JP2001264920A - Method for preparing organic silver salt composition and heat developable photosensitive material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for preparing an organic silver salt composition with enhanced productivity and to provide a heat developable photosensitive material which suppresses the rise of fog after development and has enhanced raw stock preservability. SOLUTION: In the method for preparing an organic silver salt composition, silver nitrate is added to an aqueous solution or suspension of an alkali salt of an organic acid to prepare an organic silver salt dispersion and this dispersion is immediately desalted and dehydrated by centrifugation or pressure filtration.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing an organic silver salt composition, and further relates to a photothermographic material containing the organic silver salt composition produced by using the method.

[0002]

2. Description of the Related Art As a photothermographic material, a black-and-white photothermographic material containing an organic silver salt called dry silver is well known, and US Pat. No. 5,343,043,
Research Disclosure 17029
And many patents and references.

The image forming layer applied to the photothermographic material contains organic silver salt particles. Usually, the organic silver salt grains are formed in an aqueous mother liquor and are often mixed here with preformed silver halide grains. As an outline of the most general manufacturing process, a dry powder is formed through a drying process, dispersed in an organic solvent and / or a binder, and prepared, and then applied to a support.

Various methods are known for preparing an organic silver salt as a silver supplier used in a photothermographic material.
For example, JP-A-49-93310, JP-A-49-94
No. 619, and a method of preparing an organic silver salt in a co-existing solution of water and a poorly water-soluble solvent as described in JP-A-53-68702,
JP-A-53-31611, JP-A-54-4117,
And a method for preparing an organic silver salt in an aqueous solution as described in JP-A-54-46709;
, Japanese Patent Application Laid-Open No. 47-9432 and U.S. Pat.
No. 0,458, a method of preparing an organic silver salt in an organic solvent, and the like.

[0005] Of these methods, in recent years, a method of preparing an organic silver salt in an aqueous solution is generally used. However, at that time
It was difficult to efficiently remove by-product alkali nitrate. As a countermeasure, JP-A-8-234358 discloses a method using an ultrafiltration membrane to remove by-product alkali nitrate. However, in ultrafiltration, the membrane permeation rate is slow and it takes time to remove alkali nitrate, and organic silver adheres to the pores of the ultrafiltration membrane during filtration, and the membrane is washed,
There was a problem that recovery recovery was not good.

[0006] As an improvement, the present inventors have disclosed in Japanese Patent Application No.
No. 255063 proposed a method of using a microfilter in a cross-flow system instead of ultrafiltration. According to this method, the membrane permeation rate can be increased about 10 times that of the ultrafiltration, and as a result, the time required for producing the organic silver salt can be greatly reduced. However, this case is still insufficient, and it has been desired to remove by-product alkali nitrate by a more effective method in producing an organic silver salt dispersion.

The present inventors have disclosed a method for producing an organic silver salt dispersion by adding silver nitrate to an aqueous solution or suspension of an alkali salt of an organic acid as disclosed in Japanese Patent Application No. 11-63284. Is separated from the aqueous phase by flotation separation, and the by-produced salt (alkali nitrate) is removed by removing the aqueous phase.
A desalination method to remove the water was proposed. By this desalting method,
Compared with a method using an ultrafiltration membrane or a filtration method using a microfilter in a cross-flow method, the time and the amount of treated water can be significantly reduced. The present inventors have studied further reduction of time and reduction of the amount of treated water.

The present inventors have also filed Japanese Patent Application No. 10-357.
No. 466 discloses a centrifugal dehydration method as a method for efficiently dewatering a desalted organic silver salt dispersion to reduce the drying load, shorten the drying time, and improve the photographic performance of the photothermographic material used thereafter. Alternatively, it was proposed to perform dehydration treatment by a press dehydration method. By this dehydration method, the drying load can be greatly reduced, and a heat-developable photographic light-sensitive material having a reduced fog after development can be obtained.

The present inventors have been studying a more efficient method for producing an organic silver salt by combining these efficient dehydration and desalting steps.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a more efficient method for producing an organic silver salt dispersion in which unnecessary alkali nitrate content is reduced as much as possible, and to increase fog after development. Another object of the present invention is to provide a photothermographic material in which the temperature is reduced.

[0011]

The above objects of the present invention have been attained by the following items 1 to 3.

1) An organic silver salt dispersion characterized in that silver nitrate is added to an aqueous solution or suspension of an alkali salt of an organic acid to produce an organic silver salt dispersion, and then desalination and dehydration are immediately performed by a centrifugal separation method. A method for producing the composition.

2) An organic silver salt is prepared by adding silver nitrate to an aqueous solution or suspension of an alkali salt of an organic acid to produce an organic silver salt dispersion, and immediately performing desalting and dehydration by a pressure filtration method. A method for producing a salt composition.

3) A photothermographic material comprising an organic silver salt composition produced by the production method described in 1) or 2) above.

Hereinafter, the present invention will be described in detail. In the photothermographic material, the organic silver salt is a reducible silver source, and a silver salt of an organic acid containing a reducible silver ion source, particularly a long chain (10 to 30, preferably 15 to 25 carbon atoms). Are preferred. Examples of these suitable silver salts are described in Research Disclosure (RD) 17029 and 29996, and include the following: Silver salts of organic acids (eg, gallic acid, Acid, behenic acid, arachidic acid, stearic acid, palmitic acid, silver salts such as lauric acid). Preferred silver sources are silver behenate, silver arachidate and silver stearate.

In this case, various methods for preparing an organic silver salt, typically, silver behenate, are known, but most of the conventional methods mainly use an organic solvent. From the viewpoint of the working environment, a method that does not use an organic solvent is preferable. In the present invention, an organic silver salt is mixed with an aqueous solution or suspension of an alkali salt of an organic acid (such as an alkali metal salt or an ammonium salt) and silver nitrate. Form a dispersion. As the mixing method, a forward mixing method, a reverse mixing method, a simultaneous mixing method, a controlled double jet method described in JP-A-9-127463, and the like are preferably used.

As a specific method, for example, an alkali metal hydroxide (eg, sodium hydroxide, potassium hydroxide, etc.) is added to an organic acid, and an organic acid alkali metal salt soap (eg, sodium behenate, sodium arachidate) is added. And the like, and then adding the above-mentioned soap and an aqueous solution of silver nitrate by a controlled double jet method to produce an aqueous dispersion of an organic silver salt. At that time, photosensitive silver halide grains may be mixed.

In the aqueous dispersion of the organic silver salt thus obtained, the formed organic silver salt and the by-produced alkali nitrate, protective colloid, unreacted organic acid and its alkali salt coexist. But removes by-product alkali nitrate,
That is, desalination and washing with water are required.

The aqueous dispersion of the obtained organic silver salt is usually filtered to remove an aqueous phase containing alkali nitrate by-produced, and the organic silver salt is sufficiently washed with clean water and then dried. Then, it is dispersed in a binder such as polyvinyl butyral and used for a photothermographic material.

The organic silver salt formed in the aqueous solution has a small particle size, and is usually pressed to be sufficiently dehydrated at the time of filtration. As the water repels water, the filterability deteriorates, the filtration takes a very long time, and the washing cannot be performed sufficiently, so that alkali nitrate remains.

In order to solve such a problem, the desalination method is more efficient than the flotation method proposed by the present inventors in combination with the centrifugal separation method or the dewatering method using the pressure filtration method proposed by the present inventors. As a result of repeatedly examining whether or not there is a combination with the method, immediately after forming the organic silver salt dispersion of the present invention, centrifugation or pressure filtration is performed, followed by washing, thereby efficiently and quickly. It has been found that an organic silver salt composition can be obtained.

Surprisingly, it is more surprising that continuous desalting and dewatering by centrifugation or pressure filtration according to the method of the present invention is performed by centrifugation or desalting after flotation. It was found that the desalting and dewatering efficiency was better than performing dehydration using pressure filtration. Therefore, it was found that the heat-developable photographic material using the organic silver salt formed by the method of the present invention has low fog and good preservability of the photographic material before exposure.

In the present invention, the term "immediately" means that after forming an organic silver salt dispersion in an aqueous solvent, the organic silver salt is floated and separated by taking a resting time again, or separated by adding water and diluting. Means that the solution is sent to a centrifuge or a filter press immediately after the formation of the organic silver salt dispersion without accelerating the dispersion.

That is, the term “immediately” in the present invention means that the time from the formation of the organic silver salt dispersion to the start of filtration is within 5 hours at most, preferably within 3 hours, particularly preferably within 3 hours. Is less than 1 hour, and it is most preferable to start the filtration step without any time after adding silver nitrate to the organic acid alkali salt to form an organic silver salt dispersion.

By not performing the floating separation,
The total time until desalting, dehydration, and drying after forming the organic silver salt dispersion can be significantly reduced, and some impurities remain in the aggregate formed by flotation previously proposed by the present inventors. However, from the viewpoint of photographic performance, it has been found that there is a difference in the characteristics from the photothermographic material using the organic silver salt composition obtained by the method of the present invention.

Hereinafter, a manufacturing apparatus used in the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram of an apparatus for producing an organic silver salt dispersion for mixing an organic acid alkali and silver nitrate described in Japanese Patent Application No. 11-63284, which describes a method for separating an organic silver salt dispersion by flotation. It is. Here, an organic acid alkali and an aqueous solution of silver nitrate are mixed to prepare an organic silver salt dispersion. 1 is a can as a reaction tank, 2 is an anchor mixer for stirring the whole, 3 is a homodisper as an auxiliary stirrer, 4 is an axial flow generated by high rotation and high shearing force, and a rapid flow of organic acid alkali and silver nitrate. It is a homomixer that performs uniform mixing. M represents a driving motor attached to each stirring device. Reference numeral 5 denotes an addition port for silver nitrate provided in the vicinity of the homomixer having a high rotation and a high shearing force, so that rapid and uniform mixing can be achieved by being provided in the vicinity of the homomixer.

The centrifugal separation method used in the present invention is a method in which an organic silver salt dispersion is poured together with a mother liquor into a cylindrical container, and the container is rotated at a high speed for dehydration. There is no particular limitation as long as it is a device for dehydrating by such a mechanism, and any dehydrating device can be preferably applied. Centrifugal dewatering devices include a perforated wall type having a plurality of holes for discharging water on the wall of the container, and a non-porous wall type for discharging water from the top of the container without a hole in the wall. But,
In the present invention, the former type is more preferably applied.

FIG. 2 is a schematic sectional view of a centrifugal dewatering apparatus used in the present invention. Reference numeral 6 denotes a can of a centrifugal separator, in which a basket 7 having a filtering surface is provided. The basket 7 is rotated at a high speed by a motor. Reference numeral 8 denotes a slurry supply hopper, which supplies the formed organic silver salt dispersion in a slurry state. Reference numeral 9 denotes a cleaning water supply nozzle.

FIG. 3 is a schematic sectional view showing each step of desalination and dehydration by a centrifugal separation method. In the supply of the undiluted solution in the figure, while supplying the slurry-like organic silver salt dispersion formed from the slurry supply hopper 8 to the basket 7 rotating at a high speed, the solution contains alkali nitrate dissolved as a by-product. The water is separated off as the filtrate. After the slurry supply,
In the first dehydration, part of the alkali nitrate dissolved as a by-product is separated as a filtrate. Before water is removed and cracks occur on the surface of the organic silver salt dispersion cake inside the basket, washing water is supplied from the washing water supply nozzle 9 in the desalting step to disperse the organic silver salt. The product cake is washed, and while removing by-product alkali nitrate, desalting is performed until the conductivity of the filtrate reaches a target value. After the desalination, the supply of the washing water is terminated. If necessary, the rotation speed of the basket is adjusted, and further secondary dehydration is performed to remove excess water.

When the organic silver salt composition is desalted and dehydrated by the centrifugal separation method used in the present invention, a centrifugal force G defined by the following relational expression (1) is used to improve the desalting and dehydration efficiency. Is more preferably 500 or more, and 800
More preferably, it is the above.

Relational expression (1) G = 1.119 × 10 ⁻⁵ × r × N ² where r is the radius of the basket [c
m], and N represents the rotation speed [rpm] of the basket.

Next, the pressure filtration system used in the present invention mainly comprises a filter medium such as a filter cloth, a filter plate sandwiching the filter medium, and a pressing member for pressing the filter medium. The target organic silver salt dispersion is injected together with the mother liquor into the gap between the filter medium and the filter medium held between the filter plates, and the dispersion is pressed by pressing the filter medium with the pressing member. It is a method of dehydration. There is no particular limitation as long as it is a device for dehydrating by such a mechanism, and any dehydrating device can be preferably applied.

As the dehydration apparatus of the pressure filtration system described above, for example, an apparatus as shown in FIG. 4 or 5 is preferably used.

FIG. 4 is a schematic cross-sectional view of a dehydrator using a simple press system used in the present invention. In FIG.
The slurry of the organic silver salt dispersion is supplied from the slurry supply port 19 through the valve 16 to the filter cloths 21 and 22 and the filter plates 24 and 25.
And air is sent from an air inlet 10 to an air cylinder 14 through a pressure gauge 11 and three-way valves 12 and 13 to squeeze a slurry of the organic silver salt dispersion, and a valve 17 is discharged from a filtrate outlet 20. The filtrate is discharged through to perform dehydration treatment. In addition, washing water is supplied from the washing water supply port 18 via the valve 15, and a desalting treatment of the organic silver salt dispersion is performed.

FIG. 5 is a schematic sectional view of a dehydrator using a filter press system used in the present invention. A large number of filter plates 27 and filter cloths 28 are attached to the gantry 26 by being more strongly tightened from both sides.

FIG. 6 is a schematic sectional view showing each step of desalination and dewatering by the filter press method. In the figure,
In the supply of the undiluted solution, while supplying the slurry-like organic silver salt dispersion between the filter cloths 28 sandwiched between the two filter plates 27, water containing by-produced dissolved alkali nitrate is discharged from the filtrate. It is separated as a filtrate from the outlet 29. After slurry supply, 1
In the next dehydration, pressurized water is further fed into the diaphragm 30 from the pressurized water supply port 31, and the filter cloth is squeezed to separate a part of by-produced and dissolved alkali nitrate as a filtrate. Before water is removed and cracks occur on the surface of the organic silver salt dispersion cake, washing water is supplied from the washing water supply port 32 in the subsequent desalting to wash the organic silver salt dispersion cake, While removing by-product alkali nitrate, desalting is performed until the conductivity of the filtrate reaches a target value. After the desalination, the supply of the washing water is terminated, the pressure of the pressurized water is adjusted if necessary, and the pressurized water is sent again to the diaphragm 30,
The filter cloth is squeezed and subjected to further secondary dehydration to remove excess water.

In the method for producing an organic silver salt composition of the present invention,
The temperature of the washing water at the time of desalination is more preferably 20 ° C. or higher for improving the desalination efficiency, and further preferably 30 ° C. or higher. It is considered that the reason for this is that the filtration rate when the washing water passes through the organic silver salt dispersion is inversely proportional to the viscosity of the washing water. However, in this case, if silver halide is mixed in the organic silver salt composition, particularly, 60
It is preferably performed at a temperature of not more than ℃.

The organic silver salt dispersion, which has been desalted and dehydrated through such steps, is then dried to obtain a powdery organic silver salt composition.

By the above-mentioned method, an organic silver salt composition containing less unnecessary salts and by-products can be efficiently obtained in a short time. To prepare a photothermographic material using these organic silver salt compositions, the organic silver salt composition is dispersed using a binder and a solvent, if necessary, using a ball mill or the like. , A color tone, a silver halide (which may be mixed at the time of preparing an organic silver salt) or a silver halide forming component, and other necessary additives to prepare a coating solution, and a support such as a PET base. A photothermographic material is prepared by coating on the top. The photothermographic material using the organic silver salt obtained by the method of the present invention is less affected by by-products during the preparation of the organic silver salt, and therefore has low fog, and the storage stability of the photothermographic material before exposure. It was found to be excellent. Other additives used in the photothermographic material prepared using the organic silver salt composition of the present invention and the method of adding the additives are described in detail in RD17029 and 29963.

Although the method and apparatus for producing an organic silver salt of the present invention have been specifically described above, the present invention is not limited thereto.

[0041]

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 << Preparation of silver halide emulsion A >> 7.5 g of ossein gelatin and 10 mg of potassium bromide were dissolved in 900 ml of water, the temperature was adjusted to 35 ° C. and the pH was adjusted to 3.0, and then silver nitrate 74 was dissolved.
g of an aqueous solution containing potassium bromide and potassium iodide in a molar ratio of (98/2) (equimolar to silver nitrate) and K ₂ [Ir (NO) Cl ₅ ] at a concentration of 1 × per mole of silver. 10 ^-4 mole was added over 10 minutes by controlled double jet while maintaining pAg 7.7. Thereafter, 4-hydroxy-6-methyl-1,3,3a, 7-
Tetrazaindene was added and the pH was adjusted to 5 with NaOH to obtain cubic silver iodobromide grains having an average grain size of 0.06 μm, a grain size variation coefficient of 11%, and a [100] face ratio of 87%. The emulsion was subjected to coagulation sedimentation using a gelatin coagulant and desalting treatment.
g, and adjusted to pH 5.9 and pAg 7.5. Further, it was optimally chemically sensitized with sodium thiosulfate and chloroauric acid to obtain silver halide emulsion A.

<< Preparation of Organic Fatty Acid Na Solution B >> The following preparation was carried out using Combimix SL-10 (a schematic diagram is shown in FIG. 1) manufactured by Tokushu Kika Kogyo Co., Ltd. 111.4 g of behenic acid, 83.8 g of arachidic acid were added to 4725 ml of pure water in a Combimix SL-10 type reaction vessel.
54.9 g of stearic acid were dissolved at 80 ° C. that time,
The rotation speed of the anchor mixer was set to 100 rpm, and the rotation speeds of the homodisper and the homomixer were set to 1500 rpm. Next, a 1.5 M sodium hydroxide aqueous solution 54
0.2 ml was added. Next, after adding 6.9 ml of concentrated nitric acid, the mixture was cooled to 55 ° C. to obtain an organic fatty acid Na solution B.

<< Formation of Organic Silver Salt Dispersion C >> While maintaining the temperature of the organic fatty acid Na solution B at 55 ° C., the rotation speed of the anchor mixer was set to 120 rpm, and the rotation speed of the homodisper and the homomixer was set to 2500 rpm. Then, 32.3 g of the silver halide emulsion A and 450 ml of pure water were added. Next, the rotation speed of the anchor mixer is set to 165 rpm.
m, rotation speed of homodisper and homomixer is 50
At a setting of 00 rpm, 780 ml of a 1M silver nitrate aqueous solution was passed through a silver nitrate introduction pipe over 2 minutes and added to the vicinity of the homomixer. Furthermore, the rotation speed of the homodisper and the homomixer was set to 4500 rpm, and the mixture was stirred for 10 minutes to obtain an organic silver salt dispersion C.

<< Desalting and Dehydration of Organic Silver Salt Composition D1 >> Within 1 hour after the formation of the organic silver salt dispersion C, a centrifugal separator H-122 model BS-030 manufactured by Kokusan Co., Ltd. The operation was performed. Centrifuge H-122 Model BS
The value of the centrifugal force G of −030 was set to 300 (a schematic diagram is shown in FIG. 2), and the organic silver salt dispersion C was supplied from the slurry supply hopper. After the supply is completed, dehydration is performed for 30 seconds (1
Next, washing water was supplied from the washing water supply nozzle to start cake washing. The conductivity of the filtrate was monitored, and when the conductivity became 50 μS / cm or less, the supply of the washing water was stopped to terminate the desalting (desalting step). Thereafter, dehydration was performed with the value of the centrifugal force G set to 600 (secondary dehydration). Through the above operations, an organic silver salt composition D1 was obtained.
The washing water temperature was 25 ° C., and the secondary dehydration time was 10 minutes.

<< Desalting and Dehydration of Organic Silver Salt Composition D2 >> Within one hour after the formation of the organic silver salt dispersion C, the following operation was carried out using a simple press as shown in FIG. . The organic silver salt dispersion C was supplied from a slurry supply port into a simple press. After the supply is completed, press pressure is set to 9.8 × 10 ⁴
Dehydration was performed for 1 minute at Pa (primary dehydration step), and then washing water was supplied from the washing water supply port to start cake washing. The conductivity of the filtrate was monitored and the conductivity was 50 μS /
cm, the supply of the washing water was stopped to terminate the desalination (desalting step). Then, press pressure was 3 × 9.8 ×
Dehydration was performed at 10 ⁴ Pa (secondary dehydration). Through the above operations, an organic silver salt composition D2 was obtained. The washing water temperature was 25 ° C., and the secondary dehydration time was 1 minute.

<< Desalting and Dehydration of Organic Silver Salt Composition D3 >> The organic silver salt dispersion C is transferred to a container having a capacity of 40 liters, pure water is added thereto, and the mixture is stirred and allowed to stand to float the organic silver salt dispersion. Separated. After flotation, water-soluble salts were removed by removing the lower aqueous layer. The same operation was repeated, and the desalting was terminated when the conductivity of the lower aqueous layer finally became 50 μS / cm or less. Thereafter, using a centrifugal separator H-122 model BS-030 manufactured by Kokusan Co., Ltd.
Dehydration was performed with the value of the centrifugal force G set to 600 to obtain an organic silver salt composition D3. The temperature of the washing water was 25 ° C, the number of times of desalination was 5 times,
The dehydration time was 10 minutes.

<< Desalting and Dehydration of Organic Silver Salt Composition D4 >> The organic silver salt dispersion C is transferred to a container having a capacity of 40 liters, pure water is added thereto, and the mixture is stirred and allowed to stand to float the organic silver salt dispersion. Separated. After flotation, water-soluble salts were removed by removing the lower aqueous layer. The same operation was repeated, and the desalting was terminated when the conductivity of the lower aqueous layer finally became 50 μS / cm or less. Thereafter, dehydration was performed using a simple press at a press pressure of 3 × 9.8 × 10 ⁴ Pa to obtain an organic silver salt composition D4. The washing water temperature is 2
Dehydration was performed at 5 ° C, 5 times of desalting, and 1 minute of dehydration.

(Comparative Evaluation of Desalting / Dehydrating Methods) Productivity: The time required for desalting / dehydrating the same amount of the organic silver salt dispersion, the shorter the better.

Amount of washing water used: The amount of washing water required for desalting the same amount of the organic silver salt dispersion.

Dehydration: The lower the water content after dehydration, the better. The moisture content was represented by [(wet mass-dry mass) / dry mass] × 100 (%).

Table 1 shows a comparison of the desalting / dewatering time, the amount of washing water used, and the water content after dehydration in each desalting method. The washing water amount per unit weight of the organic silver salt dispersion in terms of dry weight and the filtrate The relationship with the conductivity is shown in the graph of FIG.

[0053]

[Table 1]

As is clear from Table 1 and FIG.
It can be seen that the present invention is very effective in terms of the amount of washing water used and dehydration.

Example 2 << Preparation of photosensitive organic silver salt dispersion E1 >> Organic silver salt composition D
1 was dried with hot air at 40 ° C. using a box dryer until the water content became 0.15% or less for 71 hours to obtain a dried powder of an organic silver salt dispersion.

Polyvinyl butyral powder (Monsan
8.7 g of Butvar B-79 manufactured by To Co., Ltd.) was dissolved in 875 g of methyl ethyl ketone, and VMA-GETZMA was dissolved.
NN dissolver DISPERMAT CA-40M
While stirring in a mold, 300 g of the dried powder of the organic silver salt dispersion was gradually added and mixed well to prepare a preliminary dispersion.

A media type disperser DISPERMAT SL filled with zirconia beads of 0.5 mm in diameter (Treseram, manufactured by Toray Industries Co., Ltd.) to an inner volume of 80% so that the pre-dispersion liquid is retained in the mill for 10 minutes using a pump. -C1
2EX type (manufactured by VMA-GETZMANN),
By performing dispersion at a mill peripheral speed of 13 m / s, a photosensitive organic silver salt dispersion E1 was obtained.

<< Preparation of Photosensitive Organic Silver Salt Dispersion E2 >> Using the organic silver salt composition D2, except that the drying time was changed to 59 hours, the same procedure as in the preparation of the photosensitive organic silver salt dispersion E1 was carried out.
A photosensitive organic silver salt dispersion E2 was obtained.

<< Preparation of Photosensitive Organic Silver Salt Dispersion E3 >> Using the organic silver salt composition D3, except that the drying time was 98 hours, the same procedure as in the preparation of the photosensitive organic silver salt dispersion E1 was carried out.
A photosensitive organic silver salt dispersion E3 was obtained.

<< Preparation of Photosensitive Organic Silver Salt Dispersion E4 >> Using the organic silver salt composition D4, except that the drying time was 83 hours, the same procedure as in the preparation of the photosensitive organic silver salt dispersion E1 was carried out.
A photosensitive organic silver salt dispersion E4 was obtained.

<< Preparation of PET-Subbed Photographic Support >> A corona discharge treatment of 8 W / m ² · min. Was performed on both sides of a commercially available biaxially stretched and heat-fixed 100 μm thick PET film.
On one surface, the following undercoating coating solution a-1 was dried to a thickness of 0.8 μm.
And then dried to form a subbing layer A-1. On the other side, the following antistatic coating subbing coating solution b-1 is applied to a dry film thickness of 0.8 μm and dried. In this way, an antistatic subbing layer B-1 was obtained.

(Undercoating solution a-1) Butyl acrylate (30% by mass) t-butyl acrylate (20% by mass) Styrene (25% by mass) Copolymer latex liquid of 2-hydroxyethyl acrylate (25% by mass) (Solid content 30%) 270 g (C-1) 0.6 g hexamethylene-1,6-bis (ethylene urea) 0.8 g Finished to 1 liter with water (Subbing coating solution b-1) Butyl acrylate (40 mass) %) Styrene (20% by mass) Glycidyl acrylate (40% by mass) copolymer latex liquid (solid content 30%) 270 g (C-1) 0.6 g Hexamethylene-1,6-bis (ethylene urea) 0. 8g Finished to 1 liter with water Then, on the upper surface of the undercoat layer A-1 and the undercoat layer B-1,
A corona discharge of 8 W / m ² · min. Was performed, and the following lower coating liquid a-2 was coated on the lower coating layer A-1 with a dry film thickness of 0.1 μm.
And dried to form an undercoating upper layer A-2. On the undercoating layer B-1, the following undercoating upper layer coating solution b-2 is applied so as to have a dry film thickness of 0.8 μm. Then, the resultant was dried and coated as a subbing upper layer B-2 having an antistatic function.

(Undercoating upper layer coating solution a-2) Gelatin 0.4 g / m ² Mass (C-1) 0.2 g (C-2) 0.2 g (C-3) 0.1 g Silica particles ( (Average particle size: 3 μm) 0.1 g Finished to 1 liter with water (undercoating upper layer coating solution b-2) (C-4) 60 g Latex liquid containing (C-5) as a component (solid content: 20%) 80 g Ammonium sulfate 0 0.5 g (C-6) 12 g Polyethylene glycol (weight average molecular weight 600) 6 g Finish to 1 liter with water

[0064]

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[0065]

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(Heat treatment of the support) In the above-mentioned undercoat drying step of the undercoated support, the support was heated at 140 ° C.
Thereafter, it was gradually cooled.

<< Preparation of Photothermographic Material >> The following layers were successively coated on the PET-subbed photographic support.
Was prepared. The drying was performed at 60 ° C. for 15 minutes. Samples 2 to 4 were prepared in the same manner, except that the photosensitive organic silver salt dispersion E1 was changed to photosensitive organic silver salt dispersions E2 to E4, respectively.

(Back Layer Coating) Back layer: A solution having the following composition was applied.

Cellulose acetate (10% methyl ethyl ketone solution) 15 ml / m ² dye-B 7 mg / m ² dye-C 7 mg / m ² Matting agent: monodispersity 15% Average particle size 10 μm monodisperse silica 30 mg / m ² C _{9 H 19 -C 6 H 4 -SO 3} Na 10mg / m 2

[0070]

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(Coating on photosensitive layer side) Photosensitive layer: A solution having the following composition was applied so that the coated silver amount was 2.1 g / m ² .

Photosensitive organic silver salt dispersion E1 240 g Sensitizing dye-1 (0.1% methanol solution) 1.7 ml Pyridinium bromide perbromide (6% methanol solution) 3 ml Calcium bromide (0.1% methanol solution) 1.7 ml Antifoggant-2 (10% methanol solution) 1.2 ml 2- (4-chlorobenzoyl) benzoic acid (12% methanol solution) 9.2 ml 2-mercaptobenzimidazole (1% methanol solution) 11 ml Tri Bromomethylsulfoquinoline (5% methanol solution) 17 ml Reducing agent A-4 (20% methanol solution) 29.5 ml Hardening agent H (1% methanol solution) 3 ml

[0073]

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[0074]

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Surface protective layer: A solution having the following composition was applied on the photosensitive layer. Acetone 35 ml / m ² Methyl ethyl ketone 17 ml / m ² Cellulose acetate 2.3 g / m ² Methanol 7 ml / m ² Phthalazine 250 mg / m ² 4-Methylphthalic acid 180 mg / m ² Tetrachlorophthalic acid 150 mg / m ² Tetrachlorophthalic anhydride 170 mg / m ² matting agent: monodispersion degree 10% average particle size 4 μm monodisperse silica 70 mg / m ² C ₉ H ₁₉ -C ₆ H ₄ -SO ₃ Na 10 mg / m ² << Performance evaluation of photothermographic material >> Exposure and development treatment) The photothermographic material prepared above was exposed with an imager having a semiconductor laser of 810 nm. Then, using an automatic processor with a heat drum,
The film was heat-developed at 120 ° C. for 15 seconds. At that time, exposure and development were performed in a room conditioned at 23 ° C. and 50% RH.

(Evaluation of Photographic Performance) After thermal development, the obtained images were evaluated using a densitometer PDA-65 (manufactured by Konica). The result of the measurement is Dmin (fog) and sensitivity (Dm
(reciprocal of the ratio of the exposure amount giving a density higher than 1.0 in). The smaller the value of Dmin, the better, and the sensitivity was shown as a relative sensitivity, taking the sensitivity of Sample 3 as 100.

(Evaluation of Raw Preservability) The photothermographic material prepared as described above was stored for 3 days under conditions of humidity control at 55 ° C. and 50% RH, and then exposed and developed to evaluate photographic performance. . The evaluation of raw preservability is expressed by (fog after storage, sensitivity)-(fog before storage, sensitivity), and the closer each value is to 0, the better.

Table 2 shows the above results. The moisture content of the organic silver salt composition after dehydration and the drying time until the moisture content becomes 0.15% or less are also shown in Table 2 below.

[0079]

[Table 2]

As can be seen from Table 2, the productivity of the organic silver salt composition of the sample of the present invention was improved by shortening the drying time until the water content became 0.15% as compared with the comparative sample. An increase in fog after development of the photothermographic material containing the organic silver salt composition is suppressed. At the same time, water-soluble salts were effectively removed from the organic silver salt composition,
It is clear that the raw preservability has been improved.

[0081]

According to the present invention, there is provided a method for producing an organic silver salt composition having improved productivity, and a photothermographic material having improved raw preservability, in which the rise in fog after development is suppressed. I was able to do it.

[Brief description of the drawings]

FIG. 1 is a schematic view of an apparatus for producing an organic silver salt dispersion for mixing an organic acid alkali and silver nitrate used in the present invention.

FIG. 2 is a schematic sectional view of a centrifugal dewatering apparatus used in the present invention.

FIG. 3 is a schematic sectional view showing a desalination and dehydration step by a centrifugal separation method.

FIG. 4 is a schematic cross-sectional view of a dehydrator using a simple press method among pressure filtration methods used in the present invention.

FIG. 5 is a schematic cross-sectional view of a dehydrator using a filter press method among pressure filtration methods used in the present invention.

FIG. 6 is a schematic cross-sectional view showing a desalination and dehydration step by a filter press method among pressure filtration methods.

FIG. 7 is a graph showing the relationship between the amount of washing water and the conductivity of the filtrate depending on the difference in the dehydration method.

[Explanation of symbols]

 Reference Signs List 1 can body 2 anchor mixer 3 homodisper 4 homomixer 5 silver nitrate addition port 6 can body 7 basket 8 slurry supply hopper 9 washing water supply nozzle 10 air inlet 14 air cylinder 18 washing water supply port 26 mount 27 filter plate 28 filtration Cloth 29 Filtrate discharge port 30 Diaphragm 31 Pressurized water supply port 32 Cleaning water supply port

Claims (3)

[Claims] An organic silver salt characterized in that silver nitrate is added to an aqueous solution or suspension of an alkali salt of an organic acid to produce an organic silver salt dispersion, and then desalination and dehydration are immediately performed by a centrifugal separation method. A method for producing the composition. 2. An organic silver salt, wherein silver nitrate is added to an aqueous solution or suspension of an alkali salt of an organic acid to produce an organic silver salt dispersion, and then desalination and dehydration are immediately performed by a pressure filtration method. A method for producing a salt composition. 3. A photothermographic material comprising an organic silver salt composition produced by the method according to claim 1.