JP2001064644A - Production of photostimulable phosphor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a photostimulable phosphor having sufficient photostimulable light-emitting amount, and easily erasable and excellent erasing characteristics. SOLUTION: This method for producing a photostimulable phosphor comprises a mixing step for mixing raw materials for a photostimulable phosphor to prepare a raw material mixture for the photostimulable phosphor, a baking step for baking the obtained mixture of the raw materials for the photostimulable phosphor to provide a baked product, and a cooling step for cooling the baked product. The baking space is exhausted from an atmospheric pressure to at most 100 Torr by a vacuum pump having a designed exhausting rate of >=1.0×Va (l/min) [Va is the volume (l) of the baking space] in the baking step, and/or the cooling space is exhausted from the atmospheric pressure to at most 100 Torr by the vacuum pump having >=1.0×Vb (l/min) [Vb is the volume (l) of the cooling space] in the cooling step.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a stimulable phosphor, and more particularly, to a method for producing a stimulable phosphor having good emission characteristics and erasing characteristics.

[0002]

2. Description of the Related Art Conventionally, a divalent europium-activated barium fluorinated luminescent material which emits light (instantaneous light emission) from the near ultraviolet region to the blue region when excited by radiation such as X-rays, γ-rays, electron beams or ultraviolet rays. Stimulable phosphor (BaFX: E
u ²⁺ , wherein X represents a halogen atom other than fluorine. )
Are known and used as a stimulable phosphor for a radiographic intensifying screen used for X-ray photography or the like. In recent years, when the stimulable phosphor is irradiated with radiation such as X-rays, γ-rays, and electron beams, or ultraviolet rays, and then excited with electromagnetic waves (excitation light) in a wavelength range from visible light to infrared light, a near-ultraviolet light is emitted. It has been found that the phosphor emits light in a wavelength region ranging from a blue region to a blue region (stimulated luminescence), and such a stimulable phosphor is used as a radiation image conversion technology in radiography to replace conventional radiography. It has attracted much attention as a useful stimulable phosphor.

[0003] This radiation image conversion technique uses a radiation image conversion panel (storage phosphor sheet) in which a stimulable phosphor layer containing a stimulable phosphor is provided on a support. After the radiation transmitted through or emitted from the subject is absorbed by the stimulable phosphor on the panel, the stimulable phosphor is irradiated with an electromagnetic wave (excitation light) selected from a wavelength range from visible light to infrared light. The radiant energy accumulated in the stimulable phosphor is emitted as fluorescence (stimulated luminescence) by exciting the phosphor in a time series, and an electric signal is obtained by photoelectrically reading the obtained electric signal. Is to be imaged.

By using this radiation image conversion panel, it is possible to form an image with a smaller amount of radiation than in the conventional radiographic method, and the obtained image can be processed by a computer. Furthermore, a radiographic image with a large amount of information can be obtained, and a defective image can be relieved.

Among the divalent europium-activated barium fluorohalide stimulable phosphors (BaFX: Eu ²⁺ ), the stimulable phosphor containing iodine as a part of the halogen atom X has a stimulable emission luminance. Is high, as the iodine content increases, the peak of the photostimulated excitation spectrum moves to the longer wavelength side, and depending on the iodine content, a laser having an emission wavelength in a red region such as a He-Ne laser or a red region or It has been proposed to use in combination with a semiconductor laser having an emission wavelength in the infrared region.

The radiation image conversion panel itself hardly deteriorates even when irradiated with radiation and electromagnetic waves, and can be used repeatedly for a long period of time. Usually, the reading operation of the radiation energy stored in the radiation image conversion panel is performed by scanning the radiation image conversion panel using laser light. However, in practice, it is not possible to release all the accumulated radiation energy only by scanning with a laser beam.
As described in Japanese Patent No. 11392, there has been proposed a method of erasing remaining radiation energy by irradiating the entire radiation image conversion panel with light in an excitation wavelength region of stimulated emission after reading.

[0007] However, a radiation image conversion panel using a stimulable phosphor containing iodine usually uses, for example, a white fluorescent lamp as in the case of erasing radiation energy stored in the stimulable phosphor. It is not possible to sufficiently remove the remaining radiation energy by simply irradiating with light for a short period of time from several seconds to several minutes using the method. Further, after the erasure, a part of the remaining radiation energy is recovered with time. The phenomenon (lift of an afterimage) is recognized, which has been a problem.

[0008] When the radiation image conversion panel is used repeatedly, such erasing characteristics and afterimage characteristics are factors that adversely affect the image quality of the formed image. On the other hand, if the erasing time is lengthened for the purpose of complete erasure, the time required from reading to erasing in the reading device becomes longer, which not only reduces the processing performance of the device itself, but also causes the erasing device in the machine to generate excessive heat. This is not preferable in terms of durability and power saving of the device.

On the other hand, the bivalent europium-activated barium fluorohalide stimulable phosphor is generally produced by the following method. First, the stimulable phosphor raw material is uniformly mixed in a dry state (dry method), or the stimulable phosphor material is uniformly mixed in a slurry state, and then dried (wet method). A mixture of depleted phosphor raw materials is prepared. Next, the obtained stimulable phosphor raw material mixture is usually fired at a temperature close to the melting point of the host crystal (BaFX or the like) for several hours in a neutral atmosphere or a weakly reducing atmosphere at substantially atmospheric pressure. (Firing step). If desired, the fired product once obtained may be refired. In the firing step, at the same time as the host crystal of the stimulable phosphor grows, the activator element (Eu or the like) diffuses into the host crystal, and further, an F ⁺ center serving as a source of the stimulating center is generated. Therefore, the firing step is an important step that affects the emission characteristics of the stimulable phosphor.
After the firing, the stimulable phosphor obtained through the cooling step is subjected to washing, classification, and the like, as necessary.

Further, Japanese Patent Application Laid-Open Nos. 7-233369 and 10-195431 disclose a tetrahedral rare earth activated alkaline earth metal fluorohalide-based stimulable fluorescent material in which the particle shape and the particle aspect ratio are controlled. Body (hereinafter,
It may be simply referred to as “tetrahedral phosphor”. ) Is disclosed. In the radiation image conversion panel provided with the stimulable phosphor layer containing the tetradecahedral phosphor, in the stimulable phosphor layer, the tetradecahedral phosphor itself is not isotropic and has no directivity. Since the arrangement of the light-emitting elements is small, the spread of the excitation light and the stimulated emission in the lateral direction in the layer is reduced, and the sharpness of the image formed on the radiation image conversion panel can be improved. The tetradecahedral phosphor obtained by the production method described in the above publication has relatively high luminescence properties and sharpness, but still has a sufficient stimulable luminescence amount as a stimulable phosphor used in a radiation conversion method. Since it has not been obtained and does not have excellent erasing characteristics that can be erased more easily, further improvement in performance has been desired.

On the other hand, the stimulable phosphor raw material mixture is fired,
In order to cool the fired product, after evacuation of the firing space or the cooling space from atmospheric pressure to a vacuum, a predetermined gas is purged, firing and cooling are performed. When the rate of evacuation of the firing space or the cooling space from the atmospheric pressure to a low pressure is slow, the characteristics of the obtained stimulable phosphor are adversely affected, and in order to further improve the performance, the air is rapidly exhausted. It turned out to be necessary. At present, there is currently a demand for a method for producing a stimulable phosphor which has a sufficient stimulable light emission amount and can sufficiently improve erasing characteristics.

[0012]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems and achieve the following objects. That is, an object of the present invention is to provide a method for producing a stimulable phosphor having a sufficient amount of stimulable light emission and excellent erasing characteristics that can be easily erased.

[0013]

Means for Solving the Problems As a result of intensive studies on a method for producing a stimulable phosphor, the present inventors have found that in at least one of the firing step and the cooling step, a specific vacuum pump is used for the firing space. The inventors have found that, by evacuating the cooling space from atmospheric pressure to a predetermined pressure, it is possible to improve the stimulating light emission amount and erasing characteristics of the stimulable phosphor, and have completed the present invention. The means for solving the above problems are as follows. That is, <1> a mixing step of mixing a stimulable phosphor raw material to prepare a stimulable phosphor raw material mixture, a firing step of firing the stimulable phosphor raw material mixture to obtain a fired product, A cooling step of cooling the fired material, wherein the designed exhaust speed is 1.0 × Va (liter / liter) with respect to the volume Va (liter) of the firing space in the firing step. Minute) or more, the baking space is evacuated from the atmospheric pressure to at least 100 torr by a vacuum pump, and / or in the cooling step, the designed pumping speed is 1.0 × Vb with respect to the volume Vb (liter) of the cooling space. A method for producing a stimulable phosphor, wherein the cooling space is evacuated from atmospheric pressure to at least 100 torr by a vacuum pump (liter / min) or more. <2> After at least one of the baking space in the baking step and the cooling space in the cooling step is evacuated to 10 torr or less, at least 0.1 torr of a gas containing 1 ppm or more of oxygen is introduced into the space, and the space is further impaired. <1> purging with active gas to approximately 1 atm
3. The method for producing a stimulable phosphor described in 1. above. <3> After at least one of the baking space in the baking step and the cooling space in the cooling step is evacuated to 10 torr or less, a gas containing 1 ppm or more of oxygen is supplied to the space at a flow rate of 1 to 10000 cc / min.
The method for producing a stimulable phosphor according to <1>, wherein the stimulable phosphor is introduced for 0 second, and the space is further purged to about 1 atm with an inert gas. <4> The method for producing a stimulable phosphor according to any one of <1> to <3>, wherein the stimulable phosphor is a tetradecahedral particle represented by the following basic composition formula (I). It is. ^{_{(Ba 1-a, M II}} a) FX · bM I · cM III · dA: xLn ··· (I) [ wherein, M ^II is, Sr, at least one selected from the group consisting of Ca and Mg Alkaline earth metal, M
^I represents a compound of at least one alkali metal selected from the group consisting of Li, Na, K, Rb and Cs, and M ^III represents Al, Ga, In, Tl, Sc, Y, C
It represents at least one compound of a trivalent metal selected from the group consisting of d and Lu (excluding Al ₂ O ₃ ). X
Represents at least one halogen selected from the group consisting of Cl, Br and I. Ln is Ce, Pr, S
m, Eu, Gd, Tb, Dy, Ho, Nd, Er, Tm
And at least one rare earth element selected from the group consisting of Yb and Yb. A is Al ₂ O ₃ , SiO ₂ and ZrO ₂
Represents at least one metal oxide selected from the group consisting of a, b, c, d and x are respectively 0 ≦ a ≦
0.3, 0 ≦ b ≦ 2, 0 ≦ c ≦ 2, 0 ≦ d ≦ 0.5, 0
<X ≦ 0.2. ]

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. -Method for producing stimulable phosphor-The method for producing a stimulable phosphor of the present invention includes at least a mixing step, a baking step, and a cooling step, and further includes other steps as necessary. .

[Mixing Step] The mixing step is a step of preparing a stimulable phosphor raw material mixture by mixing the stimulable phosphor raw materials. Examples of the stimulable phosphor materials include the following materials (1) to (5). (1) BaF ₂ , BaCl ₂ , BaBr ₂ , BaI ₂ , Ba
At least one barium halide selected from the group consisting of FBr, BaFI and BaFCl. (2) CaF ₂ , CaCl ₂ , CaBr ₂ , CaI ₂ , Sr
F ₂ , SrCl ₂ , SrBr ₂ , SrI ₂ , MgF ₂ , Mg
At least one alkaline earth metal halide selected from the group consisting of Cl ₂ , MgBr ₂ and MgI ₂ . (3) CsCl, CsBr, CsI, NaCl, NaB
r, NaI, KCl, KBr, KI, RbCl, RbB
r, RbI, RbF, CsF, NaF, KF, LiF,
At least one alkali metal halide selected from the group consisting of LiCl, LiBr and LiI. (4) At least one metal oxide selected from the group consisting of Al ₂ O ₃ , SiO ₂ and ZrO ₂ . (5) At least one compound selected from the group consisting of rare earth element compounds such as halides, oxides, nitrates and sulfates. If desired, further ammonium halide (NH
₄ X ', wherein X' represents F, Cl, Br or I. )
Etc. may be used as the flux.

The stimulable phosphor raw material mixture is prepared by arbitrarily selecting a desired raw material from each of the raw materials (1) to (5) and preparing a relative ratio corresponding to the basic composition formula (I). The stimulable phosphor raw material mixture is prepared by stoichiometrically weighing and mixing such that

The method for preparing the stimulable phosphor raw material mixture can be appropriately selected from known mixing methods. For example, a tetrahedral rare earth activated alkaline earth metal fluorohalide-based stimulable phosphor having a controlled particle shape and particle aspect ratio described in JP-A-7-233369 and JP-A-10-195431. Preparation method (i) using means capable of imparting a shear force when mixing the stimulable phosphor materials, addition of each stimulable phosphor material, and timing of mixing Can be prepared by a preparation method (ii) using a means capable of controlling various conditions such as

The mixing apparatus used for the mixing in the preparation methods (i) and (ii) can be appropriately selected from known mixing apparatuses.
Mold blenders, ball mills, rod mills and the like can be mentioned.

[Firing Step] The firing step is a step of firing the stimulable phosphor raw material mixture obtained in the mixing step to obtain a fired product. In the method for producing a stimulable phosphor of the present invention, in at least one of the baking step and the cooling step, at least one of a baking space and a cooling space is formed at least from atmospheric pressure using a specific vacuum pump defined below. It is characterized by exhausting up to 100 torr. In the present invention, it is preferable to exhaust from atmospheric pressure using a specific vacuum pump in both the baking step and the cooling step.

The above-mentioned specific vacuum pump includes a vacuum pump operated from atmospheric pressure in a firing step (hereinafter, referred to as a "sintering vacuum pump") and a vacuum pump operated from atmospheric pressure in a cooling step (hereinafter, "cooling"). Vacuum pump "). These may be the same or different types. The firing vacuum pump has a designed pumping speed of 1.0 × Va (liter / minute) or more with respect to the volume Va (liter) of the firing space. On the other hand, the cooling vacuum pump has a designed pumping speed of 1.0 × Vb (liter / minute) or more with respect to the volume Vb (liter) of the cooling space. Here, the vacuum pump for firing will be described, and the vacuum pump for cooling will be described later.

The vacuum pump for firing has a designed pumping speed of 1.0 × Va with respect to the volume Va (liter) of the firing space.
(L / min) or more, but more preferably a design pumping speed of x Va (l / min) or more. If the designed pumping speed is less than 1.0 × Va (liter / minute), the phosphor raw material is oxidized before being pumped to a target pressure, and the PSL emission amount is reduced. here,
The designed pumping speed is a pumping speed peculiar to the pump, and is different from the observed pumping speed in consideration of the conductance of the space to be pumped. Further, the volume of the firing space specifically refers to the volume of a furnace for firing the stimulable phosphor raw material mixture, and usually, the volume Va of the firing space is 0.1 to 10000 (liter).
It is. The baking vacuum pump is not particularly limited as long as the designed pumping speed satisfies the above requirements,
Either can be used. Specifically, for example,
Dry pumps, rotary oil pumps, hook / claw type pumps, and the like having the above designed pumping speed are exemplified. Even if the mechanical booster pump is operated from 100 torr or more, a case where the pump is evacuated to several torr or less using a rotary pump or a dry pump is also included.

The baking space is evacuated from atmospheric pressure to at least 100 torr using the vacuum pump for baking, more preferably to 10 torr. Using the vacuum pump for firing, at least 1
If the pressure is not exhausted to 00 torr, it becomes difficult to operate a pump necessary for exhausting to a lower pressure stably. Further, the firing space can be evacuated from atmospheric pressure to vacuum using the firing vacuum pump, but usually the firing space is exhausted from atmospheric pressure to the predetermined low pressure using the firing vacuum pump. After that, the gas is evacuated from the low pressure to a vacuum using a vacuum pump having a design pumping speed larger than that of the firing vacuum pump. Examples of the vacuum pump used for evacuation from the low pressure to a vacuum include a mechanical booster pump, a turbo-molecular pump, a cryopump, and the like.

After the firing space is evacuated from the atmospheric pressure to a vacuum as described above, a gas according to the purpose is purged, and the atmosphere in the furnace is changed to a neutral atmosphere, a weak reducing atmosphere, or an oxidizing atmosphere. Set to any one and bake. After performing the firing for a certain period of time, using the above-described vacuum pump, exhaust the gas again to vacuum, purge the gas according to the purpose, change the atmosphere in the furnace to an atmosphere different from the first, and further fire. You can also.

Examples of the neutral atmosphere include a nitrogen gas atmosphere and an argon gas atmosphere. Examples of the weakly reducing atmosphere include a nitrogen gas atmosphere containing a small amount of hydrogen gas,
For example, a carbon dioxide atmosphere containing carbon monoxide may be used. When a trivalent europium compound is contained as a rare earth element of the stimulable phosphor raw material, trivalent europium is reduced to divalent europium in the firing step.

As the oxidizing atmosphere, it is preferable to use a slightly oxidizing atmosphere gas. As the slightly oxidizing atmosphere gas, 100 to 100000 ppm, preferably, in an inert gas (neutral gas) per unit volume,
Examples of the atmosphere gas include a weakly oxidizing atmosphere gas containing 150 to 50,000 ppm of oxygen, such as He, Ne, Ar, and the like.
A weakly oxidizing atmosphere gas containing the above concentration of oxygen in an inert gas such as N ₂ may be used.

The amount of oxygen introduced is preferably 0.1 to 200 ml, more preferably 0.2 to 100 ml, at room temperature, per 1 liter of the firing partial volume of the furnace. When the oxygen introduction amount is less than 0.1 ml, the effect of improving the erasing characteristics and the residual characteristics of the stimulable phosphor may not be sufficiently obtained. May drop.

In the present invention, after the baking space is evacuated from atmospheric pressure to 10 torr or less, the baking space contains at least 0.1 t of a gas containing 1 ppm or more of oxygen.
orr, and it is preferable to further purge the firing space to about 1 atm with an inert gas. 1pp of oxygen
It is preferable to introduce at least 0.1 torr of gas containing m or more from the viewpoint of improving erasing characteristics. Preferably,
In the firing space, a gas containing 1 ppm or more of oxygen
Introduce torr. Here, the above-mentioned substantially 1 atm means a pressure within a range of ± 10% with respect to 1 atm.

Further, in the present invention, after the baking space is evacuated from atmospheric pressure to 10 torr or less, a gas containing 1 ppm or more of oxygen is contained in the baking space in a range of 1 to 10000.
It is preferable that the pressure is introduced at a flow rate of cc / min for 1 to 300 seconds, and that the firing space is further purged with an inert gas to approximately 1 atm. More preferably, the flow rate is 100 to 1000
0 cc / min, and the gas introduction time is 1 to 60 seconds. If the flow rate is less than 1 cc / min, an error in the introduced amount due to a leak in the exhaust system may increase,
If it is higher than 10,000 cc / min, the flow velocity in the furnace is large, and powder may be scattered. If the introduction time is shorter than 1 second, it may be difficult to control the valve, and 3
If the time is longer than 00 seconds, the resulting phosphor may not be uniformly oxidized.

In order to fire the stimulable phosphor raw material mixture, the stimulable phosphor raw material mixture is charged into a firing vessel,
Bake in the furnace core. The material and shape of the firing container are not particularly limited, but the material is preferably quartz glass, and the shape is preferably a boat shape. The boat type here is a shape having an open upper surface, and the shape of the bottom surface may be any of a circle, an ellipse, a rectangle, and the like.

As the furnace used for firing, a furnace having a firing partial volume of 2 to 500 liters per 1 kg of the stimulable phosphor raw material mixture is required, and especially a furnace having a firing partial volume of 5 to 50 liters. Is preferred. If the calcined partial volume is less than 2 liters per 1 kg of the stimulable phosphor raw material mixture, the stimulable phosphor is densely packed in a narrow space, so that uniform calcination can be performed as a whole. When the amount exceeds 500 liters, the halogen atmosphere to be volatilized is too low, and the stimulable light emission amount and erasing characteristics of the obtained stimulable phosphor may be deteriorated.

The calcination is performed at a constant temperature, and the calcination temperature at this time is preferably 400 to 1000 ° C., more preferably 600 to 900 ° C. When the calcination temperature is lower than 400 ° C., diffusion of the activator element in the host crystal and generation of F ^{+ serving} as a source of stimulating center may be insufficient. May melt.

The firing time varies depending on the filling amount of the stimulable phosphor raw material mixture, the firing temperature, the temperature of taking out from the furnace, and the like, but is generally preferably 0.5 to 10 hours.
1-4 hours are more preferred. If the calcination time is less than 0.5 hour, the diffusion of the activator element in the host crystal and the generation of F ^{+ serving} as a source of the photostimulated center may be insufficient.
Even if the sintering is performed for more than 0 hours, the stimulable phosphor will not change much further in properties, and may lower the productivity.

[Cooling Step] The cooling step is a step of cooling the fired product obtained in the firing step. The cooling step is not particularly limited, and can be appropriately selected from known cooling methods. For example, the cooling step can be performed by letting cool, quenching, or the like.

In the cooling step, the atmosphere in the firing step is removed while the fired product after firing is shielded from the outside air.
Performing cooling by substituting an atmosphere different from the atmosphere in the vacuum state or the firing step, or removing the atmosphere in the firing step, performing first cooling by substituting a first atmosphere different from the atmosphere in the firing step, Further, it is preferable to perform a cooling method such as removing the first atmosphere, replacing the first atmosphere with the second atmosphere, and performing the second cooling. Further, in the present invention, using a manufacturing apparatus in which a firing space and a cooling space are separately provided, the cooling space is set to an intended atmosphere, and the fired material is moved from the firing space to the cooling space to perform cooling. It is preferred to do so.

As described above, in the method for producing a stimulable phosphor of the present invention, in at least one of the baking step and the cooling step, a baking vacuum pump is used in the baking step, and a cooling vacuum pump is used in the cooling step. Preferably, at least one of the firing space and the cooling space is evacuated from atmospheric pressure to at least 100 torr.

The cooling vacuum pump has a design pumping speed of 1.0 × Vb with respect to the cooling space volume Vb (liter).
(L / min) or more, but more preferably a design pumping speed of × Vb (l / min) or more. If the design pumping speed is less than 1.0 × Vb (liter / minute), it takes time to change the atmosphere during cooling, and PSL
Light emission is reduced. Specifically, the volume of the cooling space refers to the volume of a cooling chamber that cools a fired product after firing, and usually, the volume Vb of the cooling space is 0.1 to 10,000.
(Liter). As the cooling vacuum pump,
There is no particular limitation as long as the designed pumping speed satisfies the above requirements, and any of them can be used. Specifically, for example, a dry pump, a rotary oil pump, a hook / claw pump, or the like having the above-described designed pumping speed can be used. Even if the mechanical booster pump is operated from 100 torr or more, a case where the pump is evacuated to several torr or less using a rotary pump or a dry pump is also included.

The cooling vacuum pump is used to evacuate the cooling space from atmospheric pressure to at least 100 torr, more preferably to 10 torr. Using the cooling vacuum pump, at least one
If the pressure is not exhausted to 00 torr, it becomes difficult to operate a pump necessary for exhausting to a lower pressure stably. Although the cooling space can be evacuated from atmospheric pressure to vacuum using the cooling vacuum pump, the cooling space is usually evacuated from atmospheric pressure to the predetermined low pressure using the cooling vacuum pump. After that, the gas is evacuated from the low pressure to a vacuum using a vacuum pump having a design pumping speed higher than that of the cooling vacuum pump. Examples of the vacuum pump used for evacuation from the low pressure to a vacuum include a mechanical booster pump, a turbo-molecular pump, a cryopump, and the like.

After the cooling space is evacuated from the atmospheric pressure to a vacuum in this manner, the cooling may be performed in a vacuum state. Alternatively, the cooling may be performed by setting the atmosphere to a weak reducing atmosphere or an oxidizing atmosphere. After performing the cooling for a predetermined time, using the above vacuum pump, evacuate again to vacuum,
Purging the gas according to the purpose, the atmosphere in the cooling room,
The atmosphere can be changed to a different one from the first, and further cooled.

In the present invention, as in the case of the baking step, after the cooling space is evacuated from the atmospheric pressure to 10 torr or less, at least 0.1 torr of a gas containing 1 ppm or more of oxygen is introduced into the cooling space. Further, it is preferable that the cooling space is purged with an inert gas to approximately 1 atm.

Further, in the present invention, similarly to the case of the firing step, the firing space is set to 10 torr from atmospheric pressure.
After evacuation to below, 1 ppm of oxygen was added to the cooling space.
A gas containing the above gas at a flow rate of 1 to 10000 cc / min.
It is preferable that the cooling space is purged with an inert gas to about 1 atm. More preferably, the flow rate is 10 to 10000 cc / min, and the gas introduction time is 1 to 60 seconds.

The cooling is performed after the firing step is completed.
Although it may be performed immediately, from the viewpoint of producing a stimulable phosphor having a sufficient stimulating light emission amount and erasing characteristics, the firing step is completed, and a desired constant temperature is set as a first cooling start point, and the second cooling step is performed. It is also preferable to shift to the cooling step from the point of time when one cooling start point is reached. The first cooling start point indicates a furnace temperature or a fired material surface temperature.

[Other Steps] As the other steps, various general steps such as a washing step, a drying step, and a sieving step can be performed after the cooling step.

Further, between the firing step and the cooling step,
While maintaining the temperature at a constant temperature, the atmosphere in the firing step may be removed and replaced with an atmosphere different from the atmosphere to perform slow cooling. The cooling may be performed immediately before the completion of firing at a constant temperature, but is preferably performed after a predetermined time has passed while removing and replacing the atmosphere while maintaining the temperature at a constant temperature. As the predetermined time, 0 to
240 minutes is preferable, and 30 to 180 minutes is more preferable.
If the predetermined time exceeds 180 minutes, the emission characteristics of the obtained stimulable phosphor may be deteriorated.

In the above-mentioned slow cooling, the temperature is lowered by controlling a gentle temperature gradient from the slow cooling start temperature to a predetermined temperature. In this case, the temperature decreasing rate is preferably 0.2 to 5 ° C./min, more preferably 0.5 to 3 ° C./min. If the rate of temperature decrease is less than 0.2 ° C./min, the light emission characteristics may be degraded, and if it exceeds 5 ° C./min, the erasing characteristics may not be sufficiently improved.

The gradual cooling is performed 50 to 3 times below the gradual cooling start temperature.
It is preferably performed until the temperature becomes lower by 00 ° C.
It is more preferable to perform the process until the temperature becomes lower by 250 ° C. If the temperature difference between the start and end of the slow cooling is less than 50 ° C., the erasing characteristics may not be sufficiently improved.
If the temperature exceeds 00 ° C., the light emission characteristics may be deteriorated.

Further, as the slow cooling time for lowering the temperature from the slow cooling start temperature to the predetermined temperature after the atmosphere replacement, it is preferably 30 to 180 minutes, more preferably 60 to 150 minutes. If the slow cooling time is less than 30 minutes, the erasing characteristics may not be sufficiently improved, and if it exceeds 180 minutes, the light emitting characteristics may deteriorate.

-Stimulable phosphor- According to the production method of the present invention, a stimulable phosphor having a sufficient amount of stimulable light emission and excellent erasing characteristics is
It can be manufactured stably. In particular, the production method of the present invention is suitably used as a method for producing a stimulable phosphor represented by the following basic composition formula (I). ^{_{(Ba 1-a, M II}} a) FX · bM I · cM III · dA: in xLn ··· (I) formula, M ^II is at least one alkali Sr, selected from the group consisting of Ca and Mg Represents earth metal, M ^I
Represents a compound of at least one alkali metal selected from the group consisting of Li, Na, K, Rb and Cs;
M ^III represents a compound of at least one trivalent metal selected from the group consisting of Al, Ga, In, Tl, Sc, Y, Cd and Lu (excluding Al ₂ O ₃ ). X is
Represents at least one halogen selected from the group consisting of Cl, Br and I. Ln is Ce, Pr, Sm, E
u, Gd, Tb, Dy, Ho, Nd, Er, Tm and Y
represents at least one rare earth element selected from the group consisting of b. A represents at least one metal oxide selected from the group consisting of Al ₂ O ₃ , SiO ₂ and ZrO ₂ . a, b, c, d and x are respectively 0 ≦ a ≦ 0.
3, 0 ≦ b ≦ 2, 0 ≦ c ≦ 2, 0 ≦ d ≦ 0.5, 0 <x
≤ 0.2.

In the production of the stimulable phosphor represented by the basic composition formula (I), the following various additives are added for the purpose of further improving the stimulable luminescence amount, the erasing property, the remaining property and the like. It can also be added. For example, Japanese Unexamined Patent Publication No.
B described in JP-A-57-23675, As described in JP-A-57-23675, a tetrafluoroboric acid compound described in JP-A-59-27980, hexafluoro described in JP-A-59-47289 Compound, JP-A-59-564
No. 80, V, Cr, Mn, Fe, Co, Ni
Or a transition metal such as BeX " ₂ described in JP-A-59-75200 (where X" is F, Cl, Br and I
And represents at least one halogen atom selected from the group consisting of When adding the additive component,
The additive component is added and mixed when the stimulable phosphor raw material is weighed and mixed or before firing.

-Production Apparatus- A production apparatus used in the method for producing a stimulable phosphor of the present invention will be described. The manufacturing apparatus is specifically an apparatus having a firing furnace for firing the stimulable phosphor raw material mixture, inside the firing furnace, a furnace tube, and a heat source is arranged outside the furnace tube, Further, a firing vessel capable of containing the stimulable phosphor raw material mixture is provided so as to be able to be taken in and out of the furnace tube.

FIG. 1 is a schematic sectional view showing an example of the manufacturing apparatus. The stimulable phosphor manufacturing apparatus shown in FIG. 1 is roughly divided into a sintering portion A (that is, a sintering space) and a cooling portion B.
(That is, a cooling space). In FIG.
Reference numeral 10 denotes a firing furnace, in which a furnace tube 12 is disposed so as to penetrate in the left-right direction in the drawing. A heat source 14 is arranged inside the furnace 10 and outside the furnace tube 12, and the inside of the furnace 10 is heated by the heat source 14, and the furnace tube 1 is heated.
The stimulable phosphor raw material mixture 18 contained in the firing container 16 put into the furnace 2 can be fired.

A gas introduction / exhaust pipe 20 communicates with the furnace tube 12 via a valve 22 so that gas can be introduced and exhausted into the inside of the furnace tube 12. The inside of the furnace tube 12 is opened by a firing vacuum pump or a gas cylinder (not shown). The atmosphere can be adjusted appropriately. The opening at the left end in the drawing of the furnace tube 12 is closed by a sample inlet cover 24 so that the firing container 16 can be charged while ensuring the inside tightness of the furnace tube 12 during firing. Further, a sample pushing rod 26 is inserted through the sample charging port 24 so that the fired container 16 can be slid rightward in the drawing without opening the sample charging port 24.

The firing vessel 16 is composed of a heat-resistant vessel such as a quartz boat, an alumina crucible, a quartz crucible, and a silicon carbide vessel. Further, as the heat source 14, any conventionally known heat source can be used, and for example, a known electric heater can be adopted.

The opening at the right end in the drawing of the furnace tube 12 shields the sintering portion A and the cooling portion B so that the furnace tube 12 at the time of sintering is opened.
In addition, the partitioning door 30 closes the firing chamber 16 so that the firing chamber 16 can be discharged to the cooling portion B after firing while ensuring the internal sealing of the cooling chamber 28 during cooling. The partition door 30 is slid in the direction of the arrow y to enable shielding and opening between the firing part A and the cooling part B.

In firing the stimulable phosphor raw material mixture 18, the stimulable phosphor raw material mixture 18 is first placed in a firing vessel 16, and is charged into the furnace core tube 12 with the sample charging port 24 opened. . The sample charging port 24 is closed (of course, the partition door 30 is also closed), and the sample extruding rod 26 is pushed out in the direction of the arrow x so that the stimulable phosphor raw material mixture 18 is stored in the firing vessel. Slide 16 and place it in place.
Then, gas is appropriately exhausted and / or introduced through the gas introduction / exhaust pipe 20, and heat is applied from the heat source 14 while the atmosphere inside the furnace core tube 12 is kept in a predetermined state, and firing is performed. The firing conditions (atmosphere, temperature, time, firing temperature, number of atmosphere steps, and the like) at this time may be appropriately set depending on the purpose.

After firing, the partitioning door 30 is opened, and the firing container 16 containing the stimulable phosphor raw material mixture 18 fired by the sample push rod 26 is slid in the direction of the arrow z, and is moved to the cooling portion B. To move.

The cooling part B includes a cooling table 32 in the cooling chamber 28.
Is arranged in the cooling chamber 28 so that gas can be introduced and exhausted into the cooling chamber 28.
4 is communicated via a valve 36, and the atmosphere inside the cooling chamber 28 can be appropriately adjusted by a cooling vacuum pump or a gas cylinder (not shown). An opening is provided at the right end in the drawing of the cooling chamber 28, and is closed by a sample discharge port lid 38 so that the firing chamber 16 can be discharged while ensuring the airtightness of the cooling chamber 28 during cooling.

As described above, the firing container 16 containing the stimulable phosphor fired in the firing portion A (the fired material of the stimulable phosphor raw material mixture 18) is slid in the direction of the arrow z, and It is mounted on a cooling table 32 in the cooling part B, supported by the illustrated guide. Thereafter, the partition door 30 that has been in the open state is closed again (of course, the sample outlet cover 38 is also closed). Then, the cooling table 32 is cooled by a cooling means such as a water cooling means (not shown) while appropriately exhausting and / or introducing gas through the cooling chamber gas introduction / exhaust pipe 34 and keeping the atmosphere inside the cooling chamber 28 in a predetermined state. The stimulable phosphor raw material mixture 18 contained in the firing container 16 is also cooled. Cooling conditions at this time (atmosphere, temperature, time, cooling temperature, number of atmosphere stages, etc.)
May be appropriately set according to the purpose. In addition, cooling may be naturally performed by leaving the apparatus without a cooling means such as a water cooling means.

The sintering vessel 16 containing the stimulable phosphor (sintered stimulable phosphor raw material mixture 18) which has been cooled down is taken out with the sample outlet cover 38 opened. As described above, the manufacturing apparatus used in the method for manufacturing the stimulable phosphor of the present invention has been described using the apparatus in the form shown in FIG. 1; however, the present invention is not limited to this. The structure which also serves as a cooling part may be sufficient. In this case, the volume Va (liter) of the baking space is the same as the volume Vb (liter) of the cooling space.

[0059]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited to these examples. (Example 1) [Mixing step] a) BaBr ₂ aqueous solution (2.5 mol / L) 120
0 ml is placed in a 4000 ml reactor, into which E
uBr ₃ aqueous solution (0.2 mol / L) 37.5 m
1, KBr 30.9 g, CaBr ₂ .2H ₂ O 3.54
g and 1762.5 ml of water were added. The reaction mother liquor (BaBr ₂ concentration: 1.00 mol / l) in this reactor was kept at 60 ° C., and the screw-type stirring blade having a diameter of 60 mm was rotated at 500 rpm to stir the reaction mother liquor. 300 ml of an NH ₄ F aqueous solution (5 mol / l) was injected into the above reaction mother liquor kept under stirring at a rate of 5.0 ml / min using a roller pump to produce a precipitate. After completion of the injection, the precipitate was ripened by continuing the warming and stirring for 2 hours. Next, the precipitate was separated by filtration and washed with 2 liters of methanol. Next, the washed precipitate is taken out and vacuum-dried at 120 ° C. for 4 hours to prepare a europium-activated barium fluorobromide-based stimulable phosphor precursor crystal (B).
aFBr crystal) was obtained in an amount of about 350 g. This operation was repeated 40 times to obtain a total of about 14000 g of BaFBr crystals.
Observation of the obtained crystal with a scanning electron microscope revealed that most of the crystal was a tetrahedral crystal. Next, when this crystal was measured with a light diffraction type particle size distribution measuring device (LA-500, manufactured by Horiba, Ltd.), it was confirmed that the average crystal size was 5.0 μm.

B) 2850 ml of a BaI ₂ aqueous solution (4.0 mol / l) were placed in a 4000 ml reactor, and a EuI ₃ aqueous solution (0.2 mol / l) 9
0 ml and 60 ml of water were added. The reaction mother liquor (BaI ₂ concentration: 3.80 mol / l) in this reactor was
C., and a screw-type stirring blade having a diameter of 60 mm
Spin at 00 rpm and stir the reaction mother liquor. Using a roller pump, 720 ml of an aqueous HF solution (5 mol / l) was poured into the above-mentioned reaction mother liquor kept warm under stirring.
Injection was performed at a flow rate of 2 ml / min to produce a precipitate.
After completion of the injection, the keeping and stirring were continued for 2 hours to ripen the precipitate. The precipitate is then filtered off and isopropanol 2
Washed with liter. Next, the washed precipitate was taken out and vacuum dried at 120 ° C. for 4 hours to obtain about 1000 g of a europium-activated barium fluoroiodide stimulable phosphor precursor crystal (BaFI crystal). Repeat this operation three times,
A total of about 3000 g of BaFI crystals were obtained. Next, when the crystals were measured by a light diffraction type particle size distribution analyzer, it was confirmed that the average crystal size was 6.5 μm.

C) 12480 g of the above BaFBr crystal
And 2640g up the BaFI crystal, this BaF _{2 2}
48 g, and 76 g (0.5% by weight) of ultra-fine alumina (Al ₂ O ₃ ) powder to prevent sintering during firing were added, and a total of 15444 g of the stimulable phosphor raw material mixture was added to a double cone. The mixture was sufficiently stirred and mixed by a mixer to uniformly adhere ultrafine alumina powder to the crystal surface.

[Firing Step] 15444 g of the stimulable phosphor raw material mixture was filled in three quartz boats (quartz glass boats having a capacity of 6300 cc), which were firing vessels. Using an electric furnace (firing space: Va = 120 liter tubular furnace), put the quartz boat into a firing space set at 850 ° C., and use a dry pump (V090S, manufactured by ANELVA, designed pumping speed) as the vacuum pump for firing. = 1
500 liters / min) and operated from atmospheric pressure
It exhausted to 100 torr over seconds. Subsequently, as a vacuum pump operated from a low pressure, a mechanical booster pump (B601P, manufactured by ANELVA, designed pumping speed =
8300 l / min) and the firing space was evacuated to 1 torr or less over 10 minutes. Thereafter, the firing space was purged to 1 atm with nitrogen gas and heated for 2 hours.

Next, the dry pump (V090S, A
(Nelva, design pumping speed = 1500 l / min)
Was operated, and the firing space was evacuated to 100 torr over 90 seconds. Subsequently, the mechanical booster pump (B601P, manufactured by ANELVA, designed pumping speed = 830)
(0 liter / min) and the firing space was evacuated to 1 torr or less over 10 minutes. Thereafter, oxygen gas was introduced into the firing space at 10 torr, and further purged with nitrogen gas to 1 atm, followed by heating for 1 hour. Next, the dry pump (V090S, manufactured by ANELVA, designed pumping speed =
(1500 liter / min) and the firing space was evacuated to 100 torr over 30 seconds. Subsequently, the mechanical booster pump (B601P, ANELVA)
The pumping space was evacuated to 1 torr or less over 10 minutes. Thereafter, the firing space was purged with nitrogen gas to 1 atm.

[Cooling Step] The cooling space was set to the following atmosphere before moving the obtained fired product. That is,
The cooling space is a cooling chamber of Vb = 1000 liters,
The cooling space is a dry pump (V090S, manufactured by Anelva, designed pumping speed = 1) as the cooling vacuum pump.
500 liters / min) and operated from atmospheric pressure
It exhausted to 100 torr over seconds. Subsequently, as a vacuum pump operated from a low pressure, a mechanical booster pump (B601P, manufactured by ANELVA, designed pumping speed =
8300 liters / minute) and the cooling space was evacuated to 1 torr or less over 10 minutes. Thereafter, oxygen gas was introduced into the cooling space at 1 torr, and further purged with nitrogen gas to 1 atm. Then, the obtained fired product was moved from the firing space to the cooling space. After being left in the cooling space for 5 minutes, the dry pump (V090S, manufactured by ANELVA,
(Design pumping speed = 1500 l / min)
Evacuated for 0 minutes. Subsequently, 100 nitrogen gas was introduced into the cooling space.
The flow was performed at a flow rate of 0 cc / min for 30 minutes. Thereafter, the fired product was taken out to the atmosphere.

The above calcined product (1000 g) was treated with methanol (1.
After dispersing in 5 liters, roll mill (rotation speed:
(50 rpm) for 15 hours. Next, the slurry of the fired product was passed through a vibration sieve (nylon mesh; # 508) to perform wet classification. Next, the slurry was allowed to stand for 10 hours, and then the supernatant was removed to obtain a slurry from which excess alumina was removed.

The fired product slurry is filtered under reduced pressure to perform solid-liquid separation, washed with methanol, and heated at 150 ° C. for 10 minutes.
Vacuum dried for hours. Next, the fired product was again passed through a vibration sieve (nylon mesh; # 460) to perform dry classification. Thus, europium-activated barium fluorobromide-based stimulable phosphor particles were obtained. Observation of the resulting stimulable phosphor particles with a scanning electron microscope revealed that most of the particles had a tetrahedral shape as in the case of the raw material crystals. The average crystal size of the crystals measured by an optical diffraction type particle size distribution analyzer was 7.0 μm.

Example 2 In Example 1, a dry pump (V090S, AN) was used as the firing vacuum pump used in the firing step and the cooling vacuum pump used in the cooling step.
Instead of ELVA, designed pumping speed = 1500 liter / min, dry pump (V040S, ANELVA)
The stimulable phosphor was produced in the same manner as in Example 1 except that the pump speed was 700 l / min.

(Example 3) In the firing step of Example 1, instead of introducing oxygen gas into the firing space at 10 torr, oxygen gas was introduced into the firing space at a flow rate of 2000 cc / min for 40 seconds. In the cooling step, a stimulable phosphor was prepared in the same manner as in Example 1 except that oxygen gas was introduced into the cooling space at a flow rate of 2000 cc / min for 35 seconds instead of introducing oxygen gas into the cooling space at 1 torr. Manufactured.

(Comparative Example 1) In Example 1, a dry pump (V090S, AN) was used as the firing vacuum pump used in the firing step and the cooling vacuum pump used in the cooling step.
Instead of ELVA, design pumping speed = 1500 liter / min), an oil rotary pump (RPG-100, ANELV)
A, designed pumping speed = 100 liter / min), using a vacuum pump operated from the low pressure used in the firing step and a vacuum pump operated from the low pressure used in the cooling step,
Mechanical booster pump (B601P, ANELV)
A, instead of the design pumping speed = 8300 l / min), a mechanical booster pump (B101P, ANE)
A stimulable phosphor was produced in the same manner as in Example 1 except that LVA (design pumping speed = 1500 liter / min) was used.

The stimulable phosphors obtained in Examples 1 to 3 and Comparative Example 1 were evaluated as follows. <Measurement of Stimulated Luminescence Amount> Ten seconds after irradiating 200 mR of X-ray with a tube voltage of 80 kVp to the obtained predetermined amount of stimulable phosphor, 4.6 J / m2 of semiconductor laser light (wavelength 660 nm) was applied.
^2. Irradiation excites the stimulable phosphor, and stimulates the stimulable light emitted from the stimulable phosphor to an optical filter (B-410).
And the amount of stimulated emission was measured by receiving light through a photomultiplier tube. Table 1 below shows relative values when the stimulable luminescence amount of the stimulable phosphor obtained in Example 1 was set to 100. This value indicates that the larger the value, the larger the amount of stimulated emission.

<Evaluation of Erasing Characteristics> The stimulating luminescence amount measured above was defined as the initial stimulating luminescence amount, and the light of a white fluorescent lamp was applied to a stimulable phosphor to be measured by a sharp cut optical filter (SC). -46) to perform an erasing operation by irradiating 500,000 Lux · sec. With respect to the stimulable phosphor subjected to the erasing operation, the amount of stimulable luminescence was measured again in the same manner as described above except that X-ray irradiation was not performed, and the measured amount was used as the stimulable luminescence after erasure. The erasing characteristic is represented by an erasing value calculated from the following, and the smaller the value, the better the erasing characteristic. The calculation results are shown in Table 1 below. Erasure value = (stimulated luminescence after erasure / initial stimulus luminescence)

[0072]

[Table 1]

From the results shown in Table 1, in both the firing step and the cooling step, in Examples 1 and 3 using the specific vacuum pump specified in the present invention, a sufficient photostimulated luminescence amount was obtained. It can be seen that a stimulable phosphor having excellent erasing characteristics can be manufactured. Also, in Example 2 using the specific vacuum pump specified by the present invention only in the firing step, the amount of stimulated emission and the erasing characteristics are slightly inferior to those in Examples 1 and 3, but the firing step In both the cooling step and the cooling step, it is found that the stimulated emission amount and the erasing characteristics are superior to Comparative Example 1 in which the specific vacuum pump specified in the present invention is not used.

[0074]

According to the present invention, it is possible to provide a method for producing a stimulable phosphor having a sufficient amount of stimulable light emission and excellent erasing characteristics which can be easily erased.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing one example of a production apparatus used in a method for producing a stimulable phosphor of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Firing furnace 12 Furnace tube 14 Heat source 16 Firing container 18 Stimulable phosphor raw material mixture 20 Gas introduction / exhaust tube 22 Valve 24 Sample introduction lid 26 Bar 28 Cooling room 30 Door 32 Cooling stand 34 Cooling room gas introduction / exhaust tube 36 Valve 38 Sample outlet lid

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 4H001 CA04 XA03 XA08 XA09 XA11 XA12 XA13 XA14 XA17 XA19 XA20 XA21 XA31 XA35 XA37 XA38 XA39 XA40 XA48 XA49 XA53 XA55 XA56 XA71 XA81 YA58 YA66 YA66 YA66

Claims (4)

[Claims] A mixing step of mixing a stimulable phosphor raw material to prepare a stimulable phosphor raw material mixture; a firing step of firing the stimulable phosphor raw material mixture to obtain a fired product; And a cooling step of cooling the fired material, wherein in the firing step, the designed pumping speed is 1.0 × Va (liter / liter) with respect to the volume Va (liter) of the firing space.
Minute) or more, the baking space is evacuated from the atmospheric pressure to at least 100 torr by a vacuum pump, and / or in the cooling step, the designed pumping speed is 1.0 × Vb with respect to the volume Vb (liter) of the cooling space. A method for producing a stimulable phosphor, wherein the cooling space is evacuated from atmospheric pressure to at least 100 torr by a vacuum pump (liter / minute) or more. 2. A method according to claim 1, wherein at least one of the firing space in the firing step and the cooling space in the cooling step is 10 ton.
After exhausting to rr or less, oxygen was added to the space at 1 ppm.
2. The method for producing a stimulable phosphor according to claim 1, wherein at least 0.1 torr of the above-mentioned gas is introduced, and the space is further purged to about 1 atm with an inert gas. 3. At least one of the firing space in the firing step and the cooling space in the cooling step is 10 ton.
After exhausting to rr or less, oxygen was added to the space at 1 ppm.
A gas containing the above gas at a flow rate of 1 to 10000 cc / min.
2. The method for producing a stimulable phosphor according to claim 1, wherein the space is introduced for about 300 seconds, and the space is further purged to about 1 atm with an inert gas. 4. The stimulable phosphor is a tetrahedral particle represented by the following basic composition formula (I).
The method for producing a stimulable phosphor according to any one of the above. ^{_{(Ba 1-a, M II}} a) FX · bM I · cM III · dA: xLn ··· (I) [ wherein, M ^II is, Sr, at least one selected from the group consisting of Ca and Mg Alkaline earth metal, M
^I represents a compound of at least one alkali metal selected from the group consisting of Li, Na, K, Rb and Cs, and M ^III represents Al, Ga, In, Tl, Sc, Y, C
It represents at least one compound of a trivalent metal selected from the group consisting of d and Lu (excluding Al ₂ O ₃ ). X
Represents at least one halogen selected from the group consisting of Cl, Br and I. Ln is Ce, Pr, S
m, Eu, Gd, Tb, Dy, Ho, Nd, Er, Tm
And at least one rare earth element selected from the group consisting of Yb and Yb. A is Al ₂ O ₃ , SiO ₂ and ZrO ₂
Represents at least one metal oxide selected from the group consisting of a, b, c, d and x are respectively 0 ≦ a ≦
0.3, 0 ≦ b ≦ 2, 0 ≦ c ≦ 2, 0 ≦ d ≦ 0.5, 0
<X ≦ 0.2. ]