JPH0718957B2 - Radiation image conversion panel - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a radiation image conversion panel used in a radiation image conversion method using a stimulable phosphor.

[Technical Background of the Invention] As a method for obtaining a radiographic image as an image, a so-called radiographic method has conventionally been used which uses a combination of a radiographic film having an emulsion layer made of a silver salt photosensitive material and an intensifying screen. There is. Recently, as an alternative to the radiographic method, a radiographic image conversion method using a stimulable phosphor, as described in, for example, JP-A-55-12145, has been attracting attention. The radiation image conversion method uses a radiation image conversion panel (a stimulable phosphor sheet) containing a stimulable phosphor, and the radiation transmitted through the subject or the radiation emitted from the subject is radiated to the panel. It is accumulated in the photostimulable phosphor by being absorbed by the photostimulable phosphor, and then exciting the intensifying screen phosphor with electromagnetic waves (excitation light) such as visible light and infrared rays in time series. Radiation energy is emitted as fluorescence (stimulated luminescence), this fluorescence is photoelectrically read to obtain an electric signal, and the obtained electric signal is imaged.

This radiographic image conversion method has an advantage that a radiographic image with a much smaller exposure dose can be obtained as compared with the case of the conventional radiographic method. Therefore, this method has a very high utility value particularly in direct medical radiography such as X-ray photography for the purpose of medical diagnosis.

The radiation image conversion panel used in the radiation image conversion method is
The basic structure is composed of a support and a phosphor layer provided on one surface thereof. In addition, the surface of the phosphor layer opposite to the support (the surface not facing the support) is generally provided with a transparent protective film made of a polymer substance, and the phosphor layer is chemically protected. Protects against physical alteration or physical shock.

The phosphor layer is composed of a stimulable phosphor and a binder which contains and supports the stimulable phosphor in a dispersed state.
After absorbing radiation such as rays, it has a property of emitting light (stimulated emission) when irradiated with electromagnetic waves (excitation light) such as visible light and infrared rays. Therefore, the radiation transmitted through the subject or emitted from the subject is absorbed by the phosphor layer of the radiation image conversion panel in proportion to the radiation dose, and the radiation image of the subject or the subject is displayed on the radiation image conversion panel. Are formed as an accumulated image of radiation energy. This accumulated image can be emitted as stimulated emission by being excited in time series by the electromagnetic wave, and the accumulated image of radiation energy can be imaged by photoelectrically reading this stimulated emission and converting it into an electric signal. Can be converted.

Although the radiation image conversion method is a very advantageous image forming method as described above, the radiation image conversion panel used in this method is also similar to the intensifying screen used in the conventional radiographic method,
It is desired to provide an image having high sensitivity and excellent image quality (sharpness, graininess, etc.). In particular, when applying the radiation image conversion method to medical radiation imaging, it is necessary to reduce the exposure dose to the human body and obtain more information. Therefore, the radiation image conversion panel used in the method should be as sensitive as possible. Is desirable.

The sensitivity of the radiation image conversion panel basically depends on the total stimulated emission amount of the stimulable phosphor contained in the panel, and this total emission amount is not limited to the emission brightness of the stimulable phosphor itself. Also, it varies depending on the content of the phosphor in the phosphor layer. A large content of the phosphor also results in large absorption of radiation such as X-rays, so that higher sensitivity can be obtained, and at the same time, the image quality (particularly graininess) of the image is improved. On the other hand, when the phosphor content in the phosphor layer is constant, the denser the phosphor particles are, the thinner the layer can be made, and the spread of excitation light due to scattering is reduced. A relatively high sharpness can be obtained.

So far, the formation of the phosphor layer in the radiation image conversion panel is generally prepared by adding a stimulable phosphor particles and a binder to a suitable solvent to prepare a coating solution, and the coating solution is a usual coating means,
For example, it is carried out by directly applying it onto a support or another sheet using a doctor blade, a roll coater or the like and drying it. The relative density of the phosphor layer comprising the binder containing the stimulable phosphor thus obtained (volume ratio of the stimulable phosphor in the phosphor layer)
Is up to 60%. Therefore, in order to improve the sensitivity with this normal coating method, there is a method of increasing the layer thickness of the phosphor layer to increase the absolute amount of the phosphor, but this method reduces the image quality (sharpness) of the image. There is a problem of bringing. For this reason, it is desirable that the panel is such that the layer thickness of the phosphor layer is within an appropriate range and the relative density of the phosphor layer is high.

As a method of increasing the amount of the phosphor in the phosphor layer (a method of improving the relative density of the phosphor layer) without increasing the layer thickness of the phosphor layer, a compression means such as a calendar roll or a hot press is used. A method of compressing a phosphor layer (or a phosphor layer and a support) using the same is known (Japanese Patent Laid-Open Nos. 59-126299 and 59-126300).

However, the phosphor layer formed by utilizing the above method has an increased relative density, and although more phosphor particles can be present in the phosphor layer having a constant thickness, the phosphor itself is compressed to compress the phosphor itself. Distortion tends to occur and the sensitivity tends to decrease (pressure desensitization).

A method of forming a phosphor layer as a layer made of only a stimulable phosphor containing no binder is already known. For example, U.S. Pat. No. 3,859,527 describes that a storage medium is composed of a phosphor obtained by a hot pressing method, and is disclosed in JP-A-61-73100, 1985
The procedure amendment dated March 11 discloses a method of forming a phosphor layer by using a firing method. However, all of them are merely suggestions that the hot pressing method or the firing method can be used.

SUMMARY OF THE INVENTION An object of the present invention is to provide a radiation image conversion panel with improved sensitivity.

The present invention provides a radiation image conversion panel having a support and a phosphor layer made of a stimulable phosphor provided on the support, the phosphor layer having a relative density of 70% or more by sintering. In the radiation image storage panel, the phosphor sheet prepared as described above is bonded to the surface of a support.

The above-mentioned phosphor sheet can be obtained, for example, by previously pressing a powdery substance comprising a stimulable phosphor into a mold to form a sheet, and then sintering this. Alternatively, it is also possible to cast a dispersion liquid containing a stimulable phosphor dispersed in a binder solution in advance into a mold, or apply it on a flat plate to form a sheet, and then sinter this. The above phosphor sheet can be obtained.

In the present invention, the relative density of the phosphor layer refers to the ratio of the volume occupied by the phosphor to the total volume of the phosphor layer.

The present invention comprises only a stimulable phosphor obtained by sintering a phosphor layer of a radiation image conversion panel, and determines the relative density of the phosphor layer.
By increasing the density of the phosphor in the phosphor layer to 70% or more to achieve a high density, a remarkable improvement in the sensitivity of the panel is realized.

The phosphor layer formed by the conventional manufacturing method (coating method) is a layer composed of a binder that contains and supports stimulable phosphor particles in a dispersed state, and the phosphor layer has a relatively low relative density (60 % Or less). Since the packing density of the phosphor is low and the content of the phosphor in a constant layer thickness is small, there is a limit to the improvement of sensitivity. In addition, even if the thickness of the phosphor layer is increased, since a large number of bubbles are present in the phosphor layer, scattering of excitation light or scattering of stimulated emission light is liable to occur, and a large improvement in sensitivity cannot be obtained. Or, it adversely affects the image quality.

In the present invention, the phosphor layer is formed by a manufacturing method (sintering method) including a step of molding a phosphor layer-forming material containing a stimulable phosphor into a sheet shape and a step of sintering this, A phosphor layer consisting essentially of the phosphor and having a relative density of 70% or more can be obtained. The panel of the present invention having such a phosphor layer exhibits extremely high sensitivity because the packing density of the phosphor is high. That is, according to the production method of the present invention, no substance other than the stimulable phosphor (for example, a binder) is used in the step of forming the phosphor layer, or even if it is used, it is burned out in the sintering step. A phosphor layer composed of only the phosphor is obtained. Further, the phosphor layer is formed in a state where the phosphor is sintered and densely packed in the whole in the sintering step, and a phosphor layer having an extremely high relative density can be obtained. Therefore, when compared with a panel in which the layer thickness of the phosphor layer obtained by the conventional manufacturing method is the same, the phosphor layer of the panel obtained by the method of the present invention does not contain a binder and also reduces bubbles. And the phosphor is present in an extremely large amount. Therefore, the stimulated emission amount of the entire phosphor layer is increased. In addition, the amount of radiation absorbed by the entire phosphor layer is increased, which also increases the amount of stimulated emission relatively, thereby enhancing the sensitivity.

Further, in the panel of the present invention, when the sensitivities are made equal, the layer thickness of the phosphor layer can be made thinner than that of the conventional panel, so that an image with high sharpness can be obtained. Further, the amount of radiation absorbed per phosphor layer is increased to increase X
Since the quantum noise of radiation such as lines can be reduced, an image with excellent graininess can be obtained.

[Structure of the Invention] The radiation image storage panel of the present invention having the preferable characteristics as described above can be manufactured, for example, by the manufacturing method described below.

The phosphor layer, which is a characteristic requirement of the present invention, is a layer made of a sintered photostimulable phosphor and having a relative density of 70% or more.

The stimulable phosphor is a phosphor that emits stimulated emission when irradiated with excitation light after being irradiated with radiation as described above, but from a practical viewpoint, the wavelength is in the range of 400 to 900 nm. A phosphor that exhibits stimulated emission in the wavelength range of 300 to 500 nm by excitation light is desirable. Examples of stimulable phosphors used in the radiation image conversion panel of the present invention include US Pat.
SrS: Ce, Sm, SrS: E described in the specification of 3,859,527
_{u, Sm, ThO 2: Er} , and _{La 2 O 2 S: Eu,} Sm, are described in JP-A-55-12142 ZnS: Cu, Pb, Ba
O · xAl ₂ O ₃ : Eu (however, 0.8 ≦ x ≦ 10) and M ^II
O.xSiO ₂ : A (where M ^II is Mg, Ca, Sr, Zn, Cd, or Ba, A is Ce, Tb, Eu, Tm, Pb, Tl, Bi, or Mn, and x is a 0.5 ≦ x ≦ 2.5), is described in _{JP-a-55-12143 (Ba 1- x - y,} Mg
x, Cay) FX: aEu ²⁺ (where X is at least one of Cl and Br, and x and y are 0 <x + y ≦ 0.
6, and xy ≠ 0, a is 10 ⁻⁶ ≦ a ≦ 5 × 10 ⁻² ), LnOX: xA described in JP-A-55-12144 (where Ln is La, At least one of Y, Gd, and Lu, X at least one of Cl and Br, A at least one of Ce and Tb, and x is 0 <x
<0.1), as described in JP-A-55-12145 (Ba _1- x, M
²⁺ x) FX: yA (where M ²⁺ is Mg, Ca, Sr, Zn, and Cd
At least one of X, at least one of Cl, Br, and I, A is Eu, Tb, Ce, Tm, Dy, Pr, Ho,
At least one of Nd, Yb, and Er, and x
Is 0 ≦ x ≦ 0.6 and y is 0 ≦ y ≦ 0.2), M ^II FX.xA: y described in JP-A-55-160078.
Ln [However, M ^II is Ba, at least one of Ca, Sr, Mg, Zn, and Cd, A is BeO, MgO, CaO, SrO, BaO, Z
nO, Al ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ , In ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , G
At least one of eO ₂ , SnO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , and ThO ₂ , Ln is Eu, Tb, Ce, Tm, Dy, Pr, Ho, Nd, Yb,
At least one of Er, Sm, and Gd, X is Cl, B
at least one of r and I, wherein x and y are 5 × 10 ⁻⁵ ≦ x ≦ 0.5, and 0 <y ≦ 0.2, respectively] No. 116777 (Ba _1- x, M ^II
x) F ₂ · aBaX ₂ : yEu, zA [where M ^II is at least one of beryllium, magnesium, calcium, strontium, zinc, and cadmium, X is at least one of chlorine, bromine, and iodine, A Is at least one of zirconium and scandium, and a, x, y, and z are each 0.5 ≦ a ≦ 1.25,
0 ≦ x ≦ 1, 10 ⁻⁶ ≦ y ≦ 2 × 10 ⁻¹ , and 0 <z ≦ 10 ⁻²
The phosphor represented by the compositional formula [1] is described in JP-A-57-23673 (Ba _1- x, M
^II x) F ₂ · aBaX ₂ : yEu, zB [where M ^II is beryllium,
At least one of magnesium, calcium, strontium, zinc, and cadmium; X is at least one of chlorine, bromine, and iodine;
x, y, and z are 0.5 ≦ a ≦ 1.25 and 0 ≦ x ≦, respectively.
1, 10 ⁻⁶ ≦ y ≦ 2 × 10 ⁻¹ , and 0 <z ≦ 2 × 10 ⁻¹ ], which is described in JP-A-57-23675 (Japanese Patent Application Laid-Open No. 57-23675). Ba _1- x, M
^II x) F ₂ · aBaX ₂ : yEu, zA [where M ^II is beryllium,
At least one of magnesium, calcium, strontium, zinc, and cadmium, X is at least one of chlorine, bromine, and iodine, A is at least one of arsenic and silicon, and a, x, y, and z is 0.5 ≦ a ≦ 1.25, 0 ≦ x ≦ 1, 10 ⁻⁶ ≦
y ≦ 2 × 10 ⁻¹ and 0 <z ≦ 5 × 10 ⁻¹ ] The phosphor represented by the composition formula: M ^III OX: xCe described in JP-A-58-69281.
[However, M ^III is Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, E
is at least one trivalent metal selected from the group consisting of r, Tm, Yb, and Bi, X is one or both of Cl and Br, and x is 0 <x <0.1] Of the composition formula of Ba _1- xM _{x / 2} L described in JP-A-58-206678
_{x / 2} FX: yEu ²⁺ [where M is Li, Na, K, Rb, and Cs
Represents at least one alkali metal selected from the group consisting of; L is Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Gd,
Represents at least one trivalent metal selected from the group consisting of Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Ga, In, and Tl; X represents a group consisting of Cl, Br, and I. Represents at least one halogen selected; and x is 10 ^-2 ≤ x
≦ 0.5, y is 0 <y ≦ 0.1], a phosphor represented by the composition formula: BaFX · xA: yEu described in JP-A-59-27980.
²⁺ [wherein X is at least one halogen selected from the group consisting of Cl, Br and I; A is a calcined product of a tetrafluoroboric acid compound; and x is 10 ⁻⁶
≦ x ≦ 0.1, y is 0 <y ≦ 0.1], a phosphor represented by the composition formula: BaFX · xA: yEu described in JP-A-59-47289.
²⁺ [wherein X is at least one halogen selected from the group consisting of Cl, Br and I; A is a monovalent or divalent metal of hexafluorosilicic acid, hexafluorotitanic acid and hexafluorozirconic acid] Is a calcined product of at least one compound selected from the group of hexafluoro compounds consisting of the salts of the above; and x is 10 ⁻⁶ ≦ x ≦ 0.
1, y is 0 <y ≦ 0.1], a phosphor represented by the composition formula, BaFX.xNa described in JP-A-59-56479.
X ': aEu ²⁺ [where X and X'are Cl, B, respectively]
at least one of r and I, and x and a are 0 <x ≦ 2 and 0 <a ≦ 0.2, respectively]
And a phosphor represented by the composition formula of M ^II FX.xNa described in JP-A-59-56480.
X ′: yEu ²⁺ : zA [wherein M ^II is at least one alkaline earth metal selected from the group consisting of Ba, Sr, and Ca; X and X ′ are Cl, Br, and I, respectively. Is at least one halogen selected from the group consisting of; A
Is at least one transition metal selected from V, Cr, Mn, Fe, Co, and Ni; and x is 0 <x ≦ 2,
y is 0 <y ≦ 0.2, and z is 0 <z ≦ 10 phosphor represented by a composition formula of a ^{is] -2, M II FX · aM} I that are described in JP-A-59-75200
^{X '· bM' II X "} 2 · cM III X 3 · xA: yEu 2+ [ However, M ^II is Ba, Sr, and is at least one alkaline earth metal selected from the group consisting of Ca; M ^I Is Li, Na,
M ′ ^II is at least one divalent metal selected from the group consisting of Be and Mg; M ^III is A
l, Ga, In, and at least one trivalent metal selected from the group consisting of Tl; A is a metal oxide; X is Cl,
At least one halogen selected from the group consisting of Br and I; X ′, X ″, and X are F, Cl, B
at least one halogen selected from the group consisting of r and I; and a is 0 ≦ a ≦ 2, b is 0 ≦ b
≦ 10 ⁻² , c is 0 ≦ c ≦ 10 ⁻² , and a + b + c ≧ 10 ⁻⁶ ; x is 0 <x ≦ 0.5, y is 0 <y ≦ 0.2] M ^II X ₂ · aM ^II described in JP-A-60-84381
X ′ ₂ : xEu ²⁺ [wherein M ^II is at least one alkaline earth metal selected from the group consisting of Ba, Sr and Ca; X and X ′ are selected from the group consisting of Cl, Br and I At least one halogen and X ≠ X ′; and a is 0.1 ≦ a ≦ 10.0 and x is 0 <x ≦ 0.2], and a stimulable phosphor represented by the composition formula: M ^II FX / aM ^I described in JP-A-60-101173
X ′: xEu ²⁺ [wherein M ^II is at least one alkaline earth metal selected from the group consisting of Ba, Sr and Ca; M ^I is at least one alkali metal selected from the group consisting of Rb and Cs; X is at least one halogen selected from the group consisting of Cl, Br and I; X'is at least one halogen selected from the group consisting of F, Cl, Br and I; and a and x Each is 0
≦ a ≦ 4.0 and 0 <M x stimulable phosphor represented by a composition formula of ≦ 0.2 is, are described in Japanese Patent Application No. Sho 60-70484 Pat by the applicant ^{I X:} xBi [However , M ¹ is at least one alkali metal selected from the group consisting of Rb and Cs; X is
A stimulable phosphor represented by the composition formula: at least one halogen selected from the group consisting of Cl, Br and I; and x is a numerical value in the range of 0 <x ≦ 0.2. it can.

Further, the M described in the above-mentioned JP-A-60-84381
^II X ₂ · aM ^II X ′ ₂ : xEu ²⁺ stimulable phosphor contains the following additives in the following ratio per 1 mol of M ^II X ₂ · aM ^II X ′ ₂ Good.

JP bM ^{I X} that are described in 60-166379 JP "(where, M ^I is at least one alkali metal selected from the group consisting of Rb and Cs, X 'is F, Cl, Br and I At least one halogen selected from the group consisting of, and b is 0 <b≤10.0);
221483 gazette, bKX ″ · cMgX ₂ · dM ^III
X '3 _(however, M ^III is Sc, Y, La, Erabaru from the group consisting of Gd and Lu is at least one trivalent metal,
X ″, X and X ′ are all F, Cl, Br and I
Is at least one halogen selected from the group consisting of, and b, c and d are each 0 ≦ b ≦ 2.0,
0 ≦ c ≦ 2.0, 0 ≦ d ≦ 2.0, and 2 × 10 ⁻⁵ ≦ b
+ C + d); yB described in JP-A-60-228592 (where y is 2 × 10 ⁻⁴ ≦ y ≦ 2 × 10 ⁻¹ ); JP-A-60-228593. BA as described (where A is at least one oxide selected from the group consisting of SiO ₂ and P ₂ O ₅ , and b is 10 ⁻⁴ ≦ b ≦ 2 ×
10 ⁻¹ ); bSiO described in Japanese Patent Application No. 59-240452 (where b is 0 <b ≦ 3 × 10 ⁻² ); Japanese Patent Application No. 59-240454. BSnX ″ ₂ (where X ″ is at least one halogen selected from the group consisting of F, Cl, Br and I, and b is 0 <b
≦ 10 ⁻³ ); bCsX ″ · cSnX ₂ described in Japanese Patent Application No. 60-78033 (where X ″ and X are at least selected from the group consisting of F, Cl, Br and I). A halogen, and b and c are 0 <b ≦ 10.0 and 10 ⁻⁶ ≦ c ≦ 2 × 10 ⁻² respectively); and bCsX described in Japanese Patent Application No. 60-78035. ″ ・ YLn ³⁺ (where X ″ is F, Cl, Br and I
Is at least one halogen selected from the group consisting of, Ln is Sc, Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, E
at least one rare earth element selected from the group consisting of r, Tm, Yb and Lu, and b and y are 0 <b ≦ 10.0 and 10 ⁻⁶ ≦ y ≦ 1.8 × 10 ⁻¹ respectively).

Among the above-described stimulable phosphors, the divalent europium-activated alkaline earth metal halide-based phosphors are particularly preferable because they exhibit stimulated emission with high brightness. However, the stimulable phosphor used in the present invention is not limited to the above-mentioned phosphor, and may be any phosphor that exhibits stimulated emission when irradiated with excitation light after irradiation with radiation. It may be.

The phosphor layer can be formed, for example, by the following manufacturing process.

That is, the manufacturing process of the phosphor layer includes a step of molding a phosphor layer forming material containing a stimulable phosphor into a sheet shape and a step of sintering the molded product.

In the process of molding the phosphor layer forming material into a sheet,
As the phosphor layer forming material, a powdery substance composed of particles of the stimulable phosphor can be used.

Further, as the phosphor layer forming material, a dispersion liquid containing the above-described stimulable phosphor particles and a binder can also be used. In this case, the stimulable phosphor and the binder are added to an appropriate solvent and then mixed sufficiently to prepare a dispersion liquid in which the phosphor particles are uniformly dispersed in the binder solution.

As the binder, a substance having suitable properties such as dispersibility of the phosphor or divergence in the sintering step is preferable. Such examples include paraffins (eg, those having 16 to 40 carbon atoms and melting points: 37.8 to 64.5 ° C); waxes (as natural waxes: candelilla wax, carnauba wax, rice wax, wood wax, etc.) Vegetable waxes, animal waxes such as beeswax, lanolin, and whale wax, mineral waxes such as montan wax, ozokerite, ceresin, and synthetic waxes: polyethylene wax, coal-based waxes such as Fischer-Tropsch wax, hardened castor oil , Fatty acid amides, oil-based synthetic waxes such as ketones); Resins (polyvinyl butyral, polyvinyl acetate, nitrocellulose, ethyl cellulose, vinylidene chloride / vinyl chloride copolymers, polyacyl (meth) acrylates, vinyl chloride / vinyl acetate copolymers, polyureta) Down cellulose acetate butyrate, polyvinyl alcohol, linear polyester) and the like. It is also possible to use proteins such as gelatin, polysaccharides such as dextran, and gum arabic.

Examples of the solvent include lower alcohols such as methanol, ethanol, n-propanol and n-butanol; hydrocarbons containing a chlorine atom such as methylene chloride and ethylene chloride; ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone; methyl acetate, acetic acid. Mention may be made of esters of lower fatty acids and lower alcohols such as ethyl and butyl acetate; ethers such as dioxane, ethylene glycol monoethyl ether, ethylene glycol monomethyl ether; and mixtures thereof.

The mixing ratio of the binder and the stimulable phosphor in the dispersion is different depending on the type of the phosphor or the molding conditions and sintering conditions described later, but generally the mixing ratio of the binder and the phosphor is 1: It is preferably selected from the range of 1 to 1: 300 (weight ratio), and particularly preferably from the range of 1:20 to 1: 150 (weight ratio).

The dispersion liquid may be mixed with an additive such as a dispersant for improving the dispersibility of the phosphor. Examples of dispersants used for such purpose include phthalic acid, stearic acid, caproic acid, lipophilic surfactants and the like.

The powdery substance composed of the phosphor particles prepared as described above or the dispersion liquid containing the phosphor particles and the binder is then molded into a sheet.

When the phosphor layer forming material is a powder, the molding is preferably performed by pressing the powder into a molding die to form a sheet. A rectangular die is usually used as the molding die. When the phosphor layer forming material is a dispersion liquid, a usual coating method (for example, doctor blade)
Apply it on a suitable flat plate (metal plate, glass plate, ceramic plate, etc.) and mold it into a sheet, or cast it into a molding die in the same manner as the above powdered material and mold it into a sheet. Is preferred.

In the above molding step, compression treatment may be performed,
In particular, when the phosphor layer forming material is a powdery material, the compression treatment is performed. The compression treatment is performed by, for example, press molding, and is preferably performed by applying a pressure in the range of 1 × 10 ^{2 to} 1 × 10 ⁴ kg / cm ² . This makes it possible to further increase the relative density of the obtained phosphor layer.

Next, the sheet-shaped molded product obtained as described above is sintered to obtain a phosphor sheet.

Sintering is performed in a firing furnace such as an electric furnace. The sintering temperature and the sintering time vary depending on the type of phosphor layer forming material, the shape and state of the sheet-shaped molded product, and the type of stimulable phosphor used for these.

When the sheet-shaped molded product is a powdery substance composed of a stimulable phosphor, the sintering temperature is generally in the range of 500 to 1000 ° C, preferably 700 to 950 ° C. The sintering time is generally in the range of 0.5 to 6 hours, preferably
It is in the range of 1.5 to 2 hours. As a sintering atmosphere, a neutral gas atmosphere such as a nitrogen gas atmosphere or an argon gas atmosphere, a nitrogen gas atmosphere containing a small amount of hydrogen gas, or a weak reducing atmosphere such as a carbon dioxide atmosphere containing carbon monoxide is used. To do.

When the sheet-shaped molded product is a dispersion liquid containing a stimulable phosphor and a binder, the binder in the sheet-shaped molded product is preliminarily subjected to a nitrogen gas atmosphere, a neutral gas atmosphere such as an argon gas atmosphere, or the like. It is preferable to diffuse at a relatively low temperature (temperature in the range of 100 to 450 ° C.) in an oxidizing gas atmosphere such as an oxygen gas atmosphere or an air atmosphere, and then sinter under the above sintering conditions. Due to the diffusion of the binder in this low temperature range, the components other than the stimulable phosphor such as the binder are 300 to 400.
It volatilizes or carbonizes at around ℃ and becomes carbon dioxide gas, which can be easily removed. As a result, the obtained phosphor sheet is composed only of the phosphor. The time for cold vaporization is preferably in the range of 0.5 to 6 hours. In this way, the phosphor sheet is formed to have a relative density of 70% or more. The grain boundary size of the phosphor in this case is 1 to 100.
It is preferably in the range of μm.

The compression process may be performed before the sintering process as described above, but may be performed during the sintering process. That is,
You may sinter while giving a compression process. In particular, it is suitable when the sheet-shaped molded product is a powdery product composed of only phosphor particles.

The layer thickness of the phosphor sheet thus formed varies depending on the intended characteristics of the radiation image conversion panel and the like, but is usually 20 μm to 1 mm. However, this layer thickness is 50
The thickness is preferably from 500 to 500 μm.

The relative density of the phosphor sheet formed by the above method can be theoretically determined by the following formula (I).

Vp / V = aA (a + b) ρxV −−− (I) (where V: total volume of phosphor layer Vp: volume of phosphor A: total weight of phosphor layer ρx: density of phosphor a: phosphor In the present invention, the relative density of the phosphor sheet is a value calculated by the formula (I). However, since the binder has disappeared in the phosphor sheet formed by sintering, b is ˜0.

Next, a support is provided on one surface of the formed phosphor sheet.

The support used in the present invention can be arbitrarily selected from various materials used as a support for intensifying screens in conventional radiography or various materials known as a support for radiographic image conversion panels. . Examples of such materials include cellulose acetate, polyester,
Films of plastic materials such as polyethylene terephthalate, polyamide, polyimide, triacetate, polycarbonate, metal sheets such as aluminum foil and aluminum alloy foil Ceramic plate, metal plate, ordinary paper, baryta paper, resin coated paper, pigment such as titanium dioxide Examples thereof include pigment paper and paper sized with polyvinyl alcohol contained therein. This support may be kneaded with a light absorbing substance such as carbon black, or may be kneaded with a light reflecting substance such as titanium dioxide. The former is a support suitable for a radiation image conversion panel of high sharpness type, and the latter is a support suitable for a radiation image conversion panel of high sensitivity type.

In a known radiation image conversion panel, a phosphor layer is provided in order to strengthen the bond between the support and the phosphor layer or to improve the sensitivity or image quality (sharpness, graininess) of the radiation image conversion panel. The surface of the support is coated with a polymeric substance such as gelatin to form an adhesion-imparting layer, or a light-reflecting layer made of a light-reflecting substance such as titanium dioxide, or a light-absorbing substance such as carbon black. Providing a light absorption layer is also performed. Also for the support used in the present invention, these various layers can be provided.

Further, as described in JP-A-58-200200, the surface of the support on the side of the phosphor layer (adhesiveness to the surface of the support on the side of the phosphor layer is used for the purpose of improving the sharpness of the image. When an imparting layer, a light reflecting layer, a light absorbing layer, or the like is provided, it means the surface thereof) and fine irregularities may be uniformly formed.

Usually, the support is attached to the phosphor sheet by applying an adhesive that is generally used on one side of the support and pressing one side of the phosphor sheet against the surface. When the sheet-shaped molding is provided on the substrate by coating, the phosphor sheet is separated from the substrate.

A transparent protective film is preferably provided on the surface of the phosphor sheet opposite to the side in contact with the support for the purpose of physically and chemically protecting the phosphor layer.

The transparent protective film may be, for example, a cellulose derivative such as cellulose acetate or nitrocellulose; or a synthetic polymer material such as polymethyl methacrylate, polyvinyl butyral, polyvinyl formal, polycarbonate, polyvinyl acetate, vinyl chloride / vinyl acetate copolymer. It can be formed by a method of applying a solution prepared by dissolving a transparent polymer substance in a suitable solvent onto the phosphor sheet. Alternatively, a plastic sheet made of polyethylene terephthalate, polyethylene, polyvinylidene chloride, polyamide, etc .; and a protective film forming sheet such as a transparent glass plate are separately formed and adhered to the surface of the phosphor sheet with an appropriate adhesive agent. It can also be formed by the method of. The thickness of the transparent protective film thus formed is preferably about 3 to 20 μm.

Next, examples and comparative examples of the present invention will be described. However,
Each of these examples does not limit the invention.

Example 1 Powdered divalent europium-activated barium fluorobromide phosphor particles (BaFBr: 0.001Eu ²⁺ ) were pressed into a molding die and molded into a sheet. Press the press molding machine (pressure: 10 ³
kg / cm ² , temperature: 25 ° C.).

Next, this was put into a high temperature electric furnace and sintered. Sintering was performed in a nitrogen gas atmosphere at a temperature of 750 ° C. for 1.5 hours. After sintering, the sintered product was taken out of the electric furnace and cooled to form a phosphor sheet having a thickness of 250 μm and composed only of the phosphor.

Polyethylene terephthalate (support, thickness: 250μ, kneaded with carbon black on one side of the obtained phosphor sheet
A support was attached by adhering m) using a polyester adhesive.

Further, a transparent film of polyethylene terephthalate (thickness: 12 μm, with a polyester-based adhesive applied) on the other surface (the surface opposite to the support) of the phosphor sheet with the adhesive layer side facing down. A transparent protective film was formed by placing and adhering.

In this way, a radiation image conversion panel composed of the support, the phosphor layer and the transparent protective film was produced.

[Example 2] to [Example 6] In Example 1, the molding conditions and sintering conditions were as follows:
By performing the same operation as in the method of Example 1 except that the molding pressure and the sintering temperature shown in the table were changed, various radiation images composed of the support, the phosphor layer and the transparent protective film were obtained. A conversion panel was manufactured.

[Example 7] Methyl ethyl ketone was added to a mixture of powdery divalent europium activated barium fluorobromide phosphor particles (BaFBr: 0.001Eu ²⁺ ) and an acrylic resin to contain the phosphor particles in a dispersed state. A dispersion liquid was prepared. Next, this dispersion is thoroughly stirred and mixed using a propeller mixer, the phosphor particles are uniformly dispersed, and the mixing ratio of the binder and the phosphor particles is 1:20, and the viscosity is 35 to 50 PS ( 25 ° C) coating solution was prepared.

Next, the obtained coating liquid was applied uniformly on a Teflon sheet placed horizontally using a doctor blade. After the application, the Teflon sheet on which the coating film was formed was placed in a dryer, and the temperature inside the dryer was gradually raised from 25 ° C to 100 ° C to dry the coating film. After drying, the coating film was peeled from the Teflon sheet, placed on a quartz plate, placed in a high temperature electric furnace, and the binder was diffused and further sintered. The initial vaporization of the binder was carried out in an air atmosphere at a temperature of 400 ° C. for 4 hours, and then the sintering was carried out in a nitrogen gas atmosphere at a temperature of 850 ° C. for 2 hours. The obtained sintered product was taken out of the electric furnace and cooled to form a phosphor sheet having a thickness of 250 μm and composed only of the phosphor.

Polyethylene terephthalate sheet with carbon black kneaded on one side of the obtained phosphor sheet (support, thickness: 2
A support was attached by adhering to (50 μm) with a polyester adhesive.

Further, a transparent film of polyethylene terephthalate (thickness: 12 μm, with a polyester adhesive) is provided on the other surface of the phosphor sheet (the surface opposite to the support) with the adhesive layer side facing down. A transparent protective film was formed by laying it down and adhering it.

In this way, a radiation image conversion panel composed of the support, the phosphor layer and the transparent protective film was produced.

[Example 8] In Example 7, instead of applying the coating solution on a Teflon sheet horizontally placed using a doctor blade, a stainless steel mold was placed on the Teflon sheet, and the dispersion liquid was poured into the mold to form a sheet. A radiation image conversion panel composed of a support, a phosphor layer, and a transparent protective film was manufactured by performing the same operations as in the method of Example 7 except that molding was performed.

Comparative Example 1 Mailyl ethyl ketone was added to a mixture of powdery divalent europium-activated barium fluorobromide phosphor particles (BaFBr: 0.001Eu ²⁺ ) and a linear polyester resin, and the degree of nitrification was further increased to 1
A dispersion containing phosphor particles in a dispersed state was prepared by adding 1.5% of nitrocellulose. Next, tricresyl phosphate, n-butanol, and methyl ethyl ketone were added to this dispersion, and the mixture was thoroughly stirred and mixed using a propeller mixer to uniformly disperse the phosphor particles, and to form a binder and phosphor particles. The mixing ratio is 1:20 and the viscosity is 25-35PS (25
(° C) was prepared.

Next, the obtained coating solution was uniformly applied onto a carbon black-kneaded polyethylene terephthalate sheet (support, thickness: 250 μm) placed horizontally on a glass plate using a doctor blade. After coating, the glass plate on which the coating film was formed was placed in a dryer, and the temperature inside the dryer was gradually raised from 25 ° C to 100 ° C to dry the coating film. Thus, a sheet having a support and a phosphor layer having a layer thickness of about 250 μm provided on the support was obtained.

Then, by placing a transparent film of polyethylene terephthalate (thickness: 12 μm, with a polyester adhesive) on the phosphor layer of the above-mentioned sheet with the adhesive layer side facing down, and bonding, A protective film was formed.

In this way, a radiation image conversion panel composed of the support, the phosphor layer and the transparent protective film was produced.

Comparative Example 2 Methyl ethyl ketone was added to a mixture of powdery divalent europium-activated barium fluorobromide phosphor particles (BaFBr: 0.001Eu ²⁺ ) and a linear polyester resin, and the degree of nitrification was further increased to 1
A dispersion containing phosphor particles in a dispersed state was prepared by adding 1.5% of nitrocellulose. Next, tricresyl phosphate, n-butanol, and methyl ethyl ketone were added to this dispersion, and the mixture was thoroughly stirred and mixed using a propeller mixer to disperse the phosphor particles uniformly, and to form a binder and phosphor particles. Mixing ratio is 1:20, viscosity is 25-35PS
A coating solution (25 ° C) was prepared.

Next, the obtained coating solution was uniformly applied onto a carbon black-kneaded polyethylene terephthalate sheet (support, thickness: 250 μm) placed horizontally on a glass plate using a doctor blade. Then, after coating, put the glass plate on which the coating film has been formed in the dryer, gradually increase the temperature inside the dryer from 25 ° C to 100 ° C, dry the coating film, and place it on the support. A sheet having a phosphor layer was obtained.

Then, the above sheet is pressed by a press molding machine (pressure: 10 kg / c
m ^{2 at} a temperature of 25 ° C.). Thus, a phosphor layer having a layer thickness of about 250 μm was obtained on the support.

Then, by placing a transparent film of polyethylene terephthalate (thickness: 12 μm, having a polyester adhesive) on the compression-treated phosphor layer with the adhesive layer side facing down and adhering , A transparent protective film was formed.

In this way, a radiation conversion panel composed of the support, the phosphor layer and the transparent protective film was produced.

[Comparative Example 3] to [Comparative Example 4] A support was prepared in the same manner as in the method of Comparative Example 2 except that the compression treatment was carried out at the pressures shown in Table 2 below. Various radiation image conversion panels composed of a phosphor layer and a transparent protective film were manufactured.

The relative density of the phosphor layer of each radiation image conversion panel manufactured as described above was calculated by using the above formula (I). Each density of the phosphor density and binder in this case is 5.18 g / cm ^3, was 1.15 g / cm ^3.

Next, each radiation image conversion panel was evaluated by performing the following sensitivity test.

The radiation image conversion panel was irradiated with X-rays with a tube voltage of 80 KVp, and then excited with He-Ne laser light (wavelength: 633 nm) to measure the sensitivity.

The results obtained are summarized in Table 3.

As is clear from the results shown in Table 3, the radiation image conversion panels (Examples 1 to 1) obtained by the sintering method of the present invention.
In 8), the sensitivity was remarkably improved as compared with the radiation image conversion panel (Comparative Example 1) obtained by the conventional coating method. On the other hand, the radiation image conversion panels (Comparative Examples 2 to 4) obtained by the known compression method had lower sensitivity than the radiation image conversion panels (Comparative Example 1) obtained by the coating method.

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Claims (5)

[Claims] 1. A radiation image conversion panel comprising a support and a phosphor layer made of a stimulable phosphor provided thereon, the phosphor layer having a relative density of 70% or more by sintering. A radiation image conversion panel comprising the phosphor sheet prepared as described above bonded to the surface of a support. 2. A phosphor sheet is molded into a sheet shape by previously pressing a powdery material comprising a stimulable phosphor into a mold,
The radiation image storage panel according to claim 1, which is obtained by sintering this. 3. A phosphor sheet is prepared by pouring a dispersion liquid containing a stimulable phosphor dispersed in a binder solution in advance into a mold.
Alternatively, the radiation image storage panel according to claim 1, which is obtained by applying the composition onto a flat plate to form a sheet, and then sintering the sheet. 4. The grain boundary size of the stimulable phosphor is 1 to 100 μm.
The radiation image conversion panel according to claim 1, which is within the range of m. 5. The radiation image storage panel according to claim 1, wherein the stimulable phosphor is a divalent europium-activated alkaline earth metal halide phosphor.