JP2003232896A - Radiation image conversion panel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiation image conversion panel that has high sensitivity and excels in graininess in X-ray irradiation conditions at high pressure and low pressure. <P>SOLUTION: The radiation image conversion panel has at least a photostimulable phosphor layer on a support. The photostimulable phosphor layer includes a photostimulable phosphor of an RbX or CsX type (X denotes Cl, Br or I). <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a radiation image conversion panel.

[0002]

2. Description of the Related Art A radiation image represented by an X-ray image is used in various fields such as for disease diagnosis. This X-ray image is obtained by irradiating a phosphor layer (also referred to as a fluorescent screen) with radiation that has passed through a subject, and the visible light generated in the phosphor layer is converted into a silver halide photographic light-sensitive material (hereinafter simply A so-called radiographic method is mainly used in which a visible image is obtained by irradiating a (photosensitive material) or the like and then performing a developing process.

However, in recent years, a new method of directly taking out an image from a phosphor layer has been proposed instead of an image forming method using a light-sensitive material having a silver halide salt.

As the above-mentioned method, the radiation transmitted through the subject is absorbed by the phosphor, and then the phosphor is excited by, for example, light or thermal energy, and the phosphor is accumulated by absorption of X-rays. The emitted radiation energy is emitted as fluorescence, and this fluorescence is detected and imaged. Specifically, for example, U.S. Pat. No. 3,859,
No. 527 and JP-A-55-12144, and a radiation image conversion method using a stimulable phosphor.

This method utilizes a radiation image conversion panel containing a stimulable phosphor, and more specifically, irradiates the stimulable phosphor layer of this radiation image conversion panel with radiation that has passed through an object, Radiation energy corresponding to the radiation transmission density of each part of the subject is accumulated, and then the stimulable phosphor is excited in a time series with an electromagnetic wave (excitation light) such as visible light or infrared rays, whereby the stimulable phosphor is obtained. The radiation energy stored therein is emitted as stimulated luminescence, and the signal due to the intensity of this light is taken out as, for example, a photoelectrically converted electric signal, and this signal is extracted from an existing image recording material such as a silver halide photographic light-sensitive material. Alternatively, it is a method of reproducing a visible image on an image display device typified by a CRT or the like.

The above-mentioned method of reproducing a radiation image record has a radiation dose that is much smaller than that of a conventional radiographic method that uses a combination of a radiation-sensitive material and an intensifying screen, and a radiation amount that is rich in information. There is an advantage that an image can be obtained.

The radiation image conversion panel comprises a support and a photostimulable phosphor layer provided on the surface thereof or a self-supporting photostimulable phosphor layer, and the photostimulable phosphor layer is usually a photostimulable phosphor layer. Some include a fluorescent substance and a binder that disperses and supports the same, and some include only an aggregate of the stimulable fluorescent substance formed by a vapor deposition method or a sintering method. Further, it is also known that the gap between the aggregates is impregnated with a polymer substance. Furthermore, on the surface of the stimulable phosphor layer opposite to the support side,
Usually, a protective layer film composed of a polymer film or a vapor deposition film of an inorganic material is provided.

As described above, the stimulable phosphor is a phosphor which exhibits stimulated emission when irradiated with excitation light after being irradiated with radiation, but in practice, the excitation light having a wavelength in the range of 400 nm to 900 nm is used. Therefore, a phosphor that exhibits stimulated emission in the wavelength range of 300 nm to 500 nm is generally used. Examples of stimulable phosphors conventionally used in radiation image conversion panels include, for example, JP-A-55-12145.
No. 55-160078, No. 56-74175,
56-1116777, 57-23673, 5
7-23675, 58-206678, 59-
27289, 59-27980 and 59-564.
79, 59-56480, and the like, rare earth element-activated alkaline earth metal fluorohalide-based phosphors; JP-A-59-75200, 60-84381, and 60-
106752, 60-166379, 60-2
21483, 60-228592, 60-22
No. 8593, No. 61-23679, No. 61-1208
No. 82, No. 61-120883, No. 61-12088.
5, No. 61-235486, No. 61-235487.
Divalent europium activated alkaline earth metal halide phosphors described in JP-A-59-12144; rare earth element-activated oxyhalide phosphors described in JP-A-59-12144;
Cerium-activated trivalent metal oxyhalide phosphor described in JP-A-69281; Bismuth-activated alkali metal halide phosphor described in JP-A-60-70484;
0-141783 and 60-157100, the divalent europium-activated alkaline earth metal halophosphate phosphor; the divalent europium-activated alkaline earth metal haloborate described in JP-A-60-157099. Phosphor: divalent europium-activated alkaline earth metal hydrogen halide phosphor described in JP-A-60-217354; cerium-activated rare earth compound halogen described in JP-A-61-121173 and JP-A-61-21182 Compound phosphor; JP-A-61-61
No. 40390, a cerium-activated rare earth halophosphate phosphor; a divalent europium-activated cerium / rubidium halide phosphor described in JP-A-60-78151;
A divalent europium-activated halogen phosphor described in JP-A-60-78153; a tetradecahedral rare earth metal-activated alkaline earth metal fluorohalide-based phosphor precipitated from a liquid phase described in JP-A-7-233369. , Etc. are known.

Among the above-described stimulable phosphors, a divalent europium-activated alkaline earth metal fluoride halide phosphor containing iodine, and a divalent europium-activated alkaline earth metal halide phosphor containing iodine. The rare earth element-activated rare earth oxyhalide-based phosphor containing iodine, iodine, and the bismuth-activated alkali metal halide-based phosphor containing iodine exhibit stimulated emission with high brightness.

A radiation image conversion panel using these stimulable phosphors releases the stored energy by scanning the excitation light after storing the radiation image information, so that the radiation image can be stored again after the scanning. One of the advantages is that it can be used repeatedly. That is, in the conventional radiographic method, the radiation-sensitive material is consumed for each photographing, whereas in the radiographic image conversion method, since the radiographic image conversion panel is repeatedly used, resource conservation and economic efficiency are improved. It is also advantageous from the aspect.

[0011] In the above-mentioned usage form, it is strongly required that the radiation image conversion panel is provided with a performance that can be used for a long period of time without degrading the image quality of the obtained radiation image.

In recent years, particularly in mammography (breast diagnosis) and the like, there is a demand for a high quality and high sensitivity radiation image conversion panel, so that it has been conventionally used for a high sensitivity radiation image conversion panel. Kaisho 61-72
No. 087, No. 61-72088, No. 61-71212
No. 61-72091, No. 61-73786, No. 61-73787, and the like, attention is paid to the alkali halide type stimulable phosphors.

However, the above-described photostimulable phosphor used in the manufacture of a radiation image conversion panel, if left in a room under normal climatic conditions for a long time, will be affected by moisture in the environment, light such as ultraviolet rays, or the like over time. It has a problem that the characteristics are deteriorated.

For example, if the stimulable phosphor is left under a high humidity condition for a long time, the radiation sensitivity of the stimulable phosphor decreases as the amount of absorbed water increases. Further, if the photostimulable phosphor is left to stand under the light of high energy such as ultraviolet rays, a part of the stimulable phosphor is gradually decomposed and the radiation sensitivity is lowered. Generally, the latent image of the radiation image recorded on the stimulable phosphor regresses with the passage of time after irradiation, so the intensity of the reproduced radiation image signal varies from the irradiation to the scanning by the excitation light. Has a characteristic that the longer the time, the lower, the rate of latent image regression when the stimulable phosphor absorbs moisture,
It is further accelerated and causes a big problem. When a radiation image conversion panel having a stimulable phosphor that has absorbed moisture or a stimulable phosphor that has been deteriorated by light such as ultraviolet rays is used, the reproducibility of a reproduction signal is reduced when reading a radiation image.

Conventionally, in order to prevent the above deterioration phenomenon due to moisture absorption of the stimulable phosphor, the stimulable phosphor layer is coated with a moisture-proof protective layer having a low moisture permeability, or the phosphor particles are made hydrophobic. A method of reducing the amount of water reaching the phosphor layer by applying a chemical treatment has been proposed and implemented.

As the moisture-proof protective layer having low moisture permeability, a method of using a glass plate or a thick resin film having a high barrier property, or a film obtained by vapor-depositing a glass thin film such as metal oxide or silicon nitride on a polyethylene terephthalate film 2
A method of using a laminated film formed by laminating 8 sheets is known. On the other hand, in order to improve the image quality of a radiation image obtained by using a stimulable phosphor, the radiation image conversion panel design requires not only sharpness but also image graininess. This image graininess is generally the X of a stimulable phosphor.
The contributions to the line absorption characteristics, brightness, and panel structure are separated, and among these, the X-ray absorption characteristics of the stimulable phosphor have the most dominant influence. In the stimulable phosphor used as a radiation image conversion panel design, the X-ray absorption characteristics are particularly important in addition to the brightness and the structure of the panel. Further, the method for forming the layer of the stimulable phosphor may be the coating method or the vapor deposition method as described above, but the vapor deposition method is particularly preferable because the filling rate of the phosphor layer can be set particularly high.

[0017]

SUMMARY OF THE INVENTION An object of the present invention is to provide a radiation image conversion panel which has high sensitivity and is excellent in granularity under X-ray irradiation conditions of high pressure and low pressure.

[0018]

The above objects of the present invention have been achieved by the following constitutions 1 to 6.

1. In a radiation image conversion panel having at least a stimulable phosphor layer on a support, the stimulable phosphor layer is an RbX or CsX (X represents Cl, Br or I) type stimulable phosphor. A radiation image conversion panel comprising:

2. 2. The radiation image conversion panel as described in 1 above, wherein the RbX or CsX type stimulable phosphor is at least one selected from the group consisting of the general formulas (1) to (4).

3. The radiation image conversion panel according to 1 or 2 above, wherein the RbX or CsX stimulable phosphor is represented by the general formula (5).

4. 4. The radiation image conversion panel according to any one of 1 to 3 above, wherein the activator of the RbX or CsX stimulable phosphor is divalent Eu (europium).

5. 5. The radiation image conversion panel according to any one of 1 to 4 above, which has a protective layer on the stimulable phosphor layer.

6. 6. The radiation image conversion panel according to any one of 1 to 5 above, which has a sealing material that seals the entire photostimulable phosphor layer and protective layer formed on a support.

The present invention will be described in detail below. As a result of various studies, the present inventors have found that in a radiation image conversion panel having at least a stimulable phosphor layer on a support as described in claim 1, the stimulable phosphor layer is RbX or A radiation image conversion panel characterized by containing a CsX (X represents Cl, Br or I) type stimulable phosphor, thereby providing the effect described in the present invention, namely, high sensitivity and high pressure. It has been found that a radiation image conversion panel excellent in graininess under X-ray irradiation conditions at low pressure is provided.

<< Stimulable Phosphor Layer >> The stimulable phosphor layer according to the present invention will be described. The stimulable phosphor layer according to the present invention is coated with a coating liquid containing phosphor particles and a polymer resin. There are a coating type phosphor layer formed and formed, and a deposition type phosphor layer formed by a method such as vapor deposition and sputtering.

(Preparation of Coating Phosphor Layer) The coating phosphor layer is mainly composed of phosphor particles and a polymer resin (also referred to as a binder), and is applied and formed on a support using a coater. To be done. As the stimulable phosphor that can be used in the coating type phosphor layer, a phosphor that exhibits stimulated emission in the wavelength range of 300 nm to 500 nm by excitation light having a wavelength in the range of 400 nm to 900 nm is preferable.

Binder used here
Examples of the protein include proteins such as gelatin, polysaccharides such as dextran, or natural polymer substances such as gum arabic; and polyvinyl butyral, polyvinyl acetate, nitrocellulose, ethyl cellulose, vinylidene chloride / vinyl chloride copolymer, polyalkyl. (Meta)
Examples of the binder include synthetic polymers such as acrylate, vinyl chloride / vinyl acetate copolymer, polyurethane, cellulose acetate butyrate, polyvinyl alcohol and linear polyester.

Particularly preferred among the above-mentioned binders are nitrocellulose, linear polyesters, polyalkyl (meth) acrylates, mixtures of nitrocellulose and linear polyesters, nitrocellulose and polyalkyl (meth) acrylates. And a mixture of polyurethane and polyvinyl butyral. Note that these binders may be crosslinked with a crosslinking agent. The stimulable phosphor layer can be formed on the undercoat layer by the following method, for example.

First, the stimulable phosphor and the binder are added to a suitable solvent and mixed sufficiently to prepare a coating solution in which the phosphor particles and the particles of the compound are uniformly dispersed in the binder solution. To do.

The binder is preferably used in the range of 0.01 part by mass to 1 part by mass with respect to 1 part by mass of the stimulable phosphor. However, from the viewpoint of improving the sensitivity and sharpness of the obtained radiation image conversion panel, it is preferable that the amount of the binder is small, and from the viewpoint of easy coating, 0.03 parts by mass to
The range of 0.2 parts by mass is more preferable.

Examples of the solvent used for preparing the coating liquid for the stimulable phosphor layer include lower alcohols such as methanol, ethanol, isopropanol and n-butanol, acetone, methyl ethyl ketone, methyl isobutyl ketone,
Ketones such as cyclohexanone, esters of lower fatty acids and lower alcohols such as methyl acetate, ethyl acetate and n-butyl acetate, ethers such as dioxane, ethylene glycol monoethyl ether and ethylene glycol monomethyl ether, aromatic compounds such as triol and xylol , Halogenated hydrocarbons such as methylene chloride and ethylene chloride, and mixtures thereof.

The coating liquid contains a dispersant for improving the dispersibility of the phosphor in the coating liquid, and a binder between the binder and the phosphor in the stimulable phosphor layer after formation. Various additives such as a plasticizer for improving the binding strength may be mixed. Examples of dispersants used for such purpose include phthalic acid, stearic acid, caproic acid,
Examples thereof include lipophilic surfactants. Examples of the plasticizer include phosphoric acid esters such as triphenyl phosphate, tricresyl phosphate, diphenyl phosphate; phthalic acid esters such as diethyl phthalate and dimethoxyethyl phthalate; ethyl phthalyl ethyl glycolate, butyl phthalyl butyl glycolate, etc. And a polyester of polyethylene glycol and an aliphatic dibasic acid, such as a polyester of triethylene glycol and adipic acid, a polyester of diethylene glycol and succinic acid, and the like.

The coating solution prepared as described above is then uniformly applied to the surface of the undercoat layer to form a coating film of the coating solution. This coating operation can be performed by using an ordinary coating means such as a doctor blade, a roll coater or a knife coater.

Then, the formed coating film is gradually heated and dried to complete the formation of the stimulable phosphor layer on the undercoat layer.

The coating liquid for the stimulable phosphor layer is prepared by using a dispersing device such as a ball mill, a sand mill, an attritor, a three roll mill, a high speed impeller disperser, a Kady mill, and an ultrasonic disperser. The stimulable phosphor layer is formed by applying the prepared coating solution onto a support using a coating solution such as a doctor blade, a roll coater, a knife coater and drying.

The thickness of the coating type stimulable phosphor layer varies depending on the characteristics of the intended radiation image conversion panel, the type of stimulable phosphor, the mixing ratio of the binder and the stimulable phosphor, etc. 1
It is preferably selected from the range of 0 μm to 1000 μm, and more preferably selected from the range of 10 μm to 500 μm.

(Preparation of Vapor Deposition Phosphor Layer) The alkali halide stimulable phosphor according to the present invention can be formed into a stimulable phosphor layer by a method such as vapor deposition and sputtering.

Among the alkali halide phosphors, the alkali halide stimulable phosphors such as RbX and CsX (X represents Cl, Br or I) are preferable in terms of high brightness and high image quality. The photostimulable phosphor having the composition represented by any one of the above general formulas (1) to (5) described in 2 to 4 is preferable, and among them, C is Br (bromine atom), Cs.
Br-based phosphors and RbBr-based phosphors are particularly preferably used.

As a method for forming a vapor deposition type photostimulable phosphor layer on a support, for example, vapor of the photostimulable phosphor or the raw material is vapor-deposited on the support at a specific incident angle. A stimulable phosphor layer composed of independent elongated columnar crystals can be obtained by a vapor deposition (deposition) method such as. The columnar crystals can grow at a growth angle of about half the incident angle of the vapor flow of the stimulable phosphor during vapor deposition. Further, it is also possible to provide a molecular vapor deposition film by vapor deposition near room temperature.

The method of supplying the vapor flow of the stimulable phosphor at a certain incident angle with respect to the surface of the support is arranged such that the support is inclined with respect to the crucible containing the evaporation source, or the support is supported. The crucible and the crucible may be installed in parallel with each other, and a method may be adopted in which only the oblique component is vapor-deposited on the support by a slit or the like from the evaporation surface of the crucible charged with the evaporation source.

In these cases, it is appropriate that the shortest distance between the support and the crucible is set to about 10 to 60 cm according to the average range of the stimulable phosphor. The thickness of the columnar crystal tends to become thinner as the temperature of the support becomes lower.

The stimulable phosphor serving as an evaporation source is uniformly dissolved or is molded by a press or a hot press and placed in a crucible. At this time, it is preferable to perform degassing treatment. The method of evaporating the stimulable phosphor from the evaporation source is performed by scanning an electron beam emitted by an electron gun, but it can be evaporated by a method other than this.

The evaporation source does not necessarily have to be a stimulable phosphor, but may be a mixture of stimulable phosphor raw materials.

Also, an activator may be later doped into the matrix of the phosphor. For example, after vapor-depositing only the base material RbBr, the activator Tl may be doped. That is, since the crystals are independent, even if the film is thick, it can be sufficiently doped, and since crystal growth does not easily occur,
This is because the MTF does not decrease.

Doping can be performed by a thermal diffusion or ion implantation method of a doping agent (activator) in the formed base layer of the phosphor.

In the stimulable phosphor layer made of these columnar crystals, in order to reduce the haze ratio, the size of the columnar crystals (the size of each columnar crystal when the columnar crystals are observed from a plane parallel to the support) It is the average value of the circle-converted diameter of the cross-sectional area,
(Calculated from a micrograph including at least 100 columnar crystals in the field of view) is preferably about 1 μm to 50 μm,
More preferably, it is 1 μm to 30 μm.

The size of the gap between each columnar crystal is 30 μm.
The following is preferable, and 5 μm or less is more preferable. That is,
If the gap exceeds 30 μm, the scattering of laser light in the phosphor layer increases and the sharpness decreases.

The growth angle of the oblique columnar crystals of the stimulable phosphor is not particularly limited as long as it is larger than 0 ° and smaller than 90 °, but is preferably 10 to 70 °, preferably 20 ° to 55 °. is there. To make the growth angle 10 to 70 °, the incident angle is 20
The angle of incidence may be set to -80 °, and the incident angle may be set to 40-70 ° in order to set it to 20-55 °. If the growth angle is large, the columnar crystals fall too much against the support, and the film becomes brittle.

The vapor phase growth (deposition) of the stimulable phosphor includes vapor deposition, sputtering and CVD.

In the vapor deposition method, after the support is placed in the vapor deposition apparatus, the inside of the apparatus is evacuated to a vacuum of about 1.333 × 10 ⁻⁴ Pa, and then at least one of the stimulable phosphors is subjected to resistance. The stimulable phosphor is obliquely deposited on the surface of the support by heating and evaporation by a method such as a heating method or an electron beam method to a desired thickness. As a result, a stimulable phosphor layer containing no binder is formed, but it is possible to form the stimulable phosphor layer in a plurality of times in the vapor deposition step. Also, in the vapor deposition step, vapor deposition can be performed using a plurality of resistance heaters or electron beams. Further, in the vapor deposition method, a stimulable phosphor material is vapor-deposited by using a plurality of resistance heaters or an electron beam to synthesize a target stimulable phosphor on a support and simultaneously form a stimulable phosphor layer. It is also possible to form. Furthermore, in the vapor deposition method, the object to be vapor-deposited may be cooled or heated during vapor deposition, if necessary. In addition, the stimulable phosphor layer may be heat-treated after the vapor deposition is completed.

In the sputtering method, after the support is set in the sputtering apparatus as in the vapor deposition method, the inside of the apparatus is once evacuated to a vacuum degree of about 1.333 × 10 ⁻⁴ Pa, and then used as a gas for sputtering. An inert gas such as Ar or Ne is introduced into the apparatus to a gas pressure of about 1.333 × 10 ^-1 Pa. Next, by using the stimulable phosphor as a target, the stimulable phosphor is obliquely deposited on the surface of the support by oblique sputtering. In this sputtering step, it is possible to form the stimulable phosphor layer in a plurality of times in the same manner as the vapor deposition method, and by using each of them, the target is sputtered to simultaneously or sequentially sputter the stimulable phosphor layer. Can also be formed. Further, in the sputtering method, it is possible to form a target stimulable phosphor layer on a support by using a plurality of stimulable phosphor raw materials as targets and simultaneously or sequentially sputtering them. If desired, reactive sputtering may be performed by introducing a gas such as O ₂ or H ₂ . Further, in the sputtering method, the object to be vapor-deposited may be cooled or heated during the sputtering, if necessary. Further, the stimulable phosphor layer may be heat-treated after the completion of sputtering.

In the CVD method, the binder is contained on the support by decomposing the target stimulable phosphor or the organometallic compound containing the raw material of the stimulable phosphor with energy such as heat or high frequency power. In order to obtain a stimulable phosphor layer that does not have any, it is possible to vapor-deposit the stimulable phosphor layer into independent elongated columnar crystals with a specific inclination with respect to the normal direction of the support. .

The layer thickness of the stimulable phosphor layer formed by these methods differs depending on the sensitivity of the intended radiation image conversion panel to radiation, the type of stimulable phosphor, etc.
It is preferably selected from the range of 0 μm to 1000 μm, and more preferably 20 μm to 800 μm.

<< RbX or CsX-Type Stimulable Phosphor >> The RbX or CsX-type stimulable phosphor according to the present invention will be described.

As the RbX or CsX type stimulable phosphor according to the present invention, at least one selected from the group consisting of the above general formulas (1) to (5) is preferably used.

Rb represented by the general formulas (1) to (5)
The X or CsX type stimulable phosphor is disclosed in Patent Publication 7-845.
88, 7-84589, 7-84591, 5-14751, and JP-A 61-71212, and the like can be used for preparation and production.

Rb represented by the general formulas (1) to (5)
The X- or CsX-type stimulable phosphor has higher sensitivity and higher image quality than the conventionally known stimulable phosphor, and exhibits extremely good moisture resistance, but among them, divalent Eu as an activator is used.
A stimulable phosphor provided with (europium) is preferably used.

<< Protective Layer >> The protective layer according to the present invention will be described.

From the viewpoint of further improving the moisture resistance (also referred to as moisture resistance) of the stimulable phosphor layer according to the present invention, it is preferable to provide a protective layer on the stimulable phosphor layer.

As the protective layer according to the present invention, ASTMD
The haze ratio measured by the method described in -1003 is 5
% Or more and less than 60% of a polyester film having an excitation light absorption layer, a polymethacrylate film, a nitrocellulose film, a cellulose acetate film or the like can be used, but a stretched film such as a polyethylene terephthalate film or a polyethylene naphthalate film, Preferable as a protective layer in terms of transparency and strength, further, a metal oxide on these polyethylene terephthalate film or polyethylene terephthalate film,
A vapor deposition film (alumina vapor deposition PET film, silica vapor deposition PET film, etc.) in which a thin film such as silicon nitride is vapor deposited is more preferable from the viewpoint of moisture resistance.

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, those having a very high optical transparency are preferable, and various plastic films having a haze value in the range of 2 to 3% are commercially available as such a protective film material having a high transparency. Has been done.

From the viewpoint of reducing image unevenness and linear noise and obtaining an image with high sharpness, the haze ratio is preferably from 5% to less than 60%, more preferably from 10% to 5%.
It is less than 0%.

From the viewpoint of further improving the moisture-proof property of the stimulable phosphor, the moisture-proof protective film has a moisture permeability of 50 g /
preferably m is ² · day or less, further preferably not more than 10 g / m ² · day, particularly preferably 1
It is not more than g / m ² · day.

Here, the moisture permeability of the above-mentioned protective film can be measured with reference to the method defined by JIS Z 0208.

From the viewpoint of adjusting the moisture permeability of the protective film within the above range to improve the moisture resistance of the protective film,
It is preferable to use a polyethylene terephthalate film or a vapor-deposited film obtained by vapor-depositing a thin film of a metal oxide, silicon nitride or the like on a polyethylene terephthalate film.

The thickness of the protective layer is 50 μm
1000 μm is preferable, and more preferably 50 to 500.
μm.

<< Sealing Material >> The sealing material according to the present invention will be described.

In the present invention, from the viewpoint of preventing deterioration of the stimulable phosphor by moisture absorption, it is preferable that the encapsulant according to the present invention is provided with a moisture-proof property. Moisture vapor transmission rate (also called still film) is 50g / m ² · day
It is preferably less than or equal to 10 g / m.
² · day or less, particularly preferably 1 g / m ² · da
y or less. Here, the moisture permeability of the encapsulant can be measured by referring to the method defined by JISZ 0208 as in the case of the protective layer described above.

From the viewpoint of adjusting the moisture permeability of the encapsulating material (encapsulating film) within the above-mentioned range and improving the moisture resistance of the protective film, a metal oxide, silicon nitride, etc. are formed on the polyethylene terephthalate film or the polyethylene terephthalate film. A vapor-deposited film obtained by vapor-depositing the thin film of is preferably used.

The encapsulating material (encapsulating film) according to the present invention may be formed by laminating a plurality of resin films or vapor-deposited films obtained by vapor-depositing a metal oxide or the like on a resin film in accordance with the required moisture resistance. Although optimum moisture resistance can be imparted, a conventionally known method can be applied as a method for laminating the resin films.

In the present invention, by providing the excitation light absorbing layer described above between the laminated resin films,
The excitation light absorption layer is protected from physical impact and chemical alteration, and stable plate performance can be maintained for a long period of time.

From the above, the excitation light absorption layer may be provided at a plurality of positions between the laminated resin films, or the adhesive layer for lamination may contain a coloring agent to be used as the excitation light absorption layer. .

Any conventionally known method can be applied to seal the entire stimulable phosphor layer and the entire protective layer with the encapsulant according to the present invention. The outermost layer on the side in contact with the layer contains a resin having a heat-fusible property, so that the encapsulant can be fused, and the stimulable phosphor layer, the encapsulation work in the peripheral portion of the protective layer, and the like, In addition, the deterioration of the characteristics of the stimulable phosphor due to moisture absorption can be prevented more effectively.

Preferably, a sealing material is arranged not only on the stimulable phosphor layer side but also on the support opposite to the side on which the stimulable phosphor layer is provided, and the periphery of the sealant is sealed. By adopting a sealing structure in which the materials are fused, it is possible to prevent the ingress of water from the opposite support side.

More preferably, the encapsulating material (encapsulating film) has a layer containing the above-mentioned resin having a heat-fusion property only at the portion used for encapsulation.

Further, when the encapsulating material on the support surface side is a laminated moisture-proof film formed by laminating one or more layers of aluminum film, it is possible to more reliably reduce the ingress of moisture. Further, this sealing method is easy in terms of work. Also in this case,
It is preferable that the outermost layer of the protective film, which is in contact with the stimulable phosphor layer, is not substantially adhered to the heat-fusible resin layer and the phosphor surface.

"The protective film and the stimulable phosphor layer are not substantially adhered" means that the stimulable phosphor layer and the encapsulant are not optically integrated. means.
More specifically, even if the stimulable phosphor layer and the encapsulant are microscopically in point contact with each other, the stimulable phosphor layer and the protective film are almost optically and mechanically almost non-existent. It means that it can be handled as a continuum.

In the encapsulation structure described above, the stimulable phosphor layer and the moisture-proof encapsulant are considered to be in contact with each other at a microscopic point. In the present invention, the case where the layer area is 10% or less is defined as substantially no adhesion.

The heat-fusible film is a resin film that can be fused with a commonly used impulse sealer, and is, for example, ethylene vinyl acetate copolymer (EVA).
And polypropylene (PP) film, polyethylene (P
E) films and the like can be mentioned, but the present invention is not limited to these.

Any known method can be used to seal the radiation image conversion panel cut into a predetermined size with a sealing material. Examples of the method include a method of heating and fusing a peripheral edge portion sandwiched between them with an impulse sealer, and a laminating method of pressurizing and heating between two heated rollers.

In the method of heat fusion with the impulse sealer, heat fusion in a reduced pressure environment is more preferable in terms of preventing displacement of the phosphor sheet in the protective film and eliminating moisture in the atmosphere. .

<< Support >> The support according to the present invention will be described.

As the support, various polymer materials, glass, metals and the like are used. For example, plate glass such as quartz, borosilicate glass, and chemically strengthened glass, cellulose acetate film, polyester film, polyethylene terephthalate film, Plastic films such as polyethylene naphthalate film, polyamide film, polyimide film, triacetate film, polycarbonate film, aluminum, iron,
A metal sheet of copper, chromium or the like or a metal sheet having a coating layer of hydrophilic fine particles is preferable. The surface of these supports may be a smooth surface or may be a matte surface for the purpose of improving the adhesiveness with the stimulable phosphor layer. Further, in the present invention, in order to improve the adhesiveness between the support and the stimulable phosphor layer, an adhesive layer may be provided in advance on the surface of the support, if necessary.

The thickness of these supports varies depending on the material of the support used, etc., but is generally 80 μm to 2000 μm.
m, and more preferably 8 from the viewpoint of handling.
It is 0 μm to 1000 μm.

The surface of these supports may be a smooth surface, or may be a matte surface for the purpose of improving the adhesiveness with the stimulable phosphor layer.

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

[0088]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited thereto.

Example 1 << Preparation of Radiation Image Conversion Panel 1 >>: Vapor Deposition Type A radiation image conversion panel 1 having a vapor deposition phosphor layer was prepared according to the method described below.

(Preparation of Support 1) A light reflecting layer was provided on a transparent crystallized glass having a thickness of 500 μm as follows.
Support 1 was prepared.

(Formation of Light Reflecting Layer) Titanium oxide manufactured by Furuuchi Chemical Co., Ltd. and zirconium oxide manufactured by Furuuchi Chemical Co., Ltd.
The reflectance at 0 nm is 85% and the reflectance at 660 nm is 2
A film was formed on the surface of the support by using a vapor deposition device so that the content was 0%.

(Production of Photostimulable Phosphor Plate 1) The support 1 produced above was heated at 240 ° C., nitrogen gas was introduced into the vacuum chamber, and the degree of vacuum was adjusted to 0.1 Pa. On one surface, using a known vapor deposition device, CsBr:
The alkali halide phosphor made of Eu was used at an incident angle of 50 ° with respect to the normal direction of the surface of the support, and a slit made of aluminum was used to set the distance between the support and the slit (deposition source) to 60 cm. The phosphor layer A having a columnar structure with a thickness of 300 μm was formed by vapor deposition while transporting the support in the parallel direction.

Next, vapor deposition was performed on the surface opposite to the surface provided with the phosphor layer A with the support interposed therebetween in the same manner as in the above vapor deposition method except that the temperature was changed to 25 ° C., and 120
A phosphor layer B made of a particulate vapor deposition film having a thickness of μm was formed.

The haze ratio of the phosphor layer formed as described above is
As a result of measurement by the method described in TMD-1003, the haze ratio of the phosphor layer A was 50% and the haze ratio of the phosphor layer B was 60%.

A radiation image conversion panel 1 was produced using the stimulable phosphor plate 1 produced above. For more information,
An air layer as a low refractive index layer having a thickness of 100 μm was formed between each stimulable phosphor layer and the glass used as the protective layer via a spacer at the glass-like side edge portion having the stimulable phosphor layer. A protective layer made of glass was provided so that The spacer is made of glass ceramics, and the thickness of the stimulable phosphor layer and the low refractive index layer (air layer) between the support and the protective layer glass is adjusted to a predetermined value. The side edges of the glass support and the protective layer made of glass were adhered using an epoxy adhesive to prepare a radiation image conversion panel 1.

<< Preparation of Radiation Image Conversion Panels 2 and 3 >>: Radiation image conversion was carried out in the same manner as in the preparation of the vapor deposition type radiation image conversion panel 1, except that the stimulable phosphor having the composition shown in Table 1 was used. Panels 2 and 3 were produced respectively.

<< Preparation of Radiation Image Conversion Panel 4 >>: Coating type (preparation of phosphor) In order to synthesize a stimulable phosphor precursor of europium activated barium fluoroiodide, a BaI ₂ aqueous solution (3.6 mol) was prepared. / L) 2780 ml and EuI ₃ aqueous solution (0.15 mol / L) 27 ml were placed in the reactor. The reaction mother liquor in this reactor was kept warm at 83 ° C. with stirring. Next, ammonium fluoride aqueous solution (8 mol / L)
322 ml was poured into the reaction mother liquor using a roller pump to form a precipitate. Keep warm and stir 2 after injection
The precipitate was aged for a period of time. Next, the precipitate was separated by filtration, washed with ethanol, and then dried in vacuum to obtain europium-activated barium fluoroiodide crystals. In order to prevent changes in particle shape due to sintering during firing, and changes in particle size distribution due to fusion between particles, 0.2% by mass of ultrafine alumina powder was added, and the surface of the crystal was thoroughly stirred with a mixer. Ultra fine particles of alumina were uniformly adhered to the surface. This was filled in a quartz boat and fired in a hydrogen atmosphere in a tube furnace at 850 ° C. for 2 hours, and then classified to prepare a europium-activated barium fluoroiodide phosphor having an average particle size of 4 μm. .

(Preparation of Phosphor Layer Coating Solution) 100 g of the phosphor prepared above and 16.7 g of a polyester resin (Vylon 63SS, solid content concentration 30%, manufactured by Toyobo Co., Ltd.) were mixed with methyl ethyl ketone-toluene (1: 1) mixed solvent. And disperse with a propeller mixer to give a viscosity of 25-3.
The coating liquid was adjusted to 0 Pa · s to prepare a phosphor layer coating liquid.

(Preparation of Phosphor Sheet 1) Using the above prepared phosphor layer coating solution, a doctor blade was used to deposit on a polyethylene terephthalate support having a thickness of 250 μm.
After coating so as to have a coating width of 1000 mm and a film thickness of 230 μm, it was dried at 100 ° C. for 15 minutes to form a phosphor layer 1, which was used as a phosphor sheet 1.

(Production of Moisture-Proof Protective Film) As the protective film on the side of the phosphor sheet coated surface of the above-prepared phosphor sheet 1, one having the following constitution (A) was used.

Structure (A) NY15 /// VMPET12 /// VMPET12 /
// PET12 /// CPP20 NY: Nylon PET: Polyethylene terephthalate CPP: Casting polypropylene VMPET: Alumina-deposited PET (commercially available product: manufactured by Toyo Metallizing Co., Ltd.) μm).

The above "///" means the dry lamination adhesive layer, and the thickness of the adhesive layer is 3.0 μm. The used adhesive for dry lamination is
A two-component reactive urethane adhesive was used.

The protective film on the back surface side of the support of the phosphor sheet is CPP 30 μm / aluminum film 9 μm /
A dry laminated film having a constitution of polyethylene terephthalate (PET) 188 μm was used. In this case, the thickness of the adhesive layer was 1.5 μm, and a two-component reactive urethane adhesive was used.

(Preparation of Radiation Image Conversion Panel) The phosphor sheet 1 prepared above was cut into squares each having a side of 20 cm, and the periphery of the impulse sealer was reduced under reduced pressure using the moisture-proof protective film prepared above. Fusion using,
After sealing, a radiation image conversion panel 4 was produced. The distance from the fusion portion to the peripheral edge of the phosphor sheet was 1 mm. The heater of the impulse sealer used for fusing has a width of 3 mm.

<< Preparation of Radiation Image Conversion Panels 5 and 6 >>: In the same manner as in preparation of the coating type radiation image conversion panel 4, except that the composition of the stimulable phosphor was changed as shown in Table 1. Radiation image conversion panels 5 and 6 were produced.

For each of the obtained radiation image conversion panels 1 to 6, emission brightness and graininess (high pressure condition, low pressure condition)
Was evaluated.

<< Evaluation of Luminance (Sensitivity) >> Luminance was measured by irradiating each radiation image conversion panel with X-rays having a tube voltage of 80 kVp from the back surface side of the phosphor sheet support, and then illuminating the panel with He-Ne laser light ( 633 nm) to be excited, and stimulated emission emitted from the phosphor layer is received by a photodetector (photoelectron image multiplier with spectral sensitivity S-5), its intensity is measured, and this is referred to as luminance. It was defined and displayed as a relative value with the brightness of the radiation image conversion panel 4 being 1.0.

<< Evaluation of Graininess under High-Pressure Irradiation Condition >> (Evaluation of Graininess of Radiation Image Conversion Panels 1 to 6) The evaluation of the graininess of the radiation image conversion panel 1 was performed under the X-ray irradiation conditions described below for forming a radiation image. Then, the radiation image was read by using a semiconductor laser beam of 660 nm and a semiconductor laser beam of 605 nm as excitation light.
After reading, the solid exposure image of the X-ray output on the film was visually evaluated and ranked in 5 levels.

X-ray irradiation conditions: 80 kV, 200 mA,
0.1 sec Film output condition: γ (gradation) = 3.0 output 5: Very little graininess is seen very well 4: Some graininess is recognized but good 3: Graininess is recognized 2: Graininess is 1: Graininess is conspicuous << Evaluation of graininess under low-pressure irradiation conditions: evaluation of mammography suitability >> Graininess was evaluated in the same manner except that the X-ray irradiation conditions under the above high-pressure irradiation conditions were changed as follows.

X-ray irradiation conditions: 28 kV, 125 mA,
1.0 sec Film output condition: γ (grayscale) = 4.0 output The obtained results are shown in Table 1.

[0111]

[Table 1]

From Table 1, it is clear that the samples of the present invention are superior in emission brightness, granularity under high-pressure irradiation conditions, and granularity under low-pressure irradiation conditions, as compared with the comparison. Also,
Since it has excellent graininess under low-pressure irradiation conditions, it can be seen that it is particularly useful for improving the diagnostic properties in mammography.

[0113]

Industrial Applicability According to the present invention, it is possible to provide a radiation image conversion panel which has high sensitivity and which is excellent in graininess under high and low pressure X-ray irradiation conditions.

Claims (6)

[Claims] 1. A radiation image conversion panel having at least a stimulable phosphor layer on a support, wherein the stimulable phosphor layer is RbX or CsX (X is Cl,
Represents Br or I. ) Type stimulable phosphor is contained, The radiation image conversion panel characterized by the above-mentioned. 2. An RbX or CsX type stimulable phosphor,
The radiation image conversion panel according to claim 1, wherein the radiation image conversion panel is at least one selected from the group consisting of the following general formulas (1) to (4). General formula (1) M (I) X · aM (II) X ′ ₂ · bM (III) X ″ ₃ : c
A [wherein M (I) is Rb or Cs and M (II) is at least one divalent metal selected from Mg, Ca, Sr, Ba, Zn, Cd and Ni. A represents an activator, but when the activator A is Eu, Fe, Cr, Zn,
Cd and Ni are not included. M (III) is Sc, Y, L
at least one trivalent metal selected from a, Pm, Lu, Al, Ga and In, and X, X ′ and X ″
Are at least one halogen each selected from Cl, Br and I. A represents an activator, Eu, In,
Ga, Tb, Ce, Tm, Dy, Pr, Ho, Nd, Y
It is at least one metal selected from b, Er, Gd, Sm, Tl, Na, Ag and Cu. a is 0 <a <
Represents a numerical value in the range of 0.5, but 0 <a when A is Eu
<Numerical value in the range of <0.25, b is numerical value in the range of 0 ≦ b <0.5, and c is numerical value in the range of 0 <c ≦ 0.2. ] Formula (2) M (I) X · aM (II) X '2 · bM (III) X "3 · c
A: dB [wherein M (I) is Rb or Cs, M (II) is at least one divalent metal selected from Be, Mg, Ca, Sr, and Ba, and M (III) is Y. , La, Lu,
It is at least one trivalent metal selected from Al, Ga and In, and X, X ′ and X ″ are Cl and Br, respectively.
And at least one halogen selected from I. A and B each represent an activator, but A is ZnO and Al.
₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ , In ₂ O ₃ , SiO ₂ , Ti
O ₂ , ZrO ₂ , GeO ₂ , SnO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅
And at least one metal oxide selected from ThO ₂ , B is Eu, In, Ga, Tb, Ce, Tm,
Dy, Pr, Ho, Nd, Yb, Er, Gd, Sm, T
It is at least one metal selected from 1, Na, Ag and Cu, and is a metal different from M (I). Also,
a, b, c and d are 0 ≦ a ≦ 0.4 and 0 ≦ b ≦, respectively.
It is a numerical value in the range of 0.5, 0 <c <0.5, 0 <d ≦ 0.2. ] Formula (3) (1-x) CsBr · xM (I) X · aM (II) X '2
BM (III) X ″ ₃ : cEu · dA [wherein M (I) is Rb or Cs, and M (II) is at least one divalent metal selected from Be, Mg, Ca, Sr, and Ba. And M (III) is Y, La, L
It is at least one trivalent metal selected from u, Al, Ga and In, and X, X ′ and X ″ are F, Cl and B.
It is at least one halogen selected from r and I, and Eu and A each represent an activator, and the activator A is I
n, Ga, Tb, Ce, Tm, Dy, Pr, Ho, N
It is at least one metal selected from d, Yb, Er, Gd, Sm, Tl, Na, Ag and Cu. Also,
x, a, b, c and d are respectively 0 ≦ x ≦ 0.4,
0.7 ≦ x ≦ 1.0, 0 ≦ a <0.5, 0 ≦ b <0.
It is a numerical value in the range of 5, 0 <c <0.2, 0 ≦ d <0.2. ] Formula (4) (1-x) RbBr · xM (I) X · aM (II) X '2
BM (III) X ″ ₃ : cEu · dA [wherein M (I) is Rb or Cs, and M (II) is selected from Be, Mg, Ca, Sr, Ba, Zn, Cd and Ni. At least one divalent metal, M (II
I) is Sc, Y, La, Pm, Lu, Al, Ga and I
at least one trivalent metal selected from n, X,
X ′ and X ″ are at least one halogen selected from F, Cl, Br and I, and Eu and A each represent an activator, and the activator A is Eu, Tb, Ce, Tm,
Dy, Pr, Ho, Nd, Yb, Er, Gd, Sm, N
It is at least one metal selected from a, Ag, Cu, Pb, Bi and Mn. Also, x, a, b, c and d
Are 0 ≦ x ≦ 0.4, 0.7 ≦ x ≦ 1.0, and 0 ≦ a, respectively.
<0.5, 0 ≦ b <0.5, 0 <c <0.2, 0 ≦ d <
It is a numerical value in the range of 0.2. ] 3. An RbX or CsX type stimulable phosphor,
It is represented by the following general formula (5).
Alternatively, the radiation image conversion panel described in 2. General formula (5) (1-x) CsBr * xRbBr: dA [In formula, A represents an activator, A is Eu, Tb, Ce,
Tm, Dy, Pr, Ho, Nd, Yb, Er, Gd, S
It is at least one metal selected from m, Na, Ag, Cu, Pb, Bi and Mn. x represents a numerical value from 0 to 1. ] 4. The radiation image conversion panel according to claim 1, wherein the activator of the RbX or CsX type stimulable phosphor is divalent Eu (europium). 5. The radiation image conversion panel according to claim 1, further comprising a protective layer on the stimulable phosphor layer. 6. The radiation according to claim 1, further comprising an encapsulant for encapsulating the stimulable phosphor layer and the protective layer formed on the support. Image conversion panel.