JP2005179477A - Cumulative fluorophor powder, method for producing the same, and radiation image transformation panel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide cumulative fluorophor powder giving uniform and high-quality radiation images when used in radiation image transformation panels, to provide a method for producing the fluorophor powder, and to provide such a radiation image transformation panel using the fluorophor powder. <P>SOLUTION: The cumulative fluorophor powder does not contain ≥1 wt.% of particles with a diameter of larger than 8×D<SB>m</SB>μm( D<SB>m</SB>μm is a median particle diameter ). The method for producing the cumulative fluorophor powder involves classifying a granular cumulative fluorophor using a mesh filter whose opening diameter L(μm) meets the relationship:2≤L/D<SB>m</SB>≤8 ( wherein, L is the opening diameter of the mesh filter, and D<SB>m</SB>is the median particle diameter of the cumulative fluorophor powder after undergoing the classification treatment ). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a stimulable phosphor powder, and more particularly to a stimulable phosphor powder having a specific range of narrow particle size distribution. The present invention also relates to a method for producing the stimulable phosphor powder and a radiation image conversion panel produced using the stimulable phosphor powder.

  Conventionally, when radiation such as X-rays is irradiated, a part of the radiation energy is absorbed and accumulated. After that, when irradiated with electromagnetic waves (excitation light) such as visible rays and infrared rays or heated, the accumulated radiation energy is converted into the accumulated radiation energy. Accordingly, accumulative phosphors having the property of emitting light (stimulable phosphors showing stimulated light emission, etc.) are known. Further, the radiation image information of the subject is temporarily accumulated and recorded by irradiating the sheet-like radiation image conversion panel containing the stimulable phosphor with radiation transmitted through the subject or emitted from the subject. 2. Description of the Related Art Radiation image recording / reproducing methods are widely used in practice by scanning excitation light such as laser light and sequentially emitting it as emitted light, and photoelectrically reading the emitted light to obtain an image signal. After the reading of the panel is completed, the remaining radiation energy is erased, and then the panel is prepared and used repeatedly for the next imaging.

  A radiation image conversion panel (also referred to as a storage phosphor sheet) used in a radiation image recording / reproducing method includes a support and a phosphor layer provided thereon as a basic structure. However, a support is not necessarily required when the phosphor layer is self-supporting. In addition, a protective layer is usually provided on the upper surface of the phosphor layer (the surface not facing the support) to protect the phosphor layer from chemical alteration or physical impact.

  The phosphor layer is composed of a stimulable phosphor powder and a binder containing and supporting this in a dispersed state, and does not contain a binder formed by a vapor deposition method or a sintering method. Known are those composed only of aggregates, and those in which polymer substances are impregnated in the gaps between the aggregates of the stimulable phosphor.

  In addition, as another method of the above-described radiographic image recording / reproducing method, Patent Document 1 discloses at least a storage phosphor (energy storage phosphor) by separating a radiation absorption function and an energy storage function of a conventional storage phosphor. A radiation image forming method using a combination of a radiation image conversion panel containing a phosphor and a phosphor screen containing a phosphor (radiation absorbing phosphor) that absorbs radiation and emits light in the ultraviolet to visible region has been proposed. . In this method, radiation that has passed through a subject is first converted into light in the ultraviolet or visible region by the screen or panel radiation-absorbing phosphor, and then the light is imaged by the panel's energy storage phosphor. Accumulate and record as information. Next, the panel is scanned with excitation light to emit emitted light, and the emitted light is read photoelectrically to obtain an image signal. Such a radiation image conversion panel is also included in the present invention.

  The radiographic image recording / reproducing method (and the radiographic image forming method) is a method having a number of excellent advantages as described above. However, the radiographic image conversion panel used in this method is as sensitive as possible. In addition, it is desired to provide an image with good image quality (sharpness, graininess, etc.).

  Until now, in order to improve the image quality of the radiation image, the particle size and / or particle size distribution of the stimulable phosphor powder used in the radiation image conversion panel is controlled to fill the phosphor layer in the phosphor layer. It has been proposed to increase.

  Patent Document 2 discloses a method for producing a rare earth activated alkaline earth metal fluoride halide phosphor, in which a phosphor raw material mixture is filled in a container at a certain ratio and a certain thickness in a firing step, and fired. A method is disclosed. In the embodiment, after firing, the slurry of the fired product is classified by passing through a vibrating sieve (nylon mesh, # 508), and further classified by passing through a vibrating sieve (nylon mesh, # 460) to obtain europium having an average crystal size of 6.2 μm. It describes that an activated barium fluorobromide-based stimulable phosphor powder was produced.

JP 2001-255610 A JP 2001-64643 A

  In general, the smaller the central particle size of the stimulable phosphor powder, the higher the density of the phosphor powder that can be filled in the phosphor layer, and the higher the quality of the radiation image. However, even if the center particle size is small, if there are particles with a large particle size due to the sintering of the phosphor during firing, the granularity is reduced only in that part, and uniform image quality cannot be obtained. It was found that the quality of the radiation image conversion panel deteriorated. On the other hand, when a mesh filter having a small opening diameter is used for classification to remove particles having a large particle diameter, the yield of the obtained phosphor powder is reduced, resulting in an increase in manufacturing cost.

Accordingly, it is an object of the present invention to provide a stimulable phosphor powder suitable for a radiation image conversion panel that can provide a radiation image reproduction image with excellent image quality.
In particular, the present invention is to provide a stimulable phosphor powder that provides a uniform and high-quality radiation image when used in a radiation image conversion panel.

  Another object of the present invention is to provide a method for producing a stimulable phosphor powder that does not substantially contain large-diameter particles and has a high production yield.

  Furthermore, the present invention also provides a radiation image conversion panel that provides a uniform and high-quality radiation image.

The present invention resides in a stimulable phosphor powder having 99% or more of particles having a particle size of 8 × D _m μm or less, where the center particle size is D _m μm. That is, the stimulable phosphor powder of the present invention does not contain particles having a particle size of 8 × D _m μm or more in an amount of 1% or more.

Here, the central particle diameter D _m of the stimulable phosphor powder is the median particle diameter, and when a distribution curve composed of the particle diameter and frequency is obtained for the phosphor powder, the cumulative distribution on a volume basis is obtained. It means a particle size that is 50% of the total powder.

Further, the present invention is a method for producing the above-mentioned stimulable phosphor powder, comprising a step of classifying the granular stimulable phosphor, and in the classification treatment step, the opening diameter L (μm) is as follows: formula:

2 ≦ L / D _m ≦ 8

[However, L represents the opening diameter of the mesh filter, and D _m represents the central particle diameter of the stimulable phosphor powder after the classification treatment. ]
There is also a method for producing a stimulable phosphor powder characterized by classifying a granular stimulable phosphor using a mesh filter satisfying the above.

The present invention also relates to a method for producing the above-mentioned stimulable phosphor powder, the step of mixing phosphor materials in an aqueous solution and reacting them to produce a phosphor precursor, A firing step, and a step of loosening and classifying the obtained fired product, and in the loosening / classifying treatment step, an organic solvent that does not dissolve the fired product, or a monovalent or divalent metal ion. After being dispersed and loosened in the aqueous medium containing, the opening diameter L (μm) is expressed by the following formula:

2 ≦ L / D _m ≦ 8

[However, L represents the opening diameter of the mesh filter, and D _m represents the central particle diameter of the stimulable phosphor powder after the classification treatment. ]
There is also a method for producing a stimulable phosphor powder characterized by classifying a dispersion using a mesh filter satisfying the above.

  Furthermore, the present invention also resides in a radiation image conversion panel including the above-described stimulable phosphor powder.

  Since the stimulable phosphor powder of the present invention does not substantially contain particles having a large particle size that deteriorate the image quality of the radiation image, a radiation image conversion panel capable of providing a high-quality radiation image reproduction image can be produced. Can be advantageously used. In addition, according to the method of the present invention, such a suitable stimulable phosphor powder can be obtained by performing classification using a mesh filter of a specific size during the production of the phosphor. The radiation image conversion panel of the present invention containing the stimulable phosphor powder can provide a uniform and high-quality radiation image.

In the stimulable phosphor powder of the present invention, the center particle diameter D _m is preferably in the range of 2 to 5 μm. Further, it is preferable that no particle having a particle diameter exceeding 8 × D _m μm is contained.

  The stimulable phosphor is preferably a rare earth-activated alkaline earth metal fluorohalide-based stimulable phosphor having the following basic composition formula (I), and particularly preferably a tetrahedral shape.

M ^II FX: zLn (I)

[Wherein M ^II represents at least one alkaline earth metal selected from the group consisting of Ba, Sr and Ca; Ln represents Ce, Pr, Sm, Eu, Gd, Tb, Dy, Ho, Nd, Er, Tm. And at least one rare earth element selected from the group consisting of Yb; X represents at least one halogen selected from the group consisting of Cl, Br and I; and z is in the range of 0 <z ≦ 0.2 The numerical value of ]

Stimulable phosphor powders of the present invention, when the mean particle size of D _m [mu] m, in which the particle size does not include only large particles exceeding 8 times the central diameter D _m at 1% or less. Preferably, no large particles having a particle size exceeding 8 × D _m μm are included, that is, the maximum particle size is 8 × D _m μm or less. By using such a phosphor powder for a radiation image conversion panel, it is possible to effectively prevent a local decrease in graininess. In view of image quality, the center particle diameter D _m is preferably in the range of 2 to 5 μm.

  Hereinafter, the method for producing the stimulable phosphor powder of the present invention will be described with reference to the rare earth activated alkaline earth metal fluoride halide stimulable phosphor having the above basic composition formula (I).

In the photostimulable phosphor having the basic composition formula (I), the following additives may be added to the basic composition formula (I) as necessary.
bA, wN ^I , xN ^II , yN ^III
However, A represents a metal oxide such as Al ₂ O _3, SiO ₂ and ZrO _2. In preventing sintering between M ^II FX particles, it is preferable to use an average particle size of the primary particles has low reactivity with M ^II FX in the following ultrafine particles 0.1 [mu] m. N ^I represents at least one alkali metal compound selected from the group consisting of Li, Na, K, Rb and Cs, N ^II represents an alkaline earth metal compound composed of Mg and / or Be, N ^III represents a compound of at least one trivalent metal selected from the group consisting of Al, Ga, In, Tl, Sc, Y, La, Gd, and Lu. As these metal compounds, halides are preferably used, but are not limited thereto.

In addition, b, w, x, and y are the amounts added to the feed when the number of moles of M ^II FX is 1, and 0 ≦ b ≦ 0.5, 0 ≦ w ≦ 2, 0 ≦ x ≦ 0. 3 represents a numerical value within each range of 0 ≦ y ≦ 0.3. These numerical values do not represent the ratio of elements contained in the final composition with respect to the additive that is reduced by firing and various subsequent treatments. Some of the compounds remain as added in the final composition, while others react with or be taken up by M ^II FX.

  The production method of the present invention is roughly divided into a step of producing a phosphor precursor as a phosphor raw material, a step of preparing a phosphor raw material mixture by mixing the phosphor precursor and other phosphor raw materials, and the fluorescence It consists of a step of firing the body raw material mixture, and a step of loosening and classifying the obtained fired product, and further, washing and drying may be performed as necessary. However, there are many phosphor raw materials available from the market, and if these are used, the phosphor precursor generation step can be omitted.

[Phosphor precursor production process]
A phosphor powder having a smaller particle size can be produced by reacting a part of the phosphor raw material to precipitate a phosphor precursor crystal, and a phosphor powder having a tetrahedral particle shape is produced. can do. The phosphor precursor crystal can be obtained by the synthesis methods I and II described in JP-A-7-233369 and the synthesis method III shown below. In particular, the synthesis method I is preferable for obtaining tetrahedral particles having a particle aspect ratio in the range of 1.0 to 2.0, and the synthesis method II is in the range of 2.0 to 5.0 in the particle aspect ratio. And the synthesis method III is preferred for obtaining phosphor precursor crystals in high yield.

(Synthesis method I)
BaX ₂ ; water-soluble compound of Ln; and optionally M ^II halides, nitrates, nitrites or acetates other than Ba; and N ^I halides, nitrates, nitrites or acetates in an aqueous medium To prepare an aqueous solution (reaction mother liquor). The BaX ₂ concentration in the reaction mother liquor is set to 2.5 mol / liter or less when X is Cl or Br, and to 5.0 mol / liter or less when X is I.

  While maintaining the reaction mother liquor at a temperature of 20 to 100 ° C., an aqueous solution of an inorganic fluoride salt is added thereto to form a precipitate of phosphor precursor crystals. At this time, when the rate of addition is N, where the amount of the precipitate of the phosphor precursor crystal finally obtained is N, the amount of precipitate generated during the addition is 0.001 N / min to 10 N / min. Adjust to be within range. Next, the phosphor precursor crystal precipitate is separated from the aqueous solution.

(Synthesis Method II)
NH ₄ X; water-soluble compound of Ln; and optionally, a halide of M ^II other than Ba, nitrate, nitrite or acetate; and N ^I halide, nitrate, nitrite or acetate, water An aqueous solution (reaction mother liquor) is prepared by dissolving in a medium. The NH ₄ X concentration in the reaction mother liquor is adjusted to 2.0 mol / liter or more and 4.5 mol / liter or less.

While maintaining this reaction mother liquor at a temperature of 20 to 100 ° C., an aqueous solution of an inorganic fluoride salt and an aqueous solution of BaX ₂ are added thereto to form a precipitate of phosphor precursor crystals. At this time, the inorganic fluoride salt is added while keeping the molar ratio of fluorine to BaX ₂ constant. Further, when the rate of addition is N as the amount of the phosphor precursor crystal precipitate finally obtained, the amount of precipitate generated during the addition is in the range of 0.001 N / min to 10 N / min. Adjust so that Next, the phosphor precursor crystal precipitate is separated from the aqueous solution.

(Synthesis Method III)
BaX _2; BaCO _3; water-soluble compound of Ln; and optionally, a halide of M ^II other than Ba, nitrate, nitrite or acetate; and N ^I halide, nitrate, nitrite or acetate Then, a suspension (reaction mother liquor) is prepared by dissolving and dispersing in an aqueous medium. The BaX ₂ concentration in the reaction mother liquor is set to 2.5 mol / liter or less when X is Cl or Br, and to 5.0 mol / liter or less when X is I.

  While maintaining this reaction mother liquor at a temperature of 20 to 100 ° C., an aqueous solution of hydrofluoric acid is added thereto to form a precipitate of phosphor precursor crystals. At this time, when the rate of addition is N, where the amount of the precipitate of the phosphor precursor crystal finally obtained is N, the amount of precipitate generated during the addition is 0.001 N / min to 10 N / min. Adjust to be within range. Next, the precipitate of the phosphor precursor crystal (BaFX: Ln) is separated from the aqueous solution.

    In the above, the “aqueous solution” refers to a “solute” dissolved in an “aqueous medium”. The “aqueous medium” is a concept including not only water but also a liquid having a high affinity with water (for example, alcohol) or a mixture of these, or a mixture of these and water. Of these, water is most preferable. The “solute” is appropriately selected depending on the type of aqueous solution (raw material solution, reaction mother liquor, aqueous solution for addition).

[Preparation process of phosphor raw material mixture]
A raw material mixture of photostimulable phosphor is prepared. The phosphor material is not particularly limited, and may be obtained by any known method.

Examples of the phosphor material include the following materials (1) to (6).
(1) The phosphor precursor crystal obtained in the above step (BaFCl: Ln, BaFBr: Ln, BaFI: Ln, etc.). However, this phosphor precursor crystals, a rare earth element Ln, alkaline earth metals M ^II other than Ba, and may not contain an alkali metal N ^I.
(2) At least one barium halide selected from the group consisting of BaF ₂ , BaCl ₂ , BaBr ₂ , BaI ₂ , BaFCl, BaFBr and BaFI.
_{(3) MgF 2, MgCl 2} , MgBr 2, MgI 2, CaF 2, CaCl 2, CaBr 2, CaI 2, SrF 2, SrCl 2, SrBr 2 and at least one rare earth element selected from the group consisting of SrI ₂ Metal halide.
(4) At least one selected from the group consisting of LiF, LiCl, LiBr, LiI, NaF, NaCl, NaBr, NaI, KF, KCl, KBr, KI, RbF, RbCl, RbBr, RbI, CsF, CsCl, CsBr and CsI Alkali metal halides.
(5) At least one metal oxide selected from the group consisting of Al ₂ O ₃ , SiO ₂ and ZrO ₂ .
(6) From the group consisting of compounds of rare earth elements (Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb), halides, oxides, nitrates, sulfates, etc. At least one compound selected.

If desired, ammonium halide (NH ₄ X ′, where X ′ represents F, Cl, Br, or I) or the like may be further used as a flux.
A necessary raw material is selected from the phosphor raw materials (1) to (6), and stoichiometrically weighed and mixed so as to obtain a composition ratio corresponding to the basic composition formula (I).

The phosphor raw material mixture can be prepared by appropriately selecting from known mixing methods. For example, the phosphor raw material mixture may be prepared by the following methods (i) to (iv).
(I) A method in which the phosphor raw materials (1) to (6) are weighed and simply mixed.
(Ii) After weighing and mixing the phosphor raw materials (1) to (5), the mixture is heated for several hours at a temperature of 100 ° C. or higher, and then the phosphor raw material (6) is mixed with the obtained heat-treated product. Method.
(Iii) A method in which the phosphor raw materials (1) to (6) are weighed and mixed, and then the mixture is heated at a temperature of 100 ° C. or higher for several hours.
(Iv) The phosphor raw materials (1) to (5) are mixed in a suspension state, and the suspension is heated, preferably at 50 to 200 ° C. under reduced pressure, vacuum drying, spray drying, or the like. A method of mixing the phosphor raw material (6) with the obtained dried product after drying.

    Further, as a modified method of the preparation method (iv), the phosphor raw materials (1) to (6) are mixed in a suspension state and the suspension is dried (iv-2), the phosphor raw material After the suspension containing (2) and (6) is heated, preferably heated to 50 to 200 ° C. or dried by vacuum drying, vacuum drying, spray drying or the like under heating, the suspension is obtained. Method (iv-3) of mixing phosphor raw materials (3) to (5) into the obtained mixture, or, when firing is performed twice or more, phosphor raw materials (1) to (3) are suspended. The phosphor raw materials (4) to (5) were added after the primary firing, and the suspension was dried under vacuum, preferably at 50 to 200 ° C. under reduced pressure, vacuum and spray drying. The method (iv-4) etc. which dry by fluorescent material etc. and mix a fluorescent substance raw material (6) with the obtained dried material can be mentioned suitably.

  Furthermore, in mixing phosphor materials, a preparation method (v) using a means capable of imparting a shearing force, a preparation method using means capable of controlling various conditions such as the addition of each phosphor material, the timing of mixing ( vi) can also be used. As a mixing apparatus, it can select and use suitably from well-known mixing apparatuses, For example, various mixers, V-type blender, a ball mill, a rod mill, a jet mill, an automatic mortar etc. can be mentioned.

  In the production of the photostimulable phosphor, various additive components as described below can be added for the purpose of further improving the photostimulated luminescence amount, the erasing performance and the like. Elements other than the elements included in the basic composition formula (I), for example, nonmetallic elements typified by B, O, S, As; amphoteric elements typified by Al, Ge, Sn; V, Be, Mn, Metal elements represented by Fe, Ni, Co 2, Cu, Ag; and tetrafluoroboric acid compounds, hexafluoro compounds, and the like. These additive components are added and mixed when the phosphor material is weighed and mixed, or before firing.

[Baking process]
Firing of the phosphor raw material mixture is performed by firing methods I and II shown below. The firing method I is a method suitable when the precipitate of the phosphor precursor crystal obtained in the production step is used as the phosphor material. The firing method II can be applied even when a precipitate of the phosphor precursor crystal is used as the phosphor material, or when the phosphor material mixture is simply prepared by omitting the generation step.

(Baking method I)
After the phosphor raw material mixture obtained in the above process or the pre-fired phosphor raw material mixture is filled in a heat-resistant container such as a quartz boat or a quartz crucible, it is put in a furnace core of an electric furnace and a temperature of 500 to 1000 ° C. In a neutral atmosphere such as a nitrogen gas atmosphere and an argon gas atmosphere for 0.5 to 12 hours, a weak reducing atmosphere such as a nitrogen gas atmosphere containing a small amount of hydrogen gas, a carbon dioxide atmosphere containing carbon monoxide, or Baking in a reduced-pressure atmosphere or a trace oxygen introduction atmosphere.

(Baking method II)
After the phosphor raw material mixture obtained in the above step or the pre-fired phosphor raw material mixture is filled in a heat-resistant container such as a quartz crucible, it is put in a furnace core of an electric furnace at a temperature of 800 to 1300 ° C. .5-12 hours, neutral atmosphere such as nitrogen gas atmosphere, argon gas atmosphere, nitrogen gas atmosphere containing a small amount of hydrogen gas, weak reducing atmosphere such as carbon dioxide atmosphere containing carbon monoxide, or reduced pressure atmosphere, Alternatively, the first baking is performed in a trace oxygen introduction atmosphere.

  After the phosphor precursor solidified by the first firing is pulverized using a pulverizer, a sintering inhibitor made of metal oxide fine particle powder is mixed with the phosphor precursor. Next, after filling this into a heat-resistant container such as a quartz boat, it is placed in the core of an electric furnace and neutral atmosphere such as nitrogen gas atmosphere and argon gas atmosphere at a temperature of 500 to 1000 ° C. for 0.5 to 12 hours. Alternatively, the second baking is performed in a weak reducing atmosphere such as a nitrogen gas atmosphere containing a small amount of hydrogen gas, a carbon dioxide atmosphere containing carbon monoxide, a reduced pressure atmosphere, or a trace oxygen introduction atmosphere.

[Feeling and classification process]
Prior to the classification treatment, it is preferable to loosen the fired product in order to loosen the sintering and aggregation of the phosphor particles and increase the yield of the phosphor. Specifically, the fired product is dispersed and stirred in an organic solvent that does not dissolve the fired product, or an aqueous medium containing monovalent or divalent metal ions, thereby relieving sintering and aggregation caused by firing. Examples of the organic solvent that does not dissolve the fired product include lower alcohols such as methanol. Examples of the aqueous medium containing monovalent or divalent metal ions include an aqueous solution containing Li ⁺ , Na ⁺ , K ⁺ , Rb ⁺ , Cs ⁺ and / or Ba ²⁺ . These metal ions are usually added to water as a metal salt such as a halide at a saturation concentration or less (preferably 1/10 to 9/10 of the saturation concentration). As the dispersing device, the above-described mixing device can be used. The unwinding treatment time is generally 1 to 24 hours.

  Next, the dispersion (slurry of the fired product) is passed through a mesh filter and subjected to a wet classification process. In the present invention, a mesh filter whose opening diameter L (μm) satisfies the following formula is used as the mesh filter.

2 ≦ L / D _m ≦ 8

[However, L represents the opening diameter of the mesh filter, and D _m represents the central particle diameter of the phosphor powder after the classification treatment. ]

In the above formula, when L / D _m exceeds 8, when the phosphor powder is used for the radiation image conversion panel, the image quality is deteriorated. That is, if a powder larger than 8 times the center particle size D _m μm is present in the panel, the graininess that can be visually recognized on the obtained radiation image is reduced. On the other hand, when L / D _m is smaller than 2, the yield of the obtained phosphor is remarkably lowered. Therefore, for example, when the center particle diameter D _m is 5 μm, a mesh filter having an opening diameter of 10 μm or more and 40 μm or less is used.

After the classification treatment, the dispersion is separated into solid and liquid and dried.
The classification treatment is not necessarily performed in a wet process, and may be performed in a dry process after pulverizing the fired product as necessary.

In this way, when it has the following basic composition formula (I) and the center particle diameter is D _m μm, it does not contain 1% or more of the powder having a particle diameter exceeding 8 × D _m μm (or not included at all). No) Rare earth activated alkaline earth metal fluoride halide photostimulable phosphor powder is obtained.

M ^II FX: zLn (I)

[Wherein M ^II represents at least one alkaline earth metal selected from the group consisting of Ba, Sr and Ca; Ln represents Ce, Pr, Sm, Eu, Gd, Tb, Dy, Ho, Nd, Er, Tm. And at least one rare earth element selected from the group consisting of Yb; X represents at least one halogen selected from the group consisting of Cl, Br and I; and z is in the range of 0 <z ≦ 0.2 The numerical value of ]

  In addition, since composition changes may occur before and after the firing step during the production of the phosphor, the ratio of each component of the phosphor precursor and the ratio of each component of the completed phosphor may be slightly different.

  The stimulable phosphor according to the present invention is not limited to the photostimulable phosphor described above, and includes various known stimulable phosphors and stimulable phosphors. Preferably, it is a photostimulable phosphor exhibiting photostimulated luminescence in a wavelength range of 300 to 500 nm by irradiation with excitation light having a wavelength in the range of 400 to 900 nm. As another example, a cerium activated rare earth oxyhalide system Mention may be made of phosphors.

  Further, the method for producing the stimulable phosphor powder of the present invention is not limited to the above method, and after the stimulable phosphor is generated by any known method, the above-mentioned classification is performed on the generated phosphor. Processing can be performed.

  The obtained stimulable phosphor powder of the present invention can be used for various applications that require a phosphor material. In particular, it can be preferably used as a storage phosphor of a radiation conversion panel.

  Next, the radiation image conversion panel of the present invention containing the above-mentioned stimulable phosphor powder will be described in detail.

  The support is usually a sheet or film made of a flexible resin material and having a thickness of 50 μm to 1 mm. The support may be transparent, or the support may be filled with a light reflective material (eg, alumina powder, titanium dioxide powder, barium sulfate powder) for reflecting excitation light or emitted light, Or you may provide a space | gap. Alternatively, the support may be filled with a light-absorbing material (eg, carbon black) to absorb excitation light or emitted light. Examples of resin materials that can be used to form the support include various resin materials such as polyethylene terephthalate, polyethylene naphthalate, aramid resin, and polyimide resin. Furthermore, for the purpose of increasing the sharpness of the radiographic image, the surface of the support on which the phosphor layer is formed (when an auxiliary layer such as an undercoat layer, a light reflection layer or a light absorption layer is provided on the support surface) May be formed on the surface of these auxiliary layers).

  On the support, a light reflecting layer made of a light reflecting material such as alumina, titanium dioxide, barium sulfate, or carbon black is provided on the support to improve the sensitivity or image quality (sharpness, graininess) of the panel as desired. A light absorbing layer made of a light absorbing material such as may be provided. Alternatively, an undercoat layer may be provided in order to improve adhesion with a layer provided thereon.

A phosphor layer containing the above-described stimulable phosphor powder of the present invention is provided on the support.
The storage phosphor powder is dispersed and dissolved in a suitable organic solvent together with a binder to prepare a coating solution. The ratio of the binder to the phosphor in the coating solution is usually in the range of 1: 1 to 1: 100 (weight ratio), and preferably in the range of 1: 8 to 1:40 (weight ratio). Various types of resin materials are known for the binder for dispersing and supporting the stimulable phosphor powder. Also in the formation of the phosphor layer according to the present invention, any known binder resin can be used as the center. The resin material can be appropriately selected and used. Also, the organic solvent for preparing the coating solution can be appropriately selected from known organic solvents. The coating solution further includes a dispersant for improving the dispersibility of the phosphor in the coating solution, and a plastic for improving the binding force between the binder and the phosphor in the formed phosphor layer. Various additives such as an agent, a yellowing prevention agent for preventing discoloration of the phosphor layer, a curing agent, and a crosslinking agent may be mixed.

  The coating solution is uniformly applied to the support surface using a normal coating means such as a doctor blade, a roll coater, or a knife coater to form a coating film. This coating film is dried to complete the formation of the stimulable phosphor layer on the support. The thickness of the phosphor layer varies depending on the characteristics of the intended radiation image conversion panel, the type of phosphor, the mixing ratio of the binder and the phosphor, and is usually in the range of 20 μm to 1 mm, preferably It is in the range of 50 to 500 μm.

  The stimulable phosphor layer does not necessarily have to be a single layer, and may be composed of two or more layers, in which case the type and particle size of the phosphor and the mixing ratio of the binder and the phosphor are arbitrary in each layer. Can be changed to

  In addition, it is not necessary to form the stimulable phosphor layer directly on the support. After forming the phosphor layer on a separately prepared substrate (temporary support), the phosphor layer is peeled off from the substrate, Alternatively, a method of bonding using an adhesive or the like may be used.

  It is desirable to provide a protective layer on the surface of the stimulable phosphor layer in order to facilitate transportation and handling of the radiation image conversion panel and avoid characteristic changes. It is desirable that the protective layer be transparent so that it does not affect the incidence of excitation light and emission of emitted light, and the radiation image conversion panel is sufficiently protected from physical impacts and chemical effects given from the outside. It is desirable to be chemically stable, highly moisture-proof, and have high physical strength.

  As the protective layer, a solution prepared by dissolving a transparent organic polymer substance such as cellulose derivative, polymethyl methacrylate, organic solvent-soluble fluorine-based resin in an appropriate solvent is applied on the phosphor layer. Formed, or separately formed a protective layer forming sheet made of an organic polymer film such as polyethylene terephthalate, and provided with an appropriate adhesive on the surface of the phosphor layer, or by vapor deposition of an inorganic compound A film formed on the phosphor layer is used. In addition, various additives such as light scattering fine powders such as magnesium oxide, zinc oxide, titanium dioxide, and alumina, slipping agents such as perfluoroolefin resin powder and silicone resin powder, and crosslinking agents such as polyisocyanate are added to the protective layer. The agent may be dispersedly contained. The thickness of the protective layer is generally in the range of about 0.1 to 20 μm when it is made of a polymer material.

  A fluororesin coating layer may be further provided on the surface of the protective layer in order to increase the stain resistance of the protective layer. The fluororesin coating layer can be formed by coating a fluororesin solution prepared by dissolving (or dispersing) a fluororesin in an organic solvent on the surface of the protective layer and drying. Although the fluororesin may be used alone, it is usually used as a mixture of a fluororesin and a resin having a high film forming property. In addition, an oligomer having a polysiloxane skeleton or an oligomer having a perfluoroalkyl group can be used in combination. The fluororesin coating layer can be filled with a fine powder filler in order to reduce interference unevenness and further improve the image quality of the radiation image. The thickness of the fluororesin coating layer is usually in the range of 0.5 μm to 20 μm. In forming the fluororesin coating layer, additive components such as a cross-linking agent, a hardener, and a yellowing inhibitor can be used. In particular, the addition of a crosslinking agent is advantageous for improving the durability of the fluororesin coating layer.

  Although the radiation image conversion panel of the present invention is obtained as described above, the configuration of the panel of the present invention may include various known variations. For example, for the purpose of improving the sharpness of an image, at least one of the above layers may be colored with a colorant that absorbs excitation light and does not absorb emitted light.

Further, a layer containing a phosphor that absorbs radiation and emits light in the ultraviolet to visible region may be provided adjacent to the stimulable phosphor layer. Examples of such phosphors include LnTaO ₄ : (Nb, Gd), Ln ₂ SiO ₅ : Ce, LnOX: Tm (Ln is a rare earth element), CsX (X is a halogen). Gd ₂ O ₂ S: Tb, Gd ₂ O ₂ S: Pr, Ce, ZnWO ₄ , LuAlO ₃ : Ce, Gd ₃ Ga ₅ O ₁₂ : Cr, Ce, HfO _{2 and the} like. It is desirable that these phosphor powders contain only 1% or less (or no) of powder having a particle diameter exceeding 8 × D _m μm when the center particle diameter is D _m μm.

[Example 1]
(1) Production of phosphor precursor (phosphor precursor 1) Potassium bromide (KBr), calcium bromide (CaBr ₂ ) and europium bromide (EuBr ₃ ) added to an aqueous solution of barium bromide (BaBr ₂ ) And mixed. While stirring the obtained aqueous solution, an aqueous ammonium fluoride (NH ₄ F) solution was added at a constant rate and reacted to obtain a precipitate. After completion of the reaction, the precipitate is separated into solid and liquid by suction filtration, washed with methanol, dried by heating under vacuum, and a tetrahedral K- and Ca-containing europium activated barium fluorobromide phosphor precursor ( A powder of BaFBr: Eu) was obtained.

(Phosphor Precursor 2) Barium carbonate (BaCO ₃ ) was added to hydriodic acid (HI) and mixed to obtain a slurry liquid. This liquid was concentrated to obtain a barium iodide (BaI ₂ ) suspension. Next, europium iodide (EuI ₃ ) was added to the suspension and mixed. Further, hydrogen fluoride (HF) was added to the suspension at a constant rate to react. After completion of the reaction, the precipitate is separated into solid and liquid by suction filtration, washed with 2-propanol, dried by heating under vacuum, and powder of europium activated barium fluoroiodide phosphor precursor (BaFI: Eu). Got.

(2) Preparation of phosphor raw material mixture Phosphor precursors 1 and 2 were mixed in a ratio such that the composition ratio of Br and I was 85:15, and further alumina superfine powder was added to prevent sintering. Weight% was added and mixed thoroughly with a mixer to obtain a phosphor raw material mixture.

(3) Firing 100 g of this phosphor raw material mixture was put in a quartz boat and fired using a firing furnace in which a quartz tube furnace core tube was inserted into a heater section. Firing was performed in a weakly oxidizing atmosphere (at atmospheric pressure, nitrogen / oxygen mixed atmosphere, oxygen partial pressure 13.3 hPa) over 2 hours at a temperature of 850 ° C. After firing, the furnace core tube was pulled out and cooled to room temperature while the inside of the furnace core tube was evacuated.

(4) Loosening / classification treatment 100 g of methanol was added to the fired product, and the mixture was stirred and loosened for 3 hours. Then, the dispersion was passed through a nylon mesh (opening diameter L: 10 μm) to perform wet classification treatment. Further, the dispersion passed through the nylon mesh was solid-liquid separated with a filter paper, dried with warm air, and the tetrahedral K- and Ca-containing europium-activated barium fluorobromide bromide phosphor of the present invention [(Ba _0.999 , A powder of Ca _0.001 ) F (Br _0.85 , I _0.15 ): 0.0001 K, 0.005 Eu) was obtained. When measured by an electric resistance method (Coulter method) particle size distribution measuring apparatus, the center particle diameter D _m was 3.0 μm and did not contain particles having a particle diameter of 10 μm or more (the maximum particle diameter was 9.5 μm). ).

[Example 2]
The tetrahedral europium activated barium fluoride bromide system of the present invention was the same as in Example 1 except that nylon mesh (opening diameter L: 20 μm) was used in the classification treatment of Example 1 (4). A phosphor powder was obtained. The center particle size D _m was 3.0 μm and did not include particles having a particle size of 20 μm or more.

[Comparative Example 1]
A tetrahedral europium-activated barium fluoride bromide for comparison in the same manner as in Example 1 except that nylon mesh (opening diameter L: 4 μm) was used in the classification treatment of Example 1 (4). A phosphor powder was obtained. The center particle size D _m was 2.5 μm and did not include particles having a particle size of 5 μm or more.

[Comparative Example 2]
A tetrahedral europium-activated barium fluoride bromide for comparison in the same manner as in Example 1 except that nylon mesh (opening diameter L: 30 μm) was used in the classification process of Example 1 (4). A phosphor powder was obtained. The center particle size D _m was 3.0 μm, and some particles having a particle size exceeding 24 μm were included.

[Comparative Example 3]
A tetrahedral europium-activated barium fluoride bromide for comparison in the same manner as in Example 1 except that nylon mesh (opening diameter L: 50 μm) was used in (4) classification treatment of Example 1. A phosphor powder was obtained. The center particle size D _m was 3.0 μm, and some particles having a particle size of 24 μm or more were included.

[Example 3] Radiation image conversion panel (1) Production of phosphor sheet Phosphor: any one of Examples 1 and 2 and Comparative Examples 1 to 3
Stimulable phosphor powder 200g
Binder: HDI polyurethane elastomer (Pandex T-5265H
[Solid], manufactured by Dainippon Ink & Chemicals, Inc.) 7.1g
Cross-linking agent: HDI polyisocyanate (Coronate HX
[Solid content: 100%, manufactured by Nippon Polyurethane Industry Co., Ltd.] 0.90g
Yellowing inhibitor: Epoxy resin (Epicoat # 1001,
(Oilized Shell Epoxy Co., Ltd.) 2.0g
Colorant: Ultramarine (SM-1, Daiichi Kasei Kogyo Co., Ltd.) 0.022g

  After the material having the above composition is added to methyl ethyl ketone in the stirring vessel, the mixture is stirred for 2 hours at a rotational speed of 2500 rpm (circumferential speed: about 18 m / sec) while flowing cooling water around the stirring vessel to disperse the phosphor powder. A coating solution having a viscosity of 30 PS (25 ° C.) was prepared. This coating liquid is fed to a constant flow coating head by a pump, while a polyethylene terephthalate sheet (temporary support, thickness: 188 μm) whose surface is treated with a silicon release agent (0.1 μm) is fed at a speed of 1 m. The coating liquid was applied onto the release agent-treated surface of the temporary support. This temporary support was transported to an oven and dried at 70 ° C. for 10 minutes, 85 ° C. for 10 minutes and 100 ° C. for 10 minutes to form a phosphor sheet (thickness: 190 μm) on the temporary support.

(2) Formation of undercoat layer On a transparent polyethylene terephthalate sheet (support, thickness: 250 μm), a soft acrylic resin (Criscoat P-1018GS [20% toluene solution], manufactured by Dainippon Ink & Chemicals, Inc.) Was applied uniformly using a doctor blade and dried to form an undercoat layer (layer thickness: 20 μm) on the support.

(3) Attaching the stimulable phosphor layer The phosphor sheet was peeled off from the temporary support, and compressed on the surface of the undercoat layer of the support. The compression operation was performed using a calender roll at a roll temperature of 90 ° C. By this heat compression treatment, the phosphor sheet is completely adhered to the support, and the stimulable phosphor layer (layer thickness: 150 μm, packing density: 3.35 g / cm ³ ) via the undercoat layer on the support. Was attached.

(4) Formation of protective layer On the stimulable phosphor layer, a coating solution containing a transparent fluororesin and a crosslinking agent was applied and dried to form a protective layer (layer thickness: 3 μm).
As described above, various radiation image conversion panels composed of the support, the undercoat layer, the stimulable phosphor layer, and the protective layer were produced.

[Performance evaluation of radiation image conversion panel]
The image quality (granularity) of each radiation image conversion panel was evaluated. After irradiating the panel with X-rays with a molybdenum tube voltage of 28 kVp for 18 mR, the panel is irradiated with semiconductor laser light (wavelength: 660 nm) with excitation energy of 4.3 J / m ² , and the stimulated emission light from the panel is received by a photoreceiver (spectral sensitivity). A S-5 photomultiplier tube) was detected, and 2 cycle / mm winner spectra (granular values resolved into spatial frequencies) were obtained from the obtained image data. Thus, the image quality was evaluated according to the following criteria.
AA: Very good, A: Good, B: Somewhat bad,
C: Poor and has practical problems. Table 1 summarizes the results obtained.

Table 1
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Example Mesh opening size Phosphor yield Panel image quality
(Μm) (%)
────────────────────────────────
Example 1 10 88 AA
Example 2 20 92 A
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Comparative Example 1 4 62 AA
Comparative Example 2 30 98 B
Comparative Example 3 50 99 C
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As is clear from the results in Table 1, according to the present invention, the brightening of the present invention obtained by classification with a mesh filter having an opening diameter L in the range of 2 × D _m to 8 × D _m (6 to 24 μm). Both the phosphor powder and the radiation image conversion panels (Examples 1 and 2) gave a radiation image with good image quality, and the phosphor yield was high. On the other hand, the photostimulable phosphor powder for comparison and the radiation image conversion panel (Comparative Example 1) obtained by classification with a mesh filter having an opening diameter L of less than 2 × D _m (5 μm) are a radiation image. Although the image quality of was good, the yield of the phosphor was very low. In addition, both the photostimulable phosphor powder and the radiation image conversion panel (Comparative Examples 2 and 3) for comparison obtained by classification with a mesh filter having an opening diameter L exceeding 8 × D _m (24 μm) are used. Although the phosphor yield was high, the image quality was insufficient.

Claims (8)

A stimulable phosphor powder having 99% or more of particles having a particle diameter of 8 × D _m μm or less when the center particle diameter is D _m μm. 2. The stimulable phosphor powder according to claim 1, wherein the center particle diameter _Dm is in the range of 2 to 5 [mu] _m . The stimulable phosphor has the following basic composition formula (I):

M ^II FX: zLn (I)

[Wherein M ^II represents at least one alkaline earth metal selected from the group consisting of Ba, Sr and Ca; Ln represents Ce, Pr, Sm, Eu, Gd, Tb, Dy, Ho, Nd, Er, Tm. And at least one rare earth element selected from the group consisting of Yb; X represents at least one halogen selected from the group consisting of Cl, Br and I; and z is in the range of 0 <z ≦ 0.2 The numerical value of ]
The stimulable phosphor powder according to claim 1 or 2, which is a rare earth activated alkaline earth metal fluoride halide stimulable phosphor.   4. The stimulable phosphor powder according to claim 3, wherein the rare earth activated alkaline earth metal fluoride halide stimulable phosphor is in a tetrahedral particle shape. The produced stimulable phosphor powder has an opening diameter L (μm) of the following formula:

2 ≦ L / D _m ≦ 8

[However, L represents the opening diameter of the mesh filter, and D _m represents the central particle diameter of the stimulable phosphor powder after the classification treatment. ]
The method for producing a stimulable phosphor powder according to claim 1, wherein the classification is performed using a mesh filter satisfying the above.   6. The stimulable phosphor powder is dispersed in an organic solvent that does not dissolve the stimulable phosphor powder or an aqueous medium containing monovalent or divalent metal ions, and then the dispersion is wet-classified by applying a mesh filter. A method for producing the stimulable phosphor powder described. A step of mixing the raw materials of the stimulable phosphor in an aqueous solution and reacting them to produce a phosphor precursor, a step of firing the phosphor precursor, an organic solvent that does not dissolve the fired product, Alternatively, the step of dispersing in a water-based medium containing monovalent or divalent metal ions and loosening the dispersion of the fired product has an opening diameter L (μm) of the following formula:

2 ≦ L / D _m ≦ 8

[However, L represents the opening diameter of the mesh filter, and D _m represents the central particle diameter of the stimulable phosphor particles after the classification treatment. ]
The method for producing a stimulable phosphor powder according to any one of claims 1 to 4, further comprising a step of classifying using a mesh filter satisfying the requirements.   A radiation image conversion panel comprising the stimulable phosphor powder according to any one of claims 1 to 4.