JP2004137359A - Rare earth-activated alkaline earth metal fluoride halide photostimulable phosphor and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a radiation image converting panel of high sensitivity and high image quality and to stably obtain a rare earth-activated alkaline earth metal fluoride halide photostimulable phosphor having a uniform grain size which gives the radiation image converting panel of high sensitivity and high image quality. <P>SOLUTION: The method for manufacturing the rare earth-activated alkaline earth metal fluoride halide photostimulable phosphor represented by general formula (1): Ba<SB>1-x</SB>M<SP>2</SP><SB>x</SB>FBr<SB>y</SB>I<SB>1-y</SB>:aM<SP>1</SP>,bLn,cO [wherein M<SP>1</SP>is at least one alkali metal selected from the group consisting of Li, Na, K, Rb and Cs; M<SP>2</SP>is at least one alkaline earth metal selected from the group consisting of Be, Mg, Sr and Ca; Ln is at least one rare earth element selected from the group consisting of Ce, Pr, Sm, Eu, Gd, Tb, Tm, Dy, Ho, Nd, Er and Yb; x, y, a, b and c are a number within the range of 0≤x≤0.3, 0≤y≤0.3, 0≤a≤0.05, 0<b≤0.2, and 0<c≤0.1, respectively] comprises a classification step by a curved air flow classification machine. <P>COPYRIGHT: (C)2004,JPO

Description

【０１００】
以上の様に、通常の篩によって分級したものは、輝度低下を生じることがわかる。それに対し、本発明に係わる分級方法によるものは輝度低下が少なく、粒状性もよい。中でも適度な分級分散圧で分級したものは、より輝度低下が少なく、粒状性が良好である。それに対し分級せず使用したものは、輝度は良好だが、得られる画像の粒状性が悪く実用上問題を生じることがわかる。
【０１０１】
【発明の効果】
高感度、高画質の、また粒度の揃った放射線像変換パネルが得られる希土類賦活アルカリ土類金属弗化ハロゲン化物輝尽性蛍光体を安定して得ることにある。
【図面の簡単な説明】
【図１】湾曲気流型分級機の一例を示す図である。
【符号の説明】
１　湾曲気流型分級機
２、３　分級エッジ
４　コアンダブロック
５　背面ブロック
７、８、９　排気流路
１１、１２　入気流路
１４　原料選別室
１５　被分級原料
１６　原料供給ノズル
１８　ホッパ
１９　圧縮気体流
２１、２２、２３　管路[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a rare earth-activated alkaline earth metal fluoride halide stimulable phosphor, particularly to a classification method thereof, and to a radiation image conversion panel obtained by the method.
[0002]
[Prior art]
The superiority of the radiation image conversion method using the radiation image conversion panel largely depends on the stimulable emission luminance of the panel (also referred to as sensitivity) and the sharpness of the obtained image. It is said that the properties of the stimulable phosphor used have a great effect.
[0003]
The stimulable phosphor is usually filled with a phosphor precursor crystal in a heat-resistant container such as a crucible and placed in a core of an electric furnace at a temperature of about 700 to 1300 ° C., generally for a time of about 0.5 to 12 hours, Sintering is performed under a certain gas atmosphere while avoiding sintering. The firing time depends on the filling amount of the phosphor raw material mixture, the firing temperature, the temperature at which the phosphor is taken out of the furnace, and the like. The firing atmosphere is a neutral atmosphere such as a nitrogen gas atmosphere, an argon gas atmosphere, or nitrogen containing a small amount of hydrogen gas. Various conditions such as a gas atmosphere, carbon monoxide, a weakly reducing atmosphere such as a carbon dioxide atmosphere, or a trace amount of oxygen may be used. By firing, the intended stimulable phosphor is obtained.
[0004]
In this firing step, sintering or agglomeration or the like is inevitably caused in part even though firing is performed while avoiding sintering using a sintering inhibitor or the like.
[0005]
Therefore, the phosphor is used without passing through the classification process under the condition that sintering is suppressed as much as possible, or for the aggregated phosphor, the phosphor is pulverized and passed through a sieve (ie, classified) to make the particle size distribution uniform. It can also be used.
[0006]
However, if the classification process is not performed, the resulting image will have a grainy feeling, that is, a deterioration in granularity. Usually, classification is performed such as passing through a sieve after crushing in order to make the particle size of the phosphor uniform.
[0007]
Regarding the classification of the phosphor, for example, Patent Document 1 discloses a technique of performing dry classification of a rare earth activated alkaline earth metal fluorinated halide phosphor using a vibration sieve or the like.
[0008]
However, the phosphor is damaged at the time of pulverization or classification, so that the brightness of the phosphor is reduced.
[0009]
Therefore, there is a need for a method for classifying a stimulable phosphor, which causes less phosphor damage and does not cause a decrease in luminance.
[0010]
As a classification method, there is a method using centrifugal force in addition to the above-mentioned sieve and the like. For example, although not applied to a stimulable phosphor, a toner may be classified using a (curved) airflow classifier. Japanese Patent Application Laid-Open No. H11-163,086 describes a classification performed.
[0011]
[Patent Document 1]
JP 2001-11438 A (page 6, paragraph 0037)
[0012]
[Patent Document 2]
JP-A-8-89900
[0013]
[Problems to be solved by the invention]
Therefore, an object of the present invention is to obtain a radiation image conversion panel with high sensitivity and high image quality. In addition, a rare earth activated alkaline earth metal fluoride which can obtain a high sensitivity and high image quality radiation image conversion panel with uniform grain size is provided. An object of the present invention is to obtain a halide stimulable phosphor stably.
[0014]
[Means for Solving the Problems]
The above object of the present invention is achieved by the following means.
[0015]
1. A method for producing a rare earth-activated alkaline earth metal fluoride halide stimulable phosphor represented by the general formula (1), wherein the method comprises a classifying step using a curved airflow classifier. A method for producing a metal fluorinated halide stimulable phosphor.
[0016]
2. 2. The method for producing a rare earth-activated alkaline earth metal fluoride halide stimulable phosphor according to the above item 1, wherein a classification dispersion pressure by a curved airflow classifier is 0.05 MPa or more and 0.5 MPa or less.
[0017]
3. A rare earth activated alkaline earth metal fluoride halide stimulable phosphor obtained by the production method according to 1 or 2.
[0018]
4. 4. A radiation image conversion panel comprising the rare earth activated alkaline earth metal fluoride halide stimulable phosphor according to the above item 3.
[0019]
Hereinafter, the present invention will be described in detail.
The rare earth activated alkaline earth metal fluoride halide stimulable phosphor according to the present invention will be described.
[0020]
For the production of the stimulable phosphor precursor by the liquid phase method, the precursor production method described in JP-A-10-140148 and the precursor production apparatus described in JP-A-10-147778 can be preferably used. Here, the stimulable phosphor precursor indicates a state in which the substance represented by the general formula (1) has not passed through a high temperature of 600 ° C. or more. Almost no luminescence. In the present invention, it is preferable to obtain a precursor by the following liquid phase synthesis method.
[0021]
The production of the rare earth activated alkaline earth metal fluoride halide stimulable phosphor represented by the general formula (1) is not a solid phase method in which control of particle shape is difficult, but a liquid phase method in which particle size control is easy. It is preferable to carry out by: In particular, it is preferable to obtain a stimulable phosphor by the following liquid phase synthesis method.
[0022]
(Preparation of precipitate of precursor crystal by crystallization)
BaI ₂ And x in the general formula (1) is not 0, further comprises M ² When y is not 0, BaBr ₂ And M ¹ After their dissolution, the BaI ₂ Preparing a solution having a concentration of at least 3.3 mol / L, preferably at least 3.5 mol / L;
While maintaining the above solution at a temperature of 50 ° C. or higher, preferably 80 ° C. or higher, an inorganic fluoride (ammonium fluoride or alkali metal fluoride) having a concentration of 5 mol / L or more, preferably 8 mol / L or more is added thereto. Adding a solution to obtain a precipitate of rare earth activated alkaline earth metal fluorinated iodide-based stimulable phosphor precursor crystals;
Step of removing the solvent from the reaction solution while adding the above-mentioned inorganic fluoride
Separating the precursor crystal precipitate from the reaction solution;
Then, the production method includes a step of firing the separated precursor crystal precipitate while avoiding sintering.
[0023]
The particles (crystals) according to the present invention preferably have an average particle diameter of 1 to 10 μm and are monodisperse, and have an average particle diameter of 1 to 7 μm and a distribution (%) of the average particle diameter of 20% or less. The average particle diameter is preferably 1 to 5 μm, and the distribution of the average particle diameter is preferably 15% or less.
[0024]
The average particle size in the present invention is obtained by randomly selecting 200 particles from an electron micrograph of a particle (crystal) and calculating the average by a sphere-equivalent volume particle size.
[0025]
(Preparation of precipitate of precursor crystal by concentrated crystallization)
First, a starting compound other than a fluorine compound is dissolved in an aqueous medium. That is, BaI ₂ And a halide of Ln, and optionally further M ² Halide, and also M ¹ Are mixed well and dissolved in an aqueous medium to prepare an aqueous solution in which they are dissolved. However, BaI ₂ BaI so that the concentration is 3.3 mol / L or more, preferably 3.5 mol / L or more. ₂ Adjust the concentration ratio between the concentration and the aqueous solvent in advance. At this time, if the barium concentration is low, a precursor having a desired composition cannot be obtained, or even if obtained, the particles are enlarged. Therefore, it is necessary to appropriately select the barium concentration, and as a result of studies by the present inventors, it has been found that fine precursor particles can be formed at 3.3 mol / L or more. At this time, a small amount of an acid, ammonia, alcohol, a water-soluble polymer, a water-insoluble metal oxide fine particle powder or the like may be added, if desired. BaI ₂ It is also a preferred embodiment to add an appropriate amount of a lower alcohol (methanol, ethanol) as long as the solubility of the compound does not significantly decrease. This aqueous solution (reaction mother liquor) is maintained at 80 ° C.
[0026]
Next, an aqueous solution of an inorganic fluoride (such as ammonium fluoride or an alkali metal fluoride) is injected into the stirred and maintained aqueous solution at 80 ° C. This injection is preferably carried out in the area of the region where the stirring is particularly vigorous. By the injection of the inorganic fluoride aqueous solution into the reaction mother liquor, a rare earth activated alkaline earth metal fluoride halide precursor crystal corresponding to the general formula (1) is deposited.
[0027]
In the present invention, the solvent is removed from the reaction solution when adding the inorganic fluoride aqueous solution. The timing of removing the solvent is not particularly limited as long as the solvent is being added. The ratio (removal ratio) of the total mass after the removal of the solvent to the mass before the removal (the sum of the mass of the reaction mother liquor and the mass of the added aqueous solution) is preferably 0.97 or less. Below this, the crystal may not be completely BaFI. Therefore, the removal ratio is preferably 0.97 or less, more preferably 0.95 or less. In addition, even if it is excessively removed, there may be a problem in handling, such as an excessive increase in the viscosity of the reaction solution.
[0028]
Therefore, the solvent removal ratio is preferably up to 0.5. 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 for removing the solvent. 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 an intended composition can be obtained. Further, it is preferable to use another solvent removal method in combination in order to increase productivity and to keep the particle shape appropriately. The method of removing the solvent used in combination is not particularly limited. It is also 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. Vent dry gas
The reaction vessel is a closed type, provided with holes through which at least two or more gases can pass, and through which dry gas is passed. The type of gas can be arbitrarily selected. From the viewpoint of safety, air and nitrogen are preferable. Depending on the amount of saturated water vapor in the gas to be aerated, the solvent is entrained in the gas and removed. In addition to the method of ventilating the void portion of the reaction vessel, a method of ejecting gas as bubbles into the liquid phase and absorbing the solvent into the bubbles is also effective.
2. Decompression
As is well known, reducing the pressure 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 the solvent. When the solvent is water, the pressure is preferably 86 kPa or less.
3. Liquid film
The solvent can be removed efficiently by enlarging the evaporation area. As in the present invention, when heating and stirring using a reaction vessel having a constant volume to cause a reaction, the heating method is to immerse the heating means in a liquid or to attach the heating means to the outside of the vessel. The method is general. According to this method, the heat transfer area is limited to the portion where the liquid and the heating means come into contact with each other, and the heat transfer area decreases with the removal of the solvent, so that the time required for removing the solvent becomes longer. In order to prevent this, it is effective to use a pump or a stirrer to spray the solution on the wall surface of the reaction vessel to increase the heat transfer area. The method of spraying the liquid on the wall surface of the reaction vessel to form a liquid film in this manner is known as a "wet wall". Examples of the method for forming the wet wall include a method using a pump and a method using a stirrer described in JP-A-6-335627 and JP-A-11-235522.
[0029]
These methods may be used alone or 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 aerating a dry gas are effective. The former is particularly preferred, and the methods described in JP-A-6-335627 and Japanese Patent Application No. 2002-35202 are preferably used.
[0030]
Next, the phosphor precursor crystals are separated from the solution by filtration, centrifugation, etc., sufficiently washed with methanol or the like, and dried. A sintering inhibitor such as alumina fine powder or silica fine powder is added to and mixed with the dried phosphor precursor crystal to uniformly adhere the sintering inhibitor fine powder to the crystal surface. The addition of the sintering inhibitor can be omitted by selecting the firing conditions.
[0031]
(Fired)
Next, the crystal of the phosphor precursor is filled in a heat-resistant container such as a quartz port, an alumina crucible, or a quartz crucible, and placed in a core of an electric furnace to perform sintering while avoiding sintering. The firing temperature is suitably in the range of 400 to 1,300 ° C, and preferably in the range of 500 to 1,000 ° C. 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.
[0032]
As the firing atmosphere, a neutral atmosphere such as a nitrogen gas atmosphere, an argon gas atmosphere, 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 a trace amount of oxygen introduced The atmosphere is used. In the present invention, as a firing method, a method described in JP-A-2000-8034 is preferably used. By the above calcination, the desired oxygen-introduced rare earth activated alkaline earth metal fluoride halide stimulable phosphor is obtained, and a radiation image conversion panel having a phosphor layer formed using the phosphor is produced.
[0033]
Next, the obtained oxygen-introduced rare earth activated alkaline earth metal fluorohalide stimulable phosphor powder undergoes a classification step to make the particle diameter uniform.
[0034]
In the classification step, the monodisperse phosphor powder having an average particle diameter in the range of 1 to 10 μm as described above is selected by a classification operation. The light emission brightness of the body is reduced.
[0035]
This is because, depending on the classification method, due to the action of stress caused by the classification operation of the sintered or aggregated phosphor powder, for example, in the case of classification by the centrifugal method, the sintered or aggregated coarse particles are removed from the inner wall of the apparatus for classification. The fluorescent material that has been damaged due to, for example, crushing due to collision with the phosphor or the like, or the stress between the phosphor particles due to the vibration of the sieve or the like and damage to the activated phosphor due to the interaction with the mesh of the sieve. It is considered that the body is mixed into the stimulable phosphor and the emission luminance of the obtained phosphor is reduced.
[0036]
In the present invention, the classifying step using a curved airflow classifier described in Patent Document 2 (Japanese Patent Application Laid-Open No. 8-89900) or the like is performed by using the rare earth activated alkaline earth metal fluoride halide according to the present invention. It has been found that when applied to a stimulable phosphor, there is no decrease in the luminance of the phosphor, and a high-luminance stimulable phosphor can be stably obtained.
[0037]
It is not known why these curved airflow classifiers reduce the brightness of the phosphors little.However, the principle of classification by this method is that particles having different particle diameters with different inertia in airflow. It is considered that the difference in the curvature of the scattered descent path is related to the fact that the stress between particles or the collision of particles with the vessel wall and the like is small and the damage of the phosphor is small.
[0038]
Hereinafter, a configuration of a curved airflow classifier used in the present invention and a classification mechanism thereof will be described.
[0039]
The classification principle of a curved airflow classifier is based on the fact that the direction of motion changes when the particle size changes due to the inertial force acting on the particles and the resistance of the fluid generated by the motion of the particles.
[0040]
FIG. 1 shows an example of such a curved airflow classifier. The curved airflow classifier 1 has three classifying exhaust passages 7, 8, and 9 branched by the first and second classifying edges 2, 3 and the Coanda block 4 and the back block 5, and has a chamber outlet. And two inlet passages 11 and 12 are provided at the inlet side of the chamber, and the raw material separation chamber 14 is connected to the exhaust passages 7, 8 and 9 from the inlet passages 11 and 12. Supply means for pressure-feeding and injecting the raw material to be classified 15 into the raw material separation chamber 14 using a compressed gas (usually compressed air), which is not shown in the drawings, and an air flow forming means (for example, an exhaust fan) for generating a flowing air flow. 16 is provided.
[0041]
Here, the raw material to be classified 15 (the rare earth activated alkaline earth metal fluoride halide stimulable phosphor powder according to the present invention) is supplied to the inside of the raw material supply nozzle 16 by the hopper 18 communicating with the base end side of the raw material supply nozzle 16. And is dispersed by the compressed gas flow 19 supplied to the raw material supply nozzle 16 and is injected from the raw material supply nozzle 16 into the raw material selection chamber 14 as a solid-gas multiphase flow. The jet including the raw material to be classified 15 injected into the raw material separation chamber 14 from the raw material supply nozzle 16 flows along the Coanda block 4 by the Coanda effect, and a centrifugal force acts on the raw material to be classified 15, and the raw material to be classified 15 The relatively coarse phosphor particles inside jump out from the jet flowing along the Coanda block 4. Outside the jet flowing along the Coanda block 4, airflows flowing from the inlet channels 11, 12 toward the respective exhaust channels 7, 8, 9 flow out of the jet flowing along the Coanda block 4. The relatively coarse phosphor particles in the raw material to be classified 15 are separated and discharged into the corresponding exhaust passages 7, 8, and 9 for each predetermined particle size range by the difference in the scattering path for each phosphor particle due to the airflow. It has become.
[0042]
The scattering path of the phosphor particles on which the Coanda effect acts is such that the smaller the particle diameter and the smaller the inertia, the greater the curvature, and the scattering path along the airflow contact surface of the Coanda block and the exhaust passage 7 closest to the Coanda block 4. Is discharged. On the other hand, the larger the particle diameter and the greater the inertia, the smaller the curvature of the scattered descent path, so that the scattered and scattered path is scattered farther away from the Coanda block and discharged to the exhaust passage 9 farthest from the Coanda block 4. Accordingly, the exhaust passages 7, 8, 9 are arranged such that the exhaust passage 7 closest to the Coanda block 4 is for exhausting fine powder composed of phosphor particles having a small particle diameter, and the exhaust passage farthest from the raw material supply nozzle 16. The flow path 9 is used for discharging coarse powder made of phosphor particles having a large particle diameter, and the exhaust flow path 8 located in the middle is used for discharging medium powder having an intermediate particle diameter. The classified material 15 discharged to each of the exhaust passages 7, 8, and 9 is connected to each of the exhaust passages 7, 8, and 9 by a dust collector (not shown) connected to the exhaust passages 7, 8, and 9 via pipes 21, 22, and 23. Each is collected and separated into powder and air.
[0043]
Adjustment of the classification particle size is performed by adjusting the positions of the classification edges 2 and 3, the pressure of the compressed gas flow supplied to the raw material supply nozzle 16, and the airflow of the air flow from the intake channels 11 and 12 to the exhaust channels 7, 8, and 9. This is done by adjusting
[0044]
The phosphor particles according to the present invention, that is, the rare-earth-activated alkaline earth metal fluoride halide stimulable phosphor particles as the raw material to be classified 15 are dispersed in the raw material selection chamber 14 from a solid gas dispersed from a raw material supply nozzle. The pressure (classification dispersion pressure) of the compressed gas stream 19 to be injected and supplied as a multiphase flow is in a range of 0.05 MPa to 0.5 MPa. Damage to the phosphor particles due to collision between particles in a solid-gas multiphase flow. Is preferable because of the small amount, and more preferably in the range of 0.1 MPa to 0.4 MPa. Also, if the dispersion pressure is large, in addition to particle damage due to collisions between particles and the like, the curvature of the scattered descent path of particles having a large particle size and a large inertia becomes large, so that the collision with the channel wall and the like also increase. Damaged and crushed small particles are mixed, which is not preferable. If the dispersion pressure is too low, the effect of classification is small.
[0045]
By performing such classification, in the case of the rare earth activated alkaline earth metal fluoride halide stimulable phosphor particles according to the present invention, by applying this to a radiation image conversion panel, high sensitivity and granularity can be obtained. An excellent radiation image conversion panel can be obtained.
[0046]
As the stimulable phosphor that can be used in the present invention, a phosphor that emits stimulable light in a wavelength range of 300 to 500 nm by excitation light having a wavelength in the range of 400 to 900 nm is generally used. .
[0047]
The particle size of the stimulable phosphor produced through these classification steps preferably has an average particle size of 1 to 10 μm and is monodisperse as described above. ~ 7 µm, and those having a distribution (%) of average particle size of 20% or less are preferred.
[0048]
In the present invention, the stimulable phosphor layer is formed by mixing and dispersing the stimulable phosphor powder in a binder solution and applying the same.
[0049]
Examples of the binder used in the phosphor layer include proteins such as gelatin, polysaccharides such as dextran, and natural polymer substances such as gum arabic; and polyvinyl butyral, polyvinyl acetate, nitrocellulose, ethylcellulose, and chloride. Binders represented by synthetic polymer substances such as vinylidene / vinyl chloride copolymer, polyalkyl (meth) acrylate, vinyl chloride / vinyl acetate copolymer, polyurethane, cellulose acetate butyrate, polyvinyl alcohol, linear polyester and the like. However, the binder is preferably a resin mainly composed of a thermoplastic elastomer. Examples of the thermoplastic elastomer include a polystyrene-based thermoplastic elastomer and a polyolefin-based thermoplastic elastomer described above. Stomer, polyurethane-based thermoplastic elastomer, polyester-based thermoplastic elastomer, polyamide-based thermoplastic elastomer, polybutadiene-based thermoplastic elastomer, ethylene-vinyl acetate-based thermoplastic elastomer, polyvinyl chloride-based thermoplastic elastomer, natural rubber-based thermoplastic elastomer, fluorine Rubber-based thermoplastic elastomers, polyisoprene-based thermoplastic elastomers, chlorinated polyethylene-based thermoplastic elastomers, styrene-butadiene rubber, and silicone rubber-based thermoplastic elastomers are exemplified. Of these, polyurethane-based thermoplastic elastomers and polyester-based thermoplastic elastomers have good dispersibility because of their strong bonding force with the phosphor, are also rich in ductility, and have good flexibility against radiation intensifying screens. Is preferred. In addition, these binders may be crosslinked with a crosslinking agent.
[0050]
The mixing ratio between the binder and the stimulable phosphor in the coating solution varies depending on the set value of the haze ratio of the intended radiation image conversion panel, but is preferably 1 to 20 parts by mass relative to the phosphor, and more preferably 2 to 20 parts by mass. 10 parts by mass is more preferred.
[0051]
Mixing and dispersing a stimulable phosphor to prepare a stimulable phosphor layer coating solution, or preparing a binder solution or dispersing a binder and a stimulable phosphor together to produce a stimulable phosphor. Examples of the organic solvent used for preparing the layer coating solution and adjusting the coating solution concentration and viscosity include, for example, lower alcohols such as methanol, ethanol, isopropanol and n-butanol, acetone, methyl ethyl ketone, and methyl isobutyl. Ketones, ketones such as cyclohexanone, esters of lower fatty acids such as methyl acetate, ethyl acetate and n-butyl acetate with lower alcohols, dioxane, ethers such as ethylene glycol monoethyl ether, ethylene glycol monomethyl ether, fragrances such as triol and xylol Group compounds, methylene chloride, ethylene chloride, etc. Halogenated hydrocarbons and mixtures thereof and the like.
[0052]
The coating liquid has a dispersant for improving the dispersibility of the phosphor in the coating liquid, and also enhances the binding force between the binder and the phosphor in the stimulable phosphor layer after formation. Various additives such as a plasticizer may be mixed. Examples of dispersants used for such purposes include phthalic acid, stearic acid, caproic acid, lipophilic surfactants and the like. Examples of the plasticizer include phosphoric esters such as triphenyl phosphate, tricresyl phosphate, and diphenyl phosphate; phthalic esters such as diethyl phthalate and dimethoxyethyl phthalate; ethylphthalylethyl glycolate, butylphthalylbutyl glycolate; And polyesters of aliphatic dibasic acid such as polyesters of triethylene glycol and adipic acid, polyesters of diethylene glycol and succinic acid, and the like.
[0053]
Preparation of the stimulable phosphor layer coating solution, for example, by mixing the binder solution and the stimulable phosphor, ball mill, bead mill, sand mill, attritor, three-roll mill, high-speed impeller disperser, Kady mill, or This is performed by dispersing the stimulable phosphor powder in a binder using a dispersing device such as an ultrasonic disperser.
[0054]
The coating solution prepared as described above is uniformly applied to the surface of a support described later to form a stimulable phosphor layer coating film. As a coating method that can be used, a usual coating means, for example, a doctor blade, a roll coater, a knife coater, a comma coater, a lip coater or the like can be used.
[0055]
The coating film formed by the above means is then heated and dried to complete the formation of the stimulable phosphor layer on the support. The thickness of the stimulable phosphor layer varies depending on the characteristics of the intended radiation image conversion panel, the type of the stimulable phosphor, the mixing ratio of the binder and the phosphor, and is usually 10 to 1000 μm. , More preferably 10 to 500 μm.
[0056]
As the support used in the radiation image storage panel of the present invention, various polymer materials are used. Particularly, those which can be processed into a flexible sheet or web in handling as an information recording material are preferable. In this regard, cellulose acetate films, polyester films, polyethylene terephthalate films, polyethylene naphthalate films, polyamide films, polyimide films Plastic films such as films, triacetate films and polycarbonate films are preferred.
[0057]
The layer thickness of the support varies depending on the material of the support to be used and the like, 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 a mat surface for the purpose of improving the adhesion to the stimulable phosphor layer.
[0058]
Further, in these supports, an undercoat layer may be provided on the surface on which the stimulable phosphor layer is provided for the purpose of improving the adhesion to the stimulable phosphor layer.
[0059]
The undercoat layer according to the present invention preferably contains a polymer resin that can be crosslinked by a crosslinking agent and a crosslinking agent.
[0060]
The polymer resin that can be used in the undercoat layer is not particularly limited, for example, polyurethane, polyester, vinyl chloride copolymer, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, Vinyl chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (nitrocellulose, etc.), styrene-butadiene copolymer, various synthetic rubber resins, phenolic resin, epoxy resin, urea Resins, melamine resins, phenoxy resins, silicone resins, acrylic resins, urea formamide resins, and the like. Among them, polyurethane, polyester, vinyl chloride copolymer, polyvinyl butyral, nitrocellulose and the like can be mentioned. In the invention according to claim 2, the average glass transition temperature (Tg) of the polymer resin used in the undercoat layer is determined. ) Is 25 ° C. or higher, and one is to use a polymer resin having a Tg of 25 to 200 ° C.
[0061]
The crosslinking agent that can be used in the undercoat layer according to the present invention is not particularly limited, and examples thereof include a polyfunctional isocyanate and a derivative thereof, melamine and a derivative thereof, and an amino resin and a derivative thereof. It is preferable to use a polyfunctional isocyanate compound as the agent, and examples thereof include Coronate HX and Coronate 3041 manufactured by Nippon Polyurethane Co., Ltd.
[0062]
The undercoat layer according to the present invention can be formed on a support by the following method, for example.
[0063]
First, the polymer resin and the cross-linking agent described above are added to a suitable solvent, for example, a solvent used in the preparation of a stimulable phosphor layer coating solution described below, and mixed well to prepare an undercoat layer coating solution. .
[0064]
The amount of the cross-linking agent used depends on the characteristics of the intended radiation image conversion panel, the type of material used for the stimulable phosphor layer and the support, the type of polymer resin used for the undercoat layer, and the like. In consideration of maintaining the adhesive strength of the phosphor layer to the support, it is preferable to add the phosphor layer at a ratio of 50% by mass or less to the polymer resin, and particularly preferably 15 to 50% by mass.
[0065]
The thickness of the undercoat layer varies depending on the characteristics of the intended radiation image conversion panel, the type of the material used for the stimulable phosphor layer and the support, the type of the polymer resin and the cross-linking agent used for the undercoat layer, and the like. Generally, the thickness is preferably 3 to 50 μm, and particularly preferably 5 to 40 μm.
[0066]
As a protective layer provided on a radiation image conversion panel having a coating type phosphor layer, a polyester film provided with an excitation light absorbing layer having a haze ratio measured by the method described in ASTM D-1003 of 5% or more and less than 60%; Polymethacrylate film, nitrocellulose film, cellulose acetate film and the like can be used, stretched film such as polyethylene terephthalate film or polyethylene naphthalate film, transparency, preferably as a protective layer in terms of strength, further, These polyethylene terephthalate films and vapor-deposited films obtained by vapor-depositing a thin film of metal oxide, silicon nitride, or the like on the polyethylene terephthalate film are more preferable from the viewpoint of moisture resistance.
[0067]
The haze ratio of the film used in the protective layer can be easily adjusted by selecting the haze ratio of the resin film to be used, and a resin film having an arbitrary haze ratio can be easily obtained industrially. As the protective film of the radiation image conversion panel, a film having very high optical transparency is assumed. Various plastic films having a haze value in the range of 2 to 3% are commercially available as such a highly transparent protective film material. A preferable haze ratio for obtaining the effect of the present invention is 5% or more and less than 60%, and more preferably 10% or more and less than 50%. If the haze ratio is less than 5%, the effect of eliminating image unevenness and linear noise is low, and if it is 60% or more, the effect of improving sharpness is impaired, which is not preferable.
[0068]
The film used in the protective layer according to the present invention has an optimal moisture-proof property by laminating a plurality of resin films or vapor-deposited films obtained by depositing a metal oxide or the like on the resin film in accordance with the required moisture-proof property. And a moisture permeability of at least 5.0 g / m2 in consideration of prevention of deterioration due to moisture absorption of the stimulable phosphor. ² * It is preferable that it is day or less. The method for laminating the resin film is not particularly limited, and any known method may be used.
[0069]
Further, by providing the excitation light absorbing layer between the laminated resin films, the excitation light absorbing layer is preferably protected from physical impact and chemical deterioration, and stable plate performance can be maintained for a long time. In addition, a plurality of excitation light absorbing layers may be provided, or a colorant may be contained in an adhesive layer for lamination to form an excitation light absorbing layer.
[0070]
The protective film may be in close contact with the stimulable phosphor layer via an adhesive layer, but must have a structure provided to cover the phosphor surface (hereinafter, also referred to as a sealing or sealing structure). Is more preferred. In sealing the phosphor plate, any known method may be used.However, when the outermost resin layer on the side of the moisture-proof protective film in contact with the phosphor sheet is made of a heat-fusible resin film, the moisture-proof protective film cannot be sealed. This is one of the preferred embodiments in that the protective film can be fused and the sealing work of the phosphor sheet is made more efficient. Furthermore, a moisture-proof protective film is arranged above and below the phosphor sheet, and in a region where the periphery is outside the periphery of the phosphor sheet, the upper and lower moisture-proof protective films are heated and fused with an impulse sealer or the like. The use of the sealing structure is preferable because it prevents moisture from entering from the outer peripheral portion of the phosphor sheet. Further, by making the moisture-proof protective film on the support surface side a laminated moisture-proof film formed by laminating one or more aluminum films, the invasion of moisture can be reduced more reliably. This is also easy and preferable. In the method of heat-sealing with the impulse sealer, the heat-sealing under a reduced pressure environment is more preferable in terms of preventing displacement of the phosphor sheet in the moisture-proof protective film and eliminating moisture in the air.
[0071]
The heat-fusible outermost resin layer on the side of the moisture-proof protective film in contact with the phosphor surface and the phosphor surface may or may not be adhered. Here, the state of non-adhesion means that even if the phosphor surface and the moisture-proof protective film are microscopically point-contacted, the phosphor surface and the moisture-proof protective film are optically and mechanically almost discontinuous. It can be treated as a body. In addition, the above-mentioned resin film having heat fusibility is a resin film that can be fused with a generally used impulse sealer, and for example, ethylene vinyl acetate copolymer (EVA), polypropylene (PP) film, polyethylene ( PE) film, etc., but the present invention is not limited thereto.
[0072]
【Example】
Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto.
[0073]
Examples 1-3
Manufacture of radiation image conversion panels
(Formation of phosphor layer and undercoat layer)
First, an undercoat layer coating solution was prepared as follows. 100 g of a dispersion of β-copper phthalocyanine as a colorant (solid content 35%, pigment content 30%) was simultaneously added to 90 kg of a polyester resin dissolved product (Toyobo Byron 55SS: solid content 35%) using a propeller mixer for 30 minutes. did. After completion of the addition, 5 kg of Coronate HX (manufactured by Nippon Polyurethane Co., Ltd.) as a curing agent and a solvent composed of MEK, toluene and cyclohexanone were mixed to prepare an undercoat layer coating solution.
[0074]
Next, this coating solution was applied to foamed PET, 188E60L (Toray) using a doctor blade, and dried at 100 ° C. for 5 minutes to form an undercoat layer having a thickness of 50 μm and used as a support.
[0075]
Next, to synthesize a phosphor precursor of europium-activated barium fluoroiodide, BaI ₂ 2500 ml of aqueous solution (4.0 mol / L) and EuI ₃ 125 ml of an aqueous solution (0.2 mol / L) was put into the reactor. The reaction mother liquor in the reactor was kept at 70 ° C with stirring. 250 ml of an ammonium fluoride aqueous solution (8 mol / L) was injected into the reaction mother liquor using a roller pump to generate a precipitate. After completion of the pouring, the precipitate was ripened by keeping the temperature and stirring for 2 hours.
[0076]
Next, the precipitate was separated by filtration, washed with ethanol, and dried under vacuum to obtain europium-activated barium fluoroiodide crystals.
[0077]
0.1% by mass of ultrafine alumina powder is added to prevent change in particle shape due to sintering during firing, and change in particle size distribution due to fusion between particles, and the mixture is sufficiently stirred with a mixer to attach to the crystal surface. Ultrafine alumina powder was uniformly adhered.
[0078]
This was filled in a quartz boat and calcined at 850 ° C. for 2 hours in a nitrogen / hydrogen mixed gas atmosphere using a tube furnace to obtain a europium-activated barium fluoroiodide phosphor.
[0079]
(Hydrophobic treatment of stimulable phosphor)
15 g of hydrophobic silica particles having an average particle diameter of 7 nm (R976 manufactured by Nippon Aerosil Co., Ltd.), 40 g of a silane coupling agent (SH6062SILANE manufactured by Dow Corning Toray Silicone Co., Ltd.), 20 g of water, and 1,425 g of ethanol are put in a container. While keeping the temperature at 45 ° C., hydrophobic silica was dispersed in ethanol using TK ROBO MICS (manufactured by Tokushu Kika Kogyo Co., Ltd.).
[0080]
Thereafter, 4.0 kg of the obtained europium-activated barium fluoroiodide phosphor particles were added to the stirred suspension of the hydrophobic silica containing the silane coupling agent, followed by further dispersion for 4 hours.
[0081]
This europium-activated barium fluoroiodide phosphor suspension was subjected to solid-liquid separation by pressure filtration and dried at 80 ° C. for 15 hours to obtain a hydrophobized europium-activated barium fluoroiodide phosphor.
[0082]
2.0 kg of the hydrophobicized phosphor is put in a container of a multi-blender mill BLA-2001, and is operated for 10 minutes at a cutter rotation speed of 3,000 rpm (peripheral speed of 11 m / sec) and a cup rotation speed of 3 [scale]. As a result, 1.98 kg of the crushed particles of the phosphor subjected to the hydrophobic treatment were obtained.
[0083]
Next, several kinds of phosphor particle samples were prepared by changing the classification conditions of the obtained crushed phosphor particles as follows.
[0084]
Using a curved airflow classifier whose structure is shown in FIG. 1, specifically, an elbow jet MODEL EJ-P-3 (Puro) manufactured by Matsubo Corporation, using the multi-blender mill as a raw material to be classified. The crushed stimulable phosphor particles are supplied from a hopper, and the positions of classification edges 2 and 3 (distances to Coanda blocks) are fixed as shown in Table 1, respectively. The classification is performed by changing the pressure of the compressed air flow of the raw material supply nozzle 16 to be fed and sprayed as shown in Table 1, thereby obtaining phosphor particles having the particle diameters shown in Table 1 (Examples 1 to 3). Got. Note that the total air volume of the airflow flowing from the intake channels 11 and 12 to the exhaust channels 7, 8 and 9 in FIG. 1 is 2.7 m. ³ / Min.
[0085]
For comparison, the phosphor particles crushed by the multi-blender mill were passed through a vibrating sieve fitted with a nylon mesh (# 460), and the classified phosphor particles (Comparative Example 1) were separately prepared. Further, Comparative Example 2 was a phosphor particle which was not particularly classified.
[0086]
As the phosphor layer forming material, 427 g of the thus obtained europium-activated barium fluoroiodide phosphor particles (Examples 1 to 3 and Comparative Examples 1 and 2), 18 g of a polyester resin (Toyobo Byron 530) and methyl ethyl ketone, respectively , Toluene and cyclohexanone, and dispersed by a propeller mixer to prepare a coating solution having a solid content of 77%.
[0087]
Each of these coating solutions was applied to the support having the undercoat layer using a doctor blade, and then dried at 100 ° C. for 15 minutes to form a 240 μm phosphor layer. The phosphor sheets of Comparative Examples 1 and 2 were produced, respectively.
[0088]
(Production and sealing of moisture-proof protective film)
A moisture-proof protective film was produced by the method described below. A laminated protective film A containing an alumina-deposited polyethylene terephthalate resin layer represented by the following structure is covered on the phosphor layer side of each phosphor sheet, and the protective film on the support side of the phosphor sheet is cast polypropylene. Using a dry laminate film composed of (CPP) 30 μm, an aluminum film 9 μm, and polyethylene terephthalate (PET) 188 μm, the periphery was fused and sealed under reduced pressure using an impulse sealer. The thickness of the adhesive layer of the dry laminate film was 1.5 μm, and a two-component reaction type urethane-based adhesive was used.
[0089]
Laminated protective film A: VMPET12 /// VMPET12 /// PET /// CPP20
In the laminated protective film A, VMPET represents polyethylene terephthalate (commercially available: manufactured by Toyo Metallizing Co., Ltd.) deposited with alumina, PET represents polyethylene terephthalate, and CPP represents casting polypropylene. The above “///” indicates that the thickness of the two-component reaction type urethane-based adhesive layer in the dry lamination adhesive layer is 3.0 μm, and the number displayed after each resin film is Indicates the film thickness (μm).
[0090]
As described above, the radiation image conversion panels of Examples 1 to 3 and Comparative Examples 1 and 2 having the stimulable phosphor layer were obtained.
[0091]
Example 4
(Preparation of phosphor precursor and phosphor)
In order to synthesize a stimulable phosphor of europium-activated barium fluoroiodide, a BaI device with two holes was used. ₂ 2500 ml of aqueous solution (4 mol / L) and EuI ₃ 26.5 ml of an aqueous solution (0.2 mol / L) was charged. Further, 992 g of potassium iodide was added to the aqueous solution.
[0092]
The reaction mother liquor in the reactor was kept at 83 ° C. while stirring. 600 ml of an ammonium fluoride aqueous solution (10 mol / L) was injected into the reaction mother liquor using a roller pump to generate a precipitate. After completion of the injection, dry air was blown at a rate of 10 L / min for 20 minutes. The mass ratio of the solution before and after aeration was 0.94. The reaction vessel was sealed and stirred at that temperature for 90 minutes. After stirring for 90 minutes, the mixture was filtered and washed with 2000 ml of ethanol. After the alumina ultrafine powder was uniformly adhered to the phosphor crystals obtained by vacuum drying, firing and classification were performed in the same manner as in Examples 1 to 3 to obtain phosphor particles (Example 4). . The classification was performed under the same conditions as in Example 2.
[0093]
A radiation image conversion panel (Example 4) was obtained in the same manner as in Examples 1 to 3, using the stimulable phosphor particles obtained as described above.
[0094]
As described above, the radiation image conversion panels of Examples 1 to 4 and Comparative Examples 1 and 2 having the stimulable phosphor layer were obtained.
[0095]
(Characteristic evaluation of radiation image conversion panel)
The luminance of each radiation image conversion panel was measured according to the method described below.
[0096]
The luminance was measured by irradiating each radiation image conversion panel with X-rays having a tube voltage of 80 kVp from the back side of the phosphor sheet support, operating the panel with He-Ne laser light (633 nm), and exciting the panel. The photostimulated luminescence emitted from the body layer is received by a photodetector (a photomultiplier tube having a spectral sensitivity of S-5), the intensity thereof is measured, and this is defined as luminance. The relative value was displayed with the brightness of 3) being 1.00.
[0097]
Further, the image graininess was evaluated by the following method.
(Evaluation of image graininess)
Evaluation of image graininess was performed by uniformly irradiating the produced radiation image conversion panel with X-rays having a tube voltage of 80 kVp, and then scanning and exciting with semiconductor laser light (690 nm) from the side on which the phosphor layer A was provided. Then, the photostimulated light emitted from the phosphor layer is received by a photodetector (a photomultiplier tube having a spectral sensitivity of S-5), the image is read, and the image is output using a laser writing film printer. The image granularity (roughness) was visually evaluated according to the criteria described below. In addition, it was judged that the evaluation △ or less was not practically suitable for diagnosis.
[0098]
◎: Uniform solid image without roughness
：: An almost uniform solid image although slightly grainy
Δ: There is a granular feeling, and the uniform feeling is impaired.
×: Clearly visible and not uniform
[0099]
[Table 1]

[0100]
As described above, it is found that the one classified by the ordinary sieve causes a decrease in luminance. On the other hand, the method according to the classification method of the present invention has a small luminance reduction and good granularity. Among them, those classified with an appropriate classification dispersion pressure have less decrease in luminance and good granularity. On the other hand, the one used without classification has good luminance, but the obtained image has poor granularity, which causes a practical problem.
[0101]
【The invention's effect】
It is an object of the present invention to stably obtain a rare-earth activated alkaline earth metal fluoride halide stimulable phosphor capable of obtaining a radiation image conversion panel with high sensitivity, high image quality and uniform particle size.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of a curved airflow classifier.
[Explanation of symbols]
1 Curved airflow classifier
2,3 classification edge
4 Coanda block
5 Back block
7, 8, 9 exhaust passage
11, 12 Inlet flow path
14 Raw material sorting room
15 Classified raw materials
16 Raw material supply nozzle
18 Hopper
19 Compressed gas flow
21, 22, 23 pipeline

Claims (4)

A method for producing a rare earth-activated alkaline earth metal fluoride halide stimulable phosphor represented by the following general formula (1), characterized by passing through a classifying step using a curved airflow classifier, A method for producing a metal fluorinated halide stimulable phosphor.
General formula (1)
^{_{Ba 1-x M 2 x FBr}} y I 1-y: aM 1, bLn, cO
[Wherein, M ¹ is at least one alkali metal selected from the group consisting of Li, Na, K, Rb and Cs, and M ² is at least one alkali metal selected from the group consisting of Be, Mg, Sr and Ca. Is an alkaline earth metal,
Ln is at least one rare earth element selected from the group consisting of Ce, Pr, Sm, Eu, Gd, Tb, Tm, Dy, Ho, Nd, Er and Yb;
x, y, a, b and c are respectively 0 ≦ x ≦ 0.3, 0 ≦ y ≦ 0.3, 0 ≦ a ≦ 0.05, 0 <b ≦ 0.2, 0 <c ≦ 0. Represents a numerical value in the range of 1. ] 2. The method for producing a rare earth activated alkaline earth metal fluorohalide stimulable phosphor according to claim 1, wherein a classification dispersion pressure by a curved airflow classifier is 0.05 MPa or more and 0.5 MPa or less. A rare earth-activated alkaline earth metal fluorohalide stimulable phosphor obtained by the production method according to claim 1. A radiation image conversion panel comprising the rare earth activated alkaline earth metal fluoride halide stimulable phosphor according to claim 3.

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