JP2002131493A - Radiation image conversion panel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiation image conversion panel preventing degradation of sharpness due to laser light for excitation and improved in brightness. SOLUTION: The radiation image conversion panel is composed of a phosphor sheet layered with a reflection layer 13 on the support body 14, an excited light absorption layer A12 colored so as to absorb the excited light and a stimulable phosphor layer 11 in this order and a protection film 15 provided so as to cover the phosphor surface of the sheet. The protection film has a colored excited light absorption layer B. In each of the excited light absorption layers A and B, the absorbance for the peak wavelength of luminescence of stimulable phosphor is smaller than that for the peak wavelength of the excited light and the thicknesses of the excited light absorption layers A and B are A>B.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation image conversion panel using a stimulable phosphor, and more particularly, to a radiation image conversion panel having a high balance of light emission luminance and sharpness and high uniformity of light emission. It is about.

[0002]

2. Description of the Related Art Radiation images such as X-ray images are widely used for diagnosis of diseases. In order to obtain this X-ray image, the X-rays that have passed through the subject are applied to a phosphor layer (fluorescent screen).
Thus, a so-called radiograph is used, in which a visible light is generated by this, and this visible light is irradiated and developed on a film using a silver salt in the same manner as when a normal photograph is taken. However, in recent years, a method has been devised for directly taking out an image from the phosphor layer without using a film coated with a silver salt.

In this method, radiation transmitted through a subject is absorbed by a phosphor, and then the phosphor is excited by, for example, light or heat energy, so that the radiation energy accumulated by the phosphor is absorbed by the phosphor. Then, there is a method of detecting and imaging this fluorescence.

Specifically, for example, US Pat.
There is known a radiation image conversion method using a stimulable phosphor as described in JP-A No. 527 and JP-A-55-12144.

In this method, a radiation image conversion panel containing a stimulable phosphor is used. Radiation transmitted through a subject is applied to the stimulable phosphor layer of the radiation image conversion panel to transmit radiation of each part of the subject. By accumulating radiation energy corresponding to the density, and subsequently exciting the stimulable phosphor with electromagnetic waves (excitation light) such as visible light and infrared light in a time series manner, the stimulable phosphor is accumulated in the stimulable phosphor. The emitted radiation energy is emitted as stimulated emission, and a signal based on the intensity of the light is photoelectrically converted, for example, to obtain an electric signal, and this signal is converted into a visible image on a recording material such as a photosensitive film or a display device such as a CRT. Is to be played as

According to the above radiation image recording / reproducing method,
Compared with the conventional radiographic method using a combination of a radiographic film and an intensifying screen, there is an advantage that a radiographic image rich in information can be obtained with a much smaller exposure dose.

As described above, the stimulable phosphor is a phosphor that emits stimulable light when irradiated with radiation and then with excitation light. However, in practice, excitation light having a wavelength in the range of 400 to 900 nm is used. In general, phosphors exhibiting stimulated emission in the wavelength range of 300 to 500 nm are used.

The following are examples of stimulable phosphors conventionally used in radiation image conversion panels.

(1) As described in JP-A-55-12145.
(Ba_1-x, M (II)_x) FX: yA (just
And M (II) is a catalyst for Mg, Ca, Sr, Zn and Cd.
At least one of X, Cl, Br, and I
At least one A is Eu, Tb, Ce, Tm, Dy,
At least one of Pr, Ho, Nd, Yb, and Er
And x is 0 ≦ x ≦ 0.6, y is 0 ≦ y ≦
0.2) is a rare earth element activated aluminum represented by the composition formula
Potassium earth metal fluoride halide phosphor;
The body may contain the following additives:
X 'and B described in JP-A-56-74175.
eX ″, M (III) X ′ ″_Three(However, X ', X "and
And X ′ ″ are at least one of Cl, Br and I, respectively.
Is also a kind, and M (III) is a trivalent metal);
BeO, M described in JP-A-55-160078
gO, CaO, SrO, BaO, ZnO, Al_TwoO_Three, Y
_TwoO_Three, La_TwoO_Three, In_TwoO_Three, SiO_Two, TiO_Two, ZrO
_Two, GeO_Two, SnO_Two, Nb_TwoO_Five, Ta_TwoO_FiveAnd Th
O_TwoMetal oxides such as; JP-A-56-116777
Zr and Sc described in Japanese Patent Application Laid-Open No. 57-2367.
B described in JP-A-3; JP-A-57-23675.
And Si described in JP-A-58-20
No. 6678 (where M is
Selected from the group consisting of Li, Na, K, Rb, and Cs
L is Sc,
Y, La, Ce, Pr, Nd, Pm, Sm, Gd, T
b, Dy, Ho, Er, Tm, Yb, Lu, Al, G
at least selected from the group consisting of a, In, and Tl
Is also a kind of trivalent metal); JP-A-59-27980
Of tetrafluoroborate compound described in the official gazette
Product: described in JP-A-59-27289
Hexafluorosilicic acid, hexafluorotitanic acid and
Monovalent or divalent metal hexafluorozirconate
Calcined product of salt; described in JP-A-59-56479.
NaX '(where X' is Cl, Br and I
At least one of the following): JP-A-59-564
No. 80, V, Cr, Mn, Fe, C
transition metals such as o and Ni;
(I) X ', M (II) described in
X "_Two, M (III) X '"_Three, A (where M (I) is L
selected from the group consisting of i, Na, K, Rb, and Cs
M (II) is B at least one alkali metal
at least one selected from the group consisting of e and Mg
M (III) is Al, Ga, In, and divalent metal.
At least one trivalent selected from the group consisting of
A is a metal oxide, X ′, X ″, and
X '"is a group consisting of F, Cl, Br and I, respectively.
Selected from at least one halogen);
M (I) described in JP-A-60-101173
X '(where M (I) is a group consisting of Rb and Cs
At least one alkali metal selected from the group consisting of X ′
Is a small number selected from the group consisting of F, Cl, Br and I
At least one type of halogen);
M (II) 'X' described in JP-A-9_Two・ M (I
I) 'X'_Two(Where M (II) 'is Ba, Sr and C
at least one alkaline earth selected from the group consisting of
X ′ and X ″ are Cl, Br and
At least one halogen selected from the group consisting of
And X ′ ≠ X ″);
LnX ″ described in 1-264084_Three
(However, Ln is Sc, Y, La, Ce, Pr, Nd,
Pm, Sm, Gd, Tb, Dy, Ho, Er, Tm, Y
at least one member selected from the group consisting of b and Lu
A rare earth element, X ″ is from F, Cl, Br and I
At least one halogen selected from the group consisting of
(2) described in JP-A-60-84381.
M (II) X_Two・ AM (II) X '_Two: XEu²⁺(However, M
(II) is selected from the group consisting of Ba, Sr and Ca
At least one alkaline earth metal, X and
X 'is a small number selected from the group consisting of Cl, Br and I
At least one kind of halogen and X ≠ X ′,
A is 0.1 ≦ a ≦ 10.0, x is 0 <x ≦ 0.2
Is a divalent europium activated aluminum represented by the composition formula
Potassium earth metal halide phosphor;
May contain the following additives;
M (I) X 'described in JP-A-166379.
(However, M (I) is selected from the group consisting of Rb and Cs.
X 'is at least one alkali metal;
At least one selected from the group consisting of F, Cl, Br and I
Are also a kind of halogen);
KX ", MgX" "described in Japanese Patent Publication No. 3_Two, M (I
II) X ""_Three(However, M (III) is Sc, Y, La, G
at least one member selected from the group consisting of d and Lu
X ", X" "and X" "are all trivalent metals
At least one selected from the group consisting of F, Cl, Br and I
Are also a kind of halogen);
B described in Japanese Patent Publication No. 2;
SiO described in Japanese Patent Publication No. 3_Two, P_TwoO_FiveOxidation of etc.
Product: described in JP-A-61-120882
LiX ″, NaX ″ (where X ″ is F, Cl, Br, etc.)
At least one halogen selected from the group consisting of
Described in JP-A-61-120883.
SiO: described in JP-A-61-120885
SnX "on the list_Two(However, X ″ is F, Cl, B
at least one member selected from the group consisting of r and I
Described in JP-A-61-235486.
CsX ", SnX" "listed_Two(However, X "
And X '"each consist of F, Cl, Br and I
At least one halogen selected from the group);
And JP-A-61-235487.
CsX ″, Ln³⁺(However, X ″ is F, Cl, Br and
At least one halogen selected from the group consisting of
Ln is Sc, Y, Ce, Pr, Nd, Sm, G
d, Tb, Dy, Ho, Er, Tm, Yb and Lu
At least one rare earth element selected from the group consisting of
(3) described in JP-A-55-12144.
LnOX: xA (where Ln is La, Y, Gd, and
And Lu, X is Cl, Br, and
A is at least one of I, A is a small number of Ce and Tb
At least one, and x is 0 <x <0.1)
Rare earth element activated rare earth oxyhalai represented by the composition formula:
(4) described in JP-A-58-69281
M (II) OX: xCe (where M (II) is Pr, N
d, Pm, Sm, Eu, Tb, Dy, Ho, Er, T
at least selected from the group consisting of m, Yb, and Bi
Are also a type of metal oxide, where X is Cl, Br, and I
X is at least 0 <x <0.1
Activated cerium-activated trivalent metal oxyhalides represented by the following formula:
(5) described in JP-A-62-25189.
M (I) X: xBi (where M (I) is Rb and
At least one alkali selected from the group consisting of Cs
X is selected from the group consisting of Cl, Br and I
At least one halogen; and x is 0
<X ≦ 0.2).
Bismuth-activated alkali metal halide phosphor; (6) described in JP-A-60-141783
M (II)_Five(PO_Four) _ThreeX: xEu²⁺(However, M (I
I) is a small number selected from the group consisting of Ca, Sr and Ba.
At least a kind of alkaline earth metal, X is F, C
at least one selected from the group consisting of l, Br and I
X is a numerical value in the range of 0 <x ≦ 0.2
Is a divalent europium activated aluminum represented by the composition formula
Potassium earth metal halophosphate phosphor; (7) described in JP-A-60-157099
M (II)_TwoBO_ThreeX: xEu²⁺(However, M (II) is C
at least one selected from the group consisting of a, Sr and Ba
X is Cl, Br and
At least one halogen selected from the group consisting of I
And x is a numerical value in the range of 0 <x ≦ 0.2)
Bivalent europium-activated alkaline earth metal represented by the formula
(8) Loborate phosphors described in JP-A-60-157100
M (II)_Two(PO_Four) X: xEu²⁺(However, M (II)
Is at least one selected from the group consisting of Ca, Sr and Ba.
Are a kind of alkaline earth metal, X is Cl, Br and
At least one halogen selected from the group consisting of
And x is a numerical value in the range of 0 <x ≦ 0.2)
Bivalent europium activated alkaline earth gold represented by the composition formula
Genus halophosphate phosphors; (9) described in JP-A-60-217354
M (II) HX: xEu²⁺(However, M (II) is Ca,
At least one selected from the group consisting of Sr and Ba
X is Cl, Br and I
At least one halogen selected from the group consisting of
Where x is a numerical value in the range of 0 <x ≦ 0.2)
Divalent europium-activated alkaline earth metal hydrogen represented by
(10) described in JP-A-61-21173.
LnX_Three・ ALn'X '_Three: XCe³⁺(However, Ln
And Ln 'consist of Y, La, Gd and Lu, respectively.
At least one rare earth element selected from the group consisting of
X and X 'each consist of F, Cl, Br and I
At least one halogen selected from the group consisting of
And X ≠ X ′, and a is 0.1 <a ≦ 10.0
X is a numerical value in the range of 0 <x ≦ 0.2
Cerium-activated rare earth composite represented by the composition formula
(11) described in JP-A-61-21182.
LnX_ThreeAM (I) X ': xCe³⁺(However, Ln
Is a small number selected from the group consisting of Y, La, Gd and Lu.
At least one kind of rare earth element, M (I) is Li, N
a selected from the group consisting of a, K, Cs and Rb
X and X 'are each a kind of alkali metal.
At least selected from the group consisting of Cl, Br and I
Is also a kind of halogen, and a is 0 <a ≦ 10.0
X is a numerical value in the range of 0 <x ≦ 0.2
Cerium-activated rare earth composite represented by the composition formula
(12) described in JP-A-61-40390.
LnPO_Four・ ALnX_Three: XCe³⁺(However, Ln is
A small number selected from the group consisting of Y, La, Gd and Lu
At least one kind of rare earth element, X is F, Cl, Br and
At least one halogen selected from the group consisting of
And a is a number in the range of 0.1 ≦ a ≦ 10.0
X is a numerical value in the range of 0 <x ≦ 0.2)
Cerium-activated rare earth halophosphate fluorescence expressed by composition formula
(13) described in JP-A-61-236888.
CsX: aRbX ': xEu²⁺(However, X and
And X 'are selected from the group consisting of Cl, Br and I, respectively.
At least one halogen, and a is 0
<A ≦ 10.0 and x is 0 <x ≦ 0.
Divalent euro represented by the composition formula of 2)
(14) Pium-activated cesium rubidium halide phosphor described in JP-A-61-236890.
M (II) X_TwoAM (I) X ': xEu²⁺(However
M (II) is selected from the group consisting of Ba, Sr and Ca.
At least one alkaline earth metal,
(I) is selected from the group consisting of Li, Rb and Cs
X and X 'are at least one alkali metal
Each selected from the group consisting of Cl, Br and I
At least one kind of halogen, and a is 0.1 ≦ a
≦ 20.0, where x is 0 <x ≦ 0.2
Divalent europium represented by the composition formula
Activated complex halide phosphors;
You.

Among the above stimulable phosphors, a divalent europium-activated alkaline earth metal fluorohalide-based phosphor containing iodine and a divalent europium-activated alkaline earth metal halide containing iodine The iodine-containing rare earth element-activated rare earth oxyhalide-based phosphor and the iodine-containing bismuth-activated alkali metal halide-based phosphor exhibit high luminance stimulable luminescence.

A radiation image conversion panel using these stimulable phosphors emits stored energy by scanning with excitation light after accumulating radiation image information. Therefore, the radiation image can be accumulated again after scanning. It can be used repeatedly. In other words, the conventional radiographic method consumes radiographic film for each photographing, whereas the radiographic image conversion method uses the radiographic image conversion panel repeatedly, which is advantageous in terms of resource conservation and economic efficiency. It is.

Therefore, it is desirable to provide the radiation image conversion panel with a performance that can be used for a long period of time without deteriorating the image quality of the obtained radiation image.

However, the stimulable phosphor used in the manufacture of the radiation image conversion panel generally has a large hygroscopic property, and when left in a room under ordinary climatic conditions, absorbs the moisture in the air and deteriorates significantly with the passage of time. I do.

Specifically, for example, when a stimulable phosphor is placed under high humidity, the radiation sensitivity of the phosphor decreases with an increase in absorbed water. In general, since the latent image of a radiation image recorded on a stimulable phosphor regresses with the passage of time after irradiation, the intensity of the reproduced radiation image signal ranges from irradiation to scanning by excitation light. The longer the time is, the smaller the size of the latent image becomes. However, when the stimulable phosphor absorbs moisture, the regression of the latent image is accelerated. Therefore, when a radiation image conversion panel having a stimulable phosphor that has absorbed moisture is used, the reproducibility of a reproduction signal at the time of reading a radiation image is reduced.

Conventionally, in order to prevent the above-mentioned deterioration phenomenon due to moisture absorption of the stimulable phosphor, the stimulable phosphor layer is reached by covering the stimulable phosphor layer with a moisture-proof protective layer having low moisture permeability. A method of reducing moisture has been adopted. As the moisture-proof protective layer, a polyethylene terephthalate (PET) film, a polyethylene terephthalate film, a polyethylene terephthalate (PET) film, 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 is used.

As a light source of the excitation light of the stimulable phosphor plate, a laser beam having a high beam convergence is generally used. When the laser beam is scanned through a protective layer made of a polymer film such as PET, Due to the scattering of the excitation laser light inside the protective layer film, and the irregular reflection of the excitation laser light between the protective layer and the photodetector and peripheral members, the stimulable phosphor surface at a place away from the place where the excitation light was scanned is changed. The sharpness is reduced due to excitation and emission of stimulated emission. Further, even when the phosphor plate does not have a protective layer, there is a problem that high sharpness cannot be obtained due to irregular reflection of the excitation laser light between the phosphor plate surface and the photodetector or at a peripheral member.

In particular, a stretched film such as a polyethylene terephthalate film or a polyethylene naphthalate film has a large refractive index despite having excellent physical properties as a protective layer in terms of transparency, barrier properties and strength. Therefore, part of the excitation light incident on the inside of the protective film is repeatedly reflected at the upper and lower interfaces of the film and propagates to a place away from the scanned position, emits photostimulated light and reduces sharpness. Also, the excitation light reflected in the opposite direction to the phosphor surface at the upper and lower interfaces of the protective layer is re-reflected between the photodetectors and peripheral members, and the stimulable phosphor surface at a position farther from the scanned position is reflected. This excites and emits stimulated emission, which further reduces sharpness. Excitation light is coherent light of long wavelength from red to infrared, so the amount absorbed in the protective film and the space inside the reader is small unless it actively absorbs scattered light and reflected light. And it deteriorates sharpness.

When a film such as a polyethylene terephthalate film or a polyethylene naphthalate film is used as a protective layer, shading other than a radiographic image of a subject, that is, image unevenness, or a linear pattern considered to be caused during the manufacturing process of the protective layer. There is also a problem that noise and the like appear. For these image unevenness and linear noise,
JP-A-59-42500 and Japanese Patent Publication No. 1-57759 disclose means for increasing the haze ratio of the protective layer to eliminate such image unevenness and linear noise. However, there is a disadvantage that sharpness is reduced when the haze ratio of the protective layer is increased.

In order to prevent the sharpness from deteriorating, a method of thinning the protective film and shortening the propagation distance of the excitation light inside the protective film is conceivable, but the effect is small, and conversely, the protective layer is made thinner. The problem is a decrease in moisture resistance and scratch resistance.
Regarding the improvement of sharpness, Japanese Patent Publication No. 59-23400 discloses a method of coloring any one of a support, a subbing layer, a phosphor layer, an intermediate layer, and a protective layer of a radiation image conversion panel with a color absorbing excitation light. Japanese Patent Application Laid-Open No. 60-200200 discloses a method of coloring an adhesive layer between a phosphor layer and a protective layer. However, when sharpness is enhanced by these methods, the above-mentioned image unevenness and linear noise are more remarkable. There is a problem that becomes.

When the sharpness is deteriorated, or the image unevenness or the linear noise is severe, it is a fatal defect for the radiation image conversion panel used for diagnosing a disease.

[0021]

SUMMARY OF THE INVENTION An object of the present invention is to provide a radiation image conversion panel in which sharpness caused by an excitation laser beam is prevented and luminance is improved.

[0022]

The above objects of the present invention have been attained by the following constitutions.

1. A phosphor sheet, in which a reflective layer, an excitation light absorbing layer A colored to absorb excitation light, and a stimulable phosphor layer are laminated in this order on a support, is provided so as to cover the phosphor surface of the phosphor sheet. In the radiation image conversion panel composed of the obtained protective film, the protective film has a colored excitation light absorbing layer B, and in each of the excitation light absorbing layers A and B, the absorbance at the peak wavelength of the excitation light is more than A radiation image conversion panel, wherein the absorbance at the emission peak wavelength of stimulated emission is smaller, and the thickness of the excitation light absorbing layers A and B is A> B.

2. A phosphor sheet in which an excitation light absorbing layer A colored to absorb excitation light and a stimulable phosphor layer are laminated in this order on a foamable polyethylene terephthalate support containing a large number of air bubbles; A radiation image conversion panel comprising a protective film provided so as to cover a phosphor surface of a sheet, wherein said protective film has an excitation light absorbing layer B colored so as to absorb excitation light, and said excitation light absorbing layer In each of A and B, the absorbance at the emission peak wavelength of the stimulated emission is smaller than the absorbance at the peak wavelength of the excitation light, and the thickness of the excitation light absorbing layers A and B is A> B. Radiation image conversion panel.

3. The light reflectance of the reflection layer and the excitation light absorption layer A at the peak wavelength of the excitation light is 97% to 50% with respect to the light reflection layer in the case where the excitation light absorption layer A is not provided, and the film thickness is 2 μm or more and 50 μm. 3. The radiation image conversion panel according to the above item 1 or 2, wherein:

4. The light transmittance at the peak wavelength of the excitation light of the protective film having the excitation light absorbing layer B is 97% or more of the light transmittance of the protective film having no excitation light absorbing layer B.
Any one of the above 1 to 3, characterized in that it is 50%
A radiation image conversion panel according to the item.

5. 5. The radiation image conversion panel according to any one of items 1 to 4, wherein the stimulable phosphor is Eu-activated BaFI.

Hereinafter, the present invention will be described in more detail. The protective film of the present invention includes a polyester film, a polymethacrylate film, a nitrocellulose film having an excitation light absorbing layer, having a haze ratio measured by the method described in ASTM D-1003 of 5 or more and less than 60%.
Although a cellulose acetate film or the like can be used, a stretched film such as a polyethylene terephthalate film or a polyethylene naphthalate film is preferable as a protective film in terms of transparency and strength, and in particular, these polyethylene terephthalate films and polyethylene naphthalate films A vapor-deposited film in which a thin film of a metal oxide, silicon nitride, or the like is vapor-deposited thereon is more preferable from the viewpoint of moisture resistance.

The excitation light absorbing layer B colored so as to absorb the excitation light referred to in the present invention is a layer containing a colorant which selectively absorbs the excitation light, and is one of the protective films. It may be coated on the surface, may be coated on both surfaces, or the protective film itself may be colored.

The light transmittance of the excitation light absorbing layer B and the protective film at the peak wavelength of the excitation light is 97% to 50% of the light transmittance of the equivalent protective film having no excitation light absorbing layer B.
Means that the transmittance is 97% to 50% with respect to the transmittance at the same wavelength of the uncolored excitation light absorbing layer B and the protective film having the same configuration except that the excitation light absorbing layer B is not provided. .

In the light absorbing layer B, it is necessary that the absorbance at the emission peak wavelength of the stimulated emission is smaller than the absorbance at the peak wavelength of the excitation light. It is preferable that the difference in absorbance is large.

When a phosphor having a plurality of peaks is used for the stimulated emission, the emission peak wavelength of the stimulated emission refers to the wavelength of the emission peak having the highest intensity.

The protective film used in the present invention has an optimum moisture-proof property by laminating a plurality of resin films or vapor-deposited films obtained by depositing a metal oxide or the like on the resin film in accordance with the required moisture-proof property. However, considering the moisture absorption deterioration of the stimulable phosphor, at least JIS Z
The moisture permeability defined by 0208 is 50 g / m ² · day
The following is preferred.

As the resin film, for example, polyethylene terephthalate (PET) or the like is preferably used, and as an example of the film on which metal oxide is deposited, there is alumina-deposited polyethylene terephthalate (PET) or the like.

As a method for laminating the resin film, any generally known method may be used. There is a method of laminating resin films using dry lamination using a two-component reaction type urethane adhesive or the like.

In this case, by providing the excitation light absorbing layer B between the laminated resin films, the excitation light absorbing layer is protected from physical impact and chemical deterioration, and stable plate performance can be maintained for a long time. . The excitation light absorbing layer may be provided at a plurality of locations, or the adhesive layer for lamination may contain a coloring agent to form the excitation light absorbing layer.

In sealing the phosphor sheet with the protective film, any known method may be used.
By making the outermost resin layer on the side of the moisture-proof protective film that is in contact with the phosphor sheet a resin film having heat-fusibility, the moisture-proof protective film can be fused and the sealing work of the phosphor sheet is made more efficient. You.

[0038] Preferably, a moisture-proof protective film is disposed above and below the phosphor sheet, and the upper and lower moisture-proof protective films are fused in a region where the peripheral edge is outside the peripheral edge of the phosphor sheet. With this structure, it is possible to prevent moisture from entering from the outer peripheral portion of the phosphor sheet. Further, the infiltration of moisture can be reduced more reliably by forming the moisture-proof protective film on the support surface side as a laminated moisture-proof film formed by laminating one or more aluminum films. This sealing method is also easy in terms of work. FIG. 1A is a cross-sectional view of the radiation image conversion panel of the present invention manufactured as described above. Also, FIG.
(B) is a cross-sectional view of the radiation image conversion panel of the present invention using a foamable polyethylene terephthalate described later as a support.

The term "heat-fusible film" as used herein refers to a resin film which can be fused with a generally used impulse sealer, such as ethylene vinyl acetate copolymer (EVA), polypropylene (PP) film, polyethylene (PE). ) Films, etc., but are not limited thereto.

In this case, the outermost layer of the heat-fusible resin layer on the side in contact with the phosphor surface of the moisture-proof protective film may or may not be adhered.

The state of non-adhesion means that the phosphor surface and the moisture-proof protective film are optically and mechanically almost completely invisible even if the phosphor surface and the moisture-proof protective film are in point contact with each other microscopically. It can be treated as a continuum.

The haze ratio of the protective film can be easily adjusted by selecting the haze ratio of the resin film used. A resin film having an arbitrary haze ratio is industrially easily available.

As the protective film of the radiation image conversion panel, a material having very high optical transparency is preferable. As such a protective film material having high transparency, a plastic having a haze value in the range of 2 to 3% is used. Various films are commercially available.

JP-A-59-42500 and JP-B-1-5
No. 7759 discloses means for increasing the haze ratio of the protective film to eliminate image unevenness and linear noise, but the sharpness is reduced. According to the present invention, image unevenness and linear noise can be eliminated, and the sharpness can be further improved.

The haze ratio for obtaining the effect of the present invention is preferably 5% or more and less than 60%, more preferably 10% or more and less than 50%.

When the haze ratio is less than 5%, the effect of eliminating image unevenness and linear noise is small, and when it is 60% or more, the sharpness improving effect of the present invention is small.

A method of improving the sharpness by coloring the radiation image conversion panel is described in JP-B-59-23400, which describes the method of forming the support, undercoat layer, phosphor layer, intermediate layer and protective layer of the radiation image conversion panel. Although described as an example of various embodiments in which each layer is colored, there is no description or suggestion of a specific protective film.

It was found that when a dye was simply contained in the phosphor layer, the sharpness was improved, but the luminance was deteriorated. As a result of various studies, we have found that a protective film having a colored layer (excitation light absorbing layer B) provided to absorb the excitation light and a (colored) excitation light absorbing layer A between the phosphor layer / reflection layer. Simultaneously, the thickness and the thickness of the excitation light-absorbing layer A> the excitation light-absorbing layer B in the protective film were simultaneously improved to improve the brightness and sharpness at the same time, resulting in a more uniform image.

When the film thickness is such that the excitation light absorbing layer A <the excitation light absorbing layer B
In such a case, it is easy to generate luminance unevenness, and it is difficult to obtain a uniform image.

In the above radiation image conversion panel, the excitation light absorbing layer A preferably has a light reflectance at a peak wavelength of the excitation light when the reflection layer and the excitation light absorbing layer A are laminated. If you do not have A, 9
It is preferable that the thickness is 7% to 50%, and the thickness of the excitation light absorbing layer A is 2 μm or more and 50 μm or less. When the light reflectance is 97% or more, the effect of the present invention is small, and is 50%.
Below, the brightness of the radiation image conversion panel rapidly decreases. The fact that the luminance is not significantly reduced at a light reflectance of 50% or more is related to the fact that the information of the radiation image recorded on the radiation image conversion panel is unevenly distributed on the phosphor plate surface side. Guessed.

Also in the light absorbing layer A, it is necessary that the absorbance at the emission peak wavelength of the stimulated emission is smaller than the absorbance at the peak wavelength of the excitation light. The difference is preferably large.

The colorant used for the excitation light absorbing layer B in the protective film of the radiation image conversion panel of the present invention and the excitation light absorption layer A used together with the reflection layer in the radiation image conversion panel includes the radiation image conversion panel Those having a characteristic of absorbing the excitation light in the wavelength region of the excitation light are used, and as described above, the absorbance at the emission peak wavelength of the stimulated emission is smaller than the absorbance at the peak wavelength of the excitation light. is necessary.

The excitation light absorbing layer A used in the present invention may be a layer formed by laminating a colored film or a layer coated with a colored resin, and may be a colored resin layer formed by coating a reflective layer or a support. Desirably, the material of the resin is desirably composed of a polyester, polyurethane, acrylic, polyvinyl butyral, or epoxy resin.

The kind of coloring agent to be used is determined by the type of stimulable phosphor used in the radiation image conversion panel.
Usually, a phosphor is used which exhibits stimulated emission in a wavelength range of 300 to 500 nm by excitation light having a wavelength in the range of 400 to 900 nm. For this reason, as a coloring agent used for the excitation light absorbing layer, a blue to green organic or inorganic coloring agent is usually used.

Examples of blue-green organic colorants include:
Pomelo Fast Blue 3G (manufactured by Hoechst), Estrol Brill Blue N-3RL (manufactured by Sumitomo Chemical Co., Ltd.),
Sumiacryl Blue F-GSL (Sumitomo Chemical Co., Ltd.),
D & C Blue No. 1 (manufactured by National Aniline Co.), Spirit Blue (manufactured by Hodogaya Chemical Co., Ltd.), Oil Blue No. 1 603 (manufactured by Orient), Kiton Blue A
(Manufactured by Ciba-Geigy), Eisenkatilon Blue GL
H (made by Hodogaya Chemical Co., Ltd.), Lake Blue A, F, H
(Kyowa Sangyo Co., Ltd.), Rhodaline Blue 6GX (Kyowa Sangyo Co., Ltd.), Brimocyanin 6GX (Inabata Sangyo Co., Ltd.), Brill Acid Green 6BH (Hodogaya Chemical Co., Ltd.), Cyanine Blue BNRS (Toyo Ink Co., Ltd.), Lionor Blue SL (Toyo Ink Co., Ltd.)
Manufactured). Examples of blue to green inorganic colorants include, but are not limited to, ultramarine blue, cobalt blue, cerulean blue, chromium oxide, and TiO ₂ —ZnO—CoO—NiO pigments. Preferably, copper phthalocyanine is used.

Next, the reflection layer provided between the support and the stimulable phosphor layer will be described.

As the reflective layer, for example, a material in which a white pigment is dispersed and contained in a resin is used, and thereby, the sensitivity can be improved. The method for producing the light scattering layer is described below, for example. 1. A resin and a white pigment are dispersed in an organic solvent, coated on a support and dried to form a reflective layer. 2. A white pigment is dispersed in a molten resin, and is rolled or stretched into a film by coextrusion with a resin for a support to form a pigment dispersion layer on the support.

The details of the method of providing a pigment dispersion layer on these supports are described in JP-A-6-226894.

As white pigments, titanium oxide, zinc oxide,
Examples include aluminum oxide, calcium carbonate, barium sulfate, and the like. Among them, titanium oxide and calcium carbonate are preferable. Examples of the resin in which the pigment is dispersed include polyurethane, polyester (eg, polyethylene terephthalate, polyethylene naphthalate), vinyl chloride copolymer (eg, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, Vinyl-acrylonitrile copolymer, etc.), butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (nitrocellulose, etc.), styrene-butadiene copolymer, various synthetic rubber resins, phenolic resin, epoxy resin, Melamine resin, phenoxy resin, silicone resin, acrylic resin, urea formamide resin and the like can be mentioned. Among them, polyurethane, polyester,
It is preferable to use a vinyl chloride copolymer, polyvinyl butyral, or nitrocellulose.

Among these, when a pigment dispersion layer is provided on a support by the above-mentioned method 1, a polyurethane thermoplastic elastomer and a polyester thermoplastic elastomer are preferred.

When a pigment dispersion layer is provided on a support by the above two methods, the resin is preferably the same as that of the support because of coextrusion, and polyethylene terephthalate is particularly preferable. In addition, a pigment dispersion layer may be provided on both sides of the support to prevent warping and the chick.

Further, a foamable polyethylene terephthalate containing a large number of cells is used as a support as a reflective layer,
It is also preferable to adopt a structure in which the support and the reflective layer are simultaneously used. In this case, a support described later has reflectivity, and thus can be used as a support of the radiation image conversion panel of the present invention without particularly providing a reflective layer.

In addition, in order to strengthen the bond between the support and the above-mentioned reflective layer or stimulable phosphor layer, a polymer material such as polyester or gelatin is applied to the surface of the support to give an undercoat. A layer may be provided, or a light absorbing layer made of a light absorbing substance such as carbon black may be provided. These configurations can be arbitrarily selected according to the purpose, use, and the like.

As the support used in the radiation image conversion panel of the present invention, various polymer materials are used.
In particular, those which can be processed into a flexible sheet or web in handling as an information recording material are preferable, and in this regard, a cellulose acetate film, a polyester film, a polyethylene terephthalate film,
Plastic films such as polyethylene naphthalate film, polyamide film, polyimide film, triacetate film, and polycarbonate film are preferred.

In addition, it is a preferable embodiment to use a foamable polyethylene terephthalate containing a large number of air bubbles as a support which simultaneously serves as a support and a reflective layer, since the layer structure is simple. A detailed manufacturing method for mixing bubbles in the resin constituting these supports is described in JP-A-3-767.
No. 27 or JP-A-6-226894, which is also available as a commercial product and manufactured by Toray Industries, Inc. E-6.
Available as the 0L series. The use of such a support is preferable in that the reflectance is higher than that of the pigment reflection layer, so that the luminance can be further improved.

The layer thickness of the support varies depending on the material of the support to be used and the like.
00 μm, and preferably 80 μm from the viewpoint of handling.
μm to 500 μm.

The surface of these supports may be smooth, or may be a matte surface for the purpose of improving the adhesion to the reflective layer, the light absorbing layer and the stimulable phosphor layer.

Further, these supports may be provided with an undercoat layer for the purpose of improving the adhesion to the above-mentioned layers.

In the present invention, the stimulable phosphor layer is provided on a support in a state where the stimulable phosphor is dispersed in a binder. Examples of these binders used in the stimulable phosphor layer include proteins such as gelatin, polysaccharides such as dextran, or natural polymer substances such as gum arabic; and polyvinyl butyral, polyvinyl acetate,
Representative by synthetic polymer substances such as nitrocellulose, ethylcellulose, vinylidene chloride-vinyl chloride copolymer, polyalkyl (meth) acrylate, vinyl chloride-vinyl acetate copolymer, polyurethane, cellulose acetate butyrate, polyvinyl alcohol, linear polyester, etc. Binders to be used.

Particularly preferred among such binders are nitrocellulose, linear polyester, polyalkyl (meth) acrylate, a mixture of nitrocellulose and linear polyester, nitrocellulose and polyalkyl (meth) acrylate. And a mixture of polyurethane and polyvinyl butyral. In addition, these binders may be cross-linked by a cross-linking agent. The stimulable phosphor layer can be formed on a support via a reflective layer or, if necessary, an undercoat layer by the following method.

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

In general, the binder is used in an amount of 0.01 to 1 part by mass per 1 part by mass of the stimulable phosphor. However, from the viewpoint of the sensitivity and sharpness of the obtained radiation image conversion panel, it is preferable that the amount of the binder is small, and the range of 0.03 to 0.2 part by mass is more preferable in consideration of the ease of application.

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

The coating solution contains a dispersant for improving the dispersibility of the phosphor in the coating solution, and the dispersant between the binder and the phosphor in the stimulable phosphor layer after formation. Various additives such as a plasticizer for improving the bonding strength may be mixed. Examples of dispersants used for such purposes include phthalic acid, stearic acid, caproic acid, and lipophilic surfactants. Examples of the plasticizer include phosphoric esters such as triphenyl phosphate, tricresyl phosphate, and diphenyl phosphate; phthalic esters such as diethyl phthalate and dimethoxyethyl phthalate; ethylphthalylethyl glycolate and butylphthalylbutyl glycolate; Glycolic acid esters of
And polyester of polyethylene glycol and aliphatic dibasic acid, such as polyester of triethylene glycol and adipic acid, polyester of diethylene glycol and succinic acid, etc. can be mentioned.

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

Next, the formed coating film is dried by gradually heating to complete the formation of the stimulable phosphor layer. The thickness of the stimulable phosphor layer varies depending on the characteristics of the intended radiation image conversion panel, the type of the stimulable phosphor, the mixing ratio between the binder and the phosphor, and is usually 20 μm to 1 mm. . However, this layer thickness is 50 to 500 μm
It is preferred that

The preparation of the coating solution for the stimulable phosphor layer is performed 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 prepared coating solution is coated on a support using a coating solution such as a doctor blade, a roll coater, or a knife coater, and dried to form a stimulable phosphor layer.

A phosphor sheet having a phosphor layer coated on a support is cut into a predetermined size. Any general method can be used for cutting, but a cosmetic cutting machine, a punching machine, or the like is desirable in terms of workability and accuracy.

Any known method can be used to seal the phosphor sheet cut to a predetermined size with the moisture-proof protective film. For example, the phosphor sheet is placed between the upper and lower moisture-proof protective films. And a method in which the peripheral edge portion is heated and fused by an impulse sealer, or a laminating method in which pressure is applied between two heated rollers.

In the method of heat-sealing with the impulse sealer, the heat-sealing under a reduced pressure environment means that the phosphor sheet is prevented from being displaced in the moisture-proof protective film and the moisture in the air is eliminated. More preferred.

[0081]

The present invention will now be illustrated by way of examples.

(Reflective layer) Titanium oxide C manufactured by Ishihara Sangyo Co., Ltd.
100 g of R-50, 100 g of Byron 630 manufactured by Toyobo Co., Ltd., and methyl ethyl ketone having a coating viscosity of 20 Ps
(Poise) and dispersed in a ball mill for 10 hours to obtain a reflective layer paint. X30- of the above-mentioned reflective layer paint was manufactured by Toray Co., Ltd. and containing carbon-containing polyethylene terephthalate.
Dry film thickness 100μ using a doctor blade for 100
m to give a support with a reflective layer.

(Foamable support) Bubble was contained in polyethylene terephthalate according to the method described in JP-A-3-76727 and JP-A-6-226894, and the thickness was 200 μm.
An expandable polyethylene terephthalate (expandable PET) support also having the above reflective layer was prepared.

(Excitation Light Absorbing Layer A) Copper phthalocyanine manufactured by Sanyo Dyeing Co., Ltd. and Byron 630 manufactured by Toyobo Co., Ltd. were added to methyl ethyl ketone so that the paint viscosity became 20 Ps (poise), and dispersed in a ball mill for 10 hours. Thus, an excitation light absorbing paint was obtained. The above excitation light absorbing paint was applied on the polyethylene terephthalate support having a pigment reflection layer and the foamable support using a doctor blade so that the reflection density was as shown in Table 1. At this time, the mixing ratio of copper phthalocyanine and byron was adjusted so as to achieve the film thickness and reflectivity shown in Table 1.

(Preparation of Protective Film) As the protective film on the phosphor surface side of the phosphor sheet, one having the structure shown in the following (A) was used. (A) VMPET12 // VMPET12 // PET1
2 // Sealant film PET: Polyethylene terephthalate Sealant film: Heat-fusible film using CPP (casting polypropylene) or LLDPE (low-density linear polyethylene) ) The number behind each resin film is the film thickness (μ
m).

The above “//” means that the dry lamination adhesive layer has a thickness of 2.5 μm. The adhesive used for dry lamination is a two-component reaction type urethane adhesive.

By adding an organic blue colorant (Zavon Fast Blue 3G, manufactured by Hoechst Co.) previously dispersed and dissolved in methyl ethyl ketone to the adhesive solution used at this time, the entire adhesive layer is removed. Excitation light absorption layer B
And The light transmittance of the excitation light absorbing layer B was adjusted by adjusting the amount of addition at this time.

The light transmittance of the excitation light absorbing layer referred to here is
The light transmittance at the peak wavelength (633 nm) of the He-Ne laser light was a value when compared with the light transmittance of an equivalent protective film having no excitation light absorbing layer B.

At the same time, by changing the dye concentration and the film thickness of the excitation light absorbing layer B, laminated protective films having different concentrations and film thicknesses were produced.

(Synthesis of Phosphor) In order to synthesize a stimulable phosphor precursor of europium-activated barium fluoroiodide,
2780 ml of BaI ₂ aqueous solution (3.6 mol / L) and E
27 ml of a uI ₃ aqueous solution (0.2 mol / L) was charged into the reactor. 83 ° C. while stirring the reaction mother liquor in this reactor
Was kept warm. Ammonium fluoride aqueous solution (8mol / L)
322 ml were injected into the reaction mother liquor using a roller pump to produce a precipitate. Keep warm and stir even after pouring
The sediment was aged continuously over time. Next, the precipitate was separated by filtration, washed with ethanol, and dried under vacuum to obtain europium-activated barium fluoroiodide crystals. In order to prevent a change in particle shape due to sintering during firing and a change in particle size distribution due to inter-particle fusion, 0.2% by mass of ultrafine alumina powder is added, and the mixture is sufficiently stirred with a mixer. Ultrafine alumina powder was uniformly adhered to the surface.
This was filled in a quartz boat and calcined at 850 ° C. for 2 hours in a hydrogen gas atmosphere using a tube furnace to obtain europium-activated barium fluoroiodide phosphor particles. Next, particles having an average particle diameter of 7 μm were obtained by classifying the phosphor particles.

As the phosphor layer forming material, 427 g of the europium-activated barium fluoroiodide phosphor obtained above, 15.8 g of polyurethane resin (Desmolac 4125, manufactured by Sumitomo Bayer Urethane Co., Ltd.), and bisphenol A type epoxy resin 0 g of methyl ethyl ketone / toluene (1 /
1) The mixture was added to a mixed solvent and dispersed by a propeller mixer to prepare a coating solution having a viscosity of 25 to 30 Ps (poise). Using this coating solution, a phosphor layer was formed on a support shown in Table 1 or a support with an undercoat layer so as to have a dry film thickness shown in Table 1 using a doctor blade.

(Sealing of Phosphor Sheet)
It was cut into a square of 0 cm × 20 cm, and sealed by using a laminated protective film having the above-described various excitation light absorbing layers and fusing the peripheral edge thereof under reduced pressure using an impulse sealer. In this way, radiation image conversion panels of Examples 1 to 12 and Comparative Examples 1 to 7 as shown in Table 1 were produced. FIG. 1 shows a cross-sectional view of the radiation image conversion panel of the present invention.
The distance from the fused portion to the peripheral edge of the phosphor sheet was 1 mm.
It fused so that it might become. The heater of the impulse sealer used for fusion had a width of 8 mm.

The absorbance can be measured using a general spectroscopic clock (for example, U-3300 manufactured by Hitachi, Ltd.). The copper phthalocyanine, which is the excitation light absorbing layer used in this example, is used. The excitation light absorbance / stimulated luminescence absorbance was 6 in the excitation light absorbing layer containing, and 5.5 in Pomelo Fast Blue 3G.

(Evaluation of Radiation Image Conversion Panel) The produced radiation image conversion panel was evaluated as follows.

Evaluation of Sharpness Regarding the sharpness, the radiation image conversion panel was made of lead MT.
After irradiating an X-ray with a tube voltage of 80 kVp through the F chart, the panel is operated by He-Ne laser light to be excited, and stimulated emission emitted from the phosphor layer is received by a photodetector (photoelectron image tube). It is converted to an electric signal, converted from analog to digital, and recorded on a hard disk.
The modulation transfer function (MTF) of the line image was examined. Spatial frequency 1
The MTF value (%) in cycles / mm was examined for each panel. In this case, the higher the MTF value, the better the sharpness.
In Table 1, the relative values are shown with the MTF value of Comparative Example 1 set to 100.

Evaluation of Image Unevenness and Linear Noise After the radiation image conversion panel was uniformly irradiated with X-rays having a tube voltage of 80 kVp, the panel was irradiated with He-Ne laser light (633).
nm) and excited, and the stimulated emission emitted from the phosphor layer is received by the same receiver as described above and converted into an electric signal,
This was reproduced as an image by an image reproducing apparatus, printed out at twice the size of the output apparatus, and the obtained printed image was visually observed to evaluate the appearance of image unevenness and linear noise. 0 indicates no image unevenness and linear noise at all, and 5 indicates the most intense occurrence.
The results are shown in Table 1.

Evaluation of Luminance Luminance was measured by applying a tube voltage of 80 kVp to the radiation image conversion panel.
After irradiating the panel with X-rays, the panel is operated by He-Ne laser light (633 nm) to be excited, and the photostimulable light emitted from the phosphor layer is received by a photodetector (photoelectron image tube) and the intensity thereof is obtained. Was measured. The luminance in Table 1 is an average value of the entire surface of the radiation image conversion panel when the haze ratio of the protective layer is 40%, and is a relative luminance when the luminance when sealed with a protective film without an excitation light absorbing layer is 1. is there.

[0098]

[Table 1]

[0099]

As described above, a radiation image conversion panel having a high balance between emission luminance and sharpness and having high uniformity was obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of a radiation image conversion panel of the present invention.

[Description of Signs] 11 phosphor layer 12 excitation light absorbing layer 13 reflecting layer 14 support 15 laminated protective film 16 foamable polyethylene terephthalate support

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2G083 AA03 CC01 CC04 CC05 CC06 DD01 DD02 DD11 DD16 EE02 EE03 2H013 AC01

Claims (5)

[Claims] 1. A phosphor sheet in which a reflecting layer, an excitation light absorbing layer A colored to absorb excitation light and a stimulable phosphor layer are laminated on a support in this order, and the phosphor surface of the phosphor sheet is In a radiation image conversion panel comprising a protective film provided so as to cover, the protective film has a colored excitation light absorbing layer B, and each of the excitation light absorbing layers A and B has a peak wavelength of excitation light. Than the absorbance of
A radiation image conversion panel, wherein the absorbance at the emission peak wavelength of stimulated emission is smaller, and the thickness of the excitation light absorbing layers A and B is A> B. 2. A phosphor sheet in which an excitation light absorbing layer A and a stimulable phosphor layer colored to absorb excitation light are laminated in this order on a foamable polyethylene terephthalate support containing a large number of air bubbles. And, in a radiation image conversion panel comprising a protective film provided to cover the phosphor surface of the phosphor sheet, the protective film has an excitation light absorbing layer B colored so as to absorb excitation light, Further, in each of the excitation light absorbing layers A and B, the absorbance at the emission peak wavelength of the stimulated emission is smaller than the absorbance at the peak wavelength of the excitation light, and the thickness of the excitation light absorption layers A and B is A> B. A radiation image conversion panel, comprising: 3. The light reflectance of the reflection layer and the excitation light absorption layer A at the peak wavelength of the excitation light is 97% to 50% with respect to the light reflection layer in the case where the excitation light absorption layer A is not provided. The radiation image conversion panel according to claim 1, wherein the thickness is 2 μm or more and 50 μm or less. 4. The protective film having the excitation light absorbing layer B has a light transmittance at the peak wavelength of the excitation light which is higher than that of the excitation light absorbing layer B.
97% to 5 with respect to the light transmittance of the protective film having no
4. The method according to claim 1, wherein the amount is 0%.
A radiation image conversion panel according to the item. 5. The radiation image conversion panel according to claim 1, wherein the stimulable phosphor is Eu-activated BaFI.