JPH08234358A - Preparation of aqueous organic silver salt dispersion - Google Patents

Abstract

PURPOSE: To provide a stable aqueous dispersion of an organic silver salt containing no unnecessary alkali salt by removing an alkali nitrate by-produced by the addition of silver nitrate by means of ultrafiltration. CONSTITUTION: Aqueous solution of AgNO3 is added to sodium behenate generated in a raw solution tank 1 to generate sodium nitrate which is a by-product with the silver behenate particle, the resulting solution is then sent to a ceramic ultrafiltration film 10 by a non-seal pump 8 in order to remove the by-produced sodium nitrate, and the operation pressure is set to, for example 0.4MPa to remove the sodium nitrate together with the filtered water. When the operating pressure is raised to 0.6MPa, the circulating passage is switched to a ceramic ultrafiltration film 11, and hot water 12 and pressurized air 13 are mixed together and sprayed to the filtration film 10 from the filtrate outflow side to wash it. A water-soluble protective colloid is made present in the dispersion, thereby, the coagulation from the dispersion is prevented, and a homogeneous coating solution suitable to curtain application which is an economically preferred coating method can be provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preparing an aqueous organic silver salt dispersion, and particularly to an aqueous organic silver salt suitable for a so-called dry silver type heat development recording material without using an organic solvent or an aggregating agent. The present invention relates to a method for efficiently preparing a dispersion.

[0002]

2. Description of the Related Art As a dry-processed light-sensitive material which has been practically used by solving the drawbacks of silver halide wet processing while maintaining the light-sensitivity, gradation and good image quality of silver halide, 3M Company of the United States The so-called dry silver developed is famous. As an organic silver salt, which is one of the essential constituents of this dry silver, it is a colorless or white, light-stable silver salt, which is heated to 100 ° C. or higher in the presence of a light-sensitive silver halide together with a reducing agent. A material that produces silver (image) by a redox reaction when heated is used, and silver behenate is used in the case of being practically used.

There are various known methods for preparing silver behenate in this case, and the method shown in the following chemical formula 1 developed by Eastman Kodak Company in the United States, that is,

Except for the method according to [Chemical Formula 1], all of them had the drawback of using an organic solvent. The above-mentioned preparation method is not only an inexpensive method because it does not use an organic solvent and is also advantageous from the viewpoint of working environment, but it is also possible to easily prepare a high-concentration sodium behenate colloidal dispersion. There was also an advantage.

[0004]

However, the above method has a drawback that it is difficult to remove by-produced alkali nitrate. Therefore, as a result of intensive studies by the present inventors in order to solve the above-mentioned drawbacks, that the ultrafiltration method is particularly suitable for removing the by-product salt,
Further, it was found that the presence of a water-soluble protective colloid in the dispersion upon addition of silver nitrate is important for enhancing the stability of the aqueous system and the organic silver salt dispersion, and arrived at the present invention. Therefore, an object of the present invention is to provide a stable aqueous dispersion of an organic silver salt which does not contain unnecessary alkali salt.

[0005]

SUMMARY OF THE INVENTION The above objects of the present invention are as follows.
An aqueous dispersion in which a mixture of an organic acid and water is heated to a temperature above the melting point of the organic acid to disperse the organic acid in water, and then an aqueous alkaline solution is added to disperse fine particles of a salt of the corresponding organic acid. A method for preparing an aqueous dispersion of an organic silver salt, in which silver nitrate is added to the resulting dispersion after cooling to obtain an alkali nitrate by-produced by the addition of silver nitrate by an ultrafiltration method. It was achieved by a method for preparing a water-based organic silver salt dispersion, which is characterized in that a water-soluble protective colloid is allowed to coexist in the water-based dispersion liquid before removal and, if necessary, addition of silver nitrate.

The organic silver salt prepared in the present invention is a colorless to white, light-stable silver salt, which is oxidized and reduced when heated with a reducing agent in the presence of a light-sensitive silver halide. The reaction produces silver. Such an organic silver salt is a silver salt of an organic compound having an imino group, a mercapto group or a carboxyl group, and specific examples thereof include the following.

1) Silver salt of organic compound having imino group, saccharin silver, phthalazinone silver, silver benzotriazole, etc. 2) Silver salt of organic compound having mercapto group or thione group 3- (2-carboxyethyl) -4- Oxymethyl-4
-Thiazolin-2-thione silver salt, 3-mercapto-4
-Silver salt of phenyl-1,2,4-triazole, etc. 3) Silver salt of organic compound having carboxy group Silver stearate, silver behenate, etc. Among these, silver behenate is white, stable to light, excellent in moisture resistance, can be used in combination with a mild reducing agent, is known to have an excellent toning agent, and the like. Is most preferred.

In the present invention, the alkali used to form the salt of the organic acid is appropriately selected from alkali metals and alkaline earth metals, but sodium hydroxide and potassium hydroxide are particularly preferable. The mixing ratio of the organic acid and water for dispersing the molten organic acid in water is not limited as long as the dispersion is an O / W type, but generally, the larger the ratio of water, the more the dispersion. The stability of is also increased.

In particular, the inclusion of PVA and its modified products, zetillane and other known water-soluble protective colloids,
It is preferable from the viewpoint of increasing the stability of the dispersion. The above protective colloid may be added at any stage up to the addition of silver nitrate. The protective colloid is 0.01% by weight or less in water.
It is preferably added so that 30% by weight is present.

In the method for preparing an aqueous organic silver salt dispersion of the present invention, first, the mixture of the organic acid and water is heated and sublimated above the melting point of the organic acid with vigorous stirring, and the organic acid is submerged in water. After the dispersion, an aqueous alkali solution such as sodium hydroxide is added to obtain an aqueous dispersion liquid in which fine particles of an organic acid alkali salt are dispersed. Next, the temperature of the system is lowered to about 50 ° C., and then silver nitrate is added with stirring to obtain a target organic silver salt dispersion.

In this case, when it is necessary to obtain a transparent background in the transmissive recording material, it is desirable that the amount of excess organic acid is small. It is preferably slightly less than the number. On the other hand, in the case of a reflective recording material, there may be an excess of organic acid.

In the aqueous dispersion of the organic silver salt thus obtained, the organic silver salt, by-produced alkali nitrate, protective colloid, and unreacted organic acid are present. Is also a large amount and needs to be removed.
Conventionally, an organic solvent has been used for removing the alkali nitrate, but this has a drawback that a consistent aqueous process cannot be performed.

Therefore, in the present invention, alkali nitrate is removed by ultrafiltration without using the organic solvent. Ultrafiltration membranes can be desalted without causing clogging compared with the case of using filters of other kinds of fine pores, and the filter can be washed repeatedly after use, so it can be used repeatedly. In addition, there is an advantage that the yield is good because the ability to collect silver behenate is higher than that of a filter having coarse pores.

The semipermeable membrane used in the ultrafiltration may be any membrane that does not allow the organic silver salt to pass but allows the alkali nitrate to pass therethrough, and specific examples thereof include polyvinyl chloride, polyvinyl acetate,
Anisotropy of known polymers such as polyvinyl alcohol, polysulfone, polyvinyl ether, poly (meth) acrylamide, polyimide, polyester, polytetrafluoroethane, polyvinylidene fluoride, cellulose, cellulose acetate, cellulose butyrate and cellulose acetate butyrate. Examples include membranes.

As the ultrafiltration membrane, one made of ceramics (for example, NGK Insulators Co., Ltd., product name "SEFILT") is particularly desirable. Further, in order to increase the filtration efficiency, it is preferable to perform filtration while rotating the membrane to be used. Two or more sets of membranes to be used are installed in parallel and used alternately, and when the permeation pressure of one is increased, It is preferable that the membrane, which is used by switching to one side and whose permeation pressure has increased, is washed by injecting warm water and pressurized air from the permeation side. Also, other ultrafiltration conditions can be appropriately determined according to the desired degree of concentration and the like.

Usually, the pressure of the dispersion liquid sent to the ultrafiltration device is about 1 to 10 MPa (megapascal), the discharge pressure is about 0.1 MPa or less, and the pressure difference before and after the semipermeable membrane is about 0.03.
However, the filtration conditions can be appropriately set depending on the configuration of the ultrafiltration device, the viscosity of the dispersion liquid, the components in the dispersion liquid, and the like.

In the present invention, when two or more ultrafiltration devices are connected in parallel or in series, the cutoff value of each device may be the same or different. In addition, ultrafiltration is
It can also be carried out during the formation of the organic silver salt. In this case, it is necessary to form a loop for returning a part of the filtrate to the reaction tank. In the present invention, 5 to 90% of the dispersion medium in the raw dispersion liquid can be removed by ultrafiltration to obtain an aqueous organic silver salt dispersion liquid having a desired concentration.

[0018]

According to the present invention, unlike the prior art, by-products can be removed efficiently in a remarkably short time, and an extremely high concentration aqueous organic silver salt dispersion liquid can be obtained. In particular, the presence of the water-soluble protective colloid in the dispersion liquid prevents aggregation from the dispersion liquid, and a uniform coating liquid suitable for curtain coating, which is the economically most preferable coating method in the production of photosensitive materials. Is easy to obtain.

[0019]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto. Example 1. Using the equipment shown in FIG. 1, an aqueous dispersion of silver behenate was obtained as follows. Behenic acid 8.53 kg
After adding 200 liters of water to the mixture and heating the whole to 87 ° C., an aqueous solution of 1 kg of NaOH in 25 liters of water was added, and stirring was continued to obtain sodium behenate, then the system was cooled to 50 ° C. did.

Next, in 25 liters of water, AgNO ₃ 4.3 was added.
After adding an aqueous solution in which kg is dissolved to generate silver behenate particles and sodium nitrate as a by-product, first, at a rate of 25 liters per minute with a non-seal pump (8) to remove by-produced sodium nitrate. The solution was sent to a ceramic ultrafiltration membrane (10), the operating pressure was set to 0.4 MPa, and sodium nitrate was removed together with the filtered water. Operating pressure rises to 0.6MP
When it became a, the circulation flow path was switched to the ceramic ultrafiltration membrane (11), and hot water (12) and pressurized air (13) were mixed in the ceramic ultrafiltration membrane (10) to flow out the filtrate. It was sprayed from the side and washed.

When the viscosity of the stock solution reaches 300 mPa · S or higher, pure water is added to the stock solution stock tank, and 100 m
By-product salts are removed while keeping the pressure below Pa · S,
The conductivity of the filtered water was adjusted to 500 μs / cm or less. In order to further concentrate the stock solution, permeation of pure water was stopped and filtration was continued. Finally, the undiluted solution remaining in the film was pushed out into the undiluted solution tank (1) by the pressurized air (7) and collected. The yield of the aqueous dispersion of silver behenate is
It was about 100 kg.

Example 2. In the operation of Example 1, 100 kg of silver behenate emulsion was prepared in the same manner as in Example 1 except that 10 kg of polyvinyl alcohol (PVA205 (trade name) manufactured by Kuraray Co., Ltd.) was added before adding behenic acid. Obtained. The dispersion state of silver behenate particles in the obtained emulsion was better than that in Example 1, and it was possible to further concentrate.

[Brief description of drawings]

FIG. 1 is an equipment diagram for producing an aqueous dispersion of an organic silver salt of the present invention.

[Explanation of symbols]

 1 stock solution tank 2 stirrer 3 pure water 4 electric conductivity meter 5 constant temperature bath 6 vibrating viscometer 7 pressurized air 8 non-seal pump 9 storage 10 ceramic ultrafiltration membrane A 11 ceramic ultrafiltration membrane B 12 hot water 13 pressurized air ( 1 to 4 MPa) 14 Pressure gauge 15 Pressure gauge 16 Pressure gauge 17 Pressure gauge

Claims (3)

[Claims] 1. A method for preparing an aqueous dispersion of an organic silver salt in which silver nitrate is added to an aqueous dispersion in which fine particles of an alkali salt of an organic acid are dispersed, wherein alkali nitrate by-produced by the addition of silver nitrate is limited. A method for preparing an aqueous organic silver salt dispersion, which comprises removing by an external filtration method. 2. The method for preparing an aqueous organic silver salt dispersion according to claim 1, wherein a water-soluble protective colloid is allowed to coexist in the aqueous dispersion before the addition of silver nitrate. 3. The method for preparing an aqueous organic silver salt dispersion according to claim 1, wherein the organic acid is behenic acid and the alkaline aqueous solution is an aqueous sodium hydroxide solution and / or an aqueous potassium hydroxide solution.