EP0185534B1

EP0185534B1 - Radiation image storage panel

Info

Publication number: EP0185534B1
Application number: EP19850309128
Authority: EP
Inventors: Hisanori Tsuchino; Akiko Kano; Koji Amitani; Fumio Shimada
Original assignee: Konica Minolta Inc
Current assignee: Konica Minolta Inc
Priority date: 1984-12-17
Filing date: 1985-12-16
Publication date: 1990-06-20
Also published as: EP0185534A3; EP0185534A2

Description

This invention relates to a radiation image storage panel comprising a stimulable phosphor, more particularly to a radiation image storage panel which provides a radiation image of high sharpness.
A radiation image such as an X-ray image is frequently used for example in diagnosis of diseases. To provide an X-ray image, a radiation photograph is obtained by irradiating X-rays transmitted through a subject onto a phosphor layer (a fluorescent screen) to generate visible light; this visible light is then irradiated onto a film comprising a silver salt in a similar manner as in conventional photography. The film is then developed. However, in recent years, methods for obtaining images directly from the phosphor layer without the use of a film coated with a silver salt have been devised.
Thus there is the method in which radiation transmitted through a subject is absorbed onto a phosphor, which is then excited with, for example, light or heat energy so that the radiation energy accumulated in the phosphor is radiated as fluorescence, which is detected. Specifically, for example, US-A-3,859,527 and JP-B-5512144 disclose a radiation image storage method employing visible light or IR-rays as the stimulating excitation light. This method employs a radiation image storage panel having a stimulable phosphor layer formed on a support. By irradiating the stimulable phosphor layer with radiation transmitted through a subject, a radiation image corresponding to the radiation transmission of the subject is produced. Thereafter the stimulable phosphor layer is scanned with stimulating excitation light to radiate the accumulated radiation energy for the image, which is converted to light to provide an image according to the intensity of the light. The final image may be reproduced as a hard copy or reproduced on a CRT.
It is desirable that the radiation image storage panel has high radiation absorption and light conversion (hereinafter referred to as "radiation sensitivity" as inclusive of both) as a matter of course, good image graininess and yet good sharpness.
Radiation image storage panels having stimulable phosphor layers are generally made by applying and drying a dispersion containing 1 to 30 pm grains of a stimulable phopshor and an organic binder. Thus there is a low filling density of the stimulable phosphor (filling percentage 50%). Accordingly, in order to make the radiation sensitivity sufficiently high, it is necessary to use a thick phosphor layer as shown in Fig. 12(a) line (b).
The stimulable phosphor is applied in an amount of 50 mg/cm² when the thickness of the stimulable phosphor layer is 200 pm. The radiation sensitivity increases linearly until saturated at a thickness of 450 pm or more because stimulated emission within the stimulable phosphor layer will not exit due to scattering between the phosphor grains if the layer is too thick.
On the other hand, image sharpness in the above radiation image storage panel is increased as the thickness of the stimulable phosphor layer is reduced as shown in Fig. 12(b) line (b).
Additionally, since the image graininess is determined by the regional fluctuation in radiation quantum number (quantum mottle) or structural disturbance (structural mottle) of the stimulable phosphor layer, if the thickness of the layer is too thin, the radiation quantum number may be reduced which increases quantum mottle or structural disturbance may occur which increases structural mottle. This lowers image quality. Hence, to improve image graininess, a thick stimulable phosphor layer is required.
Thus the radiation image storage panel of the prior art exhibits tendencies for radiation sensitivity and image graininess entirely opposite to that for image sharpness in relation to the thickness of the phosphor layer, and therefore there is a trade-off between radiation sensitivity, graininess and sharpness to some extent.
Image sharpness in the radiation photographic method of the prior art is determined by expansion of the momentary emission (emission on irradiation of radiation) of the phosphor in the fluorescent screen, as is well known in the art. In contrast, image sharpness in the method utilizing a stimulable phosphor as described above is not determined by the expansion of the stimulated emission of the stimulable phosphor in the radiation image storage panel, but rather is determined by the expansion of the stimulating excitation light within said panel. In this method, since the radiation image information accumulated in the radiation image storage panel is obtained in a time series, the stimulated emission by the stimulating excitation light irradiated at a certain time (ti) is desirably all collected and recorded as the output from the picture element (xi, yi) which is irradiated by the stimulating excitation light at that time. Therefore, if the stimulating excitation light is expanded, for example by scattering, within said panel and also excites the stimulable phosphor outside of the picture element (xi, yi), then output from a wider region than the picture element (xi, yi) is recorded as the output from that picture element. Thus, provided that the emission stimulated by the stimulating excitation light irradiated at a time (ti) is only the emission from the picture element (xi, yi) on which the stimulating excitation light is truly irradiated at that time (ti), there is no influence on image sharpness even if the emission expands.
In the state of the art described above, some methods for improving radiation image sharpness have been proposed. For example, a white powder may be mixed in the stimulable phosphor layer as disclosed in JP-B-55146447; and the radiation image storage panel may be coloured so that the average reflectance in the stimulating excitation wavelength region of the stimulable phosphor is less than the average reflectance in the stimulated emission wavelength region of the phosphor. However, these methods necessarily markedly lower the sensitivity if the sharpness is improved, and therefore cannot be said to be preferred methods.
On the other hand, we have already proposed in JP-B-59196365 a radiation image storage panel in which the stimulable phosphor layer contains no binder, which improves over the drawbacks of the prior art described above. In this panel, since the stimulable phosphor layer contains, no binder, the filling percentage of the stimulable phosphor is improved simultaneously with improvement of inclination of the stimulable excitation light and the stimulable emission, and radiation sensitivity and image graininess are improved simultaneously with improvement of image sharpness.
However, demand for image quality with excellent sharpness without damaging sensitivity and graininess is becoming more rigorous.
The present invention seeks to provide a radiation image storage panel with improved radiation sensitivity and high image sharpness; and improved graininess and high image sharpness.
The present invention provides a radiation image storage panel having a stimulable phosphor layer on a support, wherein said stimulable phosphor layer has a fine pillar-shaped block structure, the pillar-shaped blocks in said structure being abutted or separated from each other by gaps. The pillar-shaped blocks preferably extend perpendicularly to said support.

Fig. 1 is a sectional view showing part of a radiation image storage panel of the present invention;
Figs. 2(a) to 2(d) are plan views showing parts of radiation image storage panels of the present invention;
Figs. 3(a) and 3(b) are sectional views showing part of a radiation image storage panel of the present invention and the support surface during manufacture;
Figs. 5(a) and 5(b) are sectional views showing part of a radiation image storage panel and the support surface during manufacture;
Fig. 6 is a perspective view showing distributed patterns of fine tiles;
Figs. 7(a) to 7(c) are sectional views showing part of a radiation image storage panel of the present invention and the support surface during manufacture;
Figs. 8(a) to 8(c) are sectional views showing part of a radiation image storage panel of the present invention and the support surface during manfuacture;
Figs. 9(a) and 9(b) are sectional views showing part of a radiation image storage panel of the present invention;
Fig. 10 is a plan view showing part of the base layer of a radiation image storage panel of the present invention;
Fig. 11 is a sectional view showing part of a panel of the present invention;
Fig. 12(a) is a graph showing the relationship of the thickness of the stimulable phosphor layer and its applied amount in radiation image storage panels of the present invention (a) and of the prior art (b) versus sensitivity to radiation; and Fig. 12(b) is a graph showing the relationship of the thickness of the stimulable phosphor layer and its applied amount in the present radiation image storage panel (a) and the prior art (b) versus modulation transmission function (MTF) at 2 cycles/mm space frequency;
Fig. 13 is a schematic illustration of a radiation image storage method using the panel of the present invention;
Fig. 14 is a sectional view showing part of a panel of the present invention.

The present invention is described in detail below.
Fig. 1 is a sectional view in the thickness direction of a radiation image storage panel (hereinafter sometimes referred to as "panel" when its meaning is distinct).
In the same Figure, 10 is a panel of the present invention, 11 ij are each fine pillar-shaped blocks of the stimulable phosphor extending, preferably perpendicularly from the support and (11 ij) are gaps in the form of cracks, grooves or recesses. The stimulable phosphor layer 11 with a fine pillar-shaped block structure is formed from 11ij and (11ij).
The blocks 11 ij preferably have a mean size of from 1 to 400 pm; the gaps may be of any size, provided that the blocks 11 ij are optically independent of each other, but are preferably from 0 to 20 pm on average. 13 is a protective layer which is preferably provided, and 14 is an adhesive layer which may optionally be provided to improve adhesion of the stimulable phosphor layer to the support 12.
When stimulating excitation light enters the stimulable phosphor layer described above, it reaches the bottom of the pillar-shaped blocks with repeated reflection against the inner surfaces of the pillar-shaped blocks due to the optical induction effect of the fine pillar-shaped block structure, without exiting the blocks. Thus, the image sharpness is markedly increased.
In addition to the above adhesion layer, a reflection layer or absorption layer for stimulating excitation light and/or stimulated emission may be applied to the support surface.
The pillar-shaped block structure may be of any desired pattern. Figs. 2(a), (b), (c) and (d) show examples of patterns.
The thickness of the phosphor layer 11 in the panel of the present invention, which differs, for example depending on the radiation sensitivity of the panel and the type of stimulable phosphor, is preferably from 10 to 1000 pm, more preferably from 20 to 800 pm.
For formation of the panel a support having a homogeneous smooth surface or a support having a base pattern convenient for formation of a pillar-shaped block structure by attachment or deposition of a stimulable phosphor may be used.
For a support with a homogeneous smooth surface, the mesh mask method may be used in which a metal mesh knitted with sufficiently fine metal wires (e.g. copper wires) or a perforated mesh densely perforated by means of a laser beam is pressure contacted on a support, and a stimulable phosphor is deposited by gas phase deposition, such as vacuum vapor deposition or sputtering to form pillar-shaped blocks; the moulding method may also be used in which a mould release agent, for example of the silicone type is applied as a surface coating for a mould having a convex pattern corresponding to the fine pillar-shaped block pattern, a stimulable phosphor is filled into the mould, a support is adhered onto the filled surface and the mould is removed to expose the pillar-shaped blocks. Furthermore, it is possible to use the crack method in which cracks are generated, for example by heat treatment, after uniform vapor deposition.
On the other hand, for a support having a base pattern a paint containing a stimulable phosphor suspended in a binder may be coated by means conventionally employed in printing methods, or pillar-shaped blocks may be grown according to the above gas phase deposition method.
The support having a base pattern, when intended to be coated by the above paint, can be obtained by forming a pattern corresponding to the fine pillar-shaped pattern based on the affinity of the paint for the support surface, similarly as in lithography printing.
Various resist resins conventionally employed in photographic etching may also be used under the above conditions to provide a pattern on the support surface. For good adhesion affinity of the resist resin the support may, for example, be a metal sheet having a metal oxide coat thereon.
Techniques for formation of the metal oxide coat include coating the metal oxide on a metal surface conventionally used in these technical fields, such as a hard photomask or the preparation of transparent electroconductive films, for example, a chemical coating method, a spraying method or a CVD (Chemical Vapor Deposition) method, a RF ion plating method, a RF sputtering method or a vacuum deposition method.
Examples of the resist resin are posi-type and nega-type resist resins such as a photoresist, a vacuum UV-ray photoresist, an electron beam resist or an X-ray resist. The photoresist resins include those obtained by esterification of naphthoquinoneazide or benzoquinoneazide with novalac resins.
First, the support is coated with the resist resin, a layer fractional pattern is printed and developed, and further etching is effected according to a wet or dry process to the depth at which the support surface is exposed, whereby a base layer 11 having a desired pattern comprising a texture of layer fractions 11 ij and gaps (11ij) is obtained.
On the other hand, when an aluminium plate is used as the support, a layer fraction pattern can be easily prepared by sealing treatment and subsequent heat treatment of the porous aluminium oxide formed on the surface by anodic oxidation. This method is conventionally used in aluminium surface treatment.
First, the anodic oxidation treatment of the aluminium support surface may be carried out, for example, on an aluminium plate having a thickness of about 0.5 mm, on the side where a stimulable phosphor is to be deposited, in a 8% oxalic acid solution, by passing a current of 1 A/cm² for about 2 hours, to form an anodically oxidized coating layer comprising porous aluminium oxide.
Next, the coating layer is washed with water and subsequently boiled in boiling water for about 1 hour. As a result, the porous aluminium oxide expands by incorporation of water of crystallization to form a coating layer comprising dense crystals. This operation is the so-called sealing treatment.
After the sealing treatment, heat treatment may be carried out at 250°C or higher, whereby the aluminium oxide loses the water of crystallization and shrinks to form a layer fraction pattern of fine island shapes surrounded and separated from each other by gaps formed by shrinkage.
The aluminium oxide coating obtained preferably has a thickness of some micrometers or more. In the case of a thin coating, since the layer fraction tend to become greater, it is necessary to select optimally the conditions for the anodic oxidation.
The aluminium support may be one having impurity particles on the surface thereof. For example, when an etching treatment using 5% NaOH solution is performed on the surface, impurities in the support are precipitated and remain thereon without dissolving. Examples of impurities include Si, Fe and Cu, which are dot-like shaped with an average diameter of from 0.1 to 7 pm and black to brown in colour. Fine pillar-shaped blocks of a stimulable phosphor are formed on the surface of the support still containing impurities. It is known that aluminium supports generally contain, for example Si (25%), Fe (0.4%), Cu, Mn, Mg, Zn, V (each 0.05%) and Ti (0.03%), depending upon their purity.
Furthermore, there may be a porous chromium layer on the metal support. Fig. 14 is a sectional view in a thickness direction of a radiation image storage panel of this invention. The porous chromium layer, known as porous chromium in plating technology, is a thin layer of chromium having many fine crevasses, which often have baggage-like shaped holes which are narrow at the opening thereof and broad at the bottom. In the panel of the present invention, the crevasses formed in the porous chromium layer are preferably present in a density of from 5000 to 50000 per cm^2. Furthermore, the depth of the crevasse d is preferably from 5 to 70% of the thickness of the porous chromium layer t; the porosity of the porous chromium layer is preferably from 10 to 45%.
On the surface of the porous chromium layer, fine pillar-shaped blocks of a stimulable phosphor can be formed by vapor deposition.
Moreover, between the porous chromium layer and the stimulable phosphor layer may be an adhesive layer which assists the adhesion of the stimulable phosphor, or a reflective layer or an absorption layer for stimulable excitation light and/or stimulable emission, if desired.
On the other hand, in the case of gas phase deposition, the support having a base pattern may be prepared according to the method in which ink silk or gravure printed, preferably with burning, to form a base pattern corresponding to the fine pillar-shaped pattern; the method in which a base pattern suitable for gas phase deposition of a stimulable phosphor physically and/or chemically is prepared by photographic etching; or the method in which a base pattern is prepared by application of a sealing treatment and heat treatment to an aluminium plate subjected to anodic oxidation.
Thus, a base pattern in the form of fine partitioned island regions physically and/or chemically suitable for gas phase deposition is obtained, said regions being surrounded by fine streaks, grooves, convexities or cracks, in which gas phase deposition can proceed with difficulty.
When employing the support having a base pattern, a thin pattern layer of a stimulable phosphor may be formed on the support and gas phase deposition may subsequently be applied to the base pattern.
The radiation image storage panel of the present invention preferably comprises a support having on its surface a large number of fine concavo-convex patterns, which may be produced, for example, by the above method, and a stimulable phosphor layer comprising a fine pillar-shaped block structure having the above surface structure, provided thereon.
Fig. 3(a) is a sectional view of a radiation image storage panel of the present invention. Fig. 3(b) is a sectional view in the thickness direction of a support having a concavo-convex pattern before provision of the stimulable phosphor layer having the above fine pillar-shaped block structure.
The distributed pattern on the above support may be any desired pattern, such as shown in Figs. 2(a), 2(b), 2(c) or 2(d).
In Figs. 3(a) and 3(b) the same symbols have the same meanings.
In Fig. 3(a), 10 is a panel, 12ij are convexities and (12ij) concavities of the support 12 is a support. 11 ij are each fine pillar-shaped blocks of stimulable phosphor having the above convexities, and (11 ij) are each pillar-shaped block having the above concavities (12ij).
The stimulable phosphor layer 11 is formed from 11ij and (11ij).
The convexities 12ij and concavities (12ij) preferably have a mean size of from 10 to 400 pm, more preferably from 15 to 100 pm.
The concavo-convex surface of the support may be provided with an adhesive layer to aid adhesion of the stimulable phosphor layer or a reflection layer or an absorption layer for stimulating excitation light and/or stimulated emission.
Since the phosphor layer 11 is deposited by growing crystals while maintaining the concavo-convex structure of the support surface during deposition, the boundary between the blocks (11ij) grown on the concavity (12ij) and the blocks 11ij grown on the convexity 12ij is discontinuous, so that the blocks (11ij) and the blocks 11 are optically independent.
For this reason, when stimulating excitation light enters the stimulable phosphor layer having fine pillar-shaped block structures independent of each other, it reaches the bottom of the pillar-shaped block with repeated reflections against the inner surface of the block due to the optical induction effect of the fine pillar-shaped block structure without exiting the block, where it is absorbed or reflected, and again emits in the pillar direction while reflecting against the inner surface of the block. Thus, image sharpness is markedly increased while the chances of stimulating excitation are also increased.
In the present invention, it is preferred that the radiation image storage panel of Fig. 3 has support having a surface structure in which a large number of fine tiles are separated from each other by fine gaps, and a stimulable phosphor comprising a fine pillar-shaped block structure having the above surface structure is provided thereon.
More specifically, in the radiation image storage panel of the present invention, the surface of the support has a structure in which a large number of fine tiles with sizes of from 1 to 400 µm separated from each other by gaps in the form of cracks, grooves or recesses with widths of from 0.01 to 20 _Ilm, and the stimulable phosphor layer is formed on the above fine tiles, thus providing fine pillar-shaped blocks separated from each other with the above gaps being reproduced as indentations in the surface of the block structure. With such blocks optically independent of each other, the stimulating excitation light entering the stimulable phosphor layer progresses only perpendicularly to the support with total reflection through the fine pillar-shaped block with substantially no dissipation laterally. Since the gaps on the support surface remain as such, the fine pillar-shaped blocks forming the stimulable phosphor layer are optically completely independent so that lateral dissipation of the stimulating excitation light is very low.
For formation of a stimulable phosphor layer with a fine pillar-shaped block structure, gas phase deposition such as vacuum vapor deposition or sputtering is preferred from the viewpoint of sensitivity and the technical aspect for formation of pillar-shaped blocks.
As the support with a surface structure having a large number of fine tiles surrounded by fine gaps as described above, an anodically oxidized aluminium plate subjected to sealing treatment and subsequently to heat treatment is preferred, and the production method using said support is useful.
Fig. 5(a) is a sectional view in the thickness direction of a radiation image storage panel of an embodiment of the present invention. Fig. 5(b) is a sectional view of a support having a surface structure in which the fine tiles are separated from each other by fine gaps before provision of the stimulable phosphor layer having the fine pillar-shaped block structure.
The pattern of the fine tiles on the support may be any desired. In Fig. 2, examples of distributed patterns are shown as (a), (b), (c) and (d).
In Fig. 5 and Fig. 2, the same symbols have the same meanings.
In Fig. 5, 10 is a panel of the present invention, 12ij are each fine tiles on the support surface and (12ij) are gaps in the form of cracks, grooves or recesses surrounding said fine tiles. 12' is a layer of fine tiles dispersed as islands on the support surface formed of 12ij and (12ij). 12 is a support. 11 are each fine pillar-shaped blocks of stimulable phosphor deposited by gas phase deposition on the fine tiles, and (11ij) are deep gaps between the 11 selectively deposited on 12ij.
14 is an optional adhesive layer and 13 is a protective layer which is preferably provided.
The stimulable phosphor layer 11 comprising a fine pillar-shaped block structure is formed from 11 ij and (11ij).
The gaps (11 ij) as herein mentioned include mere cracks with substantially no gap only formed on the phosphor layer surface, and therefore a fine multipyramid block structure is included within the scope of the fine pillar-shaped block structure.
As an example of the pattern formed by the fine tiles 12ij and fine gaps (12ij), a perspective view of an aluminium support subjected to anodic oxidation treatment, sealing treatment and heat treatment is shown in Fig. 6.
On the fine tiles 12ij, the adhesive layer 14, and a reflection layer or absorption layer for stimulated emission and/or stimulating excitation light may be similarly provided to give a multi-layer structure.
In the present invention, it is preferred that the radiation image storage panel has a large number of fine tiles on a support surface, a net with five strings surrounding said fine tiles separating them from each other, and a stimulable phosphor layer with a block structure extending perpendicularly to the layer of fine tiles.
Fig. 7(a) is a sectional view in the thickness direction of a radiation image storage panel of the present invention. Fig. 7(b) is a sectional view of the support bearing fine tiles and a net with five strings surrounding and separating said fine tiles provided thereon before provision of the stimulable phosphor layer having a fine pillar-shaped block structure, and Fig. 7(c) is a sectional view of the support bearing only the fine tiles without the net.
In Fig. 7(a), 10 is a panel of the present invention, 12ij are fine tiles each having a thickness d, and (12ij) are gaps in the form of cracks, grooves or recesses surrounding the fine tiles. 15ij are fine strings of a net with a height h which fill the (12ij) and separate respective 12ij from each other. h is preferably not smaller than d.
11 are each fine pillar-shaped blocks of stimulable phosphor deposited on the tiles 12ij, and (11 ij) are gaps between blocks 11 ij. The stimulable phosphor layer 11 having a fine pillar-shaped block structure according to the present invention is formed from 11 ij and (11 ij). 13 is a protective layer which is preferably provided, and 12 is a support.
The gap (11ij) as herein mentioned includes a crack with no substantial gap, and therefore the fine pillar-shaped block structure includes within its scope a fine multipyramid block structure.
The radiation image storage panel may be provided with a stimulable phosphor comprising a fine pillar-shaped block structure having crevasses developed from the gap between the fine tiles towards the layer surface by applying a shock treatment to the stimulable phosphor layer deposited perpendicularly to the surfaces of the fine tiles: It is preferred that heat treatment is combined with the shock treatment.
Fig. 8(a) is a sectional view of a radiation image storage panel in the thickness direction. Fig. 8(b) is a sectional view in the thickness direction of a panel when the above stimulable phosphor layer is deposited before shock treatment, and Fig. 8(c) is a sectional view of a previous state in which the support bears only fine tiles without the stimulable phosphor layer.
The fine tiles may be distributed on the support in any desired pattern.
In Fig. 8(a), 10 is a panel of the present invention, 12ij are each fine tiles on the support surface, (12ij) are gaps, for example in the form of cracks, grooves or recesses, surrounding the fine tiles. 12' is a pattern layer of fine tiles scattered in islands on the support surface, made of the above 12ij and (12ij).
(11ij) is a cavity within the deposition layer, which is formed during deposition of the stimulable phosphor on the distributed pattern layer 11 by first depositing the stimulable phosphor on the fine tiles 12ij and gradually expanding the deposition area until at last effecting bonding of the deposited layer; this cavity may be very small or may reach the surface to become a crevasse depending on the size of the gaps (12ij). 11 is a stimulable phosphor deposition layer including the above mentioned cavity or crevasse (11 ij). 11ij are each fine pillar-shaped blocks having the stimulable phosphors deposited on the fine tiles isolated from each other by shock treatment on the deposited layer 11 to develop each cavity (11 ij) to the surface of the deposited layer to form a crevasse. (11 ij) are crevasses between the fine pillar-shaped blocks 11 ij. The stimulable phosphor layer 11 having a fine pillar-shaped block structure is formed from 11 ij and (11ij).
12 is a support and 13 is a protective layer which is preferably provided.
Furthermore, in the present invention, in contrast to the aforesaid crevasse, a crevasse developed from the surface of the layer may be provided. In this case, after formation of the stimulable phosphor layer by means of, for example, various vapor deposition methods, the crevasse may be formed by providing a thermal shock. That is, the crevasse can be formed by heating and cooling utilizing the thermal expansion difference between the stimulable phosphor and the support.
More specifically, for example, a panel with a stimulable phosphor deposited thereon is heated to about 300°C in an inert gas such as nitrogen, and after reaching thermal equilibrium with the original panel, crevasses are formed in the stimulable phosphor layer when the panel is cooled by introducing a large amount of cooled nitrogen. In this case, since the crevasses are formed by strain due to the difference between the surface temperature of the stimulable phosphor layer and the temperature of the support based on the specific heats thereof-or speeds of cooling, almost all of crevasses occur from the surface of the stimulable phosphor layer to provide a structure as shown in Fig. 14. Further heating may be carried out for the support side and cooling on the phoshor side. If cooling provides a good effect, the heating temperature may be lower, for example about 150°C when an alcohol is employed for cooling. The above method for forming crevasses may be interposed during vapor deposition of the stimulable phosphor layer. The method for forming crevasses is not limited to thermal treatment; any method may be employed so long as it can provide crevasses without imparting the function of the panel. For example, a method may be employed in which, during the latter half of formation of the stimulable phosphor layer by vapor deposition, crevasses are formed by increasing a concentration of an inert gas such as argon to form gaps in the phosphor layer and providing a thermal shock from the layer surface side.
Crevasses can also be formed, for example, by providing an ultrasonic or electrical shock to a crystalline dislocation line directed to the layer surface, which is formed during deposition.
In this case, it is not necessary to use a support having a concavo-convex pattern on its surface. A stimulable phosphor layer may be formed on a protective layer which protects the panel surface by vapor deposition, and then crevasses can be introduced by a panel producing method to be adhered to the support after deposition.
For example, by using a protective layer film having, on the surface of the protective layer film, a surface structure where a large number of fine concavo-convex patterns or a large number of fine tile-like plates which are separated from each other by fine gaps spread all over the film, a stimulable phosphor layer can be formed by any vapor deposition method. Then, since the stimulable phosphor starts to deposit on the surface of the above protective layer film as fine prismatic crystals, gaps between these prismatic crystals form as stimulable phosphor layer crevasses extended in a direction almost perpendicular to said film surface. Thus crevasses open to the surface can be introduced by adhering them to the support.
After formation of the panel having such a structure, the above crevasses may be grown by a shock treatment such as a thermal treatment.
The thus obtained fine pillar-shaped blocks become finer-sized pillar-shaped blocks.
The radiation image storage panel of the present invention may have at least one pillar-shaped stimulable phosphor on the upper part of at least one fine grain layer on the support.
Figs. 9(a) and 9(b) are sectional views in the thickness direction of a radiation image storage panel of the above embodiment.
In the same Figure, 10 is a panel of the present invention. 11ij are each fine pillar-shaped blocks extending perpendicularly from the support surface, (11 ij) are each gaps between 1 ij in the form of cracks, grooves or recesses. The stimulable phosphor layer 11 having a fine pillar-shaped block structure is formed from 11ij and (11ij).
12 is a support, 13 is a protective layer which is preferably provided and 14 is an optional adhesive layer which improves adhesion between the stimulable phosphor layer and the support. 11a a is a layer comprising grains with a thickness of 1/2 or less of the entire film thickness, preferably 1/10 or less; the grains may be spread in at least one layer.
The grains may have a mean grain size of 50 pm or less, preferably 15 pm or less. The layer 11 a can be obtained by gas phase deposition such as vacuum deposition or sputtering.
As the material for forming the grains, various metals, metal oxides such as ZnO, Ti0₂ or A1₂0₃, metal sulfides such as ZnS, amorphous silicon, compounds such as SiC, SiN or Si0₂, or alkali halide crystals and stimulable phosphors as hereinafter described may be used. Among them, alkali halide crystals are preferred to obtain a fine pillar-shaped pillar structure 11 ij.
The layer 11a shown in Fig. 10 may be obtained by, for example, vapor deposition of, for example, alkali halide crystals in a vacuum of about 10-³ Torr (0.133 Pa).
After the layer 11a a has been obtained, fine pillar-shaped blocks 11ij can be grown on the grains by gas phase deposition. The layer 11 a also enhances adhesion to 11ij. For laminating a plurality of layers as described above, the above layer constituting operation may be repeated for the necessary number of times.
The radiation image storage panel of the present invention may also have a stimulable phosphor layer with at least two layers of a pillar-shaped block structure.
Fig. 11 is a sectional view in the thickness direction of a radiation image storage panel of the above embodiment, in which 11 is the recording layer of the panel and 12 is a support.
12' is a base layer having a thickness of 1/2 or less, preferably 1/10 or less of the film thickness of the recording layer 11, said base layer 12' comprising layer fractions 12ij dispersed in islands as exemplified in Fig. 10 and gaps (12ij) shaped in concavities or cracks therearound separating the islands from each other.
11 is a stimulable phosphor layer on the above base layer 12'. It comprises at least two layers of pillar-shaped blocks 11ij and the gaps (11 ij) formed corresponding to the above gaps (12ij). In Fig. 11, as 11ij, there are examples of pillar-shaped blocks 11Aij and 11Bij comprising stimulable phosphors A and B. The mean size of 11ij ij is preferably from 1 to 400 pm.
Between 11Aij and 11 Bij, substances suitable for mutual bonding may be present. The bonded portion may have a function such a a filter. The stimulable phosphors A and B may be either the same or different.
The stage number of the block lamination is not limited, and it is possible to make a continuous constitution (infinite stage number), in which a certain characteristic of the stimulable phosphor, for example, optical reflectance, is continuously changed. (11ij) are crevasses or boundaries between the pillar-shaped blocks 11ij corresponding to the gaps (12ij) as described above, which are provided to make respective 11 ij blocks optically independent of each other. The width of (11 ij) is preferably from 0 to 20 µm. In the present invention, (11 ij) are named comprehensively as crevasses.
13 is a protective layer and 14 is an adhesive layer between the base layer 12' and the stimulable phosphor layer 11. These layers are provided if necessary.
The stimulable phosphor in the radiation image storage panel of the present invention refers to a phosphor exhibiting stimulated emission corresponding to the dose of the first light or high energy radiation by optical, thermal, mechanical or electrical stimulation (stimulating excitation) after irradiation by the first light or high energy radiation. It is preferably a phosphor exhibiting stimulated emission by a stimulating excitation light of a wavelength of 500 nm or longer. Examples of stimulable phosphor are: BaS0₄:Ax (where A is at least one of Dy, Tb and Tm, and 0.001≦x<1 mol %) disclosed in JP-B-4880487; MgS0₄:Ax (where A is either Ho or Dy and 0.001≦x≦1 mole %) disclosed in JP-B-4880488; SrSO₄:Ax (where A is at least one of Dy, Tb and Tm and 0.001≦x<1 mole %) disclosed in JP-B-4880489; those in which at least one of Mn, Dy and Tb is added to, for example, Na₂S0₄, CaS0₄ and BaS0₄ as disclosed in JP-B-51298891976; those such as BeO, Lif, MgS0₄ and CaF₂ as disclosed in Japanese Provisional Patent Publication No. JP-B-5230487; those such as Li₂B₄0₇,Cu,Ag as disclosed in JP-B-5339277; those such as Li₂O · (B₂O₂)x:Cu where 2<x≦3) and Li₂O· (B₂O₂)x:Cu,Ag (where 2<x≦3), as disclosed in JP-B-5447883; SrS:Ce,Sm, SrS:Eu,Sm, La₂0₂S:Eu,Sm and (Zn,Cd)S:Mn,X (where X is a halogen) disclosed in US-A-3,859,527; ZnS:Cu,Pb phosphors disclosed in JP-B-5512142; and barium aluminate phosphors BaO· xAl₂O₃:Eu (where 0.8≦x≦10) and alkaline earth metallosilicate type phosphors M"O· xSi0₂:A (where M^ll is Mg, Ca, Sr, Zn, Cd or Ba, A is at least one of Ce, Tb, Eu, Tm, Pb, TI, Bi and Mn and 0.5≦x≦2.5). Additional examples of phosphors include, as disclosed in JP-B-5512143, those of the formula:
(where X is at least one of Br and CI and 0<x+y≦0.6, xy≠0 and 10^-6≦e≦10^-2); those disclosed in JP-B-5512144 which corresponds to US-A-4,236,078:
(where Ln represents at least one of La, Y, Gd and Lu; X represents CI and/or Br; A represents Ce and/or Tb; and 0<x<0.1); those disclosed in JP-B-5512145:
(where M" represents at least one of Mg, Ca, Sr, Zn and Cd; X represents at least one of Cl, Br and I; A represents at least one of Eu, Tb, Ce, Tm, Dy, Pr, Ho, Nd, Yb and Er; and O≦x≦0.6 and 0≦y≦0.2); those discdlosed in JP-B-5584389:
(where X is at least one of Cl, Br and I; A is at least one of ln, TI, Gd, Am and Zr; and 0<x≦2x10^-1 and 0<y≦5x10^-2); those disclosed in JP-B-55160078:
(where M" is at least one of Mg, Ca, Ba, Sr, Zn and Cd; A is at least one of BeO, MgO, CaO, SrO, BaO, ZnO, AI₂0₃, Y₂0₃, La₂0₃, ln₂O₃, SiO₂, TiO₂, ZrO₂, Ge0₂, SnO₂, Nb₂O₅, Ta₂O₅ and Th0₂; Ln is at least one of Eu, Tb, Ce, Tm, Dy, Pr, Ho, Nd, Yb, Er, Sm and Gd; X is at least one of Cl, Br and I; and 5x10^-5≦x≦0.5and 0<y≦0.2) (rare earth element activated divalent metal fluoride phosphors); ZnS:A, (Zn,Cd)S:A, CdS:A, ZnS:A,X and CdS:A,X (where A is Cu, Ag, Au or Mn; X is a halogen); those disclosed in JP-B-57148285/1982:

(where each of M and N represents at least one of Mg, Ca, Sr, Ba, Zn and Cd; X represents at least one of F, Cl, Br and I; A represents at least one of Eu, Tb, Ce, Tm, Dy, Pr, Ho, Nd, Er, Sb, TI, Mn and Sn; and x and y are integers satisfying the conditions 0<x≦6 and O≦y≦1);

(where Re represents at least one of La, Gd, Y and Lu; A represents at least one of the alkaline earth metals Ba, Sr and Ca; X and X' each represent at least one of F, CI and Br; and x and y are integers satisfying the conditions 1 x 10^-4<x<3x 10^-1 and 1 x 10^-4<y<1 x 10^-1, and n/m satisfies the condition 1x10^-3<n/ m<7x10-'; and
(where M'is at least one alkali metal selected from Li, Na, K, Rb and Cs, preferably Na, K, Rb and Cs; M" is at least one divalent metal selected from Be, Mg, Ca, Sr, Ba, Zn, Cd, Cu and Ni; M"' is at least one trivalent metal selected from Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Ga and In; X, X' and X" are each at least one halogen selected from F, Cl, Br and I; A is at least one metal selected from Eu, Tb, Ce, Tm, Dy, Pr, Ho, Nd, Yb, Er, Gd, Lu, Sm, Y, Tl, Na, Ag, Cu and Mg, preferably TI; and 0≦a<0.5, 0≦b<0.5 and 0<cZ0.2) (alkali halide phosphors).
Alkalide halide phosphors are preferred, because stimulable phosphor layers can be formed easily by methods such as vacuum vapor deposition and sputtering.
The stimulable phosphor is not limited to those described above; any phosphor which can exhibit stimulated fluorescence when irradiated with a stimulating excitation light after irradiation by radiation may be used.
The radiation image storage panel of the present invention may have a group of stimulable phosphor layers comprising one or more stimulable phosphor layers comprising at least one of the stimulable phosphors as mentioned above. The stimulable phosphors contained in respective stimulable phosphor layers may be identical or different.
Various polymeric materials, glasses or metals may, for example, be used as the support. Materials which can be worked into flexible sheets or webs are preferred for information recording materials, such as plastics films such as cellulose acetate film, polyester film, polyethyleneterephthalate film, polyamide film, polyimide film, triacetate film or polycarbonate film, metal sheets, for example of aluminium, iron, copper or chromium or metal sheets having coats of the oxides of said metals.
These supports may have thicknesses which differ depending on the material of the support. The thicknesses are generally from 80 µm to 1000 pm, more preferably from 80 pm to 500 pm from the standpoint of suitability of handling.
In the radiation image storage panel of the present invention, it is preferred to provide a protective layer to protect physically and chemically the exposed surface of the stimulable phosphor layers. The protective layer may be formed by direct coating of a coating liquid on the stimulable phosphor layer, or alternatively a protective layer separately formed may be adhered to the stimulable phosphor layer. The materials for the protective layer include, for example, conventional materials such as cellulose acetate, nitrocellulose, polymethyl methacrylate, polyvinyl butyral, polycarbonate, polyester, polyethyleneterephthalate, polyethylene, polyvinylidene chloride and nylon (trade name).
The protective layer may also be formed by laminating inorganic substances such as SiC, Si0₂, SiN or A1₂0₃ by, for example, vacuum deposition or sputtering.
These protective layers preferably have a thickness of from 0.1 pm to 100 pm.
Gas phase deposition methods in which the stimulable phosphor layer contains no binder are now described.
The first method is vacuum deposition. A support is first set in a vacuum deposition device and the device is evacuated to about 10-⁶ Torr (0.133x10^-3Pa).
Then, at least one of the stimulable phosphors is evaporated by heating by, for example resistance heating or electron beams, to deposit the stimulable phosphor on the support surface.
As a result, a stimulable phosphor layer containing no binder is formed. It is also possible to form the stimulable phosphor in a plurality of separate stages in the vapor deposition step. A plurality of resistance heaters or electron beams may be employed to effect co-deposition.
After completion of vapor deposition, if desired, on the side opposite to the support side of the stimulable phosphor layer, a protective layer is preferably provided.
Alternatively, it is possible to provide the support after formation of the stimulable phosphor layer on the protective layer.
In the above vacuum vapor deposition method, it is also possible to form a stimulable phosphor layer simultaneously with synthesis of the desired phosphor layer on a support by co-depositing stimulable phosphor starting materials by means of a plurality of resistance heaters or electron beams. The subject on which vapor deposition is effected (the support or protective layer) may be cooled or heated, if desired. After completion of vapor deposition, the stimulable phosphor layer may be subjected to heat treatment.
The second method is a sputtering method. In this method, after a support is set in a sputter device similarly as in the vapor deposition method, the device is internally evacuated to a vacuum degree of about 10-^s Torr (0.133x10-³ Pa), and then an inert gas such as Ar or He is introduced to adjust the pressure to about 10-³ Torr (0.133 Pa).
Then, using the above stimulable phosphor as the target, sputtering is effected to deposit the stimulable phosphor on the support surface to a desired thickness.
In the sputter step, the stimulable phosphor layer can be formed in a plurality of separate stages, similarly as in the vacuum vapor deposition method, or alternatively the stimulable phosphor layer can be formed using a plurality of targets comprising stimulable phosphors different from each other by sputtering at the same time or successively.
After completion of the sputtering, similarly as in the vacuum vapor deposition method, a protective layer may be formed, if desired, on the side opposite to the support side of the stimulable phosphor layer. Alternatively, it is possible to provide the support after formation of the stimulable phosphor layer on the protective layer.
In the sputter method, it is also possible to use a plurality of starting materials for the stimulable phosphor as the targets, sputtering these at the same time or successively to form a stimulable phosphor layer simultaneously with synthesis of the stimulable phosphor. Alternatively, reactive sputtering may be conducted by introducing a gas such as O2 or H₂ if necessary.
In the sputter method, the subject to be sputtered (the support or protective layer) may be either cooled or heated. The stimulable phosphor layer may be subjected to heat treatment after completion of sputtering.
The third method is a CVD method. An organometallic compound containing the desired stimulable phopshor or starting materials therefor is decomposed by, for example, heat or high frequency power to obtain a stimulable phosphor layer containing no binder.
Next, by referring to Figs. 3(a) and 3(b), a process for producing the panel of the present invention is described.
Production steps are in the order (b)-(a) in Figs. 3(a) and 3(b).
Step (b): Support having a fine concavo-convex pattern:

The base pattern having concavities (12ij) and convexities 12ij on the surface of the support 12 can be made by embossing the support itself, printing in which drying and curing treatments are applied after printing using an ink containing a resin capable of adhering to the support by curing with, for example, light, heat or chemicals, or photographic etching. According to the photographic etching method, when using, for example, a light-sensitive resin plate, a mask having an opaque island pattern is closely positioned on the surface of, for example, a nylon type light-sensitive resin (Printight; produced by Toyo Boseki K.K.), followed by irradiation with UV-rays at a light-sensitive wavelength region of from 250 to 400 nm. After exposure, the light-sensitive resin is developed. By this development the non-exposed portion is removed and the exposed portion remains as the convexity.

Step (a): Stimulable phosphor layer 11:

As the method for forming the stimulable phosphor layer, the gas phase deposition method is most preferred in view of the certainty of pillar-shaped block formation and sensitivity.
In the process for producing the panel shown in Fig. 5, the production steps are in the order (b)-(a).

Step (b): Distributed pattern of fine tiles plates 12ij and gaps (12ij):

Conducted according to the same method as in Fig. 11 as described above.

Step (a): Stimulable phosphor 11:

Conducted according to the same method as in Fig. 3(a) as described above.
In the process for producing the panel of the present invention as shown in Fig. 7, the production steps are in the order (c)-(b)-(a).
In Fig. 7, steps (c) and (a) are conducted in the same manner as steps (b) and (a) respectively in Fig. 5 as described above.

Step (b): Net with fine-strings 15ij:

The material for the net with fine strings 15ij surrounding the fine tiles 12ij and filling the gaps (12ij) is preferably one having different crystallization conditions and/or physical properties such as thermal expansion. It is practically a metal. The net may be prepared by electric plating.
Accordingly, when employing a plastic dielectric material as the support, an electroconductive layer such as a metal or indium oxide is provided on its surface by vacuum vapor deposition or other methods before step (c), and said electroconductive layer is exposed by etching. The same is the case when a metal sheet having a metal oxide coating layer is used.
By performing electric plating in a conventional manner on the support having satisfied the above conditions, a net with fine strings 15ij comprising, for example, nickel or chromium is formed. For depositing conveniently the stimulable phosphor as fine pillar-shaped blocks on the fine tiles 12ij in this case, it is preferable that the height h of the fine strings 15ij of the net is, equal to or greater than the thickness d of the fine tiles on the electroconductive support surface.
The steps for production of the panel shown in Fig. 8 are in the order Fig. 8(c)→Fig.8(b)→Fig. 8(a).
The step of Fig. 8(c) is conducted in the same manner as the successive combinations of Fig. 5(b) and Fig. 7(b) and the step of Fig. 8(b) in the same manner as the step of Fig. 3(a).

Step (a): Shock treatment:

The shock treatment imparts a fine pillar-shaped (including polypyramid-shaped) block structure having an inner reflective surface against the stimulating excitation light incident on the stimulable phosphor layer deposited on the fine tiles 12ij having formed crevasses or cracks formed on the surface by giving shock to the deposited layer with the acting base point, thereby propagating ruptures up to the surface.
Accordingly, any method may be employed, provided that ruptures in the form of crevasses or cracks can be provided without impairing the function of the panel.
For example, a heat treatment method may be employed in which ruptures are formed by heating or cooling using the difference in thermal expansion between the stimulable phosphor and the plastic, metal of the support or net as described above; a sonication method in which the crystal dislocation line or the structural distortion existing at the bonded point of the phosphor in the cavityi (11 ij) is vibrated to permit the cracks to grow and develop on the surface from the bonded point; or a voltage rupture method, for example simulating insulating destruction of a capacitor with an alternating current.
Since the stimulable phosphor layer 11 having a fine pillar-shaped block structure preferably has effective inner reflective surfaces against stimulating excitation light in each block and a substantially continuous and smooth surface to enhance of sensitivity and sharpness, the rupture on the surface should preferably be a crack with no substantial gap.
For the above reason, the heat treatment method may conveniently be used.
The heat treatment method may be carried out by heating the panel completed in step (b) to about 300°C in an inert gas such as nitrogen and cooling the panel after it has reached thermal equilibrium with a large amount of cold nitrogen gas, to develop the crack from the tip of the cavity (11 ij) (bonded point of the phosphor) until it reaches the surface. In the case of a good cooling effect, the heating temperature may be lower. For example, a temperature of about 150°C can be used when cold alcohol is used for cooling.
It is critical in the heat treatment method to have the stimulable phosphor sufficiently adsorbed with an inert gas prior to heating. By heat treatment, there is no peeling, damage or contamination of the stimulable phosphor.
For producing of the panel of the present invention shown in Figs. 9(a) to 9(c), the above gas phase vapor deposition method may be employed. When employing vacuum vapor deposition, the pressure in the device may be made to about 10-' Torr (1.33x10-⁵ Pa) similarly as described above and, after treatment of the support, the vacuum degree is controlled to about 4x10-' Torr (0.532 Pa) with argon.
Next, current is passed through the boat or crucible, and an alkali halide, such as rubidium bromide, present in the boat or crucible is evaporated by resistance heating. When the crystal grain layer of rubidium bromide can be vapor deposited as shown in Fig. 2, vapor deposition is stopped. In this case, the electron beam method may be used in place of resistance heating. After the vacuum degree is made to about 5x10-⁶ Torr (6.65x10-" Pa) and the temperature of the support is set to 100°C, a rubidium bromide phosphor activated with thallium is vapor deposited to a film thickness of about 250 pm. As a result, a stimulable phosphor with a fine pillar-shaped block structure is deposited on the crystal grains as in Fig. 10.
A stimulable phosphor layer containing no binder is formed; it is also possible to effect co-deposition by use of a plurality of resistance heaters or electron beams in the vapor deposition step.
After completion of vapor deposition, the radiation image storage panel can be produced following prescribed procedures.
In the case of the sputtering method, after usual operations, in order to obtain the layer 11 a in Figs. 9(a) to 9(c), sputtering is effected with the use of, for example, an alkali halide crystal Rbl as the target. Sputtering is stopped when a pattern as shown in Fig. 10 is formed. Using, for example, rubidium bromide activated with thallium as the target, sputtering is further effected on the layer 11a to deposit a stimulable phosphor with a fine pillar-shaped block structure to a desired thickness.
Thereafter, according to the same procedure as described above, a panel of the present invention can be obtained.
Furthermore, after the layer 11a has been obtained according to the sputtering method or the CVD method, a stimulable phosphor with a fine pillar-shaped block structure may be deposited to a desired thickness by vacuum vapor deposition. In this case, there are the advantages that the layer can be provided thinly and uniformly, and also that deposition of the stimulable phosphor with a fine pillar-shaped block structure can be done rapidly.
For formation of the panel of the present invention having at least two layers of pillar-shaped blocks as shown in Fig. 11, either one of the gas phase deposition methods or a successive combination of both may be used.
Since the stimulable phosphor with a pillar-shaped block structure can have a variety of optical, electromagnetic or other physical characteristics such as strength, various controlling mechanisms and composite functions can be introduced into the panel.
For example, by increasing the optical density of the uppermost layer, the light-receiving efficiency of stimulating excitation light incident obliquely on the panel can be improved. By making the uppermost layer highly abrasion resistant, durability of the panel can be improved.
Additionally, by increasing, for example, the humidity resistance of the uppermost layer, the humidity resistance of the panel can be improved to enhance storability.
Fig. 12(a) shows one example (line (a)) of the relationship of the thickness of the stimulable phosphor layer in the radiation image storage panel of the present invention obtained by gas phase deposition and the amount of the stimulable phosphor corresponding to said layer thickness versus the radiation sensitivity.
The stimulable phosphor layer formed by gas phase deposition as used in the present invention contains no binder, and therefore the amount of the stimulable phosphor applied (filling ratio) is about twice that provided by coating in the prior art. Thus not only the radiation absorption per unit thickness of the stimulable phosphor layer can be improved to increase radiation sensitivity, but also the image graininess can be enhanced.
The stimulable phosphor layer produced by gas phase vapor deposition has excellent transparency and is highly transmissive of stimulating excitation light and stimulated emission. Therefore the layer can be made thicker than the stimulable phosphor layer of the prior art to further increase radiation sensitivity.
In the panel of the present invention, due to the optical induction effect of the fine pillar-shaped block structure, the stimulating excitation light repeats reflection on the inner surface of the blocks with little dissipation out of the block, and therefore image sharpness is improved. Lowering of sharpness accompanied with an increase in thickness of the stimulable phosphor layer can be reduced.
The radiation image storage panel of the present invention can given excellent sharpness, graininess and sensitivity when employed in the radiation image storage method schematically shown in Fig. 13. In Fig. 13, 41 is a radiation generating device, 42 is a subject, 43 is a radiation image storage panel of the present invention, 44 is a stimulating excitation light source, 45 is a photoelectric converting device for detection of the stimulated emission radiated from said radiation image storage panel, and 48 is a filter for separating the stimulating excitation light from stimulated emission to permit only the stimulated emission to pass. The devices of 45 et seq are not particularly limited to those as mentioned above, provided that they can reproduce the optical information from 43 as an image in some form.
As shown in Fig. 13, radiation from the radiation generating device 41 passes through the subject 42 and enters the radiation image storage panel 43 of the present invention. The incident radiation is absorbed by the stimulable phosphor layer of the radiation image storage panel 43 to form an image corresponding to the radiation transmitted image. Next, the accumulated image is excited by stimulating excitation light from the stimulating excitation light source 44 and stimulated emission is released. In the radiation image storage panel of the present invention, since the stimulable phosphor layer has a fine pillar-shaped block structure, the diffusion of the stimulating excitation light within the stimulable phosphor layer during scanning by the above stimulating excitation light is inhibited.
The intensity of the stimulated emission radiated is proportional to the radiation energy quantity accumulated, and the optical signal can be converted photoelectrically by means of, for example, a photoelectric converting device 43, such as a photomultiplier tube, and reproduced by an image reproducing device 46 as an image, whereby the image of the subject can be observed.
The present invention is further described in the following Examples.

Example 1

A 500 pm thick aluminium sheet support was set in a depositing vessel. Next, an alkali halide stimulable phosphor (0.9 RbBr - 0.1CsF:0.01 TI) was placed in a tungsten boat and set on electrodes for resistance heating and subsequently the deposition vessel was evacuated to a vacuum degree of 2x10-⁶ Torr (0.266x10-3 Pa).
Current was passed through the tungsten boat and the alkali halide stimulable phosphor was evaporated by resistance heating to deposit a 300 pm thick stimulable phosphor layer on the aluminium sheet. Subsequently, the sheet was heated to 300°C in vacuum, and then quenched to obtain a radiation image storage panel A of the present invention.
After the panel A was irradiated with 10 mR X-rays at a tube voltage of 80 KVp, stimulation excitation was effected with a He-Ne laser beam (633 nm) and the stimulated emission radiated from the stimulable phosphor layer was photoelectrically converted by an optical detector (photomultiplier tube). The signal obtained was reproduced by an image reproducing device and recorded on a silver salt film. From the size of the signal, sensitivity of the panel A to X-rays was examined, and from the image obtained, the modulation transmission function (MTF) and image graininess were examined to give the results as shown in Table 1.
In Table 1, sensitivity to X-rays is shown as a relative value to that of the panel A, which is 100. The modulation transmission function (MTF) is the value at 2 cycles mm space frequency, and graininess is represented by 0, 0 or X meaning good, common or bad respectively.

Example 2

On the surface of a 500 pm thick aluminum sheet support, a mesh of 50 pm diameter metal wire was pressure coated, and the composite was set in a sputtering device. Next, an alkali halide stimulable phosphor (0.95 RbBr - 0.05 CsF:0.005 TI) was set in the sputtering device, followed by evacuation to a vacuum degree of 1x10^-6Torr (0.133x10^-3 Pa). Sputtering was performed with Ar as the sputter gas to effect deposition until the thickness of the layer on the metal mesh was 300 pm to obtain a radiation image storage panel B of the present invention.
The panel B was evaluated similarly as in Example 1 to obtain the results in Table 1.

Example 3

A 500 pm thick aluminium plate was coated with a photoresist resin and subjected to pattern exposure and development to form a minute concavo-convex pattern as shown in Fig. 2(d) to provide a support.
The minute concavo-convex pattern had a size of 80 umx80 µm and a thickness of 40 um.
Next, the support was set in a vapor deposition vessel, an alkali halide stimulable phosphor (0.9 RbBr . 0.1 CsF:0.01 TI) was placed in a tungsten boat and set on electrodes for resistance heating and subsequently the deposition vessel was evacuated to a vacuum degree of 2x10-⁶ Torr (0.266x10-³ Pa).
Current was passed through the tungsten boat and the alkali halide stimulable phosphor was evaporated by resistance heating to deposit a 300 pm thick stimulable phosphor layer on the support to obtain a radiation image storage panel C of the present invention.
After the panel C was irradiated with 10 mR X-rays at a tube voltage of 80 KVp, stimulation excitation was effected with a He-Ne laser beam (633 nm) and the stimulated emission radiated from the stimulable phosphor layer was photoelectrically converted by an optical detector (photomultiplier tube). The signal obtained was reproduced by an image reproducing device and recorded on a silver salt film. From the size of the signal, sensitivity of the panel C to X-rays was examined, and from the image obtained, modulation transmission function (MTF) and image graininess were examined to give the results shown in Table 2.
In Table 2, sensitivity to X-rays is shown as a relative value to that of the radiation image storage panel C, which is 100. The modulation transmission function (MTF) and graininess are shown as in Table 1.

Example 4

A radiation image storage panel D of the present invention was prepared in the same manner as in Example 3, except for using as the support a black polyethyleneterephthalate film, the surface of which was subjected to embossing to form a fine concavo-convex pattern.
The panel D was evaluated similarly as in Example 3 to give the results shown in Table 2.

Comparative Example 1

Eight parts by weight of an alkali halide stimulable phosphor (0.9 RbBr . 0.1 CsF:0.01 TI), one part by weight of a polyvinyl butyral resin and five parts by weight of a solvent (cyclohexanone) were mixed and dispersed to prepare a stimulable phosphor coating liquid. The coating liquid was applied uniformly on a black polyethylene terephthalate film as a support placed horizontally with a thickness of 300 µm, followed by natural drying, to obtain a 300 pm thick stimulable phosphor layer.
The comparative radiation image storage panel a thus obtained was evaluated similarly as in Example 3 to obtain the results listed in Table 2.

Comparative Example 2

A radiation image storage panel e was prepared in the same manner as in Comparative Example 1 except for making the thickness of the stimulable phosphor layer 130 pm.
The panel b was evaluated similarly as in Example 3 to obtain the results listed in Table 2.
As seen from Table 2, the panels C and D of the present invention have about twice the sensitivity and more excellent image than graininess panels a and b. This is because the panels of the present invention contain no binder and have better X-ray absorption with a higher filling ratio of the stimulable phosphor than the Control panels.
The panels C and D of the present invention have better sharpness than panels a and b in spite of higher X-ray sensitivity. This is because the stimulable phosphor layer of the radiation image storage panel of the present invention has a block structure in shape of fine pillars, whereby scattering of He-Ne laser stimulating excitation light within the stimulable phosphor is suppressed and reduced.

Example 5

A 500 µm thick aluminium plate was subjected to anodic oxidation treatment, sealing treatment and heat treatment to form a support with a surface structure with a large number of tiles separated from each other by fine gaps, which was set in a vapor deposition vessel. The tiles had an average size of 60 pm.
Next, an alkali halide stimulable phosphor (0.9 RbBr - 0.1 CsF:0.01 TI) was placed in a tungsten boat and set on electrodes for resistance heating; subsequently the deposition vessel was evacuated to a vacuum degree of 2x10-^s Torr (0.266x10-³ Pa).
Current was passed through the tungsten boat and the alkali halide stimulable phosphor was evaporated by resistance heating to deposite a 300 pm thick stimulable phosphor layer to obtain a radiation image storage panel E of the present invention.
After the panel E was irradiated with 10 mR X-rays at a tube voltage of 80 KVp, stimulation excitation was effected with a He-Ne laser beam (633 nm) and the stimulated emission radiated from the stimulable phosphor layer was photoelectrically converted by an optical detector (photomultiplier tube). The signal obtained was reproduced by an image reproducing device and recorded on a silver salt film. From the size of the signal, sensitivity of the panel E to X-rays was examined, and from the image obtained, modulation transmission function (MTF) and image graininess were examined to give the results shown in Table 3.
In Table 3, sensitivity to X-rays is shown as a relative value to that of the radiation image storage panel E, which is 100. Modulation transmission function (MTF) and image graininess.

Example 6

A radiation image storage panel F of the present invention was obtained in the same manner as in Example 5 except for changing the thickness of the stimulable phosphor layer to 150 pm.
The panel F was evaluated similarly as in Example 5 to obtain the results listed in Table 3.

Example 7

A radiation image storage panel G of the present invention was obtained in the same manner as in Example 5 except for changing the average size of the tiles to 120 pm.
The panel G was evaluated similarly as in Example 5 to obtain the results listed in Table 3.

Example 8

In Example 5, after a 500 pm thick aluminium plate was subjected to anodic oxidation treatment, sealing treatment and heat treatment to form a support with a surface structure having a large number of tiles separated from each other by fine gaps, metallic aluminium was vacuum deposited to a thickness of 0.1 µm, following otherwise the same procedure as in Example 5, to obtain a radiation image storage panel H of the present invention. By vapor depositing thinly the metallic aluminium, the tile-shaped surface of the aluminium suport became blackened.
The panel H was evaluated similarly as in Example 5 to obtain the results listed in Table 3.

Example 9

In Example 5, after a 500 µm thick aluminium plate was subjected to anodic oxidation treatment, sealing treatment and heat treatment to form a support with a surface structure having a large number of tiles separated from each other by fine gaps, metallic aluminium was vacuum deposited to a thickness of 1 pm, following otherwise the same procedure as in Example 5, to obtain a radiation image storage panel I of the present invention. By vapor depositing thickly the metallic aluminium, the reflectance of the tile-shaped surface of the aluminium support was improved by about 20%.
The panel I was evaluated similarly as in Examples 5 to obtain the results listed in Table 3.

Comparative Example 3

Eight parts by weight of an alkali halide stimulable phosphor (0.9 RbBr - 0.1 CsF:0.01 TI), one part by weight of a polyvinyl butyral resin and five parts by weight of a solvent (cyclohexanone) were mixed and dispersed to prepare a stimulable phosphor coating liquid. The coating liquid was applied uniformly on a black polyethylene terephthalate film as a support placed horizontally with a thickness of 300 pm, followed by natural drying, to obtain a 300 pm thick stimulable phosphor layer.
The comparative radiation image storage panels thus prepared was evaluated similarly as in Example 5 to obtain the results listed in Table 3.

Comparative Example 4

Comparative Example 3 was repeated except that the thickness of the stimulable phosphor layer was changed to 150 um to obtain a comparative radiation image storage panel d.
The panel dwas evaluated in the same manner as in Example 5 to obtain the results listed in Table 3.
As seen from Table 3, the radiation image storage panels E to I of the present invention have about twice the sensitivity and better image graininess than the radiation image storage panels c and d having corresponding thicknesses. This is beacuse the radiation image storage panel of the present invention contains no binder and has better X-ray absorption with a higher stimulable phosphor filling ratio than the Control panel.
The radiation image storage panels E to I of the present invention have better sharpness than the radiation image storage panels c and d in spite of higher X-ray sensitivity.

Example 10

A 500 pm thick aluminium plate was subjected to anodic oxidation treatment, sealing treatment and heat treatment according to the methods as described above to form a support with a surface structure having a large number of tiles separated from each other by fine gaps, which was set in a vapor deposition vessel.
The tiles had an average size of 60 µm and a thickness d of 10 pm. Subsequently, by nickel plating the aluminium plate, a net surrounding the fine tiles to partition them from each other was formed. The net had a height h of 16 pm.
Next, an alkali halide stimulable phosphor (0.9 RbBr - 0.1 CsF:0.01 TI) was placed in a tungsten boat and set on electrodes for resistance heating; subsequently the deposition vessel was evacuated to a vacuum degree of 2x10^-6 Torr (0.066x10-3 Pa).
Current was passed through the tungsten boat and the alkali halide stimulable phosphor was evaporated by resistance heating to deposit a stimulable phosphor layer at a layer thickness of 300 pm to obtain a radiation image storage panel J of the present invention.
After the panel J was irradiated with 10 mR X-rays at a tube voltage of 80 KVp, stimulation excitation was effected with a He-Ne laser beam (633 nm) and the stimulated emission radiated from the stimulable phosphor layer was photoelectrically converted by an optical detector (photomultiplier tube). The signal obtained was reproduced by an image reproducing device and recorded on a silver salt film. From the size of the signal, sensitivity of the panel J to X-rays was examined, and from the image obtained, modulation transmission function (MTF) and image graininess were examined to give the results shown in Table 4.
In Table 4, sensitivity to X-rays is shown as a relative value to that of the radiation image storage panel J, which is 100. Modulation transmission function (MTF) and image graininess are shown as in Table 1.

Example 11

A radiation image storage panel K of the present invention was obtained in the same manner as in Example 11 except for changing the thickness of the stimulable phosphor layer to 150 µm.
The panel K was evaluated similarly as in Example 10 to obtain the results listed in Table 4.

Example 12

A radiation image storage panel L of the present invention was obtained in the same manner as in Example 10 except for changing the average size of the tiles to 115 pm.
The panel L was evaluated similarly as in Example 10 to obtain the results listed in Table 4.

Example 13

A radiation image storage pattern M of the present invention was obtained in the same manner as in Example 10 except for changing the height h of the net to 11 pm.
The panel M was evaluated similarly as in Example 10 to obtain the results listed in Table 4.

Example 14

In Example 10, after a 500 µm thick aluminium plate was subjected to the treatment of Example 10 to form a net surrounding the fine tiles on the aluminium surface to separate them from each other, metallic aluminium was vacuum deposited to a thickness of 0.1 µm, following otherwise the same procedure as in Example 10, to obtain a radiation image storage panel N of the present invention. By vapor depositing thinly the metallic aluminum, the tile-shaped surface of the aluminium support became blackened.
The panel N was evaluated similarly as in Example 10 to obtain the results listed in Table 4.

Example 15

In Example 10, after a 500 µm thick aluminium plate was subjected to the treatment of Example 11 to form a net surrounding the fine tiles on the aluminium surface to separate them from each other, metallic aluminium was vacuum deposited to a thickness of 1 µm, following otherwise the same procedure as in Example 10, to obtain a radiation image storage panel 10 of the present invention. By vapor depositing thickly the metallic aluminium, the reflectance of the tile-shaped surface of the aluminium support was improved by about 20%.
The radiation image storage panel 10 of the present invention thus prepared was evaluated similarly as in Example 10 to obtain the results listed in Table 4.

Example 16

Except for using as the support a 500 pm thick aluminium plate which was coated with a photoresin resin, baked with a pattern of fine tiles, developed and further dried to form fine tiles, the procedure of Example 10 was followed to obtain a radiation image storage panel P of the present invention.
The fine tiles were square with a side length of 100 pm and a thickness d of 10 um. The gap width was 10 µm.
The panel P was evaluated similarly as in Example 10 to obtain the results listed in Table 4.

Comparative Example 5

Eight parts by weight of an alkali halide stimulable phosphor (0.9 RbBr - 0.1 CsF:0.01 TI), one part by weight of a polyvinyl butyral resin and five parts by weight of a solvent (cyclohexanone) were mixed and dispersed to prepare a stimulable phosphor coating liquid. The coating liquid was applied uniformly on a 300 µm thick black polyethylene terephthalate film support placed horizontally, followed by natural drying, to obtain a 300 µm thick stimulable phosphor layer.
The comparative radiation image storage panel e thus prepared was evaluated similarly as in Example 10 to obtain the results listed in Table 4.

Comparative Example 6

Comparative Example 5 was repeated except that the thickness of the stimulable phosphor layer was changed to 150 µm to obtain a comparative radiation image storage panel f.
The panel fwas evaluated in the same manner as in Example 10 to obtain the results listed in Table 4.
As seen from Table 4, the radiation image storage panels J to P of the present invention have about twice the sensitivity and better image graininess than the radiation image storage panels e and f having corresponding stimulable phosphor thicknesses. This is because the radiation image storage panel of the present invention contains no binder and has better X-ray absorption with a higher filling ratio of the stimulable phosphor than the Control panel.
Also, the radiation image storage panels J to P of the present invention have better sharpness than the radiation image storage panels e and f in spite of higher X-ray sensitivity.

Example 17

A 500 pm thick aluminum plate was subjected to anodic oxidation treatment, sealing treatment and heat treatment according to the methods described above to form a support with a surface structure having a large number of tiles separated from each other by fine gaps, which was set in a vapor deposition vessel. The tiles had an average size of 65 pm.
Next, an alkali halide stimulable phosphor (0.9 RbBr - 0.1 CsF:0.01 TI) was placed in a tungsten boat and set on electrodes for resistance heating; subsequently the deposition vessel was evacuated to a vacuum degree of 2x10-⁶ Torr (0.266x10-³ Pa).
Current was passed through the tungsten boat and the alkali halide stimulable phosphor was evaporated by resistance heating to deposit a 300 µm thick stimulable phosphor layer.
Next, the panel was taken out from the vapor deposition vessel, heated to 300°C in a nitrogen atmosphere, maintained in this state for 10 mins, followed by removal of the heating furnace simultaneously with quenching by increasing the nitrogen flow rate to apply shock and obtain a radiation image storage panel Q of the present invention.
After the panel Q was irradiated with 10 mR X-rays at a tube voltage of 80 KVp, stimulation excitation was effected with a He-Ne laser beam (633 nm) and the stimulated emission radiated from the stimulable phosphor layer was photoelectrically converted by an optical detector (photomultiplier tube). The signal obtained was reproduced by an image reproducing device on a silver salt film. From the size of the signal, sensitivity of the radiation image storage panel Q to X-rays was examined, and from the image obtained, modulation transmission function (MTF) and image graininess were examined to give the results shown in Table 5.
In Table 5, sensitivity to X-rays is shown as a relative value to that of the radiation image storage panel R which is 100. Modulation transmission function (MTF) and image graininess are shown as in Table 1.

Example 18

A radiation image storage panel R of the present invention was obtained in the same manner as in Example 17 except for applying the shock treatment by heating the panel to 150°C in a nitrogen atmosphere, maintaining under this state for 10 mins and then quenching the panel by dipping it in methanol.
The panel R was evaluated similarly as in Example 9 to obtain the results listed in Table 5.

Example 19

A radiation image storage panel S of the present invention was obtained in the same manner as in Example 17 except for applying the shock treatment by adsorbing nitrogen gas onto the stimulable phosphor layer of the panel, then heating the panel in vacuum to 300°C, followed by quenching.
The panel S was evaluated similarly as in Example 17 to obtain the results listed in Table 5.

Example 20

In Example 17, after a 500 pm thick aluminium plate was subjected to anodic oxidation treatment, sealing treatment and heat treatment according to the methods described above to form a surface structure having a large number of tiles separated from each other by fine gaps, nicke plating was applied to form a net surrounding the fine tiles on the aluminium surface to separate them from each other, following otherwise the same procedure as in Example 17. A radiation image storage panel T of the present invention was obtained.
In the above support, the fine tiles had an average size of 62 µm and a thickness d of 10 pm, while the height of the net was 16 pm.
The panel T was evaluated similarly as in Example 17 to obtain the results which are listed in Table 5.

Comparative Example 7

Eight parts by weight of an alkali halide stimulable phosphor (0.9 RbBr - 0.1 CsF:0.01 TI), one part by weight of a polyvinyl butyral resin and five parts by weight of a solvent (cyclohexanone) were mixed and dispersed to prepare a stimulable phosphor coating liquid. The coating liquid was applied uniformly on a 300 µm thick black polyethylene terephthalate film support placed horizontally, followed by natural drying, to obtain a 300 pm thick stimulable phosphor layer.
The comparative radiation image storage panel g thus produced was evaluated similarly as in Example 17 to obtain the results listed in Table 5.
As seen from Table 5, the radiation image storage panels Q to T of the present invention have about twice the sensitivity and better image graininess than the radiation image storage panel g having a corresponding stimulable phosphor thickness. This is because the radiation image storage panel of the present invention contains no binder and has better X-ray absorption with a higher stimulable phosphor filling ratio than the control panel.
The radiation image storage panels Q to T of the present invention had better sharpness than the radiation image storage panel g in spite of higher X-ray sensitivity.
As described above, according to the present invention, since the stimulable phosphor layer has a fine pillar block structure, scattering of the stimulation exciting light within the stimulable phosphor layer is markedly reduced, whereby image sharpness is improved.
Additionally, according to the present invention, since lowering of image sharpness, due to increase of the stimulable phosphor layer is small, radiation sensitivity and image graininess can be improved by enlargement of the stimulable phosphor layer without lowering image sharpness.
Furthermore, according to the present invention, the radiation image storage panel can be produced stably at low cost.
The present invention has great effect and is useful in industrial applications.

Claims

1. A radiation image storage panel having a stimulable phosphor layer on a support, wherein said stimulable phosphor layer has a fine pillar-shaped block structure, the pillar-shaped blocks in said structure being abutted or separated from each other by gaps.

2. A radiation image storage panel according to claim 1, wherein said pillar-shaped blocks extend perpendicularly to said support.

3. A radiation image storage panel according to claim 1 or 2, wherein the surface of the support has a concavo-convex pattern.

4. A radiation image storage panel according to claim 3, wherein said surface has a large number of fine tiles separated from each other by fine spaces.

5. A radiation image storage panel according to claim 4, wherein said surface is composed of aluminium oxide.

6. A radiation image storage panel according to claim 4 or 5, wherein said panel comprises a net with fine strings surrounding said surface separating said fine tiles.

7. A radiation image storage panel according to claim 1 or 2, which comrpises a support having a fine mesh pressed thereon.

8. A radiation image storage panel according to any one of claims 1 to 7, wherein said stimulable phosphor layer has a thickness of from 10 pm to 1000 pm.

9. A radiation image storage panel according to any one of claims 1 to 8, wherein the size of each of said pillar-shaped blocks is from 1 pm to 400 pm.

10. A radiation image storage panel according to any one of claims 1 to 9, wherein the space between said pillar-shaped blocks is less than 20 pm.

11. A radiation image storage panel according to any one of claims 1 to 10, wherein said support has impurity particles on the surface thereof.

12. A radiation image storage panel according to any one of claims 1 to 11, wherein said stimulable phosphor layer has crevasses on the surface thereof.