JPH0523640B2 - - Google Patents

Description

[Detailed description of the invention]

[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. More specifically, the present invention relates to a radiation image storage panel having a light reflecting layer between a support and a phosphor layer. [Technical Background of the Invention and Prior Art] As a method for obtaining radiation images as images, the so-called radiography method has conventionally used a combination of a radiographic film having an emulsion layer made of a silver salt photosensitive material and an intensifying screen. It's being used. Recently, a radiation image conversion method using a stimulable phosphor, as described in Japanese Patent Application Laid-open No. 55-12145, has been attracting attention as an alternative to the above-mentioned radiographic method. Summer. This radiation image conversion method uses a radiation image conversion panel (stimulable phosphor sheet) containing a stimulable phosphor. Accumulated in the stimulable phosphor by absorbing it into the stimulable phosphor and then exciting the stimulable phosphor with electromagnetic waves (excitation light) such as visible light or infrared rays in a time-series manner. Radiation energy is emitted as fluorescence (stimulated luminescence), this fluorescence is read photoelectrically to obtain an electrical signal, and the obtained electrical signal is converted into an image. This radiation image conversion method has the advantage that it is possible to obtain a radiation image with a rich amount of information with a much lower exposure dose than when using conventional radiography. Therefore, this radiation image conversion method has a very high utility value especially in direct medical radiography such as X-ray photography for the purpose of medical diagnosis. The basic structure of the radiation image conversion panel used in the radiation image conversion method is a support and a phosphor layer provided on one side of the support. Note that a transparent protective film is generally provided on the surface of the phosphor layer opposite to the support (the surface not facing the support) to protect the phosphor layer from chemical deterioration or Protects from physical impact. The phosphor layer usually consists of a stimulable phosphor and a binder that contains and supports the stimulable phosphor in a dispersed state.The stimulable phosphor absorbs radiation such as X-rays and then becomes visible. It has the property of emitting light (stimulated luminescence) when irradiated with electromagnetic waves (excitation light) such as 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 amount of radiation, and the radiation of the subject or subject is absorbed on the radiation image conversion panel. An image is formed as a cumulative image of radiation energy. This accumulated image can be emitted as stimulated luminescence by time-series excitation with the electromagnetic waves mentioned above, and by reading this stimulated luminescence photoelectrically and converting it into an electrical signal, the accumulated image of radiation energy can be imaged. It becomes possible to convert into The radiation image conversion method is a very advantageous image forming method as mentioned above, but the radiation image conversion panel used in this method is also highly sensitive and similar to the sensitizer used in conventional radiography. It is desired that the image quality (sharpness, graininess, etc.) is high and provides an image with good image quality (sharpness, graininess, etc.). In particular, when the subject is a human body, it is desired that the sensitivity of the panel be as high as possible in order to reduce the exposure dose as much as possible. Conventionally, techniques for improving the sensitivity of radiation image storage panels include vapor-depositing metals such as aluminum on the surface of the support, laminating metal foils such as aluminum foil, or adding white pigments (light-reflective substances). It is known to provide a light reflective layer on a support by coating a coating liquid dispersed in a suitable binder, and to provide a phosphor layer thereon. As white pigments, titanium dioxide, white lead, zinc sulfide, aluminum oxide, magnesium oxide, alkaline earth metal fluorohalides, etc. are used (Japanese Patent Application Laid-Open No. 12600/1983 and Patent Application No. 37838/1983). ). As a result, among the light emitted from the stimulable phosphor in the phosphor layer, the light directed toward the support is not absorbed by or transmitted through the support and is reflected by the light reflection layer. The reflected light is then reflected and emitted from the phosphor layer side surface of the panel, and this reflected light is also detected by the photoelectric conversion device and converted into an electrical signal. [Summary of the Invention] An object of the present invention is to provide a radiation image conversion panel with improved sensitivity. Another object of the present invention is to provide a radiation image conversion panel with improved sensitivity and graininess without substantially reducing image sharpness. The above object is to provide a radiation image conversion panel having, in this order, a support, a light-reflecting layer made of a supporting binder containing a light-reflecting substance in a dispersed state, and a phosphor layer containing a stimulable phosphor. This can be achieved by the radiation image conversion panel of the present invention, in which the light-reflecting layer contains hollow-structured polymer particles as a light-reflecting substance. That is, the present invention uses hollow-structured particles made of a polymer material instead of a conventional white pigment as a light-reflecting material used in the light-reflecting layer of a radiation image storage panel, thereby significantly improving the sensitivity of the panel. This will result in significant improvements. As a result of repeated research in order to prevent the stimulated luminescence light from the stimulable phosphor from scattering toward the support and disappearing, the present inventor created a large number of microscopic voids in a layer made of a polymeric material. The researchers discovered that the light reflection properties of the layer can be enhanced by taking advantage of the large difference in refractive index between the polymer material and air, and the formation of these minute voids can be reduced by forming hollow structured polymer particles. This was specifically achieved by dispersing it in the binder layer, and the present invention was achieved. According to the present invention, stimulated luminescence light directed toward the support is reflected at the boundary surface of the light reflecting layer due to the difference in refractive index between the polymer shell of the hollow particle and the air inside. It is emitted from the phosphor layer side surface of the panel (the readout side of the panel) and detected as image information. Until now, there are almost no polymer particles known to have a hollow structure, especially those with an outer diameter of 1 μm.
Only recently, such hollow polymer particles (polymer pigments) have been developed, although it has not been possible to obtain such microparticles. In the radiation image storage panel of the present invention, a coating liquid containing the hollow polymer particles dispersed in a suitable binder is applied onto the support, or a separately formed thin film in which the hollow polymer particles are dispersed is formed. By adhering using an adhesive, a binder layer having a large number of minute voids can be provided as a light reflecting layer. Accordingly, the sensitivity of the radiation image conversion panel can be increased. In particular, the hollow polymer particles used in the present invention have excellent reflective properties even in the short wavelength region of 300 to 450 nm, compared to white pigments such as titanium dioxide that have been conventionally used in light reflective layers. For this reason, as a stimulable phosphor for panels, divalent europium-activated alkaline earth metal fluorohalide phosphors (emission peak wavelength: approximately 390 nm) exhibit stimulated luminescence in the near-ultraviolet and visible regions. When using phosphors, the sensitivity of the panel can be significantly increased. Furthermore, compared to white pigments such as alkaline earth metal fluorohalides whose reflection spectra extend into the short wavelength region, the hollow polymer particles used in the present invention are fine particles by appropriately selecting the binder. The dispersibility does not deteriorate even if the resin is used, and since it is relatively inexpensive, the manufacturing cost of the panel can be reduced. Furthermore, since readout of a radiation image conversion panel is usually performed by irradiating excitation light in a time-series manner (scanning the panel with excitation light), the sharpness of the obtained image depends on the amount of stimulated luminescence light in the panel. It is affected not by the spread, but by the spread of the excitation light. In conventional radiation image conversion panels equipped with a light reflection layer, the excitation light that has passed through the phosphor layer is also reflected by the light reflection layer, which spreads out in the phosphor layer, resulting in an increase in sharpness. There was a tendency for images with a slightly lower quality to be obtained. However, according to the radiation image conversion panel of the present invention, sensitivity can be significantly increased without substantially reducing image sharpness. Furthermore, it is possible to significantly improve image graininess while improving sensitivity. In other words, if the image quality such as sensitivity and graininess is equivalent to that of conventional radiation image conversion panels, the thickness of the phosphor layer can be made thinner, and as a result, the sharpness can be increased. It is something that can be done. [Structure of the Invention] The radiation image conversion panel of the present invention having the preferable characteristics as described above can be manufactured, for example, by the method described below. The support used in the present invention can be arbitrarily selected from various materials used as supports for intensifying screens in conventional radiography methods or materials known as supports for radiation image conversion panels. . Examples of such materials include films of plastic materials such as cellulose acetate, polyester, polyethylene terephthalate, polyamide, polyimide, triacetate, polycarbonate, metal sheets such as aluminum foil, aluminum alloy foil, regular paper, baryta paper, resins, etc. Examples include coated paper, pigment paper containing pigments such as titanium dioxide, and paper sized with polyvinyl alcohol. However, when considering the characteristics and handling of the radiation image conversion panel as an information recording material,
A particularly preferred material for the support in the present invention is plastic film. This plastic film 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 high sharpness type radiation image conversion panel, and the latter is a support suitable for a high sensitivity type radiation image conversion panel. A polymeric substance such as gelatin is coated on the surface of the support to strengthen the bond with the light-reflecting layer provided on it to form an adhesion-imparting layer, or to improve the antistatic performance of the panel. in
An antistatic layer made of a conductive material such as In ₂ O ₃ or SnO ₂ may be provided. Next, a light reflective layer is provided on the support. The light-reflecting layer, which is a characteristic feature of the present invention, is a layer made of a binder containing and supporting polymer particles having a hollow structure in a dispersed state as a light-reflecting substance. The hollow structured polymer particles (polymer pigments) used in the present invention generally have an outer diameter of 0.2
~1μm range, and the small pore diameter (inner diameter)
These are fine particles in the range of 0.05 to 0.7 μm. A specific example of hollow polymer particles is styrene and/or acrylic monomers combined with a suitable crosslinking agent to form a spherical shell (core-shell polymerization).
Examples include styrene polymer particles and styrene/acrylic copolymer particles obtained by. Since these hollow polymer particles have voids inside, light passing through the polymer shell is diffusely reflected by the walls of the voids, and therefore has a white luster similar to that of inorganic pigments such as titanium dioxide. In addition, the reflection spectrum of hollow polymer particles ranges from the near-ultraviolet region to the visible region (long wavelength region of 300 nm or more).
Particularly in the near-ultraviolet region of 300 to 450 nm, it exhibits a high reflectance that cannot be obtained with white pigments such as titanium dioxide, which are conventionally known as light-reflecting substances used in light-reflecting layers. Therefore, the hollow polymer particles are particularly suitable as a light-reflecting material for a radiation image storage panel containing a stimulable phosphor that exhibits stimulated luminescence in the near-ultraviolet and visible regions. The light-reflecting layer is prepared by adding the hollow polymer particles described above to a suitable binder and mixing thoroughly to prepare a coating solution in which the hollow polymer particles are uniformly dispersed in the binder. When a coating film of the coating liquid is formed by applying the coating solution to the substrate, the coating film can be formed on the support by heating and drying the coating film. Alternatively, a coating liquid is separately applied onto a sheet such as a glass plate, metal plate, or plastic sheet and dried to form a thin film containing dispersed hollow polymer particles, and then this is bonded to a support using an adhesive. A light reflecting layer may also be provided. The binder for the light-reflecting layer can be selected from water-based polymeric substances such as acrylic acid ester copolymers, as well as those used as binders for the phosphor layer, which will be described later. The mixing ratio of the binder and the hollow polymer particles in the coating solution is generally selected from the range of 1:1 to 1:50 (weight ratio), and preferably 1:2 to 1 from the viewpoint of adhesion to the support. :20 (weight ratio). Note that a known light-reflecting substance such as a white pigment may be added to the coating liquid, and the light-reflecting layer formed may be made of a mixture of hollow polymer particles and a white pigment. For example, when mixed with titanium dioxide, the hollow polymer particles can fill the voids of the larger particle size titanium dioxide, increasing the shielding power over conventional titanium dioxide alone. Also,
The thickness of the light reflecting layer is preferably in the range of 5 to 100 μm. Further, as described in JP-A-58-200200, minute irregularities may be provided on the surface of the light reflecting layer for the purpose of improving sharpness. Next, a phosphor layer is formed on the light reflective layer.
The phosphor layer is basically a layer consisting of a binder containing and supporting particles of stimulable phosphor in a dispersed state. As mentioned above, a stimulable phosphor is a stimulable phosphor that exhibits stimulated luminescence when it is irradiated with radiation and then irradiated with excitation light, but from a practical standpoint, the wavelength
300~ by excitation light in the range of 400~900nm
A stimulable phosphor that exhibits stimulated luminescence in a wavelength range of 500 nm is desirable. Examples of the stimulable phosphor used in the radiation image conversion panel of the present invention include those described in U.S. Pat. No. 3,859,527.
SrS: Ce, Sm, SrS: Eu, Sm, ThO ₂ : Er, and La ₂ O ₂ S: Eu, Sm, described in JP-A-55-12142.
ZnS: Cu, Pb, BaO・xAl ₂ O ₃ : Eu (however, 0.8
≦x≦10), and M〓O・xSiO ₂ :A (however,
M〓 is Mg, Ca, Sr, Zn, Cd, or Ba,
A is Ce, Tb, Eu, Tm, Pb, Tl, Bi, or
(Ba _1-xy , Mg _x , Ca _y )FX: aEu ²⁺ (where X
is at least one of Cl and Br,
x and y are 0<x+y≦0.6 and xy≠0, and a is ^10-6 ≦a≦5× ^10-2 ), as described in JP-A-55-12144.
LnOX:xA (Ln is La, Y, Gd, and
At least one of Lu, X is at least one of Cl and Br, A is at least one of Ce and Tb, and x is 0<x<0.1
(Ba _1-x , M ²⁺ _x ) FX:yA (where M ²⁺² is Mg,
At least one of Ca, Sr, Zn, and Cd, X is 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; x is 0≦x≦0.6; y is 0≦y≦0.2);
FX・xA: yLn [However, M〓 is Ba, Ca, Sr,
At least one of Mg, Zn, and Cd, A
are BeO, MgO, CaO, SrO, BaO, ZnO,
Al ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ , In ₂ O ₃ , SiO ₂ , TlO ₂ ,
ZrO ₂ , GeO ₂ , SnO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , and
At least one of ThO ₂ , Ln is Eu, Tb,
Ce, Tm, Dy, Pr, Ho, Nd, Yb, Er, Sm,
and at least one of Gd, X is Cl,
At least one of Br, and I,
x and y are respectively 5×10 ^-5 ≦x≦0.5 and 0<y≦0.2] A stimulable phosphor is described in JP-A-56-116777 ( Ba _1-x , M〓 _x ) F ₂・aBaX ₂ :yEu, zA [however,
M〓 is beryllium, magnesium, calcium,
at least one of strontium, zinc, and cadmium; X is at least one of chlorine, bromine, and iodine; A is at least one of zirconium and scandium;
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 ] A photostimulable phosphor represented by the composition formula (Ba _1-x ,M〓 _x )F ₂・aBaX ₂ :yEu, zB [However,
M〓 is beryllium, magnesium, calcium,
at least one of strontium, zinc, and cadmium;
^10-6 ≦y≦2× ^10-1 , and 0<z≦2× ^10-1 ] A stimulable phosphor is described in JP-A-57-23675. (Ba _1-x , M〓 _x ) F ₂・aBaX ₂ :yEu, zA [However,
M〓 is beryllium, magnesium, calcium,
at least one of strontium, zinc, and cadmium; X is at least one of chlorine, bromine, and iodine; A is at least one of arsenic and silicon; a, x, y, and z are each 0.5 ≦a≦1.25, 0≦x≦1, 10 ^-6
≦y≦2×10 ^-1 and 0<z≦5×10 ^-1 ] A stimulable phosphor represented by the composition formula: M〓 described in JP-A-58-69281
OX: xCe [However, M〓 is Pr, Nd, Pm, Sm,
At least one trivalent metal selected from the group consisting of Eu, Tb, Dy, Ho, Er, Tm, Yb, and Bi, X is one or both of Cl and Br, and x is A stimulable phosphor represented by the composition formula: 0<x<0.1, described in JP-A-58-206678
Ba _1-x M _x/2 L _x/2 :yEu ²⁺ [However, M is Li, Na,
Represents at least one alkali metal selected from the group consisting of K, Rb, and Cs; L is Sc,
Y, La, Ce, Pr, Nd, Pm, Sm, Gd, Tb,
represents at least one trivalent metal selected from the group consisting of Dy, Ho, Er, Tm, Yb, Lu, Al, Ga, In, and Tl; X represents Cl, Br, and I;
represents at least one halogen selected from the group consisting of; and x is 10 ^-2 ≦x≦0.5, and y is 0<y≦0.1. Described in Publication No. 59-27980
BaFX・xA:yEu ²⁺ [However, 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; 10 ^-6 ≦x≦
0.1, y is 0<y≦0.1] A photostimulable phosphor is described in JP-A-59-27289.
BaFX・xA:yEu ²⁺ [However, X is at least one halogen selected from the group consisting of Cl, Br, and I; A is hexafluorosilicic acid,
x is a fired product of at least one compound selected from the hexafluoro compound group consisting of monovalent or divalent metal salts of hexafluorotitanic acid and hexafluorozirconic acid;
10 ^-6 ≦x≦0.1, y is 0<y≦0.1] A stimulable phosphor described in JP-A No. 59-56479
BaFX・xNaX′: aEu ²⁺ [However, X and X′ are
Each is at least one of Cl, Br, and I, and x and a are each 0<x≦2,
and 0<a≦0.2] A photostimulable phosphor represented by the composition formula M〓 described in JP-A No. 59-56480
FX・xNaX′: yEu ²⁺ : zA [However, M〓 is Ba,
at least one alkaline earth metal selected from the group consisting of Sr, and Ca;
X′ is at least one kind of halogen selected from the group consisting of Cl, Br, and I;
is at least one transition metal selected from V, Cr, Mn, Fe, Co, and Ni; and
A stimulable phosphor ^represented by the composition formula: Listed M〓
FX・aM〓X′・bM′〓X″ ₂・cM〓X ₃・xA：
yEu ²⁺ [where M〓 is at least one kind of alkaline earth metal selected from the group consisting of Ba, Sr, and Ca; M〓 is Li, Na, K, Rb, and Cs
is at least one kind of alkali metal selected from the group consisting of; M′〓 is at least one divalent metal selected from the group consisting of Be and Mg;
M〓 is at least one kind of trivalent metal selected from the group consisting of Al, Ga, In, and Tl; A is a metal oxide; X is at least one kind selected from the group consisting of Cl, Br, and I. X′, X″, and X are at least one kind of halogen selected from the group consisting of F, Cl, Br, and I; and a is 0≦a≦2, and 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≦
A stimulable phosphor represented by the composition formula: 0.2] M
X ₂・aM〓X′ ₂ :xEu ²⁺ [However, M〓 is at least one alkaline earth metal selected from the group consisting of Ba, Sr, and Ca;
and I, and X≠X'; and a is 0.1≦a≦10.0, and x is 0<x≦0.2]
A stimulable phosphor represented by the composition formula M〓FX・aM〓X′:xEu ²⁺ [However, M〓
is at least one alkaline earth metal selected from the group consisting of Ba, Sr and Ca; M〓 is Rb
and at least one alkali metal selected from the group consisting of Cs; X is Cl, Br and I
is at least one kind of halogen selected from the group consisting of; X' is at least one kind of halogen selected from the group consisting of F, Cl, Br and I;
and a and x are 0<a≦4.0 and 0<x≦0.2, respectively] A stimulable phosphor represented by the composition formula: M〓X:xBi [where M〓 is at least one kind of alkali metal selected from the group consisting of Rb and Cs; x is a numerical value in the range of 0<x≦0.2]. In addition, the M〓X ₂・aM〓X′ ₂ :xEu ²⁺ stimulable phosphor described in the above-mentioned Japanese Patent Application Laid-Open No. 60-84381 contains _the following additives.・aM〓X′ ₂ 1
It may be contained in the following proportions per mole. bM〓X″ (where M〓 is at least one kind of alkali metal selected from the group consisting of Rb and Cs, and X″ is F, Cl , Br and I, and b is 0<b≦10.0);
−bKX″/cMgX described in Publication No. 221483
₂・dM〓〓X′′′′′ ₃ (However, M〓 is Sc, Y, La,
is at least one trivalent metal selected from the group consisting of Gd and Lu; X″, X and X′′″ are all at least one halogen selected from the group consisting of F, Cl, Br and I; , and b, c and d are 0≦b≦2.0, 0≦
c≦2.0, 0≦d≦2.0, and 2×10 ^-5 ≦
b+c+d); yB described in the specification of Japanese Patent Application No. 59-84356 (however, y is 2×10 ^-4 ≦y≦
2×10 ^-1 ); bA described in Japanese Patent Application No. 59-84358 (However, A is SiO ₂ and P ₂ O ₅
bSiO as described in Japanese Patent Application No. ^59-240452 (however, bSiO is at least one kind of oxide selected from the group consisting ^of b is 0<b≦3×10 ^-2 ); bSnX″ ₂ described in Japanese Patent Application No. 59-240454 (however, and b is 0<b≦10 ^-3 ); bCsX″・cSnX ₂ (However, X″ and X
are at least one kind of halogen selected from the group consisting of F, Cl, Br and I, and b and c are respectively 0<b≦10.0 and
^10-6 ≦c≦2× ^10-2 )
bCsX″・yLn ³⁺ (However, X″ is at least one kind of halogen selected from the group consisting of F, Cl, Br and I, and Ln is Sc, Y, Ce, Pr, Nd, Sm,
At least one rare earth element selected from the group consisting of Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, and b and y are each 0<b≦
10.0 and 10 ^-6 ≦y≦1.8×10 ^-1 ). etc. can be mentioned. Among the above-mentioned stimulable phosphors, divalent europium-activated alkaline earth metal halide stimulable phosphors and rare earth element-activated rare earth oxyhalide stimulable phosphors exhibit high-intensity stimulated luminescence. Therefore, it is particularly preferable. However, the stimulable phosphor used in the present invention is not limited to the above-mentioned stimulable phosphor, but is a stimulable phosphor that exhibits stimulated luminescence when irradiated with radiation and then irradiated with excitation light. It can be any body. Examples of binders for the phosphor layer include proteins such as gelatin, polysaccharides such as dextran, or natural polymeric substances such as gum arabic; and polyvinyl butyral, polyvinyl acetate, nitrocellulose, ethylcellulose, and vinylidene chloride. - List binders represented by synthetic polymeric materials such as vinyl chloride copolymers, polyalkyl (meth)acrylates, vinyl chloride-vinyl acetate copolymers, polyurethanes, cellulose acetate butyrate, polyvinyl alcohol, linear polyesters, etc. I can do it. Particularly preferred among such binders are nitrocellulose, linear polyesters, polyalkyl (meth)acrylates, mixtures of nitrocellulose and linear polyesters, and mixtures of nitrocellulose and polyalkyl (meth)acrylates. be. Note that these binders may be crosslinked with a crosslinking agent. The phosphor layer can be formed on the light reflective layer, for example, by the following method. First, the above-mentioned stimulable phosphor and binder are added to a suitable solvent and thoroughly mixed to prepare a coating solution in which phosphor particles are uniformly dispersed in the binder solution. Examples of solvents for preparing coating solutions include lower alcohols such as methanol, ethanol, n-propanol, and n-butanol; chlorine-containing hydrocarbons such as methylene chloride and ethylene chloride; and ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone. ; esters of lower fatty acids and lower alcohols such as methyl acetate, ethyl acetate, and butyl acetate; ethers such as dioxane, ethylene glycol monoethyl ether, and ethylene glycol monomethyl ether; and mixtures thereof. The mixing ratio of the binder and the stimulable phosphor in the coating solution varies depending on the characteristics of the intended radiation image conversion panel, the type of phosphor, etc., but in general, the mixing ratio of the binder and the stimulable phosphor is , 1:1 to 1:100 (weight ratio), and particularly preferably 1:8 to 1:40 (weight ratio). The coating liquid also contains a dispersant to improve the dispersibility of the phosphor in the coating liquid, and a dispersant to improve the bonding force between the binder and the phosphor in the phosphor layer after formation. Various additives such as plasticizers may be mixed. Examples of dispersants used for such purposes include phthalic acid, stearic acid, caproic acid, lipophilic surfactants, and the like. Examples of plasticizers include phosphoric acid esters such as triphenyl phosphate, tricresyl phosphate, and diphenyl phosphate; phthalic acid esters such as diethyl phthalate and dimethoxyethyl phthalate; and ethyl phthalyl ethyl glycolate and butyl phthalyl butyl glycolate. Glycolic acid esters; and polyesters of polyethylene glycol and aliphatic dibasic acids, such as polyesters of triethylene glycol and adipic acid and polyesters of diethylene glycol and succinic acid. The coating solution containing the phosphor and binder prepared as described above is then uniformly applied to the surface of the light-reflecting layer to form a coating film of the coating solution.
This coating operation can be carried out using conventional coating means such as a doctor blade, roll coater, knife coater, etc. Then, the formed coating film is gradually heated and dried to complete the formation of the phosphor layer on the light reflective layer. The thickness of the phosphor layer varies depending on the characteristics of the intended radiation image conversion panel, the type of phosphor, the mixing ratio of binder and phosphor, etc., but usually
The thickness should be 20 μm to 1 mm. However, the thickness of this layer is preferably 50 to 500 μm. Note that the phosphor layer does not necessarily need to be formed by directly applying a coating liquid onto the light-reflecting layer as described above; for example, the coating liquid may be separately applied onto a sheet such as a glass plate, metal plate, or plastic sheet. After forming a phosphor layer by drying,
The light-reflecting layer and the phosphor layer may be joined by pressing onto the light-reflecting layer or using an adhesive. A transparent protective film may be provided on the surface of the phosphor layer opposite to the side in contact with the light reflection layer for the purpose of physically and chemically protecting the light reflection layer. The transparent protective film may be made of a transparent material such as 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, or vinyl chloride/vinyl acetate copolymer. It can be formed by coating the surface of the phosphor layer with a solution prepared by dissolving a polymeric substance in an appropriate solvent. Alternatively, it can also be formed by a method such as adhering a transparent thin film separately formed from polyethylene terephthalate, polyethylene, polyvinylidene chloride, polyamide, etc. to the surface of the phosphor layer using a suitable adhesive. The transparent protective film formed in this way preferably has a thickness of about 0.1 to 20 μm. In addition, JP-A-55-163500, JP-A-57-
As described in Japanese Patent No. 96300 and the like, the radiation image conversion panel of the present invention may be colored with a coloring agent, and the sharpness of the image obtained can be improved by coloring. Also, JP-A-55-
As described in Japanese Patent No. 146447, the radiation image conversion panel of the present invention may have white powder dispersed in its phosphor layer for the same purpose. Next, Examples and Comparative Examples of the present invention will be described.
However, these examples do not limit the invention. Example 1 Styrene/acrylic hollow polymer particles (VONCOAT PP-2000S, Dainippon Ink Chemical Co., Ltd.)
(manufactured by Toagosei Co., Ltd.) and an acrylic ester copolymer (Arontak A-2422H, manufactured by Toagosei Co., Ltd.) are thoroughly mixed to ensure that the hollow polymer particles are uniformly dispersed and the mixing ratio of the binder and the hollow polymer particles is adjusted. 1:5 (weight ratio)
A coating solution was prepared. This coating solution was applied uniformly onto a polyethylene terephthalate film (support, thickness: 250 μm) placed horizontally on a glass plate using a doctor blade. Then, the support on which the coating film was formed using the coating solution 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. In this way, a light reflecting layer with a layer thickness of 50 μm was provided on the support. Next, 90 parts by weight of vinyl acetate (manufactured by Kishida Chemical Co., Ltd.) and 10 parts by weight of nitrocellulose were mixed with a mixed solvent of ethanol and methyl ethyl ketone (mixing ratio: 7:
3), and further stimulable divalent europium activated barium fluoride bromide phosphor (BaFBr:Eu ²⁺ )
After adding the particles, thoroughly stir and mix using a propeller mixer to uniformly disperse the phosphor particles.
A coating liquid was prepared in which the mixing ratio of the binder and the phosphor was 1:20 (weight ratio) and the viscosity was 25 to 30 PS (at 25°C). This coating solution is applied on the light reflective layer by the same operation as above, and then dried to reduce the layer thickness.
A phosphor layer of 350 μm was formed. A transparent protective film is then formed by placing and adhering a polyethylene terephthalate film (thickness: 12 μm, coated with a polyester adhesive) on top of this phosphor layer with the adhesive layer side facing down. did. In this way, a radiation image storage panel was produced, which was composed of a support, a light reflection layer, a phosphor layer, and a transparent protective film. Comparative Example 1 A light-reflecting layer was formed on a support in the same manner as in Example 1 except that titanium dioxide was used instead of the styrene-acrylic hollow polymer particles. Next, by performing the same treatment as in Example 1 using the support provided with this light-reflecting layer, a radiation image composed of the support, the light-reflecting layer, the phosphor layer, and the transparent protective film is obtained. A conversion panel was manufactured. Next, each light reflection layer of Example 1 and Comparative Example was measured using a spectrophotometer (Hitachi Self-Recording Spectrophotometer Model 330).
The spectral reflectance was measured using The result is the first
They are summarized in the figure and Table 1. FIG. 1 shows: 1: Reflection spectrum of a light-reflecting layer made of hollow polymer particles 2: Reflection spectrum of a light-reflecting layer made of titanium dioxide.

[Table] From the results summarized in Figure 1 and Table 1,
The light reflection layer (Example 1) made of hollow polymer particles constituting the radiation image storage panel of the present invention has a reflection spectrum extending to the shorter wavelength side than the light reflection layer made of titanium dioxide (Comparative Example 1), especially
It was clear that it had excellent reflection properties in the near ultraviolet to visible region of 300 to 450 nm. In addition, each of the obtained radiation image conversion panels was evaluated by the sensitivity test, image sharpness test, and image graininess test described below. (1) Sensitivity test After irradiating the radiation image conversion panel with X-rays with a tube voltage of 80KVp, a He-Ne laser beam (wavelength:
The sensitivity was measured by excitation at 632.8 nm). (2) Image sharpness test After irradiating the radiation image conversion panel with X-rays with a tube voltage of 80KVp through a CTF chart,
The phosphor particles are excited by scanning with laser light, and the stimulated luminescence light emitted from the phosphor layer is received by a light receiver (photomultiplier tube with spectral sensitivity S-5) and converted into an electrical signal. was reproduced as an image by an image reproducing device to obtain an image of a CTF chart on a display device.
Contrast transfer function (CTF) from the obtained image
was measured and evaluated as a value at a spatial frequency of 2 cycles/mm. (2) Image graininess test The radiation image conversion panel was subjected to a tube voltage of 80KVp and a dose of
After irradiating with 100 mR of X-rays, the phosphor particles are excited by scanning with a He-Ne laser beam, and the stimulated luminescence light emitted from the phosphor layer is detected using a receiver (spectral sensitivity S-5).
The photomultiplier tube) receives the light and converts it into an electrical signal,
This was recorded on a regular photographic film using a film scanner, and the RMS of the resulting image at a photographic density D = 1.2 and a spatial frequency of 0.4 to 5 lines/mm.
I found the value. This RMS value was used as a measure of graininess. The results are summarized in Table 2. Note that the sensitivity and sharpness are expressed as relative values when the value of Comparative Example 1 is set to 100.

[Table] As is clear from the results shown in Table 2, the radiation image conversion panel of the present invention (Example 1) having a light reflection layer made of hollow polymer particles has a light reflection layer made of titanium dioxide. The sensitivity was significantly improved compared to the conventionally known radiation image conversion panel (Comparative Example 1). Furthermore, the panel of the present invention provided an image that had almost the same sharpness as a known panel and had significantly higher graininess.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the reflection spectrum 1 of a light reflection layer made of hollow polymer particles constituting the radiation image storage panel of the present invention, and the reflection spectrum 2 of a light reflection layer made of conventionally known titanium dioxide.

Claims (1)

[Scope of Claims] 1. A radiation image conversion panel comprising, in this order, a support, a light-reflecting layer made of a supporting binder containing a light-reflecting substance in a dispersed state, and a phosphor layer containing a stimulable phosphor. . A radiation image conversion panel, wherein the light-reflecting layer contains polymer particles having a hollow structure as a light-reflecting substance. 2 The outer diameter of the hollow structured polymer particles is 0.2~
Claim 1, characterized in that the pore diameter is in the range of 1 μm and the small pore diameter is in the range of 0.05 to 0.7 μm.
The radiation image conversion panel described in Section 1. 3. The radiation image storage panel according to claim 1, wherein the polymer particles having a hollow structure are styrene-based and/or acrylic-based polymers. 4. The radiation image storage panel according to claim 1, wherein the weight mixing ratio of the binder and the hollow polymer particles in the light reflecting layer is in the range of 1:1 to 1:50. 5. Claim 1, wherein the stimulable phosphor is a phosphor that exhibits stimulated luminescence in a wavelength range of 300 to 500 nm by excitation light in a wavelength range of 400 to 900 nm. The radiographic image conversion panel described. 6. The radiation image conversion panel according to claim 5, wherein the stimulable phosphor is a divalent europium activated alkaline earth metal halide phosphor. 7. The radiation image conversion panel according to claim 5, wherein the stimulable phosphor is a rare earth element-activated rare earth oxyhalide phosphor.