed agitator type, e.g., a dissolver 14, a tank 12 used for adding an organic solvent to a dispersing system, a tank 1 3 used for adding water or a combination of water and a water-soluble binder to the dispersing system, a pressure-reducing device 1 6 used for vaporizing the organic solvent, a condenser 1 5 for recovering the organic solvent vaporized away, and a vacuum gauge 1 7.

In the apparatus constructed as described above, an oily dispersion of carbon black may be prepared. Firstly, the dispersion is prepared by continuing to mix and agitate carbon black, an organic solvent and a dispersing agent in the tank 11 using the above described dissolver 14.

Subsequently, water is admixed therewith as agitation is continued. Then, the tank 11 is closed, and if necessary, may be heated by allowing hot water to pass through a heating jacket put on the tank 1. Thereafter, the pressure-reducing device 1 6 is operated to induce evaporation of the organic solvent. The evaporated organic solvent is recovered by the condenser 1 5 in an amount suitable for the end-use purpose of the aqueous dispersion of carbon black. Thus, the desired composition of aqueous dispersion of carbon black is obtained.

After obtaining the dispersion of carbon black, a hydrophobic substance or a water-soluble binder may be added, if necessary. It is possible for a hydrogphobic substance to be added at the first step of forming the oily dispersion. Furthermore, a water-soluble binder may be added in the form of a water solution simultaneously with the addition of water at the second step of adding water to the oily dispersion together with an appropriate dispersing agent, if necessary.

In addition, after the aqueous dispersion is finally prepared, it is possibie to add a watersoluble binder in a neat state or in the form of water solution with mixing and agitating.

The amount of the organic solvent mixed with carbon black is generally in the range of from 200 to 2,000 ml per 100 g of carbon black, preferably in the range of from 400 to 800 ml per 100 g of carbon black.

The amount of the water added to the oily dispersion is generally in the range of from 0.1 to 10 volume parts, preferably in the range of from 0.2 to 5 volume parts, per volume part of the organic solvent present in the oily dispersion.

In general, any organic solvent can be employed in the present invention provided that the wettability of the carbon black with respect to the solvent is high. However, a solvent is generally chosen which will have no adverse effects upon the properties of the aqueous dispersion prodced. Furthermore, the solvent should have a fast evaporation rate when mixed with water because the solvent must be evaporated away. When the dispersion of carbon black is to be employed in a photographic light-sensitive material, ethanol, methanol, ethyl acetate, acetone, isopropanol or methyl ethyl ketone is preferably used as the solvent.

The organic solvent need not always have high purity, and it may have some degree of water content, e.g. 10% or so, depending upon the grain sizes of the carbon black used as the raw material, the degree of surface treatment, and so on. When the organic solvent contains water, a water-soluble binder can be added to the organic solvent in an amount proportional to its water content at the first stage of the dispersing steps, if necessary.

The organic solvent in this dispersion process, in a sense, fulfills its function as an intermediate medium. It goes without saying that complete removal of the organic solvent is not necessarily required if the product permits the presence of the organic solvent therein.

Further, the above described oily dispersion of carbon black can be more finely dispersed using a disperser, other than high speed agitator type of disperser, such as a sand grinder, a colloid mill, a homogenizer, a kneader or the like and then water may be added thereto with mixing and agitating. Furthermore, the above described aqueous dispersion of carbon black can be further dispersed more finely using a disperser such as a sand grinder, a colloid mill, a homogenizer or the like.

Useful examples of the above described high speed agitator type of disperser include any disperser designed so that its important part having the dispersing function may rotate at high speed (e.g., 500 to 15,000 rpm and preferably 2,000 to 4,000 rpm), such as a dissolver, a polytron, a homomixer, a homoblender, a Kedy mill, a jet agitator and so on. A dissolver 14 is also called a high speed impeller disperser and an example is described in detail in published unexamined Japanese Patent Application No. 129136/80. This disperser is equipped with a shaft capable of rotating at high speed. The shaft is fitted with an impeller constructed by saw blades bent alternately in up and down directions.Further, it is preferably designed so that when the diameter of the impeller is D, the inside diameter of the tank 11 is set within the range of 2.8D to 4.OD, a space between the impeller and the bottom of the tank 11 within the range of 0.5D to 1.or, and depth of the stationary solution placed in the tank 11 within the range of 1 .OD to 4.OD.

In addition, the shaft of the dissolver 14 can also be fitted with a plurality of the above described impellers or propellers, or the dissolver 14 may be a multiple shaft dissolver having a plurality of shafts. Further, the above described tank 11 can also be provided with a paddle-type agitator, a propellor-type agitator, a colloid mill or another agitator or disperser in addition to the above described dissolver 14.

The above described condenser 1 5 is employed for recovering the organic solvent so that it can be reused.

Conventional vacuum pumps may be used as the pressure reducing apparatus 1 6. However, vacuum pumps of the type which utilize water or steam as a working medium, such as a water seal type vacuum pump, an ejector pump and the like, are preferable. Such pumps are preferred because it is difficult to completely recover the organic solvent using the above described condenser 15, and such pumps are almost unaffected by the residual organic solvent.

It is preferable for the tank 11 to have an outer heating jacket which can be used to accelerate evaporation of the organic solvent. However, the temperature inside the tank 11 should be lower than the boiling point of water in order to prevent evaporation of the water in the dispersion of carbon black.

The degree of vacuum inside the tank 11 is measured by the above described vacuum gauge 17. The evaporation speed of the organic solvent can be controlled by regulating the degree of vacuum, the temperature of the liquid in the tank 11 and the exhausing rate of the pressure reducing apparatus 1 6.

The above described dispersing agent includes a wide variety of dispersing agents described in Bunsan Gijutsu Sogo Shiryoshu (Synthetic Collection of Data Related to Dispersing Techniques), pp. 255-259 and pp. 501-539, Publishing Department of Keiei Kaihatsu Center (1978). Examples of dispersing agents which are especially useful in photographic light-sensitive materials include nonionic surface active agents such as saponin (steroid series), alkylene oxide derivatives (e.g., polyethylene glycol, polyethylene glycol/polypropylene glycol condensates, polyethylene glycol alkyl or alkyl aryl ether, polyethylene glycol esters, polyethylene glycol sorbitol esters, polyalkylene glycol alkylamine or am ides, and polyethylene oxide adducts of silicone), glycidol derivatives (e.g., alkenylsuccinic acid polyglycerides and alkylphenol polyglyceride), fatty acid esters of polyhydric alcohols, alkyl esters of sugar, urethanes of sugar or ethers of sugar; anionic surface active agents containing acidic groups such as a carboxyl group, a sulfo group, a phopho group, a sulfuric ester group, a phosphoric ester group and the like, with specific examples including triterpenoid series saponins, alkylcarboxylates, alkylsulfonates, alkylbenzenesulfonates, polyalkylbenzenesulfonates, alkylnaphthalenesulfonates, alkylsulfuric esters, alkylphosphoric esters, N-acyl-N-alkyltaurines, sulfosuccinic acid ester, sulfoalkylpolyoxyethy lene alkyl phenyl ethers, polyoxyethylene alkyphosphoric esters and the like; amphoteric surface active agents such as amino acids, aminoalkylsulfonic acids, aminoalkylsulfuric or aminoalkylphosphoric esters, alkylbetaines, amineimides, amine oxides and the like; and cationic surface active agents such as alkylamine salts, aliphatic or aromatic quaternary ammonium salts, heretocyclic quaternary ammonium salts, e.g. pyridinium, imidazolium and the like, and phosphonium or sulfonium salts containing aliphatic or heretocyclic rings. Of these dispersing agents, polyalkylbenzenesulfonates are particularly preferable.

In addition, dispersing agents described in published unexamined Japanese Patent Application No. 151936/81 and Research Disclosure, 15162 (Nov., 1976) can also be employed to advantage.

Further, the above described dispersing agents can also be used in combinations of two or more.

Examples of water-soluble binders which are especially useful in preparing aqueous dispersions to be employed in photographic light-sensitive materials include proteins such as gelatin, gelatin derivatives, graft polymers of gelatin and other macromolecules, albumin, casein and the like; cellulose derivatives such as hydroxyethyl cellulose, carboxymethyl cellulose, cellulose sulfuric ester and the like, sugar derivatives such as sodium alginate, starch derivatives and so on; and various kind of synthetic hydrophilic high polymers including homopolymers or copolymrs such as polyvinyl alcohol, polyvinyl alcohol partial acetal, poly-N-vinylpyrrolidone, polyacrylic acid, polymethacrylic acid, polyacrylamide, polvvinylimidazole, polyvinylpyrazole and the like. Of these water-soluble binders, gelatin is preferable.

Gelatin which can be contained in the aqueous dispersions includes not only lime-processed pelatin but also acid-processed gelatin and enzyme-processed gelatin as described in Bull. Soc.

Sci. Phot. Japan, No. 16, p. 30 (1966). In addition, hydrolytic or enzymatic degradation products of gelatin can also be employed. Gelatin derivatives include reaction products of gelatin with various kinds of compounds such as acid halides, acid anhydrides, isocyanates, bromoacetic acid, alkane sultones, vinylsulfone amides, maleimide compounds, polyalkylene oxides, epoxy compounds and so on. Specific examples thereof are described in U.S. Patents 2,614,928, 3,132,945, 3,186,846 and 3,312,553, British Patents 861,414, 1,033,189 and 1,005,784 and published examined Japanese Patent Application 26845/67.

The above described gelatin graft polymers which can be used include those which are obtained by qrafting onto gelatin, homo- or copolymers of vinyl monomers such as acrylic acid, methacrylic acid, esters thereof, amides thereof, acrylonitrile, styrene and the like. Of these graft polymers, polymers qrafted with polvmers compatible with gelatin to some extent, such as acrylic acid polymer, methacrylic acid polymer, acrylamide polymer, methacrylamide polymer, hydroxyalkylmethacrylate polymer and the like are particularly favorable. Specific examples of these graft polymers are described in U.S. Patents 2,763,625, 2,831,767 and 2,956,884.

Typical examples of synthetic hydrophilic high polymers include those described in German Patent Application (OLS) No. 2,312,708, U.S. Patents 3,620,751 and 3,879,205, and published examined Japanese Patent Application No. 7561/68.

Examples of the hvdrophobic substances which can be employed in photographic light sensitive materials included alkylphthalates (e.g., dibutylphthalate, dioctylphthalate), phosphates (e.g., diphenyl phosphate, triphenyl phosphate, tricresyl phosphate, dioctylbutyl phosphate), citrates (e.g., tributyl acetylcitrate), benzoates (e.g., octyl benzoate), alkylamides (e.g., diethyllaurylamide), fatty acid esters (e.g, dibutoxyethyl succinate, dioctyl azelate), lower alkyl acetates like butyl acetate, ethylpropionate, secondary butyl alcohol, methyl isobutyl ketone, cyclohexanone, fi-ethoxyethyl acetate, 2-methoxy ethyl acetate, liquid paraffin and so on.

In addition, other hydrophobic substances which can be employed in the dispersion for other purposes include those described in U.S. Patents 2,322,027, 2,533,514, 2,835,579, 2,353,262, 2,852,383, 3,287,134, 3,554,755, 3,676,137, 3,676,142, 3,700,454, 3,748,141, 3,837,863, 3,936,303 and 4,256,658, British Patents 958,441 and 1,222,753, German Patent Application (OLS) No. 2,538,889 and published unexamined Japanese Patent Application Nos. 1031/72, 29461/74, 62632/75, 82078/75, 27921/76, 27922/76, 26035/76, 26036/76, 26037/76 and 1521/78.

Methods of preparing carbon black aqueous dispersions having small mean grain sizes in a very short time are described in Bunsan Gijutsu Sogo Shiryoshu (Synthetic Collection of Data Related to Dispersing Techniques), Publishing Department of Keiei Kaihatsu Center, 1 978. Page 357 of this publication indicates that high speed impeller-type dispersers are, in principle, used for dispersion of easily dispersible pigments, softened powders or powders modified by surface treatments, but that the dispersers are considered difficult to use for dispersion of various kinds of organic pigments such as carbon black. Accordingly, it can be said that the process of the present invention is contrary to the known procedure.

The dispersing principle of the process of the present invention is presumed to be as follows: (1) In general, a pigment inevitably has both an oleophilic moiety and hydrophilic moiety with their respective inherent strengths and specific fractions. Therefore, pigment particles can be wetted completely over their individual surfaces by the oleophilic moiety which can come into contact with an organic solvent or a combination of an organic solvent and a hydrophobic substance, and by the hydrophilic moiety which can come into contact with water.

(2) But when it is an organic solvent or a combination of an organic solvent and a hydrophobic substance which first contacts the surfaces of pigment particles the pigment particles are slightly soluble to water, previous dissolution of a dispersing agent (capable of creating high dispersing stability) into the organic solvent enables the surface of the pigment particles to be adsorbed by the dispersing agent.

(3) The organic solvent can penetrate deep among primary particles of pigment, which are bonded firmly to one another, due to its low surface tension, and as the removal of the organic solvent proceeds, the residual organic solvent becomes dissolved in water which acts as a dispersing medium. This results in replacement by water and thereby water can penetrate among the primary particles of the pigment. Accordingly, the surfaces of the pigment particles become completely wet with water.

(4) The organic solvent which penetrated among the firmly bonded primary particles of pigment is boiled by applying heat and reduced pressure. The firmly bonded primary particles are then separated from one another by the boiling energy of the organic solvent.

(5) An emulsion is formed due to the copresence of a pigment, an organic solvent, water and a dispersing agent. Even though the formation of the emulsion may be a transient phenomenon, it prevents condensation of the dispersed pigment particles.

If the dispersing principle as described above is true of the process of the present invention, it can be easily analogized that the process of the present invention can be applied advantageoulsy do not only carbon black but also other general pigments, especially oleophilic pigments. In addition, owing to the above described dispersing principle, the dispersion can be produced in a comparatively short time thereby reducing the chance that carbon black surface will generate chemical activity by being scratched. For these reasons, photographic light-sensitive materials using the dispersion prepared in accordance with the process of the present invention have preferable properties.

The present invention will now be illustrated in greater detail by reference to the following examples.

Example 1 In a tank 11 as shown in the drawing, 1 kg of carbon black powder, 5 liters of methanol as an organic solvent, 509 of polyalkylbenzenesulfonate having the following structural formula:

as a dispersing agent, 309 of Aerosol OT (trade name of dioctyl sulfosuccinate, product of American Cyanamide Co.) as another dispersing agent, and 1 g of tricresyl phosphate being a hydrophobic substance were mixed at a temperature of 60"C and agitated at 3,000 rpm for 30 minutes using dissolver 14 to form an oily dispersion of carbon black. Then, 1 2 liters of water was added to the oily dispersion of carbon black obtained, and stirred by the dissolver 14 at 3,000 rpm for- 10 minutes.Thereafter, the tank 11 was closed and a water seal type vacuum pump was operated for 2 hours until the degree of vacuum in the tank reached 200 Torr. Thus, methanol added as the organic solvent was removed by evaporation and, as a result, an aqueous dispersion of carbon black was formed.

The mean grain size of the thus obtained aqueous dispersion of carbon black was 0.4cm.

It should be noted that the measurement of the mean grain size was carried out using "Microtrack" (microtrack particle size analyzer, product of Leeds 8 Northrup Co. (U.S.)) which makes use of the light scattering phenomenon.

Example 2 In the tank 11, 1 kg of carbon black beads, 5 liters of ethyl acetate as an organic solvent, and 1 5g of polyalkylbenzenesulfonate (the same as used in Example 1) were mixed at room temperature (e.g., 20 to 30'C) and agitated at 3,000 rpm for 30 minutes using the dissolver 14 to form an oily dispersion of carbon black. To the oily dispersion of carbon black was then added 5 liters of water and 25g of sodium alkylbenzenesulfoate,

and the resulting mixture was stirred at 3,000 rpm for 10 minutes using the dissolver 1 4.

Thereafter, the tank 11 was closed and the water seal type vacuum pump was continually operated for 1 hour until the degree of vacuum inside the tank reached 1 60 Torr. Thus, the ethyl acetate which was used as the organic solvent was removed by evaporation, and an aqueous dispersion of carbon black was obtained.

The mean grain size of the thus obtained aqueous dispersion of carbon black was 0.5jut.

COMPARATIVE EXAMPLE r For comparison purposes, the above described dissolver was used as a coarse disperser with a sand grinder as a fine disperser in order to make the dispersion. A coarse dispersion of carbon black was first prepared by mixing and agitating 1 kg of carbon black beads, 2 liters of water and 50g of a naphthalenesulfonateformalin condensate acting as a dispersing agent and having the following structual formula at room temperature at 3,000 rpm for 1 hour using the dissolver:

Then, the above described sand grinder was packed with glass beads each having a diameter of 1 mm and therein the coarse dispersion of carbon black was subjected to a continuous dispersing treatment for 5 hours as it was made to circulate (an average number of passing times of the coarse dispersion through the sand grinder was 15).Thus, an aqueous dispersion of carbon black was obtained. The mean grain size of the aqueous dispersion of carbon black obtained was 0.6cm. Further, the thus obtained aqueous dispersion of carbon black was subjected to continuous dispersing treatment for 50 hours (the average number of passing times of the aqueous dispersion was 150) using the same sand grinder to prepare an aqueous dispersion of carbon clack (called the carbon black aqueous dispersion (b)). The mean grain size of this carbon black aqueous dispersion (b) was 0.4cm.

EXAMPLE 3 In the tank 11, 1 kg of carbon black beads, 5 liters of ethyl acetate as an organic solvent, 1 5g of a polyalkylbenzenesulfonate (the same as used in Example 1 above) as a dispersing agent, and 259 of Aerosol OT (trade name of dioctyl sulfosuccinate, product of American Cyanamide Co.) acting as the other dispersing agent were mixed at room temperature and stirred at 3,000 rpm for 30 minutes using the dissolver 14 to prepare an oily dispersion of carbon black. Next, 5 litres of water was added to the oily dispersion obtained, and agitated at 3,000 rpm for 10 minutes using the same dissolver 14.Thereafter, the tank 1 1 was closed and heated up to 50"C and then a water seal type vacuum pump was operated for a period of 1 hour till the degree of vacuum inside the tank reached 1 60 Torr. Thereupon, ethyl acetate added as the organic solvent was evaporated and removed from the dispersion. Thus, an aqueous dispersion of carbon black (called the carbon black aqueous dispersion (a) hereinafter) was prepared.

The mean grain size of the carbon black aqueous dispersion (a) was 0.5,us. In addition, the residual content of ethyl acetate in the carbon black aqueous dispersion (a) was determined using gas chromatography and was found to be 3 x 10-3% or less.

Using the above described carbon black aqueous dispersion (a) and other ingredients described below in their prescribed amounts as described below, a viscous processing solution (A) was prepared. Similarly, using the carbon black aqueous dispersion (b), which was described in Comparative Example 1 and prepared according to the coventional process, and using the same ingredients as used in the viscous processing solution (A) in their prescribed amounts as described below, a viscous porcessing solution (B) was prepared. Each of these processing solutions was placed in two separate, pressure rupturable bag-shaped containers, and sealed respectively. One container was kept at 50"C for 1 week, and the other container was kept at 25"C for 1 week.Each of these preserved processing solutions was examined with respect to their photographic properties in accordance with a method as describe hereinafter.

Viscous Processing Solution (A): To the carbon black aqueous dispersion (a) in an amount corresponding to 1489 of carbon black were added the following amounts of ingredients and further water was added thereto in such an amount as to make the total amount 1 keg.

1 -p-Tolyl-4-hydroxymethyl-4-methyl-3pyrazolidone 8 9 Methylhydroquinone 0.3 9 5-Methylbenzotriazole 3.5 g Sodium Sulfite (anhydrous) 0.2 9 Sodium Salt of Carboxymethyl Cellulose 58 9 Potassium Hydroxide 56 9 Benzyl Alcohol 1.5 ml Viscous Processing Solution (B): Viscous processing solution (B) was prepared by replacing the carbon black aqueous dispersion (a) corresponding to 1489 of carbon black with the carbon black aqueous dispersion (b) corresponding to 1489 of carbon black in the composition of the viscous processing solution (A) described above.

A light-sensitive sheet as described hereinafter was exposed to a tungsten lamp having a temperature of 2,854"K through an optical wedge having a density difference of 0.2.

Thereafter, it was brought into face-to-face contact with a cover sheet and laminated in a fixed position and a pressure rupturable, bag-shaped container described above was inserted between the two sheets at the leading edge thereof to form a unit so that the processing solution retained in the container may be spread in the form of a layer between the two sheets when pressure is applied thereto. The thus formed unit was passed through a pressure-applying means under a temperature of 25"C and thereby the processing solution was spread in a layer having a thickness of 80pm to cause development. After one day, the density of the transferred image was measured by means of a color densitometer.

Light-Sensitive Sheet: A light-sensitive sheet was prepared by coating on a transparent polyethylene terephthalate film support the following layers in the order of description: (1) A mordanting layer cotaining copoly[styrene-N-vinylbenzyl-N,N-trihexylammonium chloride] (3.0 g/m2) and gelatin (3.0 g/m2); (2) A light-reflecting layer containing titanium dioxide (20 g/m2) and gelatin (2.0 g/m2); (3) A light-intercepting layer containing carbon black (3.0 g/m2) and gelatin (2.0 g/m2); (4) A layer containing the cyan dye releasing redox compound having the following structural formula (1) (0.44 g/m2), tricyclohexyl phosphate (0.09 g/m2) and gelatin (0.8 g/m2);;

(5) A layer containing a red-sensitive internal latent image type direct reversal silver bromide emulsion (containing 0.3 g/m2 of silver), gelatin (1.2 g/m2), a nucleating agent having the following structural formula (Il) (0.05 mg/m2) and sodium salt of 2-sulfo-5-n-pentadecylhydroquinone (0.13 g/m2);

(6) A color mixing inhibitor containing layer in which 2,5-di-t-pentadecylhydroquinone (1.0 g/m2) and gelatin (0.8 g/m2) are incorporated; (7) A layer containing the magenta dye releasing redox compound having the following structural formula (III) (0.21 g/m2), the magenta dye releasing redox compound having the following structural formula (IV) (0.11 g/m2), tricyclohexyl phosphate (0.08 g/m2) and gelatin (0.9 g/m2);;

(8) A layer containing a green-sensitive internal latent image type direct reversal silver bromide emulsion (containing 0.82 g/m2 of silver), gelatin (0.9 g/m2), the same nucleating agent as in the layer (5) (0.03 mg/m2) and sodium salt of 2-sulfo-5-n-pentadecylhydroquinone (0.08 g/m2); (9) The same layer as the layer (6); (10) A layer cotaining a yellow dye releasing redox compound having the following structural formula (V) (0.53 g/m2), tricyclohexyl phosphate (0.13 g/m2) and gelatin (0.7 g/m2);

(11) A layer containing a blue-sensitive internal latent image type direct reversal silver bromide emulsion (containing 1.09 g/m2 of silver), gelatin (1.1 g/m2), the same nucleating agent as in the layer (5) (0.04 mg/m2) and sodium salt of 2-sulfo-5-n-pentadecylhydroquinone (0.07 g/m2); (12) A layer containing gelating (1.0 g/m2).

Cover Sheet A cover sheet was prepared by coating on a transparent polyester support the following layers (1') to (3') in the order of description: (1') A layer containing acrylic acid-butylacrylate 80:20 (by weight) copolymer (22 g/m2) and 1 ,4-bis(2,3-epoxypropoxy)butane (0.44 g/m2) and 5-(ss- cyanoethylthio)-1 -phenyltetrazole (0.11 5 g/m2; (2') A layer containing acetyl cellulose (containing 39.4 9 of acetyl group per 1009 of acetyl cellulose) (3.8 g/m2), styrene-maleic anhydride 60:40 (by weight) copolymer having a molecular weight of about 50,000 (0.2 g/m2); (3') A layer containing vinylidene chloride-methylacrylateacrylic acid 85:12:3 (by weight) copolymer latex (2.5 g/m2) and polymethyl methacrylate latex (having grain size of 1-3 ym) (0.05 g/m2).

The results obtained are shown in Table 1.

TABLE 1 Storage Conditions 25"C, 1 week 50"C, 1 week Reflection Density Reflection Density Maximum Minimum Maximum Minimum Viscous Processing Solution (A) Yellow Density 1.83 0.23 1.82 0.23 Magenta Density 2.21 0.22 2.20 0.21 Cyan Density 2.05 0.32 2.06 0.32 Viscous Processing Solution (B) Yellow Density 1.80 0.24 1.55 0.24 Magenta Density 2.18 0.24 2.10 0.22 Cyan Density 2.03 0.34 2.02 0.34 It is apparent from Table 1 that the viscous processing solution (A) in which the carbon black aqueous disperion (a) of the present invention is used has excellent stability during storage. This is evidenced by the fact that the maximum yellow density of the viscous processing solution (A) provided under storage at 50"C (1 week) was identical to what it provided under storage at 25"C (1 week). However, the viscous processing solution (B) which was prepared for comparison showed a marked reduction of the maximum yellow density when stored at 50"C (1 week) as compared with the maximum yellow density attained under the storage condition of 25"C (1 week). Accordingly, the viscous processing solution (B) has poor stability during storage.

Claims (11)

1. A process of preparing an aqueous dispersion of carbon black comprising: (a) mixing and agitating carbon black together with an orgaic solvent and dispersing agent in a tank equipped with a high speed agitator type of disperser, to form an oily dispersion of carbon black; (b) adding water to the oily dispersion of carbon black with mixing and stirring; and (c) removing the organic solvent from the dispersion to form the aqueous dispersion of carbon black.

2. A process as claimed in Claim 1, wherein the amount of the organic solvent mixed with carbon black is 200 to 2,000 millilitres per 100 grams of carbon black.

3. A process as claimed in Claim 1 or 2, wherein the amount of the water added to the oily dispersion is 0.1 to 10 volume parts per volume part of the organic solvent in the oily dispersion.

4. A process as claimed in Claim 1, 2 or 3, wherein the organic solvent is methanol, ethanol, ethylacetate, acetone, isopropanol or methyl ethyl ketone.

5. A process as claimed in any preceding claim, wherein the high speed disperser is rotated at a speed of 500 to 1 5,000 rpm during the mixing, agitation and stirring.

6. A process as claimed in Claim 5, wherein the rotation is at a speed of 2,000 to 4,000 rpm.

7. A process as claimed in any preceding claim, in which a water-soluble binder is also added to the aqueous dispersion of carbon black with mixing and agitating.

8. A process as claimed in any preceding claim, wherein the disperser is comprised of a tank and a shaft having an impeller thereon wherein the diameter of the tank is within the range of 2.8 to 4 times the diameter of the impeller.

9. A process as claimed in any preceding claim, wherein the organic solvent is removed from the dispersion by means of evaporation.

10. A process as claimed in Claim 9, wherein the evaporation is carried out by a combination of heating and reduced pressure.

11. A process as claimed in any preceding claim, which is carried out in an apparatus substantially as shown in the accompanying drawing.

1 2. A process as claimed in Claim 1, substantially as hereinbefore described with reference to any of Examples 1 to 3.

1 3. An aqueous dispersion of carbon black prepared by a process as claimed in any preceding claim.

1 4. A photographic light-sensitive material which contains an aqueous dispersion of carbon black as claimed in Claim 1 3.

1 5. A light-sensitive material as claimed in Claim 14, substantially as hereinbefore described in Example 3.