JP2006232969A - Method for producing precursor for rare earth-activated alkaline earth metal fluoride halide-based photostimulable phosphor, and rare earth-activated alkaline earth metal fluoride halide-based photostimulable phosphor, and radiation image conversion panel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing photostimulable phosphor imparting an image free from unevenness of luminescence, high in sensitivity and image quality, and to provide a photostimulable phosphor, and a radiation image conversion panel. <P>SOLUTION: The invention relates to the method for producing a precursor for photostimulable phosphor, based on alkaline earth metal fluoride halide activated with rare earth metal, expressed by general formula (1) comprising a process obtaining a crystal of the precursor for the photostimulable phosphor by carrying out a process forming a precipitate of the precursor for photostimulable phosphor based on alkaline earth metal fluoride halide by adding an aqueous solution of an inorganic fluoride into a reaction mother liquid dissolving barium halide and a process concentrating and removing solvent from the reaction mother liquid at the same time, and a process forming a rare earth metal halide layer on the surface of the crystal of the precursor for photostimulable phosphor. The general formula (1); Ba<SB>1-x</SB>M2<SB>x</SB>FBr<SB>y</SB>I<SB>1-y</SB>: aM1, bLn, cO (in the formula, M1 is an alkali metal, M2 is an alkaline earth metal, Ln is a rare earth element, 0≤x≤0.3, 0≤y≤0.3, 0≤a≤0.05. 0<b≤0.2, 0≤c≤0.1). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a medical rare earth-activated alkaline earth metal fluoride halide-based stimulable phosphor precursor (hereinafter also simply referred to as stimulable phosphor precursor, phosphor precursor, precursor), rare earth The present invention relates to an activated alkaline earth metal fluoride halide photostimulable phosphor (hereinafter also referred to as photostimulable phosphor or phosphor) and a medical radiation image conversion panel.

  A radiation image recording / reproducing method using a stimulable phosphor described in Japanese Patent Application Laid-Open No. 55-12145 is known as an effective diagnostic means in place of conventional radiography. This method uses a radiation image conversion panel (also referred to as a storage phosphor sheet) containing a stimulable phosphor, and transmits the radiation transmitted through the subject or emitted from the subject. The stimulable phosphor is excited in time series by electromagnetic waves (referred to as excitation light) such as visible light and ultraviolet light, and the stored radiation energy is emitted as fluorescence (referred to as stimulated emission light). The fluorescence is photoelectrically read to obtain an electrical signal, and a radiographic image of the subject or subject is reproduced as a visible image based on the obtained electrical signal. The conversion panel after reading is subjected to erasure of the remaining image and used for the next photographing.

  According to this method, there is an advantage that a radiographic image having a large amount of information can be obtained with a much smaller exposure dose than radiography using a combination of a radiographic film and an intensifying screen. In contrast, the radiographic method consumes a film every time it is taken, whereas the radiographic image conversion panel is used repeatedly, which is advantageous in terms of resource protection and economic efficiency.

  The radiation image conversion panel comprises only a support and a photostimulable phosphor layer provided on the surface or a self-supporting photostimulable phosphor layer, and the photostimulable phosphor layer is usually a stimulable phosphor. And those composed only of aggregates of stimulable phosphors formed by vapor deposition or sintering. Also known is a polymer material impregnated in the gaps between the aggregates. Further, a protective film made of a polymer film or an inorganic vapor deposition film is usually provided on the surface of the photostimulable phosphor layer opposite to the support side.

  As the photostimulable phosphor, those that exhibit photostimulated luminescence in the wavelength range of 300 to 500 nm by excitation light in the range of 400 to 900 nm are generally used. 55-160078, 56-74175, 56-116777, 57-23673, 57-23675, 58-206678, 59-27289, 59-27980, 59 -56479, 59-56480, etc .; rare earth element-activated alkaline earth metal fluoride halide phosphors; JP-A-59-75200, 60-84381, 60-106675, 60 -166379, 60-222143, 60-228592, 60-228593, 61-23679, 61-120 Divalent europium-activated alkaline earth metal fluorohalide phosphors described in 82, 61-120883, 61-128585, 61-235486, 61-235487, etc .; Rare earth element activated oxyhalide phosphors described in JP-A No. 55-12144; Cerium-activated trivalent metal oxyhalide phosphors described in JP-A-58-69281; Bismuth-activated alkali metal halogens described in JP-A-60-70484 Fluoride phosphors; divalent europium activated alkaline earth metal halophosphate phosphors described in JP-A-60-141783, JP-A-60-157100, etc .; divalent europium described in JP-A-60-157099 Activated alkaline earth metal haloborate phosphor; divalent europium activated alkali described in JP-A-60-217354 Metal hydride halide phosphors; cerium-activated rare earth composite halide phosphors described in JP-A-61-2173, JP-A-6-211822, etc .; cerium-activated rare earth halophosphates described in JP-A-61-1390 Salt phosphors; divalent europium-activated cerium / rubidium phosphors described in JP-A-60-78151; bivalent europium-activated composite halide phosphors described in JP-A-60-78151; In particular, a divalent europium activated alkaline earth metal fluoride halide phosphor containing iodine, a rare earth element activated oxyhalide phosphor containing iodine, a bismuth activated alkali metal halide phosphor containing iodine, etc. However, there is still a demand for stimulable phosphors with high brightness.

  In addition, as the use of radiographic image conversion methods using photostimulable phosphors has progressed, further improvements in image quality of the obtained radiographic images, such as improvement in sharpness and graininess, have been further demanded.

  The method for producing a photostimulable phosphor described above is a method called a solid phase method or a sintering method, and pulverization after firing is essential, and it is difficult to control the particle shape that affects sensitivity and image performance. Have the problem. Among the means for improving the image quality of the radiation image, it is effective to make the photostimulable phosphor fine particles and to make the particle size of the fine photostimulable phosphor uniform, that is, to narrow the particle size distribution.

  The method for producing a photostimulable phosphor from a liquid phase disclosed in JP-A-7-233369, 9-291278, etc. comprises adjusting the concentration of the phosphor raw material solution to form a particulate stimulable phosphor. This is a method for obtaining a precursor, and is effective as a method for producing a photostimulable phosphor powder having a uniform particle size distribution. From the viewpoint of reducing the radiation exposure amount, it is known that among rare earth activated alkaline earth metal fluoride halide stimulable phosphors, those having a high iodine content are preferable. This is because iodine has a higher X-ray absorption rate than bromine.

The alkaline earth metal fluoroiodide-based stimulable phosphor produced in the liquid phase as described above is advantageous in terms of luminance and granularity, but when obtaining a precursor crystal in the liquid phase, Have problems like That is, as seen in the description of JP-A-10-88125 and JP-A-9-291278,
1) Dissolve barium iodide in water or an organic solvent, and add a solution of inorganic fluoride while stirring this solution.
2) Ammonium fluoride is dissolved in water, and a solution of barium iodide is added while stirring this solution.
The method is effective. However, in the method 1), it is necessary to make excess barium iodide exist in the solution. Therefore, the stoichiometric ratio of the charged barium iodide and the barium fluoroiodide obtained after solid-liquid separation is 0. In many cases, the value is as small as around .4. That is, the yield of the alkaline earth metal fluoroiodide stimulable phosphor precursor is often about 40% with respect to the charged barium iodide.

  The method 2) also requires an excess of barium iodide relative to the inorganic fluoride, and the yield is low. Thus, the liquid phase synthesis of barium fluoroiodide has the problems of low yield and poor productivity. Lowering the barium iodide concentration in the mother liquor to increase the yield leads to particle enlargement, which is undesirable from the standpoint of image quality.

  As an attempt to increase the yield of rare earth activated alkaline earth metal fluoride halide photostimulable phosphors, particularly alkaline earth metal fluoride iodide photostimulable phosphors, JP-A-11-29324 discloses a reaction. After adding the concentration of the mother liquor and the fluorine source and concentrating, the basic composition BaFI: xLn (Ln: Ce, Pr, Sm, Eu, Gd, Tb, Tm, and Yb, at least one rare earth element, x Represents a rare earth element-containing prismatic barium fluoroiodide crystal represented by 0 <x ≦ 0.1).

  However, as a result of a further examination by the present inventors, it was found that although BaFI square crystals were produced as described, productivity was remarkably low due to the use of concentration by natural evaporation, and this was not practical from an industrial viewpoint. Also, it was found that the obtained square crystals have a large particle size and a wide particle size distribution, so that the image characteristics are poor and cannot be put to practical use.

  Therefore, as a method for improving the concentration capacity, a method of ventilating dry gas, a method of reducing pressure, a method of forming a liquid film (a method of expanding the heat transfer area), and the like can be considered, and a phosphor with high yield can be obtained. Is disclosed (for example, see Patent Document 1).

However, when the photostimulable phosphor obtained by this method is used as a radiation image conversion panel, light emission unevenness occurs, and it has been confirmed that there is a problem in that the brightness and sharpness are lowered.
JP 2003-236303 A

  An object of the present invention is to provide a method for producing a photostimulable phosphor, a photostimulable phosphor and a radiation image conversion panel, which can obtain high sensitivity and high image quality characteristics without unevenness in light emission.

  The above problem could be solved by the following configuration.

(Claim 1)
In the method for producing a rare earth activated alkaline earth metal fluoride halide stimulable phosphor precursor represented by the following general formula (1), an aqueous inorganic fluoride solution is added to a reaction mother liquor in which barium halide is dissolved. The step of forming a precipitate of the alkaline earth metal fluoride halide stimulable phosphor precursor and the step of concentrating and removing the solvent from the reaction mother liquor are carried out in parallel to produce the stimulable phosphor precursor crystal. And a rare earth-activated alkaline earth metal fluoride halide-based stimulable phosphor, characterized by comprising a step of forming a rare earth metal halide layer on the surface of the obtained stimulable phosphor precursor crystal A method for producing a precursor.

General formula (1)
_{Ba 1-x M2 x FBr y} I 1-y: aM1, bLn, cO
(In the formula, M1 is at least one alkali metal atom selected from Li, Na, K, Rb, and Cs, M2 is at least one alkali earth metal atom selected from Be, Mg, Sr, and Ca, and Ln is Ce, It is at least one rare earth element selected from Pr, Sm, Eu, Gd, Tb, Tm, Dy, Ho, Nd, Er, and Yb, and x, y, a, b, and c are 0 ≦ x ≦ 0. 3, 0 ≦ y ≦ 0.3, 0 ≦ a ≦ 0.05, 0 <b ≦ 0.2, 0 ≦ c ≦ 0.1.)
(Claim 2)
In the method for producing a rare earth activated alkaline earth metal fluoride halide photostimulable phosphor precursor represented by the general formula (1), inorganic fluoride is contained in a reaction mother liquor in which barium halide and rare earth metal halide are dissolved. The process of forming a precipitate of an alkaline earth metal fluoride halide-based stimulable phosphor precursor with the addition of an aqueous fluoride solution and the process of concentrating and removing the solvent from the reaction mother liquor are performed in parallel. A rare earth-activated alkaline earth metal fluoride halide system, comprising: a step of obtaining a body precursor crystal; and a step of forming a rare earth metal halide layer on the surface of the photostimulable phosphor precursor crystal obtained. Method for producing photostimulable phosphor precursor.

(Claim 3)
3. The rare earth-activated alkaline earth metal fluoride halide-based stimulant according to claim 1 or 2, wherein the barium concentration in the reaction mother liquor in the initial step and the solvent removing step is 3.0 to 4.5 mol / L. Method for producing a fluorescent phosphor precursor.

(Claim 4)
The solvent mass after removing the reaction solvent for forming the stimulable phosphor precursor is 0.05 to 0.97 with respect to the solvent mass before removing the reaction solvent. 2. A process for producing a rare earth activated alkaline earth metal fluoride halide stimulable phosphor precursor according to item 1.

(Claim 5)
The rare earth activated alkaline earth metal fluoride according to any one of claims 1 to 4, wherein the reaction solution for removing the reaction solvent is used in combination with heating and means for removing the other solvent. For producing a halide-based stimulable phosphor precursor.

(Claim 6)
6. The rare earth-activated alkaline earth metal fluoride halide based stimulable phosphor precursor according to claim 1, wherein the halogen composition of the rare earth metal halide is iodine or bromine. Manufacturing method.

(Claim 7)
A rare earth-activated alkaline earth metal fluoride halide-based phosphor obtained by the method for producing a rare earth-activated alkaline earth metal fluoride halide-based stimulable phosphor precursor according to any one of claims 1 to 6. A rare earth-activated alkaline earth metal fluoride halide-based stimulable phosphor obtained by heating a stimulable phosphor precursor at 400 to 1300 ° C for 0.5 to 12 hours.

(Claim 8)
A radiation image conversion panel comprising the rare earth activated alkaline earth metal fluoride halide stimulable phosphor according to claim 7.

  By the method of the present invention, a stimulable phosphor precursor can be obtained with high yield, and the obtained phosphor precursor is baked to obtain a high-luminance and sharpness-free radiation image. I was able to get a return panel.

  A typical embodiment of the method for producing a rare earth activated alkaline earth metal fluoride halide photostimulable phosphor of the present invention will be described in detail below.

  For the production of stimulable phosphor precursors by the liquid phase method, the precursor production method described in JP-A No. 2003-268360 and the precursor production apparatus described in JP-A No. 2003-236303 can be preferably used. Here, the photostimulable phosphor precursor indicates a state in which the substance of the general formula (1) has not passed through a high temperature of 600 ° C. or higher, and the photostimulable phosphor precursor has a stimulable light emission property or an instantaneous light emission property. Almost not shown.

  In the present invention, the precursor is preferably obtained by the following liquid phase synthesis method.

Manufacturing method:
BaI ₂ and, if x in the general formula (1) is not 0, further contain a halide of M2, BaBr ₂ if y is not 0, and a halide of M1, and after they have dissolved, BaI 2 ₂ is a step of preparing a solution having a concentration of 3.0 mol / L or more, preferably 3.3 mol / L or more, and a halide of Ln may or may not be contained in the solution;
To this, a solution of inorganic fluoride (ammonium fluoride or alkali metal fluoride) having a concentration of 3 mol / L or more, preferably 6 mol / L or more is gradually added, and alkaline earth metal fluoride halide-based stimulable fluorescence is added. Forming a precipitate of a phosphor precursor or a rare earth activated alkaline earth metal fluoride halide stimulable phosphor precursor;
When,
Removing the solvent from the reaction mother liquor while adding the above inorganic fluoride;
And in parallel,
Separating the obtained precursor crystals from the reaction mother liquor;
Preferably, the step of drying the obtained precursor crystal;
Forming a Ln (rare earth metal) halide layer on the surface of the obtained precursor crystal;
Firing a precursor crystal having a rare earth metal halide layer formed on its surface while avoiding sintering;
It is a manufacturing method containing.

  That is, in the present invention, after forming an alkaline earth metal fluoride halide photostimulable phosphor precursor crystal, a rare earth metal halide layer as an activator is formed on the surface, and then fired. Thus, it has been found that by forming a photostimulable phosphor, a high-brightness and stable rare earth-activated alkaline earth metal fluoride halide-based photostimulable phosphor can be obtained.

  Details of the method for producing the photostimulable phosphor will be described below.

(Preparation of precursor crystal precipitate, stimulable phosphor)
First, a raw material compound other than a fluorine compound and an Ln (rare earth metal) compound is dissolved using an aqueous medium. That is, BaI ₂ is placed in an aqueous medium and mixed well and dissolved to prepare an aqueous solution. Then, if necessary, further M2 halide and further M1 halide are added, mixed well, and dissolved to prepare an aqueous solution. Ln halide is not required at this stage, but may be added. However, the quantity ratio between the BaI ₂ concentration and the aqueous solvent is adjusted so that the BaI ₂ concentration is 3.0 mol / L or more, preferably 3.3 mol / L or more. At this time, if the barium concentration is low, a precursor having a desired composition cannot be obtained, or even if obtained, the particles may be enlarged. Therefore, it is necessary to select the barium concentration appropriately, and as a result of the study by the present inventors, desired precursor particles can be formed in the range of 3.0 mol / L or more and 4.5 mol / L or less. I understood. At this time, a small amount of acid, ammonia, alcohol, water-soluble polymer, water-insoluble metal oxide fine particle powder or the like may be added. It is also a preferred embodiment that an appropriate amount of lower alcohol (methanol, ethanol) is added within a range in which the solubility of BaI ₂ is not significantly lowered. Next, inorganic fluoride (ammonium fluoride, alkali metal) is added to the stirred aqueous solution. Inject an aqueous solution such as fluoride using a pipe with a pump.

  This injection is preferably carried out in the region where the stirring is particularly intense. By injecting the inorganic fluoride aqueous solution into the reaction mother liquor, alkaline earth metal fluoride halide photostimulable phosphor precursor crystals are precipitated.

  Simultaneously with this injection, the solvent is removed from the reaction solution. The removal amount of the solvent is preferably 2% or more by mass ratio before and after the removal. Below this, the crystal may not be fully BFI. Therefore, the removal amount is preferably 2% or more, and more preferably 5% or more. Moreover, even if it removes too much, inconvenience may arise in terms of handling, such as an excessive increase in the viscosity of the reaction solution.

  Therefore, the removal amount of the solvent is preferably 97% or less in terms of the mass ratio before and after the removal.

  The time required for removing the solvent not only greatly affects the productivity, but also the shape and particle size distribution of the particles are affected by the method of removing the solvent, so the removal method needs to be appropriately selected. In general, when removing the solvent, a method of heating the solution and evaporating the solvent is selected. This method is also useful in the present invention. By removing the solvent, a precursor having the intended composition can be obtained.

  Furthermore, in order to increase productivity and to keep the particle shape appropriately, it is preferable to use another solvent removal method in combination. The method for removing the solvent used in combination is not particularly limited. For example, it is possible to select a method using a separation membrane such as a reverse osmosis membrane. In the present invention, it is preferable to select the following removal method from the viewpoint of productivity.

1. The reaction vessel for ventilating the dry gas is sealed, and at least two holes through which gas can pass are provided, and the dry gas is vented there. The kind of gas can be selected arbitrarily. Air and nitrogen are preferable from the viewpoint of safety. Depending on the amount of saturated water vapor in the gas to be vented, the solvent is entrained in the gas and removed. In addition to the method of venting the void portion of the reaction vessel, a method of jetting gas as bubbles in the liquid phase and absorbing the solvent in the bubbles is also effective.

2. Depressurization As is well known, the depressurization reduces the vapor pressure of the solvent. The solvent can be efficiently removed by the vapor pressure drop. The degree of reduced pressure can be appropriately selected depending on the type of solvent. When the solvent is water, 86 kPa or less is preferable.

3. Liquid film The solvent can be removed efficiently by increasing the evaporation area. As in the present invention, when a reaction vessel having a constant volume is used for heating and stirring to carry out the reaction, the heating method is a method of immersing the heating means in a liquid or mounting the heating means outside the container. Is common. According to this method, the heat transfer area is limited to the portion where the liquid and the heating means are in contact with each other, and the heat transfer area decreases with the removal of the solvent, and thus the time required for the solvent removal increases. In order to prevent this, a method of increasing the heat transfer area by spraying on the wall surface of the reaction vessel using a pump or a stirrer is effective. Such a method of spraying a liquid on the reaction vessel wall surface to form a liquid film is known as a “wetting wall”. Examples of the method for forming the wet wall include a method using a stirrer described in JP-A Nos. 6-335627 and 11-235522, in addition to a method using a pump.

  These methods may be used not only alone but also in combination. A combination of a method of forming a liquid film and a method of reducing the pressure in the container, a combination of a method of forming a liquid film and a method of ventilating dry gas, and the like are effective. The former is particularly preferable, and the method described in JP-A-6-335627 is preferably used.

  Next, the phosphor precursor crystals are separated from the solution by filtration, centrifugation, etc., and washed sufficiently with methanol or the like. Although it is preferable to dry here, in this invention, it does not necessarily need to dry and you may perform the next process.

Mixing the resultant precursor into a rare earth metal halide ethanol solution, such as EuI ₃ or EuBr _3, after dispersion, it was separated from the solution filtered again such as by centrifugation, and dried.

  Sintering inhibitor fine powder such as alumina fine powder or silica fine powder is added to and mixed with the dried phosphor precursor crystal having a rare earth metal halide layer formed on the surface, and the powder is sintered on the crystal surface. To evenly adhere. It should be noted that the addition of the sintering inhibitor can be omitted by selecting the firing conditions.

  Next, the phosphor precursor crystals are filled in a heat-resistant container such as a quartz port, an alumina crucible, or a quartz crucible, and placed in the core of an electric furnace and fired while avoiding sintering. The range of 400-1300 degreeC is suitable for a calcination temperature, and the range of 500-1000 degreeC is preferable. The firing time varies depending on the filling amount of the phosphor raw material mixture, the firing temperature, the temperature of taking out from the furnace, and the like, but generally 0.5 to 12 hours is appropriate.

  As the firing atmosphere, a neutral atmosphere such as a nitrogen gas atmosphere or an argon gas atmosphere, a weakly reducing atmosphere such as a nitrogen gas atmosphere containing a small amount of hydrogen gas, a carbon dioxide atmosphere containing carbon monoxide, or a small amount of oxygen introduced The atmosphere is used. As the firing method, the method described in JP-A No. 2000-8034 is preferably used.

  The desired rare earth activated alkaline earth metal fluoride halide photostimulable phosphor is obtained by the above-mentioned firing.

(Radiation image conversion panel production, phosphor layer, coating process, support, protective layer)
As the support used in the radiation image conversion panel of the present invention, various polymer materials, glass, metal and the like are used. In particular, those that can be processed into flexible sheets or webs as information recording materials are suitable. From this point, cellulose acetate films, polyester films such as polyethylene terephthalate, polyamide films, polyimide films, polycarbonate films, etc. Of these, a plastic sheet, a metal sheet of aluminum, iron, copper, chromium, or a metal sheet having a coating layer of the metal oxide is preferable.

  The layer thickness of these supports varies depending on the material of the support used, but is generally 80 μm to 1000 μm, and more preferably 80 μm to 500 μm from the viewpoint of handling.

  The surface of these supports may be a smooth surface, or may be a mat surface for the purpose of improving the adhesion to the photostimulable phosphor layer.

  Further, these supports may be provided with an undercoat layer on the surface on which the photostimulable phosphor layer is provided for the purpose of improving the adhesion to the photostimulable phosphor layer.

  Examples of binders used in the stimulable phosphor layer in the present invention include proteins such as gelatin, polysaccharides such as dextran, or natural high molecular substances such as gum arabic; and polyvinyl butyral, polyvinyl acetate, Represented by synthetic polymer materials such as nitrocellulose, ethyl cellulose, vinylidene chloride / vinyl chloride copolymer, polyalkyl (meth) acrylate, vinyl chloride / vinyl acetate copolymer, polyurethane, cellulose acetate butyrate, polyvinyl alcohol, linear polyester, etc. Can be mentioned. Particularly preferred among such binders are nitrocellulose, linear polyesters, polyalkyl (meth) acrylates, mixtures of nitrocellulose and linear polyesters, mixtures of nitrocellulose and polyalkyl (meth) acrylates and For example, a mixture of polyurethane and polyvinyl butyral. Note that these binders may be crosslinked by a crosslinking agent.

  The photostimulable phosphor layer can be formed on the undercoat layer by the following method, for example.

  First, an iodine-containing stimulable phosphor, a compound such as a phosphite for preventing yellowing, and a binder are added to a suitable solvent, and these are mixed thoroughly to add phosphor particles and A coating solution in which the compound particles are uniformly dispersed is prepared.

  In general, the binder is used in the range of 0.01 to 1 part by mass with respect to 1 part by mass of the stimulable phosphor. However, in terms of sensitivity and sharpness of the obtained radiation image conversion panel, it is preferable that the amount of the binder is small, and the range of 0.03 to 0.2 parts by mass is more preferable in view of the ease of application.

  Examples of the solvent used for the preparation of the stimulable phosphor layer coating solution include lower alcohols such as methanol, ethanol, 1-propanol, isopropanol, and n-butanol; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone. Ester of lower fatty acid such as methyl acetate, ethyl acetate, n-butyl acetate and lower alcohol; ether such as dioxane, ethylene glycol monoethyl ether, ethylene glycol monomethyl ether; aromatic compound such as triol, xylol; methylene chloride, Halogenated hydrocarbons such as ethylene chloride and mixtures thereof.

  The stimulable phosphor layer coating solution includes a dispersant for improving the dispersibility of the phosphor in the coating solution, and a binder and a phosphor in the formed stimulable phosphor layer. Various additives such as a plasticizer for improving the bonding strength between them may be mixed. Examples of the dispersant used for such purpose include phthalic acid, stearic acid, caproic acid, lipophilic surfactant and the like. Examples of plasticizers include phosphate esters such as triphenyl phosphate, tricresyl phosphate and diphenyl phosphate; phthalate esters such as diethyl phthalate and dimethoxyethyl phthalate; ethyl phthalyl ethyl glycolate, butyl phthalyl butyl glycolate, etc. And a polyester of triethylene glycol and adipic acid, a polyester of polyethylene glycol and an aliphatic dibasic acid such as a polyester of diethylene glycol and succinic acid, and the like.

  The coating liquid prepared as described above is then uniformly applied to the surface of the undercoat layer to form a coating film of the coating liquid. This coating operation can be performed by using a normal coating means, for example, a doctor blade, a roll coater, a knife coater or the like.

  Next, the formed coating film is dried by gradually heating to complete the formation of the photostimulable phosphor layer on the undercoat layer. The layer thickness of the stimulable phosphor layer varies depending on the characteristics of the intended radiation image conversion panel, the type of stimulable phosphor, the mixing ratio of the binder and the phosphor, and is usually 20 μm to 1 mm. . However, this layer thickness is preferably 50 to 500 μm.

  The stimulable phosphor layer coating solution is prepared using a dispersing device such as a ball mill, a sand mill, an attritor, a three-roll mill, a high-speed impeller disperser, a Kady mill, and an ultrasonic disperser.

  In the foregoing, examples of stimulable phosphors such as europium-activated barium fluoride iodide have been mainly described. However, europium-activated barium fluoride bromide and other alkaline earth metal halides represented by the general formula (1) have been described. The above may be referred to for the production of the fluoride-based stimulable phosphor.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, the embodiment of this invention is not limited to these.

Example 1
In order to synthesize the stimulable phosphor precursor of europium-activated barium fluoroiodide, 2500 ml of BaI ₂ aqueous solution (3.35 mol / L) was placed in a reactor in a pressure-resistant vessel having _two holes. Furthermore, 992 g of potassium iodide was added to the aqueous solution. The reaction mother liquor in this reactor was kept at 80 ° C. with stirring. While removing water in the solution at a reduced pressure of 40 kPa, 600 ml of an aqueous ammonium fluoride solution (10 mol / L) was injected into the reaction mother liquor using a roller pump to form a precipitate. After completion of the reaction, the mass ratio of the solution before and after aeration was 0.92. The mixture was stirred for 90 minutes at the same temperature. The mixture was stirred for 90 minutes, filtered and washed with 2000 ml of ethanol. Next, it was left at 80 ° C. for 12 hours to remove residual ethanol. The precursor was dispersed in 331 ml of EuI ₃ ethanol solution (0.04 mol / L) and stirred. The ethanol solution was filtered and separated, and then allowed to stand at 80 ° C. for 12 hours to remove residual ethanol. The mass of the obtained precursor was measured, and the yield was determined by the following formula from the amount of BaI ₂ charged.

Yield (%) = (Precursor yield / Theoretical precursor yield obtained from added BaI ₂ ) × 100
The obtained results are shown in Table 1.

  Next, in order to prevent changes in particle shape and changes in particle size distribution due to fusion between particles, 1% by mass of ultrafine powder of alumina is added and stirred thoroughly with a mixer, and the surface of the alumina is added to the crystal surface. The fine particle powder was uniformly attached. This was filled in a quartz boat and baked at 850 ° C. for 2 hours in a hydrogen gas atmosphere using a tube furnace to obtain europium-activated barium fluoroiodide phosphor particles.

Example 2
In order to synthesize a stimulable phosphor precursor of europium-activated barium fluoroiodide, 2500 ml of BaI ₂ aqueous solution (3.35 mol / L) and EuI ₃ aqueous solution (0.2 mol / L) were placed in a pressure-resistant container having _two holes. ) 26.5 ml was placed in the reactor. Furthermore, 992 g of potassium iodide was added to the aqueous solution. The reaction mother liquor in this reactor was kept at 80 ° C. with stirring. While removing water in the solution at a reduced pressure of 40 kPa, 600 ml of an aqueous ammonium fluoride solution (10 mol / L) was injected into the reaction mother liquor using a roller pump to form a precipitate. After completion of the reaction, the mass ratio of the solution before and after aeration was 0.92. The mixture was stirred for 90 minutes at the same temperature. The mixture was stirred for 90 minutes, filtered and washed with 2000 ml of ethanol. Next, it was left at 80 ° C. for 12 hours to remove residual ethanol. The precursor was dispersed and stirred in 331 ml of EuI ₃ ethanol solution (0.02 mol / L), and the ethanol solution was filtered and separated, and then allowed to stand at 80 ° C. for 12 hours to remove residual ethanol. The yield was determined in the same manner as in Example 1.

  Next, in order to prevent changes in particle shape and changes in particle size distribution due to fusion between particles, 1% by mass of ultrafine powder of alumina is added and stirred thoroughly with a mixer, and the surface of the alumina is added to the crystal surface. The fine particle powder was uniformly attached. This was filled in a quartz boat and baked at 850 ° C. for 2 hours in a hydrogen gas atmosphere using a tube furnace to obtain europium-activated barium fluoroiodide phosphor particles.

Example 3
Except that the EuBr ₃ ethanol solution was used, the same operation as in Example 1 was performed to obtain europium-activated barium fluoroiodide phosphor particles.

Comparative Example 1
In order to synthesize a stimulable phosphor precursor of europium-activated barium fluoroiodide, 2500 ml of BaI ₂ aqueous solution (3.35 mol / L) and EuI ₃ aqueous solution (0.2 mol / L) were placed in a pressure-resistant container having _two holes. ) 26.5 ml was placed in the reactor. Furthermore, 992 g of potassium iodide was added to the aqueous solution. The reaction mother liquor in this reactor was kept at 80 ° C. with stirring. While removing water in the solution at a reduced pressure of 40 kPa, 600 ml of an aqueous ammonium fluoride solution (10 mol / L) was injected into the reaction mother liquor using a roller pump to form a precipitate. After completion of the reaction, the mass ratio of the solution before and after aeration was 0.92. The mixture was stirred for 90 minutes at the same temperature. The mixture was stirred for 90 minutes, filtered and washed with 2000 ml of ethanol. The ethanol solution was filtered and separated, then left at 80 ° C. for 12 hours to remove residual ethanol. The yield was determined in the same manner as in Example 1.

  Next, in order to prevent changes in particle shape and changes in particle size distribution due to fusion between particles, 1% by mass of ultrafine powder of alumina is added and stirred thoroughly with a mixer, and the surface of the alumina is added to the crystal surface. The fine particle powder was uniformly attached. This was filled in a quartz boat and baked at 850 ° C. for 2 hours in a hydrogen gas atmosphere using a tube furnace to obtain europium-activated barium fluoroiodide phosphor particles.

Comparative Example 2
In order to synthesize a stimulable phosphor precursor of europium-activated barium fluoroiodide, 2500 ml of BaI ₂ aqueous solution (4.2 mol / L) and 26.5 ml of EuI ₃ aqueous solution (0.2 mol / L) were used in a reactor. I put it in. The reaction mother liquor in this reactor was kept at 83 ° C. with stirring. 290 ml of an aqueous ammonium fluoride solution (13 mol / L) was poured into the reaction mother liquor using a roller pump and added at 20 ml / min to form a precipitate. After completion of the injection, the mixture was stirred at the same temperature for 90 minutes. The mixture was stirred for 90 minutes, filtered and washed with 2000 ml of ethanol. The ethanol solution was filtered and separated, then left at 80 ° C. for 12 hours to remove residual ethanol. The yield was determined in the same manner as in Example 1.

  Next, in order to prevent changes in particle shape and changes in particle size distribution due to fusion between particles, 1% by mass of ultrafine powder of alumina is added and stirred thoroughly with a mixer, and the surface of the alumina is added to the crystal surface. The fine particle powder was uniformly attached. This was filled in a quartz boat and baked at 850 ° C. for 2 hours in a hydrogen gas atmosphere using a tube furnace to obtain europium-activated barium fluoroiodide phosphor particles.

Comparative Example 3
In order to synthesize a stimulable phosphor precursor of europium-activated barium fluoroiodide, 2500 ml of an aqueous BaI ₂ solution (4.2 mol / L) was placed in a reactor. The reaction mother liquor in this reactor was kept at 83 ° C. with stirring. 290 ml of an aqueous ammonium fluoride solution (13 mol / L) was poured into the reaction mother liquor using a roller pump and added at 20 ml / min to form a precipitate. After completion of the injection, the mixture was stirred at the same temperature for 90 minutes. The mixture was stirred for 90 minutes, filtered and washed with 2000 ml of ethanol. Next, it was left at 80 ° C. for 12 hours to remove residual ethanol. The precursor was dispersed and stirred in 265 ml of EuI ₃ ethanol solution (0.02 mol / L), the ethanol solution was filtered and separated, and then allowed to stand at 80 ° C. for 12 hours to remove residual ethanol. The yield was determined in the same manner as in Example 1.

  Next, in order to prevent changes in particle shape and changes in particle size distribution due to fusion between particles, 1% by mass of ultrafine powder of alumina is added and stirred thoroughly with a mixer, and the surface of the alumina is added to the crystal surface. The fine particle powder was uniformly attached. This was filled in a quartz boat and baked at 850 ° C. for 2 hours in a hydrogen gas atmosphere using a tube furnace to obtain europium-activated barium fluoroiodide phosphor particles.

<Production of radiation image conversion panel>
(Formation of undercoat layer)
The undercoat layer coating solution described below was applied to a 188 μm thick polyethylene foam terephthalate film (188E60L manufactured by Toray Industries, Inc.) using a doctor blade, and dried at 100 ° C. for 5 minutes. A subbing layer was applied.

(Undercoat layer coating solution)
Polyester resin dissolved product (Toyobo Co., Ltd. Byron 55SS, solid content 35%) 288.2 g, β-copper phthalocyanine dispersion 0.34 g (solid content 35%, pigment content 30%) and polyisocyanate compound (Japan) 11.22 g of Coronate HX (Polyurethane Industry Co., Ltd.) was mixed and dispersed with a propeller mixer to prepare an undercoat layer coating solution.

[Formation of phosphor layer]
(Preparation of phosphor layer coating solution)
300 g of europium-activated barium fluoroiodide phosphor particles prepared in Example 1 and 52.63 g of a polyester resin (Byron 530 manufactured by Toyobo Co., Ltd., solid content: 30% by mass, solvent: methyl ethyl ketone / toluene = 5/5) A phosphor layer coating solution was prepared by adding to a mixed solvent of 0.13 g of methyl ethyl ketone, 0.13 g of toluene and 41.84 g of cyclohexanone and dispersing by a propeller mixer.

(Formation of phosphor layer 1, production of phosphor sheet 1)
The prepared phosphor layer coating solution is applied onto the formed undercoat layer using a doctor blade so as to have a film thickness of 180 μm, and then dried at 100 ° C. for 15 minutes to form a phosphor layer. Thus, the phosphor sheet 1 was produced.

[Production of moisture-proof protective film]
The thing of the following structure (A) was used as a protective film of the phosphor layer coating surface side of the produced phosphor sheet 1.

Configuration (A)
NY 15 μm /// VMPET 12 μm // VMPET 12 μm // PET 12 μm /// CPP 20 μm
NY: Nylon PET: Polyethylene terephthalate CPP: Casting polypropylene VMPET: Alumina-deposited PET (commercial product: manufactured by Toyo Metallizing Co., Ltd.)
The above “///” is a dry lamination adhesive layer, and the thickness of the adhesive layer is 3.0 μm. As the adhesive used for dry lamination, a two-component reaction type urethane adhesive was used.

  The protective film on the back side of the support of the phosphor sheet 1 was a dry laminate film having a structure of CPP 30 μm / aluminum film 9 μm / polyethylene terephthalate 188 μm. The symbol “/” is a dry lamination adhesive layer, and the adhesive layer has a thickness of 1.5 μm and a two-component reaction type urethane adhesive is used.

[Production of radiation image conversion panel]
The prepared phosphor sheet 1 is cut into squares each having a side of 20 cm, and then sandwiched using the two types of moisture-proof protective films prepared above, and the peripheral portion is fused using an impulse sealer under reduced pressure. The radiation image conversion panel 1 was produced by sealing and cutting the periphery. In addition, it fused so that the distance from a fusion | melting part to a fluorescent substance sheet peripheral part might be set to 1 mm. The impulse sealer heater used for fusion was a 3 mm wide heater.

  Hereinafter, except that the europium activated barium fluoroiodide phosphor particles of Example 1 were changed to the europium activated barium fluoroiodide phosphor particles obtained in Examples 2 and 3 and Comparative Examples 1 to 3, the same manner was performed. The radiation image conversion panels 2 to 6 were prepared.

(Evaluation of radiation image conversion panel)
Each radiation image conversion panel was evaluated as follows.

"sensitivity"
After irradiating the radiation image conversion panel with X-rays having a tube voltage of 80 kVp, the panel is excited by operating with a He—Ne laser beam (633 nm), and the stimulated emission emitted from the phosphor layer is received by a light receiver (spectral sensitivity S). The light intensity was measured by receiving the light with a photoelectron image multiplier (-5). In Table 1, the sensitivity is shown as a relative value when Comparative Example 1 is 100.

《Sharpness》
Radiation image conversion panel is irradiated with X-ray with tube voltage of 80 kVp through lead MTF chart, then the panel is excited by operating with He-Ne laser light, and the sensitivity of stimulated luminescence emitted from phosphor layer is measured. Is received by the same receiver and converted into an electrical signal, analog / digital converted and recorded on a magnetic tape, the magnetic tape is analyzed by a computer, and the X-ray image recorded on the magnetic tape is transmitted. The function (MTF) was examined. Table 1 shows the relative value when the comparative example 1 of the MTF value (%) at a spatial frequency of 2 cycles / mm is set to 100.

  The results are shown below.

  As is clear from Table 1, it can be seen that the examples of the present invention are superior in yield, sensitivity, and sharpness as compared with the comparative examples.

Claims (8)

In the method for producing a rare earth activated alkaline earth metal fluoride halide stimulable phosphor precursor represented by the following general formula (1), an aqueous inorganic fluoride solution is added to a reaction mother liquor in which barium halide is dissolved. The step of forming a precipitate of the alkaline earth metal fluoride halide stimulable phosphor precursor and the step of concentrating and removing the solvent from the reaction mother liquor are carried out in parallel to produce the stimulable phosphor precursor crystal. And a rare earth-activated alkaline earth metal fluoride halide-based stimulable phosphor, characterized by comprising a step of forming a rare earth metal halide layer on the surface of the obtained stimulable phosphor precursor crystal A method for producing a precursor.
General formula (1)
_{Ba 1-x M2 x FBr y} I 1-y: aM1, bLn, cO
(In the formula, M1 is at least one alkali metal atom selected from Li, Na, K, Rb, and Cs, M2 is at least one alkali earth metal atom selected from Be, Mg, Sr, and Ca, and Ln is Ce, It is at least one rare earth element selected from Pr, Sm, Eu, Gd, Tb, Tm, Dy, Ho, Nd, Er, and Yb, and x, y, a, b, and c are 0 ≦ x ≦ 0. 3, 0 ≦ y ≦ 0.3, 0 ≦ a ≦ 0.05, 0 <b ≦ 0.2, 0 ≦ c ≦ 0.1.) In the method for producing a rare earth activated alkaline earth metal fluoride halide photostimulable phosphor precursor represented by the general formula (1), inorganic fluoride is contained in a reaction mother liquor in which barium halide and rare earth metal halide are dissolved. The process of forming a precipitate of an alkaline earth metal fluoride halide-based stimulable phosphor precursor with the addition of an aqueous fluoride solution and the process of concentrating and removing the solvent from the reaction mother liquor are performed in parallel. A rare earth-activated alkaline earth metal fluoride halide system, comprising: a step of obtaining a body precursor crystal; and a step of forming a rare earth metal halide layer on the surface of the photostimulable phosphor precursor crystal obtained. Method for producing photostimulable phosphor precursor. 3. The rare earth-activated alkaline earth metal fluoride halide-based stimulant according to claim 1 or 2, wherein the barium concentration in the reaction mother liquor in the initial step and the solvent removing step is 3.0 to 4.5 mol / L. Method for producing a fluorescent phosphor precursor. The solvent mass after removing the reaction solvent for forming the stimulable phosphor precursor is 0.05 to 0.97 with respect to the solvent mass before removing the reaction solvent. 2. A process for producing a rare earth activated alkaline earth metal fluoride halide stimulable phosphor precursor according to item 1. The rare earth activated alkaline earth metal fluoride according to any one of claims 1 to 4, wherein the reaction solution for removing the reaction solvent is used in combination with heating and means for removing the other solvent. For producing a halide-based stimulable phosphor precursor. 6. The rare earth-activated alkaline earth metal fluoride halide based stimulable phosphor precursor according to claim 1, wherein the halogen composition of the rare earth metal halide is iodine or bromine. Manufacturing method. A rare earth-activated alkaline earth metal fluoride halide-based phosphor obtained by the method for producing a rare earth-activated alkaline earth metal fluoride halide-based stimulable phosphor precursor according to any one of claims 1 to 6. A rare earth-activated alkaline earth metal fluoride halide-based stimulable phosphor obtained by heating a stimulable phosphor precursor at 400 to 1300 ° C for 0.5 to 12 hours. A radiation image conversion panel comprising the rare earth activated alkaline earth metal fluoride halide stimulable phosphor according to claim 7.